Eric K. Shang

Three-Dimensional Echocardiographic Analysis of Mitral Annular Dynamics Implication for Annuloplasty Selection

Background— Proponents of flexible annuloplasty rings have hypothesized that such devices maintain annular dynamics. This hypothesis is based on the supposition that annular motion is relatively normal in patients undergoing mitral valve repair. We hypothesized that mitral annular dynamics are impaired in ischemic mitral regurgitation and myxomatous mitral regurgitation. Methods and Results— A Philips iE33 echocardiographic module and X7–2t probe were used to acquire full-volume real-time 3-dimensional transesophageal echocardiography loops in 11 normal subjects, 11 patients with ischemic mitral regurgitation and 11 patients with myxomatous mitral regurgitation. Image analysis was performed using Tomtec Image Arena, 4D-MV Assessment, 2.1 (Munich, Germany). A midsystolic frame was selected for the initiation of annular tracking using the semiautomated program. Continuous parameters were normalized in time to provide for uniform systolic and diastolic periods. Both ischemic mitral regurgitation (9.98±155 cm2) and myxomatous mitral regurgitation annuli (13.29±3.05 cm2) were larger in area than normal annuli (7.95±1.40 cm2) at midsystole. In general, ischemic mitral regurgitation annuli were less dynamic than controls. In myxomatous mitral regurgitation, annular dynamics were also markedly abnormal with the mitral annulus dilating rapidly in early systole in response to rising ventricular pressure. Conclusions— In both ischemic mitral regurgitation and myxomatous mitral regurgitation, annular dynamics and anatomy are abnormal. Flexible annuloplasty devices used in mitral valve repair are, therefore, unlikely to result in either normal annular dynamics or normal anatomy.

Oxidative stress modulates vascular smooth muscle cell phenotype via CTGF in thoracic aortic aneurysm

AIMS Dissection and rupture of the ascending aorta are life-threatening conditions resulting in 80% mortality. Ascending aortic replacement in patients presenting with thoracic aortic aneurysm (TAA) is determined by metric measurement. However, a significant number of dissections occur outside of the parameters suggested by the current guidelines. We investigate the correlation among altered haemodynamic condition, oxidative stress, and vascular smooth muscle cell (VSMC) phenotype in controlling tissue homoeostasis. METHODS AND RESULTS We demonstrate using finite element analysis (FEA) based on computed tomography geometries that TAA patients have higher wall stress in the ascending aorta than non-dilated patients. We also show that altered haemodynamic conditions are associated with increased levels of reactive oxygen species (ROS), direct regulators of the VSMC phenotype in the microregional area of the ascending aorta. Using in vitro and ex vivo studies on human tissues, we show that ROS accumulation correlates with media layer degeneration and increased connective tissue growth factor (CTGF) expression, which modulate the synthetic VSMC phenotype. Results were validated by a murine model of TAA (C57BL/6J) based on Angiotensin II infusion showing that medial thickening and luminal expansion of the proximal aorta is associated with the VSMC synthetic phenotype as seen in human specimens. CONCLUSIONS Increased peak wall stress correlates with change in VSMC towards a synthetic phenotype mediated by ROS accumulation via CTGF. Understanding the molecular mechanisms that regulate VSMC towards a synthetic phenotype could unveil new regulatory pathways of aortic homoeostasis and impact the risk-stratification tool for patients at risk of aortic dissection and rupture.

Delayed complications of inferior vena cava filters: case report and literature review.

Inferior vena cava (IVC) filters are frequently placed to prevent pulmonary embolism in patients in whom anticoagulation is contraindicated or ineffective. Delayed erosion of the filter into adjacent vital structures is a rare complication. We report 3 complications of IVC filters managed with both surgical and endovascular therapies. A review of the available literature addresses incidence of delayed IVC filter complications, the approach to these problems, and the role of retrievable IVC filters.

