Stress echocardiography in horses – a review

The increasing number of publications in the field of equine stress echocardiography demonstrates the growing interest in this area. Stress echocardiography consists of Band/or M-mode echocardiography under active or passive stimulation of the heart, where the pre-stimulation images are compared to those obtained during or immediately after stimulation. In human medicine, stress echocardiography is mainly used as a routine tool in diagnosis and prognosis of coronary artery disease, but also in the evaluation of hypertrophied and dilated cardiomyopathy and valvular diseases. In horses, the principal indications include the detection of exercised-induced myocardial insufficiency and refining the prognosis of lowand mid-grade valvular diseases. The two major cardiac stressors that can be used in horses are (1) physical exercise, which has the major disadvantage of a rapid decline in heart rate in the immediate post-exercise period and (2) pharmacological stimulation, which ideally consists of dobutamine infusion in combination of a parasympatholytic drug, in order to overcome the strong dobutamine-induced baroreceptor reflex in horses. Most stress echocardiographic studies performed in horses demonstrated a significant decrease of left ventricular length, diameter, area and volume in response to stimulation. Other studies also revealed a stimulation-induced increase in the interventricular septum, left ventricular free wall thickness, and left ventricular fractional. Some of these changes seemed to be more pronounced during pharmacological stimulation than after exercise. One study described the application of a semi-quantitative wall motion scoring system in horses. Exercise as well as pharmacological stress echocardiography enhances the diagnostic possibilities in equine medicine, because it increases the chance to detect a problem that is not present at rest. Furthermore, this technique could help to investigate the relationship between valvular insufficiencies and ventricular dysfunction.