title: Defibrillation causes immediate cardiac dilation in humans.
abstract: Defibrillation Causes Dilation.
  
  
  BACKGROUND
  Prior studies in isolated heart tissue have shown both excitation and deexcitation to be the primary mechanism of defibrillation. This article presents the first evidence in man of deexcitation immediately following defibrillation by tracking the heart's mechanical response.
  
  
  RESULTS
  The geometric changes of the ventricular chambers were measured before and after defibrillation in seven human subjects receiving an implantable cardioverter defibrillator (ICD). The ICD was used to produce approximately three episodes of ventricular fibrillation and defibrillation in each subject. Twenty-two two-dimensional echocardiographic images of the right ventricle (RV) and 11 images of the left ventricle (LV) were recorded and analyzed at 30 frames per second. Just over 2 seconds of each episode were digitized, beginning half a second before the defibrillation shock. Individual frames were analyzed to yield cross-sectional, ventricular chamber area as a function of time. Immediately following defibrillation, ventricular chambers dilated with significant fractional area increase (RV: 1.58 +/- 0.25, LV: 1.10 +/- 0.06), with peak dilation at 194 +/- 114 msec.
  
  
  CONCLUSIONS
  Defibrillation causes a rapid increase in ventricular chamber area due to relaxation of the myocardium, suggesting that defibrillation synchronizes the cardiac cells to the deexcited state in man.
authors.affiliation: The University of Memphis, Memphis, Tennessee 38152, USA.
authors.forename: Erin
authors.initials: E
authors.lastname: Sylvester
authors.forename: Eric
authors.initials: E
authors.lastname: Johnson
authors.forename: Paul
authors.initials: P
authors.lastname: Hess
authors.forename: Robert
authors.initials: R
authors.lastname: Malkin
mesh_terms: D000368:Aged; D002311:Cardiomyopathy, Dilated / Q000000981:diagnostic imaging / Q000503:physiopathology; D017147:Defibrillators, Implantable; D004554:Electric Countershock / Q000379:methods*; D005260:Female; D006331:Heart Diseases / Q000175:diagnosis / Q000000981:diagnostic imaging* / Q000503:physiopathology / Q000628:therapy*; D006801:Humans; D008297:Male; D009200:Myocardial Contraction; D013318:Stroke Volume; D014463:Ultrasonography; D018487:Ventricular Dysfunction, Left / Q000000981:diagnostic imaging* / Q000503:physiopathology; D018497:Ventricular Dysfunction, Right / Q000000981:diagnostic imaging* / Q000503:physiopathology