Faculty Bibliography

The cardiac conduction system (CCS) has a vital role in initiating and coordinating nearly 3 billion heartbeats throughout a person's lifetime. The CCS comprises two primary tissue types: the impulse-generating, slow-conducting nodes and the fast-conducting components of the ventricular conduction system. Dysfunction in this system can give rise to a spectrum of clinical symptoms, including palpitations, syncope, heart failure and even sudden cardiac death. Owing to the limited therapeutic options other than electronic pacemakers, substantial research efforts have been aimed at uncovering the root causes of conduction system disorders. A comprehensive investigative approach integrating genetics, transcriptomics and proteomics has been used to unravel the complex biology of these diseases. Advances in single-cell genomic and transcriptomic technologies, together with spatial transcriptomics, are offering new insights into the cellular microenvironments that govern conduction system function. In this Review, we examine the latest progress in understanding the biology of the CCS, situating new findings within both established and emerging scientific paradigms. Additionally, we discuss how these insights can be leveraged to improve clinical risk assessment, expand drug discovery efforts, accelerate technology aimed at promoting CCS regeneration and foster the development of innovative therapies, including biological pacemakers.

Vector Doppler Imaging (VDI) addresses the limitations of traditional Doppler imaging by measuring blood flow in axial and lateral directions but will produce incorrect results if aliasing is present. Aliasing becomes more likely when using high transmit frequencies such as in small animal cardiac applications. The use of multiple transmit angles decreases the Nyquist limit, which further increases the likelihood of aliasing. A new transmission scheme, termed StaBle, is proposed to increase the Nyquist limit of conventional sequential angle VDI by multiple fold. StaBle combines the velocity limit extension of staggered multiple pulse repetition frequency (PRF) with a double transmission scheme. With three transmit angles and two PRFs, StaBle was able to achieve a 6-12 times higher velocity limit compared to sequential angle VDI. Simulation and phantom spinning disk experiments were conducted to evaluate StaBle's performance. The simulation results showed a normalized root-mean-squared error of less than 5% compared to an ideal vector field in both axial and lateral directions. Phantom results showed a 9-fold improvement in detecting peak axial velocity over sequential three angle VDI. The ability of StaBle to obtain an unaliased vector field in vivo was demonstrated by imaging a mouse left ventricle where the Doppler signal was corrupted by aliasing artifacts using just a double transmit scheme. The resolved estimated vector velocity showed consistent beat-to-beat variation in velocity, confirming StaBle's robustness under realistic conditions and its potential for use in investigative studies.

BACKGROUND/UNASSIGNED:handling and arrhythmia susceptibility. METHODS/UNASSIGNED:There are a large number of rare ITPR1 missense variants reported in open data repositories. Based on their locations in the ITPR1 channel structure, we selected and characterized 33 human ITPR1 missense variants from open databases and identified 21 human ITPR1 GOF variants. We generated a mouse model carrying a human ITPR1 GOF variant, ITPR1-W1457G (W1447G in mice). RESULTS/UNASSIGNED:release, delayed afterdepolarization, and triggered activity in Purkinje cells. To assess the potential role of ITPR1 variants in arrhythmia susceptibility in humans, we looked up a gene-based association study in the UK Biobank data set and identified 7 rare ITPR1 missense variants showing potential association with cardiac arrhythmias. Remarkably, in vitro functional characterization revealed that all these 7 ITPR1 variants resulted in GOF. CONCLUSIONS/UNASSIGNED:Our studies in mice and humans reveal that enhanced function of ITPR1, a well-known movement disorder gene, increases the risk for cardiac arrhythmias.

