WEBVTT 1 00:00:00.160 --> 00:00:04.240 We are. We're diving straight into the clinical trenches today 2 00:00:04.559 --> 00:00:07.519 with a text that, honestly it kind of fundamentally changes 3 00:00:07.559 --> 00:00:09.000 how you look at patient diagnostics. 4 00:00:09.080 --> 00:00:09.160 Oh. 5 00:00:09.240 --> 00:00:13.080 Absolutely, Yeah, we're unpacking the third edition of a really 6 00:00:13.160 --> 00:00:16.920 renowned book, one hundred and fifty Problemmas the ECG by 7 00:00:17.000 --> 00:00:20.559 doctor John R. Hampton. He's the emeritus Professor of Cardiology 8 00:00:20.600 --> 00:00:21.839 at the University of Nottingham. 9 00:00:22.480 --> 00:00:25.000 Right, and for all the medical students, the residents and 10 00:00:25.519 --> 00:00:28.160 the clinical learners joining us today, you should really consider 11 00:00:28.239 --> 00:00:30.719 this deep dive of a sort of master class. 12 00:00:30.839 --> 00:00:31.359 Exactly. 13 00:00:31.440 --> 00:00:35.600 We're taking all that dense textbook cardiology and translating it 14 00:00:35.600 --> 00:00:39.280 into actual actionable bedside knowledge because. 15 00:00:39.079 --> 00:00:41.399 The overarching mission of this book, the whole point of 16 00:00:41.439 --> 00:00:45.920 it is to bridge that gap between like theoretical electrophysiology 17 00:00:46.359 --> 00:00:50.399 and the actual living, breathing, often highly unpredictable human being 18 00:00:50.759 --> 00:00:52.479 sitting right there on your exam table. 19 00:00:52.600 --> 00:00:56.200 Yeah. Doctor Hampton basically makes the argument that sure, mastering 20 00:00:56.200 --> 00:00:59.759 the foundational books is completely necessary, but the clinical reality 21 00:00:59.799 --> 00:01:01.679 is well, it's vastly more nuanced than that. 22 00:01:01.960 --> 00:01:04.920 It's such a fascinating premise because I feel like in 23 00:01:04.959 --> 00:01:08.359 medicine we naturally crave objective precision. 24 00:01:08.439 --> 00:01:10.879 Oh, for sure, we want a clear answer, right, Like 25 00:01:11.000 --> 00:01:11.359 if a. 26 00:01:11.280 --> 00:01:14.159 Patient comes in with trauma to the forearm, you order 27 00:01:14.159 --> 00:01:16.760 an X ray, you see the jagged white line through 28 00:01:16.760 --> 00:01:19.439 the radius, and boom, you have your fracture. It's visual, 29 00:01:19.760 --> 00:01:22.000 it's structural, it is definitive. 30 00:01:22.319 --> 00:01:25.519 Yeah, but then you step into the cardiovascular realm exactly. 31 00:01:25.560 --> 00:01:28.560 You print out a twelve lead ECG and suddenly you 32 00:01:28.599 --> 00:01:32.640 are looking at a diagnostic landscape that is just incredibly murky. 33 00:01:32.760 --> 00:01:36.719 I mean, it's just a two dimensional representation of electrical vectors. 34 00:01:36.359 --> 00:01:40.519 And those squiggly lions are They're never just black and white, No. 35 00:01:40.959 --> 00:01:45.000 They require interpretation entirely through the lens of the patient's presentation. 36 00:01:45.400 --> 00:01:47.920 You just cannot separate the paper from the person. 37 00:01:47.879 --> 00:01:50.760 You really can't. I mean. The ECG is a phenomenal tool, right, 38 00:01:50.799 --> 00:01:53.319 It gives us this rapid, non invasive look at the 39 00:01:53.319 --> 00:01:54.879 heart's electrical conduction system. 40 00:01:54.959 --> 00:01:55.799 Yeah, which is amazing. 41 00:01:56.000 --> 00:01:59.319 It is. But relying on it without the clinical context 42 00:01:59.359 --> 00:02:02.480 is a really dangerous game. And that brings us to 43 00:02:02.519 --> 00:02:05.599 Hampton's golden rule for this whole deep dive, which is 44 00:02:05.640 --> 00:02:10.039 that the patient's history and their physical exam those always 45 00:02:10.120 --> 00:02:13.560 have to dictate your interpretation of the tracing, not the 46 00:02:13.680 --> 00:02:14.439 other way around. 47 00:02:14.520 --> 00:02:17.719 Right, So let's test that rule with a scenario that 48 00:02:17.759 --> 00:02:19.280 pretty much every clinician dreads. 49 00:02:19.360 --> 00:02:20.199 Okay, let's hear it. 50 00:02:20.319 --> 00:02:24.439 So a patient presents to the emergency department and they 51 00:02:24.439 --> 00:02:29.599 have a highly convincing history of an acute myocardial infarction. 