Assessment of Adequate Safety Margin Using Single Coupling Interval-Upper Limit of Vulnerability Test

Authors

  • MEHUL B. PATEL M.D.,

    Corresponding author
    1. Sparrow Thoracic and Cardiovascular Institute, Division of Cardiology, Michigan State University, Lansing, Michigan
    • Address for reprints: Mehul Patel, M.D., C.C.D.S., St Luke's Episcopal Health System, Baylor College of Medicine, 6621 Fannin Street, MC 19345-C, Houston, TX 77030. Fax: 832-825-0166; e-mail: mehul.patel@bcm.edu

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  • KHYATI PANDYA M.D.,

    1. Sparrow Thoracic and Cardiovascular Institute, Division of Cardiology, Michigan State University, Lansing, Michigan
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  • RANJAN K. THAKUR M.D., M.P.H.

    1. Sparrow Thoracic and Cardiovascular Institute, Division of Cardiology, Michigan State University, Lansing, Michigan
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  • Funding: No funding sources were used for this project.

  • Disclosures: None.

  • Conflict of interest: None.

Abstract

Purpose

Upper limit of vulnerability (ULV) testing using T-wave scanning shocks at multiple coupling intervals correlates well with defibrillation threshold (DFT), but remains underutilized in clinical practice. We measured DFT and ULV at a single coupling interval (SCI), with the aim to identify adequate safety margin at a coupling interval that correlates best with DFT.

Methods

Consecutive patients undergoing implantable cardioverter defibrillator implantation underwent simultaneous SCI-ULV and DFT assessment. Following a drive train of 400 ms, a T-wave-coupled shock was delivered. To minimize shocks, patients were randomized to programmed shock at 20 ms before peak (Group I), at peak (Group II), or 20 ms after peak (Group III) of T wave. An initial T-wave test shock at 9 J was followed by ±2 J shocks, until SCI-ULV was ascertained. Device rescue shocks were programmed at test shock +2 J and +4 J shocks followed by external rescue shock.

Results

There were 200 patients: 66 patients in Group I, 67 patients each in Groups II and III; mean age was 68.9 ± 12.4 years; 75% of patients men, 66% with ischemic heart disease and mean ejection fraction of 27.1 ± 7.1%. Overall, the mean number of ventricular fibrillation induction was 1.39 ± 0.8, mean SCI-ULV energy was 7.97 ± 3.39 J, and mean DFT was 8.68 ± 3.19 J. The correlation between SCI-ULV and DFT improved from Group I to Group III and was best in Group III (r2 = 0.689). There were no major adverse events.

Conclusions

SCI-ULV measured 20 ms after the peak of the T wave correlates well with DFT for assessment of adequate safety margin.

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