crescendo-decrescendo murmur

This murmur pattern reflects the physiology of blood flow across a stenotic valve during systole: as ventricular contraction increases, flow velocity across the narrowed valve increases (crescendo), peaks mid-systole, then decreases as ventricular pressure falls toward the end of systole (decrescendo), creating a diamond-shaped pattern on phonocardiogram. It is the hallmark murmur of aortic stenosis (AS), typically heard best at the right second intercostal space (aortic area) with radiation to the carotid arteries, and may be accompanied by a soft S2 (due to reduced aortic valve closure sound) or paradoxically split S2 in severe AS. It can also be heard in pulmonic stenosis (loudest at left upper sternal border) and hypertrophic obstructive cardiomyopathy (HOCM), though HOCM murmurs increase with Valsalva/standing (decreased preload) and decrease with squatting (increased preload), differentiating it from AS. Severity of AS correlates with later peaking of the murmur and diminished carotid upstroke (pulsus parvus et tardus). Causes of AS include age-related calcific degeneration (most common in elderly), congenital bicuspid aortic valve (common in younger patients), and rheumatic heart disease. Clinical significance includes symptoms of angina, syncope, and heart failure (mnemonic: SAD - Syncope, Angina, Dyspnea), which portend poor prognosis without valve replacement. Echocardiography is used to confirm diagnosis and assess valve area, gradient, and left ventricular function.