Myocardial Work in Echocardiography

Myocardial work is an emerging tool in echocardiography that incorporates left ventricular afterload into global longitudinal strain analysis. Myocardial work correlates with myocardial oxygen consumption, and work efficiency can also be assessed. Myocardial work has been evaluated in a variety of clinical conditions to assess the added value of myocardial work compared to left ventricular ejection fraction and global longitudinal strain. This review showcases the current use of myocardial work in adult echocardiography and its possible role in cardiac pathologies.

Left Ventricular Mechanics Differ in Subtypes of Aortic Stenosis Following Transcatheter Aortic Valve Replacement

Background

Left ventricular (LV) mechanics are impaired in patients with severe aortic stenosis (AS). We hypothesized that there would be differences in myocardial mechanics, measured by global longitudinal strain (GLS) recovery in patients with four subtypes of severe AS after transcatheter aortic valve replacement (TAVR), stratified based upon flow and gradient.

Methods

We retrospectively evaluated 204 patients with severe AS who underwent TAVR and were followed post-TAVR at our institution for clinical outcomes. Speckle-tracking transthoracic echocardiography was performed pre- and post-TAVR. Patients were classified as: (1) normal-flow and high-gradient, (2) normal-flow and high-gradient with reduced LV ejection fraction (LVEF), (3) classical low-flow and low-gradient, or (4) paradoxical low-flow and low-gradient.

Results

Both GLS (−13.9 ± 4.3 to −14.8 ± 4.3, P < 0.0001) and LVEF (55 ± 15 to 57 ± 14%, P = 0.0001) improved immediately post-TAVR. Patients with low-flow AS had similar improvements in LVEF (+2.6 ± 9%) and aortic valve mean gradient (−23.95 ± 8.34 mmHg) as patients with normal-flow AS. GLS was significantly improved in patients with normal-flow (−0.93 ± 3.10, P = 0.0004) compared to low-flow AS. Across all types of AS, improvement in GLS was associated with a survival benefit, with GLS recovery in alive patients (mean GLS improvement of −1.07 ± 3.10, P < 0.0001).

Conclusions

LV mechanics are abnormal in all patients with subtypes of severe AS and improve immediately post-TAVR. Recovery of GLS was associated with a survival benefit. Patients with both types of low-flow AS showed significantly improved, but still impaired, GLS post-TAVR, suggesting underlying myopathy that does not correct post-TAVR.

Myocardial work assessment in severe aortic stenosis undergoing transcatheter aortic valve replacement

AIMS

Myocardial work is a novel echocardiographic algorithm that corrects speckle-tracking-derived global longitudinal strain (GLS) for afterload using non-invasive systolic blood pressure as a surrogate for left ventricular systolic pressure (LVSP). Yet, in patients with severe aortic stenosis, non-invasive systolic blood pressure does not equal LVSP.

METHODS AND RESULTS

We evaluated 35 patients with severe aortic stenosis who underwent transcatheter aortic valve replacement (TAVR). Transthoracic echocardiography, including myocardial mechanics, was performed pre- and post-TAVR. We performed simultaneous echocardiographic and cardiac catheterization measurements in 23 of the 35 patients at the time of TAVR. Peak and mean aortic gradients were calculated from echocardiographic and cardiac catheterization data. Peak-to-peak LV-aortic gradient correlated highly with mean LV-aortic gradient (r = 0.96); measured LVSP correlated highly with our novel method of non-invasively estimated LVSP (non-invasive systolic blood pressure cuff + Doppler-derived mean aortic gradient, r = 0.92). GLS improved from pre- to post-TAVR (-14.2% ± 4.3 vs. -15.1% ± 3.2), and myocardial work reduced from corrected pre-TAVR to post-TAVR (global work index: 1856.2 mmHg% ± 704.6 vs. 1534.8 ± 385.0).

CONCLUSION

We propose that non-invasive assessment of myocardial work can be reliably performed in aortic stenosis by the addition of mean aortic gradient to non-invasive systolic blood pressure. From this analysis, we note the novel and unique finding that GLS can improve as myocardial work reduces post-TAVR in patients with severe aortic stenosis. Both GLS and myocardial work post-TAVR remain below normal values, requiring further studies.

