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Heart Murmurs for USMLE Step 3

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Heart Murmurs for the USMLE Step 3 Exam
Overview of Heart Murmurs
Heart murmurs arise from turbulent blood flow across heart valves and are categorized as systolic, diastolic, or continuous based on their timing in the cardiac cycle. Each murmur has distinct auscultatory findings, associated pathology, and clinical significance.
Normal heart valve pressures
Systolic Murmurs
Aortic Stenosis
  • Mechanism: LV outflow obstruction due to narrowed aortic valve.
  • Auscultation:
    • Location: Right second intercostal space, radiating to the carotids.
    • Sound: Harsh, crescendo-decrescendo murmur.
  • Clinical Significance: Symptoms include dyspnea, angina, and syncope on exertion. Severe cases require aortic valve replacement.
Mitral Regurgitation
  • Mechanism: Backflow from 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 for symptomatic or severe cases.
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 become earlier with maneuvers that reduce LV volume (e.g., Valsalva).
  • Clinical Significance: Often benign but can lead to mitral regurgitation in severe cases.
Hypertrophic Obstructive Cardiomyopathy (HOCM)
  • Mechanism: Dynamic LV outflow obstruction from asymmetric septal hypertrophy.
  • Auscultation:
    • Location: Left sternal border.
    • Sound: Crescendo-decrescendo murmur that increases with Valsalva or standing (maneuvers that decrease preload).
  • Clinical Significance: A common cause of sudden cardiac death in young athletes. Treated with beta-blockers and occasionally septal myectomy.
Diastolic Murmurs
Aortic Regurgitation
  • Mechanism: Backflow from the aorta into the LV during diastole.
  • Auscultation:
    • Location: Left sternal border.
    • Sound: High-pitched, blowing decrescendo murmur.
  • Clinical Significance: Causes include aortic root dilation and infective endocarditis. Widened pulse pressure and bounding pulses are common findings. Surgical replacement is recommended if symptomatic or with LV dysfunction.
Mitral Stenosis
  • Mechanism: Obstruction of 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.
  • Clinical Significance: Often due to rheumatic fever; symptoms include dyspnea, hemoptysis, and atrial fibrillation. 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 causes continuous blood flow.
  • Auscultation:
    • Location: Left infraclavicular area.
    • Sound: Continuous “machinery-like” murmur audible in both systole and diastole.
  • Clinical Significance: Untreated PDA can lead to pulmonary hypertension and heart failure. Closure is achieved with NSAIDs in neonates or surgical ligation if persistent.
Key Points
  • Systolic Murmurs:
    • Aortic Stenosis: 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; both move earlier with Valsalva.
    • HOCM: Crescendo-decrescendo murmur at the left sternal border, louder with maneuvers that decrease preload.
  • Diastolic Murmurs:
    • Aortic Regurgitation: High-pitched decrescendo murmur at the left sternal border, associated with widened pulse pressure.
    • Mitral Stenosis: Low-pitched, rumbling 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 diseases may lead to heart failure and require surgical intervention if severe.
    • Maneuvers (e.g., Valsalva) aid in differentiating murmurs by altering preload or afterload.
    • Echocardiography is critical for diagnosing murmur etiology, assessing severity, and determining management strategies.

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