Comparison of half-turned truncal switch and conventional operations

Abstract

 

OBJECTIVES

To compare conventional procedures with the half-turned truncal switch operation (HTTSO) for the management of complete transposition of the great arteries with left ventricular outflow tract (LVOT) obstruction using time-resolved 3-dimensional magnetic resonance phase-contrast imaging.

METHODS

We identified 2 cases that underwent the Rastelli procedure and one case that underwent the Réparation a l'étage ventriculaire before 2002 [conventional procedures group (group C)], and 16 cases of HTTSO that were performed between 2002 and 2020 [HTTSO group (group H)]. Postoperative haemodynamics were assessed using time-resolved 3-dimensional magnetic resonance phase-contrast imaging in cases in both groups.

RESULTS

The median follow-up period was 20.4 years in group C, and 6.1 years in group H. In group C, all 3 patients underwent reoperation because of postoperative right ventricular outflow tract obstruction and/or insufficiency. In addition, permanent pacemaker implantation was needed in 1 patient because of complete atrioventricular block complicated by ventricular septal defect enlargement. In group H, reoperation for LVOT/right ventricular outflow tract obstruction was not needed. A time-resolved 3-dimensional magnetic resonance phase-contrast imaging examination revealed high energy loss and wall shear stress in the winding LVOT in the group C. In contrast, low energy loss and wall shear stress, with straight and smooth LVOT, were identified in group H.

CONCLUSIONS

HTTSO was shown to be superior to conventional procedures because a straight and wide LVOT could be obtained. Therefore, HTTSO should be the first choice for complete transposition of the great arteries with LVOT obstruction.

INTRODUCTION

Conventional surgical procedures for the treatment of patients suffering from complete transposition of the great arteries (TGA) with left ventricular outflow tract (LVOT) obstruction, such as the Rastelli and Réparation a l'étage ventriculaire (REV), are associated with serious complications, including postoperative right and LVOT obstruction [1–3]. Nikaidoh [4] developed an innovative and effective aortic translocation procedure to reduce the incidence of these complications; however, some complications could still arise after this procedure, such as coronary insufficiency and right ventricular outflow tract (RVOT) obstruction [5–7].

We developed an alternative aortic translocation procedure, the half-turned truncal switch operation (HTTSO), in which both original valves are used as concordant semilunar valves [8]. In this operation, the harvested truncal block including both semi-lunar valves is anastomosed to the appropriate outflow tracts [the left ventricle to the aortic valve, and the right ventricle (RV) to the pulmonary valve] after horizontal half-turning. This procedure has excellent mid-to-long-term outcomes [9]. In this study, we aimed to verify the haemodynamic superiority of HTTSO to conventional Rastelli and REV, using time-resolved 3-dimensional magnetic resonance phase-contrast imaging (4D-flow MRI) analysis. To the best of our knowledge, this is the first study to evaluate the haemodynamic differences between conventional Rastelli/REV and the HTTSO procedure using 4D-flow MRI.

METHODS

Patients and procedures

This study was approved by the Institutional Review Board of Kyoto Prefectural University of Medicine (date of IRB approval: 23 March 2018; IRB number: ERB-C-1135). Informed consent was obtained from all patients. Clinical data were obtained from a review of the medical records, as well as operative, echocardiographic, catheterization and 4D-flow MRI reports.

The Rastelli and the REV were performed on a total of 3 patients with TGA, ventricular septal defect (VSD) and LVOT obstruction before 2002. The age and body weight of the patients at the time of surgery were 7 months and 6.9 kg (case 1), 3.7 years and 12.0 kg (case 2) and 6.9 years and 17.0 kg (case 3), respectively. In cases 1 and 2, VSD enlargement was performed as a simultaneous procedure. Complete atrioventricular block occurred in case 2 that warranted the implantation of a permanent pacemaker. In cases 1 and 3, 4D-flow MRI evaluation was performed 17 years after the first Rastelli procedure and 13 years after REV. However, in case 2, 4D-flow MRI evaluation could not be performed because of the permanent pacemaker (Table 1).

