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Heart Murmurs for USMLE Step 2

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Heart Murmurs for the USMLE Step 2 Exam
Overview of Heart Murmurs
Heart murmurs are sounds produced by turbulent blood flow across a heart valve. They are classified by timing within the cardiac cycle: systolic, diastolic, or continuous.
Normal heart valve pressures
Systolic Murmurs
Aortic Stenosis
  • Mechanism: Obstructed left ventricular (LV) outflow due to a narrowed aortic valve.
  • Auscultation:
    • Location: Right second intercostal space, radiating to the carotids.
    • Sound: Harsh, crescendo-decrescendo (diamond-shaped) systolic murmur.
  • Clinical Significance: Symptoms include dyspnea, angina, and syncope with exertion. Severe cases may require aortic valve replacement.
Mitral Regurgitation
  • Mechanism: Incompetent mitral valve allows backflow from the LV to the left atrium during systole.
  • Auscultation:
    • Location: Apex, radiating to the axilla.
    • Sound: High-pitched, holosystolic (pansystolic) murmur.
  • Clinical Significance: Common causes include mitral valve prolapse (MVP) and LV dilation. Surgical repair or replacement is indicated if symptoms or LV dysfunction develop.
Mitral Valve Prolapse (MVP)
  • Mechanism: Prolapse of one or both mitral valve leaflets into the left atrium during systole.
  • Auscultation:
    • Location: Apex.
    • Sound: Midsystolic click followed by a late systolic murmur; click and murmur move earlier with maneuvers that decrease LV volume (e.g., standing, Valsalva).
  • Clinical Significance: MVP is often benign but may progress to mitral regurgitation in severe cases.
Hypertrophic Obstructive Cardiomyopathy (HOCM)
  • Mechanism: Dynamic LV outflow obstruction due to asymmetric septal hypertrophy.
  • Auscultation:
    • Location: Left sternal border.
    • Sound: Crescendo-decrescendo systolic murmur, increasing with Valsalva or standing (decreasing preload).
  • Clinical Significance: Associated with sudden cardiac death, especially in young athletes. Managed with beta-blockers and calcium channel blockers.
Diastolic Murmurs
Aortic Regurgitation
  • Mechanism: Backflow from the aorta into the LV during diastole.
  • Auscultation:
    • Location: Left sternal border (third intercostal space).
    • Sound: High-pitched, blowing decrescendo diastolic murmur.
  • Clinical Significance: Causes include aortic root dilation and endocarditis. Findings such as widened pulse pressure and bounding pulses are common. Severe cases with LV dysfunction may require valve replacement.
Mitral Stenosis
  • Mechanism: Narrowed mitral valve restricts blood flow from the left atrium to the LV during diastole.
  • Auscultation:
    • Location: Apex, best heard in the left lateral decubitus position.
    • Sound: Low-pitched, rumbling diastolic murmur with an opening snap after S2.
  • Clinical Significance: Most commonly due to rheumatic fever; symptoms include dyspnea and fatigue. Percutaneous mitral balloon valvotomy is the treatment of choice for severe cases.
Continuous Murmurs
Patent Ductus Arteriosus (PDA)
  • Mechanism: Persistent connection between the aorta and pulmonary artery allows continuous flow.
  • Auscultation:
    • Location: Left infraclavicular area.
    • Sound: Continuous, “machinery-like” murmur heard throughout systole and diastole.
  • Clinical Significance: PDA can cause heart failure and pulmonary hypertension if untreated. In infants, closure may be achieved with NSAIDs or surgical ligation.
Key Points
  • Systolic Murmurs:
    • Aortic Stenosis: Harsh crescendo-decrescendo murmur at the right upper sternal border, radiating to the carotids; associated with delayed carotid upstroke.
    • Mitral Regurgitation: Holosystolic murmur at the apex, radiating to the axilla.
    • Mitral Valve Prolapse: Midsystolic click followed by a late systolic murmur, which shifts earlier with Valsalva.
    • HOCM: Crescendo-decrescendo murmur at the left sternal border, louder with Valsalva.
  • Diastolic Murmurs:
    • Aortic Regurgitation: High-pitched decrescendo murmur at the left sternal border; associated with widened pulse pressure.
    • Mitral Stenosis: Rumbling diastolic murmur at the apex with an opening snap; best heard in the left lateral decubitus position.
  • Continuous Murmurs:
    • PDA: Continuous “machinery” murmur in the left infraclavicular area.
  • Clinical Relevance:
    • Aortic and mitral valve disease can progress to heart failure, requiring surgical intervention.
    • Maneuvers (e.g., Valsalva) help differentiate murmurs by altering preload or afterload.
    • Echocardiography is essential for murmur evaluation and determining the need for intervention.

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