52 00:02:29.439 --> 00:02:31.080 The classic presentation, right. 53 00:02:31.120 --> 00:02:33.960 They have that heavy radiating ischemic pain, their sweating dive 54 00:02:34.039 --> 00:02:37.000 reesists the whole clinical picture. You run the ECG in 55 00:02:37.039 --> 00:02:40.199 that first hour, and it is completely pristine, I mean, 56 00:02:40.360 --> 00:02:44.639 normal sinus rhythm, no st segment deviation, completely normal tea waves. 57 00:02:44.680 --> 00:02:46.520 So it looks perfect on paper exactly. 58 00:02:46.680 --> 00:02:50.080 And the temptation for a busy, maybe overworked clinician might 59 00:02:50.120 --> 00:02:52.319 be to look at that normal tracing, feel a false 60 00:02:52.360 --> 00:02:56.319 sense of security, and just consider discharging them. 61 00:02:56.400 --> 00:02:59.199 But doing that would be completely ignoring the actual underlying 62 00:02:59.240 --> 00:03:02.120 path of physiology of aeschemia. Because if you're listening to 63 00:03:02.199 --> 00:03:05.599 this and wondering, wait, how can actively dying heart muscle 64 00:03:05.680 --> 00:03:07.960 fail to register on an ECG, Well, you have to 65 00:03:08.000 --> 00:03:09.919 look at the timeline of cellular injury. 66 00:03:09.599 --> 00:03:11.360 Because it's not instantaneous, no. 67 00:03:11.240 --> 00:03:14.840 Not at all. The ECG is measuring electrical gradients across 68 00:03:14.879 --> 00:03:19.479 cell membranes. So when a coronary artery occludes, the myocardium 69 00:03:19.479 --> 00:03:22.919 distal to that blockage becomes hypoxic. It's starving for oxygen, 70 00:03:23.520 --> 00:03:26.000 but it takes time for that lack of oxygen to 71 00:03:26.039 --> 00:03:30.280 actually deplete the cellular atp stores. And until those energy 72 00:03:30.280 --> 00:03:33.879 stores are fully depleted the sodium potassium pumps on the cells, 73 00:03:34.080 --> 00:03:37.319 they just keep working and so the resting membrane potential 74 00:03:37.759 --> 00:03:39.319 remains relatively stable. 75 00:03:39.439 --> 00:03:43.159 Wow. Okay, so the electrical signature literally hasn't changed yet 76 00:03:43.199 --> 00:03:46.439 because the cellular machinery hasn't completely failed, even though the 77 00:03:46.479 --> 00:03:49.199 tissue itself is like screaming for oxygen. 78 00:03:49.280 --> 00:03:51.879 You capture the mechanical timeline perfectly there. I mean, the 79 00:03:51.960 --> 00:03:54.919 st segment elevation that we always look for that only 80 00:03:54.960 --> 00:03:58.639 occurs after the transmembrane potential alters enough to create an 81 00:03:58.680 --> 00:04:02.680 actual current of injury. Yeah, so in those early hours, 82 00:04:02.719 --> 00:04:06.719 the tissue is definitely a schemic, but the electrical gradient 83 00:04:06.840 --> 00:04:07.960 hasn't shifted. 84 00:04:07.639 --> 00:04:10.199 Yet, which is terrifying, honestly it is. 85 00:04:10.280 --> 00:04:13.280 And this is exactly why a normal ECG in the 86 00:04:13.280 --> 00:04:17.800 face of really strong clinical suspicion means absolutely nothing, so 87 00:04:17.839 --> 00:04:20.319 you admit them always. You have to admit the patient, 88 00:04:20.480 --> 00:04:25.839 observe them, perform serial ECGs, and crucially track their plasma 89 00:04:25.839 --> 00:04:27.079 troponin levels. 90 00:04:26.759 --> 00:04:29.680 Because its opponents give you that biochemical proof, right, like 91 00:04:30.040 --> 00:04:33.720 proof of myocardial necrosis, way before the electrical vectors have 92 00:04:33.800 --> 00:04:35.000 time to catch up and change. 93 00:04:35.040 --> 00:04:35.480 Exactly. 94 00:04:35.560 --> 00:04:38.040 It's kind of like trying to drive a car by 95 00:04:38.040 --> 00:04:41.279 only looking at the dashboard gages and totally ignoring the windshield. 96 00:04:41.439 --> 00:04:43.639 That is a great analogy, Like you could. 97 00:04:43.519 --> 00:04:45.199 Look down and see you have a full tank of gas, 98 00:04:45.199 --> 00:04:47.759 the engine tip is fine, but you could literally still 99 00:04:47.759 --> 00:04:48.839 be driving off a cliff. 