Circulation June 21, 2022

Does Timing of Ventricular Tachycardia Ablation Affect Prognosis in Patients With an Implantable Cardioverter Defibrillator? Results From the Multicenter Randomized PARTITA Trial

Paolo Della Bella, Francesca Baratto, Pasquale Vergara et al.

Bottom Line

In patients with ischemic or nonischemic cardiomyopathy, performing immediate ventricular tachycardia ablation after a first appropriate ICD shock significantly reduces the composite risk of death or heart failure hospitalization compared to standard medical therapy.

Key Findings

1. Among the 47 randomized patients, the primary composite endpoint of death or heart failure hospitalization occurred in 4% (1 of 23) of the early ablation group versus 42% (10 of 24) of the standard therapy group (HR 0.11; 95% CI 0.01–0.85; P=0.034).

2. Early VT ablation resulted in a significant reduction in all-cause mortality, which occurred in 0% of the ablation group compared to 33% of the control group (P=0.004).

3. Recurrent ventricular tachycardia treated by ICD shocks was significantly lower in the immediate ablation arm (9% vs 42%; P=0.039).

4. Heart failure hospitalizations were numerically lower in the ablation arm, though the difference did not reach statistical significance (4% vs 17%; P=0.159).

5. The trial met Bayesian adaptive design criteria for overwhelming efficacy and was terminated early at the first interim analysis.

Study Design

Design

RCT

Open-Label

Sample

Patients

Duration

24.2 mo

Median

Setting

Multicenter, Europe

Population Patients with ischemic or nonischemic dilated cardiomyopathy and an ICD who received a first appropriate ICD shock during an initial observational run-in phase (N=517).

Intervention Immediate catheter ablation of ventricular tachycardia, performed within 2 months of the first appropriate ICD shock.

Comparator Continuation of standard medical therapy (deferred ablation), with amiodarone explicitly prohibited unless treating documented atrial tachyarrhythmias.

Outcome Composite of death from any cause or hospitalization for worsening heart failure.

Study Limitations

• Small randomized sample size (N=47) due to early trial termination, which limits the power for subgroup analyses and precision of the effect size.

• Trials stopped early for benefit carry an inherent risk of overestimating the true magnitude of the treatment effect (truncation bias).

• Open-label study design, although the potential for bias was mitigated by the use of objective hard endpoints like all-cause mortality.

• The strict prohibition of amiodarone for ventricular arrhythmias, while providing a clean methodological comparison, may not reflect standard real-world practice where it is frequently utilized.

Clinical Significance

The PARTITA trial represents a critical paradigm shift in electrophysiology. By demonstrating a profound survival benefit, it strongly advocates against reserving VT ablation solely as a 'last-resort' bailout for electrical storm. Instead, it establishes early catheter ablation—specifically following a first appropriate ICD shock—as a standard proactive intervention to halt the highly detrimental cycle of recurrent shocks and progressive heart failure.

Historical Context

Historically, VT ablation was reserved for patients who had failed escalating antiarrhythmic drug therapies, a strategy largely supported by the 2016 VANISH trial. Prior attempts at 'prophylactic' ablation before any ICD shocks (e.g., SMS, BERLIN VT) showed mixed results without a definitive survival advantage. PARTITA was unique in its two-phase design, identifying the exact moment of the first ICD shock as the pivotal inflection point where the prognostic trajectory worsens, and proving that intervening at this specific time confers a dramatic mortality benefit.

Guided Discussion

High-yield insights from every perspective

Med Student

Medical Student

How does the occurrence of ventricular tachycardia and subsequent ICD shocks contribute pathophysiologically to the progression of heart failure and increased mortality in patients with cardiomyopathy?

Key Response

This tests the foundational understanding that while ICD shocks terminate lethal arrhythmias, the preceding hemodynamic compromise during VT, combined with myocardial stunning, cellular injury, and the massive sympathetic surge from the shock itself, directly accelerates myocardial dysfunction and heart failure progression.

Resident

Based on the PARTITA trial, how should your management strategy evolve for a patient with ischemic cardiomyopathy who presents to the clinic having just experienced their first appropriate ICD shock for VT, compared to the traditional step-up approach?

