Doppler Echocardiographic follow up of three horses with congestive heart failure and treated with quinapril, digoxin, and diuretics

Angiotensin converting enzyme inhibitors are recommended therapy in human and canine patients with congestive heart failure (CHF), but little is known concerning their efficiency to treat horses with CHF. Enalapril has been shown to be poorly absorbed in horses and quinapril has been shown to decrease the severity of the insufficiency and to increase the stroke volume (SV) and the cardiac output (CO) in horses with mitral regurgitation (MR) without signs of CHF. The objective of this cases report was to evaluate the effect of quinapril associated with routine treatment in horses with CHF.
Three horses with clinical, echocardiographic and electrocardiographic signs of severe MR, CHF and secondary atrial fibrillation were studied (Fig 1 to 3). None of them had been previously treated for those problems. According to the ACVIM classification system for management of canine CHF, they were therefore classified in class C. They were treated with quinapril 0.2mg/kg SID PO, digoxin 0.011mg/kg BID PO, and furosemide 1mg/kg BID IM. Standard echocardiographic and Doppler measurements were performed before treatment (T0), and 1 and 4 weeks after starting treatment (W1 and W4, respectively).
All horses showed a transient clinical improvement (decrease of edemas and disappearance of the dyspnea) after 1 week of treatment, but clinical signs deteriorated within the following weeks in 2 horses that were euthanized for ethical reasons. The third horse kept a steady clinical status and was discharged with the treatment pursued at home. Evolution (in %) of main echocardiographic parameters at W1 and W4 compared to T0 values are showed in Table1. Large individual variations in response to the treatment were seen. Nevertheless, in all horses, a decrease of the Heart Rate (HR) was observed after 1 week of treatment, but the HR increased again after 1 month of treatment (Fig 4). On the contrary, no increase in SV or CO, and no decrease in LVIDd were seen in response to treatment (Fig 5). In the 2 horses that were euthanized, the fractional shortening (FS) and the pre-ejection to ejection time ratio (PEP/ET) decreased and the mitral E peak velocity increased with treatment, whereas they followed the opposite evolution in the surviving horse.
No conclusion can be drawn from this study because of the limited number of studied cases. However, it would be interesting to extend it to additional cases and to less severely affected cases (i.e. horses classified in class C after initial treatment or class B horses). Negative chronotropic effect of digoxin was suggested after 1 week of treatment since a decrease of the HR was observed in all horses. However, this effect seemed to decrease after 1 month of treatment.
Those preliminary results of echocardiography suggest that quinapril in association with digoxin and furosemide at the used dosage could be inefficient to reduce the left ventricular filling pressure and to improve the myocardial contractility in horses with severe CHF. This could however be due to the fact that the 3 studied horses were cases refractory to classic treatment (thus to be classified in class D).