What is the likely cause of a systolic ejection murmur that peaks in mid-systole, is best heard along the left sternal border, decreases with squatting, and increases with the Valsalva maneuver in a patient being evaluated for assistant football coach clearance?

Hypertrophic Cardiomyopathy (HCM)

The provider should suspect hypertrophic cardiomyopathy (HCM) as the cause of this murmur, given the classic presentation of a systolic murmur that increases with Valsalva and standing, and decreases with squatting. 1

Diagnostic Reasoning

The clinical presentation described is pathognomonic for HCM with left ventricular outflow tract obstruction (LVOTO):

Classic Murmur Characteristics in HCM

• Harsh crescendo-decrescendo systolic murmur best heard at the lower left sternal border, caused by systolic anterior motion (SAM) of the mitral valve leading to LVOTO 1

• Peaks in mid-systole as described in the patient's presentation 1

Pathognomonic Maneuver Responses

The response to provocative maneuvers is highly specific for HCM and distinguishes it from other causes of systolic murmurs:

• Valsalva maneuver increases intensity (65% sensitivity, 96% specificity for HCM) - decreased preload worsens the dynamic obstruction 1, 2

• Squatting decreases intensity (95% sensitivity, 85% specificity) - increased preload and afterload reduce the obstruction 1, 2

• Standing from squatting increases intensity (95% sensitivity, 84% specificity) - decreased venous return worsens obstruction 1, 2

These maneuver responses are essentially diagnostic: the murmur behaves opposite to most other cardiac murmurs because HCM involves a dynamic, volume-dependent outflow tract obstruction 2, 3

Immediate Next Steps

Transthoracic echocardiography (TTE) is the Class I recommendation for initial evaluation when HCM is suspected 1

• The echocardiogram should include provocative maneuvers if the resting LVOT gradient is <50 mm Hg 1

• An electrocardiogram should be obtained as part of the initial workup 1

Critical Implications for Athletic Clearance

This patient should NOT be cleared for coaching activities until HCM is definitively excluded, as this condition is associated with sudden cardiac death, particularly during or after exertion 4

• Even asymptomatic patients with HCM should be prohibited from competitive sports or strenuous activities 4

• The context of pre-participation screening for a football coaching position makes this finding particularly concerning and mandates urgent cardiology referral 1

Key Clinical Pitfall

Do not confuse this with "athlete's heart," which can present with left ventricular hypertrophy but has different murmur characteristics and does not show the pathognomonic responses to Valsalva and squatting maneuvers 1, 4