What is a murmur?

Heart Murmurs: Definition and Clinical Significance

A heart murmur is an audible sound during cardiac auscultation caused by turbulent blood flow through the heart, which may be innocent (physiologic) or pathologic, indicating potential structural cardiac abnormalities. 1

Causes of Heart Murmurs

Heart murmurs are produced by three main mechanisms:

• High blood flow rate through normal or abnormal orifices 1
• Forward flow through a narrowed or irregular orifice into a dilated vessel or chamber 1
• Backward or regurgitant flow through an incompetent valve 1

Classification of Heart Murmurs

Timing in the Cardiac Cycle

• Systolic murmurs:

  • Holosystolic (pansystolic): Occur throughout systole due to flow between chambers with widely different pressures (e.g., mitral regurgitation, ventricular septal defect) 1
  • Midsystolic (ejection): Crescendo-decrescendo configuration when blood is ejected across aortic or pulmonic outflow tracts 1
  • Early systolic: Begin with S1 and end in midsystole (e.g., tricuspid regurgitation without pulmonary hypertension) 1
  • Late systolic: Start after ejection and end before or at S2 (e.g., mitral valve prolapse) 1

• Diastolic murmurs:

  • Early diastolic: High-pitched, decrescendo murmurs (e.g., aortic regurgitation) 1
  • Middiastolic: Occur during ventricular filling (e.g., mitral stenosis) 1
  • Presystolic: Begin during atrial contraction in sinus rhythm 1

• Continuous murmurs: Span from systole into diastole (e.g., patent ductus arteriosus) 1

Clinical Significance

• Most systolic murmurs do not indicate cardiac disease and may be physiologic 1
• Diastolic murmurs virtually always represent pathological conditions requiring further evaluation 1
• Continuous murmurs generally require further evaluation, except for innocent venous hums and mammary souffles 1

Characteristics of Murmurs

Murmurs are assessed based on:

• Timing: Systolic, diastolic, or continuous 1
• Configuration: Crescendo, decrescendo, crescendo-decrescendo (diamond-shaped), or plateau 1
• Location and radiation: Where the murmur is best heard and where it radiates 1
• Pitch: High, medium, or low 1
• Intensity: Grades 1 through 6 1
• Duration: Length of the murmur within the cardiac cycle 1

Types of Innocent Murmurs

• Still's murmur: Medium-pitched, vibratory murmur at the apex and sternal borders that quiets with upright position 1
• Venous hum: Medium-pitched, blowing murmur with diastolic accentuation that disappears with jugular compression 1
• Innocent pulmonary systolic murmur: Medium-pitched, harsh murmur that disappears with upright position 1
• Physiologic pulmonary artery stenosis: Medium or high-pitched blowing murmur in infants under 6 months 1
• Mammary souffle: Medium or high-pitched blowing murmur with systolic accentuation that disappears with breast compression 1

Red Flags Suggesting Pathologic Murmurs

• Holosystolic or diastolic timing 2
• Grade 3 or higher intensity 2
• Harsh quality 2
• Abnormal S2 2
• Maximal intensity at upper left sternal border 2
• Systolic click 2
• Increased intensity with standing 2

Diagnostic Approach

• Echocardiography is essential for evaluating potentially pathologic murmurs 3, 4
• The correlation between clinical auscultation and echocardiographic findings can be poor, particularly for diastolic murmurs 4
• Dynamic auscultation (listening during various maneuvers like Valsalva, position changes, exercise) can help determine the origin and significance of murmurs 1

Clinical Implications

• Even when asymptomatic, a pathologic murmur may indicate significant cardiac disease requiring intervention 1, 5
• Echocardiography should be performed in patients with more than a soft systolic murmur, any diastolic murmur, cardiac symptoms, or ECG changes 5, 3
• The ability of cardiac examination alone to assess the exact cause of a murmur is limited, especially when multiple lesions are present 3, 4