Clinical characteristics and outcome of patients with high defibrillation thresholds. A multicenter study.

Abstract

BACKGROUND Successful defibrillation by an implantable cardioverter-defibrillator (ICD) depends on its ability to deliver shocks that exceed the defibrillation threshold. This study was designed to identify clinical characteristics that may predict the finding of an elevated defibrillation threshold and to describe the outcome of patients with high defibrillation thresholds. METHODS AND RESULTS The records of 1,946 patients from 12 centers were screened to identify 90 patients (4.6%) with a defibrillation threshold greater than or equal to 25 J. Excluding three patients who received ICDs that delivered greater than 30 J, there were 81 men and six women with a mean age of 59.5 +/- 10.1 years, a mean left ventricular ejection fraction of 0.32 +/- 0.14, and a 76% prevalence of coronary artery disease. Sixty-one patients (70%) were receiving antiarrhythmic drugs, and 45 (52%) were receiving amiodarone. Seventy-one patients (82%) received an ICD. Death occurred in 27 patients--19 of the 71 (27%) with an ICD (eight arrhythmic), and eight of the 16 (50%) without an ICD (four arrhythmic). Actuarial survival for all patients at 5 years was 67%. Actuarial survival rates at 2 years for patients with and without an ICD were 81% and 36%, respectively (p = 0.0024). Actuarial survival at 5 years for the ICD patients was 73%; no patient without an ICD has lived longer than 32 months. Actuarial survival free of arrhythmic death in the ICD patients at 5 years was 84%. Although the only variable to predict survival was ICD implantation (p = 0.003), it is entirely possible that in this retrospective analysis, clinical selection decisions to implant or to not implant an ICD differentiated patients destined to have better or worse outcomes, respectively. CONCLUSIONS Antiarrhythmic drug use may be causally related to the finding of an elevated defibrillation threshold. When patients with high defibrillation thresholds receive an ICD, arrhythmic death remains an important risk (42% of deaths in these patients were arrhythmia related, with 16% actuarial incidence at 5 years). Vigorous testing to optimize patch location can potentially benefit patients by enhancing the margin of safety for effective defibrillation.

Automated External Defibrillators and Survival from Cardiac Arrest in the Outpatient Hemodialysis Clinic

“…It is possible that there are characteristics of cardiac arrest that are unique to patients with CKD. For example, CKD is associated with high defibrillation thresholds (22), which, in itself, has been linked to poor survival (27). Third, our study design might not allow for the complete capture of relevant events.…”

Impact of the Relationship between the Defibrillation Threshold (DFT) and Clinical Outcomes in Recipients of Modern Era Implantable Cardioverter Defibrillator (ICD)

“…Early data has suggested that some deaths in ICD patients occur mostly in those with high DFTs. 19,20) Rubenstein, et al demonstrated that an elevated DFT is a significant independent predictor of the overall mortality and DFT provides incremental information about the mortality and prognosis. Further, they also showed that an elevated DFT is associated with increased mortality even in the setting of an adequate safety margin.…”

Role of Antiarrhythmic Drugs: Frequent Implantable Cardioverter-Defibrillator Shocks, Risk of Proarrhythmia, and New Drug Therapy

“…Careful testing of DFTs should be performed in all the patients, with special attention to those who have monophasic waveform ICDs, those with an epicardial lead system 39 , patients with a high DFT at baseline, and patients treated with high dose, 40 chronic amiodarone. [41][42][43][44] Azimilide has been shown to have minimal effects on the DFT or pacing thresholds in ICD patients. 24,45 Similarly, dronedarone has been shown to have no effect on defibrillation safety margin or pacing thresholds at its therapeutic dose or higher.…”