The effect of myocardial wall thickness and mass on myocardial blood flow measured by high-resolution quantitative stress perfusion CMR (RF_TH_283)

Fully quantitative stress perfusion cardiovascular magnetic resonance (CMR) allows the evaluation of myocardial blood flow (MBF) to identify coronary artery disease. A number of factors affect MBF and it has been suggested that myocardial wall thickness may have an influence.¹ The aim of the study was to assess the relationship between MBF and both myocardial maximum wall thickness (MWT) and indexed myocardial mass.

Methods:

Adult patients received stress perfusion CMR at St Thomas’ Hospital between January 2022 and May 2023. Patients with inducible regional or subendocardial hypoperfusion, evidence of hypertrophic cardiomyopathy, arrhythmia and presence of late-gadolinium enhancement were excluded. Patients were scanned at both hyperemia and at rest using a high-resolution stress perfusion sequence with automated generation of quantitative MBF maps.^2,3 From these, global, endocardial and epicardial MBF values were measured with calculation of myocardial perfusion reserve (MPR) and endocardial-to-epicardial (endo/epi) ratios. Patients receiving regadenoson were excluded from rest MBF and MPR analysis. Pearson correlation coefficient and multivariate linear regression analysis were used to evaluate statistical relationships.

Results:

248 patients fulfilled the criteria for analysis (mean age 55.5±12.7 years, 44.8% female, mean LVEF 59.6±7.6%). 45.2% patients had known hypertension, 16.5% had diabetes mellitus and 9.3% reported previous coronary intervention. Stress MBF was reduced with increasing indexed myocardial mass and MWT (p=0.001 & p< 0.001 respectively) [Figure 1]. Rest MBF was also reduced with increasing myocardial mass and MWT (p=0.012 & p=0.002 respectively). However, no relationship was observed for MPR with myocardial mass and MWT (p=0.921 & p=0.243 respectively). Furthermore, there was a reduction in both stress and rest MBF as myocardial mass and MWT increased at both endocardial and epicardial layers [Table 1]. The discrepancy between the two layers rose as the myocardial mass or MWT increased, as evidenced by the endo/epi ratio. However, no difference in endocardial or epicardial MPR was seen for either myocardial mass or MWT.

Myocardial mass and MWT correlated well with each other (R=0.51, p< 0.001). Multivariate linear regression demonstrated similar combined results to univariate analysis [Figure 2].  Controlling each variable for the other, only myocardial MWT was an independent predictor of stress and rest MBF (stress: p< 0.001; rest: p=0.028), whereas indexed myocardial mass was not (stress: p=0.305; rest: p=0.308). Neither variable was an independent predictor of MPR (MWT: p=0.192; indexed mass: p=0.551).

Conclusion:

Both myocardial mass and MWT are negatively correlated with stress and rest MBF, whilst no correlation was seen with MPR. This suggests that the decrease in stress and rest MBF with increasing myocardial mass and MWT is proportionate, and similar results were seen in global, endocardial and epicardial MBF analysis.