Frank-Starling mechanism contributes modestly to ventricular performance during atrial fibrillation

Objectives: The aim of this study was to assess whether Frank-Starling mechanism has an independent effect on left ventricular (LV) performance in atrial fibrillation (AF). Background: Ventricular performance in AF depends on variable contractility through the interval-force mechanism based on the ratio of preceding and pre-preceding RR intervals (RR_p/RR_pp). The impact of end-diastolic volume (EDV) variability, through the Frank-Starling mechanism, is not well understood. Methods: We induced AF in 16 open chest dogs. RR intervals, LV pressure, LV volume, and aortic flow were collected for > 400 beats during rapid AF (ventricular cycle length 292 ± 66 ms). In six of the dogs, additional data were collected while average ventricular cycle length was prolonged from 258 ± 34 ms to 445 ± 80 ms by selective vagal nerve stimulation of the AV node. Results: The relations of maximal LV power (LVPower) and peak LV pressure derivative (dP/dt) versus RR_p/RR_pp were fitted to the equation y = A * (1 - EXP (RR_p/RR_ppmin - RR_p/RR_pp)/C) and the residuals (RES) of these relations were analyzed. LVPower and dP/dt strongly correlated with RR_p/RR_pp (r² = 0.67 ± 0.12 and 0.66 ± 0.12, P > .0001 for all correlations). Importantly, RES-LVPower and RES-dP/dt showed linear correlation with EDV (r² = 0.20 ± 0.14 and r² = 0.24 ± 0.17, P < .01 for all correlations). In the six dogs with slowed average ventricular rate, the slope of both residual relationships (RES-LVPower vs EDV and RES- dP/dt vs EDV) decreased (P < .03 for both). Conclusions: The Frank-Starling mechanism contributes to ventricular performance in AF independently of the interval-force effects of the beat-to-beat variability in cardiac contractility. The Frank-Starling mechanism is sensitive to the average ventricular rate.