Heparin-Sparing Anticoagulation Strategies Are Viable Options for Patients on Veno-Venous ECMO.

BACKGROUND: Extracorporeal membrane oxygenation (ECMO), a rescue therapy for pulmonary failure, has traditionally been limited by anticoagulation requirements. Recent practice has challenged the absolute need for anticoagulation, expanding the role of ECMO to patients with higher bleeding risk. We hypothesize that mortality, bleeding, thrombotic events, and transfusions do not differ between heparin-sparing and full therapeutic anticoagulation strategies in veno-venous (VV) ECMO management. MATERIALS AND METHODS: Adult VV ECMO patients between October 2011 and May 2018 at a single center were reviewed. A heparin-sparing strategy was implemented in October 2014; we compared outcomes in an as-treated fashion. The primary end point was survival. Secondary end points included bleeding, thrombotic complications, and transfusion requirements. RESULTS: Forty VV ECMO patients were included: 17 (147 circuit-days) before and 23 (214 circuit-days) after implementation of a heparin-sparing protocol. Patients treated with heparin-sparing anticoagulation had a lower body mass index (28.5 ± 7.1 versus 38.1 ± 12.4, P = 0.01), more often required inotropic support before ECMO (82 versus 50%, P = 0.05), and had a lower mean activated clotting time (167 ± 15 versus 189 ± 15 s, P < 0.01). There were no significant differences in survival to decannulation (59 versus 83%, P = 0.16) or discharge (50 versus 72%, P = 0.20), bleeding (32 versus 33%, P = 1.0), thromboembolic events (18 versus 39%, P = 0.17), or transfusion requirements (median 1.1 versus 0.9 unit per circuit-day, P = 0.48). CONCLUSIONS: Survival, bleeding, thrombotic complications, and transfusion requirements did not differ between heparin-sparing and full therapeutic heparin strategies for management of VV ECMO. VV ECMO can be a safe option in patients with traditional contraindications to anticoagulation.

The Effect of Cardiac Preservation Solutions on Heart Transplant Survival.

BACKGROUND: Limited data exist that compare the predominant cardiac preservation solutions (CPSs). MATERIALS AND METHODS: The United Network for Organ Sharing database was retrospectively reviewed from January 1, 2004 to March 31, 2018, for donor hearts. Of 34,614 potential donors, 21,908 remained after applying the exclusion criteria. The CPS analyzed included saline, the University of Wisconsin (UW), cardioplegia, Celsior, and Custodiol. The primary endpoints were recipient survival and posttransplant rejection. Logistic and Cox models were used to quantify survival endpoints. RESULTS: Saline was used as the CPS in 2549 patients (12%), UW in 10,549 (48%), cardioplegia in 1307 (6%), Celsior in 5081 (23%), and Custodiol in 2422 (11%). Donor age ranged from 15 to 68 y (mean = 32.0 y, median = 30.0 y), and 71% were male. Adjusted survival probabilities of recipients whose donor hearts were procured with saline was 96% 30 d, 90% 1 y, UW: 97% 30 d, 92% 1 y, cardioplegia: 95% 30 d, 87% 1 y, Celsior: 96% 30 d, 90% 1 y, and Custodiol: 97% 30 d, 92% 1 y. When these comparisons were adjusted for donor age, sex, ethnicity, ischemic time, recipient age, sex, ethnicity, creatinine, ventricular assist device (VAD), length of stay, region and days on waiting list, cardioplegia solution was demonstrated to have a higher risk of death (30 d, 1 y, overall) and posttransplant rejection versus UW (odds ratio 1.70, P = 0.001; odds ratio 1.63, P < 0.001; hazard ratio 1.22, P < 0.001; hazard ratio 1.21, P < 0.001, respectively). CONCLUSIONS: Cardioplegia solutions for cardiac preservation are associated with a higher mortality in heart transplant recipients.

Outcomes of patients undergoing concomitant aortic and mitral valve surgery in northern new England.

