How do the CABANA trial and the CASTLE‑AF trial differ in patient selection and clinical outcomes for atrial fibrillation?

CABANA vs CASTLE-AF: Key Differences in Patient Selection and Clinical Outcomes

CASTLE-AF demonstrated mortality and heart failure hospitalization benefits in a highly selected heart failure population with reduced ejection fraction, while CABANA failed to show mortality benefit in its broader, less sick atrial fibrillation population on intention-to-treat analysis.

Patient Selection: Fundamentally Different Populations

CASTLE-AF: Sick Heart Failure Patients

• Enrolled 363 patients with severe heart failure (HFrEF) with NYHA class II-IV symptoms and LVEF ≤35% 1
• All patients had implanted defibrillators (dual-chamber ICD or CRT-D devices), indicating high-risk cardiac status 1, 2
• Included both paroxysmal and persistent AF, with 70% having persistent or long-standing persistent AF 1
• Median age and selection bias: Younger, less severely affected patients with lower peri-procedural risk were preferentially enrolled 1
• Patients with LVEF <25% showed minimal benefit from ablation (HR 1.36), while those with LVEF ≥25% had substantial benefit (HR 0.48) 1

CABANA: Broader AF Population Without Severe Heart Failure

• Enrolled 2,204 patients with new-onset or untreated AF who were ≥65 years old or younger with stroke risk factors 1
• Only 35% (778 patients) had heart failure, and of those with available ejection fraction data, only 9.3% had LVEF <40% 3
• Most patients had preserved left ventricular function and were clinically stable 3
• 43% had paroxysmal AF in the rhythm monitoring substudy 4
• Included patients with minimal symptoms and lower overall cardiovascular risk compared to CASTLE-AF 1

Clinical Outcomes: Divergent Results Explained by Population Differences

CASTLE-AF: Impressive Hard Endpoint Benefits

Mortality and hospitalization benefits were striking 1, 2:

• Primary composite endpoint (death or HF hospitalization): 28.5% vs 44.6%, HR 0.62 (P=0.007), NNT=8.3 1
• All-cause mortality: 13% vs 25%, HR 0.53 (P=0.01) 1, 2
• Cardiovascular death: 11% vs 22%, HR 0.49 (P=0.009) 1
• Heart failure hospitalization: 21% vs 36% 1
• LVEF improvement: +8.0% vs +0.2% at 5 years (P=0.005), with 68% achieving LVEF >35% 1

Critical caveat: The mortality benefit did not emerge until after 3 years of follow-up, emphasizing the need for long-term rhythm control 1

AF burden matters more than recurrence: A post-hoc analysis showed that AF burden <50% at 6 months post-ablation predicted improved outcomes (HR 0.33 for primary endpoint, HR 0.23 for mortality), while any AF recurrence >30 seconds did not predict outcomes 5

CABANA: No Mortality Benefit in General AF Population

Intention-to-treat analysis failed to show benefit 1:

• Primary composite endpoint (death, disabling stroke, serious bleeding, cardiac arrest): 8.0% vs 9.2%, HR 0.86 (P=0.3) - NOT significant 1
• Per-protocol analysis showed benefit: HR 0.67 (P=0.006) for primary endpoint and HR 0.60 (P=0.005) for all-cause mortality, but this reflects treatment received rather than randomization 1

Heart failure subgroup analysis showed benefit 3:

• In the 778 CABANA patients with clinically diagnosed heart failure (most with preserved EF):
  • Primary composite endpoint: HR 0.64 (95% CI 0.41-0.99) - 36% relative reduction 3
  • All-cause mortality: HR 0.57 (95% CI 0.33-0.96) - 43% relative reduction 3
  • Quality of life improvement: AFEQT summary score difference of 5.0 points favoring ablation 3

AF recurrence was significantly reduced 4:

• Any AF recurrence: HR 0.52 (P<0.001) - 48% reduction 4
• Symptomatic AF: HR 0.49 (P<0.001) - 51% reduction 4
• AF burden at 12 months: 6.3% in ablation vs 14.4% in drug therapy (P<0.001) 4

Rhythm Control Success: Both Trials Showed Efficacy

CASTLE-AF Rhythm Outcomes

• 63% maintained sinus rhythm at 5 years in the ablation group 1
• 50% AF recurrence rate in patients who completed 5-year follow-up after ablation 1
• Average 1.3 procedures per patient 1
• Only 53% received additional left atrial lesions beyond pulmonary vein isolation, despite 70% having persistent AF 1

CABANA Rhythm Outcomes

• Significant reduction in AF recurrence over 60 months regardless of baseline AF pattern 4
• AF burden dramatically reduced across all follow-up timepoints 4

Medical Therapy Comparators: Different Control Arms

CASTLE-AF Control Arm

• 70% opted for rate control strategy (predominantly beta-blockers, digoxin) 1
• 30% received rhythm control (predominantly amiodarone) 1
• This reflects clinical reality that antiarrhythmic drugs have poor efficacy in severe heart failure 1

CABANA Control Arm

• Patients received either rate or rhythm control based on physician and patient preference 1
• More aggressive medical therapy compared to CASTLE-AF 1

Quality of Life: Consistent Improvements with Ablation

Both trials showed QOL benefits 1, 3:

• CASTLE-AF: Functional capacity and QOL significantly improved with ablation 1
• CABANA: AFEQT and MAFSI scores favored ablation, with mean differences of 5.0 and -2.0 points respectively 3
• Frail patients in CABANA derived greater QOL benefit from ablation (MAFSI frequency score difference -1.58, P<0.001) despite no difference in clinical outcomes 6

Generalizability and Real-World Application

CASTLE-AF has limited generalizability 1:

• Only 7.8% of real-world AF/HF patients would meet CASTLE-AF eligibility criteria 7
• Selection bias toward younger, less sick patients limits applicability 1
• Real-world data shows more modest benefit (HR 0.82 in trial-eligible patients) compared to the trial 7

CABANA enrolled a broader population but still had limitations 1:

• High crossover rates (27.5% in drug arm crossed to ablation, 9.2% in ablation arm never received ablation) weakened intention-to-treat analysis 1
• Results suggest ablation benefits are most pronounced in sicker patients with heart failure 3

Clinical Implications from Current Guidelines

The 2024 ESC Guidelines recognize catheter ablation as a Class IIa indication for selected HFrEF patients to improve outcomes, based primarily on CASTLE-AF data 1

The 2024 ACC/AHA Guidelines emphasize that catheter ablation should be considered first-line or second-line for symptom reduction and quality of life improvement, with mortality benefit established only in specific HF populations 1

The European Heart Journal consensus states that AF ablation in HFrEF should be performed in experienced centers with careful patient selection, prioritizing those with LVEF ≥25%, less advanced heart failure, and evidence of AF-mediated cardiomyopathy 1

Bottom Line: Choose Ablation Based on Heart Failure Severity

For patients with AF and severe HFrEF (LVEF ≤35%, NYHA II-IV): Catheter ablation reduces mortality and heart failure hospitalizations based on CASTLE-AF, particularly if LVEF ≥25% 1, 2

For patients with AF without severe heart failure: Catheter ablation significantly improves AF burden and quality of life but does not reduce mortality based on CABANA's intention-to-treat analysis 1, 4, 3

The key difference: CASTLE-AF studied a sicker population where rhythm control could reverse AF-mediated cardiomyopathy and prevent heart failure progression, while CABANA studied a healthier population where the primary benefit was symptom control 1, 3