Preprocedure COVID-19 Testing in Early Phase of Pandemic

The COVID-19 pandemic led to a nationwide shutdown of elective medical procedures. Upon resumption of services, preprocedure nasopharyngeal swab testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was introduced for all patients requiring surgical or other aerosol-generating procedures. We investigated preprocedure COVID-19 testing in one of the largest U.S. health systems. Patients included in this retrospective, observational study were asymptomatic and scheduled for a procedure or surgery. All patients underwent a nasopharyngeal swab test for SARS-CoV-2 performed 24-72 hours prior to a planned procedure. Clinical demographics, type of procedure, test results, and subsequent procedure status were evaluated. Of 38,608 total patients, there were 277 COVID-19-positive patients (positivity rate: 0.72%). Of those 277, 244 (88%) had procedural delays or cancellations. Of the COVID-19-negative patients, 50 (0.13%) required later hospitalization for COVID-19. Median time from preprocedure negative test to admission was 46.3 ± 27.2 days. In the largest series published on preprocedure COVID-19 testing in the early phase of the pandemic, preprocedure COVID-19 positivity was low. Preprocedure COVID-19 testing had a significant impact on clinical management. Rate of COVID-19 cases requiring hospitalization in the months following the procedure was negligible, suggesting health system policies adequately protected patient safety.

Seroprevalence of SARS-CoV-2 Antibody in Echocardiography and Stress Laboratory

PURPOSE

Transesophageal echocardiography is an aerosol-generating procedure, and exercise stress testing is a potentially aerosol-generating activity. Concern has been raised about heightened risk of transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) among health care personnel participating in these procedures. We aimed to investigate the prevalence of past coronavirus disease 2019 (COVID-19) infection in echocardiography and stress laboratory staff.

METHODS

All staff who worked in the echocardiography and stress laboratories of one high-traffic urban hospital from March 15, 2020, to June 15, 2020, were asked to voluntarily participate. Those willing to participate were consented, and past COVID-19 infection was confirmed by a SARS-CoV-2 IgG antibody test (ARCHITECT, Abbott Laboratories) from June 15, 2020, to July 3, 2020. Clinical data were collected from the electronic medical record, and self-reported symptoms were documented with a participant survey.

RESULTS

A total of 43 staff members (86.0% of 50 total laboratory staff) participated. A majority of participants were less than 40 years old (69.8%), were White (86.0%), and were women (79.1%); mean body mass index was 24.9 ± 4.7 kg/m². Of the 43 staff members tested for past COVID-19 infection, 3 (7.0%) had a positive SARS-CoV-2 IgG antibody result. There were no unique features in the 3 SARS-CoV-2 antibody-positive subjects; of these, 2 had known prior COVID-19 infection and 1 was asymptomatic.

CONCLUSIONS

This study provides clinical data on the seroprevalence of SARS-CoV-2 antibody in echocardiography and stress laboratory staff who regularly participate in a variety of procedures that are or may be aerosol-generating.

Biphasic effect of metformin on human cardiac energetics

Metformin is the first-line medication for treatment of type 2 diabetes and has been shown to reduce heart damage and death. However, mechanisms by which metformin protects human heart remain debated. The aim of the study was to evaluate the cardioprotective effect of metformin on cardiomyocytes derived from human-induced pluripotent stem cells (hiPSC-CMs) and mitochondria isolated from human cardiac tissue. At concentrations ≤2.5 mM, metformin significantly increased oxygen consumption rate (OCR) in the hiPSC-CMs by activating adenosine monophosphate activated protein kinase (AMPK)-dependent signaling and enhancing mitochondrial biogenesis. This effect was abrogated by compound C, an inhibitor of AMPK. At concentrations >5 mM, metformin inhibited the cellular OCR and triggered metabolic reprogramming by enhancing glycolysis and glutaminolysis in the cardiomyocytes. In isolated cardiac mitochondria, metformin did not increase the OCR at any concentrations but inhibited the OCR starting at 1 mM through direct inhibition of electron-transport chain complex I. This was associated with reduction of superoxide production and attenuation of Ca2+-induced mitochondrial permeability transition pore (mPTP) opening in the mitochondria. Thus, in human heart, metformin might improve cardioprotection due to its biphasic effect on mitochondria: at low concentrations, it activates mitochondrial biogenesis via AMPK signaling and increases the OCR; at high concentrations, it inhibits the respiration by directly affecting the activity of complex I, reduces oxidative stress and delays mPTP formation. Moreover, metformin at high concentrations causes metabolic reprogramming by enhancing glycolysis and glutaminolysis. These effects can be a beneficial adjunct to patients with impaired endogenous cardioprotective responses.

