Present understanding of shock polarity for internal defibrillation: The obvious and non-obvious clinical implications

Mark W. Kroll*, Igor R. Efimov, Patrick J. Tchou

*Corresponding author for this work

Research output: Contribution to journalReview articlepeer-review

36 Scopus citations


Background: Uncertainty about the best electrode configuration has combined with the programming flexibility in modern implantable cardioverter- defibrillators (ICDs) to result in routine polarity reversal during an implant to deal with a high defibrillation threshold (DFT). We feel that this practice is not always supported by the clinical data and the present scientific understanding of defibrillation. Method: A meta-analysis of the clinical studies on ICD shock polarity was performed. Subgroup analyses were also performed to test the impact of high DFTs, various tilts, and the use of the hot can electrode. A review of the basic research surrounding the effects of polarity in defibrillation is also presented. Results: A total of 224 patients were studied. The use of an anodal right ventricular (RV) coil lowers the mean DFT by 14.8% (P = 0.00001). It provides thresholds equal to or lower than cathodal defibrillation in 83% of patients. The fraction of patients with lower anodal DFTs was 94/224 versus 38/224 for cathodal polarity. This phenomenon may be explained by virtual electrode effects. In particular, anodal electrodes tend to produce collapsing wavefronts while cathodal electrodes tend to produce expanding proarrhythmic wavefronts. Conclusion: In an ICD implant, the RV coil should be the anode. Furthermore, DFT testing beginning with cathodal defibrillation is most likely unnecessary and needlessly extends the procedure's duration and increases the risks for the patient.

Original languageEnglish (US)
Pages (from-to)885-891
Number of pages7
JournalPACE - Pacing and Clinical Electrophysiology
Issue number8
StatePublished - Aug 2006
Externally publishedYes


  • Biphasic waveform
  • Burping theory
  • Defibrillation threshold
  • Defibrillator electrode
  • ICD programming
  • Implantable cardioverter defibrillator
  • Polarity
  • Ventricular fibrillation

ASJC Scopus subject areas

  • Cardiology and Cardiovascular Medicine


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