Effect of Ca on duration of Q-T interval and ventricular systole in dog

¹ Division of Experimental Medicine, University of Vermont, Burlington, Vermont

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.

Note:
With the Technical Assistance of Paul Van Lith, Yvonne K. Starcheska, and Ernesto Suarez

Key Words: calcium and myocardial contraction • EDTA and myocardial contraction • calcium and ECG • hypocalcemia and ECG • hypercalcemia and ECG • EDTA and ECG • duration of electrical and mechanical activity in the heart • duration of ventricular repolarization and contraction • myocardial contraction and repolarization

Submitted on December 3, 1962

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