Cardiac Murmurs, Causes
Differential Diagnosis
| Cardiac Murmur | Lesion Identified by Echocardiography, Catheterization, or Necropsy |
|---|---|
| Functional murmurs* | No identifiable lesions |
| Congenital heart disease murmurs | Defect(s) in the atrial or ventricular septa, patent ductus arteriosus, atresia/stenosis of the tricuspid or pulmonic valve, valve stenosis, other malformations of the heart |
| Mitral regurgitation | High-level training, degenerative thickening of the valve, bacterial endocarditis, mitral valve prolapse into left atrium, rupture of a chorda tendinea, dilated-hypokinetic ventricle (dilated cardiomyopathy), papillary muscle lesion or dysfunction, valvulitis, malformation |
| Tricuspid regurgitation | High-level training,† same causes as for as mitral regurgitation, also pulmonary hypertension from severe left-sided heart failure or chronic respiratory disease |
| Aortic regurgitation | Degeneration of the aortic valve, congenital fenestration of the valve, bacterial endocarditis,‡ aortic prolapse into a ventricular septal defect or the left ventricle, flail aortic valve leaflet, valvulitis, malformation, ruptured aorta or aortic sinus of Valsalva |
| Pulmonary insufficiency | Bacterial endocarditis,‡ pulmonary hypertension, flail pulmonic valve leaflet, valvulitis, malformation, rupture of the pulmonary artery |
| Murmur associated with vegetative endocarditis | Insufficiency of the affected valve‡ |
* Functional murmur may be innocent (unknown cause) or physiologic (suspected physiologic cause). Functional murmurs are common in foals and trained athletes (athletic murmur), associated with fever and high sympathetic nervous system activity (pain, stress, sepsis), and often are heard in anemic horses. Functional murmurs depend on the physiologic state and can be altered by changing the heart rate. Such dynamic auscultation is useful in detecting functional murmurs.
† Doppler echocardiography can identify “silent” regurgitation across a right-sided cardiac valve in some horses; this is probably a normal finding of no clinical significance.
‡ Anatomic stenosis generally is caused by a large vegetation and also should be associated with a diastolic murmur of valvular insufficiency; increased flow across the valve, even in the absence of a true stenosis, may generate a murmur of “relative” valvular stenosis (eg, with aortic regurgitation a systolic ejection murmur may occur because of an increased stroke volume).
Modified from Bonagura JD: Clinical evaluation and management of heart disease. Equine Vet Educ 2:31–37, 1990.
