WEBVTT 1 00:00:00.320 --> 00:00:04.000 Usually when we talk about a medical diagnosis, there's this 2 00:00:04.559 --> 00:00:06.200 expectation of total precision. 3 00:00:06.240 --> 00:00:08.039 Oh, absolutely, like it's engineering or something. 4 00:00:08.119 --> 00:00:09.759 Right, Like you break your arm, they take an X 5 00:00:09.839 --> 00:00:11.960 ray and it shows that jagged white line and the 6 00:00:12.000 --> 00:00:13.720 doctor just points and says, well, there it. 7 00:00:13.640 --> 00:00:16.320 Is broken, clean and simple. 8 00:00:16.519 --> 00:00:19.559 Yeah, it's binary. It gives everyone in the room this 9 00:00:19.719 --> 00:00:22.000 massive sense of comfort because we like things to be 10 00:00:22.559 --> 00:00:24.519 visible and easily categorized, you. 11 00:00:24.519 --> 00:00:26.960 Know, we really do. But then you step into the 12 00:00:26.960 --> 00:00:30.679 world of cardiac electrophysiology. Oh boy, yeah, you walk into 13 00:00:30.719 --> 00:00:36.359 a chaotic emergency department and suddenly that pristine diagnostic clarity 14 00:00:37.479 --> 00:00:38.880 it just vanishes. 15 00:00:38.560 --> 00:00:41.960 It really does. We're looking at a landscape that is well, honestly, 16 00:00:42.439 --> 00:00:43.000 it's murky. 17 00:00:43.240 --> 00:00:47.399 It is the absolute definition of diagnostic muddy waters. I mean, 18 00:00:47.600 --> 00:00:49.960 navigating those waters is exactly what we are going to 19 00:00:50.039 --> 00:00:50.679 do today, and. 20 00:00:50.600 --> 00:00:53.759 That unpredictable landscape is exactly why we're doing this deep 21 00:00:53.799 --> 00:00:57.039 dive today. We are tearing into John R. Hampton's classic 22 00:00:57.079 --> 00:01:00.920 text one hundred and fifty ECG Problems specific the fourth 23 00:01:01.039 --> 00:01:02.719 edition from twenty thirteen. 24 00:01:02.560 --> 00:01:03.560 A legendary book. 25 00:01:03.759 --> 00:01:05.840 It really is. Yeah, and whether you're you know, a 26 00:01:05.879 --> 00:01:09.239 medical studient, cramming for exams, or a junior doctor finding 27 00:01:09.239 --> 00:01:10.319 your feet on the wards, or. 28 00:01:10.280 --> 00:01:12.400 A paramedic making those split second calls in the back 29 00:01:12.439 --> 00:01:13.640 of an ambulance. 30 00:01:13.280 --> 00:01:16.760 Exactly, or even just a fiercely curious learner. You are 31 00:01:16.760 --> 00:01:19.599 in the right place, because we're not just looking at 32 00:01:19.680 --> 00:01:21.439 christine textbook squiggles today. 33 00:01:21.680 --> 00:01:26.000 No, we're looking at the messy, chaotic, real world signals 34 00:01:26.239 --> 00:01:27.840 that actually save lives. 35 00:01:28.159 --> 00:01:30.640 Right. But before we even look at a single trace, 36 00:01:31.000 --> 00:01:33.640 I think we need to establish the foundational premise of 37 00:01:33.680 --> 00:01:34.760 Hampton's entire text. 38 00:01:34.879 --> 00:01:37.480 Yeah, the golden rule, if you will, which is that 39 00:01:37.640 --> 00:01:41.799 recording and reporting an ECG should never ever be an 40 00:01:41.879 --> 00:01:42.560 end in itself. 41 00:01:42.959 --> 00:01:43.200 Never. 42 00:01:43.480 --> 00:01:47.359 I mean, it is a fundamental, cheap and totally harmless tool, 43 00:01:47.840 --> 00:01:50.280 and it gives us this electrical information that we literally 44 00:01:50.319 --> 00:01:53.640 cannot obpain in any other way. But it is absolutely 45 00:01:53.719 --> 00:01:57.799 no substitute for taking a proper medical history and performing 46 00:01:57.879 --> 00:01:59.840 a careful physical examination. 47 00:02:00.120 --> 00:02:02.879 Yeah, and the structure of the book itself actually reinforces 48 00:02:02.879 --> 00:02:06.400 that golden rule. It's designed to bridge the gap between 49 00:02:06.920 --> 00:02:09.719 theoretical learning and clinical reality. 50 00:02:09.439 --> 00:02:12.280 By presenting one hundred and fifty cases completely randomly. 