The inner surfaces of the human heart are covered by a complex network of muscular strands that is thought to be a vestige of embryonic development. 1,2 The function of these trabeculae in adults and their genetic architecture are unknown. To investigate this we performed a genome-wide association study using fractal analysis of trabecular morphology as an image-derived phenotype in 18,096 UK Biobank participants. We identified 16 significant loci containing genes associated with haemodynamic phenotypes and regulation of cytoskeletal arborisation. 3,4 Using biomechanical simulations and human observational data, we demonstrate that trabecular morphology is an important determinant of cardiac performance. Through genetic association studies with cardiac disease phenotypes and Mendelian randomisation, we find a causal relationship between trabecular morphology and cardiovascular disease risk. These findings suggest an unexpected role for myocardial trabeculae in the function of the adult heart, identify conserved pathways that regulate structural complexity, and reveal their influence on susceptibility to disease. MainThe chambers of the mature human heart have a complex inner surface whose function is unknown. Unlike the smooth endothelium of the great vessels, the endocardial surfaces of both ventricles are lined by a fenestrated network of muscular trabeculae which extend into the cavity. Their embryological development is driven by highly-conserved signalling pathways involving the endocardium-myocardium and extra-cellular matrix that regulate myocardial proliferation during cardiac morphogenesis. 2,[5][6][7][8][9] 1 Cell lineage tracing suggests that trabeculae have a molecular and developmental identity which is distinct from the compact myocardium. 10 The high surface area of trabeculae enables nutrient and oxygen diffusion from blood pool to myocardium before the coronary circulation is established. 1 Trabeculae are also vital to formation of the conduction system. 11 Theoretical analyses have proposed that their complex structure may contribute to efficient intra-ventricular flow patterns. 12-14 While hypertrabeculation is observed as a feature of some genetically-characterised cardiomyopathies, 15 the physiological function of trabeculae in adult hearts, their genetic architecture, and potential role in common disease have not been determined.The distinguishing trait of trabeculae is their branching morphology and the degree of such biological complexity in the heart can be quantified by fractal dimension (FD) analysis of cardiac magnetic resonance (CMR) imaging. 8 In a replicated genomewide association study (GWAS), using FD as an image-derived phenotype, we identify loci linked with trabecular morphology. Knockout models of loci-associated genes showed a marked decrease in trabecular complexity. Using biomechanical modelling and human observational data, we find a causal relationship between myocardial trabeculation and ventricular performance, with Mendelian randomisation showing that reduced trabecula...

BackgroundLeft ventricular (LV) non-compaction (LVNC) is defined by extreme LV trabeculation, but is measured variably. Here we examined the relationship between quantitative measurement in LV trabeculation and myocardial deformation in health and disease and determined the clinical utility of semi-automated assessment of LV trabeculations.MethodsCardiovascular magnetic resonance (CMR) was performed in 180 healthy Singaporean Chinese (age 20–69 years; males, n = 91), using balanced steady state free precession cine imaging at 3T. The degree of LV trabeculation was assessed by fractal dimension (FD) as a robust measure of trabeculation complexity using a semi-automated technique. FD measures were determined in healthy men and women to derive normal reference ranges. Myocardial deformation was evaluated using feature tracking. We tested the utility of this algorithm and the normal ranges in 10 individuals with confirmed LVNC (non-compacted/compacted; NC/C ratio > 2.3 and ≥1 risk factor for LVNC) and 13 individuals with suspected disease (NC/C ratio > 2.3).ResultsFractal analysis is a reproducible means of assessing LV trabeculation extent (intra-class correlation coefficient: intra-observer, 0.924, 95% CI [0.761–0.973]; inter-observer, 0.925, 95% CI [0.821–0.970]). The overall extent of LV trabeculation (global FD: 1.205 ± 0.031) was independently associated with increased indexed LV end-diastolic volume and mass (sβ = 0.35; p < 0.001 and sβ = 0.13; p < 0.01, respectively) after adjusting for age, sex and body mass index. Increased LV trabeculation was independently associated with reduced global circumferential strain (sβ = 0.17, p = 0.013) and global diastolic circumferential and radial strain rates (sβ = 0.25, p < 0.001 and sβ = −0.15, p = 0.049, respectively). Abnormally high FD was observed in all patients with a confirmed diagnosis of LVNC. Five out of 13 individuals with suspected LVNC had normal FD, despite NC/C > 2.3.ConclusionThis study defines the normal range of LV trabeculation in healthy Chinese that can be used to make or refute a diagnosis of LVNC using the fractal analysis tool, which we make freely available. We also show that increased myocardial trabeculation is associated with higher LV volumes, mass and reduced myocardial strain.Electronic supplementary materialThe online version of this article (10.1186/s12968-017-0413-z) contains supplementary material, which is available to authorized users.

