Effects of left bundle branch block on myocardial FDG PET in patients without significant coronary artery stenoses

Cardiac PET studies in patients with left bundle branch block (LBBB) are fe w, and the results are conflicting. In particular, even if a reduced uptake of FDG is reported, confirmation in a large group of patients and exact un derstanding of the underlying cause are lacking. Methods: We selected 29 co nsecutive patients who had complete LEED and no significant stenosis on cor onary angiography scheduled for FDG and N-13-NH3 PET for myocardial viabili ty evaluation at our center. Wall motion was evaluated using 2-dimensional echocardiography. Ten volunteers without coronary stenosis or LBBB served a s a control group. Results: All LBBB patients had a reverse mismatch in the septum, defined as reduced uptake of FDG in comparison with N-13-NH3. The mismatch extended to the anterior and inferior walls in 17 patients. The me an (+/-SD) septal-to-lateral ratio was 0.57 +/- 0.11 for FDG (range, 0.28-0 .76) and 0.99 +/- 0.12 for N-13-NH3 (range, 0.75-1.18), with P < 0.0001. In contrast, no significant differences in uptake were seen in the control gr oup, which had a septal-to-lateral ratio of 0.95 +/- 0.13 for FDG (range, 0 .78-1.15; P < 0.01 with respect to LBBB patients) and 0.94 +/- 0.11 (range, 0.85-1.20) for N-13-NH3,. Conclusion: Our study suggests that in LBBB pati ents without significant coronary stenosis, FDG uptake in the septum change s without a correlating change in perfusion. To avoid possible overestimati on of necrosis, especially in the LAD territory, this phenomenon must be co nsidered in evaluations of myocardial viability using FDG images.