51 00:02:12.439 --> 00:02:15.520 Yes, you turn the page and you have no idea 52 00:02:15.599 --> 00:02:16.680 what is coming next. 53 00:02:16.599 --> 00:02:20.039 Which mimics the reality of A and E perfectly, because 54 00:02:20.080 --> 00:02:22.479 patients don't walk through the hospital doors in order of 55 00:02:22.520 --> 00:02:23.919 diagnostic difficulty right now. 56 00:02:24.000 --> 00:02:25.080 No, they definitely do. 57 00:02:25.080 --> 00:02:28.039 Not, and they don't arrive grouped by pathology. You don't 58 00:02:28.039 --> 00:02:31.360 get a neat sequence of atrial fibrillation cases on a 59 00:02:31.360 --> 00:02:34.319 Tuesday morning. That would be nice, but no, right, The 60 00:02:34.479 --> 00:02:38.599 randomness maintains your clinical vigilance. You have to interpret the 61 00:02:38.719 --> 00:02:41.080 data fresh every single time. 62 00:02:41.000 --> 00:02:45.000 And Hampton also grades each case by difficulty to help 63 00:02:45.039 --> 00:02:48.080 you gauge where you stand. So one star is for 64 00:02:48.120 --> 00:02:49.199 the medical student. 65 00:02:48.960 --> 00:02:51.199 Level, the classic presentations, right, this. 66 00:02:51.159 --> 00:02:53.639 Stuff anyone who has read the basic theory should catch. 67 00:02:54.680 --> 00:02:57.680 Then two stars step up the complexity for junior doctors, 68 00:02:57.719 --> 00:02:59.759 specialist nurses or paramedics. 69 00:02:59.800 --> 00:03:01.560 And the three star cases. 70 00:03:01.319 --> 00:03:02.639 Yeah, those are the tough ones. 71 00:03:02.719 --> 00:03:05.719 Those are designed to challenge MRCP candidates trying to gain 72 00:03:05.800 --> 00:03:07.960 memptyship of the Royal Colleges of Physicians. 73 00:03:08.319 --> 00:03:11.080 Exactly. So, you read the brief clinical scenario and you 74 00:03:11.120 --> 00:03:13.400 have to interpret the ECG before you even know if 75 00:03:13.400 --> 00:03:15.039 you're looking at a one star layup or a three 76 00:03:15.039 --> 00:03:15.759 star nightmare. 77 00:03:15.919 --> 00:03:18.800 And part of what makes those real world cases nightmarriage 78 00:03:18.840 --> 00:03:21.280 is the physical state of the tracing itself. 79 00:03:21.439 --> 00:03:22.520 Oh, the artifacts. 80 00:03:22.639 --> 00:03:26.400 Yeah. In a textbook, an ECG trace is this beautiful, 81 00:03:26.639 --> 00:03:30.879 smooth black line on a crisp pink grid, perfect baseline right. 82 00:03:31.039 --> 00:03:35.599 But Hampton intentionally includes technically poor records, records filled with 83 00:03:35.719 --> 00:03:38.120 artifact and baseline wander because. 84 00:03:37.879 --> 00:03:40.240 In a clinical setting you were often dealing with patients 85 00:03:40.240 --> 00:03:43.159 who are shivering or sweating, or moving in pain. 86 00:03:43.240 --> 00:03:47.280 Or in extreme respiratory distress. You rarely get a perfect tracing, 87 00:03:47.319 --> 00:03:49.199 and you just cannot afford to wait for one. You 88 00:03:49.280 --> 00:03:51.319 have to interpret what is in front of you. 89 00:03:51.639 --> 00:03:53.840 So let's pull a specific piece of evidence from the 90 00:03:53.879 --> 00:03:57.639 text to illustrate this. Let's look at ECG one th two. 91 00:03:58.840 --> 00:04:01.800 The presentation is a thirty year old woman admitted to 92 00:04:01.840 --> 00:04:05.240 the hospital with diabetic ketoacidosis. 93 00:04:04.520 --> 00:04:08.919 pKa a profound acute metabolic crisis right, and. 94 00:04:08.919 --> 00:04:12.280 Her ECG is described as not being a technically good record. 95 00:04:12.680 --> 00:04:16.319 It exhibits considerable artifacts. The baseline is jumping all over 96 00:04:16.319 --> 00:04:16.959 the place. 97 00:04:16.839 --> 00:04:18.519 But you can't just throw your hands. 98 00:04:18.319 --> 00:04:23.279 Up exactly looking through the noise. The rhythm is identified 99 00:04:23.319 --> 00:04:28.639 as probably being sinus, but with coupled junctional extra systelase. 100 00:04:28.160 --> 00:04:29.519 Which is a huge finding. 101 00:04:29.680 --> 00:04:31.439 Yeah, and I don't want to just gloss over that. 102 00:04:31.759 --> 00:04:34.600 We have a patient in DKA and her AV node 103 00:04:34.639 --> 00:04:38.000 is getting irritable, firing off its own beats early. Why 104 00:04:38.079 --> 00:04:41.279 is DKA causing junctional extra systelase. 105 00:04:41.560 --> 00:04:44.639 Well, it really comes down to the cellular environment. Diabetic 106 00:04:44.720 --> 00:04:47.560 ketoacidosis doesn't just mean high blood sugar. 