HY lecture notes (double-posting this lecture as Surgery #5 because it’s exceedingly HY for both shelf exams; this is the only double-posted lecture):
Stress testing may be done prior to surgery in those who are at moderate-high risk of ischemia –> the body’s cortisol-mediated stress response to surgery puts some patients at risk of perioperative MI.
This external article talks about the importance of stress testing in mitral regurgitation.
USMLE is obsessed with differentiating stroke/TIA/retinal artery occlusion caused by atrial fibrillation vs carotid plaques + management.
Carotid plaques are caused by hypertension. The strong systolic impulse from the heart pounds the carotids –> endothelial damage –> atherosclerosis.
So if you get a vignette of a guy who’s, e.g., 55, with BP of 150/90, who experiences a TIA, the first thing you want to think about is, “Does this guy have a carotid plaque that has resulted in a clot embolizing to his brain.” –> do a carotid duplex ultrasound.
In contrast, if you get a guy who’s, e.g., 80, who has good blood pressure (e.g., 110/70), and he gets a stroke or TIA, you want to think, “Does he have atrial fibrillation with a LA mural thrombus that’s now embolized to the brain.” –> do an ECG. Now in this scenario, there are two points to note:
- 8% of people over age 80 have atrial fibrillation, which is why age is a huge risk factor here. In other words, if the vignette says the guy is 58, AF is probably less likely just based on shear probability, regardless of hypertensive status.” And
- AF is often paroxysmal, meaning the USMLE might give you a scenario, e.g., with the above 80M, where they already tell you an ECG shows sinus rhythm with no abnormalities.
So regarding the second point, you’re probably like, “Wtf? So it’s not AF?” No, it is likely AF, but in order to pick up the paroxysmal aspect of it, the next best step is a Holter monitor (24-hour wearable ECG). This means that later in the day when he sits down to have dinner and then pops into AF, the Holter monitor will pick it up.
So in summary, if stroke/TIA/retinal artery occlusion:
Age 50s-60s + high BP –> answer = carotid duplex ultrasound to look for carotid plaques
Age >75 + good BP –> answer = ECG to look for AF –> if normal, do Holter monitor to pick up paroxysmal AF.
The exception to this scenario could be, e.g., a 55M + good BP + carotid bruit heard on auscultation –> answer = carotid duplex ultrasound to look for carotid plaques. –> In this case, if they are obvious and explicit about the suspected etiology of the stroke, TIA, or retinal artery occlusion, then you can just do the carotid duplex ultrasound here.
When we consider management for carotid plaques, we have to ask whether the patient is symptomatic or asymptomatic. A bruit does not count as symptoms (that’s a sign). Symptomatic means stroke, TIA, or retinal artery occlusion.
Carotid occlusion >70% if symptomatic, or >80% if asymptomatic –> answer = do carotid endarterectomy.
Below these thresholds –> answer = statin, PLUS clopidogrel OR dipyridamole + aspirin.
The USMLE will actually not be hyper-pedantic about the occlusion %s. They’ll make it obvious for you which answer they want. They’ll say either 90% –> answer = carotid endarterectomy, or they’ll say 50% –> answer = statin + anti-platelet therapy.
I had seen one question where they said a guy had 10 and 30% occlusion in the left vs right carotids, respectively, and he was already on anti-platelet therapy + a statin, and the answer was “maintain current regimen.”
For AF management:
We have to consider both arms of management: blood thinning + treating the actual AF.
For blood thinning, CHADS2 score is standard in terms of evaluating risk (there are variants, but the USMLE won’t ever be borderline with how this plays into a question; they’ll either give you a full-blown obvious high-risk patient where all are positive, or they’ll make it clear that the patient is low-risk and merely just has AF alone).
- CHADS2 = CHF, HTN, Age 75+, Diabetes, Stroke/TIA (latter is 2 points; the rest are 1 point)
- If 0 or 1 points, give aspirin (anti-platelet therapy).
- If 2+ points, give warfarin (anti-coagulation therapy).
- If valvular AF (i.e., AF in someone with a mitral or aortic valve lesion), we must give warfarin.
- If non-valvular AF, can give other agents (e.g., dabigatran, apixaban).
For the actual Tx of the AF, we do rate control before rhythm control (the management is actually heavily involved, but for the USMLE know the following):
- Rate control:
- Beta-blocker first-line (metoprolol)
- If beta-blocker contraindicated (i.e., depression, sexual dysfunction, COPD, Hx of asthma requiring oxygen or hospitalization, 2nd/3rd-degree heart block), verapamil is the next choice.
- If rate control fails, go to rhythm control.
- Rhythm control:
- Flecainide (type-Ic Na channel blocker) first-line in those without any structural (i.e., LVH or valvular problems) or coronary artery disease (any symptomatology of CVD or PVD means patient has coronary artery disease).
- In those who cannot receive flecainide, other anti-arrhythmics like amiodarone, dronedarone, and dofetilide may be used.
