Defibrillation Testing: Is it Necessary with ICD Implantation?
Defibrillation Testing: Is it Necessary with ICD Implantation?
Abstract & Commentary
By John P. DiMarco, MD, PhD. Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville. Dr. DiMarco does research for Medtronic, is a consultant for Medtronic, Novartis, and St. Jude, and is a speaker for Boston Scientific.
Source: Brignole, M, et al. Clinical evaluation of defibrillation testing in an unselected population of 2,120 consecutive patients undergoing first implantable cardioverter-defibrillator implant. J Am Coll Cardiol 2012;60:981-987.
This paper reports the results of the Safety of Two Strategies of ICD Management at Implantation (SAFE-ICD) study. This study was a registry conducted in 41 Italian centers that followed outcomes after initial implantable cardioverter-defibrillator (ICD) implant to determine if performing defibrillation testing at the time of implant had clinical value. During a 13-month period, 2120 patients who received a new ICD at the participating centers were enrolled in the registry. Defibrillation testing was at the time of the initial implant according to the centers' current practice. Intraoperative complications and events during follow-up were then used as endpoints.
The 2120 patients enrolled constituted 97% of all new ICD recipients in the 41 participating centers. The frequency of defibrillation testing was quite variable ranging from 0-100% of ICD implants at individual centers. Of the patients enrolled, 836 (39%) had defibrillation testing and 1284 (61%) did not. Patients who did not have defibrillation testing were likely sicker since they had, on average, a higher New York Heart Association functional class, lower left ventricular ejection fractions, and more frequently received cardiac resynchronization therapy devices. The method of defibrillation testing varied from center to center. Among the patients who underwent defibrillation testing, one single VF induction-defibrillation was performed in 720 patients, two inductions in 100 (12%), and more than three in 16 (2%). At least one external shock was needed at the time of testing in 30 patients (3.6%) because of an ineffective ICD shock at maximum energy. Of these 30 patients, four had a cardiopulmonary arrest requiring three or more external shocks for termination. In eight patients, the defibrillator was unable to convert VF with any internal shock at the time of implant.
The primary combined endpoint was a composite of implant-related complications and events during follow-up. These occurred in 18 patients who underwent defibrillation testing and 16 patients who did not. The slightly higher event rate in the defibrillation testing patients was due to the higher intraoperative complication rate. When the event rates were weighted for baseline clinical variables by propensity scoring, the difference between the groups remained very small. Mortality between the two groups was slightly lower among patients who had defibrillation testing than among patients who did not, but adjustment for baseline variables by propensity scoring showed that the hazard ratio (HR) was not significant (HR -0.97; 95% confidence interval: 0.76 to 1.23). During clinical follow-up, appropriate effective shocks occurred in 223 patients, with a similar proportion receiving shocks in the two groups. Appropriate ineffective shocks were seen in 13 patients and again these were evenly distributed between the two groups. There were nine sudden cardiac deaths, two instantaneous deaths, and two deaths within 5 minutes in the defibrillation testing group compared to 11 sudden cardiac deaths and three instantaneous deaths in the group that did not have testing. The authors conclude that defibrillation testing is safe but it does not appear to be necessary to ensure safety.
Commentary
There has been considerable controversy recently about the need for defibrillation testing. Some authors have proposed that defibrillation shocks by themselves may damage the heart, increase the risk for implant complications, and result in long-term adverse affects.
Defibrillation testing was an intrinsic part of the implant procedure from the early days of ICD therapy. The initial systems that used epicardial patches and the early transvenous systems often had high defibrillation thresholds and failure to defibrillate at maximum energy was not uncommon. New generation ICD systems have more effective defibrillation waveforms and pathways and much shorter charge times. The latter makes it unnecessary to program shock energy levels to the lowest effective setting. As a result, it is now rare for there to be a failure at the time of defibrillation testing and it has not been possible to correlate a testing failure at implant with failure during clinical use.
Should defibrillation testing still be routine? This study strongly suggests the answer is no. In our laboratory, we now perform testing on a limited basis, mostly in patients with unusual anatomy or lead placement and at generator changes in patients with ICD leads under recall.
In this study, the authors show that there is a low complication rate with defibrillation testing, but that defibrillation testing does not appear to offer any significant benefits. In our laboratory, we now usually do not do defibrillation testing if we can achieve a stable standard lead position.
One of the early reasons for defibrillation testing was to program the energy as low as possible. However, as the charge times have decreased, programming to a lower energy output has become less important and, therefore, I don't think this should be a reason for continuing to do defibrillation testing.
This paper reports the results of the Safety of Two Strategies of ICD Management at Implantation (SAFE-ICD) study.Subscribe Now for Access
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