How can aortic stenosis (AS) be distinguished from hypertrophic obstructive cardiomyopathy (HCM) using physical‑exam maneuvers that alter preload, afterload, and contractility?

Distinguishing Aortic Stenosis from Hypertrophic Obstructive Cardiomyopathy Using Physical Exam Maneuvers

In hypertrophic obstructive cardiomyopathy (HCM), maneuvers that decrease preload (standing, Valsalva strain) or increase contractility intensify the murmur and gradient, while in aortic stenosis (AS), these same maneuvers decrease the murmur intensity because reduced preload means less blood crosses a fixed obstruction. 1

Key Physiologic Principles

The fundamental difference lies in the nature of obstruction:

• HCM: Dynamic obstruction that worsens with decreased ventricular volume, increased contractility, or decreased afterload 1
• AS: Fixed valvular obstruction where gradient depends primarily on flow volume across the valve 1

Specific Maneuver Responses

Valsalva Maneuver (Strain Phase)

• HCM: Murmur becomes louder and gradient increases because decreased venous return reduces LV cavity size, bringing the hypertrophied septum and mitral valve closer together, intensifying systolic anterior motion and obstruction 1
• AS: Murmur becomes softer because decreased preload reduces stroke volume and flow across the fixed stenotic valve 1

Standing from Squatting

• HCM: Murmur increases in intensity as rapid decrease in preload and afterload exacerbates dynamic LVOT obstruction 1
• AS: Murmur decreases in intensity due to reduced venous return and stroke volume 1

Squatting from Standing

• HCM: Murmur decreases because increased venous return and afterload enlarge LV cavity and reduce obstruction 1
• AS: Murmur increases due to increased stroke volume across the valve 1

Handgrip Exercise (Isometric)

• HCM: Murmur decreases because increased afterload enlarges LV cavity and reduces LVOT gradient 1
• AS: Murmur intensity remains relatively unchanged or slightly increases with increased cardiac output 1

Post-Premature Ventricular Contraction (Post-PVC Beat)

• HCM: Gradient increases dramatically (Brockenbrough-Braunwald-Morrow sign) due to increased contractility with prolonged diastolic filling, despite increased stroke volume 1
• AS: Gradient increases proportionally with stroke volume without the exaggerated response seen in HCM 1

Additional Distinguishing Physical Findings

Carotid Upstroke

• HCM: Brisk, bifid ("spike and dome") pulse due to rapid early ejection followed by mid-systolic obstruction 1
• AS: Delayed and diminished (pulsus parvus et tardus), though this may be less reliable in elderly patients with stiff vessels 1

Second Heart Sound

• HCM: Normal or paradoxically split S2 (if severe obstruction) 1
• AS: Single S2 or paradoxically split S2; a normally split S2 reliably excludes severe AS 1

Murmur Characteristics

• HCM: Harsh systolic ejection murmur at apex and left sternal border, increases with maneuvers that decrease preload 1
• AS: Harsh systolic ejection murmur radiating to carotids, decreases with maneuvers that decrease preload 1

Critical Diagnostic Pitfall

When both conditions coexist (rare but documented), distinguishing the primary cause of symptoms becomes extremely challenging and requires invasive hemodynamic assessment with high-fidelity catheters to measure simultaneous LV and aortic pressures. 2, 3, 4 In such cases, the peak instantaneous gradient measured by Doppler may represent the sum of both obstructions, and transesophageal echocardiography with careful planimetry becomes essential 2, 3.

Practical Clinical Algorithm

1. Perform Valsalva maneuver while auscultating: If murmur increases → suspect HCM; if decreases → suspect AS 1

2. Assess carotid upstroke: Brisk/bifid → HCM; delayed/diminished → AS 1

3. Listen to S2 splitting: Normal split excludes severe AS; single S2 present in both but doesn't distinguish 1

4. Confirm with echocardiography: Look for asymmetric septal hypertrophy (≥15 mm), systolic anterior motion of mitral valve, and dynamic LVOT gradient in HCM 1, 5; look for calcified, restricted valve leaflets with fixed obstruction in AS 1

The dynamic nature of HCM obstruction—varying with loading conditions and contractility—is the key distinguishing feature from the fixed obstruction of AS 1, 5.