100 00:04:48.959 --> 00:04:51.959 Yeah. The ECG is essentially just a trailing indicator in 101 00:04:52.000 --> 00:04:55.439 that specific early window, right. And you know doctor Hampton 102 00:04:55.480 --> 00:04:59.720 also applies this exact same logic to heart failure. Yeah. 103 00:05:00.160 --> 00:05:03.000 He notes that while an ECG can show you signs 104 00:05:03.040 --> 00:05:07.000 of prior insults, like say, pathological Q waves from an 105 00:05:07.040 --> 00:05:11.720 old infact, it cannot definitively prove mechanical failure because it's 106 00:05:11.759 --> 00:05:16.439 just electricity exactly. It's primarily a tool for ruling out pathology. 107 00:05:16.480 --> 00:05:20.439 In this context, if the ECG is completely normal, then 108 00:05:20.680 --> 00:05:24.800 significant heart failure is highly unlikely, but an abnormal ECG 109 00:05:24.920 --> 00:05:26.720 doesn't just automatically confirm it. 110 00:05:26.879 --> 00:05:30.160 Because again, it measures electricity, not ejection fraction. Right. So 111 00:05:30.199 --> 00:05:33.120 if we take this concept that a normal ECG doesn't 112 00:05:33.120 --> 00:05:36.240 guarantee a healthy patient and we flip it, we arrive 113 00:05:36.319 --> 00:05:38.759 at another one of Hampton's core lessons. Right, Yes, that 114 00:05:38.839 --> 00:05:42.759 an abnormal looking ECG does not automatically dictate the presence 115 00:05:42.759 --> 00:05:44.199 of an actual disease. 116 00:05:43.959 --> 00:05:46.839 Which perfectly explains the really unique structure of his book. 117 00:05:46.959 --> 00:05:48.399 Yeah, I love how we organized it. 118 00:05:48.399 --> 00:05:50.480 It's so good. He doesn't group the one hundred and 119 00:05:50.519 --> 00:05:53.279 fifty cases by pathology, you know, like putting all the 120 00:05:53.279 --> 00:05:56.279 bundle branch blocks neatly in chapter four and then all 121 00:05:56.319 --> 00:05:57.800 the techacardias in chapter. 122 00:05:57.519 --> 00:05:59.639 Five, right, which is how every other textbook does it. 123 00:06:00.399 --> 00:06:03.480 Instead, he presents them completely randomly. 124 00:06:03.040 --> 00:06:04.439 Because that's what the clinic is like. 125 00:06:04.759 --> 00:06:08.120 Yes, the clinical environment does not sort your patients by 126 00:06:08.120 --> 00:06:12.319 difficulty or by anatomical system. The trioge nurse doesn't send 127 00:06:12.319 --> 00:06:15.720 you a really simple sinus arrhythmia followed neatly by a 128 00:06:15.879 --> 00:06:17.360 complex av block. 129 00:06:17.480 --> 00:06:19.120 You just never know what's coming through the door. 130 00:06:19.240 --> 00:06:21.720 You have to be prepared to interpret whatever prints out 131 00:06:21.800 --> 00:06:24.759 in real time, and a massive part of that is 132 00:06:24.879 --> 00:06:29.879 recognizing physiological adaptations that are essentially masquerading as pathology. 133 00:06:30.040 --> 00:06:35.240 Okay, yeah, like the voltage criteria for leftventricular hypertrophy or LVH. 134 00:06:35.560 --> 00:06:37.439 That is a perfect example of it. It really is, 135 00:06:37.480 --> 00:06:40.160 because you look at the precordial leads right, and the 136 00:06:40.240 --> 00:06:42.160 S wave in V one plus the R wave in 137 00:06:42.319 --> 00:06:46.439 V five is say, well over thirty five millimeters. Huge spikes, 138 00:06:46.560 --> 00:06:50.759 massive spikes on paper. It absolutely meets the textbook circle 139 00:06:50.759 --> 00:06:52.279 alion criteria for LVH. 140 00:06:52.480 --> 00:06:52.920 It does. 141 00:06:53.120 --> 00:06:57.439 But Hampton argues, if this tracing belongs to a twenty 142 00:06:57.519 --> 00:07:01.160 year old, totally asymptomatic university student is thin and active, 143 00:07:01.680 --> 00:07:04.399 this is highly likely just a normal variant. Right, But 144 00:07:04.519 --> 00:07:07.879 what is the actual physical mechanism driving that massive voltage 145 00:07:07.920 --> 00:07:10.920 on the paper if the heart muscle isn't actually hyperta feed. 146 00:07:11.120 --> 00:07:13.439 Well, it really just comes down to basic physics. It's 147 00:07:13.480 --> 00:07:16.560 all about the proximity of the recording electrodes to the 148 00:07:16.680 --> 00:07:21.680 actual myocardium. Oh y yeah, So in a young, thin individual, 149 00:07:21.839 --> 00:07:25.319 there is very little adipose tissue or even muscle mass 150 00:07:25.800 --> 00:07:29.120 between the heart itself and the chest wall where the 151 00:07:29.199 --> 00:07:29.720 leads are. 152 00:07:29.639 --> 00:07:32.319 Placed, so there's less insulation exactly. 