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Author

  • Kanter, Kirk R (4)
  • Restrepo, Maria (4)
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Search Results for all work with filters:

  • 2012
  • Yoganathan, Ajit

Work 1-8 of 8

Sorted by relevance

Article

In-vivo transducer to measure dynamic mitral annular forces

by Andrew W. Siefert; Jorge H. Jimenez; Dustin S. West; Kevin J. Koomalsingh; Robert C. Gorman; Joseph H. Gorman; Ajit Yoganathan

2012

Subjects
  • Engineering, Biomedical
  • Biophysics, General
  • File Download
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Abstract:Close

Limited knowledge exists regarding the forces which act on devices implanted to the heart's mitral valve. Developing a transducer to measure the peak force magnitudes, time rates of change, and relationship with left ventricular pressure will aid in device development. A novel force transducer was developed and implanted in the mitral valve annulus of an ovine subject. In the post-cardioplegic heart, septal-lateral and transverse forces were continuously measured for cardiac cycles reaching a peak left ventricular pressure of 90. mmHg. Each force was seen to increase from ventricular diastole and found to peak at mid-systole. The mean change in septal-lateral and transverse forces throughout the cardiac cycle was 4.4±0.2. N and 1.9±0.1. N respectively. During isovolumetric contraction, the septal-lateral and transverse forces were found to increase at peak rate of 143±8. N/s and 34±9. N/s, respectively. Combined, this study provides the first quantitative assessment of septal-lateral and transverse forces within the contractile mitral annulus. The developed transducer was successful in measuring these forces whose methods may be extended to future studies. Upon additional investigation, these data may contribute to the safer development and evaluation of devices aimed to repair or replace mitral valve function.

Article

Growth of the inferior cavopulmonary pathway in patients with a lateral tunnel fontan connection: quantification from serial magnetic resonance images

by Maria Restrepo; Lucia Mirabella; Elaine Tang; Christopher M Haggerty; Mark A Fogel; Anne Marie Valente; Doff B McElhinney; Ajit Yoganathan

2012

Subjects
  • Engineering, Biomedical
  • Engineering, Chemical
  • File Download

Article

Effect of anterior strut chordal transection on the force distribution on the marginal chordae of the mitral valve

by Muralidhar Padala; Lazarina Gyoneva; Ajit Yoganathan

2012

Subjects
  • Health Sciences, Medicine and Surgery
  • Engineering, Biomedical
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Abstract:Close

Objectives: Transection of the secondary chordae on the anterior leaflet of the mitral valve to relieve leaflet tethering and reduce regurgitation is an experimentally proven procedure to correct functional mitral regurgitation. In the present study, we sought to investigate whether transecting the secondary chordae would have an effect on the marginal chordal force on the same leaflet. Methods: Adult porcine mitral valves (n = 8) were studied in a pulsatile heart simulator, in which the papillary muscle positions can be precisely positioned. Miniature transducers were inserted into the anterior marginal chordae to measure the chordal forces. Each valve was studied under baseline conditions, 3 different tethering conditions (apical, apical-lateral, and apical-lateral- posterior), and after chordal cutting in the 3 tethering conditions. The temporal changes and peak and average marginal chordal forces under each condition are reported. Results: Apical tethering increased the marginal chordal force by an average of 96% but remained unchanged after chordal cutting. With apical-lateral tethering, the marginal chordal force increased by 210% from baseline and increased further to 350% of baseline after chordal cutting. After apical-lateral-posterior tethering, the marginal chordal force increased to 335% of baseline before transection and by 548% after transection. Conclusions: The increase in the marginal chordal force after secondary chordal cutting depends on the location of the papillary muscles and the extent of leaflet tethering. Although chordal cutting might not alter the valve mechanics under minimal leaflet tethering, it significantly affects the mechanics when the leaflet tethering is more pronounced, which is typically seen in patients with functional mitral regurgitation.

