Cardiovascular System
Physiology
Map the cardiac cycle: S1 is atrioventricular valve closure, S2 semilunar closure; S3 reflects volume overload or early filling, S4 a stiff ventricle with an atrial kick. On the pressure-volume loop, end-diastolic volume tracks preload, end-systolic volume tracks afterload and contractility. Increased contractility raises stroke volume and lowers end-systolic volume. Cardiac output equals heart rate times stroke volume, and mean arterial pressure approximates cardiac output times systemic vascular resistance.
Murmurs and lesions
Aortic stenosis: crescendo-decrescendo systolic murmur at the right upper sternal border radiating to the carotids, with pulsus parvus et tardus and concentric hypertrophy. Mitral regurgitation: holosystolic murmur at the apex radiating to the axilla. Aortic regurgitation: early diastolic decrescendo murmur with a widened pulse pressure. Mitral stenosis: opening snap with diastolic rumble. VSD: holosystolic murmur at the left lower sternal border.
Ischemia, rhythm, and shock
Know STEMI territories by lead (inferior II, III, aVF; lateral I, aVL, V5-6). Distinguish hypovolemic, cardiogenic, distributive (septic, warm with low resistance), and obstructive (tamponade, tension pneumothorax, pulmonary embolism) shock. Drug mechanisms: ACE inhibitors reduce angiotensin II and bradykinin breakdown, beta-blockers reduce rate and contractility, digoxin inhibits the sodium-potassium ATPase and increases vagal tone, nitrates venodilate.
Traps
Giving vasodilators in severe aortic stenosis. Confusing S3 with S4. Calling all systolic murmurs benign. Missing that a left bundle branch block obscures ST-segment analysis.
Worked rule
A systolic crescendo-decrescendo murmur at the right upper sternal border with delayed, low-volume carotid upstrokes means aortic stenosis.