Abstract
The aim of this study was to determine the validity of regression equations relating RR interval and heart rate to systolic time intervals in sheep. Regression equations were compiled employing the RR interval to correct systolic time intervals for heart rate in six Merino ewes. A range of heart rates was obtained by means of pharmacological intervention as well as electrical pacing. Heart rate did not affect the pre-ejection period, isovolumetric contraction time, the pre-ejection period to left ventricular ejection time ratio, the ratio QS2/QT, electrical delay (Q1), or the PR interval. Heart rate did, however, affect the duration of electromechanical systole (QS2), left ventricular ejection time and mechanical systole (S1S2). The study showed that it was preferable to correct the systolic time intervals using the RR interval rather than the heart rate. Bazett's equation to correct electrical systole (QT) for heart rate in humans was also validated in sheep.
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