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Patient-specific in vivo ventricle mechanical wall stress and strain conditions are important for cardiovascular investigations and should be calculated from correct zero-load ventricle morphologies. Cardiac magnetic resonance (CMR) data were obtained from 6 healthy volunteers and 12 Tetralogy of Fallot (TOF) patients with consent obtained. 3D patient-specific CMR-based ventricle models with different zero-load diastole and systole geometries due to myocardium contraction and relaxation were constructed to qualify right ventricle (RV) diastole and systole stress and strain values at begin-filling, end-filling, begin-ejection, and end-ejection, respectively. Our new models (called 2G models) can provide end-diastole and end-systole stress/strain values which models with one zero-load geometries (called 1G models) could not provide. 2G mean end-ejection stress value from the 18 participants was 321.4% higher than that from 1G models (p = 0.0002). 2G mean strain values was 230% higher than that of 1G models (p = 0.0002). TOF group (TG) end-ejection mean stress value was 105.4% higher than that of healthy group (HG) (17.54±7.42kPa vs. 8.54±0.92kPa, p = 0.0245). Worse outcome group (WG, n = 6) post pulmonary valve replacement (PVR) begin-ejection mean stress was 57.4% higher than that of better outcome group (BG, 86.94±26.29 vs. 52.93±22.86 kPa; p = 0.041). Among 7 selected parameters, End-filling stress was the best predictor to differentiate BG patients from WG patients with prediction accuracy = 0.8208 and area under receiver operating characteristic curve (AUC) value at 0.8135 (EE stress). Large scale studies are needed to further validate our findings., Competing Interests: The authors have declared that no competing interests exist.

Patient-specific in vivo ventricle material parameter determination is important for cardiovascular investigations. A new cardiac magnetic image (CMR)-based modeling approach with different zero-load diastole and systole geometries was adopted to estimate right ventricle material parameter values for healthy and patients with Tetralogy of Fallot (TOF) and seeking potential clinical applications. CMR data were obtained from 6 healthy volunteers and 16 TOF patients with consent obtained. CMR-based RV/LV models were constructed using two zero-load geometries (diastole and systole, 2G model). Material parameter values for begin-filling (BF), end-filling (EF), begin-ejection (BE), and end-ejection (EE) were recorded for analyses. Effective Young's moduli (YM) for fiber direction stress-strain curves were calculated for easy comparisons. The mean EE YM value of TOF patients was 78.6% higher than that of the healthy group (HG). The mean end-ejection YM value from worse-outcome TOF group (WG) post pulmonary valve replacement (PVR) surgery was 59.5% higher than that from the better-outcome TOF group (BG). Using begin-filling YM and end-ejection YM as predictors and the classic logistic regression model to different better-outcome group patients from worse-outcome group patients, the areas under Receiver Operating Characteristic (ROC) curves were found to be 0.797 and 0.883 for begin-filling YM and end-ejection YM, respectively. The sensitivity and specificity 0.761 and 0.755 using end-ejection YM as the predictor. This preliminary study suggests that ventricle material stiffness could be a potential parameter to be used to differentiate BG patients from WG patients with further effort and large-scale patient data validations., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Objective: Patients with repaired tetralogy of Fallot account for a substantial proportion of cases with late-onset right ventricular failure. The current surgical approach, which includes pulmonary valve replacement/insertion, has yielded mixed results. Therefore, it may be clinically useful to identify parameters that can be used to predict right ventricular function response to pulmonary valve replacement., Methods: Cardiac magnetic resonance data before and 6 months after pulmonary valve replacement were obtained from 16 patients with repaired tetralogy of Fallot (8 male, 8 female; median age, 42.75 years). Right ventricular ejection fraction change from pre- to postpulmonary valve replacement was used as the outcome. The patients were divided into group 1 (n = 8, better outcome) and group 2 (n = 8, worst outcome). Cardiac magnetic resonance-based patient-specific computational right ventricular/left ventricular models were constructed, and right ventricular mechanical stress and strain, wall thickness, curvature, and volumes were obtained for analysis., Results: Our results indicated that right ventricular wall stress was the best single predictor for postpulmonary valve replacement outcome with an area under the receiver operating characteristic curve of 0.819. Mean values of stress, strain, wall thickness, and longitudinal curvature differed significantly between the 2 groups with right ventricular wall stress showing the largest difference. Mean right ventricular stress in group 2 was 103% higher than in group 1., Conclusions: Computational modeling and right ventricular stress may be used as tools to identify right ventricular function response to pulmonary valve replacement. Large-scale clinical studies are needed to validate these preliminary findings., (Copyright © 2016 The American Association for Thoracic Surgery. Published by Elsevier Inc. All rights reserved.)

