Changes in left atrial function in patients undergoing cardioversion for atrial fibrillation: relevance of left atrial strain in heart failure

Background Left atrial (LA) reservoir strain provides prognostic information in patients with and without heart failure (HF), but might be altered by atrial fibrillation (AF). The aim of the current study was to investigate changes of LA deformation in patients undergoing cardioversion (CV) for first-time diagnosis of AF. Methods and results We performed 3D-echocardiography and strain analysis before CV (Baseline), after 25 ± 10 days (FU-1) and after 190 ± 20 days (FU-2). LA volumes, reservoir, conduit and active function were measured. In total, 51 patients were included of whom 35 were in SR at FU-1 (12 HF and preserved ejection fraction (HFpEF)), while 16 had ongoing recurrence of AF (9 HFpEF). LA maximum volume was unaffected by cardioversion (Baseline vs. FU-2: 41 ± 11 vs 40 ± 10 ml/m2; p = 0.85). Restored SR led to a significant increase in LA reservoir strain (Baseline vs FU-1: 12.9 ± 6.8 vs 24.6 ± 9.4, p < 0.0001), mediated by restored LA active strain (SR group Baseline vs. FU-1: 0 ± 0 vs. 12.3 ± 5.3%, p < 0.0001), while LA conduit strain remained unchanged (Baseline vs. FU-1: 12.9 ± 6.8 vs 13.1 ± 6.2, p = 0.78). Age-controlled LA active strain remained the only significant predictor of LA reservoir strain on multivariable analysis (β 1.2, CI 1.04–1.4, p < 0.0001). HFpEF patients exhibited a significant increase in LA active (8.2 ± 4.3 vs 12.2 ± 6.6%, p = 0.004) and reservoir strain (18.3 ± 5.7 vs. 22.8 ± 8.8, p = 0.04) between FU-1 and FU-2, associated with improved LV filling (r = 0.77, p = 0.005). Conclusion Reestablished SR improves LA reservoir strain by restoring LA active strain. Despite prolonged atrial stunning following CV, preserved SR might be of hemodynamic and prognostic benefit in HFpEF. Graphical abstract

A Physiology-Guided Classification of Active-Stress and Active-Strain Approaches for Continuum-Mechanical Modeling of Skeletal Muscle Tissue

The well-established sliding filament and cross-bridge theory explain the major biophysical mechanism responsible for a skeletal muscle's active behavior on a cellular level. However, the biomechanical function of skeletal muscles on the tissue scale, which is caused by the complex interplay of muscle fibers and extracellular connective tissue, is much less understood. Mathematical models provide one possibility to investigate physiological hypotheses. Continuum-mechanical models have hereby proven themselves to be very suitable to study the biomechanical behavior of whole muscles or entire limbs. Existing continuum-mechanical skeletal muscle models use either an active-stress or an active-strain approach to phenomenologically describe the mechanical behavior of active contractions. While any macroscopic constitutive model can be judged by it's ability to accurately replicate experimental data, the evaluation of muscle-specific material descriptions is difficult as suitable data is, unfortunately, currently not available. Thus, the discussions become more philosophical rather than following rigid methodological criteria. Within this work, we provide a extensive discussion on the underlying modeling assumptions of both the active-stress and the active-strain approach in the context of existing hypotheses of skeletal muscle physiology. We conclude that the active-stress approach resolves an idealized tissue transmitting active stresses through an independent pathway. In contrast, the active-strain approach reflects an idealized tissue employing an indirect, coupled pathway for active stress transmission. Finally the physiological hypothesis that skeletal muscles exhibit redundant pathways of intramuscular stress transmission represents the basis for considering a mixed-active-stress-active-strain constitutive framework.

