What is the most likely cause of a pansystolic murmur radiating to the axilla in an asymptomatic patient?

Mitral Valve Prolapse (MVP)

The most likely cause of this pansystolic murmur radiating to the axilla in an asymptomatic young patient is mitral valve prolapse (MVP), which is the most common valvular disorder in the United States, occurring in 1-2.5% of the population and frequently discovered incidentally during routine examinations. 1

Why MVP is the Correct Answer

Epidemiology Strongly Favors MVP

• MVP is by far the most common cause of mitral regurgitation in asymptomatic young adults undergoing routine screening, with a prevalence of approximately 3% in the general adult population 2, 3
• The asymptomatic presentation in a pre-employment setting is classic for MVP, as most patients remain asymptomatic throughout life with a benign prognosis and age-adjusted survival similar to the general population 1

The Murmur Characteristics Match MVP

• A pansystolic murmur radiating to the axilla is pathognomonic for mitral regurgitation, specifically indicating anterior leaflet pathology 4, 1
• While MVP classically presents with a late systolic murmur and midsystolic click, the murmur can become holosystolic (pansystolic) when regurgitation is more severe, even in asymptomatic patients 1, 5
• The radiation to the axilla and left infrascapular area specifically indicates anterior leaflet involvement 4

Why the Other Options Are Incorrect

Ischemic Mitral Regurgitation (Option B) - Highly Unlikely

• Ischemic MR is essentially impossible in a young, asymptomatic patient with no history suggesting coronary artery disease 1
• Ischemic MR occurs due to papillary muscle dysfunction or rupture following myocardial infarction, which would present acutely with symptoms of cardiogenic shock or pulmonary edema 6
• This patient has no risk factors, symptoms, or clinical context for ischemic heart disease 1

Functional Mitral Regurgitation (Option C) - Wrong Murmur Type

• Functional MR produces a midsystolic murmur, NOT a pansystolic murmur 1, 5
• Functional MR occurs secondary to left ventricular dilation from cardiomyopathy or heart failure, which would produce symptoms such as dyspnea, fatigue, and exercise intolerance 1
• An asymptomatic patient cannot have functional MR, as the underlying ventricular dysfunction would cause symptoms 1

Rheumatic Mitral Regurgitation (Option D) - Epidemiologically Rare

• Rheumatic heart disease has markedly decreased prevalence in industrialized countries and typically presents with mixed valvular disease (often combined mitral stenosis and regurgitation) 1
• Rheumatic MR usually requires a symptomatic history of acute rheumatic fever, which is not mentioned in this case 1
• While rheumatic fever can cause MVP (80% of patients with rheumatic fever and systolic murmurs have MVP on echo), the primary diagnosis in an asymptomatic young adult in a developed country is idiopathic MVP, not rheumatic disease 7

Clinical Approach and Next Steps

Confirm the Diagnosis with Dynamic Auscultation

• The murmur should become louder with Valsalva maneuver or standing (which decreases preload and increases prolapse) 4, 5
• The murmur should become softer with squatting (which increases preload and reduces prolapse) 5
• Listen for a midsystolic click, which may precede the murmur in MVP 2, 3

Echocardiography is Mandatory

• Echocardiography must be performed for any holosystolic or late systolic murmur to confirm MVP, assess severity of mitral regurgitation, evaluate leaflet morphology (especially leaflet thickness ≥5 mm, which increases complication risk), and measure left ventricular size and function 4, 1
• The ACC/AHA guidelines specifically recommend echocardiography for apical or left sternal edge holosystolic murmurs 4

Risk Stratification

• Patients with thickened mitral valve leaflets (≥5 mm) have increased risk of complications including endocarditis, progressive MR requiring surgery, and arrhythmias 1
• Approximately 5% of affected men and 1.5% of affected women ultimately require valve surgery, with complications concentrated in older men 1, 3
• The overall complication rate is approximately 2% per year 1

Common Pitfall to Avoid

• Do not dismiss this as an "innocent murmur" simply because the patient is asymptomatic - innocent murmurs are grade 1-2 midsystolic murmurs at the left sternal border with normal S2 splitting and no other abnormal findings 4
• A pansystolic murmur radiating to the axilla always indicates pathology and requires echocardiographic evaluation 4, 1