The Effect of Basic Cycle Length Stimuli on Effective Refractory Period Measurement

Refractory periods are measured by the extrastimulus technique, whereby a single extrastimulus is introduced at progressively shorter coupling intervals until a response is no longer elicited.

As refractoriness of cardiac tissues depends on prior cycle length, refractory periods should be determined at a fixed cycle length within the physiologic range. The extrastimulus is delivered after a train of 8 to 10 paced complexes to allow time for reasonable stabilization of refractoriness, which is usually accomplished after the first 3 or 4 paced beats.

We conducted this study to compare the effect of 6 vs 8 stimuli in basic cycle length (BCL) in measurement of effective refractory period (ERP).

During electrophysiologic study (EPS) of 100 consecutive patients, anterograde and retrograde ERP of atrioventricular node (AVN) were measured by introduction of 6 vs 8 stimuli in BCL and premature beat, then the results were compared.

Recorded anterograde and retrograde ERP of AVN applying 6 vs 8 stimuli in BCL were compared and no difference was detected.

We concluded that for ERP measurement of AVN, 6 stimuli in BCL is comparable to 8 stimuli in reaching the steady state.