Spect myocardial perfusion imaging in the morbidly obese: Image quality and hemodynamic response to pharmacological stress

Abstract

Background: As little is known about the characteristics of the morbidly obese (BMI ≥ 40) undergoing stress myocardial perfusion imaging (MPI), we set out to evaluate the study quality and the hemodynamic response to pharmacological stress in this population. Methods: We retrospectively studied 433 consecutive morbidly obese patients without known coronary artery disease presenting for a clinically indicated Tc-99m SPECT MPI study over a 42 month period. Studies were reviewed by consensus for image quality and the contribution of attenuation correction (Vertex, Philips/ADAC, VantagePro) to image interpretation. The hemodynamic response to adenosine (23), dipyridamole (260), and dobutamine (52) in the 335 patients undergoing pharmacologic stress was determined and compared to a group of 3,443 controls of BMI 20–30 studied during the same time period. Results: The average age was 54 ± 11 years, 69% F and 31% M, mean BMI 47.3 ± 8 kg/m 2, mean weight 278 ± 62 lbs, and 79.5% high dose studies with an average Tc99m dose of 35.6 ± 5.4 mCi. Image quality was good in 61%, adequate in 37%, and poor in 2%. By multivariate analysis, study quality was dependent (p<0.05) on weight and the stressor used (worse with dobutamine), but not BMI. Attenuation correction was used in 95% of the studies and was helpful for image interpretation in 60% of them. The utility of attenuation correction was not significantly associated with gender, stressor, weight, or BMI. Compared to control patients, heart rate response to adenosine (21 ± 12 vs 14 ± 13 bpm, p=0.02) and dipyridamole (18 ± 11 vs 14 ± 10 bpm, p<0.001) was more pronounced and the systolic blood pressure response to dipyridamole (-13 ± 20 vs -21 ± 18 mmHg, p<0.001) was less pronounced in the morbidly obese. Conclusion: Diagnostic quality MPI imaging is feasible in the majority (98%) of morbidly obese patients with the use of a dual head camera, attenuation correction, and high stress tracer dose. Increasing weight and dobutamine were associated with worse image quality. The blood pressure drop after dipyridamole was attenuated and the heart rate response was more pronounced after dipyridamole and adenosine.