Schäfer M, Di Maria MV, Jaggers J, Stone ML, Ivy DD, Barker AJ, Mitchell MB.J Thorac Cardiovasc Surg. 2021 Dec;162(6):1791-1804. doi:
10.1016/j.jtcvs.2021.01.111. Epub 2021 Feb 4. PMID: 33653609
Take Home Points:
- Geometry, i.e., smooth narrowing of the reconstructed aorta from the ascending to the descending aorta is more important than hemodynamics parameters, such as pressure difference.
- Impact of arch growth on change in energy loss is not fully understood and further study to see a serial assessment in this entity is necessary.
Commentary from Dr. Yasuhiro Kotani (Okayama, Japan), chief section editor of Congenital Heart Surgery Journal Watch:
Summary:
A total of 26 patients who underwent Norwood operation was included in this study. Patients were evaluated by 4-dimentional-flow magnetic resonance imaging and were then divided based on the degree of neoaortic tapering defined as the standard deviation of diameter values measured at the ascending aorta, transverse arch, aortic isthmus, and the descending aorta. The median tapering value of neoaortic was 0.52cm and patients were divided into 2 groups: high degree (>0.52cm)(Group H: n=13) and low degree (≦0.52cm)(Group L: n=13). Group H had a higher prevalence of abnormal recirculating flow in the neoaorta and elevated neoaortic flow-mediated viscous energy loss in the ascending aorta (Group H: 1.0±0.4 vs. Group L: 0.6±0.3 mW, p=0.004). The study concluded that oversizing neoaortic reconstruction should be avoided from the point of ventricular-aortic coupling in patients undergoing Norwood operation.
Comment:
Previous studies showed the shape of reconstructed neoaortic arch is important in terms of the afterload of systemic ventricle in HLHS patients which impacts on RV dysfunction and subsequent long-term outcomes. This study showed that suboptimal neoaortic geometry, i.e., size discrepancy among the ascending, transverse, and descending aorta, was associated with an increased flow-mediated viscous energy loss and an increased wasted RV mechanical power. This is the first study to evaluate neoaortic flow hemodynamics in a sizable group of patients with HLHS having Norwood operation. Importantly, no patients in this study had a residual hemodynamic coarctation which makes us think of the importance of cardiac MRI assessment in this particular patient group.
This study raised a couple of questions. One is do we need to routinely use MRI assessment in all patients after Norwood operation. Because of increased evidence of MRI assessment for flow dynamics and its influence on cardiac function, it is ideal to perform MRI assessment. On the other hands there are still some problems, including the costs of the examination and availability (not all hospitals have facility and staffs for cardiac MRI). Another question is that how to implicate this result in the clinical practice. This study highlighted the importance of geometry rather than physiology as even patients without no evidence of residual hemodynamic recoarctation showed higher energy loss if size discrepancy between the ascending aorta and descending aorta existed. Taken together, the lessons learned from this study is that surgeons need to reconstruct the neoaortic arch in a good shape no matter other physiologic parameters give us a green light. But again, the problem is achieving this goal is challenging due to the complex patch shape in highly variable anatomy in HLHS.
