MRI evaluation of ascending aorta biophysics: new functional indexes and their relationship with aortic size

Purpose: Ascending aorta aneurysm is one of the most common cause of death in cardiovascular patients. Prophylactic surgery to avoid higher mortality due to dissection is recommended at a aortic diameter of 5,5 cm in otherwise healthy patients. Nevertheless, there are several limitations of this criteria. Aortic size index allows to stratify patients according to the level of risk of dissection/rupture, enabling appropriate surgical decision-making. Recently two new MRI indexes of aortic wall's elastic property: maximal rate of systolic distension (MRSD) and maximal rate of diastolic recoil (MRDR) has been proposed to assess the velocity of aortic wall distension and recoil during cardiac cycle. We evaluated two new MRI-derived functional indexes to describe the elastic properties of ascending aorta in patients with different aortic size index. Methods: Twenty two adult patients (54.5±17.7y.o.;17 males) undergoing surgery for ascending aorta aneurysm were enrolled in the study. All the patients underwent comprehensive cardiac MRI study. A standard protocol to acquire the MRI images has been followed and MRSD and MRDR were calculated as cross-sectional area of the proximal ascending aorta (5 mm above the sinotubular junction) measured in each cardiac phase was indexed for the maximal end systolic cross-sectional area and plotted against the time. MRSD and MRDR were expressed as percentile of maximal area/10-3 Sec. Aortic size index (maximal aortic diameter/BSA) was calculated for all the patients. A correlation between MRSD and MRDR with Aortic size index and age of the patient was done using regression plot. Results: We have found a significant correlation between MRSD(t=-2.28; r2=0.21; p=0.0341), MRDR (t=3.59; r2=0.39; p=0.0019) and aortic size index (24.98±2.97mm/m2; range 18.05-30.12mm/ m2). As Aortic index increases, MRSD and MRDR of the aorta decreases. Increased Aortic index, which is the predictor for the negative event, correlation with decreased MRSD and MRDR suggest of aortic stiffness in these patients. Furthermore, a significant correlation between the age of the patient and decrease in the MRSD (r2=0,20, p=0,0406) and MRDR (r2=0,26, p=0,0136) of the aorta is observed. As patients get older their aorta becomes stiffer, which is confirmed by significant decrease in these two new indexes. Conclusions: MRSD and MRDR are related to aortic size index and age of the patient. They seem to describe properly the increasing stiffness of enlarged aortas. Further prospective study are needed to test the prognostic significance of these novel indexes.