DISCUSSION
This study documents the long-term outcomes of a C-ABL strategy in a population of IHD and NICM patients. In our multicentric real-world analysis, a C-ABL in patients undergoing a redo ablation was associated with increased overall survival and VT-free survival. Direct comparison of clinical outcomes between a NC-ABL and a C-ABL strategy for VT ablation has been limited by heterogeneous patient characteristics and lack of abundant comparative randomized trials4,5. ES at presentation, LVEF, NYHA class III/IV, IHD and C-ABL have been identified as independent predictors of VT-free survival, cardiovascular and all-cause mortality in our study. IHD patients with previous myocardial infarction and low ejection fraction are at an increased risk of VT and sudden cardiac death1,3, and international guidelines recommend ICD implantation1. However, recurrent VT and ES are associated with increased mortality even in patients with an ICD2. This may be related to a progressive deterioration of cardiac function resulting from frequent shocks, chronic low-cardiac output, and AAD therapy toxicity8. Several studies have shown catheter ablation superiority compared to AADs for VT treatment, with a success rate of 51% to 67%9. The VANISH randomized controlled trial10 showed that in patients with IHD and an ICD with VT despite AAD therapy, VT ablation had a lower rate of the composite primary outcome of death, ventricular tachycardia storm, or appropriate ICD compared to AAD therapy escalation. An endocardial-only ablation frequently does not eliminate all the re-entrant circuits in IHD, which may lead to relapse11. Also, the development and widespread use of reperfusion therapies in the last decades led to a higher number of patients with nontransmural necrosis and heterogeneous infarcted tissues. These scars may have multiple slow conduction channels with epicardial exit sites12, providing the rationale for a C-ABL approach. Current guidelines have an IIB class recommendation for the epicardial ablation in IHD after a failed endocardial ablation3. However, there is an important knowledge gap. Regarding this cardiomyopathy, Di Biase et all4showed that extensive scar homogenization with a combined endocardial and epicardial approach in a first ablation procedure was linked to increased VT-freedom in patients with ES. One possible explanation for their findings is a greater amount and complexity of the arrhythmic substrate in IHD with ES presentation, which can justify an initial combined approach. Izquierdo et al13 showed that a first combined endo-epicardial procedural was linked to fewer hospitalizations but failed to show an increase in survival free of VT. Sarkozy et all14 showed that two-thirds of the patients selected for epicardial mapping after a failed endocardial ablation had epicardial arrhythmic substrate and Acosta et all15 showed that an endocardial ablation in patients with transmural MI was associated with an increased risk of recurrence. Tung et all16 showed better VT-free survival for IHD patients after a combined endo-epi ablation vs. endocardial only, partly explained by the high number of previous endocardial ablation (80%) in their series. In our study, the arrhythmic relapse reduction was only verified in the population that underwent more than one procedure. Our analysis showed an increase in VT-free survival and a decrease in all-cause death with a C-ABL in IHD patients with multiple ablations, and to the best of our knowledge, this is the first individual study to show this survival benefit. A recent meta-analysis17was also consistent with our findings, showing a reduction in all-cause mortality and VT-recurrence in IHD. These combined findings suggest that an epicardial ablation is probably the most effective strategy for VT elimination and survival improvement after an initial failed endocardial ablation in IHD. VT arrhythmogenic substrate differs from NICM and IHD patients. An analysis of 445 patients undergoing VT ablation showed that some NICM VT’s critical isthmi can’t be identified in either endo and epicardium, possibly due to mid myocardial location18. Current guidelines suggest an initial endocardial ablation, or possibly a first epicardial ablation if the arrhythmia has characteristics pointing to an epicardial origin18, and NICM patients have shown VT-free survival from 41% to 70% at 1-year after the procedure19. The worse outcomes of VT ablation in NICM patients appear to be related to an intramural or epicardial localization of the myocardial isthmus20. The acute success and VT-freedom after catheter ablation in NICM patients are associated with a reduction in mortality and heart transplantation19. To the best of our knowledge, this is the first study to show an improvement in VT-free survival and reduction of all-cause death with a C-ABL compared to a NC-ABL in NICM patients undergoing a redo procedure. The fundamental PS matching principle is the homogenization of a chosen set of covariates according to a dependent variable, in a pseudo-randomized controlled design7. This statistic technique is of particular interest in this setting since we are presented with 2 heterogeneous groups with several potential confounding variables. PS matching allows the reduction of the impact of other independent variables in the outcome analysis, strengthing the findings of the initial analysis and allowing a more accurate assessment of the safety outcomes. Serious and potentially life-threating complications can be associated with the epicardial ablation technique11,14,17. Common procedure-related complications are right ventricular puncture, subxiphoid bleeding, pericardial effusion, cardiac tamponade, coronary arteries lesion, acute myocardial infarction, thoracic artery lesion, complete heart block, phrenic nerve lesion, abdominal organ puncture, and stroke. Our population has a high burden of traditional cardiovascular risk factors (Table 1), and there was a considerable amount of ES at presentation. Although this was a high-risk population, our complication rate was comparable to the current reports in the literature. In this real-world population analysis, the C-ABL strategy had a similar safety profile when compared to the NC-ABL approach, despite that the combined strategy featured a much higher number of epicardial ablations. While we can not completely exclude the influence of underpowering in the procedural complication rate analysis, the potential benefit of this combined ablation appears to outweigh the potential risks.