A mathematical model (TriSeg model) of ventricular mechanics incorporating mechanical interaction of the left and right ventricular free walls and the interventricular septum is presented. Global left and right ventricular pump mechanics were related to representative myofiber mechanics in the three ventricular walls, satisfying the principle of conservation of energy. The walls were mechanically coupled satisfying tensile force equilibrium in the junction. Wall sizes and masses were rendered by adaptation to normalize mechanical myofiber load to physiological standard levels. The TriSeg model was implemented in the previously published lumped closed-loop CircAdapt model of heart and circulation. Simulation results of cardiac mechanics and hemodynamics during normal ventricular loading, acute pulmonary hypertension, and chronic pulmonary hypertension (including load adaptation) agreed with clinical data as obtained in healthy volunteers and pulmonary hypertension patients. In chronic pulmonary hypertension, the model predicted right ventricular free wall hypertrophy, increased systolic pulmonary flow acceleration, and increased right ventricular isovolumic contraction and relaxation times. Furthermore, septal curvature decreased linearly with its transmural pressure difference. In conclusion, the TriSeg model enables realistic simulation of ventricular mechanics including interaction between left and right ventricular pump mechanics, dynamics of septal geometry, and myofiber mechanics in the three ventricular walls.

By current guidelines a considerable part of the patients selected for cardiac resynchronization therapy (CRT) do not respond to the therapy. We hypothesized that mechanical discoordination [opposite strain within the left ventricular (LV) wall] predicts reversal of LV remodeling upon CRT better than mechanical dyssynchrony. MRI tagging images were acquired in CRT candidates ( n = 19) and in healthy control subjects ( n = 9). Circumferential strain (ε_cc) was determined in 160 regions. From ε_cc signals we derived 1) an index of mechanical discoordination [internal stretch fraction (ISF), defined as the ratio of stretch to shortening during ejection] and 2) indexes of mechanical dyssynchrony: the 10–90% width of time to onset of shortening, time to peak shortening, and end-systolic strain. LV end-diastolic volume (LVEDV), end-systolic volume (LVESV), and ejection fraction (LVEF) were determined before and after 3 mo of CRT. Responders were defined as those patients in whom LVESV decreased by >15%. In responders ( n = 10), CRT increased LVEF and decreased LVEDV and LVESV (11 ± 6%, 21 ± 16%, and 30 ± 16%, respectively) significantly more ( P < 0.05) than in nonresponders (1 ± 6%, 3 ± 4%, and 5 ± 10%, respectively). Among mechanical indexes, only ISF was different between responders and nonresponders (0.53 ± 0.25 vs. 0.31 ± 0.16; P < 0.05). In patients with ISF >0.4 ( n = 10), LVESV decreased by 31 ± 18% vs. 5 ± 11% in patients with ISF <0.4 ( P < 0.05). We conclude that mechanical discoordination, as estimated from ISF, is a better predictor of reverse remodeling after CRT than differences in time to onset and time to peak shortening. Therefore, discoordination rather than dyssynchrony appears to reflect the reserve contractile capacity that can be recruited by CRT.

Dyssynchrony of myocardial deformation is usually described in terms of variability only (e.g. standard deviations SD's). A description in terms of the spatio-temporal distribution pattern (vector-analysis) of dyssynchrony or by indices estimating its impact by expressing dyscoordination of shortening in relation to the global ventricular shortening may be preferential. Strain echocardiography by speckle tracking is a new non-invasive, albeit 2-D imaging modality to study myocardial deformation.

Mechanical activation of the normal left ventricle (LV) is not simultaneous; however, the potential consequences of the ejection function of the ventricle are not entirely known. We studied contraction of the LV free wall to determine whether it reveals a contraction wave in the axial direction during ejection. Seven guinea pig hearts in situ were studied via thoracotomy. In each heart, the ventricular and aortic pressures were measured by two microtipped manometers (2-Fr, Millar). Contraction of the LV free wall was assessed with a video system (Dalsa D6-0256 camera and EPIX PIXCI D32 frame grabber; acquisition rate, 500 frames/s), and 15–18 epicardial markers were used to divide the region into 20–25 triangular areas. The area sizes were studied during contraction to locate the position of the contraction wave. For each triangular area, two variables were determined as follows: the time (t_c) from the end of diastole until the size of the area reached 80% of maximum size reduction (normalized with the duration of systole) and the normalized latitude (L_ax) of the area (determined at the end of diastole). A relationship between these two variables was determined by regression analysis. We found that the t_c at which the contraction wave reached a triangular area was in positive correlation with the L_ax value for that triangular area with a slope of 0.25 ± 0.09 and a linear correlation coefficient of 0.41 ± 0.08. Thus contraction in the guinea pig LV free wall occurs progressively from apex to base with successive areas reaching 80% contraction.

Background: On a post-discharge eLearning platform for patients with coronary artery disease, videos are used as the main educational media. Medical content takes a long time to be thoroughly explained, frequently exceeding the viewer’s attention span. To find the optimal duration for such an educational video, we studied the retention of video watching. Methods: In this study, 135 (88% male; age 62±9 years) patients with coronary artery disease actively used eLearning platform which included 60 video recordings with duration ranging from 21 sec to 303 sec. The videos were divided into two groups based on their duration (short < 100 sec and long > 100 sec). From the platform usage metadata, an average video retention rate was obtained as a ratio of video viewing time and total video duration for videos watched six times or more. Independent t-tests for mean values and f-test for variance were used to compare the groups. Results: In total, 35 (18 short and 17 long) videos were included in the study and were viewed (mean ± SD) 22 ± 11 times. The mean duration of short videos was: 80 sec ± 14 sec and of long videos it was: 160 sec ± 51 sec. The retention rate in the short and long group was 0.99 ± 0.05 and 0.94 ± 0.19 respectively. Average values were not signi­ficantly different (P = 0.33), but variances were (P < 0.05). Conclusions: This study shows that the effective attention span for a video recording of this kind, based on an eLearning set-up and local population, is up to 100 sec. Videos shorter than 100sec are mostly watched fully without a break. In contrast, longer videos are often rewound, and parts watched again or not watched to the full length at all.