BACKGROUND: Concomitant aortic (AV) and mitral (MV) valve surgery accounts for 4% of all valve procedures in northern New England. We examined in-hospital and long-term mortality. METHODS AND RESULTS: This is a report of a prospective study of 1057 patients undergoing concomitant AV and MV surgery from 1989 to 2007. The Social Security Administration Death Master File was used to assess long-term survival. Kaplan-Meier and log-rank tests were performed. In-hospital mortality was 15.5% (11.0% for patients <70 years, 18.0% for 70- to 79-year-olds, and 24% for those > or =80 years). Overall median survival was 7.3 years. Median survival without coronary artery bypass grafting was 9.5 years and with coronary artery bypass grafting was 5.7 years (P<0.001). Survival in women was worse than in men (7.3 versus 9.3, years, P=0.033). Median survival by age was 11.0 years for patients <70 years, 5.4 years for 70- to 79-year-olds, and 4.8 years for those > or =80 years. Median survival was not significantly different for patients > or =80 years compared with those who were 70 to 79 years old (P=0.245). CONCLUSIONS: Double-valve surgery has a high in-hospital mortality rate and a median survival of 7.3 years. After patients have survived surgery, long-term survival is similar between men and women, smaller and larger patients, and those receiving MV repair or replacement. Survival continues to decline after surviving surgery for patients > or =70 years old and those who undergo concomitant coronary artery bypass grafting. In patients <70 years, either mechanical valves in both positions or a tissue AV and mitral repair have the lowest in-hospital mortality and the best long-term survival. In patients > or =70 years, tissue valves in both positions have the best in-hospital and long-term survival.

Long-term survival of the very elderly undergoing aortic valve surgery.

BACKGROUND: Increasing numbers of the very elderly are undergoing aortic valve procedures. We describe the short- and long-term survivorship for this cohort. METHODS AND RESULTS: We conducted a cohort study of 7584 consecutive patients undergoing open aortic valve surgery without (51.1%; AVR) or with (48.9%; AVR + CABG) concomitant coronary artery bypass graft surgery between November 10, 1987 through June 30, 2006. Patient records were linked to the Social Security Administration's Death Master File. Survivorship was stratified by age and concomitant CABG surgery. During 39 835 person-years of follow-up, there were 2877 deaths. Among AVR, there were 3304 patients <80 years of age, 419 patients 80 to 84 years, and 156 patients > or =85 years (24 patients >90 years). Among AVR+CABG patients, there were 2890 patients <80 years of age, 577 patients 80 to 84 years, and 238 patients > or =85 years (22 patients >90 years). Median survivorship for patients undergoing isolated AVR was 11.5 years (<80 years), 6.8 years (80 to 84 years), 6.2 years (> or =85 years); for patients undergoing AVR+CABG, median survivorship was 9.4 years (<80 years), 6.8 years (80 to 84 years), and 7.1 years (> or =85 years). Among both procedures, adjusted survivorship was significantly different across strata of age (P<0.001). These findings are similar to life expectancy of the general population from actuarial tables: 80 to 84 years (7 years) and > or =85 years (5 years). CONCLUSIONS: Survivorship among octogenarians is favorable, with more than half the patients surviving more than 6 years after their surgery. Concomitant CABG surgery does not diminish median survivorship among patients >80 years of age.

Effect of Edge-to-Edge Mitral Valve Repair on Chordal Strain: Fluid-Structure Interaction Simulations.

Edge-to-edge repair for mitral valve regurgitation is being increasingly performed in high-surgical risk patients using minimally invasive mitral clipping devices. Known procedural complications include chordal rupture and mitral leaflet perforation. Hence, it is important to quantitatively evaluate the effect of edge-to-edge repair on chordal integrity. in this study, we employ a computational mitral valve model to simulate functional mitral regurgitation (FMR) by creating papillary muscle displacement. Edge-to-edge repair is then modeled by simulated coaptation of the mid portion of the mitral leaflets. in the setting of simulated FMR, edge-to-edge repair was shown to sustain low regurgitant orifice area, until a two fold increase in the inter-papillary muscle distance as compared to the normal mitral valve. Strain in the chordae was evaluated near the papillary muscles and the leaflets. Following edge-to-edge repair, strain near the papillary muscles did not significantly change relative to the unrepaired valve, while strain near the leaflets increased significantly relative to the unrepaired valve. These data demonstrate the potential for computational simulations to aid in the pre-procedural evaluation of possible complications such as chordal rupture and leaflet perforation following percutaneous edge-to-edge repair.

Percutaneous mitral valve dilatation: single balloon versus double balloon. A finite element study.

