Cardiac Fibrosis and Innervation State in Uncorrected and Corrected Transposition of the Great Arteries: A Postmortem Histological Analysis and Systematic Review

Abstract

In the transposition of the great arteries (TGA), alterations in hemodynamics and oxygen saturation could result in fibrotic remodeling, but histological studies are scarce. We aimed to investigate fibrosis and innervation state in the full spectrum of TGA and correlate findings to clinical literature. Twenty-two human postmortem TGA hearts, including TGA without surgical correction (n = 8), after Mustard/Senning (n = 6), and arterial switch operation (ASO, n = 8), were studied. In newborn uncorrected TGA specimens (1 day-1.5 months), significantly more interstitial fibrosis (8.6% ± 3.0) was observed compared to control hearts (5.4% ± 0.8, p = 0.016). After the Mustard/Senning procedure, the amount of interstitial fibrosis was significantly higher (19.8% ± 5.1, p = 0.002), remarkably more in the subpulmonary left ventricle (LV) than in the systemic right ventricle (RV). In TGA-ASO, an increased amount of fibrosis was found in one adult specimen. The amount of innervation was diminished from 3 days after ASO (0.034% ± 0.017) compared to uncorrected TGA (0.082% ± 0.026, p = 0.036). In conclusion, in these selected postmortem TGA specimens, diffuse interstitial fibrosis was already present in newborn hearts, suggesting that altered oxygen saturations may already impact myocardial structure in the fetal phase. TGA-Mustard/Senning specimens showed diffuse myocardial fibrosis in the systemic RV and, remarkably, in the LV. Post-ASO, decreased uptake of nerve staining was observed, implicating (partial) myocardial denervation after ASO.

Keywords: Mustard Senning procedure; arterial switch operation; innervation; myocardial fibrosis; transposition of the great arteries.

Figure 1

Normal circulation (left panel) and circulation in a fetus with TGA (right panel). The numbers indicate percentage of oxygen saturations in the cardiac chambers and great vessels, and are based on estimated values of umbilical blood flow and left and right ventricular output in the fetus [2]. In TGA, the subpulmonary left ventricle ejects blood into the pulmonary circulation so that blood perfusing the lungs and passing through the ductus arteriosus has a relatively high oxygen saturation. Blood entering the ascending aorta and coronary arteries has an oxygen saturation considerably lower than in the normal circulation (45% versus 65%, indicated by red squares). High oxygen saturations are illustrated by red arrows and lower oxygen saturations by purple and blue arrows. Abbreviations: TGA, transposition of the great arteries. The figure is modified and adapted from Rudolph et al. [2]. Copyright 2023 by Copyright Clearance Center.

Figure 2

Illustration study design. Study design: illustration of all consecutive steps. 1. Selection postmortem specimens: postmortem specimens were obtained from the Leiden Collection of Congenital Malformations, including the following groups: normal specimens (A), uncorrected TGA specimens (B), TGA-Mustard/Senning specimens (C) and TGA-ASO specimens (D). 2. Tissue blocks: transmural tissue blocks were obtained from three different sites in each specimen (E); right ventricle, interventricular septum, and left ventricle. 3. Stainings: the following (DAB) stainings were performed: cardiac troponin-I (F) (myocardial organization), N-Cadherin (G) (myocardial organization), PECAM1 (H) (myocardial vascularization), Picrosirius Red (I) (myocardial fibrosis), α-SMA (J) (smooth muscle cells) and βIII-tubulin (K) (myocardial innervation). Abbreviations: ASO, arterial switch operation; DAB, 3-30diaminobenzidine tetrahydrochloride; IVS, interventricular septum; LV, left ventricle; PECAM1, platelet endothelial cell adhesion molecule-1; RV, right ventricle; α-SMA, alpha smooth muscle actin; TGA, transposition of the great arteries.

Figure 3

Myocardial fibrosis patterns in control and transposition of the great arteries. Myocardial fibrosis patterns using Sirius red staining. (A) Myocardium with normal pattern and amount of collagen. (B) Diffuse distribution of interstitial myocardial fibrosis. (C) Multiple areas with patchy fibrosis.

