By Cara Pellegrini, MD
Assistant Professor of Medicine, University of California San Francisco; Cardiology Division, Electrophysiology Section, San Francisco VA Medical Center
Dr. Pellegrini reports no financial relationships relevant to this field of study.
SYNOPSIS: Acute and long-term success rates with ventricular tachycardia ablation in patients with coronary artery disease are relatively high with an acceptably low complication rate.
SOURCE: Marchlinski FE, et al. Long-term success of irrigated radiofrequency catheter ablation of sustained ventricular tachycardia. J Am Coll Cardiol 2016;67:674-683.
The role of ablation in the management of sustained monomorphic ventricular tachycardia (VT) has been somewhat unclear. Should clinicians perform it prophylactically in those with coronary heart disease, as the SMASH-VT or VTACH studies might advocate? Or is it a treatment of last resort — the classic practice? Perhaps its role is somewhere in between. Does it have a lasting effect, maybe even a mortality benefit, or are any salutatory effects transient in nature? What objective evidence exists demonstrating that it affects quality of life, hospitalizations, or other intermediate outcomes?
The multicenter NaviStar ThermoCool Catheter for Endocardial RF Ablation in Patients With Ventricular Tachycardia (THERMOCOOL VT) trial evaluated the use of irrigated radiofrequency catheter ablation for recurrent VT in drug-refractory post-myocardial infarction (MI) patients, and gained FDA approval for the open-irrigation ablation catheter for this purpose. This prospective, non-randomized, single-arm, post-approval study furthered those findings, examining long-term safety and effectiveness of ablation among patients with ≥ 4 sustained VT episodes, two episodes within 2 months, incessant VT, or spontaneous symptomatic VT despite antiarrhythmic medications or implantable cardioverter defibrillator (ICD) intervention. There were 249 patients. They were overwhelmingly male and Caucasian, with a mean age of 67.4 years. The vast majority had coronary artery disease and a previous MI and 95% had an ICD in place, with 25% sporting a biventricular pacemaker defibrillator. One-quarter had VT ablation performed previously. Operators were given a fair bit of flexibility in how they conducted the ablation and in the management of medications and ICD settings thereafter. The acute procedural endpoint was assessment of inducibility of the targeted VT, but other efficacy outcomes, including mortality, were collected for 3 years post-ablation. The primary safety endpoint was cardiovascular-specific adverse events within 7 days of the ablation.
Immediate success was high, with 75% of patients showing noninducibility of the targeted VT at the end of the procedure. This occurred with a complication rate of 3.9%, which met the protocol-established performance criteria. There were no strokes, and the three early deaths that occurred were preceded by recurrent VT, suggesting the procedure was sometimes insufficient to prevent death, but likely not its direct cause. Nearly two-thirds of patients remained VT-free at 6-month follow-up. A significant decrease in ICD therapies (shocks and ATP), amiodarone use, and hospitalizations echoed this. There was a significant improvement in anxiety scores and a trend toward improvement in depression levels. The mortality rate at 3 years was 25.4%. The authors concluded that the acute and long-term success rates with ablation for VT associated with coronary artery disease are high, and that the complication rate is acceptably low.
COMMENTARY
This study is the first large-scale study of VT ablation to demonstrate quality of life improvements and a sustained decrease in cardiac-related hospitalizations. The immediate success rate, in terms of noninducibility of targeted VT, and the 6-month recurrence-free percentage are relatively high, particularly considering the disease burden pre-ablation. The complication rate compares at least equivalently, if not favorably, to the widely performed atrial fibrillation ablation procedure. The significant decline in amiodarone use and shock burden hints at a potential for downstream benefits. Yet, the 3-year mortality rate in this study is nearly identical to that from early reports of patients treated with ICD only.
When interpreting the results of this study, there are several cautions to consider, beyond its nonrandomized comparison design, that could explain why a “hard” outcome like mortality didn’t show the same positive trajectory as the “softer” outcomes. While nearly all patients had an ICD interrogated at the 6-month follow-up visit to assess VT burden, many study outcomes relied on patient self-reporting at yearly telephone interviews, which can be subject to recall bias and could certainly have underestimated asymptomatic VT events (including those treated with ATP therapy). There were many patients lost to follow-up (26% of patients were not part of the 6-month effectiveness cohort, and 43% did not contribute to 3-year data); if those lost to follow-up were more ill, the results could look better than reality. The relative homogeneity of the study population detracts from generalizability. Decline in amiodarone use over time may track with arrhythmia burden reduction, as suggested, but also could be partly due to development of intolerances or side effects over time, as commonly occurs with this drug. Finally, carefully note that the study sponsor (the ablation catheter manufacturer) performed all statistical analyses and managed the data.
Despite these methodological weaknesses, this study is yet another addition to the literature supporting a more prominent role for VT ablation among those with coronary heart disease. Indeed, the beneficial effects of VT ablation just as easily might have been underestimated due to the biases above. Additionally, long-term effectiveness and survival may have been curtailed by the more advanced disease burden of the patients in this study. The relatively low procedural complication rate is remarkable and likely minimally affected by the concerns above. Notably, the operators in this multicenter study were highly experienced, and perhaps access to high volume centers and providers is the greatest obstacle to implementation of VT ablation earlier in the disease course.
