Interventional Electrophysiology

The successes of arrhythmia surgery using intra-operative mapping, and the realization that the majority of targets for these techniques were subendocardial or could be mapped via an endocardial approach, led to efforts to ablate arrhythmogenic foci using percutaneous, catheter-based techniques. Initial catheter ablation procedures used high-energy direct current to fulgurate endocardial tissue. This technique, initially introduced

Endocardial Mapping Josephson

Fig. 2. Left ventricular endocardial mapping schema published by Josephson and colleagues. Left ventricular catheter mapping was initially used to understand the mechanism of VT and plan surgical treatment; catheter ablation is now performed in patients with VT of various etiologies. (With permission from Cassidy DM, Vassallo JA, Buxton AE, Doherty JU, Marchlinski FE, Josephson ME. The value of catheter mapping during sinus rhythm to localize site of origin of ventricular tachycardia. Circulation 1984;69:1103-1110.)

Fig. 2. Left ventricular endocardial mapping schema published by Josephson and colleagues. Left ventricular catheter mapping was initially used to understand the mechanism of VT and plan surgical treatment; catheter ablation is now performed in patients with VT of various etiologies. (With permission from Cassidy DM, Vassallo JA, Buxton AE, Doherty JU, Marchlinski FE, Josephson ME. The value of catheter mapping during sinus rhythm to localize site of origin of ventricular tachycardia. Circulation 1984;69:1103-1110.)

in 1981 by Gonzalez and Scheinman (18) and then Gallagher and colleagues (19) to create AV block in patients with refractory AF, was extended to relatively small numbers of patients with accessory pathways, other forms of SVT, and VT.

Although it was an important innovation, direct current (DC) shock ablation had a number of features that limited its widespread use. Delivered from a catheter tip, the high-voltage discharge caused local tissue ablation from barotrauma and thermal injury. Because of the relative "brute force" of this technique, the procedure carried the risk of major complications, including cardiac perforation and rupture. In addition, general anesthesia was required for the procedure.

Radiofrequency energy quickly supplanted DC as an energy source for catheter ablation procedures. Huang and colleagues first demonstrated radiofrequency catheter ablation in a canine model in 1985 (20). Unlike direct current, radiofrequency energy created small, discrete lesions, which could be delivered using conscious sedation rather than general anesthesia. This advance ensured the success and widespread acceptance of catheter ablation procedures, and transformed electrophysiology from a descriptive specialty to an interventional field. For the first time, the electrophysiologist could cure patients with Wolff-Parkinson-White Syndrome (WPW) and A-V nodal reentrant tachycardia (21,22). In fact, radiofrequency catheter ablation for SVT was the first and remains the only instance in which a cardiologist cures a patient of disease. Over the last fifteen years, radiofrequency catheter ablation has been applied to an ever-expanding list of arrhythmias, including atrial tachycardia, atrial flutter, VT, and AF.

The development of catheter ablation can be viewed as the coalescence of diagnostic electrophysiology and arrhythmia surgery, with important contributions from a number of investigators. The other important therapeutic advance in electrophysiology was much more the brainchild of a single man. Michel Mirowski first conceived of an implantable defibrillator in the 1970s after witnessing the sudden death of a colleague. Mirowski persevered in developing an automatic implantable defibrillator despite criticism from many colleagues. The first human implant was in 1980 (23), and FDA approval followed in 1985. Though initial systems required a thoracotomy for epicardial lead placement, and abdominal placement of the large generator, it was apparent from the onset that the implantable defibrillator saved lives.

Several technological advances increased the efficacy of these devices, and greatly eased the implantation process. The development of endocardial lead systems (24), biphasic waveforms, and active can technology (25) has made epicardial lead systems of primarily historical significance, and has made device implantation only slightly more complicated than pacemaker implantation. Current devices are capable of anti-tachycardia pacing as well as cardioversion and defibrillation therapy, and provide back-up bradycardia pacing, single- or dual-chamber, with rate response if necessary. Multiple clinical trials have demonstrated the effectiveness of the implantable cardio-verter defibrillator (ICD) in saving lives, both in patients who have had ventricular arrhythmias, and in patients at risk for life-threatening ventricular arrhythmias.

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