Article

Visualization of flow structures in Fontan patients using 3-dimensional phase contrast magnetic resonance imaging

by Kartik S. Sundareswaran; Christopher M. Haggerty; Diane de Zelicourt; Lakshmi P. Dasi; Kerem Pekkan; David H. Frakes; Andrew J. Powell; Kirk R Kanter; Mark A. Fogel; Ajit Yoganathan

2012

Subjects
  • Health Sciences, Medicine and Surgery
  • Engineering, Biomedical
  • File Download
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Abstract:Close

Objective: Our objective was to analyze 3-dimensional (3D) blood flow patterns within the total cavopulmonary connection (TCPC) using in vivo phase contrast magnetic resonance imaging (PC MRI). Methods: Sixteen single-ventricle patients were prospectively recruited at 2 leading pediatric institutions for PC MRI evaluation of their Fontan pathway. Patients were divided into 2 groups. Group 1 comprised 8 patients with an extracardiac (EC) TCPC, and group 2 comprised 8 patients with a lateral tunnel (LT) TCPC. A coronal stack of 5 to 10 contiguous PC MRI slices with 3D velocity encoding (5-9 ms resolution) was acquired and a volumetric flow field was reconstructed. Results: Analysis revealed large vortices in LT TCPCs and helical flow structures in EC TCPCs. On average, there was no difference between LT and EC TCPCs in the proportion of inferior vena cava flow going to the left pulmonary artery (43% ± 7% vs 46% ± 5%; P = .34). However, for EC TCPCs, the presence of a caval offset was a primary determinant of inferior vena caval flow distribution to the pulmonary arteries with a significant bias to the offset side. Conclusions: 3D flow structures within LT and EC TCPCs were reconstructed and analyzed for the first time using PC MRI. TCPC flow patterns were shown to be different, not only on the basis of LT or EC considerations, but with significant influence from the superior vena cava connection as well. This work adds to the ongoing body of research demonstrating the impact of TCPC geometry on the overall hemodynamic profile.

Article

Preliminary Clinical Experience with a Bifurcated Y-Graft Fontan Procedure--A Feasibility Study

by Kirk R Kanter; Christopher M. Haggerty; Maria Restrepo; Diane A. de Zelicourt; Jarek Rossignac; Willie James Parks; Ajit Yoganathan

2012

Subjects
  • Health Sciences, Medicine and Surgery
  • Engineering, Biomedical
  • File Download
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Abstract:Close

OBJECTIVE Optimizing flow and diminishing power loss in the Fontan circuit can improve hemodynamic efficiency potentially improving long-term outcomes. Computerized modeling has predicted improved energetics with a Y-graft Fontan. METHODS From August to December, 2010, six consecutive children had a completion Fontan (n=3) or a Fontan revision (n=3) using a bifurcated polytetrafluoroethylene Y-graft (18×9×9 mm in 2, 20×10×10 mm in 4) connecting the inferior vena cava (IVC) to the right and left pulmonary arteries (PAs) with separate graft limbs. Patents were imaged by magnetic resonance imaging (MRI; n-5) or computerized tomography (n=1). Computational fluid dynamics (CFD) assessed Fontan hemodynamics, power loss, and IVC flow splits to the branch PAs. Clinical parameters were compared with 12 patients immediately preceding this series who had a lateral Fontan procedure. RESULTS Despite longer crossclamp and bypass times (not statistically significant), the Y-graft Fontan patients had postoperative courses similar to the conventional Fontan patients. Other than two early readmissions for pleural effusions managed with diuretics, on 6–12 months follow-up (mean 8 months), all six patients have done well. Postoperative flow modeling demonstrated balanced distribution of IVC flow to both PAs with minimal flow disturbance. Improvements in hemodynamics and efficiency were noted when the Y-graft branches were anastomosed distally and aligned tangentially with the branch PAs. CONCLUSIONS This preliminary surgical experience demonstrates clinical feasibility of the bifurcated Y-graft Fontan. CFD shows acceptable hemodynamics with low calculated power losses and balanced distribution of IVC flow to the PAs as long as the branch grafts are anastomosed distally.

Article

Effect of Flow Pulsatility on Modeling the Hemodynamics in the Total Cavopulmonary Connection

by Reza H. Khiabani; Maria Restrepo; Elaine Tang; Diane De Zelicourt; Fotis Sotiropoulos; Mark Fogel; Ajit Yoganathan

2012

Subjects
  • Engineering, Biomedical
  • Biophysics, General
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Abstract:Close