Key Response

Residents must recognize a paradigm shift: instead of automatically starting or escalating antiarrhythmic drugs like amiodarone and waiting for recurrent shocks, early referral for VT ablation after the first shock is now shown to significantly reduce the composite risk of death or heart failure hospitalization.

Fellow

The PARTITA trial included both ischemic and nonischemic cardiomyopathy patients. Given the distinct arrhythmogenic substrates between these etiologies, how do the technical approaches and expected ablation success rates differ, and does the trial support universal early ablation for both?

Key Response

Fellows should understand that ischemic VT typically involves subendocardial scar accessible via standard endocardial approaches, whereas nonischemic VT often involves mid-myocardial or epicardial substrates that are technically challenging. Evaluating subgroup data in trials like PARTITA is crucial to determine if the prognostic benefit applies equally despite these procedural differences.

Attending

Historically, VT ablation was considered a palliative procedure for symptom control and shock reduction. How does the PARTITA trial reframe the goal of VT ablation as a disease-modifying intervention, and what are the logistical or health-system barriers to implementing a first-shock ablation protocol in your practice?

Key Response

Attendings must integrate new evidence into system-wide practice. The PARTITA trial demonstrates that early ablation improves hard outcomes (mortality and HF hospitalization), necessitating a shift to view ablation as disease-modifying. However, implementing this requires adequate EP lab capacity, early referral pathways, and overcoming institutional inertia.

Scholarly Review

Critical appraisal through the lens of expert reviewers and guideline development

PhD

The PARTITA trial was stopped early for efficacy regarding its primary composite endpoint. What are the statistical and methodological risks associated with early termination for benefit in relatively small trials, and how might this impact the estimated magnitude of the treatment effect?

Key Response

Tests advanced understanding of trial methodology. Trials stopped early for benefit (truncation bias) often overestimate the true treatment effect due to random high-side fluctuations in the data at the time of interim analysis, which requires careful interpretation when calculating sample sizes for future studies.

Journal Editor

When critically appraising the PARTITA trial, how might variations in the optimization of guideline-directed medical therapy (GDMT) and antiarrhythmic drug use in the control arm threaten the internal validity of the ablation survival benefit?

Key Response

A rigorous editor would scrutinize the control arm. If patients receiving standard therapy did not receive maximum tolerated GDMT or optimal antiarrhythmic management post-shock, the observed benefit in the ablation arm might be exaggerated, reflecting inadequate control treatment rather than an intrinsic survival benefit of ablation.

Guideline Committee

Current guidelines (e.g., 2017 AHA/ACC/HRS) recommend VT ablation primarily after recurrent shocks or as a Class IIa recommendation after a first shock in ischemic patients. Does the PARTITA trial provide sufficient evidence to elevate early ablation post-first shock to a Class I recommendation for all ICD patients, or are larger confirmatory trials required?

Key Response

Evaluates the threshold for guideline modification. While PARTITA shows impressive reductions in mortality and HF hospitalization, guideline committees must weigh whether a single trial stopped early for efficacy is robust enough to mandate a Class I recommendation universally, or if it merely strengthens the current Class IIa recommendation pending larger multicenter validation.

Clinical Landscape

Noteworthy Related Trials

2007

SMASH-VT Trial

n = 128 · NEJM

Tested

Prophylactic catheter ablation

Population

Patients with prior MI and VF or hemodynamically unstable VT receiving an ICD

Comparator

ICD placement alone

Endpoint

Survival free from appropriate ICD therapy

Key result: Prophylactic ablation significantly reduced the incidence of appropriate ICD therapies compared to ICD placement alone.

2010

VTACH Trial

n = 110 · Lancet

Tested

Prophylactic catheter ablation before ICD implantation

Population

Patients with prior MI, reduced LVEF, and stable VT

Comparator

ICD implantation alone

Endpoint

Time to first recurrence of VT or VF

Key result: Prophylactic ablation significantly prolonged the time to recurrent VT or VF compared to ICD alone.

2016

VANISH Trial

n = 259 · NEJM

Tested

Catheter ablation

Population

Patients with ischemic cardiomyopathy and VT despite antiarrhythmic drugs

Comparator

Escalated antiarrhythmic drug therapy

Endpoint

Composite of death, VT storm, or appropriate ICD shock

Key result: Catheter ablation significantly reduced the primary composite endpoint compared to escalating antiarrhythmic drugs.

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