Intermittent ventricular parasystole with observations on its relationship to extrasystolic bigeminy.

Abstract 1. 1. Two cases of intermittent parasystole are described in which there is alternate extrasystolic and parasystolic impulse formation from the same focus; transitions between the two rhythms are repeatedly observed. 2. 2. It seems that intermittence results when the parasystolic focus is subjected to the enhancing effect of the sinus discharge whereby the automatic beat is prematurely precipitated, thus becoming a forced beat. 3. 3. This phenomenon can be explained on the basis of a property of automatic centers; namely, that their resting potentials exhibit a gradual upward “slope” of depolarization. With critical timing, the terminal part of the “slope” (i.e. its near threshold level) may encounter the enhancing effect of the preceding sinus beat and thus be precipitated prematurely. 4. 4. It is suggested that the form of extrasystolic bigeminal rhythm described may constitute a link between parasystolic and extrasystolic rhythm.

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