Exercise and pharmacological stress echocardiography in healthy horses.
BACKGROUND
Stress echocardiography could be a useful diagnostic test in horses suspected to suffer from exercise-induced myocardial dysfunction as a cause of exercise intolerance.


OBJECTIVE
To evaluate the effect of treadmill exercise and pharmacological stress test on left ventricular echocardiographic parameters.


METHODS
Echocardiography was performed in 2 groups of 5 healthy horses, either immediately after a near-maximal treadmill exercise (Group EXE) or during a pharmacological challenge (Group DOB) consisting of 35 microg/kg atropine, followed by incremental dobutamine infusion rates of 2-6 microg/kg bwt/min for 5 min duration each, which led to a cumulative dobutamine dose of 100 microg/kg. Left ventricular M-mode parameters were compared at rest and at heart rates of 80, 100, 110, 120 130, and 140 beats/min, within each group.


RESULTS
In 2 horses of Group EXE, echocardiographic measurements were impossible at 140 and 130 beats/min, as their heart rates dropped too fast in the immediate post exercise period. In the remaining 3 horses image quality was not always satisfactory at heart rates of 130 and 140 beats/min. Systolic left ventricular parameters and fractional shortening measured at 130 and 140 beats/min were significantly different from values obtained at lower heart rates. Horses in Group DOB reached expected heart rates of 80 and 100 beats/min, after the administration of atropine and during a dobutamine infusion rate of 2 microg/kg bwt/min, respectively. Heart rates targets of 110, 120, 130, and 140 beats/min were reached at mean (+/- s.d.) dobutamine infusion rates of 2.8 +/- 0.4, 3.2 +/- 0.4, 4.0 +/- 0.7, 5 +/- 0.7 microg/kg bwt/min, respectively. Systolic left ventricular parameters and fractional shortening at heart rates of 110, 120, 130, and 140 beats/min, were significantly different from values obtained at lower heart rates.


CONCLUSIONS
The pharmacological stress test induced changes in ventricular dimensions at heart rates of 80 to 140 beats/min. Using this test, high quality images can easily be obtained at heart rates of 140 beats/min. Conversely, in post exercise echocardiography, obtaining good quality images at heart rates of 130 and 140 beats/min is difficult, which limits use of the technique in routine clinical settings.


CONCLUSIONS
Further studies should demonstrate the potential of pharmacological stress test as a diagnostic tool in horses suffering from exercise-induced myocardial dysfunction.
Sandersen
C
C
Department of Clinical Sciences-Equine Clinic, Faculty of Veterinary Medicine, University of Liege, Blvd. de Colonster 20, B-4000 Liege, Belgium.
Detilleux
J
J
Art
T
T
Amory
H
H
D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology; D001285:Atropine / Q000009:adverse effects / Q000494:pharmacology*; D002316:Cardiotonic Agents / Q000009:adverse effects / Q000494:pharmacology*; D004280:Dobutamine / Q000009:adverse effects / Q000494:pharmacology*; D025401:Echocardiography, Stress / Q000379:methods / Q000662:veterinary; D005080:Exercise Test / Q000662:veterinary; D005260:Female; D006331:Heart Diseases / Q000175:diagnosis / Q000662:veterinary; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology*; D006734:Horse Diseases / Q000175:diagnosis; D006736:Horses / Q000502:physiology*; D008297:Male; D010805:Physical Conditioning, Animal / Q000502:physiology*; D016277:Ventricular Function, Left / Q000187:drug effects / Q000502:physiology
D000889:Anti-Arrhythmia Agents; D002316:Cardiotonic Agents; D004280:Dobutamine; D001285:Atropine