Upper limit of vulnerability is a good estimator of shock strength associated with 90% probability of successful defibrillation in humans with transvenous implantable cardioverter-defibrillators

Department of Cardiovascular Surgery, Cedars-Sinai Medical Center, Los Angeles, California, USA.

OBJECTIVES. The goals of this study were to determine the probability of successful defibrillation at the upper limit of vulnerability and to evaluate a minimal safety margin for implantable cardioverter-defibrillator first shocks based solely on the upper limit of vulnerability. BACKGROUND. The upper limit of vulnerability is the strength at or above which ventricular fibrillation is not induced when a stimulus is delivered during the vulnerable phase of the cardiac cycle. It has been proposed as an estimate of defibrillation efficacy because it correlates with the defibrillation threshold and can be determined with a single episode of fibrillation. METHODS. We studied 40 patients prospectively at implantation of transvenous cardioverter-defibrillators. Defibrillation threshold was defined as the weakest biphasic shock that defibrillated after 10 s of ventricular fibrillation. The upper limit of vulnerability was defined as the weakest biphasic shock that did not induce ventricular fibrillation when given at 0, 20 and 40 ms before the peak of the T wave in ventricular paced rhythm at cycle length 500 ms. After determination of the upper limit of vulnerability and defibrillation threshold, patients underwent six additional fibrillation-defibrillation episodes. The strength of five of the defibrillation shocks was equal to the upper limit of vulnerability; the strength of one of the six shocks was randomly selected to be equal to the upper limit of vulnerability plus 3 J. The implantable cardioverter-defibrillator was tested at the upper limit of vulnerability plus 3 J in 28 patients. RESULTS. The defibrillation threshold was 8.8 +/- 5.0 J (mean +/- SD), and upper limit of vulnerability was 11.3 +/- 4.6 J; the defibrillation threshold and upper limit of vulnerability were highly correlated (r = 0.89, p < 0.001). The success rate for the 200 defibrillation shocks with strength equal to the upper limit of vulnerability was 90% (95% confidence intervals based on proportion of successes in 40 patients: 86% to 94%). All five defibrillation test shocks at the upper limit of vulnerability were successful in 24 patients (60%); four of five were successful in 12 patients (30%); and three of five were successful in 4 patients (10%). All 40 test shocks and 28 implantable cardioverter-defibrillator shocks with a strength equal to the upper limit of vulnerability plus 3 J were successful. CONCLUSIONS. The upper limit of vulnerability is a good estimator of the shock strength associated with 90% probability of successful defibrillation (DFT90). A strength of 3 J above the upper limit of vulnerability is a good estimate of the minimal acute safety margin for implantable cardioverter-defibrillator first shocks.

This article has been cited by other articles:

				J. D. Day, R. N. Doshi, P. Belott, U. Birgersdotter-Green, M. Behboodikhah, P. Ott, K. A. Glatter, S. Tobias, H. Frumin, B. K. Lee, et al. Inductionless or Limited Shock Testing Is Possible in Most Patients With Implantable Cardioverter- Defibrillators/Cardiac Resynchronization Therapy Defibrillators: Results of the Multicenter ASSURE Study (Arrhythmia Single Shock Defibrillation Threshold Testing Versus Upper Limit of Vulnerability: Risk Reduction Evaluation With Implantable Cardioverter-Defibrillator Implantations) Circulation, May 8, 2007; 115(18): 2382 - 2389. [Abstract] [Full Text] [PDF]

				B. Rodriguez, L. Li, J. C. Eason, I. R. Efimov, and N. A. Trayanova Differences Between Left and Right Ventricular Chamber Geometry Affect Cardiac Vulnerability to Electric Shocks Circ. Res., July 22, 2005; 97(2): 168 - 175. [Abstract] [Full Text] [PDF]

				S. A. Strickberger and G. J. Klein Is defibrillation testing required for defibrillator implantation? J. Am. Coll. Cardiol., July 7, 2004; 44(1): 88 - 91. [Abstract] [Full Text] [PDF]

				C. Swerdlow, K. Shivkumar, and J. Zhang Determination of the Upper Limit of Vulnerability Using Implantable Cardioverter-Defibrillator Electrograms Circulation, June 24, 2003; 107(24): 3028 - 3033. [Abstract] [Full Text] [PDF]

				C. D. Swerdlow Implantation of Cardioverter Defibrillators Without Induction of Ventricular Fibrillation Circulation, May 1, 2001; 103(17): 2159 - 2164. [Abstract] [Full Text] [PDF]

				S. Windecker, R. E. Ideker, V. J. Plumb, G. N. Kay, G. P. Walcott, and A. E. Epstein The influence of ventricular fibrillation duration on defibrillation efficacy using biphasic waveforms in humans J. Am. Coll. Cardiol., January 1, 1999; 33(1): 33 - 38. [Abstract] [Full Text] [PDF]

				C. D. Swerdlow, J. E. Brewer, R. M. Kass, and M. W. Kroll Application of Models of Defibrillation to Human Defibrillation Data : Implications for Optimizing Implantable Defibrillator Capacitance Circulation, November 4, 1997; 96(9): 2813 - 2822. [Abstract] [Full Text]

				C. D. Swerdlow, C. T. Peter, R. M. Kass, E. S. Gang, W. J. Mandel, C. Hwang, D. J. Martin, and P.-S. Chen Programming of Implantable Cardioverter-Defibrillators on the Basis of the Upper Limit of Vulnerability Circulation, March 18, 1997; 95(6): 1497 - 1504. [Abstract] [Full Text]