In a canine model, the isovolumetric contraction interval is determined by the ratio of aortic diastolic pressure to the maximum rate of intraventricular pressure change, independent of heart rate.
The influence of the rate of change of intraventricular pressure, the aortic diastolic pressure, and the heart rate on the isovolumetric contraction interval was examined in dogs under a variety of hemodynamic states. The experimental conditions included alteration of the contractile state of the ventricle, its preload, and its afterload. Analysis of the data indicated that the isovolumetric contraction interval is inversely related to the maximum rate of intraventricular pressure change, is directly related to the aortic diastolic pressure and is independent of the heart rate. A reliable correlation was found between the ICT interval and the ratio of aortic diastolic pressure to the pressure derivative. This correlation was not altered by the experimental conditions imposed.
Agress et al. (Mon,) studied this question.