Introduction: Electrical isolation of the pulmonary veins (PVs) to treat paroxysmal atrial fibrillation (AF) has been described, using "entry block" as an endpoint for PV isolation. We describe a new technique for guiding PV isolation, using "exit block" out of the PV after ablation as a criterion for successful isolation.Methods and Results: A circular mapping catheter was positioned at the os of arrhythmogenic PVs and ablation was performed proximal to the mapping catheter until entry block into the vein was achieved. Pacing was performed from the mapping catheter and from the ablator inside the PV to document exit block out of the PV. In patients in whom cardioversion did not restore sinus rhythm, PV isolation was performed in AF. Entry and exit block were reassessed in ablated veins after a 20-minute waiting period. Ninety-five PVs were ablated in 41 patients. A total of 66 PVs in 34 patients were ablated in sinus rhythm. After entry block was achieved, exit block was present in only 38 (58%) of 66 PVs. A total of 29 PVs in 21 patients were ablated in AF. After cardioversion to sinus rhythm, there was evidence of entry block into the PV in 20 (69%) of 29 PVs and exit block in only 14 (48%) of 29 PVs. There was no significant difference between the total number of lesions applied per vein in sinus rhythm compared with AF (11.6 +/- 8.6 vs 10.3 +/- 6.2; P = NS). There was recovery of conduction after a 20-minute waiting period in 9 (11%) of 84 PVs.Conclusion: Identification of exit block after ostial PV ablation provides a clear endpoint for electrical isolation of the PVs. Isolation of the PVs can be performed during sustained AF without the need to apply excess RF lesions. Applying a 20-minute waiting period after electrical isolation will identify reconnection in approximately 10% of PVs.

Syncope is a known predictor of poor outcome and sudden death in patients with a nonischemic dilated cardiomyopathy.(1,2) Electrophysiologic testing often reveals no inducible sustained ventricular arrhythmias, and has a poor predictive value in this patient population.(3-6) Implantable cardioverter-defibrillators (ICDs) are frequently recommended in these patients. However, there are limited long-term data regarding the frequency of appropriate defibrillator therapy for sustained ventricular arrhythmias in patients with nonischemic dilated cardiomyopathies presenting with sustained ventricular arrhythmias or syncope.(6-10) The present study examines the frequency of appropriate and inappropriate ICD therapy in patients with dilated cardiomyopathy presenting with syncope, without documented clinical sustained ventricular arrhythmias.

: The goal of this project is to obtain data that will help identify the reaction mechanism and the ignition limits of aluminum at elevated temperatures and pressures. Formidable problems arise when attempting such measurements in rocket motors since conditions are unsteady and not easy to control. Therefore, it was decided to mount a pure aluminum sample to the end wall of a shock tube and to ignite the sample using a reflected shock wave. The pressures and temperatures that can be achieved (40 atm, 5000 K) are typical of rocket motor conditions and are much higher than those obtained in previous studies using incident shock waves in conventional shock tubes. The aluminum sample reacts with a test gas in which the proportions of nitrogen, hydrogen, oxygen and chlorine are the same as found in ammonium perchlorate.