Duration of the QT interval in healthy cats

OBJECTIVE: To develop a clinically useful model for predicting QT interval duration as a function of heart rate in healthy cats. ANIMALS: 20 healthy cats. PROCEDURE: For all cats, results of a physical examination, electrocardiography, and echocardiography were normal. Twenty-four hour heart rate and rhythm data were collected by means of ambulatory electrocardiography. Hourly ECG segments were obtained from the 24-hour recordings. Mean heart rate and the mean of 5 QT interval measurements were calculated for each of 479 usable ECG segments. Analysis of covariance was used to develop models to describe variability in QT interval duration. RESULTS: Prediction equations (R2 = 0.81) including terms for heart rate, (heart rate)2, age group (1 to 4 vs 8 to 14 years old), and their interactions were developed. Sex, individual cat, and time of day were of little value in predicting QT interval duration. A simplified prediction equation without age group (R2 = 0.71) also was developed and had better predictive ability than reported correction formulas for QT interval duration. CONCLUSIONS AND CLINICAL RELEVANCE: Prediction equations with 95% prediction intervals for expected QT interval duration in healthy cats were generated. Abnormal QT interval duration can be associated with cardiac electrical instability, yet QT interval duration is greatly influenced by heart rate. Results of the present study provide reference ranges for expected QT interval duration as a function of heart rate in healthy cats.