Coagulum index predicts coagulum formation in right atrial radiofrequency energy delivery to ablate atrial fibrillation.

An ongoing multicenter U.S. clinical study evaluates the safety and effectiveness of creating linear lesions with radiofrequency (RF) energy using a 3.7 Fr microcatheter used with a 9 Fr steerable guiding catheter in the right atrium (RA) to treat paroxysmal atrial fibrillation (PAF). Study entry criteria were symptomatic, drug refractory PAF. RF energy was delivered in 60-second episodes at 30 W or 50 W power settings. Electrode tissue contact was ascertained by sharp electrograms of high amplitude. Coagulum Index (C.I.), a new calculation to predict the probability of coagulum development, was derived analytically from measurements of RF power, RF current, and time to reach maximum temperature in each ablation episode. The RF data from 398 separate ablation episodes in 15 patients were used to calculate C.I. Coagulum presence was determined by postablation visual inspection of the microcatheter electrodes. A logistic model was used to estimate the probability of coagulum occurrence, with C.I. as the predictive variable. When C.I. > or = 12, the probability of coagulum formation increased significantly in this model (P < 0.0001). Prolonging the power delivery rise time and limiting maximum RF power setting to 30 W effectively lowers C.I. and minimizes coagulum formation. These results should also apply to left atrium ablation, where minimizing coagulum formation may decrease the risk of stroke or mortality.