BIOLOGICAL PROPERTIES OF DIAZOTROPH AZOSPIRILLUM BRASILENSE ISOLATED FROM SPRING TRITICALE ROOTS

Objective. Study the biological properties of the diazotroph Azospirillum brasilense 10/1, promising for improving the nitrogen nutrition of spring triticale and obtaining a high quality crop. Methods. A strain of nitrogen-fixing bacteria A. brasilense 10/1 isolated from washed roots of spring triticale Oberih Kharkivskyi by accumulation cultures method using Dobreiner semi-liquid nitrogen-free medium. Nitrogen-fixing microorganisms were isolated on potato agar with succinic acid by the Dryhalsky method. Potential nitrogenase activity on washed roots of spring triticale plants and nitrogen-fixing activity of azospirilla in pure culture were measured by gas chromatography. Electron microscopic studies of bacterial cells were performed by the method of negative contrast with uranyl acetate. Identification of azospirilla was carried out on the basis of the study of morphological, cultural, physiological and biochemical characteristics and using molecular genetic methods (16S rRNA sequence analysis). The nucleotide sequences were compared with the corresponding sequences from the international database GenBank NCBI using BLAST software. The sensitivity of bacteria to antibiotics and cereal seed pesticides was tested by disk diffusion method. Results. The active strain of nitrogen-fixing bacteria, identified as Azospirillum brasilense 10/1, was obtained by analytical selection methods. The identity of the sequences of 16S rRNA of A. brasilense 10/1 with reference strains of A. brasilense in the GenBank NCBI database is 99.5 % to 99.6 %. Diazotroph A. brasilense 10/1 is sensitive to cefotaxime, norfloxacin, chloramphenicol, gentamicin, erythromycin, kanamycin, furadonin, resistant to polymyxin, ampicillin, oxacillin, amoxicillin, ciprofloxacin, ceftriaxone. Vitavax 200FF and Fundazole dressers do not affect the development of A. brasilense 10/1, Maxim Star 025 FS somewhat inhibits the development of bacteria. Conclusion. The active strain of nitrogen-fixing bacteria A. brasilense 10/1 isolated from washed roots of triticale by methods of analytical selection, is a promising inoculant to increase yields and improve grain quality of this crop. A. brasilense 10/1 is deposited in the Depository of the Institute of Microbiology and Virology of the National Academy of Sciences of Ukraine under number B- 7317 and is protected by the patent of Ukraine No. 104212.

Active Strain Engineering of Soft Plasmene Nanosheets by Thermoresponsive Hydrogels

Epitaxy has been demonstrated to be a powerful technology to precisely engineer strains at the atomic level to modulate semiconductor device properties. However, it is not suitable for strain engineering...

Relationship between right ventricular diastolic dysfunction, right atrial phasic function and ventricular filling in pulmonary arterial hypertension

Background In pulmonary arterial hypertension (PAH) patients, the right ventricle (RV) stiffens due to hypertrophy, fibrosis and intrinsic (sarcomeric) stiffness. In these patients, end-diastolic elastance (stiffness, Eed) is associated with parameters of disease severity and predicts mortality. However, the effect of RV stiffness on RV filling and the effect of increased filling pressures on right atrial (RA) function remain elusive. Purpose To examine the relationship between RV diastolic stiffness and RA phasic function and the effect of diastolic dysfunction on ventricular filling in PAH patients. Methods Using single-beat pressure-volume analyses we determined Eed in controls (n=31) and baseline, treatment naive PAH patients (63 idiopathic, 9 hereditary and 25 connective tissue disease associated). We also measured RA reservoir, conduit and active strain by tissue tracking on cardiac magnetic resonance images. Furthermore, interventricular dyssynchrony was defined as a right to left difference in time to peak circumferential strain &gt;52ms (97.5th percentile in controls). Results End-diastolic pressure was higher in PAH patients (16±7 mmHg) than in controls (8±4 mmHg; p&lt;0.001). Median Eed in patients was 0.635 mmHg/mL (IQR: 0.40–0.99), while in controls it was 0.20 mmHg/mL (IQR: 0.15–0.24). In comparison with controls, patients had reduced RA reservoir (14.3±5.1% vs. 19.1±4.3%; p&lt;0.001) and conduit strain (−5.6±3.4% vs. −12.4±3.3%; p&lt;0.001), while RA active strain was enhanced (−9.0±4.0% vs. −7.5±2.8%; p=0.019). In patients with a stiff RV (Eed above median), RA conduit strain was worse than in patients with a more compliant RV as illustrated in figure A. However, no correlation between RA active strain and Eed was observed (Spearman rho 0.06; p=0.57). Passive filling time of the RV (end-systole until start of atrial contraction) was shorter in patients than in controls (244±136ms vs. 365±103ms; p&lt;0.001). Higher heart rate and ventricular dyssynchrony are causes of a shorter passive filling time in patients as illustrated in figure B. When comparing patients with short vs. long passive filling time (cutoff median of 220ms), the RV passive filling volume was lower (24±15ml vs. 42±19ml; p&lt;0.001). The active filling volume was slightly higher, although not significantly (25±17ml vs. 19±15ml; p=0.12). Conclusion Stiffening of the RV in PAH patients is accompanied by increased filling pressures and decreased RA conduit strain, while there is no correlation between Eed and RA active strain. Higher heart rate and ventricular dyssynchrony lead to shorter passive filling time of the RV, which in turn leads to lower passive filling volume. In contrast, the active filling volume is preserved in these patients. Funding Acknowledgement Type of funding source: Public grant(s) – National budget only. Main funding source(s): The Netherlands Organization for Scientific Research

