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

Area of Science:

• Cardiology
• Electrophysiology
• Cardiac Imaging

Background:

• Patients with reduced left ventricular ejection fraction (LVEF) and atrial fibrillation (AF) may experience improved heart function after restoring normal sinus rhythm.
• This improvement might stem from eliminating rapid, irregular heartbeats (short R-R intervals) characteristic of AF, even if the average heart rate is controlled.

Purpose of the Study:

• To introduce and evaluate a novel parameter, the restitution threshold index (RTI), which quantifies the burden of short R-R intervals during AF.
• To assess the association between RTI and reduced LVEF, and its ability to predict LVEF recovery following catheter ablation (CA).

Main Methods:

• Prospective enrollment of patients with persistent AF undergoing CA, categorized by reduced (LVEF ≤50%) or preserved LVEF.
• Measurement of sequential R-R intervals from Holter monitoring to define a restitution threshold (RT) and calculate the RTI (percentage of intervals shorter than RT).
• Statistical analysis to determine the association of RTI with reduced LVEF and its predictive value for LVEF improvement post-CA.

Main Results:

• A total of 104 patients were studied; 51% had reduced LVEF.
• At an RT of 660 ms, the RTI was significantly higher in patients with reduced LVEF (56.1% vs. 39.5%, P < 0.001), indicating a greater burden of short R-R intervals.
• RTI independently predicted left ventricular systolic dysfunction and showed high accuracy (AUC 0.74, PPV 0.97) in predicting LVEF improvement after CA.

Conclusions:

• The restitution threshold index (RTI) in persistent atrial fibrillation is significantly associated with reduced left ventricular ejection fraction (LVEF), unlike mean heart rate.
• RTI serves as a valuable predictor of LVEF recovery following catheter ablation in patients with AF-mediated cardiomyopathy.