Diagnosis: Mitral Valve Prolapse
The diagnosis is A - Mitral valve prolapse, based on the pathognomonic combination of a late systolic murmur that intensifies with standing (decreased left ventricular volume) and diminishes with handgrip (increased afterload and ventricular volume). 1
Clinical Reasoning
The key diagnostic features that distinguish mitral valve prolapse from other forms of mitral regurgitation are:
Dynamic Auscultatory Changes
Standing decreases left ventricular volume, causing the mitral leaflets to prolapse earlier in systole, which makes the murmur longer and often louder - this is unique to MVP and hypertrophic cardiomyopathy 1
Handgrip exercise increases afterload and left ventricular volume, which delays or reduces prolapse, causing the murmur to soften or move later in systole 1
This contrasts with other forms of mitral regurgitation (ischemic, functional, rheumatic), where handgrip increases murmur intensity by augmenting the regurgitant flow 1
Classic Presentation Features
Late systolic murmur (not holosystolic) indicates the leaflets prolapse partway through systole rather than leaking throughout systole 2, 3
Often accompanied by a midsystolic click from sudden tensing of the mitral apparatus as leaflets prolapse into the left atrium 2, 4
Atypical chest pain is commonly associated with MVP syndrome, occurring in patients without coronary disease, likely related to papillary muscle stretching 4, 5, 6
Why Not the Other Options
Ischemic mitral regurgitation (B) produces a holosystolic murmur that increases with handgrip due to increased afterload augmenting the regurgitant volume, and does not characteristically worsen with standing 1
Functional mitral regurgitation (C) typically causes a midsystolic murmur (not late systolic) and similarly increases with handgrip exercise rather than decreasing 1
Rheumatic mitral regurgitation (D) produces a holosystolic murmur that is relatively fixed in intensity and does not demonstrate the dynamic positional changes characteristic of MVP 1
Clinical Pitfalls
The murmur may be soft or absent at rest, becoming apparent only with provocative maneuvers like standing or Valsalva 2, 3
In severe MVP with significant regurgitation, the murmur can become holosystolic, potentially mimicking other causes of MR 3
The click may be intermittent or absent, and can be mistaken for a benign flow murmur if not carefully assessed 3
Next Steps
Echocardiography is indicated to confirm the diagnosis, assess leaflet morphology (particularly leaflet thickness as a risk marker), quantify the degree of mitral regurgitation, and evaluate left ventricular size and function 2, 3, 6