Inductionless or limited shock testing is possible in most patients with implantable cardioverter-defibrillators/cardiac resynchronization therapy defibrillators - Results of the multicenter ASSURE Study (Arrhythmia Single Shock Defibrillation Threshold Testing Versus Upper Limit of Vulnerability: Risk Reduction Evaluation with Implantable Cardioverter-Defibrillator Implantations)

University of California, Davis, Davis, California, United States
Circulation (Impact Factor: 14.95). 06/2007; 115(18):2382-9. DOI: 10.1161/CIRCULATIONAHA.106.663112
Source: PubMed

ABSTRACT Implantable cardioverter-defibrillators and cardiac resynchronization therapy defibrillators have relied on multiple ventricular fibrillation (VF) induction/defibrillation tests at implantation to ensure that the device can reliably sense, detect, and convert VF. The ASSURE Study (Arrhythmia Single Shock Defibrillation Threshold Testing Versus Upper Limit of Vulnerability: Risk Reduction Evaluation With Implantable Cardioverter-Defibrillator Implantations) is the first large, multicenter, prospective trial comparing vulnerability safety margin testing versus defibrillation safety margin testing with a single VF induction/defibrillation.
A total of 426 patients receiving an implantable cardioverter-defibrillator or cardiac resynchronization therapy defibrillator underwent vulnerability safety margin or defibrillation safety margin screening at 14 J in a randomized order. After this, patients underwent confirmatory testing, which required 2 VF conversions without failure at < or = 21 J. Patients who passed their first 14-J and confirmatory tests, irrespective of the results of their second 14-J test, had their devices programmed to a 21-J shock for ventricular tachycardia (VT) or VF > or = 200 bpm and were followed up for 1 year. Of 420 patients who underwent 14-J vulnerability safety margin screening, 322 (76.7%) passed. Of these, 317 (98.4%) also passed 21-J confirmatory tests. Of 416 patients who underwent 14-J defibrillation safety margin screening, 343 (82.5%) passed, and 338 (98.5%) also passed 21-J confirmatory tests. Most clinical VT/VF episodes (32 of 37, or 86%) were terminated by the first shock, with no difference in first shock success. In all observed cases in which the first shock was unsuccessful, subsequent shocks terminated VT/VF without complication.
Although spontaneous episodes of fast VT/VF were limited, there was no difference in the odds of first shock efficacy between groups. Screening with vulnerability safety margin or defibrillation safety margin may allow for inductionless or limited shock testing in most patients.

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    ABSTRACT: The relationship between the defibrillation threshold (DFT) and total mortality is unclear. A university hospital prospectively maintained implantable defibrillator (ICD) database identified 508 patients who underwent ICD implantation and had DFT testing performed at implant. Patients were placed in one of three groups based on the implant DFT (high (≥20 J), moderate (19-11 J), or low DFT (≤10 J)). Sixty-seven patients had a high DFT, 216 had a moderate DFT, and 225 had a low DFT. The mean left ventricular ejection fraction (LVEF) was 0.25, 0.28, and 0.30 in the high, moderate, and low DFT groups, respectively, (p = 0.04). There were significantly more patients with a subcutaneous electrode in the high DFT group (p < 0.001), more patients taking amiodarone (p < 0.001), and more patients on oral anticoagulation (p = 0.04). There were a total of 140 deaths during the follow-up period (mean 3.2 ± 1.7 years). There were 24 deaths in the high DFT group (35.8 %), 62 in the moderate DFT group (28.7 %), and 54 in the low DFT group (24.0 %) (p = 0.05). Implant DFT was a significant predictor of mortality (p = 0.01), as was age, LVEF (p < 0.001), CAD (p = 0.01), amiodarone use (p = 0.02), and hematoma at implant (p = 0.01). An elevated DFT was an independent predictor of mortality after controlling for all significant univariate variables (p = 0.004). A high-implant DFT predicts an adverse prognosis, even when an adequate ICD safety margin is present.
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    ABSTRACT: Upper limit of vulnerability (ULV) testing using T-wave scanning shocks at multiple coupling intervals correlates well with defibrillation threshold (DFT), but remains underutilized in clinical practice. We measured DFT and ULV at a single coupling interval (SCI), with the aim to identify adequate safety margin at a coupling interval that correlates best with DFT. Consecutive patients undergoing implantable cardioverter defibrillator implantation underwent simultaneous SCI-ULV and DFT assessment. Following a drive train of 400 ms, a T-wave-coupled shock was delivered. To minimize shocks, patients were randomized to programmed shock at 20 ms before peak (Group I), at peak (Group II), or 20 ms after peak (Group III) of T wave. An initial T-wave test shock at 9 J was followed by ±2 J shocks, until SCI-ULV was ascertained. Device rescue shocks were programmed at test shock +2 J and +4 J shocks followed by external rescue shock. There were 200 patients: 66 patients in Group I, 67 patients each in Groups II and III; mean age was 68.9 ± 12.4 years; 75% of patients men, 66% with ischemic heart disease and mean ejection fraction of 27.1 ± 7.1%. Overall, the mean number of ventricular fibrillation induction was 1.39 ± 0.8, mean SCI-ULV energy was 7.97 ± 3.39 J, and mean DFT was 8.68 ± 3.19 J. The correlation between SCI-ULV and DFT improved from Group I to Group III and was best in Group III (r(2) = 0.689). There were no major adverse events. SCI-ULV measured 20 ms after the peak of the T wave correlates well with DFT for assessment of adequate safety margin.
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    ABSTRACT: Background: The utility of the upper limit of vulnerability (ULV) test in patients undergoing defibrillator implantation has been reported, so the purpose of this study was to evaluate the difference in the clinical outcomes between patients with ULV ≤15J or >15J. Methods and Results: A total of 165 patients receiving an implantable cardioverter-defibrillator underwent a vulnerability test. At the time of the implantation, we delivered a 15-J shock on the T-peak and ±20ms later to cover the most vulnerable part of the cardiac cycle. The clinical outcomes were prospectively analyzed. A 15-J shock induced ventricular fibrillation (VF) in 30 patients (ULV >15J) and did not in 135 (ULV ≤15J). The characteristics of the 2 groups were comparable. After a mean follow-up of 757 days, Kaplan-Meier curve analysis showed that the ULV ≤15J group experienced less VF than the ULV >15J group (log-rank P=0.003). The occurrence of ventricular tachycardia was similar between the 2 groups (P=0.140). Furthermore, the effectiveness of ATP was comparable. After adjusting for other known predictors of shock therapy, a ULV >15J was independently associated with the occurrence of VF (hazard ratio: 6.25; 95% confidence interval: 1.913-20.40; P<0.01). Conclusions: A high ULV value was associated with a high incidence of VF, which suggests that cardiac vulnerability to electrical shock may be linked to electrical instability.
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