RESUMEN
Pediatric ventricular assist device (VAD) use is increasing. The TandemHeart PTVA system is a percutaneous VAD used in adults. Pediatric use is limited by cannula size. Trans-hepatic left atrial (LA) cannulation offers the possibility of shorter, larger-diameter cannulae, but specific requirements for cannula size and flow characteristics need to be developed. We evaluated the feasibility of trans-hepatic cannulation based on patient measurements and bench-top modeling. Two hundred patients admitted to the University of Michigan Pediatric CICU were evaluated. Patients over 14 years and dextrocardiac patients were excluded. The distance from the skin between the 10th and 11th ribs at the mid-axillary line to the left-heart border was measured on x-ray. LA size was measured on echocardiogram. From these measurements, prototype cannulae were fabricated. Benchtop testing of developed cannulae was performed with a pump speed of 8500 RPM and fluid viscosity of 4.0 cP at physiologic atrial and arterial pressures. Inlet pressure and deliverable flows were measured. The proposed design delivered sufficient flow with negative pressures low enough to avoid hemolysis. Trans-hepatic LA cannulation for percutaneous VAD placement is feasible. The shorter distance to the LA and larger hepatic vein size allows design of pediatric-appropriate cannulae with adequate flow rates.
Asunto(s)
Cateterismo Cardíaco/métodos , Procedimientos Quirúrgicos Cardíacos/métodos , Corazón Auxiliar , Ingeniería Biomédica , Tamaño Corporal , Cateterismo Cardíaco/instrumentación , Niño , Preescolar , Atrios Cardíacos , Venas Hepáticas , Humanos , Lactante , Recién NacidoRESUMEN
The spatial distributions of both wall stress and wall strength are required to accurately evaluate the rupture potential for an individual abdominal aortic aneurysm (AAA). The purpose of this study was to develop a statistical model to non-invasively estimate the distribution of AAA wall strength. Seven parameters--namely age, gender, family history of AAA, smoking status, AAA size, local diameter, and local intraluminal thrombus (ILT) thickness--were either directly measured or recorded from the patients hospital chart. Wall strength values corresponding to these predictor variables were calculated from the tensile testing of surgically procured AAA wall specimens. Backwards-stepwise regression techniques were used to identify and eliminate insignificant predictors for wall strength. Linear mixed-effects modeling was used to derive a final statistical model for AAA wall strength, from which 95% confidence intervals on the model parameters were formed. The final statistical model for AAA wall strength consisted of the following variables: sex, family history, ILT thickness, and normalized transverse diameter. Demonstrative application of the model revealed a unique, complex wall strength distribution, with strength values ranging from 56 N/cm2 to 133 N/cm2. A four-parameter statistical model for the noninvasive estimation of patient-specific AAA wall strength distribution has been successfully developed. The currently developed model represents a first attempt towards the noninvasive assessment of AAA wall strength. Coupling this model with our stress analysis technique may provide a more accurate means to estimate patient-specific rupture potential of AAA.
Asunto(s)
Envejecimiento , Aneurisma de la Aorta Abdominal , Rotura de la Aorta , Modelos Cardiovasculares , Envejecimiento/patología , Aorta Abdominal/patología , Aneurisma de la Aorta Abdominal/diagnóstico , Aneurisma de la Aorta Abdominal/epidemiología , Aneurisma de la Aorta Abdominal/patología , Rotura de la Aorta/diagnóstico , Rotura de la Aorta/epidemiología , Rotura de la Aorta/patología , Estudios de Cohortes , Bases de Datos Factuales , Femenino , Humanos , Masculino , Valor Predictivo de las Pruebas , Factores SexualesRESUMEN
Remarkable progress has been made on ventricular assist devices for adult patients. Unfortunately, similar devices are not yet available in the United States for pediatric heart patients. The goal of this project is to demonstrate the feasibility of a percutaneous ventricular assist device for pediatric patients above 2 kg. The proposed system consists of an extracorporeal centrifugal blood pump, a transseptal venous cannula that takes blood from the left atrium to the pump, an arterial cannula that returns the blood to the arterial system, and a controller to adjust pump speed/flow. Using an ad hoc pediatric pump prototype and a spectrum of specially designed cannulae of various sizes, benchtop studies showed that the proposed system could deliver blood flow in a range of 0.3 to 3.0 l/min. For smaller patients (2-35 kg), the transseptal cannula was designed to be placed in the internal jugular vein and the arterial cannula in the internal carotid artery. For larger patients (> 35 kg), the femoral vein and artery would be used. Further development effort will be focused on reducing the hemolysis of the pump design, refining the cannula design, and demonstrating the safety and functionality in animal studies.
