Cyclic bursts of ventricular premature contractions of more than one minute intervals

Strong modulation of ectopic focus as a mechanism of repetitive interpolated ventricular bigeminy with heart rate doubling

BACKGROUND

Repetitive interpolated ventricular bigeminy (RIVB) can introduce a doubling of the ventricular rate.

OBJECTIVE

To clarify the mechanism of RIVB, we hypothesized that it was introduced by a strong modulation of the ventricular automatic focus.

METHODS

RIVB, defined as more than 7 bigeminy events, was detected by instantaneous heart rate and bigeminy interval (BI) tachograms in 1450 successive patients with frequent ventricular premature contractions (≥3000 per day). Postextrasystolic interval bigeminy interval curves were plotted to determine the degree of modulation. Mean sinus cycle length bigeminy interval curves were plotted for selection. RIVB was simulated by using a computer-based parasystole model.

RESULTS

RIVB was observed in 7 patients (age 60 ± 16 years; 2 men and 5 women) with a heart rate of 58.2 ± 6.5 beats/min during a rest period both during the day and at night. The tachograms disclosed the onset of the RIVB with a doubled ventricular rate to 112.3 ± 8.5 beats/min. On the postextrasystolic interval bigeminy interval curves, compensatory bigeminy and interpolated bigeminy constituted overlapping regression lines with slopes close to 1.00 and RIVB was located in the lower left portion. RIVB lasting for up to 3 hours was quickly detected by mean sinus cycle length bigeminy interval curve. The PQ interval immediately after RIVB was prolonged in comparison with baseline (0.18 ± 0.02 to 0.21 ± 0.02 seconds; P < .001). The simulation was able to reproduce RIVB faithfully at a slow heart rate.

CONCLUSIONS

Our findings support the hypothesis that RIVB was introduced by strongly modulated ventricular pacemaker accelerated by an intervening normal QRS.

Model of bidirectional modulated parasystole as a mechanism for cyclic bursts of ventricular premature contractions

Cyclic bursts of ventricular premature contractions (VPC) coming at minute-order intervals have been discerned by analyzing ambulatory ECG recordings, and their mechanism has not been clarified. The present study simulates this phenomenon by constructing a bidirectional modulated parasystole model. With Ts and Te as the intrinsic periods of the sinus and ectopic pacemakers, there are distinct and initial condition-dependent solutions in the model with Ts / Te values close to 1, 1/2, 1/4, etc. Typically, two distinct stable solutions are found existing together around Ts / Te = 1/2. We have verified theoretically the coexistence of different solutions and their dependence on the model parameters. The solution presented switches between those by a premature stimulus and those by fluctuations in the model parameters such as Ts. Patterns of RR intervals were generated by simulation with randomly fluctuating Ts. They included cyclic bursts of bigeminy of the "flat type" and the "dome type" reported by Takayanagi et al. (1999) and other transient types with Wenckebach or reverse Wenckebach rhythm of coupling intervals. This model provides a mathematical representation of the atrioventricular feedback mechanism and enables the modulated parasystole hypothesis to be applied to wider classes of VPCs.

Direct discrimination and full-day disclosure of ventricular parasystole on new heart rate tachograms

INTRODUCTION

To discriminate ventricular parasystole from fixed coupling interval ventricular premature complexes (VPCs), we developed a new diagnostic method using a dot distribution pattern corresponding to VPCs recorded on a heart rate tachogram using ambulatory ECG monitoring data. We tested our hypothesis that widely scattered VPC dots on instantaneous heart rate tachograms indicate a constant VPC-VPC interval compatible with parasystole.

METHODS AND RESULTS

Patients with frequent VPCs > 5,000/day) were divided into two groups depending on the tachogram dot distribution patterns: group S (n = 10, aged 61 +/- 16 years) showed widely scattered VPC dot distribution, whereas group F (n = 10, 60 +/- 17 years) showed fixed VPC dot distribution limited to a narrow zone. Using digitized R-R interval data, full-day heart rate tachograms and VPC-VPC intervals were depicted simultaneously. Group S demonstrated constant basic VPC-VPC intervals (1,285 to 2,052 msec, mean 1,738 +/- 219), with a coefficient of variation (CV) of 0.061 +/- 0.018. Their VPC coupling intervals were markedly variable (651 +/- 113 msec; CV = 0.193 +/- 0.034). Each patient's basic VPC-VPC intervals showed small diurnal alterations (minimum -13% +/- 3% to maximum +15% +/- 6%). VPC-VPC intervals in group F were not constant and showed marked variation. Group F VPC coupling intervals were shorter and constant (480 +/- 30 msec, P = 0.0002; with CV = 0.076 +/- 0.013, P < 0.0001).

CONCLUSION

Ventricular parasystole with constant VPC-VPC intervals consistently became evident based on VPC dot patterns recorded on heart rate tachograms.