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Background-Microvolt T-wave alternans (TWA) is reported to be closely associated with sudden cardiac death (SCD) and ventricular tachycardia (VT). Animal experiments revealed that microvolt TWA is highly dependent on heart rate. The purpose of this study was to determine whether patients with TWA at relatively low heart rates have increased vulnerability to ventricular tachyarrhythmias. Methods and Results-Subjects were 248 consecutive patients (158 men, 90 women; mean age, 59Ϯ17 years) who underwent electrophysiological study from 1997 to 2000. TWA recording was made in sinus rhythm and at atrial pacing rates of 90, 100, 110, and 120 bpm with the Cambridge Heart CH2000 system. Alternans voltage (V alt ) was measured when the alternans ratio was Ͼ3 for a period of Ͼ1 minute in VM, X, Y, Z, or 2 adjacent precordial leads. Study end point was the first appearance of VT, ventricular fibrillation (VF), appropriate implantable cardioverter-defibrillator therapy with pacing or shocks, or SCD. During the 37Ϯ12-month follow-up period, 22 patients had sustained VT, and 5 patients died of SCD. In patients with Ͼ1.9-V V alt at rates of 90, 100, and 110 bpm, the incidence of VT/VF/SCD was 56%, 28%, and 18%, respectively. V alt of Ͼ2.9 V at a heart rate of 90 bpm had a 70% positive predictive value for VT/VF/SCD. However, when V alt was Ͻ0.9 V at a rate of 120 bpm, negative predictive value was 100%. Conclusions-Patients with TWA at relatively low heart rates are susceptible to ventricular tachyarrhythmias.

ndocardial catheter ablation is a popular treatment for various types of arrhythmias, but it has limitations, including the inability to access foci or critical circuits of arrhythmia located in the epicardium. Technological improvements, such as cooled-tip or largertip ablation catheters and different energy sources for tissue ablation, have not completely solved this problem. Mapping of the arrhythmic foci or circuits in the epicardium has been done in open-chest heart surgery 1 and with radiofrequency (RF) ablation catheters in 2 ways. First, a 2F electrode catheter is inserted into the coronary sinus and then into the branches. Epicardial circuits can sometimes be identified with this approach, but only when the veins are near the circuit or foci. 2 There is a possibility of damage to coronary arteries (CA) if the coronary sinus runs parallel to the CA, even if the circuit or foci are near the coronary sinus. Second, transthoracic epicardial ablation of ventricular tachycardia (VT) has recently been shown to be feasible, primarily in patients with Chagas heart disease, 3-5 ischemic cardiomyopathy, 6-8 and dilated cardiomyopathy. 9,10 However, the acute success rate of epicardial catheter ablation for VT using a standard RF catheter is only about 60%, because the catheter electrode is inadequately cooled by the blood and the effect of epicardial fat in the vicinity of the CA. The lack of convective cooling of the catheter-tip by the blood would be expected to limit power delivery in the pericardial space; hence, the use of cooled-tip catheter ablation might be more appropriate than conventional catheter ablation for larger and deeper epicardial lesions. Furthermore, the safety of cooled-tip catheter ablation in the vicinity of the CA is unclear. The aim of the present study was to use an animal model to characterize the size of lesions produced by ablation with a cooled-tip catheter and to establish the safety of delivering RF pulses in the vicinity of major coronary vessels. MethodsThe current study was done according to the Guidelines for the Care and Use of Laboratory Animals published by the US National Institute of Health. The study protocol was reviewed by the Committee of the Ethics on Animal Experiments of Showa University. Background Transthoracic epicardial ablation can be an alternative to conventional treatment for critical pathways of ventricular tachycardia located in the epicardium. However, the usefulness and safety of epicardial ablation close to the coronary arteries (CA) is not clear. The purpose of the present experimental animal study was to analyze the efficacy and safety of epicardial radiofrequency (RF) ablation close to the CA. Methods and ResultsOf the left ventricle-epicardium ablated sites, 35 lesions (20 with cooling and 15 without cooling) were close to the CA (left anterior descending artery ≤15 mm) and 33 lesions (23 with cooling and 10 without cooling) were further from the CA. For sites close to the CA, epicardial ablation was effective in 77% (15/20) with cooling and in 40% ...

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