This is a sequential phase 1 and phase 2 study to evaluate the efficacy of intracardiac echocardiography to detect septal and left atrial pathology as compared to transesophageal echocardiography (Phase 1) and its value in a management strategy for immediate cardioversion during cardiac catheterization procedures in patients with atrial fibrillation as compared to a conventional strategy delaying cardioversion till full anticoagulation is established for a three weeks (Phase 2). Phase 1 will enroll 100 patients at 12 centers; these patients will be undergoing clinically indicated TEE & cardiac catheterization procedures. After review of Phase 1 results by an independent DSMB & the investigators that establish efficacy of ICE, Phase 2 will be initiated. Phase 2 will enroll 300 patients in 15 centers; these patients with atrial fibrillation will be undergoing clinically indicated cardiac catheterization procedures and have a clinical indication for cardioversion. Patients will be randomized to ICE guided cardioversion strategy or a conventional strategy employing three weeks of full anticoagulation before cardioversion. ICE imaging will be used to identify a low risk group for immediate cardioversion. A composite primary study endpoint that will include mortality and major morbidity including stroke and bleeding complications will be used.

This study will examines two hypotheses in AF patients undergoing invasive cardiac procedures:

Hypothesis 1: That ICE has comparable efficacy to TEE in visualization of left atrial pathology or septal defects that can predispose patients to stroke.

This will be evaluated during the Phase I component of the study. Hypothesis 2: That ICE can identify low risk patients in whom immediate cardioversion during the procedure is safe and comparably effective to electrical cardioversion performed based on a conventional strategy of a minimum of 3 weeks of preceding anticoagulation therapy. Low risk patients are expected to have an acceptably low incidence rate of stroke, transient ischemic attack (TIA), peripheral embolism, and major hemorrhagic events following electrical cardioversion. This will be evaluated during the Phase II component of the study, after the Phase I objective is achieved.