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HY points about each drug followed by a quiz at the end
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The USMLE doesn’t care about much of the nitpicky physiology around anti-arrhythmics.
The USMLE focuses almost exclusively on MOAs and side-effects.
In other words, if you’re like, “God I hate the cardio drugs. I don’t even know where to start.” My response is: “Recognize that if you simply know the MOAs (i.e., sodium vs potassium channel blocker, etc.) + the HY side-effects, that’s sufficient for the overwhelming majority of NBME/USMLE questions.
Sodium channel blockers (Class Ia)
The Queen Proclaims Diso‘s pyramid –> Quinidine, Procainamide, Disopyramide
- Lengthen action potential duration.
- Increase risk of torsades de pointes (dangerous sinusoidal arrhythmia with high chance of progression to a fatal ventricular fibrillation).
Quinidine
- Causes cinchonism (“quinchonism”) –> headache + tinnitus.
- Displaces digoxin from bilirubin –> can cause digoxin toxicity.
- 69M + taking digoxin + started on new anti-arrhythmic + now has yellow, wavy vision; which anti-arrhythmic did he commence? –> answer = quinidine. Digoxin toxicity classically presents as “Vincent van Gogh” yellow, wavy vision.
Procainamide
- Can cause drug-induced lupus (anti-histone antibodies).
- 60F + started on anti-arrhythmic a couple months ago + now has arthritis in both hands + mediastinitis + thrombocytopenia; which agent was she started on? –> answer = procainamide.
- Can be used for Wolf-Parkinson-White syndrome.
Disopyramide
- Just know this drug blocks sodium channels.
Sodium channel blockers (Class Ib)
I‘d buy Liddy’s Mexican Tacos –> Ib – Lidocaine, Mexiletine, Tocainide
- Shorten the action potential duration.
- Preferentially affect ischemic myocardium.
- Can cause CNS dysfunction.
- 72M + started on new anti-arrhythmic + now has dizziness + tremor; which agent was he started on? –> answer = lidocaine –> that is: choose the Class Ib agent if a patient starts an anti-arrhythmic and gets miscellaneous neuro findings.
Lidocaine
- Can be used as a local anesthetic.
- If injected into a blood vessel, can cause metallic taste in the mouth (on 2CK Obgyn form).
- Associated with dizziness and tremor (as per above example).
Mexiletine, Tocainide
- Just know they’re Class Ib agents.
- Less chance of dizziness and tremor compared with lidocaine.
Sodium channel blockers (Class Ic)
Fred Entertains Properly –> Flecainide, Encainide, Propafenone
- No change to action potential duration.
- Increased risk of torsades de pointes.
- Pro-arrhythmic. Do not use if patient has ischemic heart disease.
Flecainide
- First rhythm-control agent used for atrial fibrillation (AF) if patient has no structural or coronary artery disease.
Encainide, Propafenone
- Just know these are Ic.
Beta-blockers (Class II)
- See here for a detailed post on beta-blockers and beta-agonists.
- Classified as anti-arrhythmic but considered “rate-control” rather than “rhythm-control” when discussing AF. For AF treatment, we try rate-control before rhythm-control.
- Used as first-line rate-control in atrial fibrillation (i.e., give metoprolol first to manage AF).
- For AF: use beta-blocker first (rate-control); if contraindicated, use another rate-control agent like verapamil (non-dihydropyridine calcium channel blocker; cardiac-selective).
- If rate-control fails, go to rhythm control.
- Flecainide (Ic sodium channel blocker) is the first rhythm-control agent used if patient has no structural or coronary artery disease.
- If patient has structural (e.g., LVH, DCM, etc.) or coronary artery disease, use a different rhythm-control agent like the Class III potassium channel blockers (discussed below).
- Can cause depression and sexual dysfunction.
- May mask the signs of hypoglycemia in diabetes.
- Contraindicated in depression, diabetes, 2nd/3rd-degree heart block, unstable heart failure, COPD, asthma (latter two: use β1-selective only).
Potassium channel blockers (Class III)
- Can cause torsades de pointes (really HY for these drugs).
- Can be used for rhythm control for atrial fibrillation if patient cannot take flecainide (i.e., if patient has structural or coronary artery disease).
- Can be attempted in resuscitation from ventricular fibrillation when defibrillation and epinephrine fail.
- Delay repolarization of cardiac action potential.
Amiodarone, Dronaderone
- The following side-effects are HY for for USMLE. Memorize all of these.
- Pulmonary fibrosis
- Torsades
- Blue/grey skin discolorations (amiodarone only)
- Drug-induced thyroiditis (both hyper- and hypothyroidism)
- Hepatotoxicity
Dofetilide, Ibutilide, Sotalol
- Merely be aware that these are potassium channel blockers.
Calcium channel blockers (Class IV)
- Called non-dihydropyridine calcium channel blockers (verapamil, diltiazem; cardiac-selective).
- Block L-type calcium channels –> results in prolongation of plateau phase of myocardial action potential.
- Don’t confuse with dihydropyridine CCBs (i.e., amlodipine, nifedipine; vascular-selective).
Verapamil
- Classic use is rate-control in AF if patient has contraindication to beta-blocker.
- One of the highest yield side-effects for USMLE is knowing that verapamil causes constipation (don’t confuse with dihydropyridine CCBs, which cause fluid retention / edema).
Diltiazem
-
Technically a mixed cardiac-/vascular-selective agent (i.e., an intermediate between verapamil and nifedipine/amlodipine).
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Verapamil is pure cardiac-selective (i.e., pure non-dihydropyridine).
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Nidedipine/amlodipine are pure vascular-selective (i.e., pure dihydropyridine).
- Diltiazem is in the middle.
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