Effective Arterial Elastance of Irregular Beats during Atrial Fibrillation in Canine Left Ventricle

Abstract

Effective arterial elastance (E_a) was originally defined as the end-systolic 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, and afterload widely changing among irregular beats. This has discouraged the use of E_a during arrhythmia. However, we hypothesized that E_a could serve as the effective afterload (not always arterial) elastance against ventricular ejection under arrhythmia. We tested this hypothesis by analyzing beat-to-beat changes in E_a of irregular beats during electrically induced atrial 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 became markedly high in weak beats with small SVs; 2) E_a and E_a/E_max distributed 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 preceding beat intervals; and 4) the reciprocal of mean 1/E_a closely correlated with mean ESP/mean SV. These results support our hypothesis that E_a can serve as the effective afterload elastance against ventricular ejection on a per-beat basis during AF. E_a/E_max can also quantify the ventriculo-afterload (not arterial) coupling on a per-beat basis. This study, however, warns that mean E_a and mean E_a/E_max of irregular beats cannot necessarily represent their averages during AF.