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 99mTc-methoxyisobutylisonitrile (MIBI) SPECT. Locally different contraction is also associated with LBBB. Quantitative analysis of myocardial SPECT is influ-enced by partial-volume effects depending on systolic wall thickening. Therefore, partial-volume effects may mimic perfu-sion heterogeneity in LBBB. Methods: Fifteen patients with nonischemic dilated cardiomyopathy and LBBB underwent resting 15O-water PET, 99mTc-MIBI SPECT, and gated 18F-FDG PET for analysis of wall thickening. Myocardial blood flow cor-rected for rate–pressure product (corrMBF), 99mTc-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 distri-bution was found for corrMBF (1.09 0.41 to 1.19 0.31 mL g1 min1). 99mTc-MIBI uptake and wall thickening were het-erogeneous (P 0.0001), with the lowest values septal (99mTc-MIBI, 65 % 10%; wall thickening, 16 % 14%) and the highest lateral (99mTc-MIBI, 84 % 5%; wall thickening, 55 % 17%). Similar relationships in systolic wall thickening were ob-served by M-mode echocardiography (anteroseptal, 20 % 11%; posterolateral, 37 % 18%; P 0.001). Conclusion: Heterogeneity of 99mTc-MIBI uptake in LBBB corresponds to differences in wall thickening and does not reflect distribution of corrMBF. Supplementary analysis of wall thickening is recom-mended when assessing 99mTc-MIBI SPECT in LBBB