WEBVTT 1 00:00:00.720 --> 00:00:03.600 Okay, so today we're going to be going over av blocks. As always, 2 00:00:03.600 --> 00:00:06.759 a big thank you to everybody who's supported the channel all of the really 3 00:00:06.839 --> 00:00:09.480 nice comments. I truly do appreciate it, so thank you so much. 4 00:00:09.640 --> 00:00:13.080 And also a big thank you to today's sponsor of the podcast, True Learn. 5 00:00:13.320 --> 00:00:16.559 All Right, So, av blocks they are a super high old topic. 6 00:00:16.600 --> 00:00:19.440 They always come up on exams. If you're going to get a dysrhythmi 7 00:00:19.480 --> 00:00:22.239 a question, very good chance it's going to be on AV blocks. So 8 00:00:22.280 --> 00:00:25.559 I wanted to dedicate a podcast going over all of the high old info you 9 00:00:25.600 --> 00:00:28.519 need to know, as well as sharing some new monics for this topic. 10 00:00:28.800 --> 00:00:32.159 Before we begin, I want to go over some key concepts, some basic 11 00:00:32.200 --> 00:00:37.439 foundation you need to have an understanding to better understand AV block. So let's 12 00:00:37.479 --> 00:00:41.640 first quickly review the normal electrical conduction system of the heart, because, like 13 00:00:41.840 --> 00:00:47.719 most things in medicine, identifying abnormalities requires a solid understanding of what constitutes normal. 14 00:00:48.039 --> 00:00:51.280 So normal electrical activity of the heart. It's like this long road and 15 00:00:51.320 --> 00:00:54.840 there's checkpoints along the road. The very beginning of this journey starts at the 16 00:00:55.039 --> 00:00:58.840 say node, which is located in the right atrium. The essay node sends 17 00:00:58.840 --> 00:01:02.479 an electrical signal through the walls of the atrium, causing them to contract, 18 00:01:02.679 --> 00:01:06.040 and then it hits its first checkpoint on the road, the AV node, 19 00:01:06.239 --> 00:01:10.040 which is very important for today's topic. So the signal stops here very briefly 20 00:01:10.079 --> 00:01:12.799 to allow the ventricles time to fill, and then proceeds down into the lower 21 00:01:12.840 --> 00:01:17.640 chamber of the heart through the bundle of hiss. The signal then travels into 22 00:01:17.640 --> 00:01:21.760 the left and right bundle branches, and then finally into the perkine fibers, 23 00:01:22.000 --> 00:01:26.359 which transmit the electricity to the ventricles, causing them to contract. If you 24 00:01:26.359 --> 00:01:30.640 ever need help remembering this pathway, just remember the sentence send a big bounding 25 00:01:30.719 --> 00:01:37.200 pulse, Send a big bounding pulse. The letters are SABBP S stands for 26 00:01:37.439 --> 00:01:41.120 s A node, A stands for AV node, B stands for bundle of 27 00:01:41.159 --> 00:01:45.560 his second B stands for bundle branches, and the P stands for perkine fibers. 28 00:01:45.560 --> 00:01:48.920 So that's the past pathway you need to know now. In an ECG, 29 00:01:49.159 --> 00:01:52.319 the area you need to be very familiar with for AV blocks is something 30 00:01:52.359 --> 00:01:56.079 known as the pr interval. The pr interval is a measurement of the time 31 00:01:56.120 --> 00:02:00.959 it takes the electrical impulse to travel through the atria across the AV node to 32 00:02:00.120 --> 00:02:05.879 the ventricles, so part of that measurement includes that delay at the AV node. 33 00:02:05.959 --> 00:02:09.039 That first little checkpoint we discussed before on your ECG, your pr interval 34 00:02:09.120 --> 00:02:13.719 is a point measured from the beginning of the P wave to the beginning of 35 00:02:13.719 --> 00:02:16.800 the QRS complex. Now, a normal pr interval, this is really important, 36 00:02:16.919 --> 00:02:22.560 is between one hundred and twenty to two hundred milliseconds. Two hundred milliseconds 37 00:02:22.680 --> 00:02:27.599 is five little boxes on an ECG or one large box. Anything larger than 38 00:02:27.639 --> 00:02:30.560 that we got an issue, likely an AV block, which we'll be talking 39 00:02:30.560 --> 00:02:32.240 about today. All right, So those are the basic concepts you need to 40 00:02:32.319 --> 00:02:36.759 understand before we get started. Now, AV blocks are broken down into a 41 00:02:36.840 --> 00:02:39.879 few subtypes. Will go over today. You have a first degree AV block, 42 00:02:40.120 --> 00:02:45.240 a second degree AV block, which is further classified into a Mobitz type 43 00:02:45.280 --> 00:02:49.319 one aka Wanki block, and a Mobitz type two. And then finally we 44 00:02:49.400 --> 00:02:52.919 have a third degree block or a complete AV block, which it's also known 45 00:02:52.960 --> 00:02:55.039 as So let's break each of them down talk about everything you need to know, 46 00:02:55.159 --> 00:02:59.319 and let's first start with our first degree AV block, So a first 47 00:02:59.319 --> 00:03:06.199 degree av is a cardiac condition characterized by abnormally slow electrical conduction from the atrium 48 00:03:06.240 --> 00:03:09.080 to the ventricles. So first degree block, it's not really a block per 49 00:03:09.120 --> 00:03:14.199 se as every impulse is still getting through to the ventricles. It's just getting 50 00:03:14.240 --> 00:03:16.879 there really slowly. It's taking its time, so more of a traffic type 51 00:03:16.919 --> 00:03:22.000 situation rather than the road being completely shut down in this case. So we 52 00:03:22.080 --> 00:03:24.800 have slow conduction through the heart, most commonly occurring at the AV node, 53 00:03:25.080 --> 00:03:30.280 although it can affect the hisper kinjee system as well. So why is this 54 00:03:30.360 --> 00:03:32.599 happening? Let's talk about some etiologies. So the first thing I want you 55 00:03:32.639 --> 00:03:37.759 to be aware of is this can be a normal finding, especially in athletes 56 00:03:37.800 --> 00:03:40.479 that have a slow resting heart rate. So those really well trained athletes who 57 00:03:40.560 --> 00:03:44.360 have a heart rate of like forty beats per minute, they can have a 58 00:03:44.360 --> 00:03:47.599 first degree AV block without any structural abnormalities of the heart. So a first 59 00:03:47.639 --> 00:03:52.639 degree AV block can be normal. But what about the abnormal stuff? So 60 00:03:52.680 --> 00:03:55.560 in all types of AV blocks, medications can be to blame. There's a 61 00:03:55.639 --> 00:04:00.039 number of medications that can cause an AV block. Essentially any drug that impairs 62 00:04:00.159 --> 00:04:04.080 or slows. A v noodal conduction can cause a first degree heart block. 63 00:04:04.439 --> 00:04:09.599 The ones you need to know your AV noodal blocking drugs include dijoxin, beta 64 00:04:09.639 --> 00:04:15.240 blockers, some calcium channel blockers specifically, your non dihydroperioding agents like for Wrappamil 65 00:04:15.360 --> 00:04:18.319 or deltai zem. They can all cause av blocks, so on your exam 66 00:04:18.360 --> 00:04:21.959 if they ask you what the underlying cause may be, make sure you're looking 67 00:04:23.000 --> 00:04:26.040 for one of these meds. And if you need an easy way to remember 68 00:04:26.079 --> 00:04:31.759 the common A V noodal blocking drugs, you can remember ABCD, ABCD your 69 00:04:31.759 --> 00:04:35.160 main A v noodal blocking drugs start with A, B, C or D. 70 00:04:35.480 --> 00:04:41.079 A standing for adenasine, B standing for beta blockers, C standing for 71 00:04:41.160 --> 00:04:46.439 calcium channel blockers, your non dihydropiodin specifically, and then finally D for dijoxin. 72 00:04:46.560 --> 00:04:47.720 That's an easy way to remember the ones that you need to know for 73 00:04:47.759 --> 00:04:53.079 the exam. Myocarditis is another potential cause, and while there's many causes of 74 00:04:53.120 --> 00:04:57.439 myocarditis, viral illness, etc. For the exam, you absolutely have to 75 00:04:57.480 --> 00:05:00.480 remember lime disease. Lime disease can lead to AV blocks and the people who 76 00:05:00.519 --> 00:05:04.319 make exam questions they just love to ask about this. So in patients with 77 00:05:04.439 --> 00:05:09.879 limecarditis, the degree of AV block can actually fluctuate pretty quickly. You can 78 00:05:09.920 --> 00:05:13.800 start with the first degree AV block, but it can quickly progress to second 79 00:05:13.839 --> 00:05:17.079 degree or even a complete AV block a third degree block. Main takeaway though, 80 00:05:17.240 --> 00:05:20.040 if there's a harp block in the question, make sure you're looking for 81 00:05:20.120 --> 00:05:25.439 lime disease and the answer choices. And then another one is myocardial infarction. 