Isovolumetric contraction is a phase of the cardiac cycle that occurs during ventricular systole, specifically after the ventricles have filled with blood and before they begin to eject blood into the aorta and pulmonary artery. This phase is characterized by the contraction of the ventricles with no change in volume because all the heart valves (the atrioventricular valves and the semilunar valves) are closed.
In the context of the electrocardiogram (ECG), isovolumetric contraction begins at the end of the QRS complex. The QRS complex represents the depolarization of the ventricles, leading to their contraction. During isovolumetric contraction, the pressure in the ventricles rises as the muscle fibers contract, but the volume remains constant until the pressure exceeds that in the arteries, leading to the opening of the semilunar valves and the ejection phase.
So, to clarify, isovolumetric contraction occurs after the QRS complex in the ECG, not during the blink itself. The "blink" typically refers to the mechanical activity of the heart, occurring after the electrical signals are complete (i.e., after the QRS complex).
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