Final answer:
Ventricular systole begins with the QRS complex on the ECG, lasts for approximately 270 ms, and is followed by ventricular diastole signaled by the T wave. It features two phases: isovolumetric contraction and ventricular ejection, with a stroke volume of 70-80 mL and end systolic volume remaining in the ventricles.
Step-by-step explanation:
Ventricular systole begins with the depolarization of the ventricles, which is indicated by the QRS complex on an electrocardiogram (ECG). This phase of the cardiac cycle follows atrial systole, which ends prior to ventricular systole. The ventricles, at this stage, contain the end diastolic volume (EDV) or preload, amounting to approximately 130 mL of blood in a resting adult.
Ventricular systole can be divided into two phases and persists for a total of approximately 270 milliseconds (ms). The first phase is the isovolumetric contraction phase where the ventricles contract and build pressure without ejecting blood, as the atrioventricular valves are closed and the semilunar valves have not yet opened. In the second phase, the ventricular ejection phase, blood is pumped from the ventricles, pushing open the pulmonary and aortic semilunar valves. At the end of the ejection phase, the remaining blood in the ventricles is known as the end systolic volume (ESV), while the amount ejected, termed stroke volume, ranges between 70-80 mL.
The T wave on the ECG signals the end of the ventricular systole and the beginning of ventricular diastole, which lasts approximately 430 ms.