Alternative energy sources for atrial ablation: judging the new technology

In 1987 Dr James Cox introduced a new operation for treating atrial fibrillation. The Maze procedure created several incisions throughout both the left and right atria. These incisions were designed to block the multiple macroreentrant circuits felt to be responsible for atrial fibrillation. Over the years Dr Cox and his group had developed a successful paradigm for introducing operations for cardiac arrhythmias. This paradigm was based on first developing a sound understanding of the fundamental substrates and interactive mechanisms. Successful surgical interventions were only introduced clinically after a thorough understanding of the basic electrophysiology and anatomy was developed in the laboratory in animal models [1]. After the clinical introduction of the Maze procedure it went through several iterations before settling on what has become the gold standard for treating atrial fibrillation, the Cox-Maze III procedure. Our long-term results at Washington University have revealed a cure rate of more than 96% at 10 years [2]. Despite its remarkable success the operation has not been widely adopted by surgeons, in part owing to its technical difficulty and complexity. There also is still significant morbidity associated with this operation including the need for pacemaker implantation in as many as 10% of patients. These problems have led numerous investigators around the world to develop potentially less invasive or simpler approaches to treating this extremely common arrhythmia. A common strategy has been to replace the surgical incisions with linear lines of ablation. Various energy sources have been used to perform this ablation including radiofrequency energy, microwave, laser, cryoablation, and ultrasound [3]. The objective of these new technologies is to replace the surgical incisions with lines of transmural ablation to create conduction block. Doing so would fulfill the goal of the Cox-Maze procedure to block reentrant circuits. Theoretically this would be less invasive and easier to perform as it would replace the traditional cut-and-sew technique. However because these new ablation devices are replacing a well-developed and extensively studied operation, it is imperative that they be safe and effective and at the same time provide a truly less invasive alternative treatment option. In the last several years many of these new technologies have been introduced clinically. The Food and Drug Administration has approved most of these devices only for soft-tissue coagulation. Unfortunately they have been used widely in an off-label manner for treating atrial fibrillation without adequate experimental or clinical investigation of their efficacy for arrhythmia ablation. The absence of peer-reviewed evaluation has led to many predictable problems. Because of the lack of established dose-response curves, surgeons have had to estimate appropriate ablation times to account for the varying thicknesses of pathologic atria encountered in the operating room. Moreover most of these technologies give no indication of when the lesion becomes transmural. These shortcomings have led to prolonged ablation times to ensure lesion transmurality. Not only can this lead to unintended collateral tissue injury [4] but also the lack of any verification of lesion transmurality and clinically relevant dose-response curves may explain the higher failure rate compared with the Cox-Maze III procedure that has been seen in some series [5, 6].