The relation between the duration of the Q-T interval and of the left ventricular systole was studied in dogs with induced hypo- and hypercalcemia. At all studied Ca concentrations the change in the duration of both intervals was of similar magnitude and the relation between the duration of Q-T and ventricular systole was nearly constant as long as the heart rate was regular and the ventricular end-diastolic pressure did not change abruptly. Changes in the Q-T duration were due to changes in the duration of the interval from the end of QRS to the apex of T. In the postextrasystolic beats and during alternans the duration of left ventricular systole changed independently of the duration of the Q-T interval. It was concluded that the ventricular systole adjusts its duration to the duration of repolarization, more specifically to the duration of the plateau of the ventricular action potential, within a wide range of Ca concentrations. An escape from this adjustment occurs when the ventricular filling pressure or volume changes abruptly.
Consequences of Using an Orthotropic Stress Tensor for Left Ventricular Systole
