SAN FRANCISCO — Inappropriate shocks from implantable cardioverter defibrillators are common and may cause harm, a review of the medical literature suggests.
“There are not a great deal of data that enable us to separate out the adverse effects of inappropriate versus appropriate shocks,” but both seem to be associated with an increased risk for death and other adverse outcomes, Dr. Alfred E. Buxton said at the annual meeting of the Heart Rhythm Society.
The literature suggests that 30%-60% of patients with implantable cardioverter defibrillators (ICDs) get appropriate shocks delivered to terminate a life-threatening arrhythmia, and as many as 20%-30% of patients get inappropriate shocks at other times.
“ICD shocks, while potentially life saving, have potential adverse effects,” said Dr. Buxton, professor of medicine at Brown University, Providence, R.I. Shocks have been associated with increased noncardiac mortality, reduced quality of life, and device-induced proarrhythmias.
Compared with patients who had never been shocked by their ICDs, patients who'd had any ICD shock had a quadrupled risk for death from any cause in an analysis of data from the 719-patient Multicenter Automatic Defibrillator Implantation Trial II (MADIT II). Inappropriate shocks were associated with a doubling in all-cause mortality, and appropriate shocks were associated with a tripling in all-cause mortality, compared with no shocks (J. Am. Coll. Cardiol. 2008;51:357-65).
Inappropriate shocks occurred in 12% of patients and comprised 31% of all shocks in the MADIT II trial.
Clearly, needing an ICD shock to terminate a life-threatening arrhythmia puts a person at risk for death, “but there is probably also some additive effect of inappropriate shocks,” Dr. Buxton said. He has been a consultant or speaker or received funding from companies that make cardiac devices including Boston Scientific, GEHealthcare, Medtronic, and St. Jude Medical.
Previous analyses also identified adverse effects associated with ICD shocks. Approximately half of 60 patients were shocked by their ICDs within 2 years of implantation in a 1998 study. Anxiety and sadness increased and initiation of new activities decreased in patients who'd had a shock compared with no shocks, and the same was seen in patients with five or more shocks, compared with just one or no shocks, he said.
A 1999 analysis of the Coronary Artery Bypass Graft Patch trial found no difference in quality of life after 6 months between 228 control patients without ICDs and 101 patients with ICDs who hadn't been shocked, but lower quality of life in 101 other patients with ICDs who had been shocked, compared with controls.
About a third of 373 patients with ICDs in the Antiarrhythmics vs. Implantable Defibrillators (AVID) trial received at least one shock within 1 year, and receiving more than one shock was associated with a significant reduction in mental well-being and physical function, a 2002 analysis concluded.
Data from several studies suggest that there is a complex interaction between depression and ICD shocks.
Depression may increase the likelihood of developing arrhythmias and having shocks, and has been associated with decreased heart rate variability, he said. But a 1993 study of 241 patients followed for a mean of 26 months found no significant difference in overall survival rates for patients who had or had not been shocked. At least one shock occurred in 76% of patients, and 63% of the cohort had inappropriate shocks. Mortality rates were similar for patients with appropriate shocks (38% died) and inappropriate shocks (35%).
And an unpublished secondary analysis of the 2004 Defibrillator in Acute Myocardial Infarction Trial (DINAMIT) found a significantly higher death rate in patients who had received ICD shocks, compared with non-ICD patients and those with ICDs but no shocks, Dr. Buxton said.
'ICD shocks, while potentially life saving, [also] have potential adverse effects.' DR. BUXTON