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Introduction: In comparison to conventional cardiac troponin (cTn), high sensitivity cardiac troponin (hs-cTn) assay is associated with improved detection of myocardial infarction (MI). From literature review, resource utilization seems variable across institutions. This study sought to determine the effect of converting to hs-cTn on hospital resources. Hypothesis: hs-cTn is associated with overall decrease in resource utilization Methods: We performed a descriptive retrospective analysis of resource utilization at Rush University Medical Center (Chicago, IL) over the period of transition (July 6, 2021) from a cTn to hs-cTn assay using data extracted from the electronic health record. Inclusion criteria included Emergency Department (ED) encounters between January 1, 2021 and December 31, 2021 with chief complaints of “chest pain” or “dyspnea” with an associated troponin order. The primary endpoints were percentage of ED discharges. Secondary endpoints included the number of cardiac studies ordered including troponins, electrocardiograms (ECG), echocardiograms, stress tests, and coronary angiograms. Univariable comparisons of these endpoints were performed using Student’s t-test for continuous variables and Chi-square tests for binary/categorical variables. Results: A total of 5113 encounters were analyzed. hs-cTn was associated with an overall increased ED discharge in patients with negative troponin tests (44.1% vs. 29.9%, P<0.01). In terms of cardiac testing per encounter, hs-cTn compared to cTn was associated with a marginal increase in number of troponin tests (1.9 vs. 1.6, P<0.01), electrocardiograms (3.0 vs. 2.9, P=0.01), Echocardiograms (0.5 vs. 0.4, P<0.01). There was a decrease in the utilization of stress testing (0.21 vs 0.26, P<0.01). There was a trend towards increased coronary angiography per encounter (0.11 vs. 0.09, P=0.05) and an increase in total coronary angiography use during the hs-cTn period compared to cTn (227//2471 (9.2%) vs. 195/2642 (7.4%, P=0.02)) Conclusion: Transitioning from cTn to hs-cTn was associated with increased ED discharges, marginal increase in troponin tests, ECGs, echocardiograms. There was a decrease in stress testing but increase in total coronary angiography.

Background: Transverse tubules (TT) are tunnel-like extensions of sarcolemma studded with ion channels coupling excitation, through the cytoplasm, to contraction in the sarcomere of matured cardiomyocytes (CMs). Expression timing of sub-cellular TT-related genes (TT-rgs) in individual human iPSC-derived CMs (hiPSC-CMs) has not yet been reported. Objective: Map out the gene program of TT-rgs by sub-cellular locations during hiPSC-CM differentiation using single-cell transcriptomics (scRNA Seq.). Methods: hiPSC-CMs were differentiated from 2 commercially available lines using sequential GSK3 and Wnt signaling inhibition. The %CMs were assayed by flow cytometry for sarcomeric myosin heavy chain protein, a CM biomarker. Baseline cells (iPSCs, n=24) and day 14 (n=45), 30 (n=64), and 60 (n=5) post differentiation cells were sampled for scRNA Seq. using the Fluidigm C1 platform. We categorized 73 TT-rgs by cellular location of the coded protein (i.e. sarcomere, cytoplasm or sarcolemma). The expression pattern for each location was categorized as induced, repressed, or neither based on the median transcript per million for each individual cell normalized to iPSCs. Results: CMs increased from <1% in iPSCs to 21%, 37% and 59% at D14, D30 and D60 post differentiation (adj. p <0.03 by ANOVA), respectively. 33 genes (45%) had no detectable RNA while 21 (29%) were induced to D60. See table. Conclusion: Single-cell transcriptomes in differentiating hiPSC-CMs revealed a discordance between sarcolemma (mostly not expressed) and sarcomeric genes being induced. Defining timing and within cell variability of TT sub-cellular genes will be critical to understand human CM maturation.

Background: Adrenergic receptors (AR) in an individual cardiomyocyte (CM) are not uniformly expressed at the single-cell level (Myagmar et al., 2017). The timing and cellular distribution of AR signaling (ARS) genes in individual human iPSC-derived CMs (hiPSC-CMs) have not yet been reported. Objective: To map out the transcription program of ARS genes during hiPSC-CM myogenesis using single-cell transcriptomics (scRNA Seq.). Methods: 132 ARS in CM genes curated by the Kyoto Encyclopedia of Genes and Genomes were studied. The CMs were derived from 2 commercially available hiPSC lines using sequential GSK3 and Wnt signaling inhibition. The CMs were assayed by flow cytometry with sarcomeric myosin heavy chain (MYHC6/7) protein, a biomarker of myogenesis. Baseline cells (iPSCs, n=24) and day 14 (n=45), 30 (n=64), and 60 (n=5) post differentiation cells were sampled for scRNA Seq. using the Fluidigm C1 platform. Data from 10 somatic cell preparations and iPSCs defined the signal specificity and biological noise in the system. The expression patterns were categorized as induced, repressed, or neither based on the median transcript per million for individual cells normalized to iPSCs. A p -value of <0.05 by ANOVA was used for significance. Results: The CMs had spontaneous contractions by D14 and increased from <1% in iPSCs to 21%, 37% and 59% at D14, D30 and D60 post differentiation (adj. p <0.03) respectively. None of the iPSCs had MYH6/7 transcripts, while >90% of differentiating cells did. MYH6/7 median expression increased 15-fold from D14 to D30 (p<0.0001) and 60-fold to D60 (p<0.06). Of 132 ARS genes, 60 (44%) had no detectable expression out to D60. Of the 72 genes with expression, 18 (25%) were induced in parallel to MYH6/7, while 22 (31%) were repressed. The remaining 32 genes (44%) had no distinctive pattern. From 18 induced genes (14% of all), 8 were sarcomeric genes that preceded expression to most ARS genes without induction (86% of all). Conclusion: Single-cell transcriptomes in derived hiPSC-CMs revealed a lack of uniformity between upstream ARS genes and early sarcomeric genes. Defining the timing and cell-to-cell variability of the ARS gene program will be critical to understanding its mechanistic relationship to the sarcomeric gene program in humans.