USMLE Step 1 Review/Cardiovascular

Heart sounds

 * S1: MV/TV closure
 * S2: AV/PV closure
 * Physiologic splitting of S2 on inspiration (see inset)

Conducting system of heart
Sinoatrial (SA) node in right atrium → atrioventricular (AV) node → His bundle → Purkinje fibers → ventricular myocardium

Myocardial action potentials


Ventricular action potential
 * Phase 4: outward potassium leak (resting membrane potential)
 * Phase 0: inward sodium (rapid depolarization)
 * Phase 1: outward potassium (partial repolarization)
 * Phase 2: balance of inward sodium/calcium and outward potassium (plateau)
 * Phase 3: outward potassium (repolarization)



Pacemaker potential
 * Phase 4: inward sodium/calcium (slow depolarization; SA/AV cells have no resting membrane potential)
 * Phase 0: inward calcium (rapid depolarization)
 * Phase 3: outward potassium (repolarization)

Arrhythmias

 * Atrial fibrillation: irregularly irregular rhythm (no p waves), rate often >100 (a type of supraventricular tachycardia), can result in heart failure, thrombus formation; treat with rate control (beta-blockers, non-DHP calcium channel blockers) or rhythm control (dofetilide, sotalol, amiodarone), and anticoagulation (warfarin).
 * Atrial flutter: p waves present in "sawtooth" pattern, often at rate of 300 and ventricular rate of 150 (often 2:1 conduction, but can vary); often resistant to rate control; treat refractory cases with ablation (maze procedure).
 * Wolff-Parkinson-White syndrome: supraventricular impulses conducted along accessory pathway leading to early and nonuniform depolarization of ventricles, causing QRS widening with a delta wave.

Endocarditis
Fever, malaise, embolic phenomena (eg, stroke), new murmur; vegetation on echocardiography, positive blood cultures, elevated ESR/CRP. Treat with empiric antibiotics, using culture results to guide more specific antibiotic selection.

Rheumatic fever
Diagnosis
 * J♥NES
 * Joints (migratory polyarthritis)
 * ♥ (pancarditis)
 * Subcutaneous Nodules
 * Erythema marginatum
 * Syndenham's Chorea - face, tongue, upper-limb chorea