Background During automated radiofrequency (RF) annotation-guided pulmonary vein isolation (PVI), respiratory motion adjustment (RMA) is recommended, yet lacks in vivo validation. Methods Following contact force (CF) PVI (continuous RF, 30W) using general anaesthesia and automated RF annotation-guidance (VISITAG™: force-over-time 100% minimum 1g; 2mm position stability; ACCURESP™ RMA “off”) in 25 patients, we retrospectively examined RMA settings “on” versus “off” at the left atrial posterior wall (LAPW). Results Respiratory motion detection occurred in 8, permitting offline retrospective comparison of RMA settings. Significant differences in LAPW RF auto-annotation occurred according to RMA setting, with curves displaying catheter position, CF and impedance data indicating “best-fit” for catheter motion detection using RMA “off”. Comparing RMA “on” versus “off”, respectively: Total annotated sites 82 versus 98; median RF duration per-site 13.3s versus 10.6s (p<0.0001); median force time integral 177g.s versus 130g.s (p=0.0002); mean inter-tag distance (ITD) 6.0mm versus 4.8mm (p=0.002). Considering LAPW annotated site 1-to-2 transitions resulting from deliberate catheter movement, 3 concurrent with inadvertent 0g CF demonstrated <0.6s difference in RF duration. However, 13 deliberate catheter movements during constant tissue contact (ITD range 2.1 – 7.0mm) demonstrated (mean) site-1 RF duration difference 3.7s (range: -1.3 to 11.3s): considering multiple measures of catheter position instability, the appropriate indication of deliberate catheter motion occurred with RMA “off” in all. Conclusions ACCURESP™ respiratory motion adjustment importantly delayed the identification of deliberate and clinically relevant catheter motion during LAPW RF delivery, rendering auto-annotated RF display invalid. Operators seeking greater accuracy during auto-annotated RF delivery should avoid RMA use.

Objective: Comparison of birthweight references for diagnosing SGA. To provide denominator data for suspicion and diagnosis of SGA. Design: A retrospective cohort study of 10,616 babies. Setting: A regional obstetric centre. Population: 10,616 consecutive newborns, born in Derriford Hospital, University Hospitals Plymouth NHS Trust (UPHT), whilst using the GROW package,1 compared with using Intergrowth 21st (IG21),2 and British 1990 (UK90) references.3 Methods: Statistical analysis of centile data from GROW, IG21 and UK90 references. Main outcomes: Induction rates, detection of suspected and/or diagnosed SGA. Assessment of goodness of fit to the Plymouth population. Results: GROW and IG21 showed bias. GROW had a systematic bias towards smaller centiles (skewness 0.169). IG21 had a systematic bias towards larger centiles (skewness -0.452). UK90 was best fit to the Plymouth dataset with insignificant bias across centiles (skewness -0.047). Conclusions: GROW and IG21 are not appropriate gold standards for our population for allocation of birthweight centile. The size of the population suggests the conclusions may be extrapolatable to other centres. UK90 does not have everyday accessible tools compared with GROW and IG21. A continual local audit of birthweight would be ideal, enabling accurate local centile allocation. If a national SGA screening programme monitoring units’ ability to detect SGA was introduced, it could not start without validated, unit specific birthweight data. Funding: The statistician’s funding was obtained from UHPT Research and Development generic funding.