Background: Ultra-high-power short-duration (UHPSD) ablation with the novel QDOT™ catheter allows to maintain a target temperature by automatically adjusting flow and power during a 4-second application of 90 Watt. However, the optimal contact-force for a sufficient lesion generation is yet to be determined.

Methods: This study comprised 41 patients with symptomatic atrial fibrillation undergoing pulmonary vein isolation (PVI) with the QDot catheter using the UHPSD mode with 90 W for 4 seconds. All UHPSD applications for circumferential PVI were analyzed. Suboptimal UHPSD applications were defined as either an impedance drop of ≤5% or a cumulative temperature-limited energy ≤330 W.

Results: A total of 1904 UHPSD applications (46.4 applications per patient) were performed with an average contact force (aCF) of 12.3±6.4 g with a mean maximum temperature (maxTemp) of 48.4±3.8 °C and a mean impedance drop (ImpDrop) of 10±3.2%. An ImpDrop ≤5% occurred in 67 (3.5%) UHPSD applications which was associated with lower aCF (10.6±7 vs. 12.4±6.4 g; p=0.024) and a lower maxTemp (45.8±3.8 vs. 48.5±3.8 °C; p<0.001) as compared to UHPSD applications with an ImpDrop >5%. A cumulative energy ≤330 W was observed in 39 (2%) UHPSD applications. Interestingly, low cumulative energy UHPSD applications (≤330 W) were characterized by a higher aCF (21±9.6 vs. 12.1±6.2 g; p<0.001). Furthermore, low cumulative energy was observed significantly more often in UHPSD applications with aCF <5.6 g or >21.1 g (10.2% vs 3.6%; p=0.004).

Conclusion: A low but also a high contact-force (<6 and >21g) are associated with suboptimal UHPSD applications. Thus, UHPSD applications require a ’15-gram window’ of contact-force to achieve an optimal cumulative energy.