Comprehensive Echocardiographic Findings in Critically Ill COVID-19 Patients With or Without Prior Cardiac Disease

Purpose

Coronavirus disease 2019 (COVID-19) presents with a spectrum of disease severity, the most serious cases requiring intensive care. Echocardiography is a front-line tool in evaluating cardiovascular complications of COVID-19 in the intensive care unit (ICU); we analyzed transthoracic echocardiograms obtained from this patient population with state-of-the-art ultrasound technology.

Methods

All patients with COVID-19 requiring ICU admission on whom a transthoracic echocardiogram was obtained were included in the study. Focused transthoracic protocols were performed by experienced sonographers. Echocardiographic variables, including speckle-tracking echocardiography, were collected and analyzed. Clinical information was obtained from the electronic medical record. Patients were followed until discharge.

Results

Of 52 total patients (mean age: 59.9 ± 11.6 years), 59.6% were male and 15 (29%) had known prior cardiac disease. Cardiac complications identified on echocardiography were prevalent, occurring in 55.7% of patients. Patients with known prior cardiac disease were more likely to have new or worsening left ventricular dysfunction. Right ventricular dysfunction was the most common abnormality (assessed qualitatively in 18 cases and with advanced echocardiographic methods in 34 cases). Known prior cardiac disease, right ventricular enlargement, and pulmonary hypertension were significantly associated with morbidity and mortality.

Conclusions

Patients requiring intensive care for COVID-19 face significant morbidity and mortality, and cardiac complications occur in the majority of patients admitted to the ICU with COVID-19. Those with known prior cardiac disease fare worse, and other echocardiographic findings (right ventricular enlargement, pulmonary hypertension) are also associated with worse outcomes. State-of-the-art echocardiography performed by experienced sonographers can be critical to identifying cardiac complications and guiding ICU strategy.

Abstract 344: Circulating MicroRNA Signature as a Predictive Biomarker for Postoperative Heart Failure

Background: Advancements in cardiac surgical techniques have led to decreasing operative risk. However, postoperative heart failure (PoHF) continues to be a major risk factor for adverse cardiac events in 20-35% of patients after cardiac surgery, with a 10-fold increase in 30-day mortality. Prediction of PoHF is challenging, particularly in patients with preserved ventricular function. Circulating microRNAs (miRNAs) recently were identified to predict HF or AF after surgery, but their role in predicting PoHF is not known. This study aimed to find novel noninvasive circulating biomarkers along with clinical factors that can identify patients at risk of developing PoHF immediately after surgery.

Methods: Patients undergoing CABG surgery with no previous history of HF, ventricular or supraventricular tachycardia were recruited, and preoperative blood assessed for circulating levels of protein biomarkers using ELISA. Differences in relative plasma levels of 13 miRNAs between the PoHF and no-PoHF groups were assessed by qPCR. Preoperative echocardiography was obtained. SAS was used for statistical analysis and ROC curve.

Results: Out of 68 patients, 13 developed PoHF (19.1%, mean age 64.1±11.6y, 53.8% males), whereas 55 (mean age 68.3±12.4y) remained free of HF. Patients who developed PoHF had lower LVEF (51.4±13.7 vs 58.2±9.9, P<0.05) with no differences in prevalence of hypertension, diabetes, hyperlipidemia, obesity, previous myocardial infarction, stroke, COPD, sleep apnea, or use of cardiac medications. The correlation matrix of all 13 miRNAs was transformed in a principal component (PC), resulting in 3 main clusters with eigenvalue >1. PC cluster2 consisted of miR-23a, -23b, -25 and -26a2, principally involved in oxidatives stress, fibrosis and contractility, and had the strongest association (AUC=0.797; P<0.01) with PoHF. A model combining PC cluster2 with age and LVEF improved sensitivity and specificity of the model to identify patients at risk of PoHF (AUC=0.880; 95% CL, 0.761-0.991; P<0.001)

Conclusion: Our study demonstrates that miR-23a, -23b, -25 and -26a2 may be useful predictors of PoHF. Circulating miRNA as biomarkers may have diagnostic potential to preoperatively, noninvasively identify patients at risk of developing PoHF.

