Validation of E/e' using the index beat method as an estimate of left atrial pressure in patients with atrial fibrillation

Introduction: Echocardiographic assessment of diastolic function during atrial fibrillation (AF) remains challenging due to the irregular cardiac cycle length. We sought to assess whether the index-beat method, the beat following two preceding cardiac cycles of equal duration, could provide a more reliable measurement of E/e & PRIME; (mitral E wave/diastolic tissue Doppler velocity) than the conventional averaging of consecutive beats and hence facilitate the non-invasive estimation of elevated left atrial pressure (LAP) in patients with AF. Methods: We prospectively studied 35 patients with persistent AF who had preserved left ventricular ejection fraction and underwent radiofrequency ablation. LAP was measured in conjunction with trans-septal puncture during catheter ablation. Echocardiography was performed 24 h before ablation and E/e & PRIME; was determined using the recommended averaging of 10 beats and the index-beat method, with the observers blinded to the clinical details and LAP measurements. Results: Correlation analysis showed a strong positive correlation between two methods in terms of both septal E/e & PRIME; (r = 0.841, p < 0.001) and lateral E/e & PRIME; (r = 0.930, p < 0.001). Bland-Altman analysis also showed a good agreement between the two measurement methods in terms of E/e & PRIME;. E/e & PRIME; determined using both conventional averaging and the index-beat method was significantly correlated with LAP (p < 0.05). After Fisher Z transformation, we found that the index-beat septal E/e & PRIME; had a better correlation with LAP than did the conventional averaging E/e & PRIME; (r = 0.736 vs. r = 0.392, Zr = -2.110, p = 0.035). Furthermore, the index-beat method took significantly less time to measure E/e & PRIME; (mean 33.6 s; 95% confidence intervals (CI): 32.1s to 36.2s), than did conventional averaging method (mean 96.2 s; 95% CI: 90.2s to 102.3s; p < 0.001). Receiver operating characteristic curve analysis revealed that the optimal cut-off for predicting mean LAP > 12mmHg was 11 (sensitivity 100%; specificity 77.3%) for index-beat septal E/e & PRIME; and 16 (sensitivity 61.5%; specificity 95.5%) for index-beat lateral E/e & PRIME;. Conclusions: Good correlations were found between E/e & PRIME; and LAP in patients with AF, particularly with the index-beat method. Moreover, the index-beat method can easily measure E/e & PRIME; at an accuracy similar to that for the conventional averaging of consecutive beats, which can therefore be applied to assess the diastolic dysfunction and potentially improve the diagnosis of heart failure in patients with AF.