Figure 4

Patterns and amount of fibrosis in control, uncorrected TGA, TGA-Mustard/Senning, and TGA-ASO specimens. Fibrosis patterns and quantification in postmortem hearts (Sirius red staining). Normal myocardium at 1 day (A–C) and mean reference values in 3 control hearts without congenital heart disease (D). Normal myocardium of the subpulmonary LV (E) and increased amount of interstitial fibrosis in systemic RV (F) and interventricular septum (G) in uncorrected TGA at 1 day. Mean amount of fibrosis in 8 uncorrected TGA specimens (H). Diffuse interstitial fibrosis in 2.5-year-old TGA-Mustard/Senning specimen (I–K). Mean amount of fibrosis in 5 pediatric TGA-Mustard/Senning specimens (L). Patchy fibrosis (M) in the subpulmonary LV and interstitial fibrosis in the systemic RV (N) and interventricular septum (O) in TGA-Mustard/Senning specimen at the age of 33 years. The quantified amount of fibrosis in TGA-Mustard/Senning specimen at the age of 33 years (P). Normal myocardium of the systemic LV (Q) and interstitial fibrosis patterns at the subpulmonary RV (R) and interventricular septum (S) in TGA-ASO specimen at the age of 1.5 months. The quantified amount of fibrosis in TGA-ASO at the age of 1.5 months (T). Patchy fibrosis in the systemic LV (U) and interventricular septum (W) and interstitial fibrosis in subpulmonary RV (V). The quantified amount of fibrosis in TGA-ASO at the age of 19 years (X). Abbreviations: ASO, arterial switch operation; d, days; m, months; TGA, transposition of the great arteries; y, years.

Figure 5

Myocardial organization and vascularization in control, uncorrected TGA, TGA-Mustard/Senning, and TGA-ASO specimens. Control; well-organized cardiomyocyte network (A) with expression of NCAD at the intercalated disk (B) and homogeneous distribution of capillaries (C). Uncorrected TGA; Well organized network of cardiomyocytes (D), slightly increased expression of NCAD, mostly located at the intercalated disk (E), and less homogeneous capillary distribution (F). TGA-Mustard/Senning; increased amount of extracellular matrix (G), normal distribution of NCAD at the intercalated disk (H), and normal capillary distribution (I) TGA-ASO; cardiomyocytes are well aligned (J) with increased NCAD distribution at the intercalated disk and lateral borders of the cardiomyocyte (K) and decreased amount of capillary distribution (L). Abbreviations: ASO, arterial switch operation; d, days; m, months; TGA, transposition of the great arteries; y = years.

Figure 6

Myocardial innervation in uncorrected TGA and TGA-ASO. Myocardial innervation in uncorrected TGA and after ASO. Innervation post-ASO was evaluated in carefully matched sections in areas with cross-sectioned coronary vessels and compared between controls and TGA-ASO specimens. Visualization of cross-sectioned arteries and veins was performed by α-SMA staining (A,C,E,G,I,K). Innervation staining: (B) βIII-tubulin-positive nerves around coronary arteries and veins in uncorrected TGA. (D); postmortem hearts that survived 1 day after ASO showed βIII-tubulin-positive nerves, the uptake was comparable to the control specimen. (F,H,J,L); reduced uptake of βIII-tubulin around cross-sectioned coronary vessels after 3 days, 4 days, 15 days, and 19 years after ASO. Abbreviations: ASO, arterial switch operation; TGA, transposition of the great arteries; α-SMA, α smooth muscle actin.

Figure 7

Comparison of βIII-tubulin-positive nerves in TGA-ASO and uncorrected TGA. Boxplot: the mean amount of βIII-tubulin-positive nerves between the control group (uncorrected TGA) (n = 8), TGA 1 day after ASO (n = 4), and TGA ≥ 3 days after ASO (n = 4). Abbreviations: ASO, arterial switch operation; TGA, transposition of the great arteries.