USMLE Step 1 Review/Cardiovascular

Basic scienceEdit

Heart anatomyEdit


Cardiac cycleEdit


Heart soundsEdit

Physiologic splitting of S2

Inspiration → ↓intrathoracic pressure →

↑Stretch pulmonary capacitance vessels → ↓LV filing → ↓length of LV systole →
Earlier closure of aortic valve → earlier A2
↑RV filling → ↑length of RV systole →
Delayed closure of pulmonic valve → delayed P2
  • S1: MV/TV closure
  • S2: AV/PV closure
    • Physiologic splitting of S2 on inspiration (see inset)

Heart electrophysiologyEdit

Conducting system of heartEdit

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

Myocardial action potentialsEdit

Ventricular action potential.

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 (SA and AV nodes).

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)

Cardiovascular pathologyEdit


  • 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 stigmata
Roth spots
nonspecific retinal hemorrhages (cotton-wool spots)
Osler nodes
painful lesions on fingers/toes due to immunologic phenomena
Janeway lesions
painless lesions on fingers/toes due to immunologic phenomena
Splinter haemorrhages
speculated to be caused by vasculitis in nail bed in IE
finger clubbing
mechanism unknown

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 feverEdit


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