153 00:07:32.519 --> 00:07:34.759 The electrical signal just doesn't have to travel through all 154 00:07:34.800 --> 00:07:38.360 those insulating layers to reach the leads, so naturally the 155 00:07:38.399 --> 00:07:41.240 amplitude of the signal is going to be significantly higher 156 00:07:41.240 --> 00:07:44.199 on the print out. Wow, the machine just interprets that 157 00:07:44.319 --> 00:07:47.920 strong signal as a large muscle mass, fulfilling the criteria 158 00:07:48.000 --> 00:07:51.040 for LVH. But in reality, the leads are literally just 159 00:07:51.040 --> 00:07:52.279 sitting closer to the source. 160 00:07:52.639 --> 00:07:54.439 That makes so much sense, But I feel like that 161 00:07:54.480 --> 00:07:57.800 puts the clinician in a really tough spot, especially when 162 00:07:57.839 --> 00:07:58.839 you're dealing with athletes. 163 00:07:58.920 --> 00:08:01.800 Oh. Absolutely, Or it's Cardiology's tricky. 164 00:08:01.720 --> 00:08:05.560 Right, because we know that athletes undergo physiological remodeling. You know, 165 00:08:05.639 --> 00:08:10.360 athletes heart, But we also know that asymptomatic hypertrophic cardimiopathy 166 00:08:10.519 --> 00:08:14.120 HCM is a leading cause of sudden cardiac death in 167 00:08:14.160 --> 00:08:15.680 that exact same demographic. 168 00:08:15.720 --> 00:08:16.720 It's a huge concern. 169 00:08:17.040 --> 00:08:20.040 So if a young athlete's ACG is showing this massive 170 00:08:20.120 --> 00:08:24.199 voltage and maybe even some weird repolarization abnormalities, how do 171 00:08:24.279 --> 00:08:27.439 you clinically differentiate between oh, they just have a thin 172 00:08:27.560 --> 00:08:31.360 chest wall or a physiological adaptation versus you know a 173 00:08:31.439 --> 00:08:32.879 lethal septal hypertrophy. 174 00:08:33.080 --> 00:08:36.159 That's the critical question and the answer is you have 175 00:08:36.240 --> 00:08:39.279 to step away from the electrical data entirely and gather 176 00:08:39.399 --> 00:08:43.039 anatomical data. Okay, you order an echo cardiogram. 177 00:08:42.480 --> 00:08:43.360 Right, the ultrasound. 178 00:08:43.440 --> 00:08:46.639 Yeah, the ECPO can only ever suggest hypertrophy based on 179 00:08:46.720 --> 00:08:51.919 voltage amplitude. But the echo uses ultrasound to directly visualize 180 00:08:51.919 --> 00:08:55.720 and measure the actual physical thickness of the ventricular walls 181 00:08:55.720 --> 00:08:58.440 and the innerventricular septum, like in millimeters. 182 00:08:57.919 --> 00:08:59.519 So it takes the guesswork out completely. 183 00:08:59.519 --> 00:09:02.639 It tells you definitively if there's is structural pathology that's 184 00:09:02.679 --> 00:09:06.200 actually obstructing the outflow tract. Basically, we use the ECG 185 00:09:06.639 --> 00:09:09.919 to flag the anomaly, but we use the echo to 186 00:09:10.039 --> 00:09:11.720 diagnose the reality, the real. 187 00:09:11.799 --> 00:09:14.200 I love that, Okay, So let's apply this diagnostic framework 188 00:09:14.200 --> 00:09:16.240 to some of the specific cases in Hampton's. 189 00:09:15.879 --> 00:09:16.720 Book, Let's do it. 190 00:09:16.960 --> 00:09:20.000 He uses this really cool star system to rate the 191 00:09:20.000 --> 00:09:23.679 complexity of the tracings and it escalates from like everyday 192 00:09:23.720 --> 00:09:26.960 common findings up to critical co blue emergencies. 193 00:09:27.120 --> 00:09:28.440 Yeah, it's great progression. 194 00:09:28.679 --> 00:09:30.639 So starting right at the baseline, we have one star 195 00:09:30.759 --> 00:09:33.440 case this feature is a patient with a normal chest 196 00:09:33.559 --> 00:09:37.159 X ray and an ECG showing normal sinus rhythm, but 197 00:09:37.200 --> 00:09:41.759 it's punctuated by frequent ventricular extra systelles or PVCs. 198 00:09:41.399 --> 00:09:45.320 Right, and seeing premature ventricular contractions on a rhythm strip 199 00:09:45.480 --> 00:09:46.840 is incredibly common. 