Voltage during atrial fibrillation is superior to voltage during sinus rhythm in localizing areas of delayed enhancement on magnetic resonance imaging: An assessment of the posterior left atrium in patients with persistent atrial fibrillation

BACKGROUND: Bipolar electrogram voltage during sinus rhythm (V(SR)) has been used as a surrogate for atrial fibrosis in guiding catheter ablation of persistent atrial fibrillation (AF), but the fixed rate and wavefront characteristics present during sinus rhythm may not accurately reflect underlying functional vulnerabilities responsible for AF maintenance. OBJECTIVE: The purpose of this study was determine whether, given adequate temporal sampling, the spatial distribution of mean AF voltage (V(mAF)) better correlates with delayed-enhancement magnetic resonance imaging (MRI-DE)–detected atrial fibrosis than V(SR). METHODS: AF was mapped (8 seconds) during index ablation for persistent AF (20 patients) using a 20-pole catheter (660 ± 28 points/map). After cardioversion, V(SR) was mapped (557 ± 326 points/map). Electroanatomic and MRI-DE maps were co-registered in 14 patients. RESULTS: The time course of V(mAF) was assessed from 1–40 AF cycles (∼8 seconds) at 1113 locations. V(mAF) stabilized with sampling >4 seconds (mean voltage error 0.05 mV). Paired point analysis of V(mAF) from segments acquired 30 seconds apart (3667 sites; 15 patients) showed strong correlation (r = 0.95; P <.001). Delayed enhancement (DE) was assessed across the posterior left atrial (LA) wall, occupying 33% ± 13%. V(mAF) distributions were (median [IQR]) 0.21 [0.14–0.35] mV in DE vs 0.52 [0.34–0.77] mV in non-DE regions. V(SR) distributions were 1.34 [0.65–2.48] mV in DE vs 2.37 [1.27–3.97] mV in non-DE. V(mAF) threshold of 0.35 mV yielded sensitivity of 75% and specificity of 79% in detecting MRI-DE compared with 63% and 67%, respectively, for V(SR) (1.8-mV threshold)(.) CONCLUSION: The correlation between low-voltage and posterior LA MRI-DE is significantly improved when acquired during AF vs sinus rhythm. With adequate sampling, mean AF voltage is a reproducible marker reflecting the functional response to the underlying persistent AF substrate.