Pressure-interval relationship characterizes left ventricular irregular beat contractilities and their mean level...

How left ventricular (LV) contractility relates to irregular RR intervals during atrial fibrillation (AF) is still unclear. We investigated the relationship between the LV contractility (Emax) of individual beats and their preceding RR intervals during AF in isovolumic contractions is excised cross-circulated canine hearts, and additionally in ejecting contractions in in situ canine hearts. Atrial high-frequency electrical stimulation induced AF. We recorded a LV electrocardiogram, volume and pressure, and calculated the Emax of every arrhythmic beat. Multiple linear regression analysis between Emax and the six preceding RR intervals of all arrhythmic beats during 1 min AF showed the preceding RR interval (RR1) and the pre-preceding interval (RR2) to be the predominant predictors of Emax. The Emax-RR1/RR2 scattergram was closely fitted by a linear regression line. We found Emax at RR1/RR2 = 1 on the regression line to be virtually identical with both mean Emax during AF and stable Emax obtained during irregular atrial pacing at the same intervals as the mean RR interval during AF. These results newly indicate that the pressure-interval relationship predominantly characterizes LV irregular beat contractilities and their mean level during AF.