USMLE Step 1 Review/Cardiovascular

Basic science

Heart anatomy

Cardiac cycle

Heart sounds

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 electrophysiology

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.

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 pathology

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

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 fever

Diagnosis

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