Abstract
The QT interval indicates the duration of the action potential of the ventricular muscles and it is one of the important criteria used in the evaluation of electrocardiograms. Among the many physiologic and pathologic factors that contribute to the QT interval, the heart rate plays a major role. Several formulas have been proposed to adjust the QT interval for the heart rate; and the most commonly utilized formula is the QT correction formula proposed by Bazett. However, several studies have shown that Bazett's correction formula is not optimal. This study evaluates Fridericia's cube root formula (QTc2) relative to Bazett's formula (QTc1) to characterize the RR-QT relationship in dogs. ECG was recorded from 407 privately owned dogs. The dogs fulfilled the following criteria: no history and physical examination of heart disease and normal sinus rhythm or sinus arrhythmia. The correlation between the QT interval and RR interval was the highest (r=0.676, p<0.0001) compared to QTc1 and RR (r=−0.568 (p<0.0001)) and QTc2 (r=−0.180 (p<0.0005)). The QTc2 had the lowest correlation, and our results suggest that Fridericia's cube root formula is more adequate than Bazett's square root formula to correct the heart rate-dependent QT change in dogs.