Total cavopulmonary connection is the result of a series of palliative surgical repairs performed on patients with single ventricle heart defects. The resulting anatomy has complex and unsteady hemodynamics characterized by flow mixing and flow separation. Although varying degrees of flow pulsatility have been observed in vivo, non-pulsatile (time-averaged) boundary conditions have traditionally been assumed in hemodynamic modeling, and only recently have pulsatile conditions been incorporated without completely characterizing their effect or importance. In this study, 3D numerical simulations with both pulsatile and non-pulsatile boundary conditions were performed for 24 patients with different anatomies and flow boundary conditions from Georgia Tech database. Flow structures, energy dissipation rates and pressure drops were compared under rest and simulated exercise conditions. It was found that flow pulsatility is the primary factor in determining the appropriate choice of boundary conditions, whereas the anatomic configuration and cardiac output had secondary effects. Results show that the hemodynamics can be strongly influenced by the presence of pulsatile flow. However, there was a minimum pulsatility threshold, identified by defining a weighted pulsatility index (wPI), above which the influence was significant. It was shown that when wPI < 30%, the relative error in hemodynamic predictions using time-averaged boundary conditions was less than 10% compared to pulsatile simulations. In addition, when wPI < 50, the relative error was less than 20%. A correlation was introduced to relate wPI to the relative error in predicting the flow metrics with non-pulsatile flow conditions.

Article

Comparing Pre- and Post-Operative Fontan Hemodynamic Simulations: Implications for the Reliability of Surgical Planning

by Christopher M. Haggerty; Diane A. de Zélicourt; Maria Restrepo; Jarek Rossignac; Thomas L. Spray; Kirk R Kanter; Mark A. Fogel; Ajit Yoganathan

2012

Subjects
  • Health Sciences, Medicine and Surgery
  • Engineering, Biomedical
  • File Download
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Abstract:Close

Virtual modeling of cardiothoracic surgery is a new paradigm that allows for systematic exploration of various operative strategies and uses engineering principles to predict the optimal patient-specific plan. This study investigates the predictive accuracy of such methods for the surgical palliation of single ventricle heart defects. Computational fluid dynamics (CFD)-based surgical planning was used to model the Fontan procedure for four patients prior to surgery. The objective for each was to identify the operative strategy that best distributed hepatic blood flow to the pulmonary arteries. Post-operative magnetic resonance data were acquired to compare (via CFD) the post-operative hemodynamics with predictions. Despite variations in physiologic boundary conditions (e.g., cardiac output, venous flows) and the exact geometry of the surgical baffle, sufficient agreement was observed with respect to hepatic flow distribution (90% confidence interval-14 ± 4.3% difference). There was also good agreement of flow-normalized energetic efficiency predictions (19 ± 4.8% error). The hemodynamic outcomes of prospective patient-specific surgical planning of the Fontan procedure are described for the first time with good quantitative comparisons between preoperatively predicted and postoperative simulations. These results demonstrate that surgical planning can be a useful tool for single ventricle cardiothoracic surgery with the ability to deliver significant clinical impact.

Article

CANNULATION STRATEGY FOR AORTIC ARCH RECONSTRUCTION USING DEEP HYPOTHERMIC CIRCULATORY ARREST

by Diane De Zelicourt; Philsub Jung; Marc Horner; Kerem Pekkan; Kirk R Kanter; Ajit Yoganathan

2012

Subjects
  • Health Sciences, Medicine and Surgery
  • Engineering, Biomedical
  • Engineering, General
  • File Download
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Abstract:Close

Background: Aortic arch reconstruction in neonates is commonly performed using deep hypothermic circulatory arrest. However, concerns have arisen regarding potential adverse neurologic outcomes from this complex procedure, raising questions about the best arterial cannulation approach for cerebral perfusion and effective systemic hypothermia. In this study, we use computational fluid dynamics to investigate the effect of different cannulation strategies in neonates. Methods: We used a realistic template of a hypoplastic neonatal aorta as the base geometry to investigate four cannulation options: (1) right innominate artery, (2) innominate root, (3) patent ductus arteriosus (PDA), or (4) innominate root and PDA. Performance was evaluated according to the numerically predicted cerebral and systemic flow distributions compared with physiologic perfusion under neonatal conditions. Results: The four cannulation strategies were associated with different local hemodynamics; however, this did not translate into any significant effect on the measured flow distributions. The largest difference only represented 0.8% of the cardiac output and was measured in the innominate artery, which received 23.2% of the cardiac output in option 3 vs 24% in option 4. Pulmonary artery snaring benefited all systemic vessels uniformly. Conclusions: Because of the very high vascular resistances in neonates, downstream vascular resistances dictated flow distribution to the different vascular beds rather than the cannulation strategy, allowing the surgical team to choose their method of preference. However, patients with aortic coarctation warrant further investigation and will most likely benefit from a 2-cannulae approach (option 4).
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