Which of the following murmur increases on standing?

Correct Answer: A. HOCM

HOCM (Hypertrophic Obstructive Cardiomyopathy) is the only murmur among the options that increases on standing due to its unique pathophysiology. The murmur in HOCM is a mid-to-late systolic ejection murmur caused by dynamic left ventricular outflow tract (LVOT) obstruction from the hypertrophied interventricular septum. When a patient stands, venous return decreases (reduced preload), which reduces LV cavity size. This brings the anterior mitral leaflet closer to the hypertrophied septum, increasing the degree of LVOT obstruction and intensifying the murmur. This is the hallmark bedside finding that distinguishes HOCM from other cardiac lesions. The murmur also increases with Valsalva maneuver and decreases with squatting or leg raise (which increase preload and reduce obstruction). In Indian clinical practice, HOCM is an important cause of sudden cardiac death in young athletes and must be screened for in families with unexplained syncope or sudden death. The diagnosis is confirmed by echocardiography showing asymmetric septal hypertrophy and LVOT obstruction, with Doppler demonstrating the dynamic gradient.

Why the other options are wrong

B. MS — Mitral stenosis produces a diastolic rumble (not systolic) caused by fixed mechanical obstruction at the mitral valve. The murmur intensity is determined by the pressure gradient across the stenotic valve, which depends on cardiac output and heart rate—not preload changes from postural shifts. Standing does not increase the MS murmur; it may even decrease it slightly due to reduced cardiac output. MS is a fixed lesion and does not exhibit dynamic variation with position. C. MR — Mitral regurgitation produces a pansystolic (holosystolic) murmur that radiates to the axilla. The murmur intensity depends on the regurgitant volume and the pressure gradient between LV and LA during systole. Standing reduces preload, which actually decreases LV size and reduces the regurgitant volume, thereby decreasing the MR murmur—the opposite of HOCM. MR murmur increases with leg raise or squatting (increased preload), not standing. D. VSD — Ventricular septal defect produces a pansystolic murmur at the left lower sternal border due to fixed left-to-right shunting through the defect. The shunt magnitude and murmur intensity depend on the pressure gradient between ventricles, which is relatively fixed and independent of preload changes. Standing does not significantly alter the VSD murmur because the defect size and shunt pathway remain constant. VSD murmurs are not dynamic with postural changes like HOCM.

High-Yield Facts

Mnemonics

HOCM Maneuvers (Stand-Valsalva Increase; Squat-Leg Raise Decrease) Stand/Valsalva → ↓ preload → ↑ LVOT obstruction → ↑ murmur. Squat/Leg Raise → ↑ preload → ↓ obstruction → ↓ murmur. Use this to distinguish HOCM (dynamic) from fixed lesions (MS, VSD, MR). Murmur Timing & Preload Response Systolic ejection (HOCM, AS) = dynamic; Pansystolic (MR, VSD) = fixed; Diastolic (MS) = fixed. Only HOCM's systolic ejection murmur is truly dynamic with preload.

NBE Trap

NBE often pairs HOCM with "decreases on standing" (confusing it with MR or AS) or tests whether students know the direction of murmur change with posture. The trap is assuming all systolic murmurs behave the same—HOCM is unique because its obstruction is dynamic and preload-dependent, unlike fixed lesions.

Clinical Pearl

In Indian emergency departments, a young patient presenting with syncope or palpitations and a systolic murmur that increases on standing should raise immediate suspicion for HOCM—screen with ECG (LVH, deep Q waves, T-wave inversions) and urgent echocardiography. Family screening is critical as HOCM is autosomal dominant and a leading cause of sudden cardiac death in Indian athletes.

_Reference: Harrison Ch. 269 (Cardiomyopathies); Robbins Ch. 11 (Heart disease); KD Tripathi Ch. 8 (Cardiovascular pharmacology and pathology)_