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(Circulation. 2002;105:2537.)
© 2002 American Heart Association, Inc.

Basic Science Reports

Impact of Myocardial Ischemia and Reperfusion on Ventricular Defibrillation Patterns, Energy Requirements, and Detection of Recovery

Hao Qin, MD; Gregory P. Walcott, MD; Cheryl R. Killingsworth, DVM, PhD; Dennis L. Rollins, MS; William M. Smith, PhD; Raymond E. Ideker, MD, PhD

From the Departments of Physiology and Biophysics, Medicine, and Biomedical Engineering, University of Alabama at Birmingham.

Correspondence to Raymond E. Ideker, MD, PhD, 1670 University Blvd, B-140, Volker Hall, Birmingham, AL 35294-0019. E-mail rei{at}crml.uab.edu

Background— Shocks that have defibrillated spontaneous ventricular fibrillation (VF) during acute ischemia or reperfusion may seem to have failed if VF recurs before the ECG amplifier recovers after shock. This could explain why the defibrillation threshold (DFT) for spontaneous VF appears markedly higher than for electrically induced VF.

Methods and Results— The DFT for electrically induced VF (E-DFT) was determined in 15 pigs before ischemia, followed by left anterior ascending or left circumflex artery occlusion. VF was electrically induced 20 minutes after occlusion, followed 5 minutes later by reperfusion. Whether spontaneous or electrically induced, VF during occlusion or reperfusion was treated with up to 3 shocks at 1.5xE-DFT. If all 3 shocks failed, shock strength was increased. Thirty minutes after reperfusion, the other artery was occluded and the protocol was repeated. Defibrillation was considered successful if postshock sinus/idioventricular rhythm was present for 30 seconds. VF recurring within 30 seconds after the shock was considered immediate or delayed if the first postshock activation complex in a rapidly restored ECG recording was VF or sinus/idioventricular rhythm, respectively. Defibrillation efficacy at 1.5xE-DFT was significantly higher for electrically induced ischemic VF (76%) than for spontaneous VF (31%). The incidence of delayed recurrence after electrically induced nonischemic (3%) or ischemic (20%) VF was significantly lower than after spontaneous VF (75%). Mean VF recurrence time after spontaneous VF was 4.6±5.3 seconds.

Conclusions— Spontaneous VF can be halted by a shock but then quickly restart before a standard ECG amplifier has recovered from postshock saturation, making it appear that the shock failed.

Key Words: ischemia • fibrillation • defibrillation

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