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ICD shock has adverse effect on mortality, compared with antitachycardia pacing




SAN FRANCISCO – Among patients with implantable cardiac defibrillators and cardiac resynchronization therapy defibrillators, mortality was lower in patients who received only antitachycardia pacing, compared with those who were treated with at least one ICD shock, results from a large database analysis showed.

"Over the past 5 or 10 years, there’s been an association of increasing mortality in people who get ICD shocks," lead author Dr. Adam Strickberger said in an interview at the annual scientific sessions of the Heart Rhythm Society, where the study was presented. "Trying to tease that apart has been hard to do. This study does not give us the mechanism of action for the association, but the message is that avoiding ICD shocks when you can is probably a good thing."

Dr. Adam Strickberger

For the study, Dr. Strickberger and his associates evaluated the records of 71,691 patients who were implanted with a St. Jude Medical ICD and CRT-D device during January 2007–May 2012 and monitored on They used to assess the remote transmission of tachycardia therapy records from January 2007 to November 2012, St. Jude’s device tracking registry to determine patient demographics at time of implant, and Social Security Death Index information to determine survival status as of 2012. Outcomes of interest were effectiveness of antitachycardia pacing (ATP) and mortality. ATP was considered effective if it was not followed by a shock and the patient survived the episode.

The mean age of the patients was 68 years and 73% were male. During a mean follow-up time of 2.5 years, ATP was effective in 89% of the 218,561 episodes delivered in 18,670 patients. In 77% of all ventricular tachycardia/ventricular fibrillation episodes, ATP was the only ICD therapy required.

The researchers also found that patients who received at least one ICD shock had higher mortality, compared with those who received ATP only (hazard ratio, 1.33 vs. 1.20, respectively; P value less than 0.001).

Dr. Strickberger, who is in a group arrhythmia physician practice in Fairfax, Va., acknowledged certain limitations of the study, including the fact that "it was not known what the underlying heart disease was, we don’t know ejection fraction, heart failure status, and we don’t know if the shocks delivered were appropriate or inappropriate."

Dr. Strickberger receives consulting fees from St. Jude Medical. Five of the study’s coauthors are employees of the company.

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