107 00:04:47.439 --> 00:04:48.360 Right, it's the acid. 108 00:04:48.439 --> 00:04:52.879 Yeah, it means profound systemic acidosis and massive electrolyte shifts, 109 00:04:53.120 --> 00:04:54.399 particularly potassium. 110 00:04:54.480 --> 00:04:55.959 So what happens to the potassium. 111 00:04:56.079 --> 00:04:59.720 The lack of insulin and the acidic environment forced potassium 112 00:04:59.759 --> 00:05:02.240 out of the cells and into the bloodstream, even. 113 00:05:02.040 --> 00:05:04.639 Though the total body potassium is actually being depleted through 114 00:05:04.680 --> 00:05:06.000 the urine exactly. 115 00:05:06.240 --> 00:05:09.279 And this constant shifting of potassium across the cardiac suum 116 00:05:09.279 --> 00:05:12.439 membranes directly alters the resting membrane potential. 117 00:05:12.480 --> 00:05:14.319 Okay, so they get twitchy, highly twitchy. 118 00:05:14.519 --> 00:05:18.399 The myocardial cells, particularly in secondary pacemaker sites like the 119 00:05:18.439 --> 00:05:22.839 AV junction, become hyper excitable. They reach their threshold potential 120 00:05:22.879 --> 00:05:26.319 prematurely and fire off an impulse before the sinus node 121 00:05:26.319 --> 00:05:26.680 gets a. 122 00:05:26.639 --> 00:05:29.720 Chance and boom, that's your junctional extra system, got it? 123 00:05:29.920 --> 00:05:32.399 And what about the P waves on this trace? The 124 00:05:32.439 --> 00:05:36.480 text notes they are really difficult to identify here, appearing 125 00:05:36.480 --> 00:05:38.040 almost completely flattened. 126 00:05:38.199 --> 00:05:41.399 Well, the technical artifact makes it challenging, certainly, but that 127 00:05:41.560 --> 00:05:45.800 flattening is also a direct physiological consequence of the metabolic. 128 00:05:45.319 --> 00:05:46.639 State from the potassium. Again. 129 00:05:46.800 --> 00:05:51.720 Yeah, as potassium levels fluctuate in DKA, the atrial myocardium's 130 00:05:51.759 --> 00:05:55.480 ability to depolarize robustly is blunted, So the signal's just 131 00:05:55.519 --> 00:05:59.680 weak exactly. The electrical vector generated by the atria is weakened, 132 00:06:00.040 --> 00:06:03.079 which translates to a smaller, flatter P wave on the paper, 133 00:06:03.519 --> 00:06:06.600 and it just hides underneath all that somatic tremor artifact 134 00:06:06.600 --> 00:06:07.560 from the patient. 135 00:06:07.319 --> 00:06:11.519 Which highlights another massive point the source emphasizes. Context is 136 00:06:11.600 --> 00:06:16.160 everything normal and abnormal are highly relative to the specific 137 00:06:16.199 --> 00:06:18.399 physiology of the person sitting right in front of. 138 00:06:18.319 --> 00:06:21.519 You, because the ECG is not a standalone truth machine. 139 00:06:21.639 --> 00:06:26.720 Right. For example, Hampton points out that widespread tea wave variations. 140 00:06:26.319 --> 00:06:30.319 Which in many patients would immediately signal eschemia. 141 00:06:30.199 --> 00:06:32.959 Right, but those can actually be considered a completely normal 142 00:06:33.079 --> 00:06:35.920 variant in a healthy black woman exactly. 143 00:06:36.000 --> 00:06:38.360 If you just looked at the trace without knowing the 144 00:06:38.439 --> 00:06:41.680 demographics or the history, you might sound the alarm for 145 00:06:41.680 --> 00:06:42.360 a heart attack. 146 00:06:42.639 --> 00:06:47.000 You might initiate this whole cascade of stressful, expensive, and 147 00:06:47.120 --> 00:06:49.360 potentially dangerous medical interventions. 148 00:06:49.439 --> 00:06:52.240 With blood thinners are an angiogram, yeah. 149 00:06:52.199 --> 00:06:53.839 All for a perfectly healthy heart. 150 00:06:53.959 --> 00:06:57.560 That clinical history is the absolute lens through which the 151 00:06:57.639 --> 00:06:59.079 ECG must be viewed. 152 00:06:59.319 --> 00:07:01.879 It makes me think of an analogy. An ECG is 153 00:07:01.879 --> 00:07:04.079 basically a single frame from a movie. 154 00:07:04.279 --> 00:07:04.800 I like that. 155 00:07:04.959 --> 00:07:07.040 Yeah, it tells you exactly what the electricity is doing 156 00:07:07.079 --> 00:07:10.439 for what a ten second window, But without knowing the plot. 157 00:07:10.279 --> 00:07:13.040 The patient's history, their symptoms. 