Patient-Specific Computational Fluid Dynamics Reveal Localized Flow Patterns Predictive of Post-Left Ventricular Assist Device Aortic Incompetence.
Circulation. Heart failure
BACKGROUND: Progressive aortic valve disease has remained a persistent cause of concern in patients with left ventricular assist devices. Aortic incompetence (AI) is a known predictor of both mortality and readmissions in this patient population and remains a challenging clinical problem.METHODS: Ten left ventricular assist device patients with de novo aortic regurgitation and 19 control left ventricular assist device patients were identified. Three-dimensional models of patients' aortas were created from their computed tomography scans, following which large-scale patient-specific computational fluid dynamics simulations were performed with physiologically accurate boundary conditions using the SimVascular flow solver.RESULTS: The spatial distributions of time-averaged wall shear stress and oscillatory shear index show no significant differences in the aortic root in patients with and without AI (mean difference, 0.67 dyne/cm2 [95% CI, -0.51 to 1.85]; P=0.23). Oscillatory shear index was also not significantly different between both groups of patients (mean difference, 0.03 [95% CI, -0.07 to 0.019]; P=0.22). The localized wall shear stress on the leaflet tips was significantly higher in the AI group than the non-AI group (1.62 versus 1.35 dyne/cm2; mean difference [95% CI, 0.15-0.39]; P<0.001), whereas oscillatory shear index was not significantly different between both groups (95% CI, -0.009 to 0.001; P=0.17).CONCLUSIONS: Computational fluid dynamics serves a unique role in studying the hemodynamic features in left ventricular assist device patients where 4-dimensional magnetic resonance imaging remains unfeasible. Contrary to the widely accepted notions of highly disturbed flow, in this study, we demonstrate that the aortic root is a region of relatively stagnant flow. We further identified localized hemodynamic features in the aortic root that challenge our understanding of how AI develops in this patient population.
View details for DOI 10.1161/CIRCHEARTFAILURE.120.008034
View details for PubMedID 34139862
Computational fluid dynamics simulations to predict false lumen enlargement after surgical repair of Type-A aortic dissection.
Seminars in thoracic and cardiovascular surgery
We aim to use computational fluid dynamics to investigate the hemodynamic conditions that may predispose to false lumen enlargement in this patient population. Nine patients who received surgical repairs of their type-A aortic dissections between 2017-2018 were retrospectively identified. Multiple contrast-enhanced post-operative CT scans were used to construct 3D models of aortic geometries. Computational fluid dynamics simulations of the models were run on a high-performance computing cluster using SimVascular - an open source simulation package. Physiological pulsatile flow conditions (4.9 L/min) were used at the aortic true lumen inlet, and physiological vascular resistances were applied at the distal vascular ends. Exploratory analyses showed no correlation between rate of false lumen growth and blood pressure, immediate post-op aortic diameter, or the number of fenestrations (p = 0.2). 1-year post-operative CT scans showed a median (IQR) false lumen growth rate of 4.31 (3.66, 14.67) mm/year Median (Interquartile range) peak systolic, mid-diastolic, and late diastolic velocity magnitudes were 0.90 (1.40); 0.10 (0.16); and 0.06 (0.06) cm/s respectively. Spearman's ranked correlations between fenestration velocity and 1-year false lumen growth rates were found to be statistically significant: Velocity magnitude at peak systolic (p = 0.025; rho = 0.75), mid diastolic (p = 0.025; rho = 0.75) and late diastolic phases of the cardiac cycle (p = 0.006; rho = 0.85). We have shown that false lumen growth is strongly correlated to fenestration flow velocity, which has potential implications for post-operative surveillance and risk stratification.
View details for DOI 10.1053/j.semtcvs.2021.05.012
View details for PubMedID 34091015
Long-term survival in patients with post-LVAD right ventricular failure: multi-state modelling with competing outcomes of heart transplant.