Abstract 379: Metformin Induces Energetic Reprogramming in Human Cardiomyocytes

Introduction: Metformin (Metf) is an oral hypoglycemic agent widely used to treat type 2 diabetes. It also lessens myocardial injury and reduces cardiovascular mortality. However, the exact molecular mechanisms of Metf therapeutic action in the human heart remain obscure. The aim of this study was to evaluate the cardioprotective effect of Metf on cardiomyocytes derived from human-induced pluripotent stem cells (hiPSC-CMs).

Methods: The hiPSC-CMs were derived from an hiPSC line generated from human dermal fibroblasts and treated with Metf (0-20 mM) for 24 hours. Oxygen consumption rate (OCR) was measured using XF96 Extracellular Flux Analyzer. Metabolites were profiled using a liquid chromatography coupled to tandem mass spectrometry. Tukey’s pairwise comparison and one-way ANOVA were applied for comparison between groups. P < 0.05 was considered significant.

Results: At concentrations ≤ 2.5 mM, Metf significantly enhanced the cellular OCR (Fig. A) and enhanced mitochondrial biogenesis (Fig. B) via AMPK signaling (Fig. C). This effect was abrogated by compound C, an inhibitor of AMPK. At concentrations > 5 mM, Metf reduced the cellular OCR and activated glycolysis (Fig. D) and glutaminolysis (Fig. E) in the cardiomyocytes.

Conclusion: Thus, in the human heart, Metf might improve cardioprotection owing to its dual effect on mitochondria. At low doses, it activates mitochondrial biogenesis via AMPK signaling and increases the OCR. At high doses, it causes metabolic reprogramming by enhancing glycolysis and glutaminolysis as a compensatory mechanism in response to inhibition of the mitochondrial oxidative phosphorylation.

Generation of induced pluripotent stem cells from CD34+ cells across blood drawn from multiple donors with non-integrating episomal vectors

The methodology to create induced pluripotent stem cells (iPSCs) affords the opportunity to generate cells specific to the individual providing the host tissue. However, existing methods of reprogramming as well as the types of source tissue have significant limitations that preclude the ability to generate iPSCs in a scalable manner from a readily available tissue source. We present the first study whereby iPSCs are derived in parallel from multiple donors using episomal, non-integrating, oriP/EBNA1-based plasmids from freshly drawn blood. Specifically, successful reprogramming was demonstrated from a single vial of blood or less using cells expressing the early lineage marker CD34 as well as from unpurified peripheral blood mononuclear cells. From these experiments, we also show that proliferation and cell identity play a role in the number of iPSCs per input cell number. Resulting iPSCs were further characterized and deemed free of transfected DNA, integrated transgene DNA, and lack detectable gene rearrangements such as those within the immunoglobulin heavy chain and T cell receptor loci of more differentiated cell types. Furthermore, additional improvements were made to incorporate completely defined media and matrices in an effort to facilitate a scalable transition for the production of clinic-grade iPSCs.

The common African American polymorphism SCN5A-S1103Y interacts with mutation SCN5A-R680H to increase late Na current

The common polymorphism SCN5A-S1103Y (∼13% allelic frequency in African Americans) is a risk factor for arrhythmia, sudden unexplained death (SUD), and sudden infant death syndrome. Prompted by a case of autopsy-negative SUD in a 23-year-old African American man who collapsed while playing football, we hypothesized that S1103Y interacted with other SCN5A variants to pathologically modify sodium current (I(Na)). Mutational analysis of arrhythmia-associated genes in the victim revealed the variants SCN5A-R680H and SCN5A-S1103Y. These variants were made both separately and in the same cDNA construct of the alternative splice variant backgrounds (SCN5A-Q1077del and Q1077) and expressed in HEK293 cells. In the most abundant SCN5A-Q1077del, late I(Na) for S1103Y alone was not significantly different from wild type (WT). However, late I(Na) for R680H, R680H+S1103Y (coexpressed), and R680H/S1103Y (on the same cDNA) was increased 2.1-, 3.4-, and 3.6-fold, respectively, compared with WT. Intracellular acidosis (pH 6.7) increased late I(Na) for S1103Y, R680H, R680H+S1103Y, and R680H/S1103Y by 2.2-, 2.4-, 5.0-, and 5.5-fold, respectively, compared with WT at pH 6.7. Expression in the less abundant SCN5A-Q1077 showed no increased late I(Na). This is the initial report of a functional interaction for the common polymorphism S1103Y with another mutation in the major transcript Q1077del of SCN5A. The "double hit" and environmental factor of acidosis may have converged to cause arrhythmic sudden death in this case.

