Quantifying left ventricular trabeculae function - application of image-based fractal analysis

Left ventricular trabeculation and major adverse cardiovascular events: the Copenhagen General Population Study

AIMS

Prominent left ventricular trabeculations is a phenotypic trait observed in cardiovascular diseases. In the general population, the extent of left ventricular trabeculations is highly variable, yet it is unknown whether increased trabeculation is associated with adverse outcome.

METHODS AND RESULTS

Left ventricular trabeculated mass (g/m2) was measured with contrast-enhanced cardiac computed tomography in 10 097 individuals from the Copenhagen General Population Study. The primary endpoint was a composite of major adverse cardiovascular events and defined as death, heart failure, myocardial infarction, or stroke. The secondary endpoints were the individual components of the primary endpoint. Cox regression models were adjusted for clinical parameters, medical history, electrocardiographic parameters, and cardiac chamber sizes. The mean trabeculated mass was 19.1 g/m2 (standard deviation 4.9 g/m2). During a median follow-up of 4.0 years (interquartile range 1.5-6.7), 710 major adverse cardiovascular events occurred in 619 individuals. Individuals with a left ventricular trabeculated mass in the highest quartile had a hazard ratio for major adverse cardiovascular events of 1.64 [95% confidence interval (CI) 1.30-2.08; P < 0.001] compared to those in the lowest quartile. Corresponding hazard ratios were 2.08 (95% CI 1.38-3.14; P < 0.001) for death, 2.63 (95% CI 1.61-4.31; P < 0.001) for heart failure, 1.08 (95% CI 0.56-2.08; P = 0.82) for myocardial infarction, and 1.07 (95% CI 0.72-1.57; P = 0.74) for stroke.

CONCLUSION

Increased left ventricular trabeculation is independently associated with an increased rate of major adverse cardiovascular events in the general population.

Regional dynamics of fractal dimension of the left ventricular endocardium from cine computed tomography images

We present a method to leverage the high fidelity of computed tomography (CT) to quantify regional left ventricular function using topography variation of the endocardium as a surrogate measure of strain. 4DCT images of 10 normal and 10 abnormal subjects, acquired with standard clinical protocols, are used. The topography of the endocardium is characterized by its regional values of fractal dimension (F D ), computed using a box-counting algorithm developed in-house. The averageF D in each of the 16 American Heart Association segments is calculated for each subject as a function of time over the cardiac cycle. The normal subjects show a peak systolic percentage change inF D of 5.9 % ± 2 % in all free-wall segments, whereas the abnormal cohort experiences a change of 2 % ± 1.2 % ( p < 0.00001 ). Septal segments, being smooth, do not undergo large changes inF D . Additionally, a principal component analysis is performed on the temporal profiles ofF D to highlight the possibility for unsupervised classification of normal and abnormal function. The method developed is free from manual contouring and does not require any feature tracking or registration algorithms. TheF D values in the free-wall segments correlated well with radial strain and with endocardial regional shortening measurements.

Anthropomorphic left ventricular mesh phantom: a framework to investigate the accuracy of SQUEEZ using Coherent Point Drift for the detection of regional wall motion abnormalities

We present an anthropomorphically accurate left ventricular (LV) phantom derived from human computed tomography (CT) data to serve as the ground truth for the optimization and the spatial resolution quantification of a CT-derived regional strain metric (SQUEEZ) for the detection of regional wall motion abnormalities. Displacements were applied to the mesh points of a clinically derived end-diastolic LV mesh to create analytical end-systolic poses with physiologically accurate endocardial strains. Normal function and regional dysfunction of four sizes [1, 2/3, 1/2, and 1/3 American Heart Association (AHA) segments as core diameter], each exhibiting hypokinesia (70% reduction in strain) and subtle hypokinesia (40% reduction in strain), were simulated. Regional shortening (RS CT ) estimates were obtained by registering the end-diastolic mesh to each simulated end-systolic mesh condition using a nonrigid registration algorithm. Ground-truth models of normal function and of hypokinesia were used to identify the optimal parameters in the registration algorithm and to measure the accuracy of detecting regional dysfunction of varying sizes and severities. For normal LV function,RS CT values in all 16 AHA segments were accurate to within ± 5 % . For cases with regional dysfunction, the errors inRS CT around the dysfunctional region increased with decreasing size of dysfunctional tissue.

