When does the U wave typically follow the T wave?

The U wave typically follows the T wave during the period of slow repolarization of the Purkinje fibers and the ventricles. This repolarization phase represents the reset of the heart muscle after contraction, preparing it for the next heartbeat.

Understanding the U wave's relationship with the T wave is crucial, as the U wave is not always present in every ECG tracing but can be seen in certain physiological and pathological conditions. The presence of the U wave can be associated with factors like electrolyte imbalances (especially hypokalemia), bradycardia, and improved myocardial oxygenation.

The other options do not accurately describe when the U wave follows the T wave. Deoxygenated blood flow does not play a role in the timing of the U wave, as the waveforms are primarily generated by electrical activity rather than blood flow. The statement regarding ventricular depolarization is incorrect because the U wave occurs after ventricular depolarization has completed and does not follow it directly. Atrial contraction is also unrelated, as it pertains to electrical activity in the atria that occurs earlier in the cardiac cycle and does not affect the timing of the U wave in relation to the T wave.