BACKGROUND:Myocardial infarction and heart failure are major cardiovascular diseases that affect millions of people in the US with the morbidity and mortality being highest among patients who develop cardiogenic shock. Early recognition of cardiogenic shock allows prompt implementation of treatment measures. Our objective is to develop a new dynamic risk score, called CShock, to improve early detection of cardiogenic shock in cardiac intensive care unit (ICU). METHODS:We developed and externally validated a deep learning-based risk stratification tool, called CShock, for patients admitted into the cardiac ICU with acute decompensated heart failure and/or myocardial infarction to predict onset of cardiogenic shock. We prepared a cardiac ICU dataset using MIMIC-III database by annotating with physician adjudicated outcomes. This dataset that consisted of 1500 patients with 204 having cardiogenic/mixed shock was then used to train CShock. The features used to train the model for CShock included patient demographics, cardiac ICU admission diagnoses, routinely measured laboratory values and vital signs, and relevant features manually extracted from echocardiogram and left heart catheterization reports. We externally validated the risk model on the New York University (NYU) Langone Health cardiac ICU database that was also annotated with physician adjudicated outcomes. The external validation cohort consisted of 131 patients with 25 patients experiencing cardiogenic/mixed shock. RESULTS:CShock achieved an area under the receiver operator characteristic curve (AUROC) of 0.821 (95% CI 0.792-0.850). CShock was externally validated in the more contemporary NYU cohort and achieved an AUROC of 0.800 (95% CI 0.717-0.884), demonstrating its generalizability in other cardiac ICUs. Having an elevated heart rate is most predictive of cardiogenic shock development based on Shapley values. The other top ten predictors are having an admission diagnosis of myocardial infarction with ST-segment elevation, having an admission diagnosis of acute decompensated heart failure, Braden Scale, Glasgow Coma Scale, Blood urea nitrogen, Systolic blood pressure, Serum chloride, Serum sodium, and Arterial blood pH. CONCLUSIONS:The novel CShock score has the potential to provide automated detection and early warning for cardiogenic shock and improve the outcomes for the millions of patients who suffer from myocardial infarction and heart failure.

BACKGROUND/UNASSIGNED:variants. METHODS/UNASSIGNED: RESULTS/UNASSIGNED:) related to intracellular calcium homeostasis, heart rate, RAS signaling, and induction of pacemaker-nodal-like transcriptional programming. Immunoblotting confirmed increased protein levels for genes of interest and suppressed MAPK (mitogen-activated protein kinase) activity in mutant ACMs. CONCLUSIONS/UNASSIGNED:

Reciprocal interactions between non-myocytes and cardiomyocytes regulate cardiac growth and differentiation. Here, we report that the transcription factor Ebf1 is highly expressed in non-myocytes and potently regulates heart development. Ebf1-deficient hearts display myocardial hypercellularity and reduced cardiomyocyte size, ventricular conduction system hypoplasia, and conduction system disease. Growth abnormalities in Ebf1 knockout hearts are observed as early as embryonic day 13.5. Transcriptional profiling of Ebf1-deficient embryonic cardiac non-myocytes demonstrates dysregulation of Polycomb repressive complex 2 targets, and ATAC-Seq reveals altered chromatin accessibility near many of these same genes. Gene set enrichment analysis of differentially expressed genes in cardiomyocytes isolated from E13.5 hearts of wild-type and mutant mice reveals significant enrichment of MYC targets and, consistent with this finding, we observe increased abundance of MYC in mutant hearts. EBF1-deficient non-myocytes, but not wild-type non-myocytes, are sufficient to induce excessive accumulation of MYC in co-cultured wild-type cardiomyocytes. Finally, we demonstrate that BMP signaling induces Ebf1 expression in embryonic heart cultures and controls a gene program enriched in EBF1 targets. These data reveal a previously unreported non-cell-autonomous pathway controlling cardiac growth and differentiation.

To assess the contribution of individual TGF-β isoforms to aortopathy in Marfan syndrome (MFS), we quantified the survival and phenotypes of mice with a combined fibrillin1 (the gene defective in MFS) hypomorphic mutation and a TGF-β1, 2, or 3 heterozygous null mutation. The loss of TGF-β2, and only TGF-β2, resulted in 80% of the double mutant animals dying earlier, by post-natal day 20, than MFS only mice. Death was not from thoracic aortic rupture, as observed in MFS mice, but was associated with hyperplastic aortic valve leaflets, aortic regurgitation, enlarged aortic root, increased heart weight, and impaired lung alveolar septation. Thus, there appears to be a relationship between loss of fibrillin1 and TGF-β2 in the post-natal development of the heart, aorta and lungs.

Adult hearts are characterized by inefficient regeneration after injury, thus, the features that support or prevent cardiomyocyte (CM) proliferation are important to clarify. Diploid CMs are a candidate cell type that may have unique proliferative and regenerative competence, but no molecular markers are yet known that selectively identify all or subpopulations of diploid CMs. Here, using the conduction system expression marker Cntn2-GFP and the conduction system lineage marker Etv1Cre^ERT2, we demonstrate that Purkinje CMs that comprise the adult ventricular conduction system are disproportionately diploid (33%, vs. 4% of bulk ventricular CMs). These, however, represent only a small proportion (3%) of the total diploid CM population. Using EdU incorporation during the first postnatal week, we demonstrate that bulk diploid CMs found in the later heart enter and complete the cell cycle during the neonatal period. In contrast, a significant fraction of conduction CMs persist as diploid cells from fetal life and avoid neonatal cell cycle activity. Despite their high degree of diploidy, the Purkinje lineage had no enhanced competence to support regeneration after adult heart infarction.