What type of murmur decreases in intensity when moving from standing to squatting and increases in intensity with the Valsalva maneuver, particularly in younger adults with suspected hypertrophic obstructive cardiomyopathy (HOCM)?

Hypertrophic Cardiomyopathy (HCM) Murmur

The murmur that decreases in intensity when moving from standing to squatting and increases with the Valsalva maneuver is the systolic murmur of hypertrophic cardiomyopathy (HCM), also known as hypertrophic obstructive cardiomyopathy (HOCM). 1

Characteristic Dynamic Responses

The HCM murmur has a unique and opposite response to physiologic maneuvers compared to all other cardiac murmurs:

Maneuvers That Increase the Murmur

• Valsalva maneuver: The systolic murmur of HCM becomes much louder during Valsalva, while most other murmurs decrease in length and intensity 1
• Standing from squatting: The murmur becomes louder with standing, achieving 95% sensitivity and 84% specificity for HCM diagnosis 2
• Standing position: The murmur intensifies when standing, unlike most other murmurs which diminish 1

Maneuvers That Decrease the Murmur

• Squatting from standing: The murmur softens or may disappear with brisk squatting, achieving 95% sensitivity and 85% specificity for HCM 1, 2
• Passive leg raising: The murmur decreases with passive leg elevation (85% sensitivity, 91% specificity) 2
• Handgrip exercise: The murmur diminishes with isometric handgrip (85% sensitivity, 75% specificity) 2

Physiologic Mechanism

The dynamic behavior of the HCM murmur is explained by left ventricular outflow tract (LVOT) obstruction:

• Decreased preload worsens obstruction: Maneuvers that reduce venous return (Valsalva, standing) decrease left ventricular volume, bringing the hypertrophied septum and anterior mitral leaflet closer together, thereby increasing LVOT obstruction and murmur intensity 3, 4, 5
• Increased preload reduces obstruction: Maneuvers that increase venous return (squatting, leg elevation) expand left ventricular volume, separating the septum from the mitral valve apparatus, thereby decreasing LVOT obstruction and murmur intensity 4, 5
• Increased afterload reduces obstruction: Handgrip increases systemic vascular resistance and left ventricular volume, which reduces the degree of obstruction 2

Clinical Distinction from Other Murmurs

The HCM murmur is one of only two exceptions to the general rule that murmurs diminish with standing:

• HCM: Becomes louder with standing 1
• Mitral valve prolapse (MVP): Also lengthens and intensifies with standing 1
• All other murmurs: Diminish with standing 1

However, MVP can be distinguished from HCM because MVP murmurs also become longer and louder with Valsalva but do not have the same dramatic response to squatting 1.

Diagnostic Accuracy at Bedside

The combination of dynamic maneuvers provides excellent diagnostic accuracy:

• Valsalva increase: 65% sensitivity, 96% specificity for HCM 2
• Squatting-to-standing increase: 95% sensitivity, 84% specificity 2
• Standing-to-squatting decrease: 95% sensitivity, 85% specificity 2

Important Clinical Caveat

The repetitive squat-to-stand maneuver is particularly useful when amyl nitrite is unavailable, as rising from squatting decreases both preload and afterload, maximally augmenting LVOT obstruction 4. Repetition of the maneuver enhances sensitivity, especially when exertional symptoms are reproduced during the examination 4.