200 00:09:47.080 --> 00:09:49.159 Yeah, happens all the time, it does. 201 00:09:49.039 --> 00:09:51.799 And for a lot of learners, their immediate instinct is 202 00:09:51.799 --> 00:09:56.759 to look at those ectopic beats and consider anti arrhythmic suppression, like, 203 00:09:56.960 --> 00:10:00.000 we need to fix this rhythm, but the Golden rule says, 204 00:09:59.720 --> 00:10:03.600 exc apply the Golden rule. Look at the patient. Often 205 00:10:03.759 --> 00:10:06.679 they are completely asymptomatic. They don't even feel the palpitation, 206 00:10:07.279 --> 00:10:11.159 so without any underlying structural heart disease, these ectopic beats 207 00:10:11.159 --> 00:10:14.360 are frequently just driven by totally benign factors like what 208 00:10:14.480 --> 00:10:20.639 caffe caffeine definitely or increase sympathetic tone, stress, lack of sleep. 209 00:10:21.159 --> 00:10:24.840 If the overall clinical picture is stable, those extra systelis 210 00:10:24.879 --> 00:10:26.559 are often clinically insignificant. 211 00:10:26.720 --> 00:10:29.720 Okay, so the PVCs are basically just the everyday electrical 212 00:10:29.759 --> 00:10:31.000 noise of the heart pretty much. 213 00:10:31.120 --> 00:10:32.080 Yeah, but let's. 214 00:10:31.919 --> 00:10:34.159 Look at what happens when the conduction system actually starts 215 00:10:34.200 --> 00:10:34.840 to degenerate. 216 00:10:34.960 --> 00:10:36.919 Okay, moving up to the two star cases. 217 00:10:37.039 --> 00:10:40.879 Right, Hampton presents this intermediate two star case of an 218 00:10:40.879 --> 00:10:45.080 eighty year old man. He's presenting with slowly progressive dyspnea 219 00:10:45.519 --> 00:10:49.279 ankl edema and a really brady kartic pulse like forty 220 00:10:49.279 --> 00:10:53.399 beats permitted. So he's symptomatic very and the ECG is 221 00:10:53.440 --> 00:10:57.159 super complex. It shows atrial fibrillation with a slow ventricular response, 222 00:10:57.200 --> 00:11:00.960 a left axis deviation, and a left bundle branch blow LBBB. 223 00:11:01.120 --> 00:11:02.399 That's a lot going on. 224 00:11:02.320 --> 00:11:04.200 It is. So for the learners trying to visualize this, 225 00:11:04.240 --> 00:11:06.159 can you walk us through the actual mechanics of that 226 00:11:06.240 --> 00:11:09.120 left axis deviation in the LBBB, Like, how does the 227 00:11:09.200 --> 00:11:12.879 vector of electricity actually physically shift in this patient's chest? 228 00:11:13.279 --> 00:11:15.600 Yeah, So to understand the shift, we first have to 229 00:11:15.600 --> 00:11:20.879 look at normal conduction. Typically, that electrical impulse travels rapidly 230 00:11:20.960 --> 00:11:23.480 down both the right and left bundle branches at the 231 00:11:23.600 --> 00:11:27.399 exact same time, simultaneously, right right, And because the bulk 232 00:11:27.480 --> 00:11:29.960 of the heart's muscle mass is in the left ventricle, 233 00:11:30.360 --> 00:11:33.840 the dominant mean electrical vector points downward into. 234 00:11:33.600 --> 00:11:35.399 The patient's left Okay, makes sense. 235 00:11:35.519 --> 00:11:40.360 Now introduce the left bundle branch block that rapid electrical 236 00:11:40.480 --> 00:11:44.039 highway down the left side is now completely severed. Oh wow, 237 00:11:44.080 --> 00:11:47.720 So the impulse travels down the intact right bundle and 238 00:11:47.799 --> 00:11:50.279 it depolarizes the right ventricle. First. 239 00:11:50.440 --> 00:11:52.799 Wait, so the right side of the heart actually contracts well, 240 00:11:52.840 --> 00:11:54.799 the left side is literally just sitting there waiting for 241 00:11:54.840 --> 00:11:55.279 the signal. 242 00:11:55.399 --> 00:11:57.399 Exactly, the synchrony is completely lost. 243 00:11:57.480 --> 00:11:58.879 That sounds horribly inefficient. 244 00:11:58.960 --> 00:12:01.879 It is. What happens is the electrical signal then has 245 00:12:01.960 --> 00:12:05.919 to slowly spread sell by cell from the right ventricle 246 00:12:06.159 --> 00:12:09.320 all the way across the inner ventricular septum and finally 247 00:12:09.480 --> 00:12:11.720 up into that massive left ventricle. 248 00:12:11.480 --> 00:12:13.799 Is diffusing across the tissue. 249 00:12:13.440 --> 00:12:16.480 Right instead of using the fast per KINJ fibers. And 250 00:12:16.519 --> 00:12:20.120 because this depolarization is moving in a totally abnormal direction 251 00:12:20.480 --> 00:12:23.480 from right to left and often inferior to superior, just 252 00:12:23.480 --> 00:12:27.080 to reach the lateral wall, the overall mean electrical vector 253 00:12:27.159 --> 00:12:29.279 is pulled sharply upward and leftward. 