Mitral Valve Prolapse
The most likely cause of a non-ejection click and soft late systolic murmur at the apex is mitral valve prolapse (MVP), specifically involving a prolapsing mitral leaflet (answer c). 1
Classic Auscultatory Features of MVP
The clinical presentation described is pathognomonic for mitral valve prolapse:
- The midsystolic click results from sudden tensing of the mitral valve apparatus as the leaflets prolapse into the left atrium during systole 1
- The late systolic murmur is typically medium-to-high-pitched, loudest at the cardiac apex, and may be soft or have a musical/honking quality 1
- This click-murmur complex is the principal auscultatory feature distinguishing MVP from other valvular conditions 1
Why Other Options Are Incorrect
Rheumatic valvular disease (option a) produces different findings:
- Mitral stenosis causes a mid-diastolic rumble, not a late systolic murmur
- Rheumatic mitral regurgitation typically produces a holosystolic murmur, not late systolic 2
Atrial septal aneurysm (option b) does not produce:
- Non-ejection clicks or late systolic murmurs at the apex
- ASD produces a mid-diastolic murmur at the tricuspid area from increased flow, not at the apex 3
Pulmonary stenosis (option d) produces:
- A systolic ejection murmur at the left upper sternal border, not the apex
- An ejection click (not a non-ejection/midsystolic click)
- No late systolic timing pattern
Dynamic Auscultation Confirms MVP
The diagnosis can be further supported by bedside maneuvers that characteristically alter the timing of the click-murmur complex:
- Standing or Valsalva (decreased LV volume): The click and murmur occur earlier in systole, moving closer to S1 1
- Squatting (increased LV volume): The click-murmur complex moves later toward S2 1
These predictable changes with loading conditions are unique to MVP and help distinguish it from other causes of systolic murmurs 1.
Clinical Significance
While MVP is generally benign, the presence of a late systolic murmur indicates some degree of mitral regurgitation 1. According to ACC/AHA guidelines, echocardiography is indicated for diagnosis and assessment of leaflet morphology, degree of regurgitation, and ventricular compensation in patients with physical signs of MVP 1.