Table 1:

Patient details

Patient	Diagnosis	Procedure (age, BW)	Complications	Reoperation (age, BW)	4D-flow MRI
1	TGA LVOTO	Rastelli VSD enlargement (7 months, 6.9 kg)	RVOTO	re-RVOTR (1 year, 9.5 kg)	17 years after initial operation
2	TGA LVOTO	Rastelli VSD enlargement (4 years, 12.0 kg)	cAVB (PMI) RVOTO AR	re-RVOTR AVP (6 years, 17.1 kg)
3	TGA type DORV LVOTO	REV (6 years, 17.0 kg)	RVOTO	re-RVOTR (19 years, 65.0 kg)	13 years after initial operation
4	TGA type DORV LVOTO	Half-turned truncal switch RVOTR (monocuspid patch) (1 year 7 months, 10.5 kg)	None	None	11 years after operation
5	TGA s/p PAB	Half-turned truncal switch pulmonary commissurotomy (1 year 6 months, 9.0 kg)	None	None	5 years after operation

4D-flow MRI: time-resolved 3-dimensional magnetic resonance phase-contrast imaging; AR: aortic regurgitation; AVP: aortic valvuloplasty; BW: body weight; cAVB: complete atrioventricular block; DORV: double-outlet right ventricle; LVOTO: left ventricular outflow tract obstruction; PAB: pulmonary arterial banding; PMI: pacemaker implantation; RVOTO: right ventricular outflow tract obstruction; RVOTR: right ventricular outflow tract reconstruction; TGA: complete transposition of the great arteries; VSD: ventricular septal defect.

After 2002, totally 16 patients underwent HTTSO. Their median age and body weight were 1.2 years (range 0.2–5.1 years) and 7.9 kg (range 4.4–13.3 kg), respectively. Nine patients were diagnosed with TGA with VSD and LVOT obstruction, 6 patients were diagnosed with TGA-type double-outlet right ventricle (DORV), and 1 patient was diagnosed with TGA with degenerative pulmonary valve after pulmonary arterial banding. Autologous pulmonary valves were preserved by pulmonary commissurotomy in 6 patients with adequate annular diameter and flexible valves. RVOT was augmented using a transannular patch, bearing a monocuspid fan-shaped expanded polytetrafluoroethylene valve in 8 patients with narrow pulmonary annulus.

In the HTTSO group (group H), 4D-flow MRI evaluation was performed in 2 patients. One of these patients was diagnosed with TGA-type DORV and underwent HTTSO at the age of 1.6 years and weighed 10.5 kg (case 4). RVOT reconstruction was done using a monocuspid fan-shaped expanded polytetrafluoroethylene patch. This patient had a 4D-flow MRI 11 years after HTTSO. The other patient was diagnosed with TGA with degenerative pulmonary valve after pulmonary arterial banding. HTTSO was performed when this patient was 1.5 years old and weighed 9.0 kg (case 5). The patient’s autologous pulmonary annulus diameter was adequate; thus, only pulmonary commissurotomy was performed at RVOT reconstruction. A 4D-flow MRI was done 5 years after HTTSO (Table 1).

Statistical analyses and time-resolved 3-dimensional magnetic resonance phase-contrast imaging analyses

Statistical analyses were performed using StatMate V, version 5.01 (Atoms, Tokyo, Japan). Multi-slice sagittal Steady State Free Procession image series in addition to 3D cine phase-contrast MRI were performed, and 4D-flow MRI postprocessing was done using iTFlow, version 8.1 (Cardio Flow Design Inc., Tokyo, Japan). Systemic and pulmonary circulations within the left ventricle and RV were segmented in order to visualize blood flow. Flow streamline, wall shear stress (WSS) distribution and flow energy loss (EL) change in 1 cardiac cycle were measured. Continuous data were presented as medians and ranges or means and standard deviations.

