Background-It has recently been recognized that atrial fibrillation can originate from focal sources in the pulmonary veins (PVs). However, the mechanisms of focal atrial fibrillation have not been well characterized. We assessed the electrophysiological characteristics of the PVs using high-resolution optical mapping. Methods and Results-Coronary-perfused, isolated whole-atrial preparations from 33 normal dogs were studied.Programmed electrical stimulation was performed, and a 4-cm 2 area of the PV underwent optical mapping of transmembrane voltage to obtain 256 simultaneous action potentials. Marked conduction slowing was seen at the proximal PV, compared with the rest of the vein, on both the epicardial (31.3Ϯ4.47 versus 90.2Ϯ20.7 cm/s, Pϭ0.001) and endocardial (45.8Ϯ6.90 versus 67.6Ϯ10.4 cm/s, Pϭ0.012) aspects. Pronounced repolarization heterogeneity was also noted, with action potential duration at 80% repolarization being longest at the PV endocardium. Nonsustained reentrant beats were induced with single extrastimuli, and the complete reentrant loop was visualized (cycle length, 155Ϯ30.3 ms); reentrant activity could be sustained with isoproterenol. Sustained focal discharge (cycle length, 330 to 1100 ms) was seen from the endocardial surface in the presence of isoproterenol; each focus was localized near the venous ostium. Conclusions-The normal PV seems to have the necessary substrate to support reentry as well as focal activity. Although reentry occurred more distally in the vein, focal activity seemed to occur more proximally.

Ablation of AF at the time of CTI ablation results in a significantly better long-term freedom from arrhythmias.

Idiopathic, focal ventricular tachycardia that originates from the right ventricular apex is presented. Arrhythmogenic ventricular dysplasia needs to be ruling out prior to making this diagnosis. This is a rare entity that can be cured with an ablation and therefore it needs to be considered in the differential diagnosis of idiopathic VTs before implanting a defibrillator.

We describe a focal atrial tachycardia (AT) originating from the region of the inferoposterior mitral annulus in which ablation at the site of earliest endocardial activation during AT was unsuccessful. Three-dimensional electroanatomic mapping identified the earliest atrial activation within the coronary sinus. Radiofrequency energy delivered at this site within the CS terminated this tachycardia without any complications, suggesting an origin within the CS. To our knowledge, this is the first time a three-dimensional, high-density activation map of such a tachycardia has been reported.

As a means of determining the effect of the fecal stream in the pathogenesis of experimentally produced colonic tumors in Wistar strain rats, simple colostomies were performed in the left colon of 57 female rats at approximately 4 cm above the anus. Fifty‐four rats received daily subcutaneous injections, 5 days per week, of the carcinogen 3:2'dimethyl‐4‐aminodiphenyl at a dosage of 2 mg/day/100 Gm body weight. Of the 54 rats, 17 (31.4%) developed either hyperplasia, adenomatous polyps or carcinoma of the large bowel proximal to the colostomy site. None of the 54 rats developed any lesion distal to the colostomy. None of the three control rats with colostomies developed any kind of tumor. Of the colonic lesions that developed, 12 were hyperplasias, 12 were adenomatous polyps and four were carcinomas. All hyperplasia developed at colostomy edge. Diversion of the fecal stream prevents development of colonic neoplasms in Wistar rats in this experimental situation.