Long-term Treatment of β-blocker Metoprolol for Chronic Heart Failure in a Dog with Mitral Regurgitation

Abstract

Effects of long-term treatment of β-blocker for chronic heart failure in dogs with mitral regurgitation (MR) remain unclear. The effects of long-term β-blocker therapy was evaluated in a 11-year old male Maltese dog with severe MR. The dog showed paroxysmal coughing on the first admission and his clinical status was graded as New York Heart Association (NYHA) functional class III. The dog did not demonstrate a sufficient improvement in spite of medical therapy using digitalis, diuretic and nitrate. Thus, oral administration of β-blocker metoprolol was started with a dose of 0.5 mg/kg daily and the dose was increased gradually every two week until 2.5 mg/kg daily. During ten months after the initiation, the clinical status was improved to NYHA class I or class II. Metoprolol decreased the elevated heart rate and accelerated left ventricular fractional shortening to normal ranges, and also improved impaired diastolic function. Morphologically, metoprolol did not attenuate left ventricular cavity dilatation but rather increased left ventricular wall thickness, which resulted in to a greater extent of volume-overload induced eccentric hypertrophy. The dog, however, died due to pulmonary edema 13 months after the initiation. Marked fibrotic lesions of the myocardium were not observed by histologic examination. From this case, it is suggested that β-blocker therapy has beneficial effects on the progression of heart failure in dogs with MR.