Myocardial Work in Apical Hypertrophic Cardiomyopathy.

BACKGROUND: Pressure-strain loop analysis is a novel echocardiographic technique to calculate myocardial work indices that has not been applied to patients with apical hypertrophic cardiomyopathy (ApHCM). We hypothesized that myocardial work indices differ between patients with ApHCM and those with non-ApHCM. This study aimed to (1) evaluate myocardial work indices in patients with ApHCM compared with those with non-ApHCM, (2) describe associations with relevant clinical variables, and (3) examine associations with significant late gadolinium enhancement (LGE) on cardiac magnetic resonance imaging. METHODS: We retrospectively identified 48 patients with ApHCM and 69 with non-ApHCM who had measurements of global longitudinal strain (GLS), global work index (GWI), global constructive work (GCW), global wasted work, and global work efficiency. We evaluated available cardiac magnetic resonance imaging data on 34 patients with ApHCM and 51 with non-ApHCM. Multivariable regression models correcting for traditional cardiac risk factors were used to evaluate the associations of myocardial work indices with relevant clinical variables. RESULTS: Median GLS (-11% vs -18%, P < .001), GWI (966 mm Hg% vs 1803 mm Hg%, P < .001), and GCW (1,050 mm Hg% vs 1,988 mm Hg%, P < .001) were significantly impaired in patients with ApHCM compared with those with non-ApHCM. Increasing N-terminal pro b-type natriuretic peptide, abnormal ultrasensitive troponin, and increasing maximal left ventricular wall thickness were significantly associated with reduced GWI and GCW in patients with ApHCM (P < .05). Global constructive work had only modest accuracy (area under the curve [AUC] = 0.70) to predict LGE in patients with ApHCM. However, in patients with non-ApHCM, GLS was the strongest predictor of LGE (AUC = 0.91), with a -17% cutoff yielding 81% sensitivity and 80% specificity. CONCLUSION: Myocardial work indices are significantly impaired in patients with ApHCM compared to those with non-ApHCM and correlate with important clinical variables. Global longitudinal strain, GWI, and GCW are more strongly predictive of fibrosis in patients with non-ApHCM than ApHCM.

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.

The Utility of Myocardial Work in Clinical Practice.

Myocardial work (MW) is a novel technique used in the advanced assessment of left ventricular function. In the past few years, this invasive measure has evolved to become a more attainable noninvasive technique. MW has benefits over left ventricular ejection fraction and global longitudinal strain by speckle-tracking echocardiography, as it includes the afterload-dependent limitation and dynamic myocardial contraction in relationship to various loading conditions. In this article, the authors provide a summary overview and discuss the additive value noninvasive MW provides to left ventricular systolic function assessment. The authors explore the evolution of invasive to noninvasive MW, examine how to acquire and measure, discuss normal reference values, examine its role in a multitude of cardiac conditions that have been investigated in current research, review a variety of clinical applications, and discuss potential limitations. The goal is to allow the reader to see the benefits of this rapidly emerging application and be able to incorporate it into everyday practice.

Myocardial work in Stage 1 and 2 hypertensive patients.

AIMS: Myocardial work (MW) is a novel parameter that can be used in a clinical setting to assess left ventricular (LV) pressures and deformation. We sought to distinguish patterns of global MW index in hypertensive vs. non-hypertensive patients and to look at differences between categories of hypertension. METHODS AND RESULTS: Sixty-five hypertensive patients (mean age 65 ± 13 years; 30 male) and 15 controls (mean age 38 ± 12 years; 7 male) underwent transthoracic echocardiography at rest. Hypertensive patients were subdivided into Stage 1 (n = 32) and Stage 2 (n = 33) hypertension based on 2017 American College of Cardiology guidelines. Exclusion criteria were suboptimal image quality for myocardial deformation analysis, reduced ejection fraction, valvular heart disease, intracardiac shunt, and arrhythmia. Global work index (GWI), global constructive work (GCW), global wasted work (GWW), and global work efficiency were estimated from LV pressure-strain loops utilizing proprietary software from speckle-tracking echocardiography. LV systolic and diastolic pressures were estimated using non-invasive brachial artery cuff pressure. Global longitudinal strain and LV ejection fraction were preserved between the groups with no statistically significant difference, whereas there was a statically significant difference between the control and two hypertension groups in GWI (P = 0.01), GCW (P < 0.001), and GWW (P < 0.001). CONCLUSION: Non-invasive MW analysis allows better understanding of LV response under conditions of increased afterload. MW is an advanced assessment of LV systolic function in hypertension patients, giving a closer look at the relationship between LV pressure and contractility in settings of increased load dependency than LV ejection fraction and global longitudinal strain.

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.

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.

The Cac1 subunit of histone chaperone CAF-1 organizes CAF-1-H3/H4 architecture and tetramerizes histones.

