Mitral Valve Prolapse (MVP)
In an asymptomatic 29-year-old man with a pansystolic murmur radiating to the axilla discovered on routine examination, mitral valve prolapse is the most likely diagnosis.
Clinical Reasoning
Why MVP is Most Likely
MVP is the most common valvular disorder in the United States, occurring in 1-2.5% of the population (3-6% in some studies), making it by far the most prevalent cause in a young asymptomatic adult 1, 2.
The pansystolic murmur radiating to the axilla is characteristic of mitral regurgitation, and when MVP progresses in severity, it can present with either a late systolic murmur or evolve into a pansystolic murmur depending on the degree of regurgitation 1.
Most patients with MVP are asymptomatic and the condition is frequently discovered during routine cardiac auscultation, exactly matching this clinical scenario 2, 3.
MVP has a benign prognosis in the majority of cases, with age-adjusted survival similar to the general population and a complication rate of only approximately 2% per year 1, 2.
Why Other Options Are Less Likely
Ischemic mitral regurgitation (Option B) is highly unlikely because it typically occurs in patients with coronary artery disease and prior myocardial infarction causing papillary muscle dysfunction—conditions that would be extraordinarily rare in an asymptomatic 29-year-old with no history suggesting ischemic heart disease 1.
Functional mitral regurgitation (Option C) is incorrect because it produces a midsystolic murmur, not a pansystolic murmur, and occurs secondary to left ventricular dilation from cardiomyopathy or heart failure, which would produce symptoms rather than an asymptomatic presentation 1, 4.
Rheumatic mitral regurgitation (Option D) is less likely because rheumatic heart disease has markedly decreased prevalence in industrialized countries, typically presents with mixed valvular disease, and usually has a symptomatic history of acute rheumatic fever 1.
Key Auscultatory Features of MVP
The classic finding is a midsystolic click followed by a late systolic murmur, which is usually medium-to-high-pitched and loudest at the cardiac apex 5.
However, the murmur can vary from brief and almost inaudible to holosystolic (pansystolic) and loud, depending on the severity of mitral regurgitation 5.
When MVP progresses to more severe regurgitation, the murmur becomes holosystolic while the patient may remain asymptomatic, as in this case 1.
Dynamic Auscultation Characteristics
Standing or Valsalva maneuver causes the click-murmur complex to move earlier in systole (closer to S1) because decreased left ventricular end-diastolic volume causes earlier prolapse 5.
Squatting increases left ventricular volume and moves the click-murmur complex later in systole (closer to S2), which helps confirm the diagnosis 5, 1.
This dynamic behavior distinguishes MVP from other causes of mitral regurgitation and should be performed during the physical examination 1.
Next Steps in Management
Echocardiography is indicated for diagnosis of MVP and assessment of mitral regurgitation severity, leaflet morphology, and ventricular compensation in asymptomatic patients with physical signs of MVP 5, 1.
Valve prolapse of 2 mm or more above the mitral annulus in the long-axis parasternal view indicates high likelihood of MVP, especially when leaflet coaptation occurs on the atrial side of the annular plane 5.
Leaflet thickness of 5 mm or more indicates abnormal leaflet thickness and identifies patients at higher risk for complications, including endocarditis, progressive mitral regurgitation requiring surgery, and arrhythmias 5, 1.
Risk Stratification
Patients with thickened mitral valve leaflets (≥5 mm) and/or significant mitral regurgitation have increased complication risk and require closer follow-up 1.
Approximately 5% of affected men and 1.5% of affected women ultimately require valve surgery, with complications concentrated disproportionately in older men 1.
Patients with MVP who have neither a murmur nor Doppler evidence of mitral regurgitation may be reassured that their condition is benign 3.