Is there any relation between the ventricular systolic period and heart rate?

Yes, there is a significant relationship between the ventricular systolic period and heart rate, which can be observed through several aspects of the cardiac cycle:

Ventricular Ejection Time (LVET)

The left ventricular ejection time (LVET) decreases as the heart rate increases. Studies have shown that tachycardia, induced by atrial or ventricular pacing, causes a proportional decrease in LVET. This indicates that as heart rate increases, the time during which the ventricle ejects blood into the aorta decreases13.

Systolic Intervals and Heart Rate

The ratio of contraction time (systolic interval, SI) to relaxation time (diastolic interval, DI) changes with heart rate. As the heart rate increases, the proportion of the cardiac cycle spent in contraction (systole) increases. For example, at a normal heart rate of 75 bpm, systole constitutes about 34% of the cardiac cycle, increasing to about 53% at 200 bpm3.

Phases of Ventricular Systole

Ventricular systole includes phases such as isovolumic contraction and rapid ejection. While the duration of these phases can vary with heart rate, the isovolumic contraction time and the pre-ejection period (PEP) do not necessarily change with heart rate increases. However, the overall duration of systole, particularly the ejection phase, is affected by heart rate changes15.

Electrical and Mechanical Correlation

The electrical parameters of the cardiac cycle, such as the QT interval, also correlate with mechanical systole. As heart rate increases, the QT interval decreases, and there is a corresponding decrease in the mechanical systolic time, particularly the LVET. This indicates a close relationship between electrical and mechanical aspects of systole with changing heart rates3.

In summary, the ventricular systolic period is indeed influenced by heart rate, with key changes observed in the duration of ventricular ejection and the overall proportion of the cardiac cycle dedicated to systole.