Most Likely Cause of Pansystolic Murmur Radiating to Axilla in Asymptomatic Patient
In an asymptomatic patient with a pansystolic murmur radiating to the axilla discovered on routine examination, mitral valve prolapse (MVP) is the most likely diagnosis, as it is the most common cause of mitral regurgitation in otherwise healthy individuals presenting for routine screening. 1
Understanding the Clinical Presentation
A pansystolic murmur radiating to the axilla is pathognomonic for mitral regurgitation, as this acoustic pattern reflects continuous flow from the left ventricle to the left atrium throughout systole, with the regurgitant jet directed posterolaterally toward the axilla. 2, 1, 3
The key distinguishing features in this case include:
- Pansystolic timing: The murmur begins early in contraction and lasts until relaxation is almost complete, indicating flow between chambers with widely different pressures throughout the entire cardiac cycle. 2, 3
- Axillary radiation: This specific radiation pattern confirms mitral regurgitation rather than other causes of systolic murmurs. 2
- Asymptomatic presentation: The patient's lack of symptoms on routine pre-employment screening strongly suggests a chronic, compensated process rather than acute pathology. 2
Why Mitral Valve Prolapse is Most Likely
Among the answer choices, MVP is the most common cause of mitral regurgitation in young, asymptomatic patients undergoing routine examination. 1, 4
Clinical reasoning:
- MVP typically presents with late systolic murmurs and midsystolic clicks in its classic form, but when regurgitation becomes more severe, the murmur can become holosystolic (pansystolic). 1, 4
- Most patients with MVP are asymptomatic, making it the ideal diagnosis for a pre-employment screening scenario. 4
- MVP is extremely common in the general population, particularly in younger adults who would be seeking employment. 4
Why other options are less likely:
Functional mitral regurgitation (Option C) produces a midsystolic murmur, not a pansystolic murmur, and typically occurs in patients with underlying left ventricular dysfunction or dilation—unlikely in an asymptomatic patient on routine screening. 2, 1
Ischemic mitral regurgitation (Option B) would be associated with coronary artery disease and typically presents with symptoms of heart failure or angina, not as an incidental finding in an asymptomatic patient. 5
Rheumatic mitral regurgitation (Option D) is now rare in developed countries and typically has a history of rheumatic fever, often with mixed valvular disease (combined mitral stenosis and regurgitation). 6
Important Clinical Caveats
The distinction between a late systolic murmur (classic for MVP) and a pansystolic murmur (indicating more severe regurgitation) is critical. 1, 7
- Even late systolic murmurs in MVP can be associated with significant hemodynamic consequences and adverse left ventricular remodeling, so the presence of a pansystolic murmur warrants echocardiographic evaluation. 7
- Dynamic auscultation can help confirm MVP: The murmur lengthens and intensifies with standing (which decreases preload and increases prolapse) and softens with squatting (which increases preload and reduces prolapse). 1
- Echocardiography should be performed to confirm the diagnosis, assess severity of regurgitation, evaluate left ventricular size and function, and measure mitral annular dimensions. 1, 6
Recommended Diagnostic Approach
All patients with newly discovered pansystolic murmurs of unknown cause should undergo echocardiography, as physical examination alone has limited accuracy in determining the exact cause, particularly when multiple lesions may be present. 3, 6
- Sensitivity of cardiac examination for MVP is only 55%, meaning nearly half of cases may be missed or misdiagnosed on physical examination alone. 6
- The click-murmur complex of MVP may be misdiagnosed as a benign flow murmur if the ejection click is not recognized during careful auscultation. 1
- Antibiotic prophylaxis prior to surgical or dental procedures should be considered once MVP with significant regurgitation is confirmed. 4