2.1 Study design and population
This was a retrospective, multicenter, observational study. The study protocol was approved by the institutional review board of each participating center. The data analyzed were collected from 69 patients who experienced episodes of ventricular arrhythmias. They were among 185 patients involved in the Defibrillator with Enhanced Features and Settings for Reduction of Inaccurate Detection (DEFENSE) Trial.13 Briefly, that study compared the SmartShock Technology (SST) algorithm with the conventional VT detection algorithms. The trial enrolled consecutive recipients of an ICD or cardiac resynchronization therapy defibrillator (CRT-D) that used the SST algorithm (Protecta XT ICD [DR, VR], Protecta XT CRT-D [DR], and Evera XT ICD [DR, VR]; Medtronic, Minneapolis, MN, USA). Patients whose device programming did not match the study requirements (Supplementary Table 1), or who were unable to complete two years of follow-up, or who were unable to provide informed consent were excluded from this research. The recipients were followed-up every 6 months for up to 2 years after device implantation, by remote monitoring of their device, or in the outpatient clinic. The devices were assessed at all scheduled and unscheduled follow-up visits. The DEFENSE trial revealed that, compared with the conventional algorithms, the SST discrimination algorithm significantly lowered the rate of inaccurate VT detection.
The VT episodes were evaluated as follows: of the 185 patients initially enrolled, 69 patients experienced 821 episodes of ventricular arrhythmias (VT, fast VT, or VF); of the 821 episodes, 608 (74%) were judged as true ventricular tachyarrhythmia, and 213 (26%) were judged as other episodes, including atrial fibrillation/atrial flutter (n = 26), sinus tachycardia or atrial tachycardia (AT) (n = 178), and T-wave oversensing (n = 9), leaving data from just 53 patients that exhibited true ventricular tachyarrhythmia. Each entire episode was reviewed by an independent adjudication committee to determine whether or not the diagnosis was appropriate.