Estimation of ventricular refractoriness in man by the extra stimulus method.

The effective right ventricular refractory (EVRP) period was estimated in 24 patients using the extra stimulus technique. All patients were paced from the right ventricle at basic pacing intervals of 400, 500, 600 and 800 ms, respectively. In all patients the EVRP decreased when the basic pacing rate was increased. At the same basic pacing rate there was a wide variation in the EVRP between individual patients. Within an individual patient, however, providing the position of the pacing electrode remained stable, there was no significant variation in the EVRP when estimations were performed 15-30 min apart. Thus the technique can be used to assess the effect of a drug on the EVRP in an individual patient.