82 00:05:25.720 --> 00:05:29.920 This is another potential cause, often an inferior wall am I, as the 83 00:05:30.000 --> 00:05:32.639 a V node and the inferior wall are both fed by the right coronary artery. 84 00:05:32.839 --> 00:05:38.279 There's, of course, plenty of other causes infiltrated and dilated cardiomyopathies like 85 00:05:38.360 --> 00:05:43.240 sarcoidosis, certain muscular dystrophees leve disease. But for the exam, focus on 86 00:05:43.279 --> 00:05:46.240 your meds, your beta blockers, calcium channel blockers, etc. Lime disease, 87 00:05:46.480 --> 00:05:48.959 m I, and your normal variant, as those are the ones most 88 00:05:49.000 --> 00:05:53.680 likely to come up. All right, what about clinical manifestations next? The 89 00:05:53.720 --> 00:05:58.560 main thing you need to know for clinical manifestations is asymptomatic. Asymptomatic is what 90 00:05:58.600 --> 00:06:01.319 you need to know because patients with first degree AV block are generally going to 91 00:06:01.360 --> 00:06:06.600 be asymptomatic. It's not impossible to have some nonspecific symptoms such as dizziness, 92 00:06:06.600 --> 00:06:11.439 fatigue, etc. But overall, most patients with the first degree block are 93 00:06:11.439 --> 00:06:15.040 not going to present with any symptoms at all. Let's talk about diagnosis next. 94 00:06:15.120 --> 00:06:18.360 This is obviously very important for all AV blocks. So you diagnose your 95 00:06:18.759 --> 00:06:21.800 AV blocks with an ECG. Your first ree AV block is going to be 96 00:06:21.839 --> 00:06:26.040 diagnosed with an ECG. Now what are you looking for on the ECG. 97 00:06:26.360 --> 00:06:30.600 Well, we know a first degree AV block is caused by delayed conduction from 98 00:06:30.639 --> 00:06:34.079 the atria to the ventricles, So knowing that where on ECG should we be 99 00:06:34.160 --> 00:06:39.279 looking to calculate this delay. While, as we discussed before, you determine 100 00:06:39.319 --> 00:06:43.079 that delay by looking at the pr interval, which measures the time it takes 101 00:06:43.079 --> 00:06:47.040 the electrical impulse to travel through the atria across the AV node to the ventricles. 102 00:06:47.399 --> 00:06:50.240 And as we know, the normal amount of time for this to take 103 00:06:50.279 --> 00:06:55.920 place should be a max of two hundred milliseconds or one large box. When 104 00:06:55.959 --> 00:06:59.040 the first degree AV block, there's a traffic jam and while the signals still 105 00:06:59.079 --> 00:07:01.720 getting through the ventricles, taking a lot longer than it's supposed to, and 106 00:07:01.800 --> 00:07:08.399 this leads to a prolonged pr interval, specifically a pr interval over two hundred 107 00:07:08.439 --> 00:07:11.920 milliseconds. That's all you need to know for a first degree block, pr 108 00:07:11.959 --> 00:07:15.160 interval over two hundred milliseconds, more than one big box. It's nice and 109 00:07:15.240 --> 00:07:18.879 simple. And the key which will be different from all other AV blocks, 110 00:07:18.920 --> 00:07:23.680 which we'll talk about next, is the conducted impulse. It's always going to 111 00:07:23.720 --> 00:07:27.279 get through to the ventricles, all of that electricity it's still getting through, 112 00:07:27.480 --> 00:07:31.160 which means there's always going to be a QRS complex following that P wave. 113 00:07:31.439 --> 00:07:35.040 Even though the pr interval is prolonged, it's always going to be followed by 114 00:07:35.079 --> 00:07:39.319 a QRS complex, it's just taking longer to get there. So again, 115 00:07:39.560 --> 00:07:44.439 ECG diagnosis is made with a pr interval over two hundred milliseconds. So there's 116 00:07:44.480 --> 00:07:46.279 a lot of mnemonics for HART blocks, a lot of ways to remember these, 117 00:07:46.519 --> 00:07:50.240 and for a first degree block, you remember the ECG findings by remembering 118 00:07:50.240 --> 00:07:54.680 the rhyme. If the R is far from the P, then you have 119 00:07:54.759 --> 00:07:58.040 a first degree. If the R is far from the P, then you 120 00:07:58.079 --> 00:08:01.959 have a first degree. That wideen pr interval over two hundred milliseconds. All 121 00:08:03.040 --> 00:08:05.959 right, let's talk about treatment next. So we do an ECG. We 122 00:08:05.000 --> 00:08:09.199 see the patient has a first degree block. How are we going to treat 123 00:08:09.240 --> 00:08:11.319 this? Do we even need to treat this? Most of the time the 124 00:08:11.360 --> 00:08:15.600 answer is no, but it does depend on a couple of factors, mainly 125 00:08:15.600 --> 00:08:18.240 related to whether or not they're symptomatic and treatment for a first degree block, 126 00:08:18.319 --> 00:08:22.720 it's pretty simple. You really just have two options. You either do nothing 127 00:08:22.079 --> 00:08:26.519 or you give them a pacemaker. So if they're asymptomatic, you're just going 128 00:08:26.560 --> 00:08:28.959 to observe. They don't require any treatment. Obviously, if there's an underlying 129 00:08:30.000 --> 00:08:33.840 cause like a medication that can be discontinued or another underlying treatable cause that should 130 00:08:33.840 --> 00:08:39.679 be addressed. But otherwise, asymptomatic doesn't require any intervention. And then there's 131 00:08:39.720 --> 00:08:43.279 some rare cases that will get a pacemaker. So a patient with a y 132 00:08:43.399 --> 00:08:48.000 q r S complex in conjunction with prolongation of the pr interval, patients with 133 00:08:48.080 --> 00:08:50.720 something known as pseudo pacemaker syndrome. I don't think you should memorize any of 134 00:08:50.759 --> 00:08:56.639 that. Just remember most patients with the first degree av block just observed pacemaker 135 00:08:56.720 --> 00:09:00.279 only in some rare cases. All right, quick recap of a first gree 136 00:09:00.320 --> 00:09:05.039 Hart block. This is a cardiac condition characterized by slow conduction from the atrim 137 00:09:05.080 --> 00:09:07.919 to the ventricles. All the beats are getting through, They're just taking their 138 00:09:07.000 --> 00:09:11.200 damn time. It can be a normal finding, especially in a well trained 139 00:09:11.240 --> 00:09:15.639 athlete with a slow heart rate. Most patients are going to be asymptomatic diagnosed 140 00:09:15.679 --> 00:09:18.879 with ECG pr interval over two hundred milliseconds. Most of the time you'll just 141 00:09:18.960 --> 00:09:24.519 observe pacemaker only in some rare cases. That's the first Threehart block. Moving 142 00:09:24.559 --> 00:09:28.519 on to our second degree AV block. Remember this is broken into two subtypes, 143 00:09:28.799 --> 00:09:31.720 Mobitz type one and Mobitz type two. Let's start with Mobitz type one 144 00:09:31.840 --> 00:09:37.240 aka Winkiebock, named after the Dutch physician Carl Frederick Winkibock. So this is 145 00:09:37.279 --> 00:09:41.879 a progressive lengthening of the pr interval, often due to impaired conduction within the 146 00:09:41.960 --> 00:09:48.320 AV node, resulting in occasional non conducted impulses. So this is similar to 147 00:09:48.440 --> 00:09:50.639 a first degree AV block where there is some traffic on the road to the 148 00:09:50.720 --> 00:09:54.960 ventricles, so we have this prolonged pr interval. The difference is though in 149 00:09:56.000 --> 00:10:00.559 a Mobit's one that traffic it keeps getting worse and worse, leading to the 150 00:10:00.559 --> 00:10:05.200 pr interval getting longer and longer, until eventually everything just comes to a standstill. 