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

January 24-31, 1998
Marilleva, Trento, Italy

RT-76

Non-invasive assessment of atrial refractoriness during atrial fibrillation

S.B. Olsson, M. Holm, M.P. Ingemansson, C. Meurling, S. Pehrson, L. Sörnmo*.
Depts of Cardiology and *Applied Electronics, Lund University, Lund, Sweden

Introduction

Spontaneous atrial fibrillation in man is perpetuated by multiple concomitant re-entry wavelets which often change in a seemingly unpredictable way, but often reappear cycle after cycle with slightly different cycle length and impulse direction¹. The inherent physiology of a homogenous and complete re-entry loop can be characterized according to the wave-length concept². Thus, in theory the length of a complete re-entry loop, uninfluenced by other excitation wavelets, can be calculated to equal the product of conduction velocity (CV) and refractory period (RP), provided these factors are equal throughout a piece of tissue of adequate size.

Since atrial myocardial excitation during fibrillation always spreads towards excitable tissue, variations of CV will influence the size of a complete re-entry. Thus, uniformly decreased CV with unchanged RP will permit a complete re-entry within a smaller area but the local cycle length recorded anywhere along this theoretical loop will remain unchanged. Although there is not only a certain variability of local cycle length during AF, but also of CV in atrial tissue³ as well as a dispersion of refractoriness within the atria⁴, explaining the possibility of regional entrainment during AF⁵, repeated studies have in fact demonstrated a parallelity between an estimate of local fibrillatory cycle length and refractoriness^6.8.

Shortening of atrial refractoriness, as evidenced by acceleration of atrial myocardial repolarization, was long time ago identified as a potent proarrhythmic marker concerning AF probability⁹ but has hitherto necessitated invasive recording techniques to be verified. The possible use of the fibrillatory cycle length as an index of atrial myocardial refractoriness has therefore prompted us to develop a non-invasive method for identification of an expression of the length of the atrial cycles during AF¹⁰. The method, based upon power/frequency analyses of QRST-reduced ECG-signals - frequency analyses of fibrillatory ECG - was named FAF-ECG. The purpose of this paper is to shortly describe the method and, using lead V1, illustrate its potential to identify effects of different interventions known to change atrial myocardial refractoriness during sinus rhythm.