A quantitative analysis of regional contractile function in patients with FHC demonstrated significant differences in systolic and diastolic function compared with normal subjects. The MRI technique introduced here provided noninvasive, quantitative, regional function measurements across the entire cardiac cycle. In particular, abnormalities in early-diastolic relaxation, mid-diastole, and late-diastole were all significantly different between NVs and patients with FHC. Without full-cycle imaging, total systolic strains are significantly underestimated.
The reductions in the early-diastolic strain rates and increases in mid-diastolic strain rates seen in patients with FHC were consistent with previously obtained global measures of diastolic filling and pressure decay (18
). Reduction of early-diastolic strain rates reflected a prolonged and slower filling phase during early diastole. This slow filling phase continued into late diastole, as reflected by the increase in the mid-diastolic strain rate. Reductions in early-diastolic strains, and increases in mid-diastolic strains indicate slow and impaired filling in the patients with FHC relative to the NVs.
The CAPTOR/CSPAMM technique with an echo-train readout allows the acquisition of 30 phases during the entire cardiac cycle, which was shown to be adequate for characterizing rapid events, such as early diastole. This temporal resolution resulted in four to six images over the early (rapid) filling phase, which was sufficient to demonstrate statistically different strain rates in the two studied populations. Systolic strain rates measured in patients with FHC were reduced, but were not statistically different from measures obtained in NVs, indicating similar early-systolic function. Assessment of total systolic strains revealed significant differences between NVs and patients with FHC in septal and inferior walls, but not in the anterior or lateral walls. Increased strains (relative to the septum) in the lateral wall have been observed by others in both NVs (3
) and patients with FHC (6
), suggesting there is a regional heterogeneity of function in NVs and patients with FHC. Early-diastolic strain rates showed significant regional heterogeneity. Furthermore, greater hypertrophy correlated with poorer diastolic function.
Some limitations should be considered. Acquiring each direction of stripe tags in separate breath-holds may introduce errors in quantification of regional strain; however, this is more feasible than using the longer breath-holds needed to obtain both in a single acquisition. Although through-plane motion was shown to be limited in FHC patients, collecting more short- and long-axis slices would allow further characterization of this disease. The small sample size of the current study limited our ability to make regional comparisons with other diastolic parameters, such as the transmitral filling velocities.