Background - To assess the genetic architecture of hypertrophic cardiomyopathy (HCM) in patients of predominantly Chinese ancestry. Methods - We sequenced HCM disease genes in Singaporean patients (n=224) and Singaporean controls (n=3,634), compared findings with additional populations and Caucasian HCM cohorts (n=6,179) and performed in vitro functional studies. Results - Singaporean HCM patients had significantly fewer confidently interpreted HCM disease variants (Pathogenic (P)/Likely Pathogenic (LP):18%, p<0.0001) but an excess of variants of unknown significance (exVUS: 24%, p<0.0001), as compared to Caucasians (P/LP: 31%, exVUS: 7%). Two missense variants in thin filament encoding genes were commonly seen in Singaporean HCM ( TNNI3 :p.R79C, disease allele frequency (AF)=0.018; TNNT2 :p.R286H, disease AF=0.022) and are enriched in Singaporean HCM when compared with Asian controls ( TNNI3 :p.R79C, Singaporean controls AF=0.0055, p=0.0057, gnomAD-East Asian (gnomAD-EA) AF=0.0062, p=0.0086; TNNT2 :p.R286H, Singaporean controls AF=0.0017, p<0.0001, gnomAD-EA AF=0.0009, p<0.0001). Both these variants have conflicting annotations in ClinVar and are of low penetrance ( TNNI3 :p.R79C, 0.7%; TNNT2 :p.R286H, 2.7%) but are predicted to be deleterious by computational tools. In population controls, TNNI3 :p.R79C carriers had significantly thicker left ventricular walls compared to non-carriers while its etiological fraction is limited (0.70, 95% CI: 0.35-0.86) and thus TNNI3 :p.R79C is considered a VUS. Mutant TNNT2 :p.R286H iPSC-CMs show hypercontractility, increased metabolic requirements and cellular hypertrophy and the etiological fraction (0.93, 95% CI: 0.83-0.97) support the likely pathogenicity of TNNT2 :p.R286H. Conclusions - As compared to Caucasians, Chinese HCM patients commonly have low penetrance risk alleles in TNNT2 or TNNI3 but exhibit few clinically actionable HCM variants overall. This highlights the need for greater study of HCM genetics in non-Caucasian populations.

Purpose To measure right ventricular (RV) trabecular complexity by its fractal dimension (FD) in healthy subjects and patients with pulmonary hypertension (PH) and to assess its relationship with hemodynamic and functional parameters and future cardiovascular events. Materials and Methods This retrospective study used data acquired from May 2004 to October 2013 in 256 patients with newly diagnosed PH who underwent cardiac MRI, right-sided heart catheterization, and 6-minute walk distance testing, with median follow-up of 4.0 years. A total of 256 healthy control subjects underwent cardiac MRI only. Biventricular FD, volumes, and function were assessed on short-axis cine images. Reproducibility was assessed with the intraclass correlation coefficient, correlation between variables was assessed with the Pearson correlation test, and mortality prediction was compared by using uni- and multivariable Cox regression analyses. Results RV FD reproducibility had an intraclass correlation coefficient of 0.97 (95% confidence interval [CI]: 0.96, 0.98). RV FD was higher in patients with PH (median, 1.310; interquartile range [IQR], 1.281-1.341) than in healthy subjects (median, 1.264; IQR, 1.242-1.295; P < .001), with the greatest difference near the apex. RV FD was associated with pulmonary vascular resistance (r = 0.30, P < .001). At univariable Cox regression analysis, RV FD was a significant predictor of death (hazard ratio [HR], 1.256; 95% CI: 1.011, 1.560; P = .04); however, at multivariable analysis, RV FD did not enable prediction of survival independently of conventional parameters of RV remodeling (HR, 1.179; 95% CI: 0.871, 1.596; P = .29). Conclusion Fractal analysis of RV trabecular complexity is a highly reproducible measure of remodeling in patients with PH that is associated with afterload, although the gain in survival prediction over traditional markers is not significant. Published under a CC BY 4.0 license. Online supplemental material is available for this article.