Quantification of diffuse myocardial fibrosis and its association with myocardial dysfunction in congenital heart disease

Abstract

Background: the etiology of ventricular dysfunction in adult congenital heart disease (ACHD) is not well understood. Diffuse fibrosis is a likely common final pathway and is quantifiable using MRI.

Methods and results: patients with ACHD (n=50) were studied with cardiac MRI to quantify systemic ventricular volume and function and diffuse fibrosis. The fibrosis index for a single midventricular plane of the systemic ventricle was quantified by measuring T1 values for blood pool and myocardium before and after administration of gadolinium (0.15 mmol/kg) and then adjusted for hematocrit. Results were compared to healthy volunteers (normal controls, n=14) and patients with acquired heart failure (positive controls, n=4). Patients studied (age, 37±12 years; female sex, 40%) included 11 with a systemic right ventricle (RV), 17 with tetralogy of Fallot, 10 with cyanosis, and 12 with other lesions. The fibrosis index was significantly elevated in patients with ACHD compared to normal controls (31.9±4.9% versus 24.8±2.0%; P=0.001). Values were highest in patients with a systemic RV (35.0±5.8%; P<0.001) and those who were cyanotic (33.7±5.6%; P<0.001). The fibrosis index correlated with end-diastolic volume index (r=0.60; P<0.001) and ventricular ejection fraction (r=-0.53; P<0.001) but not with age or oxygen saturation in patients who were cyanotic. Late gadolinium enhancement did not account for the differences seen.

Conclusions: patients with ACHD have evidence of diffuse, extracellular matrix remodeling similar to patients with acquired heart failure. The fibrosis index may facilitate studies on the mechanisms and treatment of myocardial fibrosis and heart failure in these patients.

Figure 1

A) Images from Look-Locker sequence for a patient with tetralogy of Fallot. Regions of interest for the LV myocardium and blood pool are drawn. B) The time vs. signal intensity curves for the blood pool (red) and myocardium (blue), which are fitted to determine the decay constant T₁. The inverse, R₁, for each is determined before gadolinium administration and at several time points after. C) The relationship of R₁ signals between the blood pool and the myocardium before and after gadolinium is linear. The slope of this relationship is the partition coefficient of gadolinium, and determines the fibrosis index. Examples from a patient with cyanosis (Eisenmenger syndrome, blue) and a normal control (pink) are shown. The steeper slope reflects the increase in gadolinium present due to an enlarged extracellular space.

Figure 2

Relationship between systemic ventricular volume index and the fibrosis index (r=0.60, 95% CI 0.42–0.73, p<0.001). Dotted vertical line is the upper limit of normal.

Figure 3

Relationship between systemic ventricular ejection fraction and the fibrosis index is linear. (r=-0.53, 95% CI -0.68 - -0.34, p<0.001). Dotted vertical line is the upper limit of normal.

Figure 4

Relationship between fibrosis index and the area LGE (area of positive late enhancement / total area of myocardium in the selected plane) for ACHD patients. There was no correlation, and many patients with significantly elevated fibrosis index had little/no detectable LGE. By comparison, patients with acquired heart disease had area LGE values of 16–20% (data not shown). Dotted vertical line is the upper limit of normal.