title: Three-dimensional mapping of earliest activation after near-threshold ventricular defibrillation shocks.
abstract: BACKGROUND
  Following shocks with a 50% defibrillation success (DFT50) delivered from electrodes at the right ventricular (RV) apex and superior vena cava (SVC), the earliest epicardial postshock activation always appears focally in the left ventricular (LV) apex for both successful and failed shocks. Because the heart is a three-dimensional (3D) structure, questions remain whether this activation truly arises from a focus or the focal pattern represents epicardial breakthrough resulting from intramural reentry. To answer these questions, 3D electrical mapping was performed.
  
  
  RESULTS
  In six pigs, 60 to 84 epoxy fiberglass needles (0.7-mm-diameter), each containing six electrodes 2 mm apart, were inserted into the LV with 3- to 5-mm spacing around the apex and 5- to 10-mm spacing near the base. Ten DFT50 shocks (RV-->SVC, biphasic, 6/4 msec) were delivered after 10 seconds of fibrillation in each animal. The first five activations after each shock were mapped. Of 60 DFT50 shocks, 31 were successful, of which the first postshock cycle was a sinus beat in 13. In the other 18 successful shock episodes, the first postshock activation was detected 63 +/- 16 msec after the shock, which was not significantly different from the 58 +/- 23 msec postshock interval for the 29 failed shock episodes. In these 47 successful and failed shock episodes, the earliest postshock activation always arose focally from the LV apex. Its origin was in the subepicardium in 76% +/- 17%, midmyocardium in 16% +/- 12%, and subendocardium in 8% +/- 6% of cases.
  
  
  CONCLUSIONS
  Following near-DFT50 shocks, the first postshock cycles did not arise by macroreentry. Instead, they originated from a true focus or microreentry, most commonly near the epicardium.
authors.affiliation: Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama 35294-0019, USA. toon@crml.uab.edu
authors.forename: Nipon
authors.initials: N
authors.lastname: Chattipakorn
authors.forename: Parwis C
authors.initials: PC
authors.lastname: Fotuhi
authors.forename: Siriporn C
authors.initials: SC
authors.lastname: Chattipakorn
authors.forename: Raymond E
authors.initials: RE
authors.lastname: Ideker
mesh_terms: D000818:Animals; D018780:Body Surface Potential Mapping; D004554:Electric Countershock; D004699:Endocardium / Q000503:physiopathology; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology; D006352:Heart Ventricles / Q000503:physiopathology; D021621:Imaging, Three-Dimensional; D008297:Male; D023421:Models, Animal; D008955:Models, Cardiovascular; D010496:Pericardium / Q000503:physiopathology; D012016:Reference Values; D013552:Swine; D013997:Time Factors