The arterial switch operation : going back to the roots
Lalezari, S.
Citation
Lalezari, S. (2011, December 21). The arterial switch operation : going back to the roots. Retrieved from https://hdl.handle.net/1887/18266
Version: Corrected Publisher’s Version
License: Licence agreement concerning inclusion of doctoral thesis in the Institutional Repository of the University of Leiden
Downloaded from: https://hdl.handle.net/1887/18266
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Summary and Conclusions
7
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7.1 Summary
The purpose of this thesis was to investigate the possible explanations for the tendency of the neo-aortic root to dilate several years after the arterial switch operation (ASO).
In Chapter 1, the formation of transposition of the great arteries (TGA) is shortly described, as well as some long-term complications after the corrective surgery for TGA, the ASO. Also, the aim of this thesis is described.
In Chapter 2, the role of vascular remodeling in the development of neo-aortic root dilatation after ASO is investigated. Samples of human aortic and pulmonary vessel wall and sinus were obtained from unoperated TGA specimens and normal heart specimens.
The patients’ age ranged from 1 day to 9 months. There were multiple interesting findings in this study. At birth, the structure of the aorta and pulmonary artery (PA) in normal hearts is different and these differences increase over time. In TGA, there is not much dissimilarity between aorta and PA. However, with increasing age, especially the decrease in expression of smooth muscle cells (SMCs) in the pulmonary sinus and vessel wall in TGA was very clear.
Vascular remodeling as a result of changes in pressure is a known phenomenon, however, these data concern the aorta or other smaller systemic arteries only. Remodeling in the PA has also been reported as a response to pulmonary hypertension mainly. In this case, especially hypertrophy of SMCs is described rather than dedifferentiation, as a result of elevated pressure in the PA. Also, flow-mediated dedifferentiation has been described in both animal studies and humans. Here, only one of the markers for identifying SMCs was decreased in high-flow arteries, but not as significant as in low-flow arteries. Therefore, the observed remodeling in our study cannot be explained by flow-mediated changes or elevated pressure conditions. This all implies that the PA in TGA develops in an essentially different way than the PA in a normal heart. We conclude that TGA is not only a difference in position of the great arteries but also a structural difference in especially the PA compared to normal great arteries.
The structural ‘build-up’ of a heart with TGA and a normal heart was investigated in Chapter 3, in the search for an explanation for neo-aortic root dilatation after ASO.
The aim of this study was to examine the amount of collagen and its distribution, as well as the myocardial support of the arterial fibrous annulus in hearts with TGA and normal
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hearts. Collagen amount and distribution were shown to be significantly decreased in hearts with TGA, especially around the fibrous annulus area in the morphological PA. Also, the myocardial support from both left and right ventricle was visibly reduced in hearts with TGA, leaving the fibrous annulus ‘on top’ of the ventricle rather than it being embedded in it and surrounded by myocardium, as is shown in normal hearts. In conclusion, these differences in collagen amount and distribution as well as lack of proper myocardial support of the arterial roots furthermore provide yet another possible explanation for the neo-aortic root dilatation after ASO.
A long-term follow-up of all patients operated on in our centre is depicted in Chapter 4. The aim of this retrospective study was to determine risk factors for early and late mortality, as well as risk factors for reoperation and neo-aortic regurgitation (neo-AR). We investigated several variables and concluded that the ASO is a safe procedure with good survival. Risk factors for early mortality were prolonged cross-clamp time and absence of the Lecompte procedure, as seen mostly in patients with side-by-side anatomy of the great vessels in TGA with Taussig-Bing anomaly. Risk factors for late mortality were coronary problems during surgery and postoperative pacemaker implantation. For reoperation, the risk factors were higher age at time of ASO, presence of arch abnormalities, coronary problems during surgery and prolonged duration of ventilation postoperatively. No risk factors were found for neo-AR. To the best of our knowledge, no previous studies have been reported with a 30-year experience and long follow-up. In conclusion, the long-term results of the ASO as the treatment for patients with TGA are good with good survival and event-free survival.
In Chapter 5, long-term follow-up of the neo-aortic root and left ventricular function is described. Thirty-nine patients that underwent an ASO between 1977 and 1989 were evaluated, including clinical assessment, ECG, echocardiography, quality of life questionnaire and perioperative and follow-up data analyses. Emphasis was on the dimensions and function of the neo-aortic root, left ventricular (LV) function and quality of life 20 years after ASO. LV function was well preserved with normal dimensions. Fifteen percent of the patients had moderate neo-AR. In up to 60% of the patient population, diameter of the neo- aortic root was dilated above normal values, and the presence of neo-AR was associated with neo-aortic root dilatation. Quality of life was good long-term after ASO. We concluded that there is a relation between the diameter of the neo-aortic root and the existence of neo-AR, however, the incidence of neo-AR remains low 20 years after ASO.
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Summary and Conclusions
87 The formation of a neo-coarctation is a rare finding after ASO, however, it does occur. In Chapter 6, we describe 5 patients who developed a neo-coarctation between 1 and 5 years after ASO. We present several theories that might explain this rare finding after ASO without presence of a coarctation prior to the ASO.
7.2 Conclusions
The ASO is the corrective operation of choice for patients with TGA. This thesis concentrates on finding explanations for the development of neo-aortic root dilatation and subsequent neo-AR, one of the late complications described after the ASO. In order to do so, histomorphological studies were combined with clinical studies. One of the most important findings was that in TGA, there are structural differences in the vessel walls and sinuses of the great arteries compared to a normal heart. Especially the PA in TGA shows the biggest structural changes compared to the PA in a normal heart. This finding might play a role in the development of neo-aortic root dilatation and subsequent neo-AR. Also, this thesis shows a marked decrease in collagen amount and distribution in the arterial roots in patients with TGA compared to normal hearts, as well as less myocardial support for the fibrous arterial annulus in patients with TGA compared to normal hearts. This might also indicate why the neo-aortic root is prone to dilate after ASO. Long-term results of the ASO are good with favourable survival and event-free survival. Several risk factors for mortality and reoperation have been determined from a patient cohort of 332 patients operated for TGA by ASO in our centre. However, no clinical risk factors could be determined for neo-AR. This implies that the surgical technique so far has no influence on the existence of neo-aortic root dilatation. Even twenty years after ASO, the amount of patients that has moderate neo-AR is small. There is, however, a correlation between the diameter of the neo-aortic root and the presence of neo-AR. Furthermore, left ventricular function remains good in all patients examined 20 years after ASO. The development of a neo-coarctation is a finding that is rare after ASO, but does occur. Although the number of patients with neo-coarctation described in this thesis is small, we felt it is important to pay attention to this rare phenomenon.
In conclusion, the ASO is the operation of choice for patients with TGA and provides good long-term results with a marked amount of patients with neo-aortic root dilatation and subsequent neo-AR, however, this late complication remains low in incidence. Patients with
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TGA, however, do not only have transposed great arteries but a structural disease of the great arteries as well.