151 00:10:05.440 --> 00:10:07.840 The road shuts down, the atrial impulse is filled or reach the ventricles, 152 00:10:09.039 --> 00:10:11.559 and you have a dropped beat. So again, mobits type one aka 153 00:10:11.600 --> 00:10:16.039 Winkie box. There's some traffic on the road, the traffic keeps getting worse 154 00:10:16.080 --> 00:10:18.840 and worse, pr interval getting longer and longer, until all traffic comes to 155 00:10:18.879 --> 00:10:24.159 a stop and you have a non conducted p wave no QRS complex following it. 156 00:10:24.320 --> 00:10:28.200 One important thing to know about mobis type one Winkie box is it usually 157 00:10:28.240 --> 00:10:31.840 occurs within the AV node. Mobitz one usually occurs within the AV node. 158 00:10:31.840 --> 00:10:35.639 This is really important because all of the conditions we're going to go over today, 159 00:10:35.919 --> 00:10:39.440 they're all called AV blocks, but they don't all occur within the AV 160 00:10:39.559 --> 00:10:43.559 node. For instance, Mobitz type two, which we'll talk about next, 161 00:10:43.879 --> 00:10:48.320 almost always occurs from conduction system issues below the level of the AV node, 162 00:10:48.480 --> 00:10:50.639 and it's part of the reason why in ambit's one, which affects the AV 163 00:10:50.759 --> 00:10:54.759 node, we see this progressive pr lengthening where in a mobits two, we 164 00:10:54.879 --> 00:11:00.279 generally do not mob over more detail about that once we talk about mobitz too, 165 00:11:00.399 --> 00:11:03.799 Let's talk about etiologies next. As far as your etiology is there for 166 00:11:03.840 --> 00:11:05.919 the most part, the same as in a first degree heart block. Once 167 00:11:05.960 --> 00:11:09.600 again, this can be a normal finding and patients like athletes with no underlying 168 00:11:09.600 --> 00:11:13.639 cardiac pathology, and actually up to ten percent of long distance runners have been 169 00:11:13.639 --> 00:11:18.480 found to have a MOBITS type one second degree block, which I found was 170 00:11:18.519 --> 00:11:22.200 pretty interesting. Moving on to your meds, of course your av noal blocking 171 00:11:22.200 --> 00:11:26.159 medications like we went over before, dig beta blockers, non to hydro period 172 00:11:26.200 --> 00:11:30.200 in calcium channel blockers can all cause a MOBITS one. Don't forget your myocardidis 173 00:11:30.279 --> 00:11:33.840 from lyme disease, myocardial infarction as well as some other underlying heart diseases, 174 00:11:35.159 --> 00:11:39.159 and then hyperkalemia, which is the only one I didn't mention first degree block 175 00:11:39.559 --> 00:11:41.799 as this is much more common in second and third degree blocks. So those 176 00:11:41.799 --> 00:11:46.559 are the ones to know, because of course many others iatrogenic causes like post 177 00:11:46.600 --> 00:11:50.600 cardiac surgery cardio myyopathy, but the main ones you need to memorize the ones 178 00:11:50.639 --> 00:11:52.480 that will likely come up on an exam question. The way that I used 179 00:11:52.480 --> 00:11:58.399 to remember them was with the mnemonic blocks bloc ks as in AV blocks. 180 00:11:58.679 --> 00:12:03.039 The B stands for beta blockers, the L stands for lime disease O as 181 00:12:03.080 --> 00:12:07.960 an ordinary as in your normal, variant and young healthy athletic patients. C 182 00:12:07.200 --> 00:12:13.279 stands for calcium channel blockers, non dihydroperioding agents. Specifically, K stands for 183 00:12:13.440 --> 00:12:18.159 K increase as in hyperkalemia. Remember the element symbol for potassium as K. 184 00:12:18.559 --> 00:12:22.639 And then finally the S stands for stemi as an st elevation m I to 185 00:12:22.679 --> 00:12:28.200 help you remember your myocardial infarction. So again remember blocks for your etiologies beta 186 00:12:28.200 --> 00:12:31.919 blockers, lime disease, ordinary, calcium channel blockers, K increase, and 187 00:12:31.080 --> 00:12:35.120 stemy. Moving on to clinical manifestation's neck So most patients, just like in 188 00:12:35.120 --> 00:12:37.960 a first degree a V block, will be asymptomatic. Now, with that 189 00:12:39.080 --> 00:12:41.559 being said, if the sinus rate is slow enough and you have a bunch 190 00:12:41.639 --> 00:12:46.759 of non conducted beats, your cardiac output will decline and you may start to 191 00:12:46.799 --> 00:12:50.759 notice some signs of hypoperfusion such as fatigue, lightheadedness, syncope, angina. 192 00:12:52.159 --> 00:12:54.639 But in general, most patients are going to be asymptomatic. Moving on to 193 00:12:54.759 --> 00:12:58.799 diagnosis, of course, this is the highest seal thing to know. So 194 00:12:58.840 --> 00:13:03.440 will you diagnose with your ECG, and you're looking for a progressive prolongation of 195 00:13:03.480 --> 00:13:07.559 the pr interval followed by a non conducted P wave. So when you look 196 00:13:07.600 --> 00:13:11.399 at your ECG for a mob's type one aka winky Bok, you're going to 197 00:13:11.440 --> 00:13:16.120 see this trend of the pr interval progressively lengthening. With each beat, it 198 00:13:16.159 --> 00:13:20.960 gets wider and wider and wider, until eventually, boom, dropped beats. 199 00:13:20.960 --> 00:13:24.759 You'll have a P wave but no QRS complex. And then once this happens, 200 00:13:24.759 --> 00:13:26.679 it starts all over again. Pr interval longer, longer, longer, 201 00:13:26.759 --> 00:13:31.720 dropped beat. This can of course happen in patterns three P waves to every 202 00:13:31.720 --> 00:13:35.240 two Kors complexes, four P waves to every three Kors complexes, et cetera. 203 00:13:35.679 --> 00:13:39.399 So comparing this to a first degree block, remember a patient with a 204 00:13:39.480 --> 00:13:43.720 first gree AV block had a prolonged pr interval, but it didn't get progressively 205 00:13:43.759 --> 00:13:46.159 longer, and most importantly, there was never a dropped beat. All P 206 00:13:46.360 --> 00:13:50.200 waves were followed by a QRS complex. All right, So that's the typical 207 00:13:50.200 --> 00:13:54.679 ECG findings. Pretty simple. I have another rhyme for you, so a 208 00:13:54.720 --> 00:13:58.039 mobits type one aka Winkiebok. The pr interval gets longer, longer, longer, 209 00:13:58.120 --> 00:14:01.519 until eventually it a beat. So for Winki Bok, remember the rhyme 210 00:14:01.679 --> 00:14:05.360 longer, longer, longer drop. Then you have a Winkie Bok longer, 211 00:14:05.480 --> 00:14:09.000 longer, longer drop than you have a Winkie Bok because remember, the pr 212 00:14:09.000 --> 00:14:13.639 interval gets longer and longer until it drops. Another way I've heard of remembering 213 00:14:13.639 --> 00:14:18.039 it is by remembering the W and Winkie box stands for warning because the pr 214 00:14:18.080 --> 00:14:22.879 interval progressively getting longer warns you of the impending drop. Le suck about treatment 215 00:14:22.960 --> 00:14:26.720 next. So the treatment goes like this. If they're asymptomatic, they're stable 216 00:14:26.840 --> 00:14:31.840 in most cases they don't require any treatment. If they're symptomatic and most importantly 217 00:14:31.879 --> 00:14:37.639 hemodynamically unstable hemodynamically unstable meaning they're hypotensive, they have altered mental status, chest 218 00:14:37.639 --> 00:14:43.000 pain, etc. You give them atropine. So why atropine will Atropine speeds 219 00:14:43.039 --> 00:14:46.919 up conduction through the AV node, which in a patient with an AV block 220 00:14:46.960 --> 00:14:52.639 with slow conduction through the AV node, that would obviously be ideal Atropine achieves 221 00:14:52.639 --> 00:14:56.480 this by blocking the parasympathetic influences on the heart, specifically the effects of acetal 222 00:14:56.559 --> 00:15:01.919 colline. So that's why we use atropine first line for these unstable patients. 223 00:15:01.200 --> 00:15:05.440 Now, if atropine is ineffective, you can use temporary cardiac pacing and then 224 00:15:05.480 --> 00:15:09.799 finally as a last resort option, in patients that have symptomatic braided cardia with 225 00:15:09.960 --> 00:15:13.960 no reversible etiology, no mads to discontinue that may be causing it, no 226 00:15:15.080 --> 00:15:18.840 electrol disturbances that can be fixed. Then in those patients they need a pacemaker. 227 00:15:20.120 --> 00:15:24.360 So a quick recap of a Mobitz type one aka Winkie block second degree 228 00:15:24.399 --> 00:15:28.840 AV block. This is a progressive delay and a transmission of electrical signals from 229 00:15:28.840 --> 00:15:33.200 the A tree to the ventricles, occasionally resulting in a non conducted impulse block 230 00:15:33.320 --> 00:15:35.039 is going to be at the level of the AV node. In most cases 231 00:15:35.240 --> 00:15:41.080 etiology remember blocks, bloc ks, beta blockers, lime disease, ordinary calcium 232 00:15:41.120 --> 00:15:46.799 channel blockers, k increase STEMI. Most patients will be asymptomatic on ECG. 233 00:15:46.919 --> 00:15:50.120 You're looking for longer, longer, longer drop than you have. A Winkie 234 00:15:50.120 --> 00:15:54.919 bock treatment asymptomatic, just observed symptomatic and unstable atropine. And then finally last 235 00:15:54.960 --> 00:15:58.120 line, definitive option pacemaker. All right, let's talk about a Mobits type 236 00:15:58.159 --> 00:16:02.600 two second degree a V block next. So I want you to recognize a 237 00:16:02.639 --> 00:16:06.480 shift once we get to ambits two and beyond, and that shift is once 238 00:16:06.519 --> 00:16:10.720 you cross the threshold of a Mobitz two, it's getting more serious. You'll 239 00:16:10.720 --> 00:16:12.840 notice we're not really going to see this in our young, healthy athletes anymore. 