Defibrillation efficacy comparing a subcutaneous array electrode versus an"active can" implantable cardioverter defibrillator and a subcutaneous array electrode in addition to an "active can" implantable cardioverter defibrillator: Results from active can versus array trials I and II

Introduction: Placement of implantable cardioverter defibrillators (ICDs) h as been simplified by using the shell of a pectorally implanted ICD as a de fibrillation electrode in combination with an endocardial right ventricular defibrillation lead. However, a sufficiently low defibrillation threshold (DFT) cannot be obtained in a few patients. Therefore, alternative approach es were systematically tested in the Active Can versus Array Trial (ACAT). Methods and Results: In the first of two prospective randomized studies, th e DFT of a subcutaneous left dorsolateral array anode introduced from a pec toral incision was compared to that of a standard active can anode in 68 pa tients. Intraoperatively, the DFT was determined twice in each patient usin g either the active can or, in patients with a subcutaneous array lead, onc e with all three fingers and once omitting the middle finger of the array. The second prospective randomized study included 40 patients. DFT also was determined twice in each patient using an active can in a left pectoral pos ition as anode alone and combined with a left dorsolateral array electrode with two fingers. In ACAT I, stored energy at DFT decreased from 13.1 +/- 7 .7 J (active can) to 9.6 +/- 6.1 J (three-finger array lead) (P = 0.04), im pedance decreased from 53 +/- 8 Omega to 40 h 6 Omega (P < 0.0001). Omittin g the middle finger of the array lead, stored energy at DFT increased by 0. 9 J (P = 0.47) and impedance by 2 Omega (P < 0.0001). In ACAT II, DFT and i mpedance using an active can device were significantly lower when a two-fin ger array lead was added that decreased stored energy at DFT from 10.1 +/- 5.2 J to 6.9 +/- 3.9 J (P = 0.001) and impedance from 56 +/- 5 Omega to 42 +/- 5 Omega (P < 0.0001). Conclusion: In combination with a right ventricular defibrillation electrod e, a left pectoral subcutaneous array lead improves defibrillation efficacy if used instead of, or in addition to, a left pectoral active can ICD devi ce. Implantation of the array lead can be simplified by using two instead o f three fingers, without a significant loss of defibrillation efficacy.