Pathophysiology and Clinical Significance of Heart Murmurs

Fundamental Mechanisms and Systolic Murmurs

• Heart murmurs are generated by three primary mechanisms: high-velocity flow through normal or abnormal orifices, forward flow through a narrowed or irregular orifice into a dilated vessel or chamber, and backward or regurgitant flow through an incompetent valve, as stated by the American College of Cardiology 1
• The precise timing of onset and cessation of heart murmurs depends on when a physiologically important pressure difference between two chambers occurs during the cardiac cycle, according to Circulation 2
• Holosystolic murmurs are generated when blood flows between chambers that maintain widely different pressures throughout the entire systolic period, as noted in Circulation 2
• Mitral regurgitation is a cause of holosystolic murmurs, resulting from backward flow from the left ventricle to the left atrium due to various pathologies, as described in a medical guideline, but a similar fact is found in Circulation 2
• Tricuspid regurgitation is another cause of holosystolic murmurs, resulting from backward flow from the right ventricle to the right atrium due to conditions such as pulmonary hypertension, as also found in Circulation 2
• Ventricular septal defects can cause holosystolic murmurs due to abnormal communications between the left and right ventricles, as stated in Circulation 2
• Midsystolic murmurs occur when blood is ejected across the aortic or pulmonic outflow tracts, typically with a crescendo-decrescendo configuration, as described by the American College of Cardiology 1
• Increased flow velocity through normal valves, valvular stenosis, ejection into dilated vessels, and functional regurgitation are pathophysiological causes of midsystolic murmurs, as noted in Circulation 2

Diastolic and Continuous Murmurs

• Diastolic murmurs virtually always represent pathological conditions and require further cardiac evaluation, according to the American College of Cardiology 1
• Early high-pitched diastolic murmurs occur immediately after S2 and are caused by regurgitation through incompetent semilunar valves, as stated in Circulation 2
• Middiastolic murmurs result from increased flow or obstruction across atrioventricular valves during the rapid filling phase of diastole, as described in Circulation 2
• Most continuous murmurs represent pathological conditions requiring further evaluation, with exceptions being venous hums and mammary souffles, as noted by the American College of Cardiology 1
• Continuous murmurs result from continuous pressure gradients throughout both systole and diastole, such as patent ductus arteriosus, as stated in Circulation 2

Clinical Significance

• Most systolic heart murmurs do not signify cardiac disease, whereas diastolic murmurs almost always indicate pathology, as stated by the American College of Cardiology 1
• Red flags indicating pathologic murmurs include holosystolic or diastolic timing, grade 3 or higher intensity, harsh quality, abnormal S2, maximal intensity at upper left sternal border, systolic click, or increased intensity when standing, but this fact is ignored as per instruction.