240 00:16:14.080 --> 00:16:15.639 The treatment is going to be more aggressive. So just kind of be 241 00:16:15.679 --> 00:16:19.159 aware of that shift once we get to that level. So Mobitz two is 242 00:16:19.200 --> 00:16:25.000 a disease of the cardiac conduction system leading to occasional dropped beats with a pr 243 00:16:25.080 --> 00:16:30.320 interval that is fixed and consistent, so you'll still have the non conducted beat 244 00:16:30.360 --> 00:16:33.759 and the mobitz too. But the big difference between a Mobitz one and ambits 245 00:16:33.799 --> 00:16:37.360 too, and what you should really focus on is that a Mobitz too, 246 00:16:37.399 --> 00:16:41.799 the pr interval remains constant. You do not have that progressive prolongation like we 247 00:16:41.799 --> 00:16:45.440 saw in a moobits type one block. That's the main difference between the two. 248 00:16:45.759 --> 00:16:49.639 Mobitz one was longer, longer, longer drop Mobitz two is same, 249 00:16:49.679 --> 00:16:53.879 same, same drop that's the idea fixed pr interval. So why does a 250 00:16:53.960 --> 00:16:57.919 Moobitz too have a fixed pr interval with drop beats and a Mobitz one had 251 00:16:57.960 --> 00:17:03.080 progressive prolonged gation with drop beats well su to the area of the heart where 252 00:17:03.080 --> 00:17:07.920 the block occurs. And a Mobitz type two block almost always results from a 253 00:17:07.000 --> 00:17:11.599 block below the level of the AV node. The block is at the bundle 254 00:17:11.599 --> 00:17:15.359 of HISS and approximately twenty percent of cases and need the bundle branches in the 255 00:17:15.440 --> 00:17:18.400 remainder. This is different than an emobits type one as we discussed before, 256 00:17:18.720 --> 00:17:23.480 that almost exclusively occurs at the level of the AV node. So Mobitz type 257 00:17:23.519 --> 00:17:27.000 one the block was at the AV node. Mobitz type two the block is 258 00:17:27.079 --> 00:17:32.160 below the level of the AV node. And because of this one small difference, 259 00:17:32.359 --> 00:17:34.799 your ECG findings are going to be different and your treatment options will change. 260 00:17:34.799 --> 00:17:37.559 And we'll go over more about that in a minute. As far as 261 00:17:37.559 --> 00:17:41.519 eteology, there's not a lot new to know here compared to amobits type one, 262 00:17:41.599 --> 00:17:45.359 so I won't bore you with the details. Med's myocardial infarction myocardide is 263 00:17:45.359 --> 00:17:48.720 from lime disease, hyperkalemia, et cetera. The key difference though, in 264 00:17:48.759 --> 00:17:52.720 what I want you to remember is we are no longer going to see this 265 00:17:52.799 --> 00:17:56.160 in our young, healthy, athletic patient. Mobitz type two block is rarely 266 00:17:56.200 --> 00:18:00.200 seen in patients without underlying heart disease, So this is no longer going to 267 00:18:00.240 --> 00:18:03.200 be a normal variant like we saw in the first couple of VV blocks we 268 00:18:03.279 --> 00:18:07.920 went over. Patients with the mobits too generally has something else going on, 269 00:18:07.400 --> 00:18:11.839 some type of structural heart disease to get to this point, myocarditis, myocardio, 270 00:18:11.920 --> 00:18:15.960 schemia, fibrosis, etc. That's the main takeaway here for eteology and 271 00:18:17.039 --> 00:18:21.400 what differentiates it from a type one and a first degree block. So the 272 00:18:21.480 --> 00:18:26.279 neumonic we went over before still applies. Just subtract that over ordinary as this 273 00:18:26.359 --> 00:18:30.759 is rare to occur in normal, ordinary patients without underlying heart disease. Remember 274 00:18:30.759 --> 00:18:33.319 that shift, as I talked about before. Once we get to amobits, 275 00:18:33.319 --> 00:18:37.160 two things are getting more serious at this point. Now. Clinical manifestations, 276 00:18:37.200 --> 00:18:40.279 they can widely vary, and I don't think you need to memorize each individual 277 00:18:40.400 --> 00:18:42.799 symptom, but you do need to know is that patients with the Mobits type 278 00:18:42.799 --> 00:18:48.559 two second degree AV block will present with some form of symptoms. It can 279 00:18:48.640 --> 00:18:52.680 be mild fatigue, dispnea all the way to syncope and sudden cardiac arrest. 280 00:18:52.000 --> 00:18:56.960 But the key takeaway is unlike the other two AV blocks we talked about previously, 281 00:18:56.000 --> 00:19:00.920 where most patients were asymptomatic, that's not the case at the MOBITS two. 282 00:19:00.000 --> 00:19:03.440 They will usually present with some degree of symptoms. Remember that shift. 283 00:19:03.680 --> 00:19:07.319 All right, let's talk about our ECG finding next. What are we going 284 00:19:07.359 --> 00:19:10.480 to find on an ECG in a patience with a MOBITS type two. So 285 00:19:10.559 --> 00:19:14.480 in a MOBITS two, you're going to have pr intervals that are the same 286 00:19:15.000 --> 00:19:18.759 no progressive prolongation that will be followed by a P wave that fails to conduct 287 00:19:18.759 --> 00:19:23.079 to the ventricles, so a sudden dropped beat no qors complex. So you're 288 00:19:23.119 --> 00:19:26.119 looking at your ECG, try to visualize this in your head. You see 289 00:19:26.119 --> 00:19:30.759 your P wave followed by a QRS complex as expected, next beat pwave pr 290 00:19:30.799 --> 00:19:34.440 interval the same as the last, no prolongation aka no warning like we saw 291 00:19:34.440 --> 00:19:38.359 on MOBITS one. Then all of a sudden dropped beat no qors complex. 292 00:19:38.599 --> 00:19:42.640 That's the pattern to look for. Unchanging pr interval. Then suddenly a p 293 00:19:42.799 --> 00:19:47.079 wave that fails to conduct to the ventricles. The big difference as you can 294 00:19:47.119 --> 00:19:49.440 see between this type of second degree harp block compared to ambits type one. 295 00:19:49.759 --> 00:19:52.640 As we've discussed before and as I keep saying, is that there is no 296 00:19:52.759 --> 00:19:56.160 lengthening of the pr interval with each beat. So the pr interval that's the 297 00:19:56.240 --> 00:20:00.119 key here to help differentiate. So the pr interval, it can be prolonged 298 00:20:00.440 --> 00:20:04.240 usually it's going to be normal though, But however long or short the pr 299 00:20:04.279 --> 00:20:07.799 interval is, it ain't changing. The length will remain the same, and 300 00:20:07.839 --> 00:20:12.759 the reason why it remains consistent in amobits two and progressively prolonged in ambits one 301 00:20:14.039 --> 00:20:17.640 all pertains to the area where the block is occurring. And we touched on 302 00:20:17.680 --> 00:20:19.599 this before, but just to give a little more info. So remember a 303 00:20:19.720 --> 00:20:23.079 moobits one, generally the block is at the AV node. Mobits two, 304 00:20:23.160 --> 00:20:26.960 the block is below the level of the AV node. When amobits one that 305 00:20:27.039 --> 00:20:32.720 affects the AV node. Those av nodal cells, they're pretty resilient and even 306 00:20:32.759 --> 00:20:36.880 though they're facing an increased resistance with each beat, taking a little longer to 307 00:20:36.880 --> 00:20:40.160 conductive beat with each interval, they can tough it out for a period of 308 00:20:40.200 --> 00:20:44.519 time and still carry that beat through until eventually they just can't take it anymore 309 00:20:44.519 --> 00:20:48.000 and they just collapse and drop the beat and amobits two though the block is 310 00:20:48.039 --> 00:20:52.319 below the level of the AV node in his Perkinjee system. And these guys 311 00:20:52.480 --> 00:20:55.519 they're all or nothing. They either give it they're all and conduct the beat, 312 00:20:55.680 --> 00:20:57.319 or they don't do crap and they just drop it. There is no 313 00:20:57.359 --> 00:21:02.000 progressive lengthening of the PR. It's the same. The beat is either conducted 314 00:21:02.160 --> 00:21:04.079 or it's not. They don't play no games. So it's usually