158 00:07:12.639 --> 00:07:16.160 Right, Without that, you're going to completely misinterpret the scene. 159 00:07:16.680 --> 00:07:20.000 A character crying in a freeze frame could be experiencing 160 00:07:20.040 --> 00:07:22.720 a profound tragedy, or it could be tears of joy. 161 00:07:23.160 --> 00:07:23.920 You need the plot. 162 00:07:24.000 --> 00:07:25.160 You definitely need the plot. 163 00:07:25.319 --> 00:07:28.399 So if we need to synthesize the plot with the picture, 164 00:07:29.040 --> 00:07:32.480 how does a clinician systematically train their eye to look 165 00:07:32.519 --> 00:07:36.480 past the technical noise of artifacts without missing a subtle 166 00:07:36.720 --> 00:07:37.920 life threatening signal. 167 00:07:38.079 --> 00:07:42.000 The training requires rigid, unyielding discipline. I mean, you don't 168 00:07:42.000 --> 00:07:44.040 just glance at the movie frame and try to guess 169 00:07:44.079 --> 00:07:45.959 the emotion based on a general vibe. 170 00:07:46.040 --> 00:07:48.240 Right, no vibes based medicine, No vibes. 171 00:07:48.399 --> 00:07:52.120 You follow a strict analytical sequence every single time you 172 00:07:52.120 --> 00:07:55.040 pick up the paper. You calculate the rate, You determine 173 00:07:55.040 --> 00:07:58.279 the rhythm, check the axis, assess the cardiac axis. Yes, 174 00:07:58.720 --> 00:08:01.800 then you analyze the more fall, the P waves, the 175 00:08:01.839 --> 00:08:05.480 pr interval, the QRS complex, the st segment, and the 176 00:08:05.519 --> 00:08:08.959 T waves as a checklist, a rigorous checklist. By forcing 177 00:08:09.000 --> 00:08:11.600 your brain through that sequence, the somatic tremor and the 178 00:08:11.639 --> 00:08:14.279 baseline wander kind of fade into the background, and the 179 00:08:14.360 --> 00:08:16.560 true electrical narrative reveals itself. 180 00:08:16.639 --> 00:08:18.439 Well, if we're relying on the plot, let's look at 181 00:08:18.480 --> 00:08:21.720 what happens when the plot screams danger. Because when things 182 00:08:21.759 --> 00:08:23.600 go wrong in the heart, they go wrong. 183 00:08:23.480 --> 00:08:25.040 Fast, Oh incredibly fast. 184 00:08:25.199 --> 00:08:29.439 Let's break down ECG twenty two. The presentation is a 185 00:08:29.480 --> 00:08:32.080 forty eight year old man who comes in. He has 186 00:08:32.120 --> 00:08:34.840 had severe central chest pain for one hour. 187 00:08:35.120 --> 00:08:38.679 See that history alone dictates your response. One hour of 188 00:08:38.799 --> 00:08:41.440 severe central chest pain in a middle aged man is 189 00:08:41.440 --> 00:08:44.039 an acute coronary syndrome until proven otherwise. 190 00:08:44.240 --> 00:08:46.440 Right, So we get the trace and the findings are 191 00:08:46.519 --> 00:08:48.919 very specific sinus rhythm at seventy five beats per minute, 192 00:08:48.960 --> 00:08:53.639 we have left axis deviations, specifically left anterior hemi block. Okay, 193 00:08:53.919 --> 00:08:56.799 the qrs complexes are largely normal, but there's a small 194 00:08:57.240 --> 00:09:01.519 probably septle q wave in lead VL. And then crucially 195 00:09:01.679 --> 00:09:04.440 we see deeply inverted tea waves and leads V one 196 00:09:04.519 --> 00:09:05.320 through V five. 197 00:09:05.480 --> 00:09:06.600 That's the kicker right there. 198 00:09:06.720 --> 00:09:09.879 Yeah, so looking the clues an hour of crushing pain 199 00:09:10.480 --> 00:09:13.080 and those inverted tea waves and the anterior leads are 200 00:09:13.080 --> 00:09:14.639 practically screaming. 201 00:09:14.159 --> 00:09:15.879 A schemia loud and clear. 202 00:09:16.039 --> 00:09:18.360 Even without the ST segment elevation. We have to be 203 00:09:18.440 --> 00:09:22.519 looking at an acute anti non ST segment elevation myocardial infarction. 