Relation between sinus rates preceding and following ectopic beats occurring in isolation and as episodes of bigeminy in young healthy subjects

[...]the correlation between the number of beats constituting an episode (5 to 54, mean 18) and HRTO was weak (r2 = 0.042). [...]analyzing the immediate effects of isolated VPCs on sinus rhythm in young subjects with no detectable evidence of structural heart disease appeared justified. In 1955, Langendorf et al9 showed that when there were wide fluctuations in RR intervals (as in atrial fibrillation and marked sinus arrhythmia) VPCs tend to occur after long, or relatively long, RR intervals. Because the compensatory pause constituted another long RR interval, the latter in turn favored the appearance of another VPC, thus tending to perpetuate an episode of VB (“Rule of Bigeminy”).9 However, even as early as 1965, Schamroth10,11 noted that this rule did not always apply. [...]the mechanisms of heart rate turbulence have not been fully determined.