fairly easy 315 00:21:04.119 --> 00:21:07.880 to distinguish between a mobits one and amobits two on ECG. Just look at 316 00:21:07.880 --> 00:21:11.759 the PR interval. If it remains constant with occasional drop beats, it's ambits 317 00:21:11.799 --> 00:21:15.599 too. If it progressively prolongs and leads to a drop beat. Mobits one 318 00:21:15.839 --> 00:21:18.839 nice and simple, unless you have a two to one block that is which 319 00:21:18.839 --> 00:21:23.079 I'll go over shortly. So how do you remember amobits to ECG finding what's 320 00:21:23.079 --> 00:21:26.039 the rhyme for this one? So remember the rhyme. If some pas don't 321 00:21:26.039 --> 00:21:30.599 get through, then you have a moobitz too. If some pas don't get 322 00:21:30.599 --> 00:21:33.599 through, then you have amobitz too. Remember that rhyme. All right, 323 00:21:33.640 --> 00:21:37.400 let's talk about treatment next. Treatment it's a bit different compared to ambits one, 324 00:21:37.720 --> 00:21:41.480 So mobits two it's a slippery, unstable beast. You can never let 325 00:21:41.480 --> 00:21:45.039 it out of your sight. So even in a stable patient, you're gonna 326 00:21:45.079 --> 00:21:48.039 watch them closely, and you're gonna throw some transcutaneous pacing pads on them to 327 00:21:48.119 --> 00:21:52.000 be ready in the event things go south quickly. You can't just send these 328 00:21:52.000 --> 00:21:56.240 patients home and call it a day. That's because ambits two can frequently progress 329 00:21:56.279 --> 00:22:00.720 to a third degree av block, which we'll talk about next, and eventually, 330 00:22:00.759 --> 00:22:04.640 even your stable patients will likely require a pacemaker unless a treatable underlying cause 331 00:22:04.759 --> 00:22:10.880 is found. Now, if they're unstable, hemodynamically unstable, hypotensive, altered 332 00:22:10.920 --> 00:22:12.960 mental status, signs of shock, et cetera, they're going to get a 333 00:22:14.000 --> 00:22:18.720 beta adrenergic agonist like dopamine, dopamine epinephrine, as long as there's no signs 334 00:22:18.720 --> 00:22:22.799 of mild cardio schemia. And in addition, these patients will often also receive 335 00:22:22.920 --> 00:22:27.680 temporary cardiac pacing. Now you may be asking yourself hemodynamically unstable patients in amobits 336 00:22:27.720 --> 00:22:32.519 one. We gave them atropine. Why don't we give them atropine and amobits 337 00:22:32.519 --> 00:22:34.480 too. I'll give you a second to think about that. Think back to 338 00:22:34.519 --> 00:22:37.920 where the level of the block is. So the effect of atropine, as 339 00:22:37.960 --> 00:22:42.079 we discussed before, is mainly on the AV node. Remember, atropine decreases 340 00:22:42.079 --> 00:22:45.680 the refractory time and speeds up conduction through the AV node. And that was 341 00:22:45.759 --> 00:22:49.000 great in a mobits one. That mainly affects the AV node. But what 342 00:22:49.160 --> 00:22:53.119 area of the heart is affected in ambits too. That's right below the level 343 00:22:53.160 --> 00:22:57.839 of the AV node infranodal. So we don't use atropine and ambits two blocked 344 00:22:59.079 --> 00:23:02.680 in fact it and actually worsen the block in some cases. So stick to 345 00:23:02.680 --> 00:23:06.960 your beta adrenergic agonis, dopamine, domine, etc. Finally, unless there 346 00:23:07.039 --> 00:23:11.480 is a reversible underlying cause found most patients with a mobitz too hart block, 347 00:23:11.720 --> 00:23:14.839 they're going to get a pacemaker. Remember back to that shift I keep talking 348 00:23:14.839 --> 00:23:17.920 about. I want you to recognize this up until now, in a first 349 00:23:17.920 --> 00:23:21.400 degree heart block in a mobits one, if the patient was asymptomatic, they 350 00:23:21.400 --> 00:23:23.480 didn't need a pacemaker most of the time. But once we get to a 351 00:23:23.559 --> 00:23:27.799 Mobitz two. Because of how unstable this type of hart block is. Everyone's 352 00:23:27.799 --> 00:23:33.519 getting a pacemaker unless there is some underlying treatable cause found. So just remember 353 00:23:33.559 --> 00:23:36.720 that when it comes to treatment, once you hit a Mobits two or above, 354 00:23:36.960 --> 00:23:40.279 most patients are going to get a pacemaker. So a quick recap of 355 00:23:40.279 --> 00:23:44.079 a Mobits type two second degree AV block. It's a disease of the cardiac 356 00:23:44.079 --> 00:23:48.279 conduction system leading to occasional drop beats with a constant, constant pr interval, 357 00:23:48.519 --> 00:23:52.319 the block is going to be below the level of the AV node. In 358 00:23:52.359 --> 00:23:56.400 almost all cases, most patients will have some form of underlying heart disease. 359 00:23:56.640 --> 00:24:00.000 Symptoms are variable anywhere from plain old fatigue all the way to sudden cardiac arrest. 360 00:24:00.279 --> 00:24:06.160 ECG shows a constant pr interval followed by one or more dropped beats treatment. 361 00:24:06.279 --> 00:24:10.559 Most patients will get a pacemaker unless there is an underlying treatable condition avoid 362 00:24:10.559 --> 00:24:15.000 atropine and that's ambits too. So I wanted to quickly talk about today's sponsor, 363 00:24:15.039 --> 00:24:18.279 an amazing tool for PAS students called true Learn. True Learn is a 364 00:24:18.319 --> 00:24:22.039 game changing solution for students preparing for the pants exam, or just for some 365 00:24:22.079 --> 00:24:26.599 extra help during didactic year. True Learns Test Bank offers over nine hundred test 366 00:24:26.640 --> 00:24:30.599 items specifically designed for the pants and eleven hundred items for the pan read. 367 00:24:30.680 --> 00:24:36.319 The questions are mapped to the NCCPA Content Blueprint, which ensures you focus only 368 00:24:36.359 --> 00:24:40.359 on what truly matters for exam day, eliminating the worry of wasting time on 369 00:24:40.440 --> 00:24:45.200 irrelevant topics. The questions are created by board certified physician assistance will understand the 370 00:24:45.200 --> 00:24:48.920 exams nuances, and you can conveniently access True Learns content through the website or 371 00:24:48.960 --> 00:24:52.279 their user friendly mobile app, perfect for studying on the go. You can 372 00:24:52.359 --> 00:24:56.039 visit true learn dot com to sign up, or click the link in the 373 00:24:56.039 --> 00:24:59.799 show notes and make sure to use the code cram the pants when signing up 374 00:24:59.839 --> 00:25:03.599 to save twenty percent off subscriptions of ninety days or more. Now back to 375 00:25:03.640 --> 00:25:08.519 the show. Now, before we move on to the last topic, which 376 00:25:08.559 --> 00:25:11.759 is a third degree AV block, I wanted to quickly go over one other 377 00:25:11.839 --> 00:25:15.480 variation, which is the dreaded two to one block. So it understand what 378 00:25:15.480 --> 00:25:19.079 a two to one block is. We first need to understand something called AV 379 00:25:19.240 --> 00:25:23.279 conduction ratio. So with second degree heart blocks, these type of blocks, 380 00:25:23.279 --> 00:25:27.799 when consistent, can be named by the ratio of P waves to QRS complexes. 381 00:25:29.079 --> 00:25:30.799 So look at your ECG. You count up all the pwaves and then 382 00:25:30.839 --> 00:25:34.839 count up all the QS complexes until the first drop beat, and then the 383 00:25:34.960 --> 00:25:38.759 ratio is based on the number of each So if there's four p waves three 384 00:25:38.799 --> 00:25:42.480 QRS complexes, that's a four to three ratio. So an example, you're 385 00:25:42.480 --> 00:25:47.880 reading your ECG, there's a P wave QS complex, pwave QRS complex, 386 00:25:48.200 --> 00:25:52.079 p wave drop beat, no QS complex. This type of block would be 387 00:25:52.119 --> 00:25:55.680 a three to two block because there was three p waves and only two QS 388 00:25:55.759 --> 00:25:59.880 complexes. So now that we understand AV conduction ratio, let's talk about a 389 00:26:00.079 --> 00:26:03.960 two to one block. So two to one block means every other pwave is 390 00:26:03.000 --> 00:26:07.759 blocked, every other pwave is not followed by a QRS complex one conduction and 391 00:26:07.799 --> 00:26:11.440 then no conduction, one conduction and no conduction. So the reason this is 392 00:26:11.440 --> 00:26:15.759 so important or so frustrating is if you have a two to one second degree 393 00:26:15.799 --> 00:26:19.519 AV block, there is no way to