Thoracoscopic, hybrid, and catheter ablation: comparing apples to oranges to pears

This editorial refers to ‘Long-term outcome of thoracoscopic ablation and radiofrequency catheter ablation for persistent atrial fibrillation as a de novo procedure,’ by J. Kim et al., https://doi.org/10.1093/europace/euad096.

Ablation for persistent (and particularly long-standing persistent) atrial fibrillation (AF) remains challenging, with a successful ablation rate estimated at about 50–60%.¹ Recent data have suggested that thoracoscopic ablation (TA) may be more effective in achieving rhythm control, particularly in longer-standing persistent AF patients.^2,3 However, TA as a stand-alone procedure is not commonly performed because it is more invasive than catheter ablation, requires longer hospitalization, and has never definitively been shown to be better than CA. Therefore, it is considered a therapeutic alternative only for patients who have failed CA or with a high risk of CA failure (recommendation Class II LOEb).⁴ The TA could represent an underutilized therapeutic opportunity for patients with persistent atrial fibrillation, but comparative data on its safety and efficacy compared to CA is scarce and inconsistent.^5,6

In this issue of Europace, Kim et al.⁷ attempt to address the evidence gap by performing a single-centre retrospective study analysing the incidence of AF recurrence and the composite endpoint of death, stroke, and heart failure hospitalization after performing TA as a stand-alone procedure compared to radiofrequency CA, and hybrid ablation in patients with persistent AF. Among 575 patients included, 281 (49%), 228 (40%), and 66 (11%) underwent TA, CA, and hybrid ablation, respectively. The mean follow-up was 43.9+/−30.4 months. Most of the hybrid ablation data were older (between 2012 and 2015). There were substantial differences in the baseline characteristics of the three patient groups. The TA and hybrid groups have significantly more patients with long-standing persistent AF (62% and 39%) compared to the CA group (33%). The duration of AF diagnosis was also longer in the TA and hybrid groups, and the left atrial volume index was also much larger (51 and 48 mL/m²) compared to the CA group (42 mL/m²). Comparing the three groups, there were no differences in atrial arrhythmia recurrence.

To account for the baseline differences, the authors then propensity matched the three groups using a stratified Cox regression analysis based on all the baseline variables. This left 306 patients for comparison. In this subset, there was still no significant difference in atrial arrhythmia recurrence (51.4% vs. 62.5%) for TA and CA, respectively. Total procedural adverse events were also reported as similar with 7% for TA compared to 5% for CA. Similar outcomes were described for hybrid ablation. The authors thus concluded that TA, CA, and hybrid ablation have comparative efficacy and safety outcomes.

The authors should be congratulated that they have attempted to address the under-studied topic of comparing surgical and catheter ablation. Even fewer studies have attempted to compare surgical, catheter, and hybrid techniques. It must be appreciated that this publication also addressed an understudied population of patients with advanced persistent AF, including a high percentage of long-standing persistent patients (47%). The number of patients studied overall was substantial, and the follow-up was very long compared to most ablation studies (nearly 4 years). Although monitoring was intermittent, it was performed rigorously with a minimum of three 24-hour Holters in the first year and bi-annually thereafter. For all these reasons, the study is an important addition to the ablation literature.

However, the study also has several important limitations. This was a retrospective analysis, not a randomized trial, and there was obviously selection bias in the patients chosen to receive each type of ablation strategy. This is clearly demonstrated in the important baseline differences of the three groups. Although the authors attempted to correct for this using propensity score matching, this technique can never correct for all the differences in the groups and can never fully eliminate selection bias. Although the matched patients had similar left atrial volumes and incidences of long-standing persistent AF, other non-measurable biases in the patients chosen are likely to persist. In this light, the similar success rate achieved by TA and hybrid ablation could be considered a ‘success’ since similar freedom from atrial arrhythmia was achieved in a more diseased sub-group of patients compared to CA.

The biggest limitation of this study, however, is that the ablation targets and endpoints used in the three groups were very different. In addition to pulmonary vein isolation (PVI), the TA group received posterior wall isolation and vein of Marshall dissection in about 97% of the cases. Furthermore, ganglionated plexi (GP) was ablated in 63%, superior vena cava (SVC) isolation was performed in 43%, and the left atrial appendage (LAA) was ligated in 97%. In the CA group, patients mostly received PVI, but extra lines could be added at the physician's discretion (roof line 46%, inferior line 38%, mitral line 42%, and SVC isolation 20%), and there was no consistent posterior wall or LAA isolation. For the hybrid group, the approach was again different, since patients had PVI with most receiving posterior wall, ligament of Marshall, and GP ablation along with 100% LAA ligation. With so many permutations and combinations of ablation targets used in these three groups, how can they realistically be compared for outcomes? The graphical abstract of the manuscript is somewhat misleading since the CA procedure illustrated was not consistently performed in all patients. Furthermore, how do we know how any of these techniques would have compared to a simpler, wide-antral PVI procedure alone?

There is also not much clarity in the acute endpoint for each of the targeted ablation regions. For PVI, it seems that entrance block was assessed by a circular catheter in the CA and hybrid groups, but in the TA group, it is just stated that pacing was used to confirm PVI—was this pacing within the vein (exit block), pacing outside of the vein (entrance block), or just failure to capture venous tissue? The GPs were identified by high frequency stimulation, but how was elimination of GP input confirmed? Moreover, the authors state that either CT or transesophageal echo was used to confirm LAA exclusion, but the results are not reported. Finally, there is no detail on how block was demonstrated across the linear ablations in any group. It is perhaps not surprising then that the durability of these lesion sets was not optimal. One of the supposed advantages of surgical ablation is the ability to achieve more durable lesions because of direct visualization of both the structures targeted and the ablation tools used. Indeed, the authors claim that PV reconnection rates in patients undergoing repeat ablation for AA recurrence were much lower in the TA and hybrid groups (about 8%) compared to the CA group (33%). Yet, in the 46 patients of the hybrid group who underwent posterior wall isolation during the surgical part of the procedure, durable isolation of the wall was demonstrated in only 16 (35%) at the time of the CA part of the procedure. Clearly, many of the surgical lines created were not durable. The creation of incompletely blocked lines has been previously shown to be pro-arrhythmic.⁸

Finally, the authors conclude that the complication rates of the three groups were comparable. It is true that in terms of overall percentages, there were no statistically significant differences amongst the groups. However, the severity of the complications was not comparable. In the surgical groups combined, the numerical incidence of surgical wound infection (0.6%), stroke (0.9%), pericarditis (5%), and atrioesophageal fistula (0.3%) were all higher than in the CA group. From the patient point of view, both surgical procedures are more invasive and require more recovery. From a health system point of view, the surgical procedures also required significantly longer hospitalizations of 9 and 12 days for the TA and hybrid procedures, respectively, compared to 3 days for CA (P < 0.001).

As limited as this study is, Kim et al. should be congratulated on addressing an important topic in AF ablation. Their work should hopefully inspire more controlled, and hopefully randomized, comparisons in surgical and catheter ablation in patients with advanced persistent AF. Meticulous study design will be necessary for these future studies to avoid comparing apples to oranges to pears.

Funding

None declared

References

Author notes