Programming of implantable cardioverter-defibrillators on the basis of the upper limit of vulnerability

Charles D. Swerdlow, C. Thomas Peter, Robert M. Kass, Eli S. Gang, William J. Mandel, Chun Hwang, David J. Martin, Peng Sheng Chen

Research output: Contribution to journalArticle

48 Scopus citations


Background: A patient-specific measure of defibrillation efficacy that requires a minimum number of ventricular fibrillation (VF) episodes would be valuable for programming implantable cardioverter-defibrillators (ICDs). The upper limit of vulnerability (ULV) is the weakest shock strength at or above which VF is not induced when a stimulus is delivered during the vulnerable phase of the cardiac cycle. It correlates with the defibrillation threshold (DFT) and can be determined with a single episode of VF. The objective of this study was to test the hypothesis that ICDs programmed on the basis of the ULV convert spontaneous ICD-detected VF reliably. Methods and Results: We studied 100 consecutive patients at ICD implantation and during follow-up of 20±7 months. At implantation, the ULV and DFT were determined, and the ICD system was tested at a shock strength equal to the ULV+3 J. During follow- up, the strength of the first shock was programmed to the ULV+5 J for arrhythmias detected in the VF zone (cycle length <292±17 ms). We reviewed stored detection intervals and electrograms from spontaneous episodes of ICD- detected VF to determine the success rate for appropriate first shocks. The programmed first-shock strength was 17.5±5.2 J. During follow-up, there were 120 appropriate first shocks in 37 patients. The arrhythmia was rapid monomorphic ventricular tachycardia (VT) in 70% of episodes (31 patients), VF in 11% (13 patients), polymorphic VT in 1%, and unclassified in 17% (15 patients). The first shock was successful in 119 of 120 episodes (99%; 95% CI, 93% to 100%). One unclassified episode required two shocks. No patient had syncope associated with an ICD shock or arrhythmic death. Conclusions: ICD shocks can be programmed on the basis of the ULV, a measurement made in regular rhythm, without a direct measure of defibrillation efficacy.

Original languageEnglish (US)
Pages (from-to)1497-1504
Number of pages8
Issue number6
StatePublished - 1997


  • defibrillation
  • heart-assist device
  • upper limit of vulnerability

ASJC Scopus subject areas

  • Cardiology and Cardiovascular Medicine
  • Physiology (medical)

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    Swerdlow, C. D., Thomas Peter, C., Kass, R. M., Gang, E. S., Mandel, W. J., Hwang, C., Martin, D. J., & Chen, P. S. (1997). Programming of implantable cardioverter-defibrillators on the basis of the upper limit of vulnerability. Circulation, 95(6), 1497-1504.