Author + information
- Received October 3, 1994
- Revision received December 30, 1994
- Accepted February 2, 1995
- Published online June 1, 1995.
- Merritt H. Raitt, MD*,1,
- George Johnson, BSEE1,
- G. Lee Dolack, MD, FACC1,
- Jeanne E. Poole, MD, FACC1,
- Peter J. Kudenchuk, MD, FACC1 and
- Gust H. Bardy, MD, FACC1
- ↵*Address for correspondence:Dr. Merritt H. Raitt, Portland Veterans Affairs Medical Center, 3710 SW US Veterans Road, P.O. Box 1034 (111B), Portland, Oregon 97207.
Objectives. The purpose of this study was to determine the relation between clinical variables and the defibrillation threshold by using a standardized testing protocol and a uniform implantable defibrillator system.
Background. Past studies have not revealed useful correlations between clinical variables and the energy required to terminate ventricular fibrillation. Most of these studies did not use a uniform implantable defibrillator system or a standardized protocol to measure the defibrillation threshold and, thus, did not control for the influence of these technical influences. We postulated that defibrillator and defibrillation threshold measurement-based sources of variability overshadowed important clinical predictors.
Methods. The defibrillation threshold was measured by using a standardized protocol in 101 consecutive patients. We used a transvenous unipolar pectoral defibrillation system that employed a single endocardial right ventricular defibrillation coil as the anode and the shell of an 80-cm3pulse generator as the cathode to deliver a 65% tilt biphasic pulse.
Results. Several clinical variables were found to be significantly associated with the defibrillation threshold: patient gender, height, weight, body surface area, heart rate at rest, QRS and corrected QT (QTc) intervals, left ventricular mass and several measures of heart and chest size by chest roentgenogram. None of these variables had a correlation coefficient >0.45 with the defibrillation threshold. On multivariate analysis, left ventricular mass and heart rate at rest were the only independent predictors of the defibrillation threshold and explained only 25% of the observed variability.
Conclusions. Despite the use of a uniform transvenous defibrillation system and a standardized protocol to measure the defibrillation threshold, no clinically relevant correlation was found between clinical variables and the defibrillation threshold. The defibrillation threshold is probably a function of a complex interaction of anatomic, physiologic and cellular variables that are not adequately represented by easily obtainable clinical information. It is probably not possible to predict defibrillation outcome from standard clinical variables.
↵1 We thank Charles Troutman, RN and Jill Anderson, RN for nursing care of the patients, Joan McDaniel for secretarial assistance and Susan Shattuc, MS for preparation of the figures.
This work was supported in part by a grant from the National Heart, Lung, and Blood Institute. National Institutes of Health, Bethesda, Maryland; Medtronic Corporation, Minneapolis, Minnesota; and the Tachycardia Research Foundation, Seattle, Washington. Dr. Bardy is a consultant for Medtronics, Inc., Minneapolis.
- Received October 3, 1994.
- Revision received December 30, 1994.
- Accepted February 2, 1995.
- American College of Cardiology