Shock-Energy Testing with ICDs Provides No Benefit

February 07, 2014

KFAR SABA, ISRAEL – Defibrillation-threshold (DFT) testing performed at the time of ICD implantation failed to reduce the risk of death, malignant ventricular arrhythmias, or inappropriate shocks when compared with individuals implanted without DFT, a new study shows[1].

The results, from a prospective cohort analysis of 3596 patients implanted with an ICD between 2010 and 2013, add to a growing body of evidence that DFT testing with more modern ICDs might not be necessary at the time of implantation.

"Accumulated data from previous reports and from this study suggest the possibility that DFT testing might be avoided during routine practice or applied only for selected high-risk patients," write Dr Yoav Arnson (Meir Medical Center, Kfar Saba, Israel) and colleagues in their report, published online January 31, 2014 in Heart Rhythm. "A firm conclusion can be drawn only after supporting data are available from prospective trials."

Of those included in the Israeli ICD Registry analysis, 17% underwent DFT testing and 83% did not. Those undergoing DFT testing were more likely to be receiving an ICD for secondary prevention, have a prior ventricular arrhythmia, and be undergoing treatment with the use of antiarrhythmic medication.

DFT testing was not associated with improved one-year mortality, the delivery of appropriate or inappropriate shocks, or the rate of ventricular arrhythmias/death. There was no difference in clinical outcomes when the patients were stratified into those who received ICDs for primary vs secondary prevention.

Clinical End Points

End points No DFT, n=2982 (%) DFT, n=614 (%) p
1-y mortality 5.1 5.3 0.74
Delivery of appropriate shocks 5.6 8.6 0.16
Ventricular arrhythmias and death 11.3 12.9 0.45
Inappropriate discharges 2.1 3.9 0.2

The authors point out that modern ICDs have better sensing algorithms and can deliver higher-energy shocks than previous devices. They are more capable in sensing and identifying ventricular tachyarrhythmias and provide effective defibrillation.

The group adds, however, that the database contains few patients with hypertrophic cardiomyopathy and congenital arrhythmogenic cardiomyopathies or channelopathies, so their registry results, like other analyses, need to be confirmed in future randomized trials.

The study was supported by an unrestricted grant from Boston Scientific. The authors declare no conflicts of interest.

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