Stepwise application of ECG and electrogram-based criteria to ensure electrical resynchronization with left bundle branch pacing.

AIMS: To define a stepwise application of left bundle branch pacing (LBBP) criteria that will simplify implantation and guarantee electrical resynchronization. Left bundle branch pacing has emerged as an alternative to biventricular pacing. However, a systematic stepwise criterion to ensure electrical resynchronization is lacking. METHODS AND RESULTS: A cohort of 24 patients from the LEVEL-AT trial (NCT04054895) who received LBBP and had electrocardiographic imaging (ECGI) at 45 days post-implant were included. The usefulness of ECG- and electrogram-based criteria to predict accurate electrical resynchronization with LBBP were analyzed. A two-step approach was developed. The gold standard used to confirm resynchronization was the change in ventricular activation pattern and shortening in left ventricular activation time, assessed by ECGI. Twenty-two (91.6%) patients showed electrical resynchronization on ECGI. All patients fulfilled pre-screwing requisites: lead in septal position in left-oblique projection and W paced morphology in V1. In the first step, presence of either right bundle branch conduction delay pattern (qR or rSR in V1) or left bundle branch capture Plus (QRS ≤120 ms) resulted in 95% sensitivity and 100% specificity to predict LBBP resynchronization, with an accuracy of 95.8%. In the second step, the presence of selective capture (100% specificity, only 41% sensitivity) or a spike-R <80 ms in non-selective capture (100% specificity, sensitivity 46%) ensured 100% accuracy to predict resynchronization with LBBP. CONCLUSION: Stepwise application of ECG and electrogram criteria may provide an accurate assessment of electrical resynchronization with LBBP (Graphical abstract).

The DNA-binding domain as a functional indicator: the case of the AraC/XylS family of transcription factors.

The AraC/XylS family of transcription factors, which include proteins that are involved in the regulation of diverse biological processes, has been of considerable interest recently and has been constantly expanding by means of in silico predictions and experimental analysis. In this work, using a HMM based on the DNA binding domain of 58 experimentally characterized proteins from the AraC/XylS (A/X), 1974 A/X proteins were found in 149 out of 212 bacterial genomes. This domain was used as a template to generate a phylogenetic tree and as a tool to predict the putative regulatory role of the new members of this family based on their proximity to a particular functional cluster in the tree. Based on this approach we assigned a functional regulatory role for 75% of the TFs dataset. Of these, 33.7% regulate genes involved in carbon-source catabolism, 9.6% global metabolism, 8.3% nitrogen metabolism, 2.9% adaptation responses, 8.9% stress responses, and 11.7% virulence. The abundance of TFs involved in the regulation of metabolic processes indicates that bacteria have optimized their regulatory systems to control energy uptake. In contrast, the lower percentage of TFs required for stress, adaptation and virulence regulation reflects the specialization acquired by each subset of TFs associated with those processes. This approach would be useful in assigning regulatory roles to uncharacterized members of other transcriptional factor families and it might facilitate their experimental analysis.