254 00:12:29.480 --> 00:12:31.960 And that upward and leftward pull is the left axis 255 00:12:31.960 --> 00:12:33.600 deviation on the ECG. 256 00:12:33.360 --> 00:12:36.879 Precisely, and that slow cell to cell spread through the 257 00:12:36.919 --> 00:12:41.799 myocardium is exactly what creates that wide, bizarre looking QRS 258 00:12:41.840 --> 00:12:43.600 complex that you see on the paper. 259 00:12:43.360 --> 00:12:46.399 That is so cool to visualize, and tracing this back 260 00:12:46.440 --> 00:12:49.799 to the eighty year old patient symptoms. This electrical detour is, 261 00:12:50.039 --> 00:12:53.159 like we said, highly inefficient, very The age fifty relation 262 00:12:53.360 --> 00:12:56.039 means he has totally lost his agrial kick and the 263 00:12:56.159 --> 00:12:59.080 LBBB means his ventricles are contracting asynchronously. 264 00:12:59.200 --> 00:13:02.399 Right, so his over cardiac output just drops, which directly 265 00:13:02.480 --> 00:13:05.000 leads to the dysmya and the Perferl edema. 266 00:13:05.080 --> 00:13:07.679 Yes, like the tracing is literally showing us the mechanical 267 00:13:07.679 --> 00:13:09.039 failure of his aging heart. 268 00:13:09.200 --> 00:13:13.399 It really highlights the progression of conduction system disease, and 269 00:13:13.440 --> 00:13:16.039 that actually leads us directly into the territory of. 270 00:13:16.039 --> 00:13:17.879 The three star cases, the scary ones. 271 00:13:18.120 --> 00:13:21.879 Yeah, these are the critical precipice scenarios. So the text 272 00:13:21.960 --> 00:13:26.519 highlights a tracing showing a bifisicular block. Okay, specifically it's 273 00:13:26.559 --> 00:13:30.320 a right bundle branch block paired with a left posterior 274 00:13:30.360 --> 00:13:34.679 hemiblock and Hampton flags this as a massive warning sign 275 00:13:34.879 --> 00:13:38.320 because it carries a really high risk of progressing to complete. 276 00:13:38.039 --> 00:13:42.519 Heart block, complete electrical failure. To really grasp why this 277 00:13:42.600 --> 00:13:45.240 is so precarious. I feel like we need to picture 278 00:13:45.799 --> 00:13:49.080 the anatomy of the his perking system because we always 279 00:13:49.080 --> 00:13:50.720 talk about the right and left bundles, but it's not 280 00:13:50.799 --> 00:13:54.480 just two pathways. It's really a trifascicular system, isn't it 281 00:13:54.480 --> 00:13:54.799 it is. 282 00:13:54.919 --> 00:13:57.399 Yeah, So the right bundle branch is a single distinct 283 00:13:57.519 --> 00:14:00.639 pathway supplying the right ventricle, but the left bundle branch 284 00:14:00.720 --> 00:14:03.919 it splits almost immediately into two main fascicles. Okay, the 285 00:14:04.000 --> 00:14:06.840 left antier vesicle and the left post sterior fascicle. So 286 00:14:06.919 --> 00:14:09.919 essentially you have three main electrical highways supplying the ventricle. 287 00:14:10.000 --> 00:14:11.879 So if we have a right bundle branch block and 288 00:14:11.919 --> 00:14:14.840 a left posterior hammiblock, two of those three highways are 289 00:14:14.840 --> 00:14:19.159 totally shut down. Yes, the entire depolarization of both ventricles 290 00:14:19.559 --> 00:14:23.279 is now relying entirely on that one single remaining left 291 00:14:23.320 --> 00:14:24.320 anterior fascicle. 292 00:14:24.960 --> 00:14:25.559 Exactly. 293 00:14:25.679 --> 00:14:29.240 That's crazy. It's literally like a major interstate highway where 294 00:14:29.279 --> 00:14:32.240 two lanes are closed for construction and all the traffic 295 00:14:32.320 --> 00:14:35.960 is being forced over a single superfragile detour bridge. 296 00:14:36.080 --> 00:14:38.159 That is a brilliant way to picture it. And it's 297 00:14:38.159 --> 00:14:41.440 a fragile bridge that often shares the exact same compromised 298 00:14:41.440 --> 00:14:43.879 blood supply as the pathways that just failed. 299 00:14:44.039 --> 00:14:45.639 Oh no, yeah. 300 00:14:45.879 --> 00:14:48.679 In many cases, these fascicles are supplied by the septal 301 00:14:48.720 --> 00:14:51.960 branches of the left anterior descendant artery. So if a 302 00:14:51.960 --> 00:14:55.799 schemic disease or maybe degenerative fibrosis like LEFS disease or 303 00:14:55.919 --> 00:15:00.679 Lenagre's disease has already destroyed the right bundle and the posterior. 