BACKGROUND AND AIM OF THE STUDY: Percutaneous mitral valve (MV) dilatation is routinely performed for mitral stenosis using either a single balloon (SB) or double balloon (DB) technique. The study aim was to compare the two techniques using the finite element (FE) method. METHODS: An established FE model of the MV was modified by fusing MV leaflet edges at commissure level to simulate a stenotic valve (orifice area = 180 mm2). FE models of a 30 mm SB (low-pressure, elastomeric balloon) and an 18 mm DB system (high-pressure, non-elastic balloon) were created. RESULTS: Both, SB and DB simulations, resulted in the splitting of commissures and consequent relief of stenosis (final MV areas of 610 mm2 and 560 mm2, respectively). Stresses induced by the two balloon systems varied across the valve. At full inflation, SB showed a higher stress in the central part of the leaflets and at the commissures compared to DB simulation, which demonstrated a more uniform stress distribution. This was due to mismatch of the round shape of the SB within an oval mitral orifice. Due to its high compliance, commissural splitting was not easily accomplished with the SB. Conversely, the DB guaranteed commissural splitting, even when a high force was required to break the commissure welds. CONCLUSION: The FE model demonstrated that MV dilatation can be accomplished by both SB and DB techniques. However, the DB method resulted in a higher probability of splitting the fused commissures, with less potential for damage to the MV leaflets by overstretching, even at higher pressures.

Multivariable prediction of renal insufficiency developing after cardiac surgery.

BACKGROUND: Renal insufficiency after coronary artery bypass graft (CABG) surgery is associated with increased short-term and long-term mortality. We hypothesized that preoperative patient characteristics could be used to predict the patient-specific risk of developing postoperative renal insufficiency. METHODS AND RESULTS: Data were prospectively collected on 11,301 patients in northern New England who underwent isolated CABG surgery between 2001 and 2005. Based on National Kidney Foundation definitions, moderate renal insufficiency was defined as a GFR <60 mL/min/1.73 m2 and severe renal insufficiency as a GFR <30. Patients with at least moderate renal insufficiency at baseline were eliminated from the analysis, leaving 8363 patients who became our study cohort. A prediction model was developed to identify variables that best predicted the risk of developing severe renal insufficiency using multiple logistic regression, and the predictive ability of the model quantified using a bootstrap validated C-Index (Area Under ROC) and Hosmer-Lemeshow statistic. Three percent of the patients with normal renal function before CABG surgery developed severe renal insufficiency (229/8363). In a multivariable model the preoperative patient characteristics most strongly associated with postoperative severe renal insufficiency included: age, gender, white blood cell count >12,000, prior CABG, congestive heart failure, peripheral vascular disease, diabetes, hypertension, and preoperative intraaortic balloon pump. The predictive model was significant with chi2 150.8, probability value <0.0001. The model discriminated well, ROC 0.72 (95%CI: 0.68 to 0.75). The model was well calibrated according to the Hosmer-Lemeshow test. CONCLUSIONS: We developed a robust prediction rule to assist clinicians in identifying patients with normal, or near normal, preoperative renal function who are at high risk of developing severe renal insufficiency. Physicians may be able to take steps to limit this adverse outcome and its associated increase in morbidity and mortality.

Perioperative increases in serum creatinine are predictive of increased 90-day mortality after coronary artery bypass graft surgery.

BACKGROUND: Impaired renal function after coronary artery bypass graft (CABG) surgery is a key risk factor for in-hospital mortality. However, perioperative increases in serum creatinine and the association with mortality has not been well-studied. We assessed the hypothesis that perioperative increases in creatinine are associated with increased 90-day mortality. METHODS AND RESULTS: We studied 1391 patients in northern New England undergoing CABG in 2001 and evaluated preoperative and postoperative creatinine. Patients with preoperative dialysis were excluded. Data were linked to the National Death Index to assess 90-day survival. Kaplan-Meier and log-rank techniques were used. Patients were stratified by percent increase in creatinine from baseline: <25%, 25% to 49%, 50% to 99%, > or =100%. We assessed 90-day survival and calculated adjusted hazard ratios (HR) and 95% confidence intervals (95% CI) for creatinine groups, adjusting for age and sex. Patients with the largest creatinine increases (50% to 99% or > or =100%) had significantly higher 90-day mortality compared with patients with a smaller increase (<50%; P<0.001). Adjusted HR and 95% CI confirmed patients in the higher 2 groups had an increased risk of mortality compared with the <25% (referent); however, the 25% to 49% group was not different from the referent: 1.80 (95% CI: 0.73 to 4.44), 6.57 (95% CI, 3.03 to 14.27), and 22.10 (95% CI, 11.25 to 43.39). CONCLUSIONS: Patients with large creatinine increases (> or = 50%) after CABG surgery have a higher 90-day mortality compared with patients with small increases. Efforts to identify patients with impaired renal function and to preserve renal function before cardiac surgery may yield benefits for patients in the future.