The Journal of heart and lung transplantation : the official publication of the International Society for Heart Transplantation
BACKGROUND: Multicenter data on long term survival following LVAD implantation that make use of contemporary definitions of RV failure are limited. Furthermore, traditional survival analyses censor patients who receive a bridge to heart transplant. Here we compare the outcomes of LVAD patients who develop post-operative RV failure accounting for the transitional probability of receiving an interim heart transplantation.METHODS: We use a retrospective cohort of LVAD patients sourced from multiple high-volume centers based in the United States. Five- and ten-year survival accounting for transition probabilities of receiving a heart transplant were calculated using a multi-state Aalen Johansen survival model.RESULTS: Of the 897 patients included in the study, 238 (26.5%) developed post-operative RV failure at index hospitalization. At 10 years the probability of death with post-op RV failure was 79.28% vs 61.70% in patients without (HR 2.10; 95% CI 1.72 - 2.57; p=< .001). Though not significant, patients with RV failure were less likely to be bridged to a heart transplant (HR 0.87, p=.4). Once transplanted the risk of death between both patient groups remained equivalent; the probability of death after a heart transplant was 3.97% in those with post-operative RV failure shortly after index LVAD implant, as compared to 14.71% in those without.CONCLUSIONS AND RELEVANCE: Long-term durable mechanical circulatory support is associated with significantly higher mortality in patients who develop post-operative RV failure. Improving outcomes may necessitate expeditious bridge to heart transplant wherever appropriate, along with critical reassessment of organ allocation policies.
View details for DOI 10.1016/j.healun.2021.05.002
View details for PubMedID 34167863
Resection of a Giant Epithelioid Hemangioendothelioma Arising from the Superior Vena Cava.
The Annals of thoracic surgery
Epithelioid hemangioendothelioma is a rare malignant vascular sarcoma. Here we present a patient with a very large tumor arising from the superior vena cava (SVC), in whom a resection with negative margins was accomplished using veno-venous bypass and bovine pericardial patch reconstruction of the SVC.
View details for DOI 10.1016/j.athoracsur.2021.01.034
View details for PubMedID 33529605
Use of patient-specific computational models for optimization of aortic insufficiency after implantation of left ventricular assist device.
The Journal of thoracic and cardiovascular surgery
Aortic incompetence (AI) is observed to be accelerated in the continuous-flow left ventricular assist device (LVAD) population and is related to increased mortality. Using computational fluid dynamics (CFD), we investigated the hemodynamic conditions related to the orientation of the LVAD outflow in these patients.We identified 10 patients with new aortic regurgitation, and 20 who did not, after LVAD implantation between 2009 and 2018. Three-dimensional models of patients' aortas were created from their computed tomography scans. The geometry of the LVAD outflow graft in relation to the aorta was quantified using azimuth angles (AA), polar angles (PAs), and distance from aortic root. The models were used to run CFD simulations, which calculated the pressures and wall shear stress (rWSS) exerted on the aortic root.The AA and PA were found to be similar. However, for combinations of high values of AA and low values of PA, there were no patients with AI. The distance from aortic root to the outflow graft was also smaller in patients who developed AI (3.39 ± 0.7 vs 4.07 ± 0.77 cm, P = .04). There was no significant difference in aortic root pressures in the 2 groups. The rWSS was greater in AI patients (4.60 ± 5.70 vs 2.37 ± 1.20 dyne/cm2, P < .001). Qualitatively, we observed a trend of greater perturbations, regions of high rWSS, and flow eddies in the AI group.Using CFD simulations, we demonstrated that patients who developed de novo AI have greater rWSS at the aortic root, and their outflow grafts were placed closer to the aortic roots than those patients without de novo AI.