204 00:09:22.679 --> 00:09:25.919 Right and then, Stemmy, You've diagnosed it perfectly. The electrical 205 00:09:25.960 --> 00:09:28.799 repolarization of the anterior wall of the left ventricle is 206 00:09:28.879 --> 00:09:31.720 deeply disturbed. But let's look at the mechanism at why 207 00:09:31.759 --> 00:09:35.279 those two waves invert Exactly. The heart muscle is starving 208 00:09:35.320 --> 00:09:39.039 for oxygen because a coronary artery is partially blocked, and 209 00:09:39.200 --> 00:09:42.840 this lack of oxygen cripples the ATP dependent potassium channels 210 00:09:42.840 --> 00:09:47.000 in the CARDIAXL membranes. Okay, Normally, repolarization spreads from the 211 00:09:47.039 --> 00:09:49.519 outside of the heart inwards from the epicardium to the 212 00:09:49.639 --> 00:09:50.399 endocardi Right. 213 00:09:50.440 --> 00:09:51.919 That's the standard healthy pathway. 214 00:09:51.960 --> 00:09:55.639 But is schemia changes the action potential duration. It actually 215 00:09:55.720 --> 00:09:59.600 forces the repolarization wave to travel backward away from the 216 00:09:59.600 --> 00:10:01.759 explore oring electrodes on the patient's chest. 217 00:10:01.919 --> 00:10:05.320 In an electrical wave, moving away from a positive electrode 218 00:10:05.360 --> 00:10:06.879 records as a negative. 219 00:10:06.559 --> 00:10:09.879 Deflection, Hence the inverted teawave wow. 220 00:10:09.480 --> 00:10:12.720 And the textbook demands immediate action for this and stemmy. 221 00:10:13.399 --> 00:10:16.720 The medical management outline includes short and long acting nitrates, 222 00:10:16.960 --> 00:10:19.399 beta blockers, and calcium. 223 00:10:18.879 --> 00:10:20.720 Antagonists standard protocol. 224 00:10:20.799 --> 00:10:23.759 But we shouldn't just list medications. Let's talk about how 225 00:10:23.759 --> 00:10:26.480 they are actually saving this man's heart tissue in real time. 226 00:10:26.639 --> 00:10:29.279 Well, the pharmacology is all about altering the supply and 227 00:10:29.360 --> 00:10:33.519 demand mismatch. Nitrates are vasodilators. They open up the coronary 228 00:10:33.559 --> 00:10:36.120 vessels to improve whatever blood flow can still get past. 229 00:10:36.120 --> 00:10:39.519 The blockage is widening the pipes exactly. But beta blockers 230 00:10:39.559 --> 00:10:42.360 are arguably the most fascinating intervention. 231 00:10:41.960 --> 00:10:43.639 Here because they slow the heart down. 232 00:10:43.960 --> 00:10:48.639 Yes, by blocking sympathetic nervous system stimulation. They force the 233 00:10:48.639 --> 00:10:52.000 heart rate to drop, meaning the heart spends more time 234 00:10:52.080 --> 00:10:54.279 in diastol the relaxation phase. 235 00:10:54.399 --> 00:10:55.639 Okay, and why is that so. 236 00:10:55.639 --> 00:10:58.919 Critical Because unlike every other organ in the body, the 237 00:10:59.000 --> 00:11:02.720 heart muscle only he receives its own blood supply during diastyl. 238 00:11:03.000 --> 00:11:05.919 Oh, wow, I didn't realize it was only during relaxation. 239 00:11:06.080 --> 00:11:09.120 Yeah, when it squeozes, the vessels are clamped shut. So 240 00:11:09.240 --> 00:11:12.840 by artificially prolonging diastol with a beta blocker, you are 241 00:11:12.879 --> 00:11:16.960 maximizing the time the coronary arteries have to actually feed 242 00:11:17.000 --> 00:11:17.919 that starving tissue. 243 00:11:18.000 --> 00:11:20.519 That is brilliant, But the pills just stabilize him. Right. 244 00:11:21.039 --> 00:11:24.840 The text states he also needs urgent coronary angiography. 245 00:11:24.320 --> 00:11:28.879 Yes, to physically look inside those arteries with contrast dye. 246 00:11:28.559 --> 00:11:32.200 With a view to performing a percutaneous coronary intervention, right, 247 00:11:32.559 --> 00:11:35.559 putting in a stent to crush the plaque against the artery. 248 00:11:35.320 --> 00:11:40.000 Wall or potentially a coronary artery bypass graft. Plus for 249 00:11:40.080 --> 00:11:43.039 long term survival, he has to address the underlying plot 250 00:11:43.120 --> 00:11:46.120 of his movie. His risk factor is like smoking, weight 251 00:11:46.200 --> 00:11:47.360 and hypercholesterolemia. 252 00:11:47.480 --> 00:11:52.320 Right, it is a massive coordinated systemic response entirely triggered 253 00:11:52.320 --> 00:11:55.080 by combining inverted tea waves with his clinical story. 254 00:11:55.200 --> 00:11:56.600 It's beautiful when it works. 