Troponin Structural Dynamics in the Native Cardiac Thin Filament Revealed by Cryo Electron Microscopy

Cardiac muscle contraction occurs due to repetitive interactions between myosin thick and actin thin filaments (TF) regulated by Ca2+ levels, active cross-bridges, and cardiac myosin-binding protein C (cMyBP-C). The cardiac TF (cTF) has two nonequivalent strands, each comprised of actin, tropomyosin (Tm), and troponin (Tn). Tn shifts Tm away from myosin-binding sites on actin at elevated Ca2+ levels to allow formation of force-producing actomyosin cross-bridges. The Tn complex is comprised of three distinct polypeptides - Ca2+-binding TnC, inhibitory TnI, and Tm-binding TnT. The molecular mechanism of their collective action is unresolved due to lack of comprehensive structural information on Tn region of cTF. C1 domain of cMyBP-C activates cTF in the absence of Ca2+ to the same extent as rigor myosin. Here we used cryo-EM of native cTFs to show that cTF Tn core adopts multiple structural conformations at high and low Ca2+ levels and that the two strands are structurally distinct. At high Ca2+ levels, cTF is not entirely activated by Ca2+ but exists in either partially or fully activated state. Complete dissociation of TnI C-terminus is required for full activation. In presence of cMyBP-C C1 domain, Tn core adopts a fully activated conformation, even in absence of Ca2+. Our data provide a structural description for the requirement of myosin to fully activate cTFs and explain increased affinity of TnC to Ca2+ in presence of active cross-bridges. We suggest that allosteric coupling between Tn subunits and Tm is required to control actomyosin interactions.

Impact of Abrupt Interruption of Home Psychotropic Medications at ICU Admission

Background: Abrupt discontinuation of home psychotropic medications is common among critically ill patients but may precipitate clinically significant withdrawal. Objective: To determine the percent of patients with interruptions in home psychotropic medications upon intensive care unit (ICU) admission and to identify outcomes associated with these interruptions. Methods: This was an institutional review board-approved, single-center, retrospective study of critically ill patients with a history of mental illness taking an antipsychotic or antidepressant medication. The primary outcome was the percent of patients with interruption in at least one home psychotropic medication for ≥24 hours upon ICU admission. Secondary outcomes included time to psychotropic re-initiation, percent of home psychotropic medications restarted in the ICU, ICU length of stay (LOS), delirium, withdrawal-related complications, need for acute antipsychotics or benzodiazepines, and reasons for psychotropic interruption. Results: Among 183 patients, 93 (50.8%) had interruptions in home psychotropic therapy for ≥24 hours upon ICU admission. Mean time to reinitiation of at least one psychotropic agent was 1.4 days, and 16.4% of patients did not have any home psychotropics restarted. Patients with psychotropic interruption had a longer ICU LOS (P = 0.01) and greater incidence of ICU delirium (P < 0.01). Withdrawal-related complications were similar between groups. Acute antipsychotic use was greater in patients with psychotropic interruption (P < 0.01). Acute benzodiazepine use was not different between groups (P = 0.87). Most patients did not have a documented reason for therapy interruption. Conclusion and Relevance: Unless contraindicated, clinicians should attempt to restart home psychotropic medications as soon as possible in critically ill patients.

Sex disaggregated analysis of risk factors for adverse outcomes in hypertrophic cardiomyopathy

Background

Patient sex has been associated with differences in disease penetrance and clinical expression in HCM. We sought to investigate sex-disaggregated differences in risk factors for adverse outcomes in a large international HCM registry.

Methods

This is a retrospective study of HCM patients from the Sarcomeric Human Cardiomyopathy Registry. Cox proportional hazards models were fit with a sex interaction term to determine significant differences between sexes.

Results

6647 (38% women) probands with HCM were included. After a mean follow-up of 6.4 years from first encounter, women had a higher risk of heart failure (HF) composite (HR 1.77; 95% CI 1.56–1.99, p&lt;0.0001), and death (1.22; 1.03–1.45, p=0.02) compared to men. No sex difference existed for ventricular arrhythmia composite (p=0.2) or atrial fibrillation (p=0.6). Sarcomere positive status (Sarc+) and causative variants in MYBPC3 reduced the risk of the HF composite for women, while for men there was no change in risk (P-heterogeneity=0.016 and &lt;0.0001, respectively). Baseline LVEF &lt;35% and larger LA size increased the risk of the HF composite for both sexes but to a greater magnitude in men (P-heterogeneity=0.0003 and 0.04 respectively) (Figure 1). Sarc+ increased the risk of death in men but not women (P-heterogeneity=0.041). Having the HF composite increased the risk of death by 45% in and 240% in men (P-heterogeneity=0.003) (Figure 2).

Conclusion

There are important sex differences in the risk of heart failure and death in those with HCM, with significant heterogeneity of outcomes based on subgroups defined by genetic and imaging factors.

Funding Acknowledgement

Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): The Sarcomeric Human Cardiomyopathy Registry (SHaRe) is supported by an unrestricted research grant from Bristol Myer Squibb, including funds to individual sites for database support.

