ORTHODROMIC RECIPROCATING TACHYCARDIA AND HEART-FAILURE IN A DOG WITHA CONCEALED POSTEROSEPTAL ACCESSORY PATHWAY

A 4-month-old male Labrador Retriever was presented for recurrent bout s of pulmonary edema associated with tachycardia. Initial physical exa mination and echocardiography were unremarkable, and the electrocardio gram revealed only an intraventricular conduction disturbance. Subsequ ent recordings showed paroxysmal supraventricular tachycardia (SVT) (3 40 beats/min), which consistently produced pulmonary edema. The suprav entricular tachycardia was unresponsive to adenosine, esmolol, and pro pranolol; was variably and transiently responsive to various vagal man euvers and precordial thumps; and was always responsive to IV diltiaze m. Multiple life-threatening episodes of SVT occurred, however, despit e the chronic administration of oral diltiazem, propranolol, and proca inamide. Diastolic cardiac dysfunction was documented by Doppler echoc ardiography and was thought to contribute the development of pulmonary edema. A subsequent electrophysiologic study confirmed the presence o f an atrioventricular posteroseptal accessory pathway that participate d in orthodromic reciprocating tachycardia. This pathway was determine d to conduct only in the retrograde direction (''concealed accessory p athway''). Intraoperative IV procainamide titration terminated the arr hythmia, which could not be reinduced when procainamide blood concentr ation approximated 20 mu g/dL. Increasing the oral procainamide dose t o achieve such plasma concentrations was successful in eliminating ort hodromic reciprocating tachycardia, preventing heart failure, and retu rning Doppler indices of diastolic function to normal. (C) 1995 by the American College of Veterinary Internal Medicine.