Review Article: Heart murmurs in horses: determining their significance with echocardiography

Abstract

Summary Physiological flow murmurs occur frequently in horses and may be difficult to distinguish from murmurs associated with underlying cardiac disease. The significance of heart murmurs auscultated in horses is often difficult to determine if the horse is not exhibiting any clinical signs or if the signs, such as poor performance, are nonspecific. A complete echocardiographic examination (M‐mode, 2‐dimensional (2‐D) and Doppler) provides an objective assessment of the severity of the horse's underlying cardiac disease. Valvular regurgitation and ventricular septal defects (VSDs) occur frequently and may impair performance, result in the horse's premature demise or have no apparent effect on the horse's life expectancy or performance capabilities. The echocardiographic findings that are used to formulate a prognosis for longevity and performance in horses with valvular regurgitation include the abnormalities detected on the valve leaflets, degree of cardiac chamber enlargement, severity of the resultant volume overload, size of the regurgitant jet, and relative relationship of jet size to chamber size. The echocardiographic findings that are used to formulate a prognosis for horses with VSDs are the number, size and location of the defect(s), degree of left ventricular volume overload, maximal velocity and direction of shunt flow through the defect and the presence and severity of concurrent valvulus regurgitation. Knowledge of the natural progression of the common types of cardiovascular disease in horses, coupled with the echocardiographic findings, clinical history and owner's or trainer's expectations can help the veterinarian form en accurate prognosis for life and performance in horses with heart murmurs.

Effect of left‐sided valvular regurgitation on mortality and causes of death among a population of middle‐aged and older horses

“…When this was taken into account, there was no longer a significant difference between the mortality of the horses with and without LSVR, in agreement with other reports that both AR and MR can be well tolerated by horses for many years (Reef 1993, 1995, Marr 1995). The inclusion of cardiac murmurs of all grades may have influenced these results, because in general terms quieter murmurs are less likely to be associated with severe valvular regurgitation.…”

Subclinical diseases underlying poor performance in endurance horses: diagnostic methods and predictive tests

“…Colour-flow and pulse-wave Doppler echocardiography was also used; flow mapping of valvular regurgitation, if present, was performed to obtain a semi-quantitative measurement of the severity of the valvular regurgitation (Reef 1995). …”

Prevalence and Risk Factors for Cardiac Diseases in a Hospital‐Based Population of 3,434 Horses (1994–2011)

“…Indeed, most cardiac murmurs and arrhythmias are physiologic in horses . However, investigation of these with ECG and Doppler echocardiography is recommended as even mild cardiac abnormalities might lead to important cardiac disease and cause poor performance in sport horses …”