Aorta size mismatch predicts decreased exercise capacity in patients with successfully repaired coarctation of the aorta.
Mandell JG, Loke YH, Mass PN, Opfermann J, Cleveland V, Aslan S, Hibino N, Krieger A, Olivieri LJ.
J Thorac Cardiovasc Surg. 2020 Oct 7:S0022-5223(20)32707-0. doi: 10.1016/j.jtcvs.2020.09.103. Online ahead of print.
Take Home Points:
In patients with repaired coarctation of the aorta:
- Ascending to descending aorta size mismatch is associated with a decrease in exercise tolerance.
- Patients with ascending : descending aortic diameter of close to 1 had the best exercise capacity.
- The geometry of the aortic arch and the normalized aortic dimension were not associated with exercise capacity.
Commentary from Dr. M.C. Leong (Kuala Lumpur, Indonesia), section editor of ACHD Journal Watch: Despite a successful initial repair, patients with coarctation of the aorta (CoA) remain to be at risk of long term morbidities. One of such is the decreased in exercise capacity. A decreased in exercise capacity does not only affects the quality of lives of patients, but it also increases the risk of hospitalization and death. In this paper, the authors sought to evaluate the relationship between aortic arch geometry, size and flow characteristics, and exercise capacity in patients with repaired CoA.
The authors studied the above mentioned in an interesting way. Firstly, they looked at the patients with repaired CoA, who had a cardiac magnetic resonance (CMR) and cardiopulmonary stress test and achieved anaerobic threshold, within their database. Correlations were sought between the aortic arch geometry (Romanesque which is normal and Crenel and Gothic which are abnormal – Figure 1), the dimensions of the aorta measured at the usual locations, and the ascending and descending aortic flow measured on phase contrast imaging. Subsequently, the authors, innovatively, created a mock circulatory system to mimic circulatory flow within the arch by printing the 3D model of repaired CoA of all the subjects and measured the flow and pressures within the 3D arch models at rest and exercise, to simulate the effect of the flow of blood within the repaired arches during these conditions – Figure 2.
15 patients (mean age 26.8 8.6 years), of which 6 had bicuspid aortic valve, were recruited. Baseline characteristics were as tabulated in Table 1 and 2. The authors found that exercise capacity had a significantly positive correlation with normalized descending aortic diameter (DAo) diameter. Patients with a smaller ascending aorta: descending aorta diameter ratio (DAAo/DDAo) had better exercise capacity – Table 3 & Figure 3. Patients with DAAo/DDAo close to 1 had the best exercise capacity while worse peak oxygen consumption (VO2) was associated with a smaller DAo and a larger AAo. Normalised aortic root, sinotubular junction, AAo and isthmus diameters did not correlate with exercise capacity. Similarly, the geometry of the arch did not correlate to the VO2.
In the mock circulatory simulation study, the percentage of DAo flow at rest and during exercise correlated negatively to DAAo/DDAo (rho = -0.68, p<0.01; and rho = -0.59, p=-0.02) and the ratio of percent of DAo flow in exercise to rest was positively correlated with DAAo/DDAo (rho=0.64, p<0.01) and negatively correlated with VO2 (rho =-0.60, p=0.02) – Figure 6.
This study demonstrated that the ascending : descending aortic size mismatch is an important cause of exercise intolerance. Our initial perception that a smaller size aortic arch or an abnormal geometry of the aortic arch might cause an increased in flow resistance and a long term implication to the left ventricular muscles was not translated into a decrease in exercise capacity, nor is a dilated aortic root which may potentiate energy loss as blood flows through a large AAo. Rather, a smaller DAo is more closely related to exercise capacity rather than the dilated AAo which may be due to limited perfusion to the lower limbs.