The Restitution Threshold Index Characterizes the Association Between Atrial Fibrillation Ventricular Rate and Ejection Fraction

Background: Patients with reduced left ventricular ejection fraction (LVEF) and rate-controlled atrial fibrillation (AF) may improve after restoring sinus rhythm. This may be due to the elimination of the short R-R intervals during AF even when mean heart rate is acceptable.

Objectives: This work aims to evaluate a novel parameter representing the burden of short R-R intervals during AF and its association with reduced LVEF and LVEF recovery after catheter ablation (CA).

Methods: Patients with persistent AF were prospectively enrolled pre-CA and grouped as having reduced (LVEF ≤50%) or preserved LVEF. Sequential R-R intervals on resting Holter monitoring were measured. We sought to define a threshold R-R interval at which the difference in the percentage of short R-R intervals is greatest when comparing patients with reduced and preserved ejection fraction. We termed this threshold the restitution threshold (RT) in the belief that this may be possible to apply as a threshold to identify patients with AF-mediated cardiomyopathy. This percentage burden of intervals shorter than the RT was defined as the restitution threshold index (RTI). The association with reduced LVEF in AF and predicting improvement in LVEF after CA was then evaluated.

Results: One hundred four patients were enrolled; 53 (51%) had a reduced LVEF. There was no difference in mean heart rate; however, at an RT of 660 ms, the RTI was higher in the reduced LVEF arm (56.1% ± 23.1% vs 39.5% ± 26.0%; P < 0.001). It was an independent predictor of left ventricular systolic dysfunction. The RTI in the reduced LVEF arm had an area under the receiver operating characteristic of 0.74 (95% CI: 0.47-0.95) and positive predictive value of 0.97 for LVEF improvement after CA, which was observed in 39 of 47 (83.0%) participants in sinus rhythm.

Conclusions: The RTI in persistent AF was associated with a reduced LVEF, whereas mean heart rate was not. The RTI could be used to predict LVEF improvement after CA.