Alpha1-syntrophin mutations identified in sudden infant death syndrome cause an increase in late cardiac sodium current

BACKGROUND

Sudden infant death syndrome (SIDS) is a leading cause of death during the first 6 months after birth. About 5% to 10% of SIDS may stem from cardiac channelopathies such as long-QT syndrome. We recently implicated mutations in alpha1-syntrophin (SNTA1) as a novel cause of long-QT syndrome, whereby mutant SNTA1 released inhibition of associated neuronal nitric oxide synthase by the plasma membrane Ca-ATPase PMCA4b, causing increased peak and late sodium current (I(Na)) via S-nitrosylation of the cardiac sodium channel. This study determined the prevalence and functional properties of SIDS-associated SNTA1 mutations.

METHODS AND RESULTS

Using polymerase chain reaction, denaturing high-performance liquid chromatography, and DNA sequencing of SNTA1's open reading frame, 6 rare (absent in 800 reference alleles) missense mutations (G54R, P56S, T262P, S287R, T372M, and G460S) were identified in 8 (approximately 3%) of 292 SIDS cases. These mutations were engineered using polymerase chain reaction-based overlap extension and were coexpressed heterologously with SCN5A, neuronal nitric oxide synthase, and PMCA4b in HEK293 cells. I(Na) was recorded using the whole-cell method. A significant 1.4- to 1.5-fold increase in peak I(Na) and 2.3- to 2.7-fold increase in late I(Na) compared with controls was evident for S287R-, T372M-, and G460S-SNTA1 and was reversed by a neuronal nitric oxide synthase inhibitor. These 3 mutations also caused a significant depolarizing shift in channel inactivation, thereby increasing the overlap of the activation and inactivation curves to increase window current.

CONCLUSIONS

Abnormal biophysical phenotypes implicate mutations in SNTA1 as a novel pathogenic mechanism for the subset of channelopathic SIDS. Functional studies are essential to distinguish pathogenic perturbations in channel interacting proteins such as alpha1-syntrophin from similarly rare but innocuous ones.

Caveolin-3 associates with and affects the function of hyperpolarization-activated cyclic nucleotide-gated channel 4

Targeting of ion channels to caveolae, a subset of lipid rafts, allow cells to respond efficiently to extracellular signals. Hyperpolarization-activated cyclic nucleotide-gated channel (HCN) 4 is a major subunit for the cardiac pacemaker. Caveolin-3 (Cav3), abundantly expressed in muscle cells, is responsible for forming caveolae. P104L, a Cav3 mutant, has a dominant negative effect on wild type (WT) Cav3 and associates with limb-girdle muscular dystrophy and cardiomyopathy. HCN4 was previously shown to localize to lipid rafts, but how caveolae regulate the function of HCN4 is unknown. We hypothesize that Cav3 associates with HCN4 and regulates the function of HCN4 channel. In this study, we applied whole-cell patch clamp analysis, immunostaining, biotinylation, and immunoprecipitation methods to investigate this hypothesis. The immunoprecipitation results indicated an association of HCN4 and Cav3 in the heart and in HEK293 cells. Our immunostaining results showed that HCN4 colocalized with Cav3 but only partially colocalized with P104L in HEK293 cells. Transient expression of Cav3, but not P104L, in HEK 293 cells stably expressing HCN4 caused a 45% increase in HCN4 current (IHCN4) density. Transient expression of P104L caused a two-fold increase in the activation time constant for IHCN4 and shifted the voltage of the steady-state inactivation to a more negative potential. We conclude that HCN4 associates with Cav3 to form a HCN4 macromolecular complex. Our results indicated that disruption of caveolae using P104L alters HCN4 function and could cause a reduction of cardiac pacemaker activity.