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.