In this interview, we speak with Dr. William Sauer, Director of the Electrophysiology Laboratories at the University of Colorado Hospital, about his recent research on the utility of postoperative testing of ICDs.1 What was the purpose of this study? Tell us about the study population and time frame. The study was meant to evaluate the potential role of post-operative defibrillation threshold testing by looking at the results of this procedure at the University of Colorado Hospital over the past 14 years. Everyone who received an implanted defibrillator (ICD) who was subsequently tested more than 3 months after implantation over this time frame was included in our analysis. What are some of the main reasons why defibrillation testing is questioned? Defibrillation testing has risks and it is unclear whether there is a clinical benefit to the test. Defibrillation testing involves the induction of ventricular fibrillation and the delivery of a high-energy shock. There has been recent data demonstrating an association between shocks and subsequent risk of death in patients with ICDs, suggesting (but without definitive proof) a potential causative effect. In addition, many of these patients have severe cardiomyopathy, and there exists a small risk for immediate post-shock electromechanical dissociation or subsequent heart failure exacerbation. Knowing of these small but serious risks, the information gained from the test needs to be substantial in order for the procedure to be justified. What other complications can occur during post-implant testing? In addition to the risks mentioned above, there is the possibility of anesthesia-related complications and the induction of atrial fibrillation requiring additional shocks for restoration of sinus rhythm. Describe the testing failures that required intervention. What were the most common causes of failure during ICD testing? The most common reason for testing failure was identification of an elevated defibrillation threshold (DFT). We defined an acceptable DFT as defibrillation with a 10 Joule safety margin relative to the maximum output of the ICD confirmed once or a 5 Joule safety margin confirmed twice. If a patient did not have an acceptable DFT, the device was changed to a higher output model, the ICD lead was moved, or a subcutaneous shocking coil was added to the system. Other testing failures included failure to sense ventricular fibrillation and failure to deliver a shock, and would likewise involve system modification. Tell us about some of the comparisons found between ICD systems implanted from 1996–2002 and 2003–2009. We found that systems implanted later in the study period were associated with fewer failures identified on ICD testing. This could be because older components may be more likely to fail over time. In addition, ICD systems have improved over time with the ability to deliver higher amounts of energy and provide accurate lead parameter measurements automatically. Describe the observed ICD testing failure rate over time in this study. Patients with older systems had a testing failure rate of 3.6% compared to a failure rate of 1% in patients with newer systems. The observed failure rate could be further diminished if a large defibrillation safety margin was achieved at implant. What percentage of patients may still be using these older ICD components? Most patients have newer ICD systems because of the expansion of indications to include primary prevention of sudden death that occurred after 2002. Which patients receive the greatest benefit from postoperative ICD testing? Our study results support a strategy of limiting the use of post-implant testing to those individuals who may have a marginal DFT at implant. What is significant about this study? The most significant finding of this study is that while there may have been a role for post-implant testing in the past, there appears to a lower observed rate of testing failures in newer systems. The results of the study strongly support a more selective use of this procedure limited to only those with a concern for testing failure. Have these study findings caused you to make changes in your practice of serial post-operative DFT testing? Yes. We discontinued the use of post-operative DFT testing several years ago based on a preliminary analysis of these results. Is there anything else you’d like to add? I still believe that there is a role for non-invasive programmed stimulation and ICD testing for select patients who may be at high risk for device failure. I don’t think that the results of our study advocate complete elimination of this procedure despite the very low observed rate of ICD testing failure.
- Sauer WH, Lowery CM, Bargas RL, et al. Utility of postoperative testing of implantable cardioverter-defibrillators. Pacing Clin Electrophysiol 2011;34:186–192.