Models of cardiac mechanics are increasingly used to investigate cardiac physiology. These models are characterized by a high level of complexity, including the particular anisotropic material properties of biological tissue and the actively contracting material. A large number of independent simulation codes have been developed, but a consistent way of verifying the accuracy and replicability of simulations is lacking. To aid in the verification of current and future cardiac mechanics solvers, this study provides three benchmark problems for cardiac mechanics. These benchmark problems test the ability to accurately simulate pressure-type forces that depend on the deformed objects geometry, anisotropic and spatially varying material properties similar to those seen in the left ventricle and active contractile forces. The benchmark was solved by 11 different groups to generate consensus solutions, with typical differences in higher-resolution solutions at approximately 0.5%, and consistent results between linear, quadratic and cubic finite elements as well as different approaches to simulating incompressible materials. Online tools and solutions are made available to allow these tests to be effectively used in verification of future cardiac mechanics software.

During the contraction of the ventricles, the ventricles interact with the atria as well as with the pericardium and the surrounding tissue in which the heart is embedded. The atria are stretched, and the atrioventricular plane moves toward the apex. The atrioventricular plane displacement (AVPD) is considered to be a major contributor to the ventricular function, and a reduced AVPD is strongly related to heart failure. At the same time, the epicardium slides almost frictionlessly on the pericardium with permanent contact. Although the interaction between the ventricles, the atria and the pericardium plays an important role for the deformation of the heart, this aspect is usually not considered in computational models. In this work, we present an electromechanical model of the heart, which takes into account the interaction between ventricles, pericardium and atria and allows to reproduce the AVPD. To solve the contact problem of epicardium and pericardium, a contact handling algorithm based on penalty formulation was developed, which ensures frictionless and permanent contact. Two simulations of the ventricular contraction were conducted, one with contact handling of pericardium and heart and one without. In the simulation with contact handling, the atria were stretched during the contraction of the ventricles, while, due to the permanent contact with the pericardium, their volume increased. In contrast to that, in the simulations without pericardium, the atria were also stretched, but the change in the atrial volume was much smaller. Furthermore, the pericardium reduced the radial contraction of the ventricles and at the same time increased the AVPD.

BackgroundLong axis strain (LAS) has been shown to be a fast assessable parameter representing global left ventricular (LV) longitudinal function in cardiovascular magnetic resonance (CMR). However, the prognostic value of LAS in cardiomyopathies with reduced left ventricular ejection fraction (LVEF) has not been evaluated yet.Methods and resultsIn 146 subjects with non-ischemic dilated cardiomyopathy (NIDCM, LVEF ≤45 %) LAS was assessed retrospectively from standard non-contrast SSFP cine sequences by measuring the distance between the epicardial border of the left ventricular apex and the midpoint of a line connecting the origins of the mitral valve leaflets in end-systole and end-diastole. The final values were calculated according to the strain formula.The primary endpoint of the study was defined as a combination of cardiac death, heart transplantation or aborted sudden cardiac death and occurred in 24 subjects during follow-up. Patients with LAS values > −5 % showed a significant higher rate of cardiac events independent of the presence of late gadolinium enhancement (LGE). The multivariate Cox regression analysis revealed that LVEDV/BSA (HR: 1.01, p < 0.05), presence of LGE (HR: 2.51, p < 0.05) and LAS (HR: 1.28, p < 0.05) were independent predictors for cardiac events. In a sequential cox regression analysis LAS offered significant incremental information (p < 0.05) for the prediction of outcome in addition to LGE and LVEDV/BSA. Using a dichotomous three point scoring model for risk stratification, including LVEF <35 %, LAS > −10 % and the presence of LGE, patients with 3 points had a significantly higher risk for cardiac events than those with 2 or less points.ConclusionAssessment of long axis function with LAS offers significant incremental information for the prediction of cardiac events in NIDCM and improves risk stratification beyond established CMR parameters.

Ventricular wall deformation is widely assumed to have an impact on the morphology of the T-wave that can be measured on the body surface. This study aims at quantifying these effects based on an in silico approach. To this end, we used a hybrid, static-dynamic approach: action potential propagation and repolarization were simulated on an electrophysiologically detailed but static 3-D heart model while the forward calculation accounted for ventricular deformation and the associated movement of the electrical sources (thus, it was dynamic). The displacement vectors that describe the ventricular motion were extracted from cinematographic and tagged MRI data using an elastic registration procedure. To probe to what extent the T-wave changes depend on the synchrony/asynchrony of mechanical relaxation and electrical repolarization, we created three electrophysiological configurations, each with a unique QT time: a setup with physiological QT time, a setup with pathologically short QT time (SQT), and pathologically long QT time (LQT), respectively. For all three electrophysiological configurations, a reduction of the T-wave amplitude was observed when the dynamic model was used for the forward calculations. The largest amplitude changes and the lowest correlation coefficients between the static and dynamic model were observed for the SQT setup, followed by the physiological QT and LQT setups.

Measurements of bone mineral density (BMD) are useful for the assessment of fracture risk in osteoporosis. First prospective studies showed that quantitative ultrasound as measured at the calcaneus also predicts future hip fracture risk, independently of BMD and as accurately as BMD. The aim of this study was to compile a reference population for a new ultrasound device that determines amplitude-dependent speed of sound (AD-SOS) through the proximal phalanges of the hand and to prove its ability to distinguish between health volunteers and osteoporotic patients. In a case-control study we examined 139 healthy women aged 21-94 years and a group of 24 female patients aged 69-94 years with recent hip fractures. In the healthy reference population additional BMD measurements were performed with dual-energy X-ray absorptiometry (DXA) and quantitative ultrasound measurements at the calcaneus were carried out. In vivo precision of AD-SOS measurements through the phalanges was 0.52% CV. Simple regression analyses showed a negative correlation with age (r = -0.73, p < 0.001); modest significant correlations with BMD of the lumbar spine (r = 0.36, p < 0.001) and BMD of the femoral neck (r = 0.37, p = 0.002) as measured with DXA were shown. The comparison with another ultrasound device measuring SOS and broadband ultrasound attenuation (BUA) through the calcaneus showed correlation with SOS (r = 0.50, p < 0.001); no significant correlation was found with BUA measurements. Furthermore a dependency of AD-SOS values in anthropometric factors such as body mass index (r = 0.37, p < 0.001), height (r = 0.40, p < 0.001) and weight (r = 0.23, p < 0.05) was shown. First study results on 24 clinically diagnosed osteoporotic patients, defined as patients with recent (< 1 week) pertrochanteric or femoral neck fractures, showed a good separation between age- and sex-matched controls and osteoporotic patients (Z = -2.0 SD). Receiver operating characteristic (ROC) curves showed an area under the fitted curve of 0.83 +/- 0.06. These results are powerful for a device measuring AD-SOS through the proximal phalanges of the hand, and further prospective studies have proven the capability of phalangeal ultrasound in fracture risk assessment.