Forgoing Defibrillation Testing at ICD Insertion Found to Be Safe

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An Observational Study Can’t Conclusively Resolve the Issue

The study by Dr. Brignole and colleagues makes a "meaningful contribution to the collective evidence that routine determination of defibrillation thresholds has more risks than benefits for many patients at the time of initial ICD insertion," said Dr. N.A. Mark Estes III.

However, the absence of randomization resulted in confounding differences in the clinical profiles of the patients who were enrolled in the two strategies, he added. For example, patients who underwent defibrillation testing had lower rates of atrial fibrillation, New York Heart Association class III and IV heart failure, and use of diuretics and digoxin. In addition, as the authors pointed out, the lower-than-anticipated number of patients reaching the primary end point rendered the study underpowered to detect a difference between the two groups.

Thus, this observational study cannot provide definitive proof that omitting this step is clinically justified, so it is not yet time to abandon the practice. "Implanting physicians will have to decide on the basis of the best available data, their experience, and judgment whether to omit defibrillation testing selectively in low-risk patients," Dr. Estes noted.

Dr. Estes is professor of medicine at Tufts University and director of the cardiac arrhythmia center at Tufts Medical Center, Boston. He reported ties to Boston Scientific, Medtronic, and St. Jude Medical. These remarks were taken from his editorial comment accompanying Dr. Brignole’s report (J. Am. Coll. Cardiol. 2012 Aug. 1 [doi:10.1016/j.jacc.2012.05.016]).



Patients who did not undergo defibrillation testing during the insertion of their first implantable cardioverter defibrillator had outcomes similar to those who did undergo defibrillation testing of the device in the largest study to date comparing the two approaches, which was reported online August 1 in the Journal of the American College of Cardiology.

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The study findings indicate that "the clinical relevance of defibrillation testing is limited."

This finding supports a strategy of omitting defibrillation testing in most such patients – a strategy that clinicians are already adopting in increasing numbers, said Dr. Michele Brignole, chief of cardiology at Ospedale del Tigullio, Lavagna, Italy, and his associates.

Defibrillation testing has been considered a standard procedure at ICD insertion "to ensure adequate sensing of ventricular fibrillation, appropriate connection of high-voltage electrodes, and the ability of the device to terminate VF with a shock. Nevertheless, implant techniques and technology have evolved in recent years, and deviations from this clinical practice are frequent," the investigators noted.

To assess the safety of omitting this step in the implantation process, Dr. Brignole and his colleagues performed SAFE-ICD (Safety of Two Strategies of ICD Management at Implantation), a prospective study of 2,120 consecutive procedures in adults at 41 Italian medical centers. The treating physicians were allowed either to perform or not perform defibrillation testing according to their standard practice; patients were followed for 2 years.

The frequency of performing defibrillation testing varied widely among the different medical centers, with some of them conducting the test in all patients and others doing so in no patients. Overall, 836 study subjects (39%) underwent defibrillation testing during insertion of their ICD, and the remaining 1,284 (61%) did not.

The primary end point was a composite of severe implant-related complications periprocedurally plus serious events during follow-up, such as sudden cardiac death or resuscitation after delivery of ineffective but appropriate ICD shocks.

This end point was reached in 18 patients who underwent defibrillation testing and 16 who did not. The estimated yearly incidence of this composite end point was 1.15% with defibrillation testing and 0.68% without it, a "negligible" difference.

In addition, 2-year all-cause mortality was not significantly lower for patients who underwent defibrillation testing (12.9%) than for those who did not (14.6%).

During follow-up, the devices delivered appropriate and effective shocks in a similar proportion of patients in the two study groups.

These findings indicate that "the clinical relevance of defibrillation testing is limited, thus supporting the practice of omitting [it] at implant," Dr. Brignole and his associates said (J. Am. Coll. Cardiol. 2012 Aug. 1 [doi:10.1016/j.jacc.2012.05.014]).

ICD recipients "are very well protected from sudden cardiac death irrespective of performing defibrillation testing or not," the authors said. Moreover, performing defibrillation testing is not likely to decrease the rate of sudden cardiac death to a clinically relevant degree, below the already low 1% rate observed in this study population, they added.

The strengths of this study included its large population that represented the general ICD population in Western countries, its very low (3%) dropout rate, and the use of any commercially available ICD devices.

However, the study was limited in that the unexpectedly low incidence of sudden cardiac death may have been insufficient to show a true difference between the two study groups.

The observational design of SAFE-ICD, unlike that of a randomized clinical trial, "does not allow us to draw a definitive conclusion" as to the safety of omitting defibrillation testing. But there is such a large, prospective, multicenter, randomized clinical trial – SIMPLE (Shockless Implant Evaluation), taking place now – that should provide a definitive answer, the researchers said.

This study was funded by Boston Scientific. One of Dr. Brignole’s associates is an employee of Boston Scientific, and others reported ties to Boston Scientific and Medtronic. Dr. Estes reported ties to Boston Scientific, Medtronic, and St. Jude Medical.

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