Characteristics of reflection as a mechanism of reentrant arrhythmias and its relationship to parasystole.

A model of "reflection" was developed in a sucrose gap preparation of Purkinje fibers. In this preparation, a driven impulse on the proximal side of a sucrose gap is electrotonically transmitted after a delay to the tissue distal to the gap. When the delay is long enough, electrotonic transmission in the reverse direction over the same blocked segment can reexcite the proximal segment. Frequency-dependent alterations of patterns of ectopic activity were qualitatively similar to those of a parasystolic model and to those described in previous in vivo demonstrations presumed to represent circus movement reentry. Moderate changes of frequency or in the degree of block were shown to convert a manifest bigeminal rhythm to a trigeminal or more complex rhythm with or without intervening periods of silence. Our observations suggest that reflection and parasystolic pacemaker activity are examples of a continuous spectrum of ectopic impulse generation.