Comparison of Mechanical Properties of Human Ascending Aorta and Aortic Sinuses
Ali N. AzadaniSam ChitsazPeter B. C. MatthewsNicolas JaussaudJames LeungTonia TsinmanLiang GeElaine E. Tseng
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Biomechanics
Especially among elderly patients embolisms originating from atheromatous plaques in the ascending aorta are responsible for cardiac and cerebral events during coronary bypass surgery. Unfortunately smooth atheromatous degeneration of the aorta often can not be detected even by transoesophageal echocardiography.In four patients with unexpected atheromatous material of the punched ascending aorta the so called "wash out technique" was performed. A side-to-end anastomosis between a segment of vein and the partially clamped ascending aorta was performed. For several minutes the ascending aorta was left to bleed through the venous stump. Without further manipulation of the ascending aorta the coronary bypass graft was completed by an end-to-end anastomosis between the venous stump and the venous graft. Oral anticoagulation in combination with a low dose platelet antiaggregation drug was given for at least one year.All patients had an uncomplicated postoperative course, especially with regard to neurological damage or ECG changes.In patients with unexpected atheromatous pathology of the ascending aorta the "wash out technique" of coronary artery bypass grafting minimises direct embolisation into the cardiac area perfused by the new bypass grafts.
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External wrapping is a surgical method performed to prevent the dilatation of the aorta and to decrease the risk of its dissection and rupture. However, it is also believed to cause degeneration of the aortic wall. A biomechanical analysis was thus performed to assess the stress of the aortic wall subjected to external wrapping.A stress analysis using the finite elements method was carried out on three models: a non-dilated aorta, a moderately dilated aorta and a wrapped aorta. The models were subjected to a pulsatile flow (120/80 mmHg) and a systolic aortic annulus motion of 11 mm.The finite elements analysis showed that the stress exerted on the outer surface of the ascending aorta in the wrapping model (0.05-0.8 MPa) was similar to that observed in the normal aorta (0.03-0.7 MPa) and was lower than in the model of a moderately dilated aorta (0.06-1.4 MPa). The stress on the inner surface of the ascending aorta ranged from 0.2 MPa to 0.4 MPa in the model of the normal aorta, from 0.3 to 1.3 MPa in the model of the dilated aorta and from 0.05 MPa to 0.4 MPa in the wrapping model.The results of this study suggest that the aortic wall is subjected to similar stress following a wrapping procedure to the one present in the normal aorta.
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Aortic surgery
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In 632 consecutive primary operations for coronary bypass grafting, the effect of instrumentation of the ascending aorta on the prevalence of stroke was evaluated. There were five surgical pathology groups: group A: soft aorta with no palpable disease, 463 patients; group B: distinctly palpable aorta with focal atheromas necessitating minor surgical modifications, 132 patients; group C, unclampable aorta (no plane for crossclamping the aorta without compression of atheromas was present), 16 patients; group D, untouchable aorta, in which the entire ascending aortic wall was involved by atheromatosis (these aortas were not touched), 14 patients; group E, aneurysmal aorta with soft walls, 7 patients. There were four strokes (0.63%), all related to instrumentations of the aorta. There were no cerebrovascular accidents in patients in whom precautions were taken. Of all risk factors studied, age was the only predictive one for major atheromatosis of the aorta (chi 2 test, p less than 0.001). Of the 30 patients in groups C and D, only one was younger than 60 years.
Stroke
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Root (linguistics)
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The authors analyzed dependence between the presence of preoperative predictors of aorta-associated complications and risk for the development of these complications in the remote period after prosthetic repair of the aortic valve. The study included a total of 231 patients subjected to aortic valve prosthetic repair with no additional intervention on the root and ascending portion of the aorta. The follow up duration varied from 12 to 62 months. As predictors of the development of aorta-associated complications we examined such factors as the bicuspid structure of the aortic valve, dilatation of the aortic ascending portion relative to the upper border of the individually calculated norm, disordered configuration of the complex "aortic root - ascending portion of the aorta", resistant arterial hypertension, diabetes mellitus. Depending on the number of predictors for the development of aorta-associated complications the patients were subdivided into 2 groups: Group One consisting of 105 patients with two and more predictors of the development of aorta-associated complications, and Group Two comprising 126 patients with not more than one predictor of the development of aorta-associated complications. It was determined that in the first group of patients the total number of aorta-associated complications in the remote period after prosthetic repair of the aortic valve amounted to 25.7% (27 of 105 patients). The total number of aorta-associated complications in the second group amounted to 1.6% (2 of 126 patients). All detected aorta-associated complications were divided into "critical" and "noncritical". The critical complications were those the detection of which required performing a second operation in the patient: formation of an ascending aortic aneurysm and type A aortic dissection. To the "noncritical" aorta-associated complications belonged dilatation of the ascending portion of the aorta progressing at a rate of 2 mm/year. Resulting from the performed study it was determined that each specific of the examined predictors exerted no influence on the risk for the development of aorta-associated complications in the remote period after prosthetic repair of the aortic valve (p>0.05). Any combination of two and more predictors in one patient considerably increased the risk for the development of complications (p<0.001). A conclusion was made that revealing two and more predictors of the development of aorta-associated complications in one patient it is appropriate to perform a simultaneous operation of prosthetic repair of the aortic valve and the ascending aortic portion.
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We assessed the ability of transesophageal echocardiography (TEE) to examine the entire length of the ascending aorta. TEE-derived data were compared with anatomic measurements and epiaortic scanning. There were 27 patients (19 male, 8 female; aged 67 ± 12 yr) studied during cardiac surgery. The surgeon measured the distance between the aortic anulus near the right coronary artery to the origin of the innominate artery (AV→IN) and to the level of the aortic cannulation site (AV→C). Independently, the ascending aorta was imaged by biplane TEE and the maximum length of aorta visualized was measured (TEE-MAX). Additionally, TEE was used to detect atheromas in the aorta and to visualize the aortic cannula. Epiaortic scanning was also performed in 14 patients. Direct measurement of the ascending aorta revealed a length of 8.9 ± 1.3 cm (mean ± SD) and the TEE-MAX was 7.4 ± 1.1 cm. The range of the difference between the two measurements was 0.2-4.5 cm. The aortic cannula was visualized only in 1 of 27 patients, and severe atherosclerotic plaques (>3 mm thick), not seen on TEE, were detected in five patients with epiaortic scanning. As much as 42% (4.5 cm of 10.7 cm) of the length of the ascending aorta was not visualized and potentially embolic plaques were not imaged by TEE. These findings suggest that even biplane TEE may have limited use in the precannulation assessment of the aorta for plaque and the detection of distal ascending aortic pathology.
Descending aorta
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