SUPRAVENTRICULAR TACHYCARDIA IN 4 YOUNG-DOGS

Rapid, clinical supraventricular tachycardia (SVT), without apparent u nderlying heart disease, was identified in 3 young Labrador Retrievers and 1 Labrador Retriever-type dog. The electrocardiographic character istics, identification of ventricular preexcitation in 2 dogs, age at onset, response to antiarrhythmic agents, and recent electrophysiologi c documentation of a concealed accessory pathway in another young Labr ador Retriever suggested orthodromic atrioventricular reciprocating ta chycardia as the mechanism of SVT. As observed in this group of dogs, chronic SVT can lead to systolic or diastolic dysfunction, overt conge stive heart failure, or secondary valvular dysfunction, all of which a re potentially reversible with control of the tachyarrhythmia. Intrave nous administration of calcium-channel blockers appeared to be the mos t effective antiarrhythmic treatment for acute termination of the tach yarrhythmia in these dogs, whereas procainamide hydrochloride has been most efficacious for chronic management. One dog died during direct-c urrent cardioversion for incessant SVT; another was euthanatized becau se of refractory congestive heart failure secondary to sustained SVT.