255 00:11:56.919 --> 00:12:01.159 But let's contrast that ischemic and stemic presentation with structural one. 256 00:12:01.279 --> 00:12:04.559 ECG one nine carries a three star difficulty rating. 257 00:12:04.600 --> 00:12:05.799 Oh this is a heavy one. 258 00:12:05.919 --> 00:12:08.799 Yeah. A fifty year old man who has had attacks 259 00:12:08.840 --> 00:12:12.679 of dizziness and palpitations for several years suddenly collapses at work. 260 00:12:13.159 --> 00:12:15.879 He is brought into a and E cold and clammy. 261 00:12:16.200 --> 00:12:18.679 His heart rate is rapid and his blood pressure is 262 00:12:18.679 --> 00:12:23.120 completely unrecordable. Wow, there are clinical signs of left ventricular failure. 263 00:12:22.799 --> 00:12:25.639 So he is in profound cardiogenic shock. His pump has 264 00:12:25.639 --> 00:12:26.840 failed entirely. 265 00:12:26.679 --> 00:12:30.320 Exactly, and the ECG shows gross massive tea wave inversion 266 00:12:30.360 --> 00:12:33.600 in the intralateral leads. And according to the text, this 267 00:12:33.759 --> 00:12:36.879 gross teawave inversion, coupled with the history of dizziness leading 268 00:12:36.879 --> 00:12:40.519 to a sudden collapse suggests hypertrophic cardiomyopathy. 269 00:12:40.799 --> 00:12:43.960 This is a phenomenal case because it perfectly illustrates how 270 00:12:44.080 --> 00:12:49.320 structural muscle changes broadcasts themselves as electrical anomalies. How so 271 00:12:49.840 --> 00:12:53.919 well in hypertrophic cardiomyopathy, the heart muscle of the left 272 00:12:54.000 --> 00:12:56.039 ventricle grows abnormally thick. 273 00:12:56.320 --> 00:12:58.720 But it's not just a big, strong muscle, is it. 274 00:12:58.799 --> 00:13:01.720 To use an analogy, a healthy heart's electrical system is 275 00:13:01.759 --> 00:13:05.279 like a high speed fiber optic network. The signal travels 276 00:13:05.320 --> 00:13:09.960 fast and clean. But in hypertrophic cordiumyopathy, the muscle fibers 277 00:13:09.960 --> 00:13:13.480 haven't just grown. They are disorganized and chaotic. It's like 278 00:13:13.519 --> 00:13:15.919 trying to send that same high speed signal through a 279 00:13:16.000 --> 00:13:17.480 tangled knot of copper wire. 280 00:13:17.799 --> 00:13:20.639 That is an excellent way to conceptualize it. The cellular 281 00:13:20.759 --> 00:13:23.919 architecture is literally called myocardial disarray. 282 00:13:24.120 --> 00:13:25.919 Myocardial disarray that sounds bad. 283 00:13:26.039 --> 00:13:29.399 It is because the cells are disorganized. The electrical signal 284 00:13:29.440 --> 00:13:33.879 slows down, distorts, and causes chaotic inverted repolarization waves on 285 00:13:33.919 --> 00:13:34.679 the paper. 286 00:13:34.480 --> 00:13:37.399 Which explains the massive T wave inversions exactly. 287 00:13:37.840 --> 00:13:42.159 Furthermore, that thick, disorganized muscle can physically obstruct the outflow 288 00:13:42.240 --> 00:13:44.639 of blood from the heart during contraction. 289 00:13:44.399 --> 00:13:46.799 So it's squeezing but nothing gets out right. 290 00:13:47.120 --> 00:13:49.840 If the blood can't get out, the stroke volume drops 291 00:13:49.840 --> 00:13:53.559 to near zero, the blood pressure becomes unrecordable, the brain 292 00:13:53.679 --> 00:13:56.519 loses perfusion, and the patient collapses. 293 00:13:56.159 --> 00:13:58.799 Exactly as described in the case. Yes, but hold on, 294 00:13:59.000 --> 00:14:01.600 if we are relying so heavily on the exact shape 295 00:14:01.639 --> 00:14:05.120 of these squiggles and reading the plot of these tangled wires, 296 00:14:05.720 --> 00:14:08.720 isn't there a massive diagnostic blind spot here? 297 00:14:09.000 --> 00:14:09.559 What do you mean? 298 00:14:09.879 --> 00:14:12.919 Well, what if a patient comes in clutching his chest, 299 00:14:13.240 --> 00:14:18.279 feeling absolutely terrible, but his resting ECG is pristine, not 300 00:14:18.360 --> 00:14:20.559 a single te wave out of place? Do we just 301 00:14:20.600 --> 00:14:21.159 send him home? 302 00:14:21.279 --> 00:14:23.519 Oh? That is a life or death question, and the 303 00:14:23.600 --> 00:14:26.480 answer is an emphatic no. You absolutely do not send 304 00:14:26.519 --> 00:14:26.840 them home. 305 00:14:26.919 --> 00:14:27.480 Okay, good. 306 00:14:27.639 --> 00:14:30.480 A normal resting ECG does not guarantee a healthy heart. 