14th International Congress
THE "NEW FRONTIERS"
OF ARRHYTHMIAS 2000

Jan. 29 - Feb. 5, 2000
Marilleva, Trento, Italy

RT-213

Noninvasive estimation of atrial fibrillatory rate as an index of atrial refractoriness. Short and long-term intra-individual variability following physiological and pharmacological interventions

S. Bertil Olsson, M.Ph. Ingemansson, C.-J. Lindholm, C. Meurling, M. Stridh, L. Sörnmo.
Depts of Cardiology and Applied Electronics, Lund University, Lund, Sweden

Introduction

Atrial fibrillation (AF) is perpetuated by a continuos electrical reentry, locally evidenced as reexcitation of the atrial tissue during the phase of repolarization of the preceding electrical wavelet. Although the reexcitation sometimes has a latency beyond the refractory period to an extent that allows capture by pacing, the reentry mostly follows the principle that any non-refractory tissue is immediately reexcited. Hence, the AF rate is likely to reflect the refractory state of the tissue. This assumption was explored in three different studies, which could support the hypothesis as well in animal experiments as in clinical studies^1-3. Thus, although there is a certain variability around a line of complete agreement, it may by safely interpreted that the averaged atrial fibrillatory cycle length can be used as an index of atrial myocardial refractoriness. Therefore changes of the average fibrillatory cycle length are also likely to reflect changes of the state of atrial myocardial refractoriness. Since shortening and increased dispersion of atrial refractoriness are important proarrhythmic factors, the observation of the average fibrillatory cycle length and its variability may therefore be a route to reach additional important information not only for the understanding of the mechanism of AF, but perhaps also for the benefit of treatment of individual patients.

The purpose of this paper is to describe the findings from our studies exploring the atrial fibrillatory rate in patients with different types of AF. A second purpose is to describe and discuss the identified physiological and pathophysiological reasons for variability of these findings, including the effect of different autonomic interventions.