View details for DOI 10.1016/j.jtcvs.2020.04.164
View details for PubMedID 32653292
- Modeling conduit choice for valve-sparing aortic root replacement on biomechanics with a 3-dimensional-printed heart simulator JOURNAL OF THORACIC AND CARDIOVASCULAR SURGERY 2019; 158 (2): 392–403
Modeling conduit choice for valve-sparing aortic root replacement on biomechanics with a 3-dimensional-printed heart simulator.
The Journal of thoracic and cardiovascular surgery
OBJECTIVE: The optimal conduit for valve-sparing aortic root replacement is still debated, with several conduit variations available, ranging from straight tubular grafts to Valsalva grafts. Benefits of neosinus reconstruction include enhanced flow profiles and improved hemodynamics. Curiously, however, some clinical data suggest that straight grafts may have greater long-term durability. In this study, we hypothesized that straight tubular grafts may help maintain the native cylindrical position of the aortic valve commissures radially, resulting in preserved leaflet coaptation, reduced stresses, and potentially improved valve performance.METHODS: Using 3D printing, a left heart simulator with a valve-sparing root replacement model and a physiologic coronary circulation was constructed. Aortic valves were dissected from fresh porcine hearts and reimplanted into either straight tubular grafts (n=6) or Valsalva grafts (n=6). Conduits were mounted into the heart simulator and hemodynamic, echocardiographic, and high-speed videometric data were collected.RESULTS: Hemodynamic parameters and coronary blood flow were similar between straight and Valsalva grafts, although the former were associated with lower regurgitant fractions, less peak intercommissural radial separation, preserved leaflet coaptation, decreased leaflet velocities, and lower relative leaflet forces compared with Valsalva grafts.CONCLUSIONS: Valsalva grafts and straight grafts perform equally well in terms of gross hemodyanics and coronary blood flow. Interestingly, however, the biomechanics of these 2 conduits differ considerably, with straight grafts providing increased radial commissural stability and leaflet coaptation. Further investigation into how these parameters influence clinical outcomes is warranted.
View details for PubMedID 30745047
Heart-lung transplantation over the past 10 years: an up-to-date concept.
European journal of cardio-thoracic surgery : official journal of the European Association for Cardio-thoracic Surgery
OBJECTIVES: Heart-lung transplantation has been established as an effective treatment for patients with advanced cardiopulmonary failure. Over the years, the number of operations performed has declined. In 2015, only 38 adult heart-lung transplants were reported worldwide. Since then, we have performed 16 operations in high-acuity patients with excellent postoperative outcomes. Herein, we review our single-centre experience with heart-lung transplantation over the past 10 years.METHODS: We retrospectively reviewed 49 heart-lung transplant recipients between 2008 and 2018 to investigate the patient characteristics and outcomes while comparing those results across 2 cohorts (2008-2015, Era I, n=30 and 2016-2018, Era II, n=19).RESULTS: Our patient demographics and waitlist time did not significantly change over time. However, the lung allocation score was significantly higher in Era II compared to Era I (51.1±19.8 in Era II and 41.6±19.5 in Era I; P=0.006). We also observed a higher rate-while not statistically significant-of preoperative and postoperative use of mechanical circulatory support in the present era. Although there is a trend of higher acuity in the present era, we continue to have excellent outcomes with 100% 30-day and 1-year survival.CONCLUSIONS: These results suggest that in a high-volume heart-lung transplant programme, excellent postoperative outcomes can be achieved even in patients with rapid and severe cardiopulmonary decline and that, to this day, heart-lung transplantation remains a viable option for patients with advanced cardiopulmonary disease.
View details for PubMedID 30260389
- To repair or to replace: four decades in the making ANNALS OF TRANSLATIONAL MEDICINE 2018; 6 (7)
Ambulating femoral venoarterial extracorporeal membrane oxygenation bridge to heart-lung transplant.
The Journal of thoracic and cardiovascular surgery
View details for PubMedID 29628344
To repair or to replace: four decades in the making.
Annals of translational medicine
2018; 6 (7): 125
View details for PubMedID 29955585