Our study indicates that HPSD lesions applied with force-sensing catheters achieve the bidirectional CTI block in the shortest time. Our data also show that externally irrigated catheters with force sensing can accomplish a set of effective lesions faster than non-irrigated and internally irrigated catheters.

Our data suggest similar acute effectiveness of all catheters in achieving CTI block. Past studies comparing the efficacy of gold, platinum-iridium, and externally irrigated-tip catheters showed mixed results, with either equivalency of effectiveness and an advantage with gold-tip catheters and irrigated catheters, in the acute success of the procedure [7, 8]. Furthermore, the reported rate of failure to achieve CTI block of 5% with gold and platinum-iridium-tip catheters was similar to our data. The success of 8-mm and 10-mm-sized catheter tips has been demonstrated in multiple trials over the past 10 years. A study performed by Ventura et al. confirmed this by showing successful ablation using 8-mm catheter tips in patients resistant to ablation using 4-mm catheter tips [8]. Shorter procedure times are reported with the larger-tip ablation catheters than standard 4- or 5-mm-tip ablation catheters, with comparable or greater efficacy, no significant increase in complications, and improved quality of life. Larger-tip ablation electrodes do require the use of higher-power radiofrequency generators up to 100 W. A study comparing the efficacy of 8- and 10-mm ablation catheters and high energy (100 W) showed that the actual number of ablations required (i.e., 10 vs. 14) as well as total lesion time was less for the 10-mm-tip catheter, however with almost 7% failure to achieve CTI block [9]. However, it is not unusual to experience difficulty in delivering full power during those ablations due to inadequate catheter cooling, particularly in areas of CTI indentations where blood flow is restricted.

Irrigated-tip catheter technology was designed to cool the electrode tip, prevent excessive temperatures at the electrode tip–tissue interface, and thus allow continued delivery of RF current into the surrounding tissue. This ablation system creates larger and deeper ablation lesions and minimizes steam pops and thrombus formation. Compared to small-tip catheters, irrigated-tip ablation catheters require fewer lesions to achieve CTI block and shorten the procedure [10].

Irrigated catheters can be divided into open and closed types of irrigation. In open irrigation, there are holes in the tip of the catheter through which (typically) normal saline is pumped. Closed-irrigation catheters have a system within the tip that allows 5% glucose solution to pass through the interior and then be removed. Yokoyama et al. compared a closed-irrigation catheter (Chilli®, Boston Scientific, Natick, MA, USA) versus an open-irrigation catheter (ThermoCool) for RF lesion morphology and depth, thrombus formation, and occurrence of steam pops in a dog model [11]. It was found that the resultant ablation lesion was similar to closed- and open-irrigated electrodes yet more thrombus formation on the electrode with closed irrigation [12]. Our data confirm the equivalent performance of closed- and open-irrigated catheters in AFL ablation.

HPSD was designed to limit resistive heating and therefore produces less collateral tissue damage while achieving similar success [13,14,15,16]. In a single non-randomized study, HPSD ablation resulted in a shortened ablation time, as seen in our study [17, 18]. We have not seen a reduction in the number of lesions needed to achieve CTI block, as typically, HPSD ablation creates similar size lesions to traditional irrigated catheter ablation [13].

We could not identify factors associated with ablation failure due to the low incidence of inability to achieve CTI block. Typical predictors of failed ablation are previous atrial fibrillation and presence of complex congenital heart disease (transposition of great arteries, systemic ventricle dilation) [18]. Previous data suggest that HPSD helps achieve CTI block in all patients [17, 19].

The observational nature of the design limits our study. Nevertheless, the presence of a single operator performing the procedure eliminates some of the bias that might be present with multiple operators, even in a randomized study. We do not believe that operator’s experience has influenced the outcomes, as we do not see differences between non-irrigated catheters and internally and externally irrigated catheters (as the latter were available more recently). Having the ability to objectively assess the force exerted by the catheter during ablation is certainly advantageous as evident in our data set. Beyond this feature of the mapping software, we do not believe that different versions of the mapping system have significantly affected outcomes in this study.