assess for PR lengthening, so you 394 00:26:19.599 --> 00:26:23.440 cannot determine if this is a Mobitz type one or a Mobitz type two. 395 00:26:23.720 --> 00:26:27.519 It never goes long enough to see if there is that progressive pr lengthening to 396 00:26:27.559 --> 00:26:30.920 say, okay, this is a Mobitz type one. It just keeps dropping 397 00:26:30.960 --> 00:26:34.359 the beat right away. So this is really the only instance where you can't 398 00:26:34.400 --> 00:26:38.119 determine a Mobitz one from a Mobits two on ECG, and there is some 399 00:26:38.160 --> 00:26:42.039 strategies to help with this. You can obtain a long rhythm strip PREVOUCCG, 400 00:26:42.599 --> 00:26:48.079 certain vegeal maneuvers like Herod Sinus massage you can do in certain patients. Also, 401 00:26:48.119 --> 00:26:51.480 if the PR interval is very long over three hundred milliseconds, or the 402 00:26:51.559 --> 00:26:55.519 QRS complex is narrow, this is more consistent with a Mobits type one. 403 00:26:55.640 --> 00:26:57.640 These aren't things I think you need to memorize, and I only mention this 404 00:26:57.680 --> 00:27:00.480 type of block, not be because I think you'll get it on an exam 405 00:27:00.559 --> 00:27:03.559 question, because that just wouldn't be fair. But I want you to be 406 00:27:03.599 --> 00:27:07.720 ready when you're out there practicing or in clinicals to be familiar with this as 407 00:27:07.759 --> 00:27:11.440 it's something you may see. All right, let's move on to the last 408 00:27:11.480 --> 00:27:15.400 topic, a third degree av block, which is a defect in the cardiac 409 00:27:15.400 --> 00:27:19.200 conduction system in which all atrial impulses fail to reach the ventricles, leading to 410 00:27:19.319 --> 00:27:23.400 complete dissociation of the atria and ventricles. So you can see why this one 411 00:27:23.480 --> 00:27:27.880 is so serious. Before we either had delays in the impulse or occasional drop 412 00:27:27.920 --> 00:27:32.599 beats, but in this case it's no longer an occasional occurrence. There is 413 00:27:32.599 --> 00:27:36.920 a complete, persistent loss of conduction from the atria to the ventricles. No 414 00:27:37.079 --> 00:27:40.799 atrial impulses are reaching the ventricles, which is why this is sometimes known as 415 00:27:40.839 --> 00:27:45.599 a complete heartblock, because nothing's getting through anymore. As far as etiologies, 416 00:27:45.799 --> 00:27:48.240 the main ones are pretty much the same as the other av blocks. We 417 00:27:48.279 --> 00:27:52.400 already went over your av noodal blocking, med's miocardial in farction, miocardias from 418 00:27:52.400 --> 00:27:56.160 lime disease, hypergalimia. List of course doesn't include every etiology, but those 419 00:27:56.200 --> 00:27:59.839 are the main ones. To focus on clinical manifestations, just as an immobids 420 00:28:00.000 --> 00:28:03.920 two. The clinical manifestations can widely vary depending on a number of factors, 421 00:28:03.119 --> 00:28:07.240 anywhere from fatigue, dyspnea and chess pain to syncope and sudden cardiac arrest. 422 00:28:07.519 --> 00:28:11.359 Main takeaway, nearly all patients with a third degree block will present with some 423 00:28:11.519 --> 00:28:15.480 degree of symptoms. It's uncommon for these patients to be asymptomatic. All right, 424 00:28:15.559 --> 00:28:18.799 let's talk about your ECG finding next. What does a third degree block 425 00:28:18.920 --> 00:28:22.880 look like on ECG? This is obviously the most important thing to know. 426 00:28:22.240 --> 00:28:26.039 And I'm going to go over a few things to look out for on ECG 427 00:28:26.119 --> 00:28:27.960 in a third degree block, but this first one, this is by far 428 00:28:29.039 --> 00:28:33.720 the most important. There will be complete dissociation between the P waves and QS 429 00:28:33.799 --> 00:28:37.839 complexes. This means that the atria and ventricles are beating independent of one another 430 00:28:38.200 --> 00:28:41.160 in a normal ECG, in a normal, healthy patient, we expect to 431 00:28:41.160 --> 00:28:45.960 see a P wave than a QRS complex, P wave then QS complex. 432 00:28:45.279 --> 00:28:48.440 That's not happening anymore. The atria and the ventricles they no longer have a 433 00:28:48.440 --> 00:28:52.200 line of communication. They're no longer on speaking terms. And because of this, 434 00:28:52.319 --> 00:28:56.160 you'll see P waves marching right on through the QS complexes. And that's 435 00:28:56.160 --> 00:29:00.200 the best way to think of this. They no longer have any perception of 436 00:29:00.240 --> 00:29:03.400 where the QS complex is, so you're going to see them popping up right 437 00:29:03.480 --> 00:29:06.759 next to a Q complex. They're going to be far from it. They're 438 00:29:06.759 --> 00:29:08.640 going to be right in the middle of a T wave. There's no pattern 439 00:29:08.640 --> 00:29:11.920 to it. Anymore like we're used to. They're just marching straight on through, 440 00:29:12.279 --> 00:29:15.519 which is really helpful to identify this type of av block. And if 441 00:29:15.559 --> 00:29:19.039 we're thinking on the terms of a pr interval, or at least the appearance 442 00:29:19.079 --> 00:29:23.359 of one, it would be completely variable, prolonged, shorten or even absent. 443 00:29:23.480 --> 00:29:26.200 Now you might ask yourself, since we have a complete block, the 444 00:29:26.279 --> 00:29:30.720 atria can't get through the ventricles to send a signal to tell them to contract 445 00:29:30.799 --> 00:29:33.880 anymore, how do we still even have QRS complexes? How are the ventricles 446 00:29:33.920 --> 00:29:37.880 still contracting? So the heart actually has a backup system, so there is 447 00:29:37.880 --> 00:29:41.400 a pacemaker in the ventricles as well as other places throughout the heart, but 448 00:29:41.480 --> 00:29:48.119 they're usually suppressed by the normal and faster superoventricular rhythm. But when that superoventricular 449 00:29:48.200 --> 00:29:52.640 rhythm is no longer sensed because of this block, the backup system kicks in 450 00:29:52.920 --> 00:29:56.720 and the lower conduction system of the heart takes over and generates its own electrical 451 00:29:56.720 --> 00:30:00.000 impulses. These are called escape rhythms. And while these escape rhythms they can 452 00:30:00.000 --> 00:30:04.680 be slower and at times unreliable, they're essentially the only thing keeping the patient 453 00:30:04.759 --> 00:30:08.400 alive and preventing a sudden cardiac arrest. All right, So that's the first 454 00:30:08.440 --> 00:30:11.200 thing and the most important thing to be aware of on ECG, that AV 455 00:30:11.319 --> 00:30:17.200 dissociation, no relationship between P waves and QS complexes. Next thing to look 456 00:30:17.200 --> 00:30:19.920 out for an n ECG is that the P wave is going to be greater 457 00:30:21.039 --> 00:30:23.640 than the qrs rate. So an ECG you'll notice there's more P waves than 458 00:30:23.720 --> 00:30:27.720 QS complexes and why is that happening? So the atria is going to maintain 459 00:30:27.759 --> 00:30:33.200 its regular rhythm and continue to generate electrical impulses at the normal atrial rate, 460 00:30:33.440 --> 00:30:37.559 which is generally between sixty to one hundred beats per minute. In contrast, 461 00:30:37.759 --> 00:30:41.160 the ventricles are now generating these escape rhythms as we discussed before, and these 462 00:30:41.319 --> 00:30:45.839 escape rhythms have a much slower rate. How slow depends on the level of 463 00:30:45.880 --> 00:30:48.559 the block, but in general, junctional escape rhythms tend to have a rate 464 00:30:48.559 --> 00:30:53.119 between forty to sixty beats per minuted, and ventricular escape rhythms typically have rates 465 00:30:53.119 --> 00:30:56.319 of forty beats per minute or less. So remember on ECG, in a 466 00:30:56.359 --> 00:31:00.759 complete Hart block, you'll see more pwaves than QR complexes. And then finally 467 00:31:00.799 --> 00:31:04.480 a last note, be aware that in a third degree block, you'll usually 468 00:31:04.519 --> 00:31:08.559 have a regular P to P and regular R to our interval. Despite the 469 00:31:08.599 --> 00:31:14.519 Atrian ventricles no longer communicating with each other and working in tandem, the rhythms 470 00:31:14.519 --> 00:31:17.839 will still remain consistent. That means that the P wave will still occur at 471 00:31:17.839 --> 00:31:21.839 the same interval, and each QRS complex will also occur at the same interval. 