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ICD shocks not associated with increased risk for death or acute decompensated HF

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Implantable cardioverter defibrillator shocks delivered during induced ventricular arrhythmias at the time of noninvasive electrophysiology study testing did not increase the risk for death or acute decompensated HF as compared with recipients of appropriate implantable cardioverter defibrillator shocks, study data indicated.

The cohort evaluation consisted of 1,372 patients undergoing ICD implantation from December 1997 to January 2007. Researchers evaluated the probability of all-cause mortality and hospitalization for acute decompensated HF based on the type of ICD shock received using multivariable Cox proportional analyses. The four analyzed shocks included implantation shocks only (n=694), additional noninvasive electrophysiology study shocks only (n=319), additional appropriate shocks only (n=128) or additional inappropriate shocks only (n=104).

The risk for death (adjusted HR=0.91; 95% CI, 0.69-1.20) or acute decompensated HF (adjusted HR=0.71; 95% CI, 0.46-1.16) were similar between recipients of noninvasive electrophysiology study shocks and recipients of implantation shocks. Patients who received appropriate ICD shocks had an increased risk for death (adjusted HR=2.09; 95% CI, 1.38-2.69) and acute decompensated HF (adjusted HR=2.40; 95% CI, 1.51-3.81) vs. those receiving implantation shocks, and also increased risk for death (adjusted HR=2.61; 95% CI, 1.86-3.67) and acute decompensated HF (adjusted HR=2.29; 95% CI, 1.33-3.97) vs. noninvasive electrophysiology study shocks.

“ICD shocks delivered for induced arrhythmias at the time of noninvasive electrophysiology study testing do not increase the risk of death or acute decompensated HF in this study. The occurrence of spontaneous arrhythmias in vulnerable substrates may explain the increased risk,” the researchers concluded.

In an accompanying editorial, Harikrishna Tandri, MD, of The Johns Hopkins University School of Medicine in Baltimore, said the conclusion may not be as decisive as the results indicated.

“A high-energy shock may be more detrimental to a failing heart, in which the cellular reparative mechanisms are already overburdened,” Tandri wrote. “Electrophysiologic and mechanical consequences of shock may be just more than the ‘straw that broke the camel’s back’ and may send the patients into a downward spiral of HF and, ultimately, death.”

Bhavnani S. Heart Rhythm. 2010;7:755-760.

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