Fluid-structure interaction and structural analyses using a comprehensive mitral valve model with 3D chordal structure.

Over the years, three-dimensional models of the mitral valve have generally been organized around a simplified anatomy. Leaflets have been typically modeled as membranes, tethered to discrete chordae typically modeled as one-dimensional, non-linear cables. Yet, recent, high-resolution medical images have revealed that there is no clear boundary between the chordae and the leaflets. In fact, the mitral valve has been revealed to be more of a webbed structure whose architecture is continuous with the chordae and their extensions into the leaflets. Such detailed images can serve as the basis of anatomically accurate, subject-specific models, wherein the entire valve is modeled with solid elements that more faithfully represent the chordae, the leaflets, and the transition between the two. These models have the potential to enhance our understanding of mitral valve mechanics and to re-examine the role of the mitral valve chordae, which heretofore have been considered to be 'invisible' to the fluid and to be of secondary importance to the leaflets. However, these new models also require a rethinking of modeling assumptions. In this study, we examine the conventional practice of loading the leaflets only and not the chordae in order to study the structural response of the mitral valve apparatus. Specifically, we demonstrate that fully resolved 3D models of the mitral valve require a fluid-structure interaction analysis to correctly load the valve even in the case of quasi-static mechanics. While a fluid-structure interaction mode is still more computationally expensive than a structural-only model, we also show that advances in GPU computing have made such models tractable. Copyright © 2016 John Wiley & Sons, Ltd.

Fluid-Structure Interaction Analysis of Ruptured Mitral Chordae Tendineae.

The chordal structure is a part of mitral valve geometry that has been commonly neglected or simplified in computational modeling due to its complexity. However, these simplifications cannot be used when investigating the roles of individual chordae tendineae in mitral valve closure. For the first time, advancements in imaging, computational techniques, and hardware technology make it possible to create models of the mitral valve without simplifications to its complex geometry, and to quickly run validated computer simulations that more realistically capture its function. Such simulations can then be used for a detailed analysis of chordae-related diseases. In this work, a comprehensive model of a subject-specific mitral valve with detailed chordal structure is used to analyze the distinct role played by individual chordae in closure of the mitral valve leaflets. Mitral closure was simulated for 51 possible chordal rupture points. Resultant regurgitant orifice area and strain change in the chordae at the papillary muscle tips were then calculated to examine the role of each ruptured chorda in the mitral valve closure. For certain subclassifications of chordae, regurgitant orifice area was found to trend positively with ruptured chordal diameter, and strain changes correlated negatively with regurgitant orifice area. Further advancements in clinical imaging modalities, coupled with the next generation of computational techniques will enable more physiologically realistic simulations.

Fluid-Structure Interaction Analysis of Papillary Muscle Forces Using a Comprehensive Mitral Valve Model with 3D Chordal Structure.

Numerical models of native heart valves are being used to study valve biomechanics to aid design and development of repair procedures and replacement devices. These models have evolved from simple two-dimensional approximations to complex three-dimensional, fully coupled fluid-structure interaction (FSI) systems. Such simulations are useful for predicting the mechanical and hemodynamic loading on implanted valve devices. A current challenge for improving the accuracy of these predictions is choosing and implementing modeling boundary conditions. In order to address this challenge, we are utilizing an advanced in vitro system to validate FSI conditions for the mitral valve system. Explanted ovine mitral valves were mounted in an in vitro setup, and structural data for the mitral valve was acquired with [Formula: see text]CT. Experimental data from the in vitro ovine mitral valve system were used to validate the computational model. As the valve closes, the hemodynamic data, high speed leaflet dynamics, and force vectors from the in vitro system were compared to the results of the FSI simulation computational model. The total force of 2.6 N per papillary muscle is matched by the computational model. In vitro and in vivo force measurements enable validating and adjusting material parameters to improve the accuracy of computational models. The simulations can then be used to answer questions that are otherwise not possible to investigate experimentally. This work is important to maximize the validity of computational models of not just the mitral valve, but any biomechanical aspect using computational simulation in designing medical devices.

High-resolution subject-specific mitral valve imaging and modeling: experimental and computational methods.

