Heart Murmur Causes and Diagnostic Considerations

Primary Pathophysiological Mechanisms

• High blood flow rate through normal or abnormal orifices, such as in pregnancy, thyrotoxicosis, anemia, or arteriovenous fistula, can cause heart murmurs in adults 1
• Forward flow through a narrowed or irregular orifice into a dilated vessel or chamber can also lead to heart murmurs 1
• Backward or regurgitant flow through an incompetent valve is another primary mechanism of heart murmur production 1

Common Causes by Murmur Type

• Aortic stenosis is the most frequent pathological cause requiring valve replacement in adults, with incidence increasing with age, according to the American College of Cardiology 2
• Aortic sclerosis, or focal thickening without significant obstruction, is extremely common in older adults, particularly those with hypertension, as noted by the American College of Cardiology 3
• Physiological flow murmurs can occur in increased cardiac output states, such as pregnancy, thyrotoxicosis, or anemia, as reported by the American College of Cardiology 1
• Pulmonic stenosis or flow into dilated great vessels can also cause systolic murmurs, as described by the American College of Cardiology 1
• Hypertrophic cardiomyopathy with left ventricular outflow tract obstruction is another cause of systolic murmurs, according to the American Heart Association, as published in Circulation 4
• Tricuspid regurgitation can cause holosystolic murmurs, as noted by the American Heart Association, as published in Circulation 4
• Ventricular septal defect can also lead to holosystolic murmurs, as reported by the American Heart Association, as published in Circulation 4
• Mitral valve prolapse with late systolic regurgitation can cause late systolic murmurs, as described by the American College of Cardiology 5
• Aortic regurgitation can cause early diastolic murmurs, as noted by the American Heart Association, as published in Circulation 4
• Pulmonic regurgitation with pulmonary hypertension can also lead to early diastolic murmurs, as reported by the American Heart Association, as published in Circulation 4
• Mitral stenosis can cause mid-diastolic murmurs, as described by the American Heart Association, as published in Circulation 4
• Tricuspid stenosis can also lead to mid-diastolic murmurs, as noted by the American Heart Association, as published in Circulation 4
• Increased diastolic flow across normal valves, such as in severe regurgitation or shunts, can cause mid-diastolic murmurs, as reported by the American Heart Association, as published in Circulation 4
• Austin-Flint murmur, a functional mitral stenosis caused by severe chronic aortic regurgitation, can also lead to mid-diastolic murmurs, as described by the American Heart Association, as published in Circulation 4
• Patent ductus arteriosus and other high-to-low pressure shunts can cause continuous murmurs, as noted by the American Heart Association, as published in Circulation 4

Clinical Context and Prevalence

• Most systolic heart murmurs in adults do not signify cardiac disease and are related to physiological increases in blood flow velocity, as reported by the American College of Cardiology 1
• Diastolic murmurs virtually always represent pathological conditions and require further cardiac evaluation, according to the American College of Cardiology 1

Diagnostic Considerations

• Echocardiography should be performed for any diastolic murmur, except confirmed venous hum, as recommended by the American College of Cardiology 6
• Echocardiography is also recommended for holosystolic murmurs, grade ≥3/6 systolic murmurs, and any murmur with associated symptoms, such as syncope, angina, heart failure, or dyspnea, as noted by the American College of Cardiology 2
• Asymptomatic young adults with grade 1-2/6 midsystolic murmurs and no other cardiac physical findings may need no further workup after initial history and physical examination, as reported by the American College of Cardiology 3