Objective: Patients with repaired tetralogy of Fallot account for most cases of late-onset right ventricle failure. The current surgical approach, which includes pulmonary valve replacement/insertion, has yielded mixed results. A new surgical option of placing an elastic band in the right ventricle is proposed to improve right ventricular cardiac function as measured by the ejection fraction., Methods: A total of 20 computational right ventricular/left ventricular/patch/band combination models using cardiac magnetic resonance imaging from a patient with tetralogy of Fallot were constructed to investigate the effect of band material stiffness variations, band length, and active contraction. These models included 4 different band material properties, 3 band length, 3 active contracting band materials, and models with patch and scar replaced by contracting tissue., Results: Our results indicated that the band insertion, combined with active band contraction and tissue regeneration techniques that restore right ventricular myocardium, has the potential to improve right ventricular ejection fraction by 7.5% (41.63% ejection fraction from the best active band model to more than 34.10% ejection fraction from baseline passive band model) and 4.2% (41.63% from the best active band model compared with cardiac magnetic resonance imaging-measured ejection fraction of 37.45%)., Conclusions: The cardiac magnetic resonance imaging-based right ventricular/left ventricular/patch/band model provides a proof of concept for using elastic bands to improve right ventricular cardiac function. Band insertion, combined with myocardium regeneration techniques and right ventricular remodeling surgical procedures, has the potential to improve ventricular function in patients with repaired tetralogy of Fallot and other similar forms of right ventricular dysfunction after surgery. Additional investigations using in vitro experiments, animal models, and, finally, patient studies are warranted., (Copyright © 2013 The American Association for Thoracic Surgery. Published by Mosby, Inc. All rights reserved.)

Introduction: Right ventricle (RV) failure is one of the most common symptoms among patients with repaired tetralogy of Fallot (TOF). The current surgery treatment approach including pulmonary valve replacement (PVR) showed mixed post-surgery outcomes. A novel PVR surgical strategy using active contracting bands is proposed to improve the post-PVR outcome. In lieu of testing the risky surgical procedures on real patients, computational simulations (virtual surgery) using biomechanical ventricle models based on patient-specific cardiac magnetic resonance (CMR) data were performed to test the feasibility of the PVR procedures with active contracting bands. Different band combination and insertion options were tested to identify optimal surgery designs. Method: Cardiac magnetic resonance data were obtained from one TOF patient (male, age 23) whose informed consent was obtained. A total of 21 finite element models were constructed and solved following our established procedures to investigate the outcomes of the band insertion surgery. The non-linear anisotropic Mooney–Rivlin model was used as the material model. Five different band insertion plans were simulated (three single band models with different band locations, one model with two bands, and one model with three bands). Three band contraction ratios (10, 15, and 20%) and passive bands (0% contraction ratio) were tested. RV ejection fraction was used as the measure for cardiac function. Results: The RV ejection fraction from the three-band model with 20% contraction increased to 41.58% from the baseline of 37.38%, a 4.20% absolute improvement. The RV ejection fractions from the other four band models with 20% contraction rate were 39.70, 39.45, and 40.70% (two-band) and 39.17%, respectively. The mean RV stress and strain values from all of the 21 models showed only modest differences (5–11%). Conclusion: This pilot study demonstrated that the three-band model with 20% band contraction ratio led to 4.20% absolute improvement in the RV ejection fraction, which is considered as clinically significant. The passive elastic bands led to the reduction of the RV ejection fractions. The modeling results and surgical strategy need to be further developed and validated by a multi-patient study and animal experiments before clinical trial could become possible. Tissue regeneration techniques are needed to produce materials for the contracting bands. [ABSTRACT FROM AUTHOR]

Patients with repaired Tetralogy of Fallot (ToF), a congenital heart defect which includes a ventricular septal defect and severe right ventricular outflow obstruction, account for the majority of cases with late onset right ventricle (RV) failure. The current surgical approach, which includes pulmonary valve replacement/insertion (PVR), has yielded mixed results. A computational parametric study using 7 patient-specific RV/LV models based on cardiac magnetic resonance (CMR) data as "virtual surgery" was performed to investigate the impact of patch size, RV remodeling and tissue regeneration in PVR surgery design on RV cardiac functions. Two patch sizes, three degrees of scar trimming (RV volume shrinkages: 9%, 17%, 25%) and hypothetical use of regenerated myocardium as replacement of patch and scar were considered in these models. Our preliminary results indicate that each of the three techniques (smaller patch, RV remodeling, and myocardium regeneration) had modest improvement on post-PVR RV ejection fraction (from 1.76%-4% over the conventional PVR procedure) and combination of all three techniques had the best performance (a 4.74% improvement in ejection fraction over the conventional PVR, for the patient studied). Changes in RV stress, strain and curvatures were also observed. However, their linkages to RV ejection fraction were less clear. Further investigations are required to confirm our findings. [ABSTRACT FROM AUTHOR]