The histone chaperone Chromatin Assembly Factor 1 (CAF-1) deposits tetrameric (H3/H4)2 histones onto newly-synthesized DNA during DNA replication. To understand the mechanism of the tri-subunit CAF-1 complex in this process, we investigated the protein-protein interactions within the CAF-1-H3/H4 architecture using biophysical and biochemical approaches. Hydrogen/deuterium exchange and chemical cross-linking coupled to mass spectrometry reveal interactions that are essential for CAF-1 function in budding yeast, and importantly indicate that the Cac1 subunit functions as a scaffold within the CAF-1-H3/H4 complex. Cac1 alone not only binds H3/H4 with high affinity, but also promotes histone tetramerization independent of the other subunits. Moreover, we identify a minimal region in the C-terminus of Cac1, including the structured winged helix domain and glutamate/aspartate-rich domain, which is sufficient to induce (H3/H4)2 tetramerization. These findings reveal a key role of Cac1 in histone tetramerization, providing a new model for CAF-1-H3/H4 architecture and function during eukaryotic replication.

Reversed-phase ion-pair liquid chromatography method for purification of duplex DNA with single base pair resolution.

Obtaining quantities of highly pure duplex DNA is a bottleneck in the biophysical analysis of protein-DNA complexes. In traditional DNA purification methods, the individual cognate DNA strands are purified separately before annealing to form DNA duplexes. This approach works well for palindromic sequences, in which top and bottom strands are identical and duplex formation is typically complete. However, in cases where the DNA is non-palindromic, excess of single-stranded DNA must be removed through additional purification steps to prevent it from interfering in further experiments. Here we describe and apply a novel reversed-phase ion-pair liquid chromatography purification method for double-stranded DNA ranging in lengths from 17 to 51 bp. Both palindromic and non-palindromic DNA can be readily purified. This method has the unique ability to separate blunt double-stranded DNA from pre-attenuated (n-1, n-2, etc) synthesis products, and from DNA duplexes with single base pair overhangs. Additionally, palindromic DNA sequences with only minor differences in the central spacer sequence of the DNA can be separated, and the purified DNA is suitable for co-crystallization of protein-DNA complexes. Thus, double-stranded ion-pair liquid chromatography is a useful approach for duplex DNA purification for many applications.

CAF-1-induced oligomerization of histones H3/H4 and mutually exclusive interactions with Asf1 guide H3/H4 transitions among histone chaperones and DNA.

Anti-silencing function 1 (Asf1) and Chromatin Assembly Factor 1 (CAF-1) chaperone histones H3/H4 during the assembly of nucleosomes on newly replicated DNA. To understand the mechanism of histone H3/H4 transfer among Asf1, CAF-1 and DNA from a thermodynamic perspective, we developed and employed biophysical approaches using full-length proteins in the budding yeast system. We find that the C-terminal tail of Asf1 enhances the interaction of Asf1 with CAF-1. Surprisingly, although H3/H4 also enhances the interaction of Asf1 with the CAF-1 subunit Cac2, H3/H4 forms a tight complex with CAF-1 exclusive of Asf1, with an affinity weaker than Asf1-H3/H4 or H3/H4-DNA interactions. Unlike Asf1, monomeric CAF-1 binds to multiple H3/H4 dimers, which ultimately promotes the formation of (H3/H4)(2) tetramers on DNA. Thus, transition of H3/H4 from the Asf1-associated dimer to the DNA-associated tetramer is promoted by CAF-1-induced H3/H4 oligomerization.

Human Immunodeficiency Virus nef signature sequences are associated with pulmonary hypertension.

Severe pulmonary hypertension (PH) associated with vascular remodeling is a long-term complication of HIV infection (HIV-PH) affecting 1/200 infected individuals vs. 1/200,000 frequency in the uninfected population. Factors accounting for increased PH susceptibility in HIV-infected individuals are unknown. Rhesus macaques infected with chimeric SHIVnef virions but not with SIV display PH-like pulmonary vascular remodeling suggesting that HIV-Nef is associated with PH; these monkeys showed changes in nef sequences that correlated with pathogenesis after passage in vivo. We further examined whether HIV-nef alleles in HIV-PH subjects have signature sequences associated with the disease phenotype. We evaluated specimens from participants with and without HIV-PH from European Registries and validated results with samples collected as part of the Lung-HIV Studies in San Francisco. We found that 10 polymorphisms in nef were overrepresented in blood cells or lung tissue specimens from European HIV-PH individuals but significantly less frequent in HIV-infected individuals without PH. These polymorphisms mapped to known functional domains in Nef. In the validation cohort, 7/10 polymorphisms in the HIV-nef gene were confirmed; these polymorphisms arose independently from viral load, CD4(+) T cell counts, length of infection, and antiretroviral therapy status. Two out of 10 polymorphisms were previously reported in macaques with PH-like pulmonary vascular remodeling. Cloned recombinant Nef proteins from clinical samples down-regulated CD4, suggesting that these primary isolates are functional. This study offers new insights into the association between Nef polymorphisms in functional domains and the HIV-PH phenotype. The utility of these polymorphisms as predictors of PH should be examined in a larger population.