Possible Late Potentials in 4 Dogs with Sustained Ventricular Tachycardia

Signal-averaged electrocardiograms (SAEKGs) were performed on 4 dogs with sustained ventricular tachycardia. Quantitative and qualitative analyses of SAEKGs were consistent with the presence of late potentials. Two of the 4 dogs subsequently died suddenly, and ventricular tachycardia and ventricular fibrillation were observed in 1 dog. High-frequency QRS durations (75–90 milliseconds), duration of low amplitude (less than 40 μV) signals during the terminal QRS complex (LAS₄₀) (28–40 milliseconds), root mean square voltages of the terminal 40 milliseconds of the QRS complex (RMS₄₀) (124–6.5 μV), and root mean square voltages of the terminal 30 milliseconds of the QRS complex (RMS₃₀) (13–2.1 μV) differed from results obtained in 68 of 70 control dogs. Echocardiographic data suggested dilated cardiomyopathy in 2 dogs and the cause of the arrhythmia in 2 dogs was not determined. The SAEKG may be a useful adjunct in identifying a subset of dogs with ventricular tachyarrhythmias that are at high risk for sustained ventricular tachycardia and sudden death. The sensitivity, specificity, and predictive accuracies of the technique remain to be determined.