13th International Congress
THE "NEW FRONTIERS"
OF ARRHYTHMIAS 1998

January 24-31, 1998
Marilleva, Trento, Italy

RT-174

The role of fluctuations in heart rate and ectopic beat frequency in the onset of paroxysmal atrial fibrillation

Johan E.P. Waktare, Katerina Hnatkova, Francis D. Murgatroyd, Xiaohua Guo, A. John Camm, Marek Malik.
St. Georges Hospital Medical School, London, UK

Introduction

Paroxysmal atrial fibrillation (PAF) is a common clinical cardiac arrhythmia, characterised by self-terminating episodes of atrial fibrillation (AF). These episodes occur with variable frequency and duration, with the onset occurring apparently at random and similarly random spontaneous reversion to sinus rhythm. One approach to treatment is to attempt to modify the circumstances surrounding AF initiation, but this has not previously been systematically studied. Anecdotal experience suggests that bradycardia may be important in the AF onset in patients with underlying sick sinus syndrome, as well as in those with PAF which is vagally mediated, and that the arrhythmia may be suppressed by atrial pacing. It has been clearly demonstrated that atrial pacing in sick sinus syndrome reduces the incidence of permanent AF^1-3, but this situation is not directly comparable. Also, the benefit may derive from the maintenance of atrio-ventricular synchrony rather than prevention of atrial bradycardia. Increasing atrial ectopic activity has also been suggested to precede AF, but an initial algorithm of intermittent atrial pacing to suppress PAF met with only limited success⁴. If these and other strategies are to become more widely applicable then documentation that the mode of onset was consistent (e.g. bradycardia, sudden deceleration of heart rate - HR - or increasing ectopic activity) is required.

Both increased sympathetic and parasympathetic tone are known to shorten the atrial refractory period⁵, and therefore increased autonomic tone would be expected to favour the onset of AF. Coumel has described a subgroup of patients with PAF in whom the AF onset was indeed triggered by high autonomic tone, usually vagal⁶. Although such patients are seen in clinical practice, it is unknown whether high autonomic tone is a frequent precipitant to the onset of PAF episodes in a wider, unselected population. Such influences might be detectable by examination of heart rate, or fluctuation in heart rate, prior to AF onset. Since AF is currently believed to be mediated by macro-reentry of multiple wavelets, as originally hypothesised by Moe and Abildskov⁷, it seems likely that like other re-entrant arrhythmias, ectopic beats will have a role to play in arrhythmia initiation. An increase in the background atrial ectopic activity may occur prior to the onset of PAF, or may purely be seen immediately prior to AF onset. Furthermore, sequences of alternating cycle lengths are recognised to precipitate other cardiac arrhythmias and may have a role in PAF⁸.

Whilst these hypotheses seem pathophysiologically plausible, their comprehensive evaluation has never been reported and it is unknown whether they play a significant role in a majority of patients with PAF. The goal of this study was to perform such a comprehensive investigation. The study presents a description and systematic analysis of the 2 min of sinus rhythm (SR) segments prior to the onset of 231 episodes of AF in 33 patients.