Effective arterial elastance of irregular beats during atrial fibrillationin canine left ventricle

Effective arterial elastance (E-a) was originally defined as the end-systol ic pressure (ESP)/stroke volume (SV) ratio of the left ventricle (LV). E-a combined with LV contractility (E-max), E-a/E-max, proved to be powerful in analyzing the ventriculo-arterial coupling of normal and failing hearts in regular beats. However, E-a sensitively changes with LV E-max, preload, an d afterload widely changing among irregular beats. This has discouraged the use of E-a during arrhythmia. However, we hypothesized that E-a could serv e as the effective afterload (not always arterial) elastance against ventri cular ejection under arrhythmia. We tested this hypothesis by analyzing bea t-to-beat changes in E-a of irregular beats during electrically induced atr ial fibrillation (AF) in normal canine in situ hearts. We newly found that during AF in each heart: 1) E-a changed widely among irregular beats and be came markedly high in weak beats with small SVs; 2) E-a and E-a/E-max distr ibuted non-normally with large skewness but 1/E-a distributed more normally ; 3) 1/E-a correlated closely with end-diastolic volume, E-max and precedin g beat intervals; and 4) the reciprocal of mean 1/E-a closely correlated wi th mean ESP/mean SV. These results support our hypothesis that E-a can serv e as the effective afterload elastance against ventricular ejection on a pe r-beat basis during AF. E-a/E-max can also quantify the ventriculo-afterloa d (not arterial) coupling on a per-beat basis. This study, however, warns t hat mean E-a and mean E-a/E-max of irregular beats cannot necessarily repre sent their averages during AF.