304 00:15:00.120 --> 00:15:02.919 Fac then that anti your fascicle is probably highly diseased 305 00:15:02.919 --> 00:15:03.360 as well. 306 00:15:03.480 --> 00:15:05.080 Exactly, it's hanging by a thread. 307 00:15:05.519 --> 00:15:07.519 And if that final fascicle fails. 308 00:15:07.279 --> 00:15:10.080 Then the electrical connection between the atria and the ventricles 309 00:15:10.159 --> 00:15:12.240 is completely severed. You have complete heart block. 310 00:15:12.399 --> 00:15:12.720 Wow. 311 00:15:12.759 --> 00:15:16.919 The ventricles might generate a slow, totally unreliable escape rhythm, 312 00:15:17.360 --> 00:15:19.960 or they might just stop entirely, which leads to a 313 00:15:20.000 --> 00:15:21.840 systal and sudden cardiac arrest. 314 00:15:22.000 --> 00:15:25.759 So by recognizing that specific biphysiculo pattern on the ECG, 315 00:15:26.240 --> 00:15:29.080 you can actually anticipate that total failure before it happens. 316 00:15:29.200 --> 00:15:31.840 That's the whole point. It prompts you to prepare for 317 00:15:31.919 --> 00:15:36.919 transcutaneous pacing or get cardiology involved immediately. You are treating 318 00:15:36.960 --> 00:15:39.200 the trajectory of the disease, not just the rhythm you 319 00:15:39.200 --> 00:15:40.360 see in that exact moment. 320 00:15:40.519 --> 00:15:44.000 Man, the conduction system is just fascinating. But as Hampton 321 00:15:44.039 --> 00:15:45.919 points out, it doesn't operate in the vacuum. 322 00:15:46.000 --> 00:15:47.080 No, it definitely doesn't. 323 00:15:47.200 --> 00:15:49.879 The heart is bathed in the patient's blood. And he 324 00:15:49.960 --> 00:15:53.279 makes this really compelling case for the ECG acting as 325 00:15:53.320 --> 00:15:54.720 a sort of systemic mirror. 326 00:15:54.919 --> 00:15:55.960 I love that concept. 327 00:15:56.120 --> 00:15:59.720 Yeah, where chemical changes in the body profoundly alter the 328 00:15:59.759 --> 00:16:02.720 all electrical signature on the paper. Let's talk about that well. 329 00:16:02.799 --> 00:16:06.759 Electrolyte imbalances are probably the classic example of this systemic reflection, 330 00:16:06.879 --> 00:16:09.840 particularly when you're looking at the tea wave. So hypercolemia, 331 00:16:09.919 --> 00:16:13.600 which is elevated serum potassium that classically presents with tall, 332 00:16:13.720 --> 00:16:18.559 peaked and narrow tea waves, but hypocolemi low potassium manifests 333 00:16:18.600 --> 00:16:22.159 with T wave inversion, s T depression and these really 334 00:16:22.240 --> 00:16:23.320 prominent EU waves. 335 00:16:23.639 --> 00:16:27.360 But why does potassium specifically target the repolarization phase of 336 00:16:27.440 --> 00:16:30.360 the ECG, like what is actually happening at the ion 337 00:16:30.440 --> 00:16:33.559 channel level to physically change the shape of that wave 338 00:16:33.600 --> 00:16:34.159 on the paper. 339 00:16:34.440 --> 00:16:37.399 Okay, for that, it requires looking at phase three of 340 00:16:37.399 --> 00:16:38.799 the cardiac action potential. 341 00:16:38.879 --> 00:16:39.879 Okay, take us back to. 342 00:16:39.840 --> 00:16:45.799 Physiology, right, So after the myocardial cell depolarizes and physically contracts, 343 00:16:46.240 --> 00:16:48.799 it has to reset its electrical gradient to prepare for 344 00:16:48.840 --> 00:16:49.399 the next beat. 345 00:16:49.559 --> 00:16:50.039 Makes sense. 346 00:16:50.519 --> 00:16:54.159 This rapid repolarization phase is driven almost entirely by the 347 00:16:54.240 --> 00:16:56.919 rapid e flux of potassium ions rushing out of the cell, 348 00:16:57.360 --> 00:17:00.159 and the speed and the slope of that eflux that 349 00:17:00.320 --> 00:17:03.000 is what dictates the actual shape of the teawave. 350 00:17:03.120 --> 00:17:04.720 Okay, so it's a direct reflection. 