R-Peak Time: An Electrocardiographic Parameter with Multiple Clinical Applications

In the 12-lead electrocardiogram (ECG), the time from the onset of the QRS complex (Q or R wave) to the apex or peak of R or to R' (when present), using indirect or semidirect surface unipolar precordial leads, bipolar limb leads or unipolar limb leads, is called ventricular activation time (VAT), R wave peak time (RWPT), R-peak time or intrinsicoid deflection (ID). The R-peak time in a specific ECG lead is the interval from the earliest onset of the QRS complex, preferably determined from multiple simultaneously recorded leads, to the peak (maximum) of the R wave or R' if present. Irrespective of the relative height of the R and R' waves, the R-peak time is measured to the second peak. The parameter corresponds to the time of the electrical activation occurring from the endocardium to the epicardium as reflected by the recording electrode located at a variable distance on the body surface, depending on the lead type: a unipolar precordial lead, a bipolar or unipolar limb lead. In normal conditions, the R-peak time for the thinner-walled right ventricle is measured from lead V1 or V2 and its upper limit of normal is 35 ms. The R-peak time for the left ventricle (LV) is measured from leads V5 to V6 and 45 ms is considered the upper limit of normal. In this manuscript, we review the clinical applications of this parameter.