Lung-to-heart ratio on thallium-201 myocardial perfusion imaging in patients with chronic obstructive pulmonary disease

BACKGROUND: In thallium-201 (Tl-201) stress myocardial perfusion imaging (MPI), elevated lung-to-heart ratio (LHR) can help to predict adverse cardiac events and identify coronary artery disease. However, few studies have evaluated the LHR values on Tl-201 MPI in patients with chronic obstructive pulmonary disease (COPD). OBJECTIVE: To examine whether LHR in COPD may be altered, considering the combined effects of hypoxia, inflammation, and capillary loss. METHODS: We retrospectively evaluated patients with normal Tl-201 pharmacologic stress MPI, no adverse cardiac events in the subsequent 2 years, and pulmonary function tests, coronary angiography, and echocardiography results obtained within 6 months. Patients with COPD (study group) were matched 1:1 by sex and age to controls with normal pulmonary function (control group). Subgroups within the study group were established based on COPD severity determined by spirometry. MPI images were interpreted using a 17-segment american heart association (AHA) model and a 0-4-point scale. LHR and right ventricle/left ventricle (RV/LV) ratios were also documented. RESULTS: Patients with severe COPD exhibited lower poststress LHR values than those with mild-to-moderate COPD. Compared with the control group, the moderate COPD group displayed higher stress LHR, stress RV/LV ratio, and tricuspid regurgitation maximum pressure gradient (TRmaxPG) values. Moreover, poststress LHR showed a positive correlation with the stress RV/LV ratio and TRmaxPG value. These findings were statistically significant ( P < 0.05). CONCLUSION: In Tl-201 pharmacologic stress MPI, our study suggests a nuanced relationship between COPD severity and LHR, emphasizing the need to reconsider normal LHR thresholds in COPD. Larger studies are warranted to validate and expand upon these findings.