Peak Wall Stress Predicts Expansion Rate in Descending Thoracic Aortic Aneurysms

BACKGROUND Aortic diseases, including aortic aneurysms, are the 12th leading cause of death in the United States. The incidence of descending thoracic aortic aneurysms is estimated at 10.4 per 100,000 patient-years. Growing evidence suggests that stress measurements derived from structural analysis of aortic geometries predict clinical outcomes better than diameter alone. METHODS Twenty-five patients undergoing clinical and radiologic surveillance for thoracic aortic aneurysms were retrospectively identified. Custom MATLAB algorithms were employed to extract aortic wall and intraluminal thrombus geometry from computed tomography angiography scans. The resulting reconstructions were loaded with 120 mm Hg of pressure using finite element analysis. Relationships among peak wall stress, aneurysm growth, and clinical outcome were examined. RESULTS The average patient age was 71.6 ± 10.0 years, and average follow-up time was 17.5 ± 9 months (range, 6 to 43). The mean initial aneurysm diameter was 47.8 ± 8.0 mm, and the final diameter was 52.1 ± 10.0 mm. Mean aneurysm growth rate was 2.9 ± 2.4 mm per year. A stronger correlation (r = 0.894) was found between peak wall stress and aneurysm growth rate than between maximal aortic diameter and growth rate (r = 0.531). Aneurysms undergoing surgical intervention had higher peak wall stresses than aneurysms undergoing continued surveillance (300 ± 75 kPa versus 229 ± 47 kPa, p = 0.01). CONCLUSIONS Computational peak wall stress in thoracic aortic aneurysms was found to be strongly correlated with aneurysm expansion rate. Aneurysms requiring surgical intervention had significantly higher peak wall stresses. Peak wall stress may better predict clinical outcome than maximal aneurysmal diameter, and therefore may guide clinical decision-making.

A modern experience with saccular aortic aneurysms

OBJECTIVE Repair of saccular aortic aneurysms (SAAs) is frequently recommended based on a perceived predisposition to rupture, despite little evidence that these aneurysms have a more malignant natural history than fusiform aortic aneurysms. METHODS The radiology database at a single university hospital was searched for the computed tomographic (CT) diagnosis of SAA between 2003 and 2011. Patient characteristics and clinical course, including the need for surgical intervention, were recorded. SAA evolution was assessed by follow-up CT, where available. Multivariate analysis was used to examine potential predictors of aneurysm growth rate. RESULTS Three hundred twenty-two saccular aortic aneurysms were identified in 284 patients. There were 153 (53.7%) men and 131 women with a mean age of 73.5±10.0 years. SAAs were located in the ascending aorta in two (0.6%) cases, the aortic arch in 23 (7.1%), the descending thoracic aorta in 219 (68.1%), and the abdominal aorta in 78 (24.2%). One hundred thirteen (39.8%) patients underwent surgical repair of SAA. Sixty-two patients (54.9%) underwent thoracic endovascular aortic repair, 22 underwent endovascular aneurysm repair (19.5%), and 29 (25.6%) required open surgery. The average maximum diameter of SAA was 5.0±1.6 cm. In repaired aneurysms, the mean diameter was 5.4±1.4 cm; in unrepaired aneurysms, it was 4.4±1.1 cm (P<.001). Eleven patients (3.9%) had ruptured SAAs on initial scan. Of the initial 284 patients, 50 patients (with 54 SAA) had CT follow-up after at least 3 months (23.2±19.0 months). Fifteen patients (30.0%) ultimately underwent surgical intervention. Aneurysm growth rate was 2.8±2.9 mm/yr, and was only weakly related to initial aortic diameter (R2=.19 by linear regression, P=.09 by multivariate regression). Decreased calcium burden (P=.03) and increased patient age (P=.05) predicted increased aneurysm growth by multivariate analysis. CONCLUSIONS While SAA were not found to have a higher growth rate than their fusiform counterparts, both clinical and radiologic follow-up is necessary, as a significant number ultimately require surgical intervention. Further clinical research is necessary to determine the optimal management of SAA.

