Regional cardiac 31P-MRSI at 7T: detection of spatially heterogeneous patterns of myocardial energetic impairment

Background The phosphocreatine-to-ATP ratio (PCr/ATP), measurable by 31P magnetic resonance spectroscopic imaging (31P-MRSI), is a sensitive marker of myocardial energetic reserve. Regional energetic-mechanical coupling, evaluable only per-segment to avoid confounding from spatially heterogeneous disease, represents an important target for cardiac metabolic trials. We extend our previously validated 7T regional 31P-MRSI approach to patients with cardiovascular disease. Methods Twenty-one participants underwent same-day 7T 31P-MRSI and 3T CMR: 9 healthy volunteers, 4 with type 2 diabetes, 5 with heart failure, and 3 with ischaemic cardiomyopathy. PCr/ATP was mapped across six mid-ventricular AHA segments. Ejection fraction, global longitudinal strain, peak filling rate, and regional circumferential and radial strain were derived from 3T CMR. Group differences were assessed by Kruskal-Wallis test with Bonferroni-corrected pairwise comparisons; segment-level associations by per-segment Spearman correlation and linear mixed effects models. Results PCr/ATP differed significantly across groups (p = 0.005, eta^2 = 0.58), ranging from 1.78 +/- 0.21 in healthy volunteers to 1.10 +/- 0.28 in heart failure. Mean PCr/ATP correlated with ejection fraction (rs = 0.65, p = 0.002), global longitudinal strain (rs = -0.63, p < 0.001), and peak filling rate (rs = 0.52, p = 0.023). Segment-level energetic-mechanical coupling was significant in the anteroseptal and inferoseptal segments (circumferential strain rs = -0.49 to -0.56; radial strain rs = 0.43 to 0.57, all p < 0.05), with no significant associations in other segments, consistent with a displacement-related measurement quality gradient. In ischaemic patients, PCr/ATP was significantly lower in infarct segments (0.79 +/- 0.20) than remote myocardium (1.33 +/- 0.22, p = 0.008, r = 0.62). All three ischaemic patients demonstrated remote PCr/ATP below the healthy volunteer median, with two below the 5th percentile (rank-sum p = 0.018; Fisher p = 0.045). Conclusions Regional 7T 31P-MRSI detects segment-level energetic differences across cardiovascular disease states and reveals spatially specific energetic-mechanical coupling confined to the septal segments in the current ungated acquisition. Energetic impairment in ischaemic cardiomyopathy extends into structurally preserved remote myocardium. These findings support larger studies using regional 31P-MRSI to investigate regional energetic-mechanical coupling as a target for metabolic cardiac therapies.