Using Carotid-Subclavian Artery Index and Isthmus-Descending Aorta Ratio with Cardiac MR for the Detection of Coarctation

The diagnosis of the coarctation of the aorta is difficult in the presence of complex cardiac defects, congenital disease, or poor echocardiographic window. The carotid- subclavian artery index (CSAI) and the isthmus-descending aorta ratio (I/D) have been used in echocardiography in many studies, but only a few studies have utilized cardiac magnetic resonance imaging (MRI) for the detection of coarctation. In this prospective cohort study, all MRI cases (aged 0-40) with a diagnosis of coarctation between 2010 and 2011 were reviewed. The MRI measurement of the aortic arch was performed in order to calculate the CSAI and the I/D ratio. The CSAI is the ratio of the distal aortic arch diameter to the distance between the left carotid artery and the left subclavian artery and is highly suggestive of a coarctation when it is less than 1.5. The I/D ratio is defined as the diameter of the isthmus to the descending aorta and suggests an aortic coarctation when it is less than 0.64. Sixty-five patients with coarctation had a lower CSAI than the controls (84) (1.27±0.06 vs. 2.82± 0.9; P <0.05). The I/ D ratio was lower (0.4±0.14) than that in the previous study (0.64) (P <0.05). Associated cardiac defects, age, and sex did not have an effect on the CSAI or I/D ratio (P > 0.05). A cut-off point of 1.5 had 96% sensitivity and 76% specificity in the detection of the coarctation of the aorta. The positive and negative predictive values were 84.4% and 94.1%, respectively. The association between both indices improved sensitivity and permitted the diagnosis of coarctation in all the patients based solely on cardiac MRI measurements. The CSAI and I/D ratio, independent of clinical status, associated anomalies, age, and sex, are useful tools for detecting aortic coarctation via cardiac MRI.