307 00:14:30.720 --> 00:14:33.120 And ECG is a static test. I mean it's a 308 00:14:33.159 --> 00:14:36.039 ten second snapshot taken while the patient is lying quietly 309 00:14:36.039 --> 00:14:39.000 in a hospital bed with minimal physical exertion. 310 00:14:38.759 --> 00:14:42.000 Which brings us to the severe limitations of the resting ECG. Yeah, 311 00:14:42.000 --> 00:14:44.159 and what happens when we force the heart to work harder? 312 00:14:44.240 --> 00:14:47.840 The stress test exactly? Yeah, let's look at ECG thirty eight. 313 00:14:48.480 --> 00:14:50.600 We have a seventy year old man with long standing 314 00:14:50.639 --> 00:14:53.639 high blood pressure who has been having attacks of dizziness 315 00:14:53.679 --> 00:14:57.200 over several weeks, and he has a known history's. 316 00:14:56.840 --> 00:14:58.879 Angina classic risk factors. 317 00:14:59.039 --> 00:15:02.960 But his resting EA is completely one hundred percent. 318 00:15:02.720 --> 00:15:06.919 Normal because at rest, his coronary arteries, even if they 319 00:15:06.919 --> 00:15:10.360 are diseased and narrowed, are still capable of delivering enough 320 00:15:10.440 --> 00:15:13.600 blood to meet the low oxygen demands of a resting body. 321 00:15:13.720 --> 00:15:17.399 Ah, so there's no aeschemia happening at that exact moment. 322 00:15:17.200 --> 00:15:20.080 Right, So there is no electrical abnormality to record. 323 00:15:20.279 --> 00:15:23.240 But the clinician didn't stop there because the resting ECG 324 00:15:23.480 --> 00:15:26.519 didn't match the clinical suspicion of the plot. They put 325 00:15:26.600 --> 00:15:29.039 him on a treadmill for a low level exercise. 326 00:15:28.639 --> 00:15:30.840 Stress test, and that is when the truth came out. 327 00:15:31.000 --> 00:15:35.279 YEP, during exercise st segment, elevation suddenly appeared on the tracing. 328 00:15:35.440 --> 00:15:38.519 The action in the movie started and the pathology. 329 00:15:37.919 --> 00:15:40.120 Was unmasked because he needed more oxygen. 330 00:15:40.240 --> 00:15:43.559 Exactly when the patient exercises, the heart rate increases, the 331 00:15:43.600 --> 00:15:48.120 blood pressure increases, and the heart muscle demands vastly more oxygen. 332 00:15:47.720 --> 00:15:51.960 But his narrow, diseased coronary arteries physically cannot dilate to 333 00:15:52.000 --> 00:15:53.399 provide that extra blood flow. 334 00:15:53.679 --> 00:15:58.639 Right, A supplying demand mismatch occurs instantly the subndocardial tissue 335 00:15:58.639 --> 00:16:02.919 becomes a schemic, the cellular metabolism shifts to anaerobic. 336 00:16:02.440 --> 00:16:04.279 Pathways, lactic acid builds up. 337 00:16:04.399 --> 00:16:08.159 Yes, lactic acid builds up, and the electrical baseline shifts, 338 00:16:08.519 --> 00:16:11.320 presenting as st elevation on the monitor. 339 00:16:11.399 --> 00:16:15.559 So the falsely reassuring resting test hit a severe underlying 340 00:16:15.600 --> 00:16:18.919 coronary artery disease. Good, And the text dictates that a 341 00:16:19.000 --> 00:16:22.639 positive exercise test at a low level of exertion urgently 342 00:16:22.639 --> 00:16:26.240 indicates a coronary angiogram along with strict long term medical 343 00:16:26.279 --> 00:16:29.799 management aspirin statins and an ACE inhibitor. 344 00:16:29.960 --> 00:16:32.639 And we should note the mechanism of that acee inhibitor 345 00:16:32.679 --> 00:16:36.279 because it's important for it blocks the angutensin converting enzyme, 346 00:16:36.360 --> 00:16:38.879 preventing the formation of angi tensin the second which is 347 00:16:38.879 --> 00:16:40.360 a potent vasoconstrictor. 348 00:16:40.440 --> 00:16:43.159 Okay, So it stops the vessels from clamping down right. 349 00:16:43.399 --> 00:16:46.799 By relaxing the blood vessels body wide, the ACE inhibitor 350 00:16:46.840 --> 00:16:49.919 lowers the overall pressure the failing heart has to pump against, 351 00:16:50.320 --> 00:16:52.679 reducing its workload and its oxygen demand. 