RESUMO
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.
Assuntos
Aneurisma Aórtico/diagnóstico por imagem , Dissecção Aórtica/diagnóstico por imagem , Idoso , Dissecção Aórtica/fisiopatologia , Angiografia , Aneurisma Aórtico/fisiopatologia , Simulação por Computador , Feminino , Humanos , Hidrodinâmica , Imageamento Tridimensional , Masculino , Pessoa de Meia-Idade , Estudos Retrospectivos , Tomografia Computadorizada por Raios XRESUMO
OBJECTIVE: Aortic wall thickness (AWT) is important for anatomic description and biomechanical modeling of aneurysmal disease. However, no validated, noninvasive method for measuring AWT exists. We hypothesized that semiautomated image segmentation algorithms applied to computed tomography angiography (CTA) can accurately measure AWT. METHODS: Aortic samples from 10 patients undergoing open thoracoabdominal aneurysm repair were taken from sites of the proximal or distal anastomosis, or both, yielding 13 samples. Aortic specimens were fixed in formalin, embedded in paraffin, and sectioned. After staining with hematoxylin and eosin and Masson's trichrome, sections were digitally scanned and measured. Patients' preoperative CTA Digital Imaging and Communications in Medicine (DICOM; National Electrical Manufacturers Association, Rosslyn, Va) images were segmented into luminal, inner arterial, and outer arterial surfaces with custom algorithms using active contours, isoline contour detection, and texture analysis. AWT values derived from image data were compared with measurements of corresponding pathologic specimens. RESULTS: AWT determined by CTA averaged 2.33 ± 0.66 mm (range, 1.52-3.55 mm), and the AWT of pathologic specimens averaged 2.36 ± 0.75 mm (range, 1.51-4.16 mm). The percentage difference between pathologic specimens and CTA-determined AWT was 9.5% ± 4.1% (range, 1.8%-16.7%). The correlation between image-based measurements and pathologic measurements was high (R = 0.935). The 95% limits of agreement computed by Bland-Altman analysis fell within the range of -0.42 and 0.42 mm. CONCLUSIONS: Semiautomated analysis of CTA images can be used to accurately measure regional and patient-specific AWT, as validated using pathologic ex vivo human aortic specimens. Descriptions and reconstructions of aortic aneurysms that incorporate locally resolved wall thickness are feasible and may improve future attempts at biomechanical analyses.
Assuntos
Aorta Torácica/diagnóstico por imagem , Aneurisma da Aorta Torácica/diagnóstico por imagem , Aortografia/métodos , Tomografia Computadorizada Multidetectores , Interpretação de Imagem Radiográfica Assistida por Computador , Idoso , Algoritmos , Aorta Torácica/cirurgia , Aneurisma da Aorta Torácica/cirurgia , Automação , Feminino , Humanos , Masculino , Valor Preditivo dos Testes , Reprodutibilidade dos TestesRESUMO
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.
Assuntos
Aorta Abdominal/diagnóstico por imagem , Aneurisma da Aorta Abdominal/diagnóstico por imagem , Aortografia/métodos , Simulação por Computador , Modelos Cardiovasculares , Tomografia Computadorizada por Raios X , Idoso , Idoso de 80 Anos ou mais , Aorta Abdominal/fisiopatologia , Aneurisma da Aorta Abdominal/fisiopatologia , Fenômenos Biomecânicos , Progressão da Doença , Feminino , Análise de Elementos Finitos , Hemodinâmica , Humanos , Masculino , Pessoa de Meia-Idade , Valor Preditivo dos Testes , Prognóstico , Interpretação de Imagem Radiográfica Assistida por Computador , Estudos Retrospectivos , Estresse Mecânico , Fatores de TempoRESUMO
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.
Assuntos
Aneurisma da Aorta Torácica/diagnóstico por imagem , Interpretação de Imagem Assistida por Computador/métodos , Imageamento Tridimensional/métodos , Tomografia Computadorizada por Raios X/métodos , Idoso , Idoso de 80 Anos ou mais , Aneurisma da Aorta Torácica/fisiopatologia , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Estudos RetrospectivosRESUMO
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.
Assuntos
Angioplastia/instrumentação , Doenças das Artérias Carótidas/terapia , Hemodinâmica , Complicações Pós-Operatórias/epidemiologia , Complicações Pós-Operatórias/fisiopatologia , Stents , Idoso , Angioplastia/efeitos adversos , Angioplastia/mortalidade , Bradicardia/epidemiologia , Bradicardia/fisiopatologia , Doenças das Artérias Carótidas/diagnóstico , Doenças das Artérias Carótidas/mortalidade , Doenças das Artérias Carótidas/fisiopatologia , Distribuição de Qui-Quadrado , Feminino , Humanos , Hipertensão/epidemiologia , Hipertensão/fisiopatologia , Hipotensão/epidemiologia , Hipotensão/fisiopatologia , Incidência , Modelos Logísticos , Masculino , Pessoa de Meia-Idade , Análise Multivariada , Razão de Chances , Philadelphia/epidemiologia , Complicações Pós-Operatórias/mortalidade , Estudos Retrospectivos , Fatores de Risco , Acidente Vascular Cerebral/epidemiologia , Acidente Vascular Cerebral/fisiopatologia , Fatores de Tempo , Resultado do TratamentoRESUMO
Aneurysms of the extracranial vertebral artery are uncommon, with most cases attributed to penetrating head and neck trauma. We report a 29-year-old man with a symptomatic proximal extracranial vertebral artery aneurysm of unclear etiology. This patient's aneurysm was definitively treated after a successful balloon occlusion test of his affected vertebral artery. An endovascular approach was used combining coil embolization of the distal vertebral artery and a covered stent graft in the subclavian. Although aneurysms of this size and location are traditionally repaired with open aneurysmectomy, we show that endovascular approaches can be a safe and effective alternative.