Increasingly, cardiac CT or MRI scans are being obtained prior to catheter ablation of AF to delineate the pulmonary venous and left atrial anatomy. These images are then “merged” with real-time 3-D mapping data sets obtained during the ablation itself. However, this approach has several limitations. First, it is costly to obtain these preprocedural radiographic studies. In the case of cardiac CT scans, there is the additional issue of exposure to radiocontrast agent and radiation. Second, the images are often obtained days or weeks prior to the ablation; in the interim, there can be a change in the patient’s underlying rhythm, which can lead to a discrepancy between the previously acquired and real-time data sets. Third, images cannot be updated during the procedure; volume loading (as is common with open-irrigated ablation catheters) and ablation lesions may dynamically alter the left atrial anatomy and make it necessary to have the ability to intermittently update the data.

Real-time imaging during catheter ablation of AF is clearly desirable to the electrophysiologist. Goals of imaging include facilitation of the transseptal puncture, visualization of the pulmonary venous and left atrial appendage anatomy, visualization of the esophagus, early identification of procedural complications (pulmonary vein stenosis, pericardial effusion, thrombus formation), and identification of the
tissue-electrode interface and assessment of the efficacy of delivered lesions (8). To date, real-time imaging has only been possible using intracardiac echocardiography.

The ideal energy source for catheter ablation of AF would have the following characteristics:

Although radiofrequency energy is the most commonly used energy source used during catheter ablation of AF, as an energy source it fails to meet any of these desired attributes. Radiofrequency energy is effective only when the ablation catheter is in direct contact with the region of interest; even when delivered, it is difficult to ensure transmurality. In fact, in patients with a recurrence of AF following ablation, resumption of left atrial pulmonary vein conduction is almost always demonstrated (16,17). Delivery of radiofrequency energy in the vicinity of the pulmonary veins is associated with increased intimal thickness, thrombus formation, endocardial contraction, and proliferation of the elastic laminae, which can lead to development of pulmonary vein stenosis or lead to a thromboembolic event (18). Finally, collateral damage to the phrenic nerve and esophagus are feared complications of radiofrequency energy. Clearly, alternative energy sources would be welcome.