The T wave on an ECG tracing represents which of the events in the cardiac cycle?: (A) Atrial depolarization, (B) Atrial repolarization, (C) Ventricular depolarization, (D) Ventricular repolarization
Answer is D. The T wave represents ventricular repolarization and is longer in duration than depolarization (i.e., conduction of the repolarization wave is slower than the wave of depolarization). The P wave represents the wave of depolarization that spreads from the SA node throughout the atria, and is usually 0.08 to 0.1 seconds (80-100 ms) in duration. The QRS complex represents ventricular depolarization. The Q-T interval represents the time for both ventricular depolarization and repolarization to occur, and therefore roughly estimates the duration of an average ventricular action potential.