PAUSE-SCD Strengthens Case for First-line VT Ablation Before ICD

August 16, 2021

Catheter ablation isn't as mature a therapy for ventricular tachycardia (VT) as it is for atrial fibrillation (AF), but it may be catching up.

The risk for arrhythmia recurrence or other events fell more than 40% for patients in a randomized trial who underwent ablation for monomorphic VT, compared with no ablation, prior to receiving an implantable defibrillator.

The VT-recurrence risk by itself dropped by one-half in the study, which entered patients with low ejection fractions and varied etiologies of structural heart disease, including more than one-third with nonischemic cardiomyopathy. It was conducted at 11 centers in China, Japan, Korea, and Taiwan that were experienced in AF ablation but not ablation for VT.

Typically, such patients would receive an implantable cardioverter defibrillator (ICD) and stay on medical therapy, with ablation held in reserve as a late-stage palliative option, observed Roderick Tung, MD, University of Chicago Medicine.

But the new findings suggest that a rethink about sudden cardiac death (SCD) management might be in order in such cases, especially in patients with nonischemic cardiomyopathy (NICM), Tung told | Medscape Cardiology.

Perhaps, he said, "ablation needs to be introduced in the dialogue between patients at risk for sudden cardiac death at the time of ICD implantation." A defibrillator alone, even with good medical therapy, "may not be the best choice for these patients."

Tung presented findings from the Pan-Asia United States Prevention of Sudden Cardiac Death (PAUSE-SCD) trial, including 121 randomized patients, during the Heart Rhythm Society (HRS) 2021 Scientific Sessions, which was held virtually and live in Boston.

Of note, the trial featured a registry of patients who underwent VT ablation but turned down an ICD, so could not be randomized. Those 47 patients, Tung said, "appeared to do equally as well" as the patients assigned to ablation plus ICD for the same composite endpoint of VT recurrence, cardiovascular (CV) hospitalization, and death.

The registry cohort, however, differed from the randomized patients in important ways. For example, Tung observed, they were about a decade younger, on average, and had substantially higher left ventricular ejection fractions (LVEF), a greater prevalence of arrhythmogenic right ventricular cardiomyopathy (ARVC), and a lot less ischemic cardiomyopathy.

Still, the registry results suggest a clinical trial of first-line VT ablation in such patients not receiving ICDs "may be justifiable," Tung said.

Analyses by subgroups of the randomized cohort showed a consistent benefit regardless of age, symptom status, presence of diabetes or renal disease, and use of amiodarone or other antiarrhythmics. Antiarrhythmic therapy, Tung said, was discretionary in the trial to mimic real-world practice.

Although the subgroup analysis saw little or no effect of VT ablation on the primary endpoint in patients with NICM, the value for interaction between outcomes and type of cardiomyopathy was not significant, suggesting a consistent beneficial effect by etiology.

Still, there were hints that ablation had more effect on the composite endpoint in patients with LVEF greater than 30% and those with ARVC. The latter group accounted for 35% of the randomized cohort; the other 35% and 30% had ischemic and nonischemic cardiomyopathy, respectively.

The finding in ARVC is probably a first, Tung said, as such patients were not included in the three major preceding VT-ablation trials, that is SMASH-VT, VTACH, and VANISH, all of which entered patients with ischemic cardiomyopathy.

The findings build on those earlier trials but extend the treatment's benefits to patients with NICM, for whom "there's been a dearth of information on early VT ablation," Mina K. Chung, MD, Cleveland Clinic, Ohio, observed as an invited discussant following Tung's presentation of PAUSE-SCD.

That VT ablation provided benefit on top of ICD therapy in NICM, Chung noted, adds a twist to interpretation of the randomized DANISH trial, in which primary-prevention ICDs failed to improve on guideline-directed meds alone in prolonging survival in older, low-LVEF patients with NICM. Although speculation, together the two studies imply that the ICD may not add much to VT ablation in cutting the risk of sudden death in patients with NICM.

Far and away most ICDs are for primary prevention, and few are implanted due to spontaneous or inducible monomorphic VT, which raises questions about broad applicability of the PAUSE-SCD results, said Paul A. Friedman, MD, Mayo Clinic, Rochester, Minnesota, also as an invited discussant.

Moreover, Friedman pointed out, the randomized ablation group's 8% rate of procedural complications—including an aortic dissection, an atrioventricular leaflet prolapse, a case each of left and right ventricular perforation, and a delayed pericardial effusion—wasn't negligible. However, there was only one procedure-related complication in the registry cohort.

The potential for such complications may partly explain why the three previous VT-ablation trials "failed to move the needle" toward more routine, first-line use of the procedure in patients with ICD indications, Friedman proposed.

"When we weigh the calculus, as we're approaching a patient with monomorphic ventricular tachycardia, we have to decide whether to take on that 8% risk of a potentially serious complication" in exchange for fewer bouts of VT, some of which might be manageable with antitachycardia pacing, he said.

PAUSE-SCD assigned 60 patients slated to receive ICDs to first undergo VT ablation, guided by high-resolution electrophysiologic mapping, and 61 others to ICD therapy without ablation. All patients had primary or secondary prevention indications for the devices and structural heart disease, an LVEF less than 50%, and monomorphic VT.

Of those assigned to ablation, 49% experienced the primary endpoint of VT recurrence, CV hospitalization, or death over a median follow-up of 18 months. That compares to 66% of those in the ICD group, for an adjusted hazard ratio of 0.58 (95% CI 0.35 - 0.96, P = .035) favoring patients who had ablation.

The corresponding HR for VT recurrence alone was 0.51 (95% CI 0.29 - 0.90, P = .021). Differences for other components of the primary endpoint were nonsignificant.

Amiodarone usage didn't differ significantly in the ablation and ICD-only groups, at 33% and 36% respectively.

The composite endpoint HR in a speculative comparison of the 61 ICD-only randomized patients and the 47 ablation-only registry patients was 1.88 (95% CI 1.08 - 3.29, P = .019). There was no significant difference between the ablation-plus-ICD group and the registry patients.

Tung touted PAUSE-SCD as the first trial of its kind to be conducted in Asia, and said it suggests the ablation techniques are "teachable" and "generalizable" even at centers expert in AF ablation but without a lot of VT-ablation experience.

PAUSE-SCD was supported by Abbott. Tung discloses receiving speaking fees or serving on advisory boards for Abbott, Biotronik, Boston Scientific, and Medtronic; and receiving grant support from Abbott. Chung had no relevant disclosures. Friedman discloses receiving research grants from Medtronic and Abbott; holding intellectual property rights with AliveCor, Inference, Medicool, Eko, and Anumana; and receiving honoraria or fees for speaking or consulting from Boston Scientific.

Heart Rhythm Society 2021 Scientific Sessions: LBCT01 Late-Breaking Clinical Trials and Registry, Presented July 29, 2021.

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