Native left ventricular myocardial T₁ spatial heterogeneity in non-ischemic dilated cardiomyopathy

Background

Myocardial fibrosis is involved in the pathology of non-ischemic dilated cardiomyopathy (NICM). Recently, the application of native (non-contrast) myocardial T₁ measurement has been proposed as an imaging biomarker of cardiac remodeling. However, spatial heterogeneity in T₁ measurements has been observed across different segments and slices. Furthermore, T₁ values measured with current T₁ mapping sequences are influenced by myocardial T₂ values. The objective of this study was to 1) assess the spatial heterogeneity of T₁ measurements across different segments and slices in healthy subjects and patients, and 2) determine the association of native T₁ with myocardial structure and function.

Methods

We prospectively studied 39 NICM patients (LVEF≤50% without evidence of prior infarction by CMR) and 30 subjects with normal LV systolic function without known cardiovascular disease. CMR was performed using a 1.5-T MRI scanner (Philips Achieva). Native T₁ mapping was performed using slice-interleaved T₁ mapping sequence (STONE) [1]. T₂ mapping was performed using slice-interleaved T₂ mapping [2]. Voxel-wise T₁ and T₂ were estimated using a 2-parameter and 3-parameter model [3]. All images were corrected for motion [4]. T_1, T_2, and extra-cellular volume (ECV) measurements were measured using a 16 segments AHA model across the base, mid, and apical LV.

Results

NICM participants (57 ± 15 years) were predominantly male (74%). By design, all had a reduced LV ejection fraction (mean LVEF 34 ± 10%). Figure 1 shows native T1, T2, and ECV in two patients with a NICM. Parametric maps to the right in each panel demonstrate full ventricular coverage. The regional distribution of native myocardial T₁ was similar in patients with and without NICM[RN1], as shown in Figure 2. Relative to subjects without NICM, subjects with NICM had a higher native T₁ (1131 ± 51 vs. 1070 ± 28 msec; p < 0.0001), a higher ECV (0.28 ± 0.04 vs. 0.25 ± 0.02, P = 0.001) and a longer myocardial T₂ (52 ± 8 vs. 47 ± 5 msec; P = 0.01). After multivariable adjustment, a lower global native T₁ time was associated with a higher LVEF (b = -0.59, P = 0.0003), higher right ventricular ejection fraction (b = -0.47, P = 0.006), and lower left atrial volume index (b = 0.51, P = 0.001).

Figure 1

(A) Images from a 47-year-old woman with a NICM with moderate reduction in LV function (LV ejection fraction 30%). (B) Images from a 39-year-old heathy male (LV ejection fraction 61%).

Figure 2

Variability in segmental native T ₁ across all 16 myocardial segments in individuals with normal LV function (red) and study participants with NICM (blue). The error bars represent standard error of the mean.

Conclusions

In NICM, native myocardial T₁ is elevated in a homogeneous manner, suggesting a global (not regional) abnormality in myocardial tissue composition. This low variability is similar between healthy and NICM patients across different segments. For subjects with NICM, native T₁ is associated with biventricular systolic function and left atrial volume, and may represent a non-contrast marker of tissue remodeling in this cohort.