The diversity of mitral valve (MV) geometries and multitude of surgical options for correction of MV diseases necessitates the use of computational modeling. Numerical simulations of the MV would allow surgeons and engineers to evaluate repairs, devices, procedures, and concepts before performing them and before moving on to more costly testing modalities. Constructing, tuning, and validating these models rely upon extensive in vitro characterization of valve structure, function, and response to change due to diseases. Micro-computed tomography ([Formula: see text]CT) allows for unmatched spatial resolution for soft tissue imaging. However, it is still technically challenging to obtain an accurate geometry of the diastolic MV. We discuss here the development of a novel technique for treating MV specimens with glutaraldehyde fixative in order to minimize geometric distortions in preparation for [Formula: see text]CT scanning. The technique provides a resulting MV geometry which is significantly more detailed in chordal structure, accurate in leaflet shape, and closer to its physiological diastolic geometry. In this paper, computational fluid-structure interaction (FSI) simulations are used to show the importance of more detailed subject-specific MV geometry with 3D chordal structure to simulate a proper closure validated against [Formula: see text]CT images of the closed valve. Two computational models, before and after use of the aforementioned technique, are used to simulate closure of the MV.

Non-linear fluid-coupled computational model of the mitral valve.

BACKGROUND AND AIM OF THE STUDY: The dynamics of the mitral valve result from the synergy of left heart geometry, local blood flow and tissue integrity. Herein is presented the first coupled fluid-structure computational model of the mitral valve in which valvular kinematics result from the interaction of local blood flow and a continuum representation of valvular microstructure. METHODS: The diastolic geometry of the mitral valve was assembled from previously published experimental data. Anterior and posterior leaflets were modeled as networks of entangled collagen fibers, embedded in an isotropic matrix. The resulting non-linear continuum description of mitral tissue was implemented in a three-dimensional membrane formulation. Chordal tension-only behavior was defined from experimental tensile tests. The computational model considered the valve immersed in a domain of Newtonian blood, with an experimentally determined viscosity corresponding to a shear rate of 180 s(-1) at 37 degrees C. Ventricular and atrial pressure curves were applied to ventricular and atrial surfaces of the blood domain. RESULTS: Peak closing flow and volume were 51 ml/s and 1.17 ml, respectively. Papillary muscle force ranged dynamically between 0.0 and 2.6 N. Acoustic pressure (RMS) was found to be 3.3 Pa, with a peak frequency of 72 Hz at 0.064 s from the onset of systole. Model predictions showed excellent agreement with available transmitral flow, papillary force and first heart sound (S1) acoustic data. CONCLUSION: The addition of blood flow and an experimentally driven microstructural description of mitral tissue represent a significant advance in computational studies of the mitral valve. This model will be the foundation for future computational studies on the effect of pathophysiological tissue alterations on mitral valve competence.

Potassium supplementation, diet vs pills: a randomized trial in postoperative cardiac surgery patients.

BACKGROUND: Cardiac surgery patients are commonly treated with diuretics, which can result in hypokalemia requiring potassium supplementation. OBJECTIVE: Our objective was to determine whether cardiac surgery patients receiving therapy with potassium-wasting diuretics can safely and beneficially maintain serum potassium levels by eating potassium-rich foods. DESIGN: A prospectively randomized trial of diet vs medication supplementation of potassium was undertaken. Patients who were to undergo cardiac surgery and who would be receiving therapy with oral furosemide postoperatively were eligible for the study. Forty-eight patients were enrolled in the trial, and 38 patients completed the study. Patients received either potassium-rich foods (diet) or potassium chloride pills (medication). RESULTS: There was no significant difference in mean (+/- SD) serum potassium concentrations between groups preoperatively (4.25 +/- 0.30 vs 4.29 +/- 0.33 mEq/L, respectively), on postoperative day 3 (4.23 +/- 0.40 vs 4.27 +/- 0.40 mEq/L, respectively), or postoperative day 4 (4.23 +/- 0.48 vs 4.24 +/- 0.33 mEq/L, respectively) for the diet and medication groups. Length of stay was significantly lower in the diet group (5.0 +/- 0.9 vs 6.3 +/- 2.2 days, respectively). When asked their preferences for method of supplementation, 79% of patients preferred the diet method. CONCLUSIONS: Cardiac surgery patients receiving therapy with diuretics can maintain serum potassium levels at clinically adequate concentrations by eating potassium-rich foods. Length of stay was significantly reduced. This method of potassium supplementation demonstrates the potential for reduced costs and increased patient satisfaction.