Right ventricular function correlates of right atrial strain in pulmonary hypertension: a combined cardiac magnetic resonance and conductance catheter study

The functional relevance of right atrial (RA) function in pulmonary hypertension (PH) remains incompletely understood. The purpose of this study was to explore the correlation of cardiac magnetic resonance (CMR) feature tracking-derived RA phasic function with invasively measured pressure-volume (P-V) loop-derived right ventricular (RV) end-diastolic elastance ( Eed) and RV-arterial coupling [ratio of end-systolic elastance to arterial elastance ( Ees/ Ea)]. In 54 patients with severe PH, CMR was performed within 24 h of diagnostic right heart catheterization and P-V measurements. RA phasic function was assessed by CMR imaging of RA reservoir, passive, and active strain. The association of RA phasic function with indexes of RV function was evaluated by Spearman’s rank correlation and linear regression analyses. Median [interquartile range] RA reservoir strain, passive strain, and active strain were 19.5% [11.0–24.5], 7.0% [4.0–12.0], and 13.0% [7.0–18.5], respectively. Ees/ Ea was 0.73 [0.48–1.08], and Eed was 0.14 mmHg/mL [0.05–0.22]. RV diastolic impairment [RV end-diastolic pressure (EDP) and Eed] was correlated with RA phasic function, but Ea and Ees were not. In addition, RA phasic function was correlated with inferior vena cava diameter. In multivariate linear regression analysis, adjusting for key P-V loop indexes, Eed and EDP remained significantly associated with RA phasic function. We conclude that RA phasic function is altered in relation to impaired diastolic function of the chronically overloaded right ventricle and contributes to backward venous flow and systemic congestion. These results call for more attention to RA function in the management of patients with PH. NEW & NOTEWORTHY There is growing awareness of the importance of the right atrial (RA)-right ventricular (RV) axis in pulmonary hypertension (PH). Our results uncover alterations in RA phasic function that are related to depressed RV lusitropic function and contribute to backward venous return and systemic congestion in chronic RV overload. Assessment of RA function should be part of the management and follow-up of patients with PH.

An orthotropic electro-viscoelastic model for the heart with stress-assisted diffusion

We propose and analyse the properties of a new class of models for the electromechanics of cardiac tissue. The set of governing equations consists of nonlinear elasticity using a viscoelastic and orthotropic exponential constitutive law, for both active stress and active strain formulations of active mechanics, coupled with a four-variable phenomenological model for human cardiac cell electrophysiology, which produces an accurate description of the action potential. The conductivities in the model of electric propagation are modified according to stress, inducing an additional degree of nonlinearity and anisotropy in the coupling mechanisms, and the activation model assumes a simplified stretch–calcium interaction generating active tension or active strain. The influence of the new terms in the electromechanical model is evaluated through a sensitivity analysis, and we provide numerical validation through a set of computational tests using a novel mixed-primal finite element scheme.