RESULTS

Clinical results

In the group of patients who underwent conventional procedures, such as Rastelli and REV, the median follow-up period was 20.4 (range 14.3–23.3) years. Early mortality and late death were not indicated. In 1 case, intraventricular rerouting and RVOT reconstruction (RVOT conduit exchange) due to RVOT obstruction were required 8 months after the initial Rastelli operation. In the second case, RVOT conduit exchange and aortic valvuloplasty were required because of postoperative RVOT obstruction and moderate aortic insufficiency about 3.3 years after the initial Rastelli procedure. In the third case, RVOT conduit exchange was performed 13 years after undergoing REV. Freedom from reoperation rate for both LVOT and RVOT at 10 years was 33.3% (Fig. 1A and B).

Figure 1:

Kaplan–Meier analysis shows (A) freedom from reoperation for left ventricular outflow tract obstruction and (B) freedom from reoperation for right ventricular outflow tract obstruction between the Rastelli procedure and the half-turned truncal switch operation.

In the HTTSO group, the median follow-up period was 6.1 (range 0.2–15.0) years. No early mortality was encountered. Only 1 patient died, due to arrhythmia, 11 months after surgery. The freedom from reoperation rate for LVOT at 10 years was 80.0% (Fig. 1A). One patient with moderate aortic regurgitation, who had a bicuspid aortic valve, required aortic valvuloplasty 8 years after HTTSO. Reintervention for RVOT was not necessary in all patients (Fig. 1B).

Time-resolved 3-dimensional magnetic resonance phase-contrast imaging evaluation

In case 1, no flow acceleration in the LVOT was observed, but highly curved LVOT flow was detected, resulting in high WSS in the flow collided portion of the LVOT. As WSS is a mechanical stress caused by blood flow on the endothelial intima, it typically causes intimal hyperplasia in the long term. Furthermore, EL in the left-heart system was measured at 4.88 mW, which was mainly caused by the curved collided flow of LVOT, and this was around triple the value in healthy volunteers (Fig. 2A, Video 1). In case 3, the LVOT was relatively straight, but the direction of outflow pathway was different from those of normal individuals. EL in the left-heart system was measured as 3.29 mW, which was slightly higher than the normal value (Fig. 2B, Video 1). Furthermore, in case 1, the intraventricle tunnel portion showed evidence of dyskinetic motion, resulting in dyskinetic motion of the left ventricular chamber and impaired cardiac output. On the other hand, in cases 4 and 5, the VSD patch was flat and straight; thus, only limited dyskinetic motion was detected (Fig. 3, Video 2).

Figure 2:

Time-resolved 3-dimensional magnetic resonance phase-contrast imaging evaluation of the left ventricle after the Rastelli procedure. Curved left ventricular outflow tract and turbulent blood flow in the same region are clearly visualized (white arrow). Wall shear stress and energy loss also showed high values. White arrows indicated intraventricular rerouting patch. Ao: aorta; LV: left ventricle.

Figure 3:

Time-resolved 3-dimensional magnetic resonance phase-contrast imaging evaluation of left ventricular outflow tract after the Rastelli procedure. After the Rastelli procedure, the intraventricular tunnel (white arrows) became very long; therefore, the left ventricular outflow tract showed dyskinetic motion, and this caused high energy loss in the left heart system. Ao: aorta; LV: left ventricle.

In cases 4 and 5, straight and non-restrictive LVOT was found and flow acceleration was not detected in the LVOT in both TGA-type DORV and TGA cases. Thus, the WSS was sufficiently low. The EL was 1.77 mW (case 3) and 1.49 mW (case 4), and these values were almost equal to those of healthy volunteers (Fig. 4, Video 1).

Figure 4:

Time-resolved 3-dimensional magnetic resonance phase-contrast imaging evaluation of left ventricle post half-turned truncal switch procedure. The left ventricular outflow tract was reconstructed in a straight manner, so wall shear stress and energy loss were low. Ao: aorta; LV: left ventricle.

