Papillary muscle native T₁ time is associated with severity of functional mitral regurgitation in patients with non-ischemic dilated cardiomyopathy

Background

Functional mitral regurgitation is one of the important complications of non-ischemic dilated cardiomyopathy (DCM). Non-contrast native T₁ mapping enables non-invasive quantification of myocardial fibrosis. We sought to assess the potential relationship between papillary muscle T₁ time and severity of mitral regurgitation in DCM patients.

Methods

Forty DCM patients (55 ± 13 years) and 20 healthy adult control subjects (54 ± 13 years) were enrolled. Slice interleaved T₁ mapping sequence (STONE) was employed for the native T₁ mapping, which enables acquisition of 5 slices in the short-axis plane within a 90 sec free-breathing scan. For calculating papillary muscle native T₁ time, both anterior and posterior papillary muscles were manually traced on custom software (MediaCare, Boston, MA, USA). We measured papillary muscle diameter, length and shortening on cine MRI. Phase contrast images were acquired perpendicular to the proximal ascending aorta to quantify blood flow. Mitral regurgitation volume was calculated as the difference between the LV stroke volume and ascending aorta forward flow. DCM patients were allocated into 2 groups based on the presence or absence of functional mitral regurgitation.

Results

Papillary muscle T₁ time was significantly elevated in DCM patients with mitral regurgitation (n = 22) in comparison to those without mitral regurgitation (n = 18) (anterior papillary muscle: 1127 ± 36 msec vs 1063 ± 16 msec, p < 0.001; posterior papillary muscle: 1124 ± 30 msec vs 1062 ± 19 msec, p < 0.001), but LV T₁ time was similar (1129 ± 38 msec vs 1134 ± 58 msec, p = 0.93). Multivariate linear regression analysis showed that papillary muscle native T₁ time (β=0.109, 95%CI: 0.048-0.170, p = 0.001) and tenting height (β=1.334, 95%CI: 0.434-2.234, p = 0.005) are correlated with mitral regurgitant fraction (Table 1). Elevated papillary muscle T₁ time was associated with larger diameter, longer length and decreased papillary muscle shortening (all p values <0.05).

Table 1 Determinants for Severity of Functional Mitral Regurgitation in Non-ischemic Dilated Cardiomyopathy

Conclusions

In DCM, papillary muscle native T₁ time is significantly elevated and related to mitral regurgitant fraction. These results suggest that papillary muscle diffuse fibrosis might be associated with severity of functional mitral regurgitation in this population.