Relationship between systolic time intervals and heart rate during atrial or ventricular pacing in normal subjects.

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Abstract
Systolic time intervals (STI) are regarded as good indices of cardiac performance in many heart diseases. They are temporally related to the cardiac contraction cycle and may be modified by heart rate changes. The possible relationship between STI and heart rate changes are defined in humans. Changes in heart rate were induced by atrial and ventricular pacing. Tachycardia caused a proportional decrease of left ventricular ejection time (LVET) but did not modify the pre-ejection period (PEP) and the isometric contraction time (ICT) and the electromechanical interval (QS1). While LVET must be corrected for the changes in heart rate, no correction of PEP and ICT is necessary.