Is gold cooler than platinum–iridium?

This editorial refers to ‘Gold vs. platinum–iridium tip catheter for cavotricuspid isthmus ablation: the AURUM 8 study’ by T. Lewalter et al., on page 102

In the current issue of Europace, the AURUM 8 study group describe the results of a multicentre, randomized, prospective comparative study¹ of the procedural results of catheter ablation of typical flutter with an 8 mm 99.9% gold or conventional platinum–iridium alloy non-irrigated ablation electrode.

So, what did the AURUM 8 investigators find? That there was no significant difference in the primary endpoint of the study which was the cumulative duration of radiofrequency (RF) delivered in order to achieve stable conduction block in the cavotricuspid isthmus. However, a slightly higher overall ablation success rate, a higher rate of rapid isthmus block achievement, and lower cross-over rates to the platinum–iridium tip catheter were observed. There were no differences in recurrence rates during follow-up. The underlying reason for this procedural advantage is evident from the bio-physical data. Lower mean and maximal electrode temperatures during ablation and a lower incidence of electrode char and coagulum formation attest to the gold electrode's higher thermal conductivity (about four times that of platinum–iridium) and therefore greater cooling efficacy. The greater cooling effect allowed the delivery of higher powers because of the temperature controlled algorithm governing RF power output. These data imply a higher peak temperature within the target tissue as well as a larger volume within the >50–55°C isotherm that defines the region of irreversible tissue necrosis during RF-induced myocardial heating. A further reflection of these effects is the higher incidence of significant impedance rise with the gold-tip electrode, which approached, but however did not reach, statistical significance (19.2 vs. 12.8%, P = 0.06). It is, however, reassuring that audible pops occurred with a similar frequency in both groups and that there were no tamponades in either group nor any differences in complications such as atrioventricular blocks.

Overall, this is a well-designed study, appropriately powered and dealing with a standardized procedure with a well-accepted procedural endpoint. Nevertheless, a few questions remain. It is not clear what the targeting technique for ablation in the cavotricuspid isthmus was: point by point, electrogram guided or anatomical, drag based. Was a long sheath used to support the ablation catheter or extend its reach to complete or facilitate cavotricuspid isthmus block? Was a steerable sheath used at all? Was a non-fluroscopic imaging/guiding system or a robotic/remote manipulation system used and if so, how often? It is unclear how the presence of coagulum and char was evaluated. Was the ablation catheter withdrawn after every RF delivery to verify the presence of coagulum–char or checked only in the case of impedance rise? What was the inner diameter of the introducer sheath used for the ablation catheter? In the case of a close-fitting sheath, there is a greater likelihood of coagulum or char being wiped off the electrode tip during withdrawal. One could accept the findings of this study with even greater confidence if there were no differences in both groups with respect to the above questions.

Despite these caveats, it is likely that the 8 mm gold electrode offers similar procedural efficacy with a lower incidence of char and coagulum formation compared with the conventional 8 mm platinum–iridium electrode. Is that a sufficient advantage to warrant changing to this catheter–electrode combination? Currently, a 3.5 mm open irrigated-tip catheter is widely used for cavotricuspid isthmus ablation. It offers better electrogram resolution and probably better protection from char and coagulum, with at least equal procedural efficacy and rapidity compared with the 8 mm electrode catheter.^2,3 There may even be an advantage of open irrigated-tip catheters in the case of anatomical abnormalities such as deep pouches or recesses, where lesion creation is dependent on both catheter–electrode reach and cooling efficacy. A deep pouch may represent a greater access challenge to the longer 8 mm electrode and the thermal efficiency of its passive, flow-dependent cooling likely to be lower than for the actively cooled open irrigated-tip catheter.

The poorer electrogram resolution of 8 mm electrodes is probably less of a handicap in the case of anatomic lesion making, typically a ‘dragging burn’. In that case, the choice between a conventional platinum–iridium alloy vs. gold electrode would probably depend upon local cost differentials. In the wider context, despite the absence of similar large-sized prospective studies comparing the 8 mm gold electrode with the 3.5 mm open irrigated-tip catheter, one may want to consider the 8 mm gold electrode on the right side if the fluid load resulting from the use of the open irrigated-tip catheter warrants concern, for example, in patients with heart failure and/or renal failure. Direct comparative data focusing on the thrombo-embolic potential of the 8 mm gold electrode vs. the 3.5 mm open irrigated-tip catheter is, however, necessary before considering using the 8 mm gold electrode on the left side.

Conflict of interest: none declared.

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Author notes