In the electrocardiogram, the time of the onset of the intrinsicoid deflection, also referred to as the R wave peak time, is measured from the beginning of the QRS complex to the peak of the R wave. The intrinsicoid deflection reflects the depolarization vector from the endocardium to the epicardium.
In the presence of bundle branch block or ventricular hypertrophy, the depolarization impulse takes a longer than normal period of time to reach the recording electrode. This delays the onset of the intrinsicoid deflection. This prolongation or delay is an important criterion for diagnosing bundle branch block and ventricular hypertrophy. Onset of intrinsicoid deflection > 0.05 seconds (just over one small box) is used as a non-voltage related criterion to diagnose left ventricular hypertrophy.