{Reference Type}: Journal Article {Title}: Increased Heart Rate Fragmentation in Those with Williams-Beuren Syndrome Suggests Non-autonomic Mechanistic Contributors to Sudden Death Risk. {Author}: Cathey BM;Bellach A;Troendle J;Smith K;Osgood S;Raja N;Kozel BA;Levin MD; {Journal}: Am J Physiol Heart Circ Physiol {Volume}: 0 {Issue}: 0 {Year}: 2024 Jun 21 {Factor}: 5.125 {DOI}: 10.1152/ajpheart.00601.2023 {Abstract}: Williams-Beuren Syndrome (WBS) is a rare genetic condition caused by a chromosomal microdeletion at 7q11.23. It is a multi-system disorder characterized by distinct facies, intellectual disability, and supravalvar aortic stenosis. Those with WBS are at increased risk of sudden death, but mechanisms underlying this remain poorly understood. We recently demonstrated autonomic abnormalities in those with WBS that are associated with increased susceptibility to arrhythmia and sudden cardiac death (SCD) risk. A recently introduced method for HRV analysis called 'heart rate fragmentation' (HRF) correlates with adverse cardiovascular events and death in studies where HRV failed to identify high-risk subjects. Some argue that HRF quantifies non-autonomic cardiovascular modulators. We, therefore, sought to apply HRF analysis to a WBS cohort to: 1) determine if those with WBS show differences in HRF compared to healthy controls and 2) determine if HRF correlates with traditional HRV measures in those with WBS. Similar to studies of those with CAD and atherosclerosis, we found significantly higher HRF in those with WBS compared to healthy controls. In general, HRF shows minimal correlation with traditional HRV metrics, suggesting that HRF may quantify some non-autonomic modulators of sudden death risk in those with WBS. We also introduce a new metric inspired by the HRF methodology, Significant Acute Rate Drop (SARD), which may permit vagal activity detection more directly. HRF and SARD increase the ability of non-invasive HRV measures to identify those at greatest risk for sudden cardiac death both in those with WBS as well as populations more broadly.