EXPLANATION


Endocardial fibroelastosis (EFE) is an abnormal thickening of the endocardium caused by an abnormal deposition of collagen by fibroblasts, resulting in systolic and diastolic myocardial dysfunction. Although primary EFE is associated with numerous diseases, in the context of congenital heart disease, it is usually caused by a reduction of blood flow through the cardiac chambers leading to significant systolic and diastolic dysfunction with restrictive physiology.


During embryologic development, endocardial endothelial cells undergo transformation to mesenchymal cells which then form the endocardial cushions and valves. This endothelial-to-mesenchymal transition is altered by inflammation, hypoxia-ischemia, and mechanical flow disturbances, giving rise to the fibroblasts that form the fibrotic layer of EFE. Imbalances between transforming growth factor beta (TGF-β) and bone morphogenetic protein (BMP) signaling have been shown to contribute to the formation of EFE in mice. Exogenous supplementation with BMP has been shown to decrease EFE in this same mouse model (Xu et al).


EFE has been described as an opaque porcelain-like layer which may be several millimeters thick (see illustration below). Although EFE can be diagnosed by echocardiogram with 95% sensitivity and 75% specificity, computed tomography (CT) scanning and magnetic resonance imaging (MRI) have also been used. MRI is particularly useful for measuring chamber volumes and flows.


Macroscopic appearance of endocardial fibroelastosis. From: Luca AC, Lozneanu L, Miron IC, et al. Endocardial fibroelastosis and dilated cardiomyopathy - the past and future of the interface between histology and genetics. Rom J Morphol Embryol. 2020;61(4):999-1005. doi:10.47162/RJME.61.4.02. Used under Creative Commons License.


The severity of EFE on fetal echocardiograms can be used to predict prognosis after in-utero aortic balloon valvuloplasty for evolving hypoplastic left heart syndrome. The rate of change of left ventricular end-diastolic volume after the procedure was significantly greater in fetuses with mild EFE compared to those with severe EFE. Similarly, the severity of EFE can predict the likelihood that the child will be able to have biventricular repair as compared to a univentricular palliation postnatally after having undergone in-utero balloon aortic valvuloplasty. A significant proportion of patients within the spectrum of HLHS have borderline left heart structures in whom it may be possible to utilize a staged left ventricle recruitment strategy to eventually facilitate a biventricular repair. The underlying principle is to promote a flow and load-mediated growth of the left ventricle. These procedures include: (1) Interventions to relieve obstruction of the mitral and aortic valves; (2) resection of EFE to improve systolic and diastolic function; (3) restriction of the atrial communication to promote more flow into the LV; (4) adding accessory pulmonary blood flow. In a retrospective, single institution study of 34 patients undergoing a staged LV recruitment strategy, EFE resection was perfomed in the majority of patients at all three stages of palliation. There was a significant increase in left heart dimensions and ejection fraction. Thirteen of the 34 patients underwent successful biventricular repair with no mortality after a median follow-up of 2.9 years.


Although conduction abnormalities can be seen with EFE resection, there have been no reports of heart block requiring permanent pacemaker insertion. In a 2009 retrospective study by Emani and colleagues of nine patients who had undergone EFE resection, three patients had evidence of right bundle branch block or hemifascicular block with mild prolongation of the QRS complex but none required pacemaker placement. In a separate study by Czosek and colleagues of 27 patients who had undergone EFE resection, 14 patients had varying degrees of QRS prolongation or fascicular blocks but no complete heart block requiring pacemaker placement.


There is a high rate of recurrence of EFE after resection. In a retrospective review by Diaz-Gil of 49 patients with a small LV who had undergone EFE resection, the risk of recurrence was 76% over a 10 year period.


REFERENCES


Aldawsari, K.A., Alhuzaimi, A.N., Alotaibi, M.T. et al. Endocardial fibroelastosis in infants and young children: a state-of-the-art review. Heart Fail Rev .(2023); 28:1023–1031. https://doi.org/10.1007/s10741-023-10319-0


Weixler V, Marx GR, Hammer PE, Emani SM, Del Nido PJ, Friehs I. Flow disturbances and the development of endocardial fibroelastosis. J Thorac Cardiovasc Surg. 2020;159(2):637-646. doi: 10.1016/j.jtcvs.2019.08.101


Emani SM, McElhinney DB, Tworetzsky W et al. Staged left ventricular recruitment after single-ventricle palliation in patients with borderline left-heart hypoplasia. J Am Coll Cardiol . 2012. ;60:1966-74.


Emani SM, Bacha EA, McElhinney DB et al. Primary left ventricular rehabilitation is effective is effective in maintaining two-ventricle physiology in the borderline left heart. J Thorac Cardiovasc Surg . 2009;138:1276-82.


Diaz-Gil D, Piekarski BL, Marx GR, Del Nido PJ, Emani S, Friehs I. Endocardial fibroelastosis recurrence: Comparing single ventricle palliation versus biventricular repair. Thorac Cardiovasc Surg .2022. 70(S02): S67-S103. DOI: 10.1055/s-0042-1742956


Czosek RJ, Atallah J, Emani S, Hasan B, del Nido P, Berul CI. Electrical dyssynchrony and endocardial fibroelastosis resection in the rehabilitation of hypoplastic left cardiac syndrome. Cardiol Young. 2010;20(5):516-521. doi:10.1017/S1047951110000600


Han RK, Gurofsky RC, Lee KJ, et al. Outcome and growth potential of left heart structures after neonatal intervention for aortic valve stenosis. J Am Coll Cardiol .2007;50(25):2406-2414. doi:10.1016/j.jacc.2007.07.082


Xu X, Friehs I, Zhong Hu T, et al. Endocardial fibroelastosis is caused by aberrant endothelial to mesenchymal transition. Circ Res .2015;116(5):857-866. doi:10.1161/CIRCRESAHA.116.305629


McElhinney DB, Vogel M, Benson CB, et al. Assessment of left ventricular endocardial fibroelastosis in fetuses with aortic stenosis and evolving hypoplastic left heart syndrome. Am J Cardiol .2010;106(12):1792-1797. doi:10.1016/j.amjcard.2010.08.02