A nurse is interpreting a client's ECG strip. Which of the following components of the ECG should the nurse examine to determine the time it takes for ventricular depolarization and repolarization?

ECG interpretation relies on electrical depolarization and repolarization phases of the cardiac cycle. The key measurement representing total ventricular electrical activity includes ventricular depolarization, ventricular repolarization, action potential duration, and QT interval prolongation, which reflects both systole and electrical recovery. Rationale: A. The QRS complex represents ventricular depolarization only, indicating the time required for electrical activation of the ventricles. It does not include ventricular repolarization, so it only reflects part of ventricular electrical activity rather than the full cycle. B. The QT interval measures the total time for ventricular depolarization and repolarization, encompassing the entire ventricular action potential. Prolongation or shortening can indicate arrhythmia risk such as torsades de pointes or electrolyte disturbances. C. The PR interval reflects atrial depolarization and AV node conduction delay before ventricular activation. It does not represent ventricular electrical activity or repolarization, making it unrelated to ventricular timing. D. The ST segment represents the period when ventricles are fully depolarized and corresponds to the plateau phase of the action potential. It does not include the full repolarization phase and therefore does not represent total ventricular electrical timing.