A supraventricular tachycardia with a possible accessory pathway in a young Labrador Retriever

Supraventricular tachycardias (SVTs) are fast heart rhythms originating from the sinus node, atrial tissue or atrioventricular junctional tissue. They include physiological sinus tachycardia but are often taken to refer to pathological SVTs. They can cause clinical signs such as weakness, and if sustained, can lead to tachycardia-induced cardiomyopathy and congestive heart failure (Shinbane et al, 1997). One particular type of SVT is caused by the presence of an accessory pathway of conducting tissue between the atria and ventricles, bypassing the atrioventricular node, allowing a rapid re-entrant conducting circuit to occur. This case report describes a case of a pathological SVT in a young Labrador Retriever, with differential diagnoses of an accessory pathway-mediated tachycardia or a focal atrial tachycardia.

A 3-year-old male Labrador Retriever was referred following the detection of a sustained tachycardia while undergoing investigations following a two-day history of lethargy and vomiting. Physical examination revealed a laterally recumbent, normothermic (38.3°C) dog in good body condition (37 kg). The dog had congested mucous membranes and an elevated respiratory rate (48 breaths per minute) with no adventitious lung sounds. The dog's heart rate was approximately 300 beats per minute (bpm), with a regular rhythm and no audible murmur. The femoral pulses were very hypokinetic, making possible deficits difficult to appreciate.