Final answer:
The end of the T wave on an ECG signifies the start of ventricular relaxation (diastole), marking the return to the isoelectric line as the ventricles prepare for the next cycle of filling and contraction.
Step-by-step explanation:
The start of T wave deflection back to the isoelectric line on an electrocardiogram (ECG) marks the beginning of ventricular relaxation or diastole. This phase occurs after the T wave, which represents the repolarization of the ventricles. The conclusion of the T wave signifies that the ventricles are transitioning from the active phase of contraction to the resting phase where they are relaxed and refilled with blood. The duration of ventricular diastole is approximately 430 ms.
During an ECG, the P wave indicates the depolarization of the atria, followed by atrial contraction. The QRS complex signifies the depolarization of the ventricles leading to their contraction and pumping of blood. As the T wave concludes, it signifies repolarization of the ventricles, and this marks the start of ventricular relaxation or diastole. Understanding the relationship between these waves and cardiac cycle phases helps in diagnosing various cardiac conditions.