Utility of advanced echocardiographic deformation measures to delineate cause of pathological left ventricular hypertrophy: value of a multiparametric approach

Background

Early diagnosis of cardiac amyloidosis (CA) is warranted to initiate specific treatment and improve outcomes. Conventional echocardiography is unable to reliably differentiate CA from other causes of increased left ventricular (LV) wall thickness.

Purpose

To demonstrate the value of a multiparametric approach utilising both standard and advanced echocardiographic measures to distinguish CA from other pathological causes of increased LV wall thickness.

Results

Patients with HCM had the highest septal thickness, maximum LV wall thickness, septum/posterior wall (Sep/PW) thickness ratio and left ventricular outflow tract (LVOT) gradient and lowest PW thickness (p&lt;0.0001) among all groups. Patients with CA had the lowest global longitudinal strain (GLS), tissue Doppler-derived myocardial systolic and diastolic velocities and LV ejection fraction (EF) (p&lt;0.0001). EF strain ratio (EFSR=LVEF/GLS) and LV longitudinal strain (apex/base) ratio were highest (largest number) in CA patients (p&lt;0.0001). Multivariate linear regression identified 5 independent predictors (PW thickness, Sep/PW thickness ratio, LVOT gradient, LV longitudinal strain (apex/base) ratio and GLS) that discriminated CA from other causes of increased LV wall thickness. A regression equation (using multivariate linear regression) {CA prediction value = (0.230*LS apex/base) − (0.002*LVOT gradient) − [0.068*(Sep/PW ratio)] + (0.007*PW thickness) + (0.022*GLS) + 0.189; r=0.667)} was derived which allowed reliable distinction of CA with a sensitivity of 92.3% and specificity of 91.2% at the optimal cut-off.

Conclusion

PW thickness, Sep/PW thickness ratio, LVOT gradient, LV longitudinal strain (apex/base) ratio and GLS are independent predictors of CA. We developed a multiparametric regression equation which allowed discrimination of CA from other causes of increased LV wall thickness. Future studies involving larger cohorts are required to validate these findings.

Funding Acknowledgement

Type of funding sources: None.

Use of advanced echocardiographic modalities to discriminate preclinical HCM mutation carriers from non-carriers

Background

It is a challenging goal to identify which family members of patients with hypertrophic cardiomyopathy (HCM) will subsequently develop HCM. Previous studies evaluating the utility of two-dimensional conventional Doppler echocardiography in HCM families with a known pathogenic variant identified on genetic testing have been unable to reliably distinguish preclinical genotype-positive, phenotype-negative (G+P−) individuals from their healthy genotype-negative, phenotype-negative (G−P−) relatives.

Purpose

To determine if advanced echocardiographic modalities can discriminate preclinical HCM mutation carriers (G+P−) from non-carriers (G−P−).

Methods

A total of 199 participants who had undergone genetic testing from HCM families with a known pathogenic variant were included in the study: 39 G−P−; 58 G+P− and 102 overt HCM patients (G+P+). Speckle tracking echocardiography (STE) and colour M-mode were performed on all participants and longitudinal, circumferential and radial strain, and torsion were compared.

Results

Patients with overt HCM had the highest septal, posterior wall thickness, septum/posterior wall (Sep/PW) thickness ratio and left ventricular outflow tract (LVOT) gradient and lowest global longitudinal, circumferential and radial strain, and tissue Doppler-derived myocardial systolic and diastolic velocities. Comparing G−P− and G+P− individuals, there were no significant differences in LV cavity size, wall thickness, LVOT gradient, LVEF and tissue Doppler-derived myocardial systolic and diastolic velocities. However, G+P− individuals had significantly higher peak apical rotation, peak twist and colour M-mode flow propagation velocity (Vp). Multivariate linear regression identified two independent predictors (peak apical rotation and Vp), and a regression equation (using multivariate linear regression) {Mutation carrier prediction value = (0.210×peak apical rotation) − (0.002×Vp) + 0.156; r=0.655)} was derived which allowed reliable discrimination of G+P- individuals with a sensitivity of 95.2% and specificity of 94.1% at the optimal cut-off.

Conclusion

In HCM family members without overt HCM, peak apical rotation and Vp provide good sensitivity and specificity for identifying mutation carriers and may be a clinically useful early marker of HCM before the onset of hypertrophy. Future longitudinal studies involving larger cohorts are required to validate these findings.

Funding Acknowledgement

Type of funding sources: None.

A survey of practice in the management of haemolysis, icterus and lipaemia in blood specimens in the United Kingdom and Republic of Ireland

BACKGROUND

Haemolysis, icterus and lipaemia (HIL) are common interferants in laboratory medicine, potentially impacting patient care. This survey investigates HIL management in medical laboratories across the UK and Republic of Ireland (ROI).

METHODS

A survey was sent to members of key professional organisations for laboratory medicine in the UK and ROI. Questions related to the detection, monitoring, quality control, and management of HIL.

