Spontaneous arrhythmic episodes in the study of a modular, communicative, leadless pacing-defibrillator system (Modular ATP trial)

Abstract Background MODULAR ATP, a multicenter, international trial, assesses a subcutaneous ICD (S-ICD) in wireless communication to a leadless pacemaker (LP) capable of pace terminating ventricular arrhythmias in addition to providing shock therapy for VT/VF. The clinical trial met 6-month safety and efficacy endpoints1, but the specific details of ventricular episodes and behavior of this novel system have not been described. Methods Eligible patients had an ICD indication, were considered have a high risk for VT, and did not require chronic pacing. All patients were implanted with the investigational device. An independent events committee and the sponsor adjudicated arrhythmia type before and after therapy. Device therapy was re pre-specified as appropriate for persistent arrhythmia of ventricular origin, whose calculated heart rate is greater than the device-programmed conditional zone cutoff. Fine-Gray analysis was performed to identify risk of therapy delivery, accounting for mortality as a competing risk. Results At the time of data cutoff, 297 patients were enrolled (17.5% female, age 59±12 yrs, 57.2% primary prevention, LVEF 35±13%) and 286 patients underwent successful implantation. At a median follow-up of 15 months, 66 patients had 296 episodes: 42 patients had 105 discrete episodes (89% were VT) and 8 patients had 10 storms of VT (Figure 1). ATP-only therapy was delivered in 64% of appropriate episodes in 28 patients with a 68% ATP success rate. In 87% of appropriate episodes with ATP-only therapy, the first ATP burst terminated VT. ATP accelerated VT in 10 episodes in 7 patients. Appropriate therapy (ATP or shock) and appropriate shock rates were 12.4% and 7.5% at one year, respectively (Figure 2) Inappropriate therapy was delivered to 69 episodes in 26 subjects, yet 24/69 of these (in 10 patients) were due to overcounting of true VT whose true rate was lower than the conditional. ATP-only therapy was delivered in 14% of inappropriate episodes. Inappropriate therapy and shock rates were 8.1% and 5.9% at one year, respectively (Figure 2). Therapy was appropriately withheld in 52 episodes in 20 patients. No patient experienced lack of ATP therapy due to communication failure and no patient requested ATP or pacing therapy to be inactivated for any reason. Conclusion An investigational LP, receiving ATP requests from an S-ICD via wireless communication, effectively pace-terminated VT/VF in 68% of S-ICD detected episodes. The LP appropriately withheld ATP in 43% inappropriately S-ICD sensed events. This device holds promise in refining S-ICD detected events and reducing inappropriate and appropriate S-ICD shocks.Episode Flow Chart and Classification Appropriate and Inappropriate Therapy