Right ventricular shape and function: cardiovascular magnetic resonance reference morphology and biventricular risk factor morphometrics in UK Biobank

Abstract

Background: The associations between cardiovascular disease (CVD) risk factors and the biventricular geometry of the right ventricle (RV) and left ventricle (LV) have been difficult to assess, due to subtle and complex shape changes. We sought to quantify reference RV morphology as well as biventricular variations associated with common cardiovascular risk factors.

Methods: A biventricular shape atlas was automatically constructed using contours and landmarks from 4329 UK Biobank cardiovascular magnetic resonance (CMR) studies. A subdivision surface geometric mesh was customized to the contours using a diffeomorphic registration algorithm, with automatic correction of slice shifts due to differences in breath-hold position. A reference sub-cohort was identified consisting of 630 participants with no CVD risk factors. Morphometric scores were computed using linear regression to quantify shape variations associated with four risk factors (high cholesterol, high blood pressure, obesity and smoking) and three disease factors (diabetes, previous myocardial infarction and angina).

Results: The atlas construction led to an accurate representation of 3D shapes at end-diastole and end-systole, with acceptable fitting errors between surfaces and contours (average error less than 1.5 mm). Atlas shape features had stronger associations than traditional mass and volume measures for all factors (p < 0.005 for each). High blood pressure was associated with outward displacement of the LV free walls, but inward displacement of the RV free wall and thickening of the septum. Smoking was associated with a rounder RV with inward displacement of the RV free wall and increased relative wall thickness.

Conclusion: Morphometric relationships between biventricular shape and cardiovascular risk factors in a large cohort show complex interactions between RV and LV morphology. These can be quantified by z-scores, which can be used to study the morphological correlates of disease.

Keywords: Atlases; Cardiovascular magnetic resonance; UK biobank; Ventricular function.

Fig. 1

Biventricular coarse mesh (left) and its Catmull Clark subdivision at level 2 (right). The left ventricle (LV) is shown in green, the right ventricle (RV) in blue and the epicardium in red. The mitral valve is highlighted in cyan, the aortic valve in yellow, the tricuspid valve in magenta and the pulmonary valve in green

Fig. 2

Atlas construction pipeline: a 3D contour points extracted from 2D contour points. Mitral points are shown in blue and tricuspid points in red. b Registration framework. c Registration results. d Principal component analysis of shape variation. Upper and lower panel show ±2 std. dev in the fourth mode at end-diastole (ED)

Fig. 3

Bland-Altman agreement plots between biventricular mesh fitting and manual analysis. a LV end-diastolic volume index, b LV end-systolic index, c RV end-diastolic index, and d RV end-systolic index. Mean biases and ± 2 std. dev of measurement differences are shown as horizontal dashed lines. LV = left ventricle. RV = right ventricle

Fig. 4

First four components of variation for the combined end-diastole (ED) and end-systole (ES) atlas. The ED is shown in wireframe and the ES in solid mesh. The right ventricle is shown in blue, the LV in green and the LV epicardium in red. The mitral valve is shown in pink and the tricuspid valve in yellow. The red arrow shows changes in the motion of the tricuspid valve. The left and right shapes of each mode correspond to the mean ± 2 std. dev. Animations of these shape components have been provided in the Additional file 1: Figure S2

Fig. 5

Percentage of variance explained as a function of mode for the atlas

Fig. 6

Receiver Operating Characteristics (ROC) curves and Precision-Recall curves for each risk factor regression model. MassVol and PCA50 models are shown by red and blue curves, respectively

Fig. 7

Shape changes due to high blood pressure (a) and smoking (b), adjusted for age, sex, height and other factors. Colors denote difference from the mean shape in mm (red outward, blue inward) for factor positive (Positive) and factor negative (Negative) groups. Outward directions are shown on the top right picture. Top row: anterior view of the RV (left) and LV (right). Bottom row: posterior view (left: LV, right: RV). Histograms show morphometric scores for reference healthy group and factor positive group