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The impact of carvedilol on the defibrillation threshold

      Background

      Defibrillation threshold (DFT) is the minimum energy required to successfully terminate ventricular fibrillation. Epinephrine has been shown to increase the DFT in the beta-blocker naïve, but using cardioselective beta-blockers leads to a reduction in the DFT on infusion of epinephrine and norepinephrine. We sought to determine the impact of carvedilol therapy on the DFT after infusion of epinephrine and norepinephrine.

      Methods

      DFT was determined in patients receiving carvedilol by the step-down method (baseline DFT), and then patients (n = 27, 67.3 years, 70.0% were male, average left ventricular ejection fraction = 19%) were randomized to a 7-minute infusion of norepinephrine, epinephrine, or placebo in a double-blind manner. After the study drug infusion, DFT testing was repeated (experimental DFT) and results were compared between groups.

      Results

      No differences in intragroup DFTs were observed among carvedilol-treated patients receiving norepinephrine (9.4 ± 4.6 J vs 11.1 ± 7.8 J; P = .589), epinephrine (10.6 ± 5.3 J vs 9.8 ± 6.3 J; P = .779), or placebo (11.1 ± 7.0 vs 8.5 ± 4.2; P = .349).

      Conclusions

      Carvedilol prevents alterations in DFT produced by stress levels of catecholamines.
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