Patient-Specific MRI-Based Right Ventricle Models Using Different Zero-Load Diastole and Systole Geometries for Better Cardiac Stress and Strain Calculations and Pulmonary Valve Replacement Surgical Outcome Predictions

Abstract

BackgroundAccurate calculation of ventricular stress and strain is critical for cardiovascular investigations. Sarcomere shortening in active contraction leads to change of ventricular zero-stress configurations during the cardiac cycle. A new model using different zero-load diastole and systole geometries was introduced to provide more accurate cardiac stress/strain calculations with potential to predict post pulmonary valve replacement (PVR) surgical outcome.MethodsCardiac magnetic resonance (CMR) data were obtained from 16 patients with repaired tetralogy of Fallot prior to and 6 months after pulmonary valve replacement (8 male, 8 female, mean age 34.5 years). Patients were divided into Group 1 (n = 8) with better post PVR outcome and Group 2 (n = 8) with worse post PVR outcome based on their change in RV ejection fraction (EF). CMR-based patient-specific computational RV/LV models using one zero-load geometry (1G model) and two zero-load geometries (diastole and systole, 2G model) were constructed and RV wall thickness, volume, circumferential and longitudinal curvatures, mechanical stress and strain were obtained for analysis. Pairwise T-test and Linear Mixed Effect (LME) model were used to determine if the differences from the 1G and 2G models were statistically significant, with the dependence of the pair-wise observations and the patient-slice clustering effects being taken into consideration. For group comparisons, continuous variables (RV volumes, WT, C- and L- curvatures, and stress and strain values) were summarized as mean ± SD and compared between the outcome groups by using an unpaired Student t-test. Logistic regression analysis was used to identify potential morphological and mechanical predictors for post PVR surgical outcome.ResultsBased on results from the 16 patients, mean begin-ejection stress and strain from the 2G model were 28% and 40% higher than that from the 1G model, respectively. Using the 2G model results, RV EF changes correlated negatively with stress (r = -0.609, P = 0.012) and with pre-PVR RV end-diastole volume (r = -0.60, P = 0.015), but did not correlate with WT, C-curvature, L-curvature, or strain. At begin-ejection, mean RV stress of Group 2 was 57.4% higher than that of Group 1 (130.1±60.7 vs. 82.7±38.8 kPa, P = 0.0042). Stress was the only parameter that showed significant differences between the two groups. The combination of circumferential curvature, RV volume and the difference between begin-ejection stress and end-ejection stress was the best predictor for post PVR outcome with an area under the ROC curve of 0.855. The begin-ejection stress was the best single predictor among the 8 individual parameters with an area under the ROC curve of 0.782.ConclusionThe new 2G model may be able to provide more accurate ventricular stress and strain calculations for potential clinical applications. Combining morphological and mechanical parameters may provide better predictions for post PVR outcome.

Trifecta St. Jude medical® aortic valve in pulmonary position

“…[52] General agreement exists on the indication for PV implantation in asymptomatic patients in the presence of any of the following criteria, as judged by echocardiography and/or magnetic resonance imaging: (a) PV regurgitation >20%; (b) indexed end-diastolic right ventricular volume >120–150 ml m –2 BSA; or (c) indexed end-systolic right ventricular volume >80–90 ml m –2 BSA. [14,18,19,22,24,25] In our experience, all asymptomatic patients were matching all the accepted criteria of indication for PV implantation. The only two patients with indexed right ventricular end-diastolic volume < 150 ml m –2 BSA (respectively 130 and 142 ml m –2 BSA) were two of the four patients with associated right ventricular outflow tract obstruction.…”

Comparisons of Simulation Results between Passive and Active FSI Models for Left Ventricle in Hypertrophic Obstructive Cardiomyopathy

“…In the construction process of both of active and passive models, the initial shrinkage rate was set as 5% to receive the zero-load geometry which is the starting geometry for the numerical simulation [33,34]. When the pressure was applied at inlet, The finite element meshes was generated by the volume component-fitting method [22,32].…”

Ventricle stress/strain comparisons between Tetralogy of Fallot patients and healthy using models with different zero-load diastole and systole morphologies

“…Two different zero-load (diastole and systole) geometries are needed to simulate ventricle diastole and systole phases, respectively. These models are called 2G models since two zero-load geometries are used [13]. The 2G model is our way to change ventricle zero-load geometry between systole and diastole phases.…”

“…Early cardiac magnetic resonance imaging (CMR)-based ventricle models were introduced by Axel and Saber et al for mechanical analysis and investigations [11, 12]. We have introduced patient-specific CMR image-based computational right and left ventricle (RV/LV) models with fluid-structure interactions (FSI) to assess outcomes of various RV reconstruction techniques with different scar tissue trimming and patch sizes [4, 5, 13, 14, 15]. A recent review can be found in [15].…”