T1 characteristics in different disease stages of hypertrophic cardiomyopathy

Background

Hypertrophic cardiomyopathy (HCM) is marked by left ventricular hypertrophy and is often linked to microvascular dysfunction and myocardial fibrosis, even in the early stages of the disease. Cardiovascular magnetic resonance (CMR) allows for tissue characterization through T1 mapping, where T1 values provide insights into the myocardial content of water, protein, and lipids, and are notably influenced by fibrosis [1]. Recent research suggests that stress T1 and the change in T1 values between stress and rest (ΔT1) could potentially serve as indicators of (micro)vascular dysfunction [2]. This study aimed to evaluate native rest T1, stress T1, and ΔT1 across various stages of HCM.

Methods

The study included three patient groups: overt HCM (maximum wall thickness [MWT] ≥ 15 mm), mild HCM (MWT 12–15 mm), and carriers (MWT < 12 mm), all of whom carried a class 4 or 5 pathogenic variant in MYH7 or MYBPC3. Genotype-negative family members served as a control group. CMR with native and adenosine-induced stress T1 mapping was performed on all participants using a 3T MR scanner. Two short-axis slices (basal-mid and mid-apical) were acquired, each divided into six segments according to the American Heart Association (AHA) segmentation model, yielding a total of 12 myocardial segments per participant (Figure 1a). Data were analyzed using CVI42 software with a 10% offset, and ΔT1 was calculated as the relative percentage change in T1 between rest and stress.

Results

A total of 78 participants were included in the study: 22 overt HCM, 21 mild HCM, 24 carriers, and 11 healthy controls. Baseline characteristics, along with global rest T1, stress T1, and ΔT1 values, are summarized in Table 1. All groups showed a significant increase in T1 values during stress. HCM patients had significantly higher global rest T1 values and lower ΔT1 compared to the other groups (Table 1).

Segmental analysis revealed that HCM patients had significantly higher rest T1 values in segments 1, 2, 3, 4, 7, 8, and 9 compared to the other groups (p<0.05) (Figure 1b). These segments corresponded closely to areas where the MWT was present. There was no significant difference in segmental stress T1 values between groups (Figure 1c). Additionally, HCM patients showed a significantly lower ΔT1 in segment 1 compared to those with mild HCM (3.6±4.8 vs. 8.3±4.3, p=0.001) (Figure 1d).

Conclusion

These preliminary results suggest that global rest T1 is elevated and ΔT1 is reduced in HCM patients. Segmental analysis also revealed significant differences, particularly in regions corresponding to myocardial hypertrophy. These findings were not observed in mild HCM or carriers, and could therefore be due to progressive remodeling. Studies are needed to validate these findings and further investigate the relationships between T1 metrics, perfusion imaging, and fibrosis assessed with late gadolinium enhancement.