What is the likely diagnosis for a healthy 45-year-old woman with a faint murmur at the second right intercostal space and a mid-systolic click on heart auscultation?

Likely Diagnosis: Mitral Valve Prolapse

The most likely diagnosis is mitral valve prolapse (MVP), as the midsystolic click is the pathognomonic auscultatory hallmark of this condition, though the location at the second right intercostal space is atypical since MVP clicks are classically heard best at the apex. 1

Clinical Reasoning

Characteristic Auscultatory Findings of MVP

• The midsystolic click represents sudden tensing of the mitral valve apparatus as the leaflets prolapse into the left atrium during systole. 1
• The click may be followed by a late systolic murmur that is medium-to-high pitched and loudest at the cardiac apex, occasionally with a musical or honking quality. 1
• Clicks can be intermittent, variable in timing and intensity, and may occur without an accompanying murmur. 1

Important Caveat About Location

• MVP murmurs and clicks are typically heard best at the cardiac apex (4th left intercostal space), NOT at the second right intercostal space. 1
• The second right intercostal space is the classic location for aortic stenosis, which typically presents with a midsystolic murmur and may have an ejection click (not a midsystolic click) if the valve is bicuspid and not calcified. 1
• However, a midsystolic click specifically suggests MVP regardless of location, as aortic stenosis produces ejection clicks (early systolic) rather than midsystolic clicks. 1

Dynamic Auscultation to Confirm MVP

Perform these maneuvers to confirm the diagnosis: 1

• Standing: The click moves earlier in systole (closer to S1) and the murmur lengthens and intensifies as left ventricular end-diastolic volume decreases. 1
• Squatting: The click moves later in systole (closer to S2) and the murmur softens or disappears as left ventricular volume increases. 1
• Valsalva maneuver: The murmur of MVP becomes longer and often louder, unlike most other murmurs which decrease. 1

Recommended Diagnostic Workup

Echocardiography Indication (Class I)

Obtain transthoracic echocardiography to confirm MVP, assess mitral regurgitation severity, evaluate leaflet morphology, and determine ventricular compensation—this is a Class I indication per ACC/AHA guidelines. 1, 2

Echocardiographic Diagnostic Criteria

• Valve prolapse of ≥2 mm above the mitral annulus in the parasternal long-axis view, especially when leaflet coaptation occurs on the atrial side of the annular plane. 1, 2
• Leaflet thickness ≥5 mm indicates abnormal leaflet thickness and confirms MVP with higher certainty. 1, 2
• Do not rely solely on apical 4-chamber views, as anterior leaflet billowing in this view alone is unreliable. 2

Risk Stratification on Echo

High-risk features that predict complications include: 2

• Leaflet thickness ≥5 mm (predicts endocarditis, need for surgery, complex ventricular arrhythmias) 2
• Moderate-to-severe mitral regurgitation (strongest predictor of cardiovascular mortality and need for surgery) 2
• Left ventricular internal diameter ≥60 mm (predicts need for mitral valve replacement) 2
• Leaflet redundancy with enlarged mitral annulus and elongated chordae 2

Management Approach

For Asymptomatic Patients with Mild MVP

Provide reassurance about the benign prognosis and encourage normal lifestyle with regular exercise. 2

• Most patients with MVP have an excellent prognosis with annual mortality rates <1% per year. 1
• No specific treatment is needed beyond reassurance and endocarditis prophylaxis when indicated. 3

Baseline ECG

• Obtain a baseline ECG, though it is often normal. 1, 2
• May show nonspecific ST-T changes, T-wave inversions, prominent Q waves, or QT prolongation. 1, 2
• Do NOT obtain ambulatory ECG monitoring routinely in asymptomatic patients—reserve this for those with palpitations. 1, 2

Follow-up Strategy

• Patients without a murmur or Doppler evidence of mitral regurgitation can be reassured their condition is benign. 4
• The presence and severity of mitral regurgitation govern the frequency and intensity of follow-up. 4
• Routine repetition of echocardiography is not indicated for asymptomatic MVP patients with no or mild MR and no changes in clinical signs or symptoms (Class III). 1

Alternative Consideration

If dynamic auscultation does NOT confirm MVP characteristics (i.e., the click does not move with positional changes), consider aortic stenosis with a bicuspid aortic valve, which can produce an ejection click at the second right intercostal space. 1 However, ejection clicks occur in early systole, not mid-systole, making this less likely. 1