gated myocardial perfusion spect in patients with left bundle block but having low probability of coronary artery disease; as compared to the patients with normal electrocardiogram

introduction: we aimed to investigate of effect of left bundle branch block (lbbb) on perfusion and functional parameters in dipyridamole tc99m-mibi gated myocardial perfusion spect which may be helpful in interpretation of myocardial perfusion imaging. methods: we studied 70 patients with low pre-test probability of coronary artery disease in two groups:  35 patients with lbbb and  35 subjects with normal ecg. both groups underwent two-day dipyridamole stress–rest tc99m-mibi gspect. results: from 35 patients with lbbb, 6, 12, and 3 patients had reversible, fixed and partially reversible defects respectively. in 35 patients with lbbb, 8 (22.9%), 6(17.1%)  15( 42.9%) and 10 (28.6%) patients had perfusion defects in the apicoseptal,  mid-anterior segments , mid-anteroseptal and mid-inferoseptal segments respectively. there was significant difference in tid ratio between two groups:  lbbb group: 1.07±0.21 and control group: 0.96±0.14 (p=0.01). there was a significant difference in end systolic volume and ejection fraction between lbbb patients group and control group, while no significant difference was noticed in end-diastolic volume. nineteen, 14 and 2 from 35 patients with lbbb had normal lv wall motion, paradoxical septal wall motion, and septal hypokinesia respectively. conclusion: false positive septal, anterior and apicoseptal perfusion abnormalities are frequently seen on tc99m-mibi gspect, in patients with lbbb without cad. moreover reversible defects are frequently seen with tc99m-mibi. even tc99-mibi and vasodilator stress do not increase diagnostic accuracy to clinically useful levels. lower systolic performance and higher tid ratio could be seen in these patients.