Significant Differences in Charge Times Among Currently Available Implantable Cardioverter Defibrillators

Capacitor charging accounts for most of the delay between arrhythmia detection and therapy delivery in ICDs. Long capacitor charge times may increase the risk of syncope in patients with poorly tolerated arrhythmias. To determine if there are clinically important differences in charge time among currently available devices, we analyzed charge times at various delivered energy levels in three manufacturers' devices: Medtronic, CPI, and Ventritex. Charge times were measured for shocks delivered for spontaneous or induced arrhythmias occurring from time of implant to 4 months after implant. A total of 343 shocks were assessed in 63 patients with ICDs: 16 Medtronic (MicroJewel II, model 7223Cx), 14 CPI (Mini II, model 1762), and 33 Ventritex (Cadet and Contour, models V-115 and V-145). The curves of the relationship between charge time and delivered energy for the three types of devices were significantly different, with Medtronic charge times shorter than CPI or Ventritex (P < 0.0001), and CPI charge times shorter than Ventritex (P = 0.002). The difference in mean charge times between the Ventritex and Medtronic devices ranged from 1.7 seconds at a delivered energy of 10 +/- 2.5 J to 8.0 seconds at a delivered energy of 30 +/- 2.5 J. Thus, clinically important differences in charge time exist among the three types of defibrillators studied. These results should be considered in selecting an ICD for patients with poorly tolerated arrhythmias.