351 00:17:05.000 --> 00:17:09.200 Yes, If you alter the extracellular concentration of potassium, you 352 00:17:09.279 --> 00:17:12.839 alter the concentration gradient across that cell membrane. So in 353 00:17:12.880 --> 00:17:16.119 hypercolemia you have too much potassium outside the cell. That 354 00:17:16.200 --> 00:17:20.440 altered gradient actually causes a much faster, steeper repolarization, which 355 00:17:20.480 --> 00:17:22.119 is what narrows and peaks the teawave. 356 00:17:22.240 --> 00:17:22.720 Oh wow. 357 00:17:22.759 --> 00:17:26.599 And then in hypocalmia, the repolarization is prolonged, which flattens 358 00:17:26.640 --> 00:17:29.359 the tea wave and actually exposes the U wave, and 359 00:17:29.400 --> 00:17:32.799 that uwave is generally thought to represent the delay repolarization 360 00:17:32.880 --> 00:17:34.039 of the Perkini fibers. 361 00:17:34.400 --> 00:17:36.960 It is just incredible to think that you are visually 362 00:17:37.000 --> 00:17:40.759 observing the altered kinetic flow of ions on a piece 363 00:17:40.759 --> 00:17:43.880 of graph paper. It really is, and this interplay between 364 00:17:43.920 --> 00:17:47.519 systemic chemistry and electrical function it becomes literally deadly. In 365 00:17:47.559 --> 00:17:49.720 Case one seventeen from the book, Oh, this is a 366 00:17:49.759 --> 00:17:53.599 great case, Hampin presents this patient with atrial fibrillation who 367 00:17:53.680 --> 00:17:58.039 suddenly develops frequent ventricular extra systillies. Now on the surface, 368 00:17:58.039 --> 00:17:59.880 it just looks like the cardac tissue is becoming irrit 369 00:18:00.799 --> 00:18:04.319 but the actual diagnosis requires looking at the patient's medication 370 00:18:04.440 --> 00:18:08.279 list and their metabolic panel. It's a case of digitalis 371 00:18:08.359 --> 00:18:11.319 toxicity exacerbated by hypocalemia. 372 00:18:11.480 --> 00:18:15.480 Yeah. So digoxin. It's an older cardiac glycoside that we 373 00:18:15.599 --> 00:18:17.839 use for rate control in a fib and sometimes for 374 00:18:17.839 --> 00:18:21.640 heart failure. Its mechanism of action is absolutely critical to 375 00:18:21.720 --> 00:18:25.519 understand here. It worked by inhibiting the sodium potassium at 376 00:18:25.720 --> 00:18:29.599 pace pump on the myocardial cell membrane. Okay, by blocking 377 00:18:29.640 --> 00:18:34.000 this pump, the intracellular sodium levels increase, and that buildup 378 00:18:34.000 --> 00:18:37.599 of sodium reduces the activity of the sodium calcium exchange, 379 00:18:37.680 --> 00:18:41.279 which means which ultimately traps more calcium inside the cell, 380 00:18:41.559 --> 00:18:43.920 and that increases the force of the heart's contraction. 381 00:18:44.359 --> 00:18:49.640 But the therapeutic window for digoxin is notoriously like razor thin. 382 00:18:49.720 --> 00:18:50.279 Very narrow. 383 00:18:50.519 --> 00:18:54.759 Where does the hypocolemia actually factor in to trigger the toxicity. 384 00:18:54.799 --> 00:18:58.039 Well, potassium and digoxin actually compete for the exact same 385 00:18:58.119 --> 00:19:01.079 binding site on that sodium potassium atipasee pump. 386 00:19:01.119 --> 00:19:01.799 Oh I didn't know that. 387 00:19:02.000 --> 00:19:05.359 Yeah, So if the patient is hypocolemic, say maybe they're 388 00:19:05.400 --> 00:19:09.000 on a loop diuretic like furosmide that's wasting their potassium, 389 00:19:09.440 --> 00:19:14.799 there is just less extracellular potassium to compete with the digoxin. 390 00:19:14.480 --> 00:19:15.839 So the digoxin just takes over. 391 00:19:16.000 --> 00:19:19.680 Exactly, The drug binds much more extensively to those pumps 392 00:19:19.720 --> 00:19:24.240 and severely inhibits them. And this massive intracellular calcium overload 393 00:19:24.480 --> 00:19:27.680 leads to delayed after depolarizations. 394 00:19:26.799 --> 00:19:27.799 Which are what exactly. 395 00:19:27.839 --> 00:19:31.319 They're essentially the spontaneous releases of calcium from the sarcoplasmic 396 00:19:31.319 --> 00:19:34.839 reticulum during the resting phase, and those spontaneous releases are 397 00:19:34.839 --> 00:19:38.039 what trigger the early ectopic beats that you see on 398 00:19:38.079 --> 00:19:39.960 the strip as ventricular extra systiles. 399 00:19:40.240 --> 00:19:42.759 So if a clinician just looked at the strip, merely 400 00:19:42.799 --> 00:19:46.599 saw the extra systiles and administered an anti arrhythmic without 401 00:19:46.680 --> 00:19:49.160