352 00:16:53.039 --> 00:16:56.000 So the ECG is an incredible tool, but you have 353 00:16:56.080 --> 00:16:57.919 to know its blind spots, and sometimes you have to 354 00:16:57.919 --> 00:17:00.759 put the system under stress to see the cracks. Absolutely, 355 00:17:00.919 --> 00:17:03.879 but it's not just about the coronary arteries supplying the 356 00:17:03.919 --> 00:17:08.839 heart itself. Hampton's text beautifully illustrates how the ECG acts 357 00:17:08.839 --> 00:17:11.319 as a window to systemic issues happening throughout the rest 358 00:17:11.319 --> 00:17:11.839 of the body. 359 00:17:12.039 --> 00:17:14.440 Yeah, the heart doesn't exist in a vacuum. It is 360 00:17:14.599 --> 00:17:17.359 deeply sensitive to the systemic environment. 361 00:17:17.559 --> 00:17:19.759 If you look at the index references in the book, 362 00:17:19.799 --> 00:17:23.640 the ECG frequently acts as a systemic alarm bell. Take 363 00:17:23.680 --> 00:17:28.720 atrial fibrillation APHIB. Yeah, the atriar quivering chaotically instead of 364 00:17:28.759 --> 00:17:33.119 contracting smoothly, firing hundreds of erratic electrical impulses down into 365 00:17:33.119 --> 00:17:33.759 the ventricles. 366 00:17:34.039 --> 00:17:38.079 Most people associate APHIB purely with structural heart disease, but 367 00:17:38.119 --> 00:17:42.519 the text explicitly links it to systemic external triggers like 368 00:17:42.559 --> 00:17:47.559 what well. Hypothermia can trigger atrial fibrillation. Didoxin toxicity can 369 00:17:47.559 --> 00:17:51.000 present with APHIB, sometimes with a controlled ventricular rate because 370 00:17:51.000 --> 00:17:54.759 the drug increases intercellular calcium and enhances vagal tone at 371 00:17:54.759 --> 00:17:59.279 the AV node. And the text also highlights hypokalemia, which 372 00:17:59.319 --> 00:18:01.680 is low blood potassium, as the trigger. 373 00:18:01.839 --> 00:18:04.640 Let's connect that back to what we discussed earlier with DKA. 374 00:18:05.480 --> 00:18:09.279 Low potassium in the bloodstream means a larger concentration ingredient 375 00:18:09.319 --> 00:18:10.839 across the cell membrane. 376 00:18:10.480 --> 00:18:15.039 Right exactly, which prolongs phase three of the cardiac action potential, 377 00:18:15.079 --> 00:18:16.880 the repolarization phase. 378 00:18:16.519 --> 00:18:17.880 So it takes longer to reset. 379 00:18:18.079 --> 00:18:22.759 Yes, and this extended vulnerable period gives ectopic pacemakers in 380 00:18:22.799 --> 00:18:27.680 the atria the perfect opportunity to fire spontaneously, triggering the 381 00:18:27.759 --> 00:18:29.960 chaotic cascade of atrial fibrillation. 382 00:18:30.559 --> 00:18:33.279 So the electrical trace is demanding that you investigate the 383 00:18:33.319 --> 00:18:36.359 whole patient. Check their temperature, check their electrolytes, check their 384 00:18:36.440 --> 00:18:37.000 drug levels. 385 00:18:37.039 --> 00:18:38.400 You have to look at the whole picture. 386 00:18:38.720 --> 00:18:41.599 We see the heart responding to systemic mechanical problems too 387 00:18:42.240 --> 00:18:45.400 severe aortic stenosis the physical narrowing of the main valve 388 00:18:45.480 --> 00:18:48.519 leaving the heart. It forces the left ventricle to pump 389 00:18:48.519 --> 00:18:50.759 against immense pressure just to get blood. 390 00:18:50.480 --> 00:18:53.240 To the body right, and over time, the physical toll 391 00:18:53.279 --> 00:18:56.440 of pushing against the stenotic valve forces the heart muscle 392 00:18:56.440 --> 00:18:56.920 to adapt. 393 00:18:56.960 --> 00:18:57.640 It gets bigger. 394 00:18:57.759 --> 00:19:01.960 The muscle fibers undergo hypertrophy, They thicken and grow to generate. 395 00:19:01.640 --> 00:19:05.279 More force and on the ECG, this presents as left 396 00:19:05.319 --> 00:19:09.279 atrial and left ventricular hypertrophy. Because there is literally more 397 00:19:09.359 --> 00:19:13.759 muscle mass generating electricity, the amplitude of the QRS complexes 398 00:19:13.920 --> 00:19:15.160 dramatically increases. 399 00:19:15.319 --> 00:19:19.359 Yes, the electrical squiggles get much taller, reflecting the increased 400 00:19:19.440 --> 00:19:22.759 voltage required to depolarize that massive wall of muscle. 401 00:19:23.000 --> 00:19:26.160