Immediate Impact of Prosthetic Graft Replacement of the Ascending Aorta on Circumferential Strain in the Descending Aorta

Abstract

The results of this study demonstrate graft induced increases in circumferential deformation and distensibility in the native descending aorta in the presence of unchanged haemodynamics and stroke volume after proximal aortic graft replacement, suggesting that replacing native aorta with a graft increases pulse pressure and energy propagation downstream to the graft. This observation may have important clinical implications and may be a mechanism contributing to the reported risk of aneurysm formation or expansion, dissection, or rupture of the aorta distal to graft. Objectives: Prosthetic replacement of the ascending aorta (AA) can potentially modify energy propagation to the distal aorta and contribute to adverse aortic remodelling. This preliminary study employed intra-operative transoesophageal echocardiography (TOE) to assess the immediate impact of prosthetic graft replacement of the AA on circumferential strain in the descending aorta. Methods: Intra-operative TOEs in patients undergoing AA graft replacement were analysed for circumferential strain, fractional area change (FAC), dimensions (end diastolic area [EDA], and end systolic area [ESA]) in the descending aorta immediately before and after graft replacement. Deformation was assessed via global peak circumferential aortic strain (CAS), together with pulse pressure corrected strain, time to peak strain (TTP), and aortic distensibility. Results: Forty-five patients undergoing AA replacement with prosthetic graft (91% elective) were studied. Following grafting, descending thoracic aortic circumferential strain increased (6.3 AE 2.8% vs. 8.9 AE 3.4%, p ¼ .001) paralleling distensibility (5.7 [3.7e8.6] 10 À3 mmHg vs. 8.5 [6.4e12.4] 10 À3 mmHg, p < .001). Despite slight increments in post graft left ventricular ejection fraction (LVEF) (52.3 AE 10.8% vs. 55.0 AE 11.9, p < .001), stroke volume was similar (p ¼ .41), and magnitude of increased strain did not correlate with change in stroke volume (r ¼ À.03, p ¼ .86), LVEF (r ¼ .18, p ¼ .28), or pulse pressure (r ¼ .28, p ¼ .06). Descending aortic size (EDA 4 [2.7e4.6] cm 2 vs. 3.7 [2.5e5] cm 2 , p ¼ .89; ESA 4.3 [3.2e5.3] cm 2 vs. 4.5 [3.3e5.8] cm 2 , p ¼ .14) was similar pre-and post graft. In subgroup analysis, patients with cystic medial necrosis had a significantly higher post procedure CAS than patients with atherosclerotic aneurysms (9.7 AE 3.5% vs. 7.0 AE 2.3%, p ¼ .03). Conclusions: Prosthetic graft replacement of the AA increases immediate aortic circumferential strain of the descending aorta, particularly in patients with cystic medial necrosis. Our findings suggest that grafts augment energy transfer to the distal aorta, a potential mechanism for progressive distal aortic dilation and/or dissection.

Aortic Strain in Patients with Marfan Syndrome Long-Term After Proximal Graft Replacement Surgery – Novel Insights Enabled by Cine-CMR Biomechanical Characterization

“…One reason for aortic events after TAA replacement surgery may stem from biomechanical properties of grafts: Prosthetic grafts are stiffer than native aortic tissue and tubular in shape, thus providing a nidus for energy propagation to the distal aorta that increases stress on native tissue. Consistent with this, prior studies from our group using echocardiography showed that proximal grafts increase distal aortic wall excursions (strain) intra- 6 and post-operatively. 7 Our cardiac MRI (CMR) studies demonstrated further that proximal grafting produces short-term increases in both ascending and descending aortic flow velocity, flow-induced wall shear stress, and pressure-induced wall strain.…”

“…Whereas this is the first study that we are of aware of to examine ascending and descending aortic compliance patterns in patients long-term after proximal graft implantation, our findings add literature by our group and others demonstrating that differences in mechanical properties between current prosthetic grafts and the native aorta alter aortic wall biomechanics in regions distal to surgically treated territories. This premise is supported by both imaging 6–8 and computational modeling studies. 13–15 In clinical studies, graft-induced changes in the distal aorta have been shown to be greatest in patients with genetically triggered TAA – in whom we 16 and others 17–19 have shown aortic stiffness to be greatest.…”

Prosthetic aortic graft replacement of the ascending thoracic aorta alters biomechanics of the native descending aorta as assessed by transthoracic echocardiography

“…Prosthetic grafts differ from the native aorta with respect to geometry and distensibility [9][10][11][12], and thus provide a stiff conduit to propagate high velocity flow into distal (non-grafted) segments. Consistent with this, prior studies by our group have shown ascending aortic grafts to acutely increase energy transmission to the native descending aorta, resulting in increased descending aortic distension as measured via intra-operative transesophageal echocardiography [13]. However, it remains uncertain whether such changes persist post-operatively in ambulatory patients (without modulatory effects of cardiac anesthesia), or whether magnitude of prosthetic graft-induced alterations in native aortic distension varies between patients with and without congenital or genetically associated aortopathies.…”

TEVAR and EVAR, the unknown knowns of the cardiovascular hemodynamics; and the immediate and long-term consequences of fabric material on major adverse clinical outcome

“…Rong et al ( 15 ) demonstrated amplification of circumferential strain in the descending thoracic aorta, paralleling distensibility by using intra-operative transoesophageal echocardiography to study the effect of endograft on the haemodynamic alteration. They showed that prosthetic replacement of the ascending aorta could interfere with the propagation of energy to the distal aorta resulting in adverse aortic remodelling.…”