Epicardial organization of human ventricular fibrillation Kumaraswamy Nanthakumar, MD, a Gregory P. Walcott, MD, a Sharon Melnick, AAS, a Jack M. Rogers, PhD, b Matthew W. Kay, PhD, b William M. Smith, PhD, b Raymond E. Ideker, MD, PhD, a,b,c William Holman, MD d a From Division of Cardiovascular Medicine, b Division of Biomedical Engineering, c Department of Physiology, and d Division of Cardiovascular Surgery, University of Alabama at Birmingham, Birmingham, Alabama. OBJECTIVE The objective of this study was to test the hypothesis that on the epicardium of the in vivo human heart, ventricular fibrillation (VF) consists of chaotic small wavefronts that constantly change paths. BACKGROUND Despite the significance of VF to cardiovascular mortality, little is known about the wavefronts that constitute VF in humans. METHODS In 9 patients undergoing cardiac surgery, a single VF episode was induced by rapid pacing immediately after institution of cardiopulmonary bypass while recordings were made from 504 electrodes spaced 2 mm apart in a 20 cm 2 plaque held against the anterior left ventricle epicardium. A total of 26 segments of VF, each 2 s long, were analyzed. A computer algorithm identified individual wavefronts and classified them into groups that followed similar activation sequences. RESULTS The mean activation rate was 5.8  1.8 (mean  SD) cycles/s. The wavefronts during each epoch were grouped into 9.4  7.1 different activation pathways, and 8.3  2.3 wavefronts followed each pathway. Individual wavefronts spread to activate an area of 5.1  3.0 cm 2 in the mapped region. The majority of the wavefronts propagated into the mapped region and/or propagated out of the mapped region into adjacent tissue, suggesting that the wavefronts were larger than 5.1 cm 2 . Reentry was identified in only 16 of the 26 (62%) 2-s segments, always completed 2 cycles, and lasted for 9.5  6.6% of these 16 epochs, which is 5.8% of the total duration of all the segments analyzed. CONCLUSION VF wavefronts on the human epicardium are usually large, repeatedly follow distinct pathways, and only occasionally reenter. If these results for the left ventricular epicardium are representative of those for the entire ventricular mass, they do not support the hypothesis that human VF consists of small, constantly changing wavefronts, but rather suggest that there is significant organization of human VF. © 2004 Heart Rhythm Society. All rights reserved. KEYWORDS Ventricular fibrillation; Electrical mapping; Sudden cardiac death Introduction Ventricular fibrillation (VF) is an important etiology of sudden cardiac death. 1,2 Despite its clinical significance, the degree of organization of human VF activation sequence has not been studied in vivo. It is generally believed that VF in humans is the result of chaotic small wavefronts that change paths cycle to cycle. 3 However, recent publications suggest significant spatiotemporal organization of VF in small 4,5 and large 6–8 animal hearts. While epicardial multisite mapping in Langendorff-per- fused, explanted, dilated, human hearts has been per- formed, 9 in vivo recordings of VF in humans have been Address reprint requests and correspondence: K. Nanthakumar, M.D., University of Alabama at Birmingham, 1670 University Blvd., B140 Volker Hall, Birmingham, AL 35294-0019. E-mail address: kn@crml.uab.edu. (Received December 1, 2003; accepted January 27, 2004.) 1547-5271/$ -see front matter © 2004 Heart Rhythm Society. All rights reserved. doi:10.1016/j.hrthm.2004.01.007 Heart Rhythm (2004) 1, 14 –23 www.heartrhythmjournal.com