Heterogeneous perfusion in left bundle branch block (LBBB) has been demonstrated by (99m)Tc-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 (15)O-water PET, (99m)Tc-MIBI SPECT, and gated (18)F-FDG PET for analysis of wall thickening. Myocardial blood flow corrected for rate-pressure product (corrMBF), (99m)Tc-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)). (99m)Tc-MIBI uptake and wall thickening were heterogeneous (P < 0.0001), with the lowest values septal ((99m)Tc-MIBI, 65% +/- 10%; wall thickening, 16% +/- 14%) and the highest lateral ((99m)Tc-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 (99m)Tc-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 (99m)Tc-MIBI SPECT in LBBB.