Asunto(s)
Diseño de Equipo , Corazón Auxiliar , Adolescente , Velocidad del Flujo Sanguíneo , Niño , Preescolar , Estudios de Factibilidad , Hemólisis , Humanos , Lactante , Recién Nacido , Modelos Anatómicos , Modelos CardiovascularesRESUMEN
OBJECTIVE: A femoral artery cannula is used for certain types of circulatory support but can cause ischemia, especially during prolonged perfusion. This study tests the function of a femoral cannula designed to allow proximal and distal blood flow. METHODS: Five pigs were used in the study. In each animal a distal-flow cannula was implanted in the femoral artery of one leg, and the same-sized standard cannula was implanted in the other. Blood was drained from the left atrium and delivered to the femoral artery through the distal-flow cannula or standard cannula by using a centrifugal pump. An ultrasonic flow probe and microspheres were used to quantify flow and perfusion distal to the cannula. RESULTS: Distal femoral flow and tissue perfusion were present in all animals (5/5) with the distal-flow cannula but only in 1 of 5 animals with the standard cannula (P < .048). Distal flow did not change with pump flow. Mean distal flow at each level of pump flow was higher with the distal-flow cannula (P < .05). Tissue perfusion was also higher with the distal-flow cannula (0.052 +/- 0.028 vs 0.010 +/- 0.022 mL x min(-1) x g(-1), P < .03). CONCLUSIONS: In the swine model the distal-flow cannula allowed greater and more consistent distal flow than the standard cannula. The use of a distal-flow cannula for circulatory support might reduce the risk of distal limb ischemia.
Asunto(s)
Cateterismo Periférico/instrumentación , Arteria Femoral , Miembro Posterior/irrigación sanguínea , Animales , Velocidad del Flujo Sanguíneo , Cateterismo Cardíaco/instrumentación , Diseño de Equipo , Arteria Femoral/fisiología , PorcinosRESUMEN
PURPOSE: The role of intraluminal thrombus (ILT) on abdominal aortic aneurysm rupture is still not clear. Rupture of an aneurysm occurs when the wall stress exceeds the wall strength at any location on the wall. The purpose of this study was to address the hypothesis that the presence of ILT alters the wall stress distribution or wall stress magnitude in AAA. METHODS: Patient-specific 3D AAA geometries were reconstructed from computed tomographic images. Two geometric features, ILT surface ratio (ILT surface area divided by the total AAA surface area) and ILT volume ratio (ILT volume divided by the total AAA volume), were calculated for each AAA. Two models were created for each patient: one with ILT and one without ILT. Systolic pressure measured at the time of computed tomographic imaging was applied to the internal surface of each model. A nonlinear large deformation algorithm was used to compute wall stress distribution with the finite element method. The Wilcoxon matched pairs test was used to compare the peak wall stress between the two models of each patient. RESULTS: Four patients were studied with ILT surface ratios that ranged from 0.29 to 0.72 and ILT volume ratios that ranged from 0.12 to 0.66. The peak wall stress was reduced (range, 6% to 38% reduction; P =.067) for all models with ILT included (range, 28 to 37 N/cm(2)) as compared with models with no ILT (range, 30 to 44 N/cm(2)). Visual inspection also revealed a marked effect of ILT on the wall stress distribution. CONCLUSION: The presence of ILT alters the wall stress distribution and reduces the peak wall stress in AAA. For this reason, ILT should be included in all patient-specific models of AAA for evaluation of AAA wall stresses.