Back
ditki Logo
medical & biological sciences
All Access Pass - 1 FREE Month!
Institutional email required, no credit card necessary.

Heart Murmurs for USMLE Step 1

Free One-Month! Institutional (.edu or .org) email required
Log in or start your One-Week Free Trial!
Heart Murmurs for the USMLE Step 1 Exam
Overview of Heart Murmurs
Heart murmurs are extra sounds produced by turbulent blood flow across a valve. They can be classified as systolic, diastolic, or continuous, depending on when they occur in the cardiac cycle.
Normal heart valve pressures
Systolic Murmurs
Aortic Stenosis
  • Mechanism: Stenosis creates an obstruction to left ventricular (LV) outflow during systole.
  • Auscultation:
    • Location: Right second intercostal space, radiating to the carotids.
    • Sound: Crescendo-decrescendo (diamond-shaped) systolic murmur.
  • Clinical Significance: Symptoms include exertional dyspnea, angina, and syncope. Severe cases may require valve replacement.
Mitral Regurgitation
  • Mechanism: Incomplete closure of the mitral valve allows backflow from LV to left atrium during systole.
  • Auscultation:
    • Location: Apex, radiating to the axilla.
    • Sound: Holosystolic (pansystolic), high-pitched blowing murmur.
  • Clinical Significance: Common causes include mitral valve prolapse (MVP) and LV dilation. Severe cases may lead to heart failure.
Mitral Valve Prolapse (MVP)
  • Mechanism: Prolapse of the mitral valve leaflets into the left atrium during systole.
  • Auscultation:
    • Location: Apex.
    • Sound: Midsystolic click followed by a late systolic murmur; the click and murmur move earlier with Valsalva maneuver.
  • Clinical Significance: Often benign, though severe cases can lead to mitral regurgitation.
Hypertrophic Obstructive Cardiomyopathy (HOCM)
  • Mechanism: Dynamic obstruction of LV outflow caused by asymmetric septal hypertrophy.
  • Auscultation:
    • Location: Left sternal border.
    • Sound: Crescendo-decrescendo systolic murmur that increases with Valsalva and standing (maneuvers that reduce preload).
  • Clinical Significance: Associated with sudden cardiac death in young athletes; managed with beta-blockers.
Diastolic Murmurs
Aortic Regurgitation
  • Mechanism: Backflow from the aorta into the LV during diastole.
  • Auscultation:
    • Location: Left sternal border.
    • Sound: High-pitched, blowing decrescendo diastolic murmur.
  • Clinical Significance: Causes include aortic root dilation and endocarditis. Findings often include widened pulse pressure and bounding pulses.
Mitral Stenosis
  • Mechanism: Narrowed mitral valve restricts blood flow from left atrium to LV during diastole.
  • Auscultation:
    • Location: Apex, best heard in the left lateral decubitus position.
    • Sound: Low-pitched, rumbling diastolic murmur with an opening snap following S2.
  • Clinical Significance: Often caused by rheumatic fever, presenting with dyspnea and atrial fibrillation.
Continuous Murmurs
Patent Ductus Arteriosus (PDA)
  • Mechanism: Persistent connection between the aorta and pulmonary artery, causing continuous flow.
  • Auscultation:
    • Location: Left infraclavicular area.
    • Sound: Continuous “machinery-like” murmur that spans systole and diastole.
  • Clinical Significance: PDA can cause heart failure and pulmonary hypertension if untreated. Treated with NSAIDs in neonates or surgery if persistent.
Key Points
  • Systolic Murmurs:
    • Aortic Stenosis: Crescendo-decrescendo murmur at the right upper sternal border, radiating to the carotids.
    • Mitral Regurgitation: Holosystolic murmur at the apex, radiating to the axilla.
    • Mitral Valve Prolapse: Midsystolic click with late systolic murmur; click occurs earlier with Valsalva.
    • HOCM: Crescendo-decrescendo murmur at the left sternal border, increases with maneuvers that reduce 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 with an opening snap at the apex, best heard in the left lateral decubitus position.
  • Continuous Murmurs:
    • PDA: Continuous “machinery” murmur in the left infraclavicular area.
  • Clinical Relevance:
    • Aortic stenosis and regurgitation are common and may require surgical intervention if severe.
    • Maneuvers like Valsalva and position changes can help distinguish murmurs and identify valve lesions.
    • Echocardiography confirms murmur etiology and assesses severity; invasive procedures are reserved for severe cases or diagnostic uncertainty.

Related Tutorials