RESULTS

In total, responses from 124 laboratories were analysed, predominantly from England (52%) and ROI (36%). Most responses were from public hospitals with biochemistry services (90%), serving primary care (91%), inpatients (91%), and outpatients (89%). Most laboratories monitored H (98%), I (88%), and L (96%) using automated indices (93%), alone or in combination with visual inspection.Manufacturer-stated cut-offs were used by 83% and were applied to general chemistries in 79%, and immunoassays in 50%. Where HIL cut-offs are breached, 64% withheld results, while 96% reported interference to users. HIL were defined using numeric scales (70%) and ordinal scales (26%). HIL targets exist in 35% of laboratories, and 54% have attempted to reduce HIL. Internal Quality Control for HIL was lacking in 62% of laboratories, and just 18% of respondents have participated in External Quality Assurance. Laboratories agree manufacturers should: standardise HIL reporting (94%), ensure comparability between platforms (94%), and provide information on HIL cross-reactivity (99%). Respondents (99%) showed interest in evidence-based, standardised HIL cut-offs.

CONCLUSIONS

Most respondents monitor HIL, although the wide variation in practice may differentially affect clinical care. Laboratories seem receptive to education and advice on HIL management.

Treatment with incretins does not increase the risk of pancreatic diseases compared to older anti-hyperglycaemic drugs, when added to metformin: real world evidence in people with Type 2 diabetes

AIMS

In people with metformin-treated diabetes, to evaluate the risk of acute pancreatitis, pancreatic cancer and other diseases of the pancreas post second-line anti-hyperglycaemic agent initiation.

METHODS

People with Type 2 diabetes diagnosed after 2004 who received metformin plus a dipeptidyl peptidase-4 inhibitor (DPP-4i, n = 50 095), glucagon-like peptide-1 receptor agonist (GLP-1RA, n = 12 654), sulfonylurea (n = 110 747), thiazolidinedione (n = 17 597) or insulin (n = 34 805) for at least 3 months were identified in the US Centricity Electronic Medical Records. Time to developing acute pancreatitis, other diseases of the pancreas and pancreatic cancer was estimated, balancing and adjusting anti-hyperglycaemic drug groups for appropriate confounders.

RESULTS

In the DPP-4i group, the adjusted mean time to acute pancreatitis was 2.63 [95% confidence intervals (CI) 2.38, 2.88] years; time to pancreatic cancer was 2.70 (2.19, 3.21) years; and time to other diseases of the pancreas was 2.73 (2.33, 3.12) years. Compared with DPP-4i, the insulin group developed acute pancreatitis 0.48 years (P < 0.01) earlier and the GLP-1RA group developed pancreatic cancer 3 years later (P < 0.01). However, with the constraint of no event within 6 months of insulin initiation, the risk of acute pancreatitis in the insulin group was insignificant. No other significant differences were observed between groups.

CONCLUSIONS

No significant differences in the risk of developing pancreatic diseases in those treated with various anti-hyperglycaemic drug classes were found.

Management of Helicobacter pylori infection-the Maastricht V/Florence Consensus Report

Important progress has been made in the management of Helicobacter pylori infection and in this fifth edition of the Maastricht Consensus Report, key aspects related to the clinical role of H. pylori were re-evaluated in 2015. In the Maastricht V/Florence Consensus Conference, 43 experts from 24 countries examined new data related to H. pylori in five subdivided workshops: (1) Indications/Associations, (2) Diagnosis, (3) Treatment, (4) Prevention/Public Health, (5) H. pylori and the Gastric Microbiota. The results of the individual workshops were presented to a final consensus voting that included all participants. Recommendations are provided on the basis of the best available evidence and relevance to the management of H. pylori infection in the various clinical scenarios.

Preanalytical errors in medical laboratories: a review of the available methodologies of data collection and analysis

Preanalytical errors have previously been shown to contribute a significant proportion of errors in laboratory processes and contribute to a number of patient safety risks. Accreditation against ISO 15189:2012 requires that laboratory Quality Management Systems consider the impact of preanalytical processes in areas such as the identification and control of non-conformances, continual improvement, internal audit and quality indicators. Previous studies have shown that there is a wide variation in the definition, repertoire and collection methods for preanalytical quality indicators. The International Federation of Clinical Chemistry Working Group on Laboratory Errors and Patient Safety has defined a number of quality indicators for the preanalytical stage, and the adoption of harmonized definitions will support interlaboratory comparisons and continual improvement. There are a variety of data collection methods, including audit, manual recording processes, incident reporting mechanisms and laboratory information systems. Quality management processes such as benchmarking, statistical process control, Pareto analysis and failure mode and effect analysis can be used to review data and should be incorporated into clinical governance mechanisms. In this paper, The Association for Clinical Biochemistry and Laboratory Medicine PreAnalytical Specialist Interest Group review the various data collection methods available. Our recommendation is the use of the laboratory information management systems as a recording mechanism for preanalytical errors as this provides the easiest and most standardized mechanism of data capture.