Abstract 20654: Automated Vulnerability Testing Accurately Identifies Patients with Inadequate Defibrillation Safety Margin
Introduction: The upper limit of vulnerability (ULV) is the weakest T-wave shock that does not induce ventricular fibrillation (VF). Because ULV correlates closely with defibrillation threshold, vulnerability safety margin (VSM) testing can determine defibrillation safety margin for implantable cardioverter-defibrillators (ICDs) without inducing VF. Testing requires delivery of T-shocks at the most vulnerable time intervals. Presently the operator determines these intervals from the latest T-wave peak in multiple surface ECG leads (TP). Automated VSM testing would be more efficient and provide a consistent standard.
Methods: This multicenter prospective study of automated VSM testing used the recovery time, TR, (inflection point of the far-field electrogram (EGM) T-wave), as a fiducial interval. We downloaded custom software into clinically-approved implantable cardioverter-defibrillators (ICDs). The software first measured TR during pacing at cycle length 500 ms. Then it delivered 18 J T-wave shocks during successive pacing trains at intervals of −30, −10, −50, and +10 ms relative to TR until VF was induced or all 4 shocks were delivered. If VF was not induced, the VSM was considered adequate. Patients subsequently underwent defibrillation testing. Defibrillation safety margin was considered adequate if shocks at 25J or lower (10 J safety margin) defibrillated VF on 2 of 2 trials.
Results: Vulnerability and defibrillation safety margin data were obtained in 54 patients, and TP obtained in 44 patients. During VSM, VF was induced in 10 patients (19%) and not induced in 44 patients (81%). Inadequate defibrillation safety margin occurred in 2/10 patients with inadequate VSM vs. 0/44 patients with adequate VSM, p = 0.03. Given an adequate VSM, the 95% lower CI for defibrillation success was 92%. The automated measure of ICD-EGM TR correlated with operator-measured ECG TP (r = 0.65) but was slightly longer (TR = 382 ± 20 ms, TP = 367 ± 28 ms, TR- TP = 15 ± 21 ms).
Conclusions: Automated VSM testing permits efficient and accurate assessment of defibrillation efficacy without measuring multiple surface ECG leads. Using a T-shock strength of 18 J, it identified all patients with inadequate defibrillation safety margin, while inducing VF in only 19%.
- © 2010 by American Heart Association, Inc.