Ambulatory intraaortic balloon pump use as bridge to heart transplant.

BACKGROUND: This study evaluates a modification of an ambulatory intraaortic balloon pump (IABP) technique used in patients with heart failure of ischemic origin for bridge to transplant. METHODS: In this retrospective review we evaluated the ability to place the ambulatory IABP, any complications, time on device, and success in bridging to transplant on the ambulatory IABP device. In addition, the cost as compared to current ventricular assist devices was determined. RESULTS: Between July 2000 and November 2001, 4 patients have been managed with ambulatory IABP in our combined University of Wisconsin and William S. Middleton Veterans Administration programs. All 4 patients had ischemia as their mode of heart failure, and each had a relative contraindication to standard ventricular assist device use. All 4 patients had ambulatory IABPs successfully placed through the left axillary artery without complication, and were able to ambulate early after ambulatory IABP placement, and increased their rehabilitation status before transplantation. Ambulatory IABP support ranged from 12 to 70 days. All 4 patients have been successfully transplanted and discharged from the hospital. Use of the ambulatory IABP support, even with multiple replacements, translated to 10- to 50-fold savings for each of the reported patients versus standard ventricular assist device use. CONCLUSIONS: As a result of our initial experience, we believe that ambulatory IABP is an excellent mode of support in selected patients, and is cost-effective, as compared to conventional ventricular assist device therapy.

Biaxial mechanical properties of porcine ascending aortic wall tissue.

BACKGROUND AND AIM OF THE STUDY: Biaxial mechanical properties have been reported for porcine aortic valve leaflets, but not for the aortic root wall. These data are important for understanding the relationship between tissue material properties and function, providing a baseline for diseased tissue, and for providing a basis for numerical models of aortic mechanics. The study aim was to determine the biaxial material properties of porcine aortic root wall tissue. METHODS: Tissue samples (20 mm x 20 mm) were obtained from the aortic root walls of 18 pigs (anterior and posterior samples from each pig) and tested with a custom-built biaxial tensile testing apparatus. The data were fitted to the strain energy formulation: W = ?[a(long)E11(2) + a(circ)Ecc(2) + 2a(int)E11Ecc], where W is the strain energy, E11 = longitudinal strain, Ecc = circumferential strain, along, a(circ), and aint are the constants that were determined, and represent the longitudinal and circumferential elastic moduli, and interaction between the two axes, respectively. RESULTS: The root wall tissue was less stiff in the longitudinal direction (along = 115.8 +/- 8.4 kPa) than the circumferential direction (a(circ) = 169.9.3 +/- 7.4 kPa). As expected, there was mechanical interaction between the two axes (a(int) = 45.7 +/- 3.4 kPa). Additionally, anterior tissue samples were less stiff than posterior samples. All tissue samples exhibited a linear stress-strain relationship up to 40% strain, in contrast to aortic leaflet tissue, which was highly non-linear. CONCLUSION: These results demonstrated that the porcine aortic root wall tissue is an anisotropic material with linear elastic properties, in contrast to leaflet tissue. Additionally, the data suggest that a finite element model using an isotropic material as a basis for the aorta is insufficient for a physiologically accurate representation.

A coupled fluid-structure finite element model of the aortic valve and root.

BACKGROUND AND AIM OF THE STUDY: The study aim was to develop a three-dimensional coupled fluid-structure finite element model of the aortic valve and root. This model extends previous purely structural finite element models, and represents a significant step toward realistic simulation of the complex interactions among tissue material properties and valvular function. METHODS: The aortic root and valve geometry were extracted from magnetic resonance images and imported into the LS-Dyna explicit finite element package. Leaflet and root tissue were modeled with elastic material properties, and blood was modeled as a Newtonian liquid. A dynamic, fully unsteady analysis was performed in which blood flow through the valve was computed along with the motion of the leaflets and root in response to standard physiologic pressure wave profiles. RESULTS: The opening and closing of the aortic valve under physiological loading conditions was successfully simulated, and feasibility of the model illustrated. The motion of the simulated leaflets was consistent with that seen in intact hearts. Analysis of fluid flow patterns revealed eddy structures in the sinus regions and flow into the coronary circulation. CONCLUSION: The addition of blood flow to structural models of the aortic valve and root is a significant advance in modeling, and allows a closer simulation of valvular function. The model will be used to further assess normal and abnormal physiology as well as the effects of surgical intervention.

