ECG of the Month

IntroductionAn 11-year-old 13-kg (28.6-lb) castrated male Standard Schnauzer was presented to the cardiology service at Oregon State University Veterinary Teaching Hospital for potential pacemaker implantation because of recent syncopal episodes. A diagnosis of sinus node dysfunction had previously been made for the dog on the basis of analysis of 24-hour Holter monitoring data. On physical examination, a grade 2/6 left apical systolic murmur and an irregular, tachycardic rhythm were ausculted. The femoral arterial pulses were variable in strength, and jugular venous distension was observed. The dog was noted to be blind bilaterally, which had been previously documented, and had