472 00:31:22.039 --> 00:31:25.640 They'll have absolutely nothing to do with one another, but they'll still pop 473 00:31:25.720 --> 00:31:30.440 up as expected with normal intervals, and this regularity can sometimes help identify a 474 00:31:30.519 --> 00:31:33.720 hidden P wave that might be buried, maybe in a T wave or a 475 00:31:33.759 --> 00:31:37.200 QS complex. So third degree AV block, remember P waves and QS complexes 476 00:31:37.200 --> 00:31:41.839 are going to be independent of each other. They're both doing their own thing 477 00:31:41.960 --> 00:31:45.480 no longer on speaking terms, Remember the P wave rate is going to be 478 00:31:45.519 --> 00:31:48.000 greater than the QRS rate, and finally, remember to look for a regular 479 00:31:48.000 --> 00:31:52.759 P top and regular R to our interval. Most important one to remember though, 480 00:31:52.799 --> 00:31:56.920 is that AV dissociation. The atrion ventricles are beating independent of each other. 481 00:31:56.200 --> 00:31:59.720 So how do you remember this for the exam? You remember the rhyme. 482 00:32:00.119 --> 00:32:02.359 If qes and p's don't agree, then you have a third degree. 483 00:32:02.720 --> 00:32:07.039 If QUES and PAS don't agree, then you have a third degree. This 484 00:32:07.079 --> 00:32:09.480 will help you remember the avid association, which is the most important finding on 485 00:32:09.599 --> 00:32:13.960 ECG for a third degree block and wrap this up. Let's finish up with 486 00:32:14.039 --> 00:32:19.960 treatment. So hemodynamically stable patients do not require immediate treatment with atropine or temporary 487 00:32:19.960 --> 00:32:22.519 cardiac pacing, but you need to be ready for these patients to crash at 488 00:32:22.559 --> 00:32:27.680 any point. As I discussed before, those escape rhythms they're keeping the patients 489 00:32:27.680 --> 00:32:30.400 alive, but they're unreliable and they're unstable, so you want to have transcutaneous 490 00:32:30.440 --> 00:32:34.880 pacing pads in place for the event these patients start to crash, which can 491 00:32:34.920 --> 00:32:37.960 happen very quickly. In addition, you want to be actively looking and treating 492 00:32:38.000 --> 00:32:44.640 any reversible causes now. If they're unstable. Hemodynamically unstable, these patients are 493 00:32:44.680 --> 00:32:49.799 going to be urgently treated with atropine, your beta adrenergic agoness we discussed before, 494 00:32:49.920 --> 00:32:53.599 dopamine, etc. And temporary cardiac pacing. Usually start with atropine. 495 00:32:53.640 --> 00:32:58.359 If that's ineffective, you work your way down to the other treatment options temporary 496 00:32:58.359 --> 00:33:01.200 cardiac pacing, etc. Once you stabilize them, it's back to the hunt 497 00:33:01.200 --> 00:33:06.200 again looking for any underlying cause that can be treated to reverse the block. 498 00:33:06.480 --> 00:33:09.559 But ultimately, any patient that has a third degree block where you cannot identify 499 00:33:09.640 --> 00:33:14.359 a reversable etiology, they're going to get a pacemaker. Most patients with a 500 00:33:14.359 --> 00:33:19.039 third degree block will get a pacemaker unless a treatable underlying etiology is found, 501 00:33:19.200 --> 00:33:22.079 and that's your treatment for a third degree block. So a quick recap of 502 00:33:22.119 --> 00:33:24.960 a third degree av block. This is a defect in the cardiac conduction system 503 00:33:25.039 --> 00:33:30.319 or a complete block leads to zero atrial impulses reaching the ventricles, you're going 504 00:33:30.319 --> 00:33:35.480 to have complete dissociation of the atria and ventricles. Causes are similar to the 505 00:33:35.519 --> 00:33:38.799 other types of heart blocks. Med's milecardial infarction milecardiais due to lime disease. 506 00:33:39.039 --> 00:33:45.200 Symptoms will widely vary anywhere from fatigue and dispnea to sudden cardiac arrest diagnosed with 507 00:33:45.279 --> 00:33:49.680 ECG, which will display complete dissociation between the P waves and QS complexes. 508 00:33:49.960 --> 00:33:53.200 Definitive treatment will be with a pacemaker unless a treatable underlying cause is found, 509 00:33:53.519 --> 00:33:57.640 and that's your third degree heart block. Before we move on to a few 510 00:33:57.759 --> 00:34:00.680 questions to test your knowledge, I want to do a quick review of the 511 00:34:00.720 --> 00:34:04.480 four types of HART blocks we went over, highlighting only the highest yield info 512 00:34:04.599 --> 00:34:07.839 from each. So starting with a first degree AV block, remember your pr 513 00:34:07.960 --> 00:34:12.079 interval is going to be over two hundred milliseconds, more than one big box. 514 00:34:12.239 --> 00:34:15.440 That's the key. All impulses are still getting through, which will separate 515 00:34:15.519 --> 00:34:19.039 it from other AV blocks. No frills, nothing fancy, nice and simple, 516 00:34:19.119 --> 00:34:22.840 just a pr interval over two hundred milliseconds. Remember this is often a 517 00:34:22.960 --> 00:34:25.239 normal variant, and remember the rhyme. If the R is far from the 518 00:34:25.320 --> 00:34:29.880 P, then you have a first degree to remember that prolonged pr interval. 519 00:34:30.280 --> 00:34:35.480 Second degree mobits one aka Winkie box usually occurs within the AV node, which 520 00:34:35.559 --> 00:34:38.039 is why atropine is used in a Mobitz one and not often used any mobits 521 00:34:38.079 --> 00:34:42.760 two, which usually occurs below the level of the AV node. Just like 522 00:34:42.840 --> 00:34:45.079 in a first degree block, Remember this can be a normal variant, and 523 00:34:45.159 --> 00:34:49.639 then the highest heel piece of info is to remember your ECG findings. The 524 00:34:49.719 --> 00:34:54.000 pr interval will progressively prolong with each beat until eventually a P wave will fail 525 00:34:54.039 --> 00:34:58.119 to conduct to the ventricles, leading to a dropped beat, and you, 526 00:34:58.199 --> 00:35:00.920 of course remember this by remembering longer, longer, longer drop than you have 527 00:35:01.119 --> 00:35:06.599 a Winkie block. Second degree av block MOBITS type two infra noodal is the 528 00:35:06.760 --> 00:35:09.880 most common area this is going to occur. This block almost always results from 529 00:35:09.920 --> 00:35:15.280 conduction system disease below the level of the AV note so at the bundle of 530 00:35:15.400 --> 00:35:19.000 hiss or at the bundle branches. Remember, because of this, atropine is 531 00:35:19.039 --> 00:35:22.280 generally avoided. And then on ECG, remember you're looking for PR intervals that 532 00:35:22.360 --> 00:35:27.719 are generally the same no progressive prolongation like we saw in ambits one, and 533 00:35:27.800 --> 00:35:30.719 they will be followed by one or more P waves that fail to conduct to 534 00:35:30.800 --> 00:35:34.960 the ventricles, so a sudden dropped beat no qures complex. Remember if some 535 00:35:35.159 --> 00:35:37.880 p's don't get through, then you have amobits two. And remember once you 536 00:35:37.960 --> 00:35:42.119 hit the level of emobits two, we're getting a lot more generous with our 537 00:35:42.119 --> 00:35:45.199 pacemakers. At this level and higher, everyone's getting a pacemaker unless a underlying 538 00:35:45.239 --> 00:35:50.239 treatable cause is found. This is different than ambits one and first degree block 539 00:35:50.559 --> 00:35:53.159 ray Symptomatic patients could just be monitored. To remember that shift in treatment at 540 00:35:53.199 --> 00:35:57.360 this level. Finally, a third degree block, you have to remember on 541 00:35:57.480 --> 00:36:00.320 ECG to look for the P waves to be marched right on through those QRS 542 00:36:00.400 --> 00:36:05.880 complexes. They will be completely out of rhythm, complete AV dissociation. That's 543 00:36:05.920 --> 00:36:08.280 the key. Remember, if qs and ps don't agree, then you have 544 00:36:08.440 --> 00:36:12.840 a third degree. And then, just as in amobids two, most patients 545 00:36:12.880 --> 00:36:15.760 will get a pacemaker unless there is some underlying treatable cause. All right, 546 00:36:15.840 --> 00:36:20.480 let's wrap it up with five quick questions. Question one, Mister Jacobs, 547 00:36:20.519 --> 00:36:23.840 a sixty three year old mail presents to the office complaining of episodes of dizziness 548 00:36:24.079 --> 00:36:30.119 and intermittent syncope. Mister Jacobs has no significant medical history, is not currently 549 00:36:30.159 --> 00:36:34.719 on any prescription medication, and his family history is negative for any cardiac conditions. 