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Introduction. When using Lesion Size index (LSI) to guide catheter ablation, it is unclear what combination of power, contact force and time would be preferable to use and what LSI target value to aim for. This study aimed at identifying desirable ablation settings and LSI targets by using tissue impedance drop as indicator of lesion formation. Methods. Consecutive patients, undergoing their first left atrial (LA) catheter ablation for atrial fibrillation, with RF powers of 20, 30 and 40 W were enrolled. Tissue impedance, contact force (CF), Force Time Integral (FTI) and LSI values were continuously recorded during ablation and sampled at 100 Hz. Mean CF and Contact Force Variability (CFV) were calculated for every lesion. The effect of RF power, ablation time, CF and CFV on impedance drop and LSI were assessed. Results. A total of 3258 lesions were included in the analysis. For any target LSI value, use of higher RF powers translated into progressively higher impedance drops. The impact of lower CF and higher CFV on impedance drop was more relevant when using lower powers. Target LSI values corresponding to maximum impedance drop were identified depending on RF power, mean CF and CFV used. Conclusions. Even in the context of an LSI-guided ablation strategy, use of lower or higher powers might lead to different lesion sizes. Different LSI targets might be needed depending on the combination of RF power, CF and CFV used for ablation. Incorporating indicators of catheter stability, like CFV, in the LSI formula could improve the predictive value of LSI for lesion size. Studies with clinical outcomes are required to confirm the clinical relevance of these findings.

The National Institute for Health and Care Excellence (NICE) released an updated atrial fibrillation (AF) guideline in April 2021.1 This article provides an overview of the key changes relevant to primary care, which are also covered in RCGP Essential Knowledge Updates (EKU) e-learning. It focuses on stroke and bleeding risk assessment, choice of anticoagulation, and advice on remote monitoring and AF detection.

Amiodarone and beta blockers are common treatments for new-onset atrial fibrillation (NOAF) in patients treated on an intensive care unit (ICU). How these treatments affect patients’ haemodynamic status is unclear, yet purported differences often affect clinicians’ treatment choice. We undertook a multicentre observational study of ICUs in one United States of America (USA) centre and two United Kingdom (UK) centres to explore the changes in blood pressure and cardiovascular support associated with amiodarone or beta blocker therapy for NOAF. We identified 2017 patients who developed NOAF during their ICU stay, of which 958 were treated with amiodarone or beta blockers as first line therapy. Neither amiodarone nor beta blockers were associated with significant changes in blood pressure over the 3h post-treatment initiation (amiodarone mean blood pressure (MBP +0.04mmHg/h, p = 0.90 and systolic blood pressure (SBP) +0.11mmHg/h, p = 0.83; beta blocker MBP -0.41mmHg/h, p = 0.17 and SBP -0.15mmHg/h, p = 0.75). Amiodarone was associated with a very slight increase in vasoactive medication use. In a subgroup of patients with lower blood pressures, amiodarone was associated with a slight improvement in blood pressure (+1.36mmHg/h, p = 0.02), whereas beta blocker therapy was not associated with any change (+0.24mmHg/h, p = 0.72). These data do not support the commonly held belief that beta blockers result in hypotension or increased vasoactive medication requirements when used for NOAF treatment within an ICU. These findings from observational data need investigating in well-designed randomised trials.