2005 Volume 14 Issue 2 Pages 51-57
The purpose of this study was to assess the safety and efficacy of a β-blocker in dogs with naturally acquired mitral regurgitation (MR) because its long-term effects in dogs with chronic heart failure (CHF) have not been reported, although beneficial effects of β-blocker therapy for CHF have been demonstrated in humans. The case records of MR in 26 dogs treated with a β-blocker were analyzed retrospectively. First, the dogs were classified according to the functional classification of the New York Heart Association (NYHA); ten dogs were classified as NYHA functional Class II, and 16 dogs as severer classes, class III or IV. A β-blocker, metoprolol tartrate, was started at 0.5 mg/kg/day, and gradually increased to our target dosage, 2.0 mg/kg/day. When the β-blocker was initiated, almost all the dogs were already on regular medication for CHF with digoxin, angiotensin-converting enzyme inhibitors, and/or frosemide, and these medicines were also given during the therapy. Clinical symptoms and radiographic and echocardiographic findings were compared before and after the therapy. One-, three-, and six-month treatment respectively promoted 40%, 45.0%, and 30.8% of the dogs to milder classes. The thickness of the left ventricular wall remained unchanged despite cardiac enlargement on radiographs. Drug-related side effects occurred during the early phase of the therapy in nine dogs (34.6%). The side effects were more likely to occur in severely ill dogs. In summary, combination therapy with conventional regular medication for CHF and long-term treatment with a β-blocker such as metoprolol tartrate may be a new therapeutic strategy for both mild and severe CHF in dogs with MR, although close attention is required during the early phase of the therapy.