In case 1, the prosthetic RV-pulmonary artery (PA) conduit became restrictive with growth, resulting in flow acceleration in the RVOT. In addition, in case 3, the anterior-translocated PA was compressed by the sternum and resulted in RVOT obstruction. Accordingly, WSS was high in the flow-accelerated portion, and EL in the right heart system was 7.84 mW (almost 7 times of that in a healthy volunteer) in case 1 and 5.83 mW in case 3 (almost 5 times of that in a healthy volunteer) [10]. This indicated severe afterload in the RV (Fig. 5, Video 1).

Figure 5:

Time-resolved 3-dimensional magnetic resonance phase-contrast imaging evaluation of right ventricle post Rastelli procedure. In the Rastelli procedure, the prosthetic conduit from the right ventricle to the pulmonary artery became restrictive as the patient’s heart grew. This led to acceleration of flow. Wall shear stress and energy loss had very high values. PA: pulmonary artery; RV: right ventricle.

In cases 4 and 5, the RVOT flow straight and no acceleration was observed, but pulmonary regurgitation was detected in both cases. In case 4, pulmonary regurgitation was moderate; it was inevitable because of the monocuspid expanded polytetrafluoroethylene patch. In case 5, pulmonary regurgitation was mild because the patient’s pulmonary annulus was preserved. On the other hand, El was measured at 2.65 mW in case 4 and 1.52 mW in case 5. In case 4, EL was almost twice that of healthy volunteer. Volume overload due to pulmonary regurgitation could be reduced to a minimum (Fig. 6, Video 1).

Figure 6:

Time-resolved 3-dimensional magnetic resonance phase-contrast imaging evaluation of the right ventricle after the half-turned truncal switch procedure. In the case where a monocuspid expanded polytetrafluoroethylene patch was used (case 1), wall shear stress and energy loss at the right ventricular outflow tract is shown to be slightly high. In case 2, a tiny acceleration flow was visualized at the pulmonary bifurcation, but it was not related to the energy loss in this case. PA: pulmonary artery; RV: right ventricle.

DISCUSSION

Rastelli and REV are commonly performed on patients with TGA, VSD, and LVOT obstruction [11, 12]; however, these conventional procedures have several drawbacks, such as LVOT/RVOT obstruction, that may require further surgeries [1–3]. It is important to select surgical procedures not only on the basis of LVOT morphology but also on the basis of the size and the location of VSDs, right ventricular volume, and coronary arterial pattern [13]. After conventional procedures, such as Rastelli and REV, the flow of blood from the left ventricle to the aorta winds through an intraventricular tunnel. Turbulent blood flow is unavoidable in these procedures as the direction of flow is usually curved. Turbulent blood flow causes haemodynamic disadvantages, such as inefficient outflow with high EL, resulting in ventricular deterioration, and oscillated high WSS in portions with distorted flow or collisions, resulting in endothelial thickening and subsequent narrowing of the intraventricular tunnel and LVOT obstruction [14, 15].

A small VSD is a serious problem if intraventricular rerouting leads to LVOT obstruction; however, effective enlargement of VSDs without conduction disturbance or deterioration in interventricular septal performance is technically difficult [16, 17]. A remote VSD is also an uncomfortable situation after conventional operations because the LVOT passes through the intraventricular route, and it is curved and long. From the perspective of fluid dynamics, a long, curved intraventricular outflow route has serious disadvantages, such as a high EL due to turbulence, and disorganized ventricular contraction due to the long rerouting patch. Therefore, small VSD and remote VSD are considered exclusion criteria for conventional Rastelli and REV.