Fluid-Structure Interactions of the Mitral Valve and Left Heart: Comprehensive Strategies, Past, Present and Future.

The remodeling that occurs after a posterolateral myocardial infarction can alter mitral valve function by creating conformational abnormalities in the mitral annulus and in the posteromedial papillary muscle, leading to mitral regurgitation (MR). It is generally assumed that this remodeling is caused by a volume load and is mediated by an increase in diastolic wall stress. Thus, mitral regurgitation can be both the cause and effect of an abnormal cardiac stress environment. Computational modeling of ischemic MR and its surgical correction is attractive because it enables an examination of whether a given intervention addresses the correction of regurgitation (fluid-flow) at the cost of abnormal tissue stress. This is significant because the negative effects of an increased wall stress due to the intervention will only be evident over time. However, a meaningful fluid-structure interaction model of the left heart is not trivial; it requires a careful characterization of the in-vivo cardiac geometry, tissue parameterization though inverse analysis, a robust coupled solver that handles collapsing Lagrangian interfaces, automatic grid-generation algorithms that are capable of accurately discretizing the cardiac geometry, innovations in image analysis, competent and efficient constitutive models and an understanding of the spatial organization of tissue microstructure. In this manuscript, we profile our work toward a comprehensive fluid-structure interaction model of the left heart by reviewing our early work, presenting our current work and laying out our future work in four broad categories: data collection, geometry, fluid-structure interaction and validation.

Long-term survival of the very elderly undergoing coronary artery bypass grafting.

BACKGROUND: Increasing numbers of the very elderly are undergoing coronary artery bypass graft surgery (CABG). Short-term results have been studied, but few data are available concerning long-term outcomes. METHODS: We conducted a cohort study of 54,397 consecutive patients undergoing primary, isolated CABG surgery between July 1, 1987, and June 30, 2006. Patient records were linked to the Social Security Administration's Death Master File. RESULTS: During 390,871 person-years of follow-up, there were 17,352 deaths. There were 51,149 patients younger than 80 years, 2,661 patients aged 80 to 84 years, and 587 patients aged 85 or more years who underwent isolated CABG surgery. Crude in-hospital survival was 97.2% for those less than 80 years, 98.3% for those aged 80 to 84 years, and 87.6% for those aged 85 or more years. Patients aged 80 or more years were more likely to be female (46.9%), more likely to be emergency priority (10.2%), and more likely to have associated comorbidities than younger patients. Patients aged 85 or more years were more likely to have intraoperative and postoperative morbid events. Among patients younger than 80, median survival was 14.4 years with an annual incidence of death of 4.2%. Among patients 80 to 84 years old, median survival time was 7.4 years, with an annual incidence rate of death of 10.3%. Among patients aged 85 or more years, median survival was 5.8 years, and the annual incidence of death was 13.7%. CONCLUSIONS: Although very elderly CABG patients have more comorbidities and more acute presentation than younger patients and their in-hospital mortality rate is high, their long-term survival is surprisingly good.

Appropriateness of coronary artery bypass graft surgery performed in northern New England.

OBJECTIVES: The goal of this study was to assess the concordance between the American College of Cardiology (ACC) and the American Heart Association (AHA) 2004 Guideline Update for Coronary Artery Bypass Graft Surgery and actual clinical practice. BACKGROUND: There is substantial geographic variability in the population-based rates of coronary artery bypass graft (CABG) procedures, and in recent years, there have been several public concerns about unnecessary cardiac care. The actual rate of inappropriate cardiac procedures is unknown. METHODS: We evaluated 4,684 consecutive isolated coronary artery bypass graft procedures performed in 2004 and 2005 in northern New England. Our regional registry data were used to categorize patients into clinical subgroups. Detailed clinical criteria were then used to categorize procedures within these subgroups as class I (useful and effective), class IIa (evidence favors usefulness), class IIb (evidence less well established), and class III (not useful or effective). RESULTS: Among these 4,684 procedures, we were able to classify 99.6% (n = 4,665). The majority of procedures were class I (87.7%). Class II procedures totaled 10.9%. The remaining 1.4% of procedures were class III. CONCLUSIONS: In this regional study, we found that 98.6% of CABG procedures that could be classified were considered to be appropriate. In these data, actual clinical practice closely follows the recommendations of the 2004 ACC/AHA guidelines for CABG surgery.