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.