While the currently used point by point ablation is reasonably effective, it remains complex and time consuming prompting search for simpler but equally effective strategies. High density mesh ablation (HDMA) catheter which allows for single shot ablation and cryoablation are some of the strategies being evaluated in this regard. Initial studies with the 30 mm HDMA catheter were disappointing, highlighting the need for further refinement in design(2).

In the current study, De Greef et al. compare the efficacy of the more recent 35 mm HDMA catheter (larger and more flexible) vis-à-vis the 30 mm HDMA catheter(1).  This was a single center trial involving 64 patients with paroxysmal Atrial Fibrillation (AF) resistant to at least 1 anti-arrhythmic drug (AAD). Twenty six patients were treated with the 30 mm catheter and 38 were treated with 35 mm catheter. Follow up was adequate and included symptom based, EKG and Holter monitoring at 1, 3 and 6 months.

Both groups were similar at baseline with respect to duration of AF, age and use of AAD. Acutely, HDMA was successful in 79% of pulmonary veins (PV) using 30 mm catheter and 97% of PV using the 35 mm catheter. Complete isolation of all 4 PV was achieved in 54% and 89% of patients respectively. There was no significant difference in th­­e procedure, catheter dwell or fluoroscopy times. Ablation time was shorter with the 35 mm catheter. There were no major complications except for an isolated case of cardiac tamponade requiring emergent pericardiocentesis. Need for touch up ablation was significantly higher in the 30 mm group (21/26 vs 3/38). At 6 month follow up 5/26 (19%) and 7/38(18%) patients respectively were free from AF (symptomatic or asymptomatic) without use of AAD anti-arrhythmic drugs. Another 5 patients (19%) in the 30 mm group and 8 (21%) patients in the 35 mm group remained free of AF with AAD. Repeat ablation was done in 9, 10 patients respectively in the 2 groups and >2/3 of PV were noted to be reconnected.

The major finding of this study is the superior acute efficacy of the 35 mm HDMA catheter over the 30 mm catheter. Furthermore, this study reinforces the safety of the HDMA catheter. However, despite the excellent acute results, the midterm results were extremely disappointing. Less than 20% in either group were free from AF at 6 month follow up despite the low risk study population (paroxysmal AF, mild left atrial enlargement, low frequency of structural heart disease and preserved left ventricular systolic function in the majority). Small and selected study population, lack of systematic randomization and blinded outcome assessment are notable limitations of the study. 

In summary, durable and complete electrical pulmonary vein isolation (PVI) remains the most critical factor determining the long term success of any ablative strategy for AF. Despite excellent acute efficacy and safety, the 35 mm HDMA catheter remains ineffective in the long term. Potential reasons for this could be poor contact resulting in sub optimal lesions during ablation. Alternatively, inadequate circumferential recordings could create a false sense of security despite lack of complete electrical isolation. It remains to be seen whether further refinements in catheter size / design and technique can help us achieve the elusive goal of durable electrical PVI in a single shot.

Reference:

1.       De Greef Y, Tavernier R, Duytschaever M, Stockman D. Pulmonary vein isolation with the 30 and 35 mm high-density mesh ablator. Europace. 2010 Oct;12(10):1428-34.

2.       Steinwender C, Hönig S, Leisch F, Hofmann R. One-year follow-up after pulmonary vein isolation using a single mesh catheter in patients with paroxysmal atrial fibrillation. Heart Rhythm. 2010 Mar;7(3):333-9.