Regarding the haemodynamics of the RV, the use of a long extracardiac prosthetic conduit from the RV to the PA with reduced right ventricular volume is inevitable in the Rastelli procedure. Furthermore, in the REV, harvested autologous PA (or augmented autologous PA with transannular patch) must run in a very narrow space between the ascending aorta and the sternum. This is a disadvantage as in the long term, right ventricular function and haemodynamics where turbulent flow within a distorted RVOT causes high EL. In addition, the long-term availability and durability of conventional conduits, such as homograft and bovine jugular vein conduits (Contegra: Medtronic, Minneapolis, MN, USA) is insufficient because of calcification, intimal proliferation [18–20] and mismatch of the size of the conduit as the patient grows.

HTTSO overcame these drawbacks described above and showed excellent long-term results [9]. The LVOT reconstruction was straightforward with sufficient outflow space due to of posterior translocation of the aortic valve and simple VSD closure with a flat patch. Straight laminar blood flow through the LVOT drastically reduced postoperative flow EL and led to preserve left ventricular performance in the long term. A Low WSS reduces the need of reoperation for LVOT.

In HTTSO, an extra-cardiac prosthetic conduit is not always necessary because an autologous pulmonary valve is available in almost all cases. If the pulmonary annular diameter is not sufficient, the RVOT is routinely augmented with a transannular patch bearing a monocuspid valve [21]. Only pulmonary commissurotomy is performed for sufficient annular diameter and a flexible pulmonary valve. In HTTSO, a half-turned native pulmonary valve is anastomosed to the RVOT defect created by harvesting and deviating the aortic valve posteriorly. A straight RVOT using native tissue in front of the posteriorly deviated aorta can be obtained. Thus, HTTSO is suitable for patients with pulmonary/aortic annular diameter ratio of 0.3 or higher [8, 9].

The anteriorly translocated PA can be reconstructed without excessive tension and is not compressed by the sternum. Pulmonary bifurcation stenosis is avoidable. Several reports have shown that the growth of tubular structures, and the functions of both semilunar valves were preserved and showed harmonious growth in the late phase [22–24]; therefore, the growth potential of the PA can be maintained with minimal reoperation risk in this procedure.

The 4D-flow MRI is a novel and useful in vivo blood flow imaging tool that can be used to obtain haemodynamic and anatomic information of the entire heart and/or all major thoracic vessels simultaneously without radiation exposure [25]. Haemodynamic information includes vorticity and helicity, WSS, flow streamlines, flow passlines, EL and turbulent kinetic energy, which are not available from conventional imaging modalities, such as cardiac computerized tomography or echocardiography. In this study, we focused on EL and WSS in the left ventricular and right ventricular outflow. As EL is defined as the sum of the square of the spatial differentials of flow velocity vectors, EL increases in regions with drastic changes in diameter and direction, without stenosis or valve regurgitation [26, 27]. Shibata et al. [28] demonstrated the validity of a formula for calculating EL inside the RVOT after tetralogy of Fallot and a related disease caused right ventricular deterioration through elongation of the QRS duration in their electrocardiographic study. EL is a good predictor for ventricular deterioration caused by ventricular workload, a subclinical maker for ventricular dysfunction and a predictive factor of prognosis in heart failure [29].

WSS leads to stress on the endothelial wall due to the near wall blood flow, and high WSS with oscillated flow is thought to be a predictor of intimal damage leading to vascular lumen hyperplasia. In our study, the value of WSS of RVOT and LVOT were good predictors for RVOT and/or LVOT obstruction in the late phase.

In our study (Rastelli, case 1), flow acceleration was not observed but a curved LVOT flow streamline was detected and this caused high EL and WSS in the same patient. Not only was the risk for LVOT obstruction high in the late phase, but future left ventricular performance may also deteriorate due to high EL at the LVOT in the patient who underwent the Rastelli procedure. Furthermore, the long intraventricular rerouting patch resulted in dyskinetic motion which may make the flow streamline more winding, leading to higher EL.

