Supravalvular aortic stenosis repair: surgical training of 2 repair techniques using 3D-printed models

Abstract

There are a number of techniques used in the surgical treatment of supravalvular aortic stenosis with excellent results; however, junior surgeons’ experience may be limited due to its rare nature. Simulation with 3D-printed models provides a safe platform for surgeons to rehearse surgical techniques prior to patient application but must replicate all features of surgical anatomy. Here, we describe how software manipulation can be used to accurately reproduce the surgical anatomy in supravalvular aortic stenosis and be used to train surgeons in 2 different techniques.

Supravalvular aortic stenosis (SVAS) is a rare congenital cardiac anomaly that usually affects the sinotubular junction and the ascending aorta and may infrequently involve the aortic arch and descending aorta [1].

INTRODUCTION

Supravalvular aortic stenosis (SVAS) is a rare congenital cardiac anomaly that usually affects the sinotubular junction and the ascending aorta and may infrequently involve the aortic arch and descending aorta [1]. There are number of techniques described for SVAS repair ranging from single-patch to a 3-patch technique; however, the optimal technique remains unclear [1–3]. 3D-printed models provide a safe platform to rehearse a variety of techniques [4], but must fully replicate all features of the surgical anatomy. This article demonstrates how software manipulation of an image dataset can be used to produce 3D-printed models that accurately reproduce the surgical anatomy and be used to train surgeons.

METHODS

Contrast-enhanced computed tomograms (CT) of a patient with hour-glass type of SVAS were used to develop the model (Fig. 1A). CT cannot fully define the characteristic thickening of the aortic wall and its relationship to the coronary ostia. Therefore, the outer boundary of the aortic wall was graphically re-created using a commercially available software program (Mimics 14 and 3-Matic 15, Materialise NV, Leiden, Belgium). First, the lumen of the left ventricle and the aorta were segmented using a thresholding tool and the centreline of these structures was acquired (Fig. 1B). Circles matching the measured external diameters of the sinotubular junction, the narrowest part of the aorta, and the distal descending aorta were drawn perpendicular to the centreline and the external border of the aorta was extrapolated. The surfaces of the segmented aortic lumen and the newly designed tube were added to the original model (Fig. 1C). The course of coronary arteries was defined and graphically designed along with the aortic and mitral valves to complete the model (Fig. 1D) (IRB approval: 1000060696, date: 19 March 2019).

Figure 1:

(A) Computed-tomography angiogram of a patient with supravalvular aortic stenosis. Green arrow = left anterior descending artery. (B) Computer-aided design of the new ascending aorta. (C) A longitudinal cut through the left ventricular outflow tract demonstrating the thickened aortic wall and supravalvular ridge. (D) 3D-printed model showing the hour-glass deformity (red-dotted line) and difference in luminal diameter between the thickened aortic segment (green arrow) and normal aorta (blue arrow). Ao: aorta; LA: left atrium; LV: left ventricle; PA: pulmonary artery; RA: right atrium; RCA: right coronary artery.

Surgical technique

Two techniques of SVAS repair were taught during the Hands-on Surgical Training course for congenital heart surgical fellows at our institution. First the Doty technique was demonstrated which involves an inverted, bifurcated patch plasty (Fig. 2A). A vertical incision was commenced on the aorta and was extended proximally down into middle of the non-coronary sinus. The ‘Y’ was completed with an incision made into the right coronary sinus between the coronary artery ostium and commissure (Video 1).

Figure 2:

The 2 different techniques in supravalvular aortic stenosis repair during a Hands-on Surgical Training course. (A) Inverted ‘Y’ patch/Doty technique. (B) Novel ‘H’ technique. Ao: aorta; PA: pulmonary artery; RCA: right coronary artery.

A second technique was then shown that involves a novel ‘H’ repair (Fig. 2B) [5]. This technique involves a horizontal incision of ∼10 mm above the ST junction followed by 2 vertical incisions that descended laterally into the right and non-coronary sinuses and extend distally into the ascending aorta. Two oval-shaped patches were used to reconstruct the lateral aspects of the aorta. The repair was completed with the direct suturing of the original horizontal incision in the anterior aortic wall. The rationale of this repair was to create an anatomical, symmetrical repair, which relieved the stenotic segment in 2 locations. The vertical incisions could be extended into the aortic arch using a longer patch if a more extensive repair was necessary. Following the 2 demonstrations, the fellows rehearsed both techniques that were evaluated objectively using a procedure-specific assessment tool.

DISCUSSION

The rarity of SVAS coupled with the variety of surgical techniques described significantly limits a surgical trainee’s exposure and the ability to compare these different surgical techniques. For this reason, SVAS is a good example of simulation training, since excellent long-term survival rates of surgically repaired SVAS can be achieved with different techniques, yet the optimal technique remains unclear [2, 3, 6]. Adverse outcomes or the likelihood for reintervention are more related to patient characteristics rather than the surgical technique used [2, 3], which will again hamper the ability of the trainee to objectively assess the merits of the different operative repairs.

Currently, the techniques surgeons learn are dependent on their training institutions and trainers, potentially limiting the breath of practices developed. With the increase in online educational material, such as intraoperative videos and virtual hands-on simulation sessions, this format presents an opportunity for existing and future surgeons to rehearse new techniques in a safe, non-consequential manner prior to patient application. Surgeons can use the models to familiarize themselves with all the techniques reducing any learning curves associated with performing a new technique and potentially remove selection biases.

However, any simulation model needs to replicate the appropriate morphology in addition to emphasizing the key technical challenges and pitfalls that the surgeon may encounter. The imaging dataset used cannot always reproduce these characteristics as emphasized in SVAS whereby the thickened aortic wall is not well appreciated by CT angiography. Furthermore, the relationship of the coronary artery ostia and course to the supra-aortic narrowing is key as the surgeon needs to incise the aorta and suture the patches accurately to avoid coronary damage or distortion in order to ensure a successful repair. Therefore the model has to be able to reflect these key anatomical features. In this example, limitations of the 3D-printing process were overcome to accurately represent the pathology and surgical challenges. This was achieved by graphically-designing the original model to both re-create the thickening of the aortic wall and accentuate the coronary artery definition. However, models could be further improved to include more challenging variations of the disease such as diffuse types involving the aortic arch/descending aorta and obstructive coronary artery lesions.

This type of simulation also enabled senior surgeons to trial a novel repair technique and evaluate its ability to correct the anatomy [5]. The ‘H’ repair splits the supra-aortic ring at 2 separate points but uses 2 symmetrical patches rather than a Y-shaped patch, which can be technically difficult to judge in order to maintain symmetry. The technique also allows the surgeon to potentially extend the incisions into the aortic arch if the patient had more extensive disease, a well-recognized association in up to 30% of cases with the condition [7].

This article highlights how 3D-printed models can be used to train surgeons in various surgical techniques. As technology rapidly progresses, there is a realistic possibility that repairs on 3D-printed models could be assessed objectively by utilizing pulsatile pumps and 4D-flow magnetic resonance imaging [8]. Studies could also be developed to objectively assess the haemodynamic characteristics of the different techniques to improve understanding of the optimal repair methods. If successful, there is an increased possibility that this modality will be used in research applications in addition to patient care and training in congenital heart surgery.

Funding

The Cardiac 3D Printing Program at the Hospital for Sick Children is generously supported through the work of Mr. Peter and Mrs. Fabiola Butler.

Conflict of interest: none declared.

Reviewer information

Interactive CardioVascular and Thoracic Surgery thanks Sertac M. Cicek and Francois G. Lacour-Gayet for their contribution to the peer review process of this article.