title: 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: BACKGROUND
  Accurate 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.
  
  
  METHODS
  Cardiac 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.
  
  
  RESULTS
  Based 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.
  
  
  CONCLUSIONS
  The 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.
authors.affiliation: School of Biological Science & Medical Engineering, Southeast University, Nanjing, China.|Mathematical Sciences Department, Worcester Polytechnic Institute, Worcester, MA, United States of America.
authors.forename: Dalin
authors.initials: D
authors.lastname: Tang
authors.affiliation: Department of Cardiac Surgery, Boston Children's Hospital, Department of Surgery, Harvard Medical School, Boston, MA, United States of America.
authors.forename: Pedro J
authors.initials: PJ
authors.lastname: Del Nido
authors.affiliation: Mathematical Sciences Department, Worcester Polytechnic Institute, Worcester, MA, United States of America.|China Information Tech. Designing & Consulting Institute Co., Ltd., Beijing, China.
authors.forename: Chun
authors.initials: C
authors.lastname: Yang
authors.affiliation: Mathematical Sciences Department, Worcester Polytechnic Institute, Worcester, MA, United States of America.
authors.forename: Heng
authors.initials: H
authors.lastname: Zuo
authors.affiliation: Mathematical Sciences Department, Worcester Polytechnic Institute, Worcester, MA, United States of America.|School of Mathematical Sciences, Xiamen University, Xiamen, Fujian, China.
authors.forename: Xueying
authors.initials: X
authors.lastname: Huang
authors.affiliation: Department of Cardiology, Boston Children's Hospital, Department of Pediatrics, Harvard Medical School, Boston, MA, United States of America.
authors.forename: Rahul H
authors.initials: RH
authors.lastname: Rathod
authors.affiliation: Department of Cardiology, Boston Children's Hospital, Department of Pediatrics, Harvard Medical School, Boston, MA, United States of America.
authors.forename: Vasu
authors.initials: V
authors.lastname: Gooty
authors.affiliation: Department of Cardiology, Boston Children's Hospital, Department of Pediatrics, Harvard Medical School, Boston, MA, United States of America.
authors.forename: Alexander
authors.initials: A
authors.lastname: Tang
authors.affiliation: Mathematical Sciences Department, Worcester Polytechnic Institute, Worcester, MA, United States of America.
authors.forename: Zheyang
authors.initials: Z
authors.lastname: Wu
authors.affiliation: Department of Biomedical Engineering, Worcester Polytechnic Institute, Worcester, MA, United States of America.|Department of Surgery, University of Massachusetts Medical School, Worcester, MA, United States of America.
authors.forename: Kristen L
authors.initials: KL
authors.lastname: Billiar
authors.affiliation: Department of Cardiology, Boston Children's Hospital, Department of Pediatrics, Harvard Medical School, Boston, MA, United States of America.
authors.forename: Tal
authors.initials: T
authors.lastname: Geva
mesh_terms: D000293:Adolescent; D000328:Adult; D003971:Diastole / Q000502:physiology; D005260:Female; D006352:Heart Ventricles / Q000000981:diagnostic imaging* / Q000503:physiopathology; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011664:Pulmonary Valve / Q000000981:diagnostic imaging / Q000601:surgery*; D011665:Pulmonary Valve Insufficiency / Q000000981:diagnostic imaging / Q000503:physiopathology; D013599:Systole / Q000502:physiology; D016896:Treatment Outcome; D055815:Young Adult