Distribution of fast heart rate episodes during paroxysmal atrial fibrillation

Abstract

Objective: To investigate the defibrillator waiting time (time between the recognition of atrial fibrillation and the actual shock) by studying paroxysmal atrial fibrillation episodes with RR intervals shorter than a certain limit (that is, episodes during which defibrillation should not be attempted).

Methods: Long term 24 hour Holter recordings from a digoxin v placebo crossover study in patients with paroxysmal atrial fibrillation were analysed. In all, 23 recordings with atrial fibrillation episodes of at least 1000 ventricular cycles and with < 20% Holter artefacts or noise were used (11 recorded on placebo and 12 on digoxin). For each recording, the mean ("mean waiting time") and maximum ("maximum waiting time") duration of continuous sections of atrial fibrillation episodes with all RR intervals shorter than a certain threshold were evaluated, ranging the threshold from 400 to 1000 ms in 10 ms steps. For each threshold, the mean and maximum waiting times were compared between recordings on placebo and on digoxin.

Results: Both the mean and maximum waiting times increased exponentially with increasing threshold. Practically acceptable mean waiting times less than one minute were observed with thresholds below 600 ms. There were no significant differences in mean waiting times and maximum waiting times between recordings on placebo and digoxin, and only a trend towards shorter waiting times on digoxin.

Conclusions: Introduction of a minimum RR interval threshold required to deliver atrial defibrillation leads to practically acceptable delays between atrial fibrillation recognition and the actual shock. These delays are not prolonged by digoxin treatment.

Figure 1

Mean waiting times—that is, mean durations of atrial fibrillation sections with RR intervals shorter than a given threshold (x axis). Vertical axes use a logarithmic scale in seconds, the dashed lines correspond to 1 s, 1 min, and 1 h waiting times. The mean waiting times were averaged separately in recordings made on placebo and on digoxin. The averages and standard errors used in the graphs were obtained from the mean waiting times in individual tapes rather than from individual atrial fibrillation episodes. Panel A illustrates the results from pooled data, panel B shows the results from case controlled data (see the text for details).

Figure 2

Maximum waiting times—that is, maximum durations of atrial fibrillation sections with RR intervals shorter than a given threshold (x axis). Details and layout as in fig 1.