On the other hand, in patients who underwent HTTSO (cases 4 and 5), laminar blood flow through the straight LVOT with sufficient space was visualized; this contributed to a low EL and preservation of left ventricular performance. A straight VSD patch resulted in a streamlined flow in both systemic and diastolic phases; it is a very important to have a low EL in the left ventricular system. The same fluid dynamic advantages concerning LVOT were also achieved by the Nikaidoh operation [4, 30].

In the Rastelli/REV case (cases 1 and 3), RVOT obstruction due to relative conduit stenosis or compression by sternum was observed; this led to a high EL in the RV, so conduit exchange or re-RVOT reconstruction was inevitable in the late phase. On the other hand, in the HTTSO cases (cases 4 and 5), the straight RVOT led to a low EL. Relatively high WSS was detected in 2 patients; however, turbulent blood flow and high EL were not detected. Postoperative haemodynamic features were excellent, and the EL of both systemic and pulmonary pathways was almost normal. The better fluid dynamics after HTTSO was also verified by 4D-flow MRI analysis.

Limitations

There are a few limitations to this study. This report was a comparison of few cases and there was a difference between the Rastelli group and the HTTSO group in the follow-up period; thus, further investigation on this topic is needed. However, all Rastelli/REV cases required reoperation because of RVOT obstruction. Even after they underwent further procedures, the LVOT was curved towards the intraventricle tunnel and turbulent flow was inevitable, leading to high WSS and EL.

CONCLUSION

HTTSO has many obvious advantages over conventional procedures, such as a wide and straight LVOT, low WSS, low EL, and a PA with growth potential. HTTSO offers a useful alternative technique for TGA and TGA-type DORV with LVOT obstruction. 4D-flow MRI analysis is a novel and useful method that can be used to evaluate such complex haemodynamics and assess the function of the whole heart.

ABBREVIATIONS

4D-flow

Time-resolved 3-dimensional magnetic resonance

MRI

phase-contrast imaging

DORV

Double-outlet right ventricle

EL

Energy loss

group C

Conventional procedures group

group H

Half-turned truncal switch operation group

HTTSO

Half-turned truncal switch operation

LVOT

Left ventricular outflow tract

PA

Pulmonary artery

REV

Réparation a l'étage ventriculaire

RV

Right ventricle

RVOT

Right ventricular outflow tract

TGA

The complete transposition of the great arteries

VSD

Ventricular septal defect

WSS

Wall shear stress

 

Presented at the 34th Annual Meeting of the European Association for Cardio-Thoracic Surgery, Barcelona, Spain, 8–10 October 2020.

Author contributions

Hisayuki Hongu: Conceptualization; Data curation; Formal analysis; Funding acquisition; Investigation; Methodology; Project administration; Resources; Software; Validation; Visualization; Writing—original draft; Writing—review & editing. Masaaki Yamagishi: Conceptualization; Data curation; Formal analysis; Funding acquisition; Investigation; Methodology; Project administration; Resources; Software; Supervision; Validation; Visualization; Writing – original draft; Writing—review & editing. Yoshinobu Maeda: Conceptualization; Investigation; Supervision; Writing—review & editing. Keiichi Itatani: Conceptualization; Data curation; Formal analysis; Funding acquisition; Investigation; Project administration; Supervision; Visualization; Writing—review & editing. Satoshi Asada: Conceptualization; Investigation; Project administration; Supervision. Shuhei Fujita: Conceptualization; Investigation; Project administration; Supervision. Hiroki Nakatsuji: Conceptualization; Investigation; Project administration. Hitoshi Yaku: Conceptualization; Investigation; Project administration; Supervision.

Conflict of interest: Keiichi Itatani is an endowed chair of the Kyoto Prefectural University of Medicine, financially supported by Medtronic Japan, and he has a stock option in Cardio Flow Design Inc. Masaaki Yamagishi is a consultant for W.L. Gore & Associates, Inc. All other authors have declared no conflict of interest.

Reviewer information

Interactive CardioVascular and Thoracic Surgery thanks Attilio A. Lotto, Constantine Mavroudis and René Prêtre for their contribution to the peer-review process of this article.