Automated Vulnerability Testing Identifies Patients With Inadequate Defibrillation Safety Margin

Abstract

Background-Implantable cardioverter-defibrillator system efficacy is tested at implant by induction of ventricular fibrillation (VF). Defibrillation safety margin can be assessed without VF induction using upper limit of vulnerability methods, but these methods have required manual determination of T-wave timing. Methods and Results-To test the feasibility of an inductionless system of implant testing, a multicenter prospective study of an automated vulnerability safety margin system was conducted, which measured T-wave timing using an intracardiac electrogram during a ventricular pacing train. The system delivered up to 4 T-wave shocks of 18 J. Lack of VF induction by all 4 shocks was considered evidence of defibrillation adequacy. Patients subsequently underwent conventional defibrillation testing to meet a standard implant criterion. The 95% lower CI for defibrillation success at 25 J for noninduced patients was found using Bayesian statistics. Sixty patients were enrolled at 6 centers. Vulnerability testing and defibrillation success results were obtained from 54 patients. Vulnerability testing induced VF in 10 (19%) patients, of whom 2 required system revision. All patients not induced by vulnerability testing were successfully defibrillated twice at ≤25 J. The Bayesian credible interval was 97% to 100% for the population success rate of defibrillation at 25 J for automated vulnerability safety margin noninduced patients. Conclusions-An automated system identified all patients who failed conventional safety margin testing, while inducing only 19% of patients. Although limited by sample size, this study suggests the feasibility of automated implant testing that substantially reduces the need for VF induction in patients receiving implantable cardioverter-defibrillators. (Circ Arrhythm Electrophysiol. 2012;5:1073-1080.)

Upper Limit of Vulnerability During Defibrillator Implantations Predicts the Occurrence of Appropriate Shock Therapy for Ventricular Fibrillation

“…7,8,10, 34 Furthermore, an automated vulnerability safetymargin system has been invented, which measures the T-wave timing using the ECG of the implanted device system. 35 Similar to those protocols, the high safety and feasibility of our protocol have been reported. 10 Although differences in the protocol of the vulnerability test might have influenced our results, it may have been relatively small because the peak of the T-wave is in the middle of the vulnerable period in any protocol.…”

Optimal Strength and Number of Shocks at Upper Limit of Vulnerability Testing Required to Predict High Defibrillation Threshold Without Inducing Ventricular Fibrillation

“…Recently, the usefulness of automated vulnerability test for predicting high DFT has been reported. 21 The vulnerable period that was automatically calculated by their software was well correlated with the St-T peak interval. The 18-J vulnerability test at 4 coupling intervals could correctly detect high-DFT patients with 19% of VF inducibility.…”

“…But in patients with sinus rhythm R-wave sensing amplitude >5 mV, R-wave sensing during VF was thought to be almost always reliable, and critical delay in detecting VF was not observed in previous reports. 21 Determination of the vulnerable period using 12-lead ECG is essential for the ULV test. This process requires extra time and adequate experience.…”

“…A close correlation between the ULV and the defibrillation threshold (DFT) has been validated in some studies of humans and other animals, 12-14 and the safety and reliability of ICD implantation and programming of the lower first-shock strength using vulnerability testing without VF induction as a surrogate for DFT assessment has been demonstrated. [15][16][17][18][19][20][21] The present study evaluated the usefulness of vulnerability testing to confirm acceptable DFT at the time of ICD implantation and to predict high DFT (>20 J). Optimal strength and number of shocks at ULV testing to predict high DFT without inducing VF were assessed.…”

Implantable Cardioverter Defibrillator

“…9,10 The principle advantage of vulnerability testing is that, when applied in a safety-margin strategy, it can determine that defibrillation is reliable without inducing VF in 80% to 95% of patients. 8,11,12 In contrast, fibrillation-defibrillation testing requires inducing VF with the attendant risks of circulatory arrest in all patients. 13 Until recently, the principle disadvantage of vulnerability testing was that it required accurate, operator-performed timing measurement using multiple surface leads to ensure that the T wave shock is delivered at the most vulnerable interval.…”