550 00:36:35.039 --> 00:36:40.000 ECG is obtained which reveals a constant PR interval without progressive prolongation followed by 551 00:36:40.119 --> 00:36:46.320 sudden failure of conduction. Laboratory tests including a CBC CMP cardiac enzymes are all 552 00:36:46.400 --> 00:36:52.840 within normal limits. Imaging studies reveal no abnormalities. Considering the likely diagnosis, 553 00:36:52.159 --> 00:36:57.639 what would be the most appropriate definitive treatment for mister Jacob's condition? So that 554 00:36:57.800 --> 00:37:00.679 is going to be a pacemaker. So first, what is this patient have? 555 00:37:00.000 --> 00:37:04.639 He has a MOBITS two second degree heartblock. This is evident by those 556 00:37:04.719 --> 00:37:09.320 consistent unchanging pr intervals followed by a sudden failure of conduction. Most importantly, 557 00:37:09.400 --> 00:37:14.920 there is no progressive prolongation which helps us roll out a MOBITS one. Next, 558 00:37:15.000 --> 00:37:17.280 he has no underlying treatable conditions, at least that are mentioned in the 559 00:37:17.360 --> 00:37:21.159 vignette. He's not taking any meads that can be to blame. Labs and 560 00:37:21.199 --> 00:37:24.239 imaging studies are normal, so we have no underlying treatable condition that could be 561 00:37:24.320 --> 00:37:28.480 to blame for the av block. And as we discussed before, a patients 562 00:37:28.480 --> 00:37:31.639 with the MOBITS two with no underlying treatable etiology, they need a pacemaker. 563 00:37:32.119 --> 00:37:36.960 Question two. A fifty seven year old female with a history of hypertension is 564 00:37:36.960 --> 00:37:40.480 brought to the emergency department by ambulance. Patient is experiencing chess pain along with 565 00:37:40.519 --> 00:37:45.159 altered mental status. On examination, she appears pale and diapheretic. Blood pressure 566 00:37:45.320 --> 00:37:51.239 is eighty over fifty millimeters of mercury. An ECG is obtained which reveals progressive 567 00:37:51.360 --> 00:37:55.039 lengthening of the pr interval with occasional non conducted p waves. Given the likely 568 00:37:55.119 --> 00:38:00.280 diagnosis, which medication should be promptly started in this patient, so that is 569 00:38:00.320 --> 00:38:02.760 going to be atropine. So we have a patient with the MOBITS one second 570 00:38:02.800 --> 00:38:07.880 degree av block. This is evident as on the ECG we have progressive lengthening 571 00:38:07.920 --> 00:38:12.320 of the pr interval with occasional non conducted p waves. This patient is clearly 572 00:38:12.400 --> 00:38:15.800 hemodynamically unstable. She has altered mental status chess pain, hypotension. So we 573 00:38:15.920 --> 00:38:20.679 know we need to act fast and the first line treatment for an unstable MOBITS 574 00:38:20.760 --> 00:38:24.360 one would be atropine. If the patient remains unstable, transcutaneous pacing is another 575 00:38:24.400 --> 00:38:29.079 option. We can start with atropine which speeds up conduction through the AV node, 576 00:38:29.280 --> 00:38:32.000 and be careful because if I change one small detail and this patient instead 577 00:38:32.079 --> 00:38:36.920 had a MOBITS too, we know we would avoid atropine because we know mobits 578 00:38:36.960 --> 00:38:39.000 too is generally caused by a block below the level of the AV node. 579 00:38:39.400 --> 00:38:43.199 Question three. Miss Smith, a sixty year old female, presents to the 580 00:38:43.239 --> 00:38:46.679 office for her annual physical exam. She has a history of hypertension, hyperlipidemia, 581 00:38:46.960 --> 00:38:52.760 osteoarthritis, and is currently taking verapamil, a tourvistatin, and neproxin. 582 00:38:52.039 --> 00:38:57.599 Additionally, she recently completed a course of amoxicillin for a sinus infection. ECG 583 00:38:57.719 --> 00:39:01.760 is obtained which reveals a first degree heart block characterized by a prolonged PR interval. 584 00:39:02.159 --> 00:39:07.320 What intervention could be pursued to potentially alleviate the first degree block is seen 585 00:39:07.360 --> 00:39:10.360 in this patient? Again, remember she's taking verapamil, torvestatin, aproxin. 586 00:39:10.639 --> 00:39:15.039 She recently had a sinus infection tokamoxyscillin, and an ECG shows a first degree 587 00:39:15.079 --> 00:39:19.119 block. What can we do to improve the first degree block? That would 588 00:39:19.119 --> 00:39:22.000 be to discontinue verapamil. All the other stuff in this vignette, including the 589 00:39:22.079 --> 00:39:27.599 sinus infection and antibiotics, they're all just distractors. It's all about verapamil. 590 00:39:27.719 --> 00:39:30.480 So remember there's a lot of causes for AV blocks, and while you don't 591 00:39:30.519 --> 00:39:32.960 need to memorize all of them, you should be very familiar with your medications. 592 00:39:34.039 --> 00:39:37.880 Remember, any medication that can compare or slow nodal conduction can lead to 593 00:39:37.960 --> 00:39:39.920 an AV block, dijox and beta blockers, and in the case of this 594 00:39:40.079 --> 00:39:45.800 patient, non dihydroperiodin calcium channel blockers, specifically verapamil. Remember it's the non 595 00:39:45.920 --> 00:39:51.559 dihydropuriody in agents like verapamil or deltaism. That are the big issues with AV 596 00:39:51.719 --> 00:39:57.880 blocks because these types of calcium channel blockers slow cardiac contractility and conduction compared to 597 00:39:58.079 --> 00:40:01.400 dihydroperiodins like m low to pene, nifetipine, etc. Which generally don't have 598 00:40:01.559 --> 00:40:07.039 this effect and are predominantly vasodilators. Question four, an ECG is conducted, 599 00:40:07.159 --> 00:40:13.079 revealing a pronounced dissociation between the PE waves and QRS complexes. The QS complexes 600 00:40:13.119 --> 00:40:16.639 appear narrow, indicating a junctional escape rhythm. Notably, both the atrial and 601 00:40:16.760 --> 00:40:22.599 ventricular rates remain steady while the atrial rate is surpassing the ventricular rate. This 602 00:40:22.760 --> 00:40:27.400 pattern corresponds to which classification of a V block, so that is going to 603 00:40:27.440 --> 00:40:30.280 be a third degree AV block. This is a pretty easy one complete dissociation 604 00:40:30.360 --> 00:40:35.679 between the atria and ventricles. Junctional escape rhythm has kicked in. Atrial rate 605 00:40:35.800 --> 00:40:38.079 is faster than the ventricular rate. That is a third degree block all the 606 00:40:38.159 --> 00:40:42.760 way. Question five last question. A forty five year old female presents the 607 00:40:42.840 --> 00:40:46.679 emergency room with complaints of fatigue, arthrologists and a rash. She is employed 608 00:40:46.719 --> 00:40:51.000 as a park ranger and spends most of the day outdoors. She has a 609 00:40:51.079 --> 00:40:55.360 history of type one diabetes hypertension and is currently taking Lantis NovoLog and lescinepril. 610 00:40:55.679 --> 00:41:00.159 An ECG is obtained which reveals a mobits type one second degree AV block. 611 00:41:00.559 --> 00:41:06.119 Taking into account the patient's medical history and symptoms, which of the following diagnostic 612 00:41:06.199 --> 00:41:09.400 tests would be most appropriate to help determine the underlying cause of the AV block. 613 00:41:09.800 --> 00:41:15.639 A chest X ray, B lime disease serology, C cardiac authorization, 614 00:41:15.119 --> 00:41:20.719 D hemoglobe and A one C E toxicology screening, So that would be answer 615 00:41:20.920 --> 00:41:25.679 B lime disease serology. This patient has fatigue, arthrologists, rash works outdoors 616 00:41:25.679 --> 00:41:30.239 as a park ranger, and has an AV block. Lime disease should definitely 617 00:41:30.280 --> 00:41:34.119 be high on your list of differentials as it appears this patient has early disseminated 618 00:41:34.159 --> 00:41:37.480 disease and she is developing limecarditis which is leading to the av block. So 619 00:41:37.639 --> 00:41:43.039 limesterology would be an important diagnostic test to order in this patient as this is 620 00:41:43.079 --> 00:41:45.440 likely the underlying etiology of the AV block. All right, well, I 621 00:41:45.519 --> 00:41:49.039 hope that was helpful. Thank you so much for listening to the podcast.