Computational biomechanical models are widely used in cardiovascular research for better understanding of mechanisms governing disease development, quantitative diagnostic strategies and improved surgical designs with better outcome. Patients with repaired tetralogy of Fallot (TOF) account for the majority of cases with late onset right ventricle (RV) failure. The current surgical approach, which includes pulmonary valve replacement/insertion (PVR), has yielded mixed results. An innovative PVR surgical approach was proposed using active contracting bands to help ventricle to contract and improve RV function measured by ejection fraction [1]. Muscle active contraction caused by sarcomere shortening leads to change of zero-load configurations. In lieu of experimenting using real surgery, computational simulations (called virtual surgery) were performed to test different band combination and insertion options to identify optimal surgery design and band insertion plan. Cardiac magnetic resonance (CMR) data were obtained from one TOF patient (sex: m, age: 22.5 y) before pulmonary valve replacement surgery. The RV end-systole volume was 254.49 ml, end-diastole volume was 406.91 ml, and ejection fraction was 37.46%. A total of 15 computational RV/LV/Patch/Band combination models based on (CMR) imaging were constructed to investigate the impact of band insertion surgery. These models included 5 different band insertion models: Model 1 with one band at anterior to the middle of papillary muscle; Model 2 with one band at posterior to the middle of papillary muscle; Model 3 with 2 bands which are the ones from Models 1 & 2 combined; Model 4 with a band at the base of the papillary muscle; Model 5 with 3 bands which is a combination of Models 3 & 4. Simulations will be performed using the 5 models with 3 different band contraction ratio (10%, 15% and 20% band zero-stress length reduction). A pre-shrink process was performed on in-vivo begin-filling and end-systole MRI data to obtain diastole and systole zero-load ventricle geometries. An extra 5-8% shrinkage was applied to obtain corresponding systole zero-load geometry reflecting myocardium sarcomere shortening. The nonlinear Mooney- Rivlin model was used to describe the ventricle material properties with their material parameter values adjusted to match MRI data. The band material properties were in the same scale with healthy right ventricle. The RV/LV/Band model construction and solution procedures were the same as described in [1]. Model 5 with band contraction ratio of 20% has the ability to improve RV ejection fraction to 41.07%, which represented a 3.61% absolute improvement, or 9.6% relative improvement using pre-PVR ejection fraction as the baseline number. The ejection fractions for Models 1-4 were 39.28%, 38.87%, 40.34, and 39.47, respectively. This pilot work demonstrated that the band insertion surgery may have great potential to improve post-PVR RV cardiac function for patients with repaired TOF. Further investigations using in-vitro animal experiments and final patient studies are warranted. [ABSTRACT FROM AUTHOR]

Ventricle mechanical stress and strain calculations play an important role in cardiovascular investigations. Patients with repaired tetralogy of Fallot (TOF) account for the majority of cases with late onset right ventricular (RV) failure. The current surgical approach, including pulmonary valve replacement(PVR), has yielded mixed results with some patients recover RV function after pulmonary valve insertion with or without concomitant RV remodeling surgery but some do not[Therrien, Siu and McLaughlin (2000);]. Cardiac magnetic resonance (CMR) data were collected from 6 healthy volunteers and 12 Tetralogy of Fallot (TOF) patients before PVR with consent obtained. 12 patients were divided into two groups depending on right ventricle post-surgery recover (6 for each group). 3D patient-specific CMR-based ventricle models with different zero-load diastole and systole geometries were constructed to qualify right ventricle (RV) stress and strain values at begin-filling, end-filling, begin-ejection, and end-ejection, respectively. The models are solved with ADINA. Our new models (called 2G models) could provide end-diastole and end-systole stress/strain values which the old models with only one zero-load geometries (called 1G models) could not provide [Tang, Del Nido, Yang et al. (2016)]. Logistic regression with 5-fold cross validation was adopted to predict pulmonary valve replacement outcome. The results showed 2G mean end-ejection stress value from the 18 participants was 321.4% higher than that from 1G models (p=0.0002). 2G mean strain values was 230% higher than that of 1G models (p=0.0002). TOF group (TG) end-ejection mean stress value was 105.4% higher than that of healthy group (HG) (17.54±7.42 kPa vs. 8.54±0.92kPa, p=0.0245). Worse outcome group (WG) begin-ejection mean stress was 57.4% higher than that of better outcome group (bG, 86.94±26.29 vs. 52.93±22.86 kPa; p=0.041). Among 7 chosen parameters (stress, strain, age, gender, right volume end-diastole volume index, right volume end-systole volume index and ejection fracture), end-filling stress was the best predictor to differentiate BG patients from WG patients with prediction accuracy=0.8208. 2G models may provide more accurate stress/strain results than 1G models and be applied in clinical situation, potentially. Large scale studies are still needed for validation. [ABSTRACT FROM AUTHOR]