Efficacy and Safety of Appropriate Shocks and Antitachycardia Pacing in Transvenous and Subcutaneous Implantable Defibrillators: Analysis of All Appropriate Therapy in the PRAETORIAN Trial

Abstract

Background: The PRAETORIAN trial showed non-inferiority of the subcutaneous implantable cardioverter-defibrillator (S-ICD) compared to the transvenous ICD (TV-ICD) with regard to inappropriate shocks and complications. In contrast to the TV-ICD, the S-ICD cannot provide antitachycardia pacing (ATP) for monomorphic ventricular tachycardia (VT). This pre-specified secondary analysis evaluates appropriate therapy and whether ATP reduces the number of appropriate shocks. Methods: The PRAETORIAN trial was an international, investigator-initiated randomized trial, which included patients with an indication for ICD therapy. Patients with prior VTs below 170 bpm or refractory recurrent monomorphic VTs were excluded. In 39 centers, 849 patients were randomized to receive an S-ICD (N=426) or TV-ICD (N=423) and were followed for a median of 49.1 months. ICD programming was mandated by protocol. Appropriate ICD therapy was defined as therapy for ventricular arrhythmias. Arrhythmias were classified as discrete episodes and storm episodes (≥3 episodes within 24 hours). Analyses were performed in the modified intention-to-treat population. Results: In the S-ICD group, 86/426 patients received appropriate therapy, versus 78/423 patients in the TV-ICD group, during a median follow-up of 52 months (48-month Kaplan-Meier estimates 19.4% and 17.5%, P=0.45). In the S-ICD group, 83 patients received at least one shock, versus 57 patients in the TV-ICD group (48-month Kaplan-Meier estimates 19.2% and 11.5%, P=0.02). Patients in the S-ICD group had a total of 254 shocks, compared to 228 shocks in the TV-ICD group (P=0.68). First shock efficacy was 93.8% in the S-ICD group and 91.6% in the TV-ICD group (P=0.40). The first ATP attempt successfully terminated 46% of all monomorphic VTs, but accelerated the arrhythmia in 9.4%. Ten S-ICD patients experienced 13 electrical storms, versus 18 TV-ICD patients with 19 electrical storms. Patients with appropriate therapy had an almost two-fold increased relative risk of electrical storms in the TV-ICD group compared to the S-ICD group (P=0.05). Conclusions: In this trial, no difference was observed in shock efficacy of the S-ICD compared with the TV-ICD. Although patients in the S-ICD group were more likely to receive an ICD shock, the total number of appropriate shocks was not different between the two groups.

Perplexing Results From the PRAETORIAN Trial: Revisiting the Debate About the Value of Antitachycardia Pacing

“…Whereas the main article reported on the rates of appropriate ICD shocks (ie, delivered for ventricular arrhythmias), it did not include detailed information on appropriate ICD therapies (shocks and antitachycardia pacing [ATP]) and did not provide results on the efficacy of ATP at terminating ventricular arrhythmias in the transvenous ICD group. 13 In this issue, Knops et al 14 report the results of a prespecified secondary analysis of the PRAETORIAN trial intended to examine appropriate ICD therapies and to determine whether ATP reduces the number of appropriate ICD shocks in the transvenous ICD group of the trial. They found that 86 of 426 (20.2%) patients in the S-ICD group received appropriate ICD therapy compared with 78 of 423 (18.4%) patients in the transvenous ICD group (P=NS).…”

“…Patients with a transvenous ICD and appropriate ICD therapy appeared to be at an increased relative risk of experiencing electric storms compared with the S-ICD group, but this comparison did not reach statistical significance. 14 The authors are to be commended for conducting this analysis, which provides helpful insights into the PRAE-TORIAN trial and sheds light on important and clinically relevant issues related to appropriate ICD therapies. Their analysis has several strengths, including the use of randomized clinical trial data, protocol-driven programming of ICDs, and central adjudication of events and electrograms.…”

“…Second, whereas the authors attempted to provide an explanation for the smaller number of patients with at least 1 appropriate ICD shock in the transvenous ICD group, it remains unclear as to whether this observation was attributable to the ability of transvenous ICDs to provide ATP or to the fact that 11 patients with an S-ICD had 18 shocks for VT below the programmed therapy zone attributable to cardiac oversensing. Third, although the authors attempted to explain the lower success rate of ATP than what has been reported in previous studies by highlighting that patients were excluded from their trial if they had VT at a rate >170 beats per minute or recurrent monomorphic VT, previous trials have demonstrated a much higher efficacy of ATP than what was observed by Knops et al 14 in patients with faster VT who were arguably similar to patients enrolled in the PRAETORIAN trial. 15 It is not clear why the results of the current analysis diverge from those of previous studies.…”

“…Despite the limitations of the analysis by Knops et al, 14 their recommendation that a shared decision-making process should be used in counseling patients about the type of ICD cannot be overemphasized. This process should take into account the patient’s health goals, preferences, and values and should underscore the fact that ICD shock efficacy is similar between the S-ICD and transvenous ICD; device-related complications are higher with the transvenous ICD; and inappropriate ICD shocks, although lower with the new generation S-ICDs, appear to be increased with this type of device.…”

“…As the medical community continues to deliberate about some of the findings provided by Knops et al, 14 their article is poised to catalyze more research in this area and the advancement of S-ICD and transvenous ICD technologies that will improve patient outcomes.…”