Computational modeling of human left ventricle to assess the role of trabeculae carneae on the diastolic and systolic functions

Trabeculae carneae are irregular structures that cover the endocardial surfaces of both ventricles and account for a significant portion of human ventricular mass. The role of trabeculae carneae in diastolic and systolic functions of the left ventricle (LV) is not well understood. Thus, the objective of this study was to investigate the functional role of trabeculae carneae in the LV. Finite element analyses of ventricular functions were conducted for three different models of human LV derived from high-resolution magnetic resonance imaging (MRI). The first model comprised trabeculae carneae and papillary muscles, while the second model had papillary muscles and partial trabeculae carneae, and the third model had a smooth endocardial surface. We customized these patient-specific models with myofiber architecture generated with a rule-based algorithm, diastolic material parameters using Fung strain energy function derived from bi-axial tests and adjusted with the empirical Klotz relationship, and myocardial contractility constants optimized for average normal ejection fraction of the human LV. Results showed that the partial trabeculae cutting model had enlarged end-diastolic volume, reduced wall stiffness and even increased end-systolic function, indicating that the absence of trabeculae carneae increased the compliance of the LV during diastole, while maintaining systolic function.

Left ventricular noncompaction: a distinct cardiomyopathy or a composite anatomical syndrome?

Left ventricular non-compaction (LVNC) is characterized by hypertrabecularity (thickened non-compact layer) with deep intertrabecular recesses that are continuous with the ventricle cavity, and a thin compact layer. The phenotypes of LVNС are extremely variable: the left or right ventricular variant, biventricular form, LVNC with symptoms of heart failure or arrhythmia, asymptomatic forms or variants with thromboembolic events. In 30-50 % of patients with LVNC genetic mutations of genes encoding sarcomeric or cytoskeletal proteins are revealed by a genetic study. The article presents a literature review on the problems of diagnosis, visualization, pathogenesis, variability of clinical manifestations of LVNC and its genetic heterogeneity. Clinical cases demonstrating LVNC as a concomitant anatomical syndrome due to monogenic Danone disease, as well as the family cardiomyopathy with the digenic inheritance of two phenotypes (LVNC with DCM) and the unique case of peripartum evolution of the acquired LVNC syndrome, all these cases are reflect the current uncertainty regarding to the pathogenesis and significance of LVNC. The main question is whether LVNC is a distinct cardiomyopathy or a morphologic trait and a composite anatomical syndrome of congenital heart disease or other cardiomyopathies (DCM, HCM, ARVC) remains controversial. Achievement of professional consensus guidelines about unification of diagnostic criteria and risk-stratification of LVNC, improvement of visualization tools and expansion of genetic testing will help to significantly expand our knowledge and understanding of the pathogenesis, clinical significance and prognosis of LVNC for optimization of the treatment strategy.

Fractal analysis of left ventricular trabeculations is associated with impaired myocardial deformation in healthy Chinese

BACKGROUND

Left 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.

METHODS

Cardiovascular 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).

RESULTS

Fractal 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.

CONCLUSION

This 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.

Left Ventricular Noncompaction: A Distinct Genetic Cardiomyopathy?

Left ventricular noncompaction (LVNC) describes a ventricular wall anatomy characterized by prominent left ventricular (LV) trabeculae, a thin compacted layer, and deep intertrabecular recesses. Individual variability is extreme, and trabeculae represent a sort of individual "cardioprinting." By itself, the diagnosis of LVNC does not coincide with that of a "cardiomyopathy" because it can be observed in healthy subjects with normal LV size and function, and it can be acquired and is reversible. Rarely, LVNC is intrinsically part of a cardiomyopathy; the paradigmatic examples are infantile tafazzinopathies. When associated with LV dilation and dysfunction, hypertrophy, or congenital heart disease, the genetic cause may overlap. The prevalence of LVNC in healthy athletes, its possible reversibility, and increasing diagnosis in healthy subjects suggests cautious use of the term LVNC cardiomyopathy, which describes the morphology but not the functional profile of the cardiomyopathy.