Origins of heart rate variability - Inducibility and prevalence of a discrete, tachycardic event

Background-We propose that heart period sequences are linearly organized, l ike sentences, and that there is a lexicon of recurrent, similarly shaped t ransient structures like words. Each word (or lexon) has a characteristic p hysiological basis. One potential lexon is the transient, reversible tachyc ardia that is induced by exercise initiation under laboratory conditions. W e hypothesized that this lexon was inducible and observable on ambulatory E CGs of most or all subjects, was morphologically similar in both induced an d detected bursts, and shared a plausible origin in both circumstances. Methods and Results-Ten healthy subjects (mean age, 36 years) underwent a p rotocol in which subjects rolled themselves from supine to lateral decubitu s positions and back. Transient tachycardias ("bursts") were seen in 36 of 40 rollovers. Bursts were characterized by an initial monoexponential heart period decay (K=0.39+/-0.23 s(-1)), a maximum heart period decrease of 277 +/-109 ms after 10.8+/-4.5 seconds, and a subsequent return to baseline 23. 3+/-10.8 seconds after roll initiation. The roll-induced bursts were detect ed with 97% sensitivity and 99% specificity with a search algorithm that in corporated morphological parameters. In 24-hour ambulatory ECGs of 10 healt hy subjects (mean age, 38 years; range, 17 to 69 years), 117+/-59 bursts we re detected. Induced and detected bursts were similar in most morphological parameters. Finally, many bursts occurred at night, when rolling over also occurs. Conclusions-Bursts are inducible, transient tachycardias that occur clinica lly and constitute a lexon with an understandable physiology.