Accurate evaluation of QT interval in conscious rhesus monkeys (Macaca mulatta) by use of Holter ECG.

The aim of this study was to determine the best method to evaluate the QT interval with respect to the heart rate in rhesus monkeys. Rhesus monkeys (Macaca mulatta) are widely used in cardiovascular research, but the characteristics of QT-RR formulas as regards rhesus monkeys has not been sufficiently related. We analyzed the physiological QT-RR relation for practical evaluation of the QT interval in conscious rhesus monkeys by use of 24-h Holter ECG monitoring. As the QT interval varies with dependency on the RR interval, 14 QT regression functions were evaluated by use of about 50 pairs of QT-RR points per animal in 5 male rhesus monkeys. The accuracy of fit with the measured data was assessed according to the minimum Akaike information criterion. Among one-parameter linear regression functions, QT = a x (RR)(1/2), where "a" is the regression coefficient, gave the best fit, which was almost comparable to that of all multi-parameter regression functions. Our results also suggest that the QTc formula derived from the square root regression function is the most practical for evaluation of QT intervals in rhesus monkeys. In conclusion, concerning the heart rate of rhesus monkeys, we propose the modification of Bazett's formula (QTc = QT x (500)(1/2)/(RR)(1/2), where the dimension of RR and QT interval is milliseconds). We believe the information herein is quite useful for cardiovascular studies on rhesus monkeys.