Local wall thickness in finite element models improves prediction of abdominal aortic aneurysm growth

OBJECTIVE Growing evidence suggests that peak wall stress (PWS) derived from finite element analysis (FEA) of abdominal aortic aneurysms (AAAs) predicts clinical outcomes better than diameter alone. Prior models assume uniform wall thickness (UWT). We hypothesize that the inclusion of locally variable wall thickness (VWT) into FEA of AAAs will improve its ability to predict clinical outcomes. METHODS Patients with AAAs (n = 26) undergoing radiologic surveillance were identified. Custom MATLAB algorithms generated UWT and VWT aortic geometries from computed tomography angiography images, which were subsequently loaded with systolic blood pressure using FEA. PWS and aneurysm expansion (as a proxy for rupture risk and the need for repair) were examined. RESULTS The average radiologic follow-up time was 22.0 ± 13.6 months and the average aneurysm expansion rate was 2.8 ± 1.7 mm/y. PWS in VWT models significantly differed from PWS in UWT models (238 ± 68 vs 212 ± 73 kPa; P = .025). In our sample, initial aortic diameter was not found to be correlated with aneurysm expansion (r = 0.26; P = .19). A stronger correlation was found between aneurysm expansion and PWS derived from VWT models compared with PWS from UWT models (r = 0.86 vs r = 0.58; P = .032 by Fisher r to Z transformation). CONCLUSIONS The inclusion of locally VWT significantly improved the correlation between PWS and aneurysm expansion. Aortic wall thickness should be incorporated into future FEA models to accurately predict clinical outcomes.

Use of computational fluid dynamics studies in predicting aneurysmal degeneration of acute type B aortic dissections

OBJECTIVE Whereas uncomplicated acute type B aortic dissections are often medically managed with good outcomes, a subset develop subacute or chronic aneurysmal dilation. We hypothesized that computational fluid dynamics (CFD) simulations may be useful in identifying patients at risk for this complication. METHODS Patients with acute type B dissection complicated by rapidly expanding aortic aneurysms (N = 7) were compared with patients with stable aortic diameters (N = 7). Three-dimensional patient-specific dissection geometries were generated from computed tomography angiography and used in CFD simulations of pulsatile blood flow. Hemodynamic parameters including false lumen flow and wall shear stress were compared. RESULTS Patients with rapid aneurysmal degeneration had a growth rate of 5.3 ± 2.7 mm/mo compared with those with stable aortic diameters, who had rates of 0.2 ± 0.02 mm/mo. Groups did not differ in initial aortic diameter (36.1 ± 2.9 vs 34.4 ± 3.6 mm; P = .122) or false lumen size (22.6 ± 2.9 vs 20.2 ± 4.5 mm; P = .224). In patients with rapidly expanding aneurysms, a greater percentage of total flow passed through the false lumen (78.3% ± 9.3% vs 56.3% ± 11.8%; P = .016). The time-averaged wall shear stress on the aortic wall was also significantly higher (12.6 ± 3.7 vs 7.4 ± 2.8 Pa; P = .028). CONCLUSIONS Hemodynamic parameters derived from CFD simulations of acute type B aortic dissections were significantly different in dissections complicated by aneurysm formation. Thus, CFD may assist in predicting which patients may benefit from early stent grafting.

Validated model for predicting postoperative respiratory failure: analysis of 1706 abdominal wall reconstructions.

Background: Abdominal wall reconstruction can be associated with significant rates of respiratory events. In this current study, the authors aim to characterize perioperative risk factors associated with postoperative respiratory failure and derive a model with which to predict postoperative respiratory failure. Methods: The authors reviewed the 2005 to 2010 American College of Surgeons National Surgical Quality Improvement Program databases, identifying encounters for Current Procedural Terminology codes for both hernia repair (49560, 49561, 49565, 49566, and 49568) and component separation (15734). A predictive model of postoperative respiratory failure was developed using logistic regression analyses and validated using a bootstrap technique. Results: Of 1706 patients undergoing complex abdominal reconstructions in the study period, 102 (6.0 percent) experienced postoperative respiratory failure. Patients experiencing postoperative respiratory failure had longer admissions (21.0 ± 18.5 versus 5.9 ± 5.5 days, p < 0.001) and a higher mortality rate (14.7 percent versus 0.1 percent, p < 0.001). Multivariate logistic regression revealed eight variables significantly associated with postoperative respiratory failure. A history of chronic obstructive pulmonary disease (p < 0.001), dyspnea at rest (p = 0.032), dependent functional status (p = 0.032), malnutrition (p < 0.001), recurrent incarcerated hernia (p = 0.006), concurrent intraabdominal procedure (p = 0.041), American Society of Anesthesiologists score greater than 3 (p < 0.001), and prolonged operative time (p < 0.001) were independently associated with higher rates of postoperative respiratory failure. The multivariate model was internally validated using a bootstrap technique and had good discrimination (c statistic = 0.78). Conclusions: A validated predictive model and clinical risk-assessment tool of postoperative respiratory failure following abdominal wall reconstruction is presented. Respiratory complications were associated with significantly longer hospital stays and higher rates of mortality. Data derived from this large cohort can be used to risk-stratify patients and to enhance perioperative decisionmaking. CLINICAL QUESTION/LEVEL OF EVIDENCE: Risk, III.

