Reproducibility of measurements of ventricular activation time using the signal-averaged Frank vectorcardiogram.

Interobserver and day-to-day variability in detecting delayed potentials and in measuring duration of ventricular depolarization using the signal-averaged Frank vectorcardiogram were investigated in 20 patients, 12 with and 8 without ventricular tachycardia (VT). No patients were taking antiarrhythmic medications, digoxin or beta blockers at the time of study. The presence of delayed potentials and duration of ventricular activation were measured 2 times a mean of 5 days apart by 2 observers. Analysis of variance showed no significant interobserver variability in ventricular activation time. Day-to-day differences in ventricular activation times were small in patients without VT, none of whom had delayed potentials at either study. Delayed potentials were present in all 12 patients with VT at the first recording and in 11 at the repeat recording. However, significant (p less than 0.01) day-to-day variability was found in ventricular activation times, and 3 of the 12 patients had marked (more than 20 ms) day-to-day changes. It is concluded that in the absence of medical or surgical intervention, delayed potentials detected on 1 day have a high chance of being present at a repeat recording. However, the exact timing of these delayed potentials shows marked day-to-day variation in some patients. Interobserver variability is not significant with this method of detecting delayed potentials.