TRAC-VT (isrctn.com identifier: ISRCTN84509594) was a prospective, multicenter, observational single-arm study enrolling patients at five hospitals in five European countries. The DTA system used in this study was market-approved in Europe at the time of enrollment. Ablation procedures were performed, and patients were followed for 12 months according to routine hospital practice and standard of care. Follow-up timepoints were protocol required at 3 and 6 months, and telephone follow-ups were required at 1 and 12 months post-ablation. Adverse events, changes in medication(s), and protocol deviations were assessed during all follow-ups. Additionally, at 3- and 6-month follow-up, a physical examination was performed, and cardiac arrhythmia status was assessed via 12-lead electrocardiogram, implantable cardioverter-defibrillator (ICD), or implantable cardiac resynchronization therapy defibrillator (CRT-D) device interrogation (including reading of VT events since prior follow-up).

Subjects were enrolled with an indication for catheter ablation due to sustained monomorphic VT treated with a device shock or anti-tachycardia pacing (ATP) within the past 6 months in the presence of SHD. Patients with left ventricular ejection fraction (LVEF) less than 20%, recent stroke, myocardial infarction, or cardiac surgery were excluded from enrollment. A complete list of inclusion and exclusion criteria is found in Supplement Table 1. The Institutional Review Boards of each participating center reviewed and approved the study protocol. Written informed consent was obtained from all patients in accordance with the Declaration of Helsinki before enrollment.

The DTA generator is a temperature-controlled closed-loop system that modulates power to reach and sustain a programmable temperature set-point (default at 60 °C) and an irrigation pump that operates at 8 ml/min while RF energy is delivered, 4 ml/min nominal. The EnSite cardiac mapping system (Abbott, Inc., Chicago, IL) was used in all procedures to describe the myocardial substrate and navigate the DTA catheter.

In this study, RF ablation was performed in a temperature-control mode for all deliveries, and the temperature set-point was 55 °C or 60 °C, with power output limited to 50 W. RF energy was applied for a maximum of 45 s per target site. When considering a steam pop, the protocol required the catheter to be withdrawn with the tip electrode to be observed for the presence of char or coagulum formation.

Conventional substrate-guided ablation was performed using the Ensite mapping system. In brief, voltage maps defined low voltage substrate during intrinsic rhythm and/or during right ventricular pacing and were compared with scar imaging data using intracardiac echocardiography (ICE) where available. Areas of late potentials and/or local abnormal ventricular activities (LAVAs) were identified with functional substrate mapping techniques used at investigator discretion to define slow conduction zones. Programmed electrical stimulation (PES) was performed to induce VT, and in cases of hemodynamically stable VT, entrainment mapping and VT activation mapping were employed to identify the critical components of the reentry circuit.

The ablation was performed to modify arrhythmogenic substrate, interrupt channels of slow conduction, and/or abolish late potentials or LAVAs. Following ablation, remapping of the substrate was performed to identify and eliminate residual substrate, and PES was performed to assess for the acute outcome. The PES protocol to evaluate acute success was based on local standards of care at each center using up to three extra-stimuli. Acute success was defined as non-inducibility of clinically relevant VT (excluding polymorphic VT, ventricular flutter, and ventricular fibrillation). Post-procedural antiarrhythmic medication maintenance was at the investigator’s discretion, and all patients received a minimum of 90-day oral anticoagulation.

The primary effectiveness endpoint (acute success) was achieved when all clinically relevant VTs (episodes that were documented earlier and responsible for patient symptoms) were terminated and no longer inducible. Classification of clinical relevance of VT was at investigator discretion. The primary safety endpoint was defined as freedom from cardiovascular-specific serious, procedure-related adverse events occurring within 30 days post-ablation. Cardiovascular-specific was defined as the following composite of events, including cardiovascular-related death, cardiac tamponade or perforation, major bleed requiring a transfusion or resulting in a ≥ 20% fall in hematocrit (denoted bleeding complication), myocardial infarction, stroke, transient ischemic attack, thromboembolism, or pulmonary edema. All serious adverse events were adjudicated by an independent event committee consisting of cardiologists experienced in VT ablation.

Endpoints to further characterize the performance of the DTA system included chronic effectiveness (defined as the percentage of patients without documented sustained or treated VT which included arrhythmias that were faster than 100 beats/min for at least 30 s or treated by shock or ATP through 6 months post-ablation). The DTA system was further evaluated by assessing procedure-related endpoints, including the incidence of suspected steam pop formation, presence of char or coagulum formation, total number of RF ablations per procedure, total fluid infused through the assigned ablation catheter, and procedure times (including total procedure time, total RF treatment time, duration of RF ablations, and fluoroscopy time).

Analysis included all enrolled patients where the study device was inserted. Descriptive statistics were used to summarize baseline and procedural characteristics. Specifically, categorical variables were reported as counts and proportions and displayed as percentages (%). For continuous variables, mean ± standard deviations were reported. The primary objectives of assessing acute efficacy and acute safety were calculated using a proportion and 95% exact binomial confidence intervals. The long-term procedural efficacy results were evaluated using Kaplan–Meier curves and estimates of the survival with 95% confidence intervals using the log–log transformation. Analyses were conducted with R version 4.3.1 (R Core Team 2023) and SAS Software, Version 9.4 of the SAS System.