Risk factors for thromboembolism in patients with AF are well established (CHADS
2 and CHA
2DS
2-VASc).
22,23 These factors have been also evaluated for predicting thromboembolism in patients undergoing ablation therapy. In a study by Choi et al.,
24 the CHADS
2 and CHA
2DS
2-VASc scores were used to predict events in 565 patients with AF who underwent catheter ablation. The clinical endpoints of thromboembolic event or death occurred in 4.8% patients during 40 months follow-up. The CHADS
2 and CHA
2DS
2-VASc scores were independent predictors of adverse events inseparate multivariate models. It was noted that patients with CHADS
2 score â„2 had significantly higher events than patients with risk score of <2. There was no difference between CHADS
2 and CHA
2DS
2-VASc scores in predicting events. As regards to the independent factors, age, congestive heart failure, hypertension, prior stroke/TIA were associated with events while gender and diabetes mellitus were not. Though no specification on the timing of the adverse events was reported, it appears that most events occurred months after the ablation therapy. A very different finding was noted in a study to assess the occurrence of intra-cardiac thrombus formation during AF ablation. In this study of 232 patients undergoing pulmonary vein ostial ablation, the occurrence of intra-cardiac thrombus as identified by intracardiac echocardiography, none of these factors (age, gender, heart disease, and history of prior embolic event) were associated with thrombus formation.
12 LA diameter, spontaneous echo contrast and history of persistent AF were associated with left atrial thrombusformation on univariate analysis.
12 On multivariate analysis only spontaneous echo contrast was associated with LA thrombus. In another trial of 232 consecutive patients with paroxysmal or persistent AF who were candidates for RF ablation, none of the clinical parameters such as age, hypertension, diabetes mellitus, previous history of stroke, type of atrial fibrillation, and preablation antithrombotic treatment showed significant correlation with ischemic cerebral embolism.
11 The anticoagulation level during the procedure as assessed by ACT value, correlated significantly with the incidence of cerebral embolism. Amongst patients with ACT < 250 seconds, 17% had positive MRI, whereas for those with ACT value >250 seconds, 9% of the patients were positive for silent embolism. Intraprocedural cardioversion represents a pertinent risk factor with a significantly increased odds ratio of 2.75. In a study to determine if the intensity of anticoagulation reduces LA thrombus formation as detected by ICE during RF ablation in patients with spontaneous echo contrast, the incidence of LA thrombus was 45% in patients with activated clotting time 250-300 seconds and 5% in patients with ACT of more than 300 seconds.
25 In patients with and without SEC, keeping ACT above 300 reduced LA thrombus incidence from 11% to 3%. Total procedure time and time to heparin administration have been associated with the levels of vWf and DD concentrations (endothelial markers of thrombosis) after RF ablation in 30 patients underoing pulmonary vein isolation procedure.
16
In a study comparing cryoablation with RF ablation for management of AF, the incidence of MRI detected cerebral embolism was 7.9% within 1 day after pulmonary vein isolation, without statistically significant difference between the group treated by cryoenergy (8.9%) and radiofrequency ablation (6.8%).
26 In an observational study of 74 patients undergoing ablation therapy for AF, the incidence of cerebral infarcts was significantly higher in patients in the pulmonary vein radiofrequency ablation non-irrigated catheters when compared to irrigated RF and cryoballoon ablation.
27 In this study 27 patients underwent irrigation RF ablation while 24 patients underwent cryoballoon ablation.
25 patients underwent non-irrigation RF ablation with a circular mapping and ablation system capable of duty-cycled phased unipolar and bipolar RF delivery. On imaging with MRI on all patients, 7.4% of irrigated RF patients, 4.3% of cryoballoon patients, and 37.5% of non-irrigated circular mapping and ablation patients had new embolic events (p=0.003). A similar finding of silent cerebral thromboembolism was noted by Gaita et al.
28 In this study of 108 patients undergoing ablation therapy for paroxysmal AF, pulmonary vein ablation with multielectrode non-irrigated catheter increased the risk of thromboembolism by 1.5 times when compared to irrigated RF and cryoballoon ablation.