Accepted Manuscript. Will the fourth dimension guide us toward the perfect Norwood arch reconstruction? Minoo N. Kavarana, MD, FACS

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1 Accepted Manuscript Will the fourth dimension guide us toward the perfect Norwood arch reconstruction? Minoo N. Kavarana, MD, FACS PII: S (19) DOI: Reference: YMTC To appear in: The Journal of Thoracic and Cardiovascular Surgery Received Date: 8 March 2019 Accepted Date: 11 March 2019 Please cite this article as: Kavarana MN, Will the fourth dimension guide us toward the perfect Norwood arch reconstruction?, The Journal of Thoracic and Cardiovascular Surgery (2019), doi: doi.org/ /j.jtcvs This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

2 Commentary: Will the fourth dimension guide us toward the perfect Norwood arch reconstruction? Conflict of Interest: I have no conflicts to declare Contact Information: Professor of Surgery Section of Pediatric cardiothoracic surgery Charleston, SC Tel: Fax: kavarana@musc.edu Section of Pediatric cardiothoracic surgery, Charleston, SC.

3 Commentary: Will the fourth dimension guide us toward the perfect Norwood arch reconstruction? Professor of Surgery Section of Pediatric cardiothoracic surgery Charleston, SC Central Message: 4-D flow magnetic resonance imaging (MRI) can identify inefficient flow patterns, which may increase single ventricle workload and performance following Norwood arch reconstruction. Although rapid strides have been made in the short-term and medium-term survival following stage 1 Norwood palliation for single ventricle disease, long term survival is limited by the failing Fontan circulation [1]. Residual coarctation and aortic arch obstruction is common and has been associated with poor long-term single ventricular function and survival [2]. However even despite normal 2-D aortic-arch specific parameters based on standard echocardiography and cardiac catheterization, studies have demonstrated that abnormal shape, size-mismatch and contour can lead to maladaptive ventricular-aortic interaction and systemic ventricular dysfunction [3]. 3-D MRI studies using computational fluid dynamic (CFD) modeling have shown that even after a successful coarctation repair in two ventricle patients those that had abnormal arch shapes and contours i.e. a gothic arch had worse ventricular function when compared with those that had a natural Romanesque shape [4]. In single ventricle patients altered arch morphology was associated with higher Glenn pressures and longer ICU and hospital length of stay [5]. Based on these previous 3-D MRI CFD modeling studies there is evidence that reconstructed aortic arch morphology is independently associated with ventricular function and late outcomes [4, 5]. However while 3-D flow models have clear advantages over standard 2-D imaging, they are based on theoretical modeling and geometric-flow assumptions. In contrast, 4D flow MRI directly measures actual flow patterns thus quantifying viscous or abnormal kinetic energy dissipation due to frictional forces. Schafer et al evaluated 4-D flow MRI characteristics to calculate viscous energy losses at the ascending aorta, aortic arch and descending aorta in four patients that had undergone Norwood arch reconstruction, two at the pre-fontan and two at the post- Fontan stage [6]. They found that ascending aortas that were bulky demonstrated diastolic blood pooling and recirculation with increased viscous energy loss at all three levels. A significantly dilated arch with increased size mismatch where the arch transitions to the descending aorta was also associated with a high-energy loss throughout the aorta. They demonstrated that despite normal aortic arch hemodynamics based on cardiac catheterization and echocardiography abnormal aortic arch shape and morphology is associated with abnormal flow patterns and energy loss. Multiple factors determine optimal Norwood arch reconstruction including technique, final shape and the prosthetic material utilized which can result in varying

4 degrees of compliance mismatch with the native aortic tissue. Long-term survival following a Fontan is dependent on good ventricular function for which an unobstructed systemic ventricular outflow tract is a prerequisite [1]. In order to achieve the ideal Norwood arch reconstruction we will need to tailor the arch to patient specific anatomic variations and dimensions. 4-D flow MRI that complements 3-D MRI with CFD modeling may help preoperatively determine the size and shape of an ideal aortic arch reconstruction for a specific patient sub-type. Along with the growing interest and experience with 3-D printed models for congenital heart defects, advanced imaging techniques may soon be able to provide reproducible templates for Norwood arch reconstructions and minimize the incidence of recurrent arch obstruction, late ventricular dysfunction and Fontan failure. References: 1. Lee MGY, Brizard CP, Galati JC, etal. Outcomes of patients born with singleventricle physiology and aortic arch obstruction: the 26-year Melbourne experience. J Thorac Cardiovasc Surg 2014; 148: Larrazabal LA, Tierney ES, Brown DW, et al. Ventricular function deteriorates with recurrent coarctation in hypoplastic left heart syndrome. Ann Thorac Surg 2008;86: Biglino G, Giardini A, Ntsinjana HN, Schievano S, Hsia TY, Taylor AM. Ventriculoarterial coupling in palliated hypoplastic left heart syndrome: noninvasive assessment of the effects of surgical arch reconstruction and shunt type. J Thorac Cardiovasc Surg 2014; 148: Bruse JL, Khushnood A, McLeod K, Biglino G, Sermesant M, Pennec X et al. How successful is successful? Aortic arch shape after successful aortic coarctation repair correlates with left ventricular function. J Thorac Cardiovasc Surg 2017;153: Bruse JL, Cervi E, McLeod K, et al. Looks do matter! Aortic arch shape after hypoplastic left heart syndrome palliation correlates with cavopulmonary outcomes. Ann Thorac Surg 2017;103(2): Schafer M, DiMaria M, Jaggers J, Mitchell MB. Suboptimal neo-aortic arch geometry correlates with inefficient flow patterns in hypoplastic left heart syndrome. J Thorac Cardiovasc Surg 2019 (current issue).

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