Comparison of regional myocardial blood flow and perfusion in dilated cardiomyopathy and left bundle branch block: Role of wall thickening

Heterogeneous perfusion in left bundle branch block (LBBB) has been demonstrated by Tc-99m-methoxyisobutylisonitrile (MIBI) SPECT. Locally different contraction is also associated with LBBB. Quantitative analysis of myocardial SPECT is influenced by partial-volume effects depending on systolic wall thickening. Therefore, partial-volume effects may mimic perfusion heterogeneity in LBBB. Methods: Fifteen patients with nonischemic dilated cardiomyopathy and LBBB underwent resting O-15-water PET, Tc-99m-MIBI SPECT, and gated F-18-FDG PET for analysis of wall thickening. Myocardial blood flow corrected for rate-pressure product (corrMBF), Tc-99m-MIBI uptake, and wall thickening were determined in 4 left ventricular wall areas. In 14 patients, M-mode echocardiographic recordings were available for comparison. Results: Homogeneous distribution was found for corrMBF (1.09 +/- 0.41 to 1.19 +/- 0.31 mL x g(-1) x min(-1)). Tc-99m-MIBI uptake and wall thickening were heterogeneous (P < 0.0001), with the lowest values septal (Tc-99m-MIBI, 65% +/- 10%; wall thickening, 16% +/- 14%) and the highest lateral (Tc-99m-MIBI, 84% +/- 5%; wall thickening, 55% +/- 17%). Similar relationships in systolic wall thickening were observed by M-mode echocardiography (anteroseptal, 20% +/- 11%; posterolateral, 37% +/- 18%; P < 0.001). Conclusion: Heterogeneity of Tc-99m-MIBI uptake in LBBB corresponds to differences in wall thickening and does not reflect distribution of corrMBF. Supplementary analysis of wall thickening is recommended when assessing Tc-99m-MIBI SPECT in LBBB.