What is the mechanism of cardiac murmurs?

From the Guidelines

Cardiac murmurs are abnormal heart sounds caused by turbulent blood flow through the heart or great vessels, resulting from high blood flow rate through normal or abnormal orifices, forward flow through a narrowed or irregular orifice into a dilated vessel or chamber, or backward or regurgitant flow through an incompetent valve, as described in the 2008 focused update incorporated into the ACC/AHA 2006 guidelines for the management of patients with valvular heart disease 1. The mechanism of cardiac murmurs involves disruption of laminar blood flow, creating vibrations that can be heard with a stethoscope.

• Murmurs are classified by timing (systolic or diastolic), intensity (grades I-VI), pitch, location, radiation, and quality.
• Systolic murmurs occur when the ventricles contract, often due to valve stenosis or regurgitation.
• Diastolic murmurs happen during ventricular filling and typically indicate more serious pathology. Some key points to consider when evaluating cardiac murmurs include:
• The intensity of a murmur doesn't always correlate with severity; some serious conditions produce soft murmurs while innocent murmurs can sometimes be quite loud.
• Understanding these mechanisms is crucial for accurate diagnosis and appropriate management of underlying cardiac conditions, as emphasized in the ACC/AHA 2006 guidelines for the management of patients with valvular heart disease 1. The production of murmurs is due to 3 main factors:
• High blood flow rate through normal or abnormal orifices
• Forward flow through a narrowed or irregular orifice into a dilated vessel or chamber
• Backward or regurgitant flow through an incompetent valve, as outlined in the 2008 focused update incorporated into the ACC/AHA 2006 guidelines for the management of patients with valvular heart disease 1.

From the Research

Mechanism of Cardiac Murmurs

• Cardiac murmurs originate from the transition from laminar to turbulent blood flow in patients with a structural cardiomyopathy (so-called "organic" murmurs) or in patients with normal hearts (so-called "innocent" murmurs) 2
• The mechanism of cardiac murmurs can be attributed to various factors, including:
  • Structural cardiomyopathy, such as valve dysfunctions and rapid blood flow 2, 3
  • Turbulent blood flow, which can be detected through echocardiography 3, 4
  • Valve disorders, such as aortic regurgitation, mitral regurgitation, and tricuspid regurgitation 3, 4, 5
• The characteristics of murmurs can vary depending on the underlying condition, including:
  • Systolic murmurs, which are the most common type of murmur 3, 4
  • Diastolic murmurs, which are often associated with valvular heart disease 3, 5
  • Continuous murmurs, which are often pathologic and warrant further workup 2

Classification of Cardiac Murmurs

• Cardiac murmurs can be classified into different types based on their characteristics, including:
  • Innocent murmurs, which are minor, crescendo-decrescendo, and mostly position-dependent 2
  • Organic murmurs, which are associated with underlying structural cardiomyopathy 2, 3
  • Functional murmurs, which are not associated with any underlying structural cardiomyopathy 3, 6
• The classification of cardiac murmurs can be done using various methods, including:
  • Feature extraction and selection, which can be used to identify the characteristics of murmurs 6
  • Echocardiography, which can be used to detect turbulent blood flow and valve disorders 3, 4