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Multidimensional Characterization of Left Atrial Anatomy:

It is clear that the left atrium (LA) plays a central role in the initiation and sustenance of atrial fibrillation in man. Less clear is whether and how therapies targeting the LA can achieve long-term suppression of this dysrhythmia. A therapy of intense interest, percutaneous endocardium-based catheter ablation, is as yet immature. Its recent evolution has been toward larger volumes of ablated or electrically isolated LA myocardium. Concurrently, methods for direct multidimensional LA endocardial (DMLAE) imaging using computed tomography (CT)1-4 or magnetic resonance imaging (MRI)5-7 are being developed. In this issue of the Journal, Mansour et al.8 contribute to this literature by describing their experience with MRI in patients referred for catheter ablation. Their data are consistent with previous reports. They also speculate as to how anatomy might influence catheter ablation techniques and technologies. This is a fine piece of work for which the authors should be commended, but it has several limitations that are worthy of comment. First, although the data are described as multidimensional, the analysis is decidedly two dimensional. As such, I believe that the authors underutilize the potential of DMLAE imaging to convey the true complexity of the anatomy. For example, although they correctly describe the venoatrial junction as noncircular, it also is nonplanar. Similarly, they provide no insight into the anatomy of ridges (topography, dimensions) occurring between veins, within veins, and between veins and other atrial structures. In addition, they provide no insight into variation in venoatrial junction morphology during the atrial mechanical cycle. Each of these areas is important for guiding catheter ablation, whether using current technology or designing improvements. Second, they provide no prospective data to assess whether specific anatomies actually are best suited to specific mapping/ablation technique. Third, they make little mention of the technical challenges associated with MR image acquisition and processing. In our experience using the same technology, image quality has been highly variable, due in part to items such as ventricular rate and regularity, contrast bolus timing, and patient tolerance/cooperation. Image equivalence, coupled with the relative brevity of data acquisition, has resulted in our preferential use of CT.9 Finally, the authors utilize a construct for catheter development centering on the “longitudinal axis” of the LA. With regard to interventional tools designed for atrial transseptal access, this metric is of dubious significance. Apart from it being a two-dimensional