Incidence, predictors, and outcomes of hemodynamic instability following carotid angioplasty and stenting

OBJECTIVE To explore the incidence, predictors, and outcomes of hemodynamic instability (HI) following carotid angioplasty and stenting (CAS). METHODS We retrospectively evaluated data on 257 CAS procedures performed in 245 patients from 2002 to 2011 at a single institution. The presence of periprocedural HI, as defined by hypertension (systolic blood pressure >160 mm Hg), hypotension (systolic blood pressure <90 mm Hg), and/or bradycardia (heart rate <60 beats per minute), was recorded. Clinically significant HI (CS-HI) was defined as periprocedural HI lasting greater than 1 hour in total duration. Logistic regression was used to analyze the role of multiple demographic, clinical, and procedural variables. RESULTS Mean age was 70.9 ± 9.9 years (67% male). HI occurred following 84% (n = 216) of procedures. The incidence of hypertension, hypotension, and bradycardia was 54%, 31%, and 60%, respectively. Sixty-three percent of cases involved CS-HI. Recent stroke was an independent risk factor for the development of CS-HI (odds ratio, 5.24; confidence interval, 1.28-21.51; P = .02), whereas baseline chronic obstructive pulmonary disease was protective against CS-HI (odds ratio, 0.34; confidence interval, 0.15-0.80; P = .01). Patients with CS-HI were more likely to experience periprocedural stroke compared to other patients (8% vs 1%; P = .03). There were no significant differences in the incidence of mortality or other major complications between those with and without CS-HI. CONCLUSIONS HI represents a common occurrence following CAS. While the presence of periprocedural HI alone did not portend a worse clinical outcome, CS-HI was associated with increased risk of stroke. Expeditious intervention to prevent and manage CS-HI is of critical importance in order to minimize adverse clinical events following CAS.

Impact of Wall Thickness and Saccular Geometry on the Computational Wall Stress of Descending Thoracic Aortic Aneurysms

Background— Wall stress calculated using finite element analysis has been used to predict rupture risk of aortic aneurysms. Prior models often assume uniform aortic wall thickness and fusiform geometry. We examined the effects of including local wall thickness, intraluminal thrombus, calcifications, and saccular geometry on peak wall stress (PWS) in finite element analysis of descending thoracic aortic aneurysms. Methods and Results— Computed tomographic angiography of descending thoracic aortic aneurysms (n=10 total, 5 fusiform and 5 saccular) underwent 3-dimensional reconstruction with custom algorithms. For each aneurysm, an initial model was constructed with uniform wall thickness. Experimental models explored the addition of variable wall thickness, calcifications, and intraluminal thrombus. Each model was loaded with 120 mm Hg pressure, and von Mises PWS was computed. The mean PWS of uniform wall thickness models was 410±111 kPa. The imposition of variable wall thickness increased PWS (481±126 kPa, P<0.001). Although the addition of calcifications was not statistically significant (506±126 kPa, P=0.07), the addition of intraluminal thrombus to variable wall thickness (359±86 kPa, P⩽0.001) reduced PWS. A final model incorporating all features also reduced PWS (368±88 kPa, P<0.001). Saccular geometry did not increase diameter-normalized stress in the final model (77±7 versus 67±12 kPa/cm, P=0.22). Conclusions— Incorporation of local wall thickness can significantly increase PWS in finite element analysis models of thoracic aortic aneurysms. Incorporating variable wall thickness, intraluminal thrombus, and calcifications significantly impacts computed PWS of thoracic aneurysms; sophisticated models may, therefore, be more accurate in assessing rupture risk. Saccular aneurysms did not demonstrate a significantly higher normalized PWS than fusiform aneurysms.