Spect myocardial perfusion imaging in the morbidly obese: Prognosis and diagnostic value

Abstract

Background: Obesity is a growing epidemic in the US. As little is known about the diagnostic accuracy of myocardial perfusion imaging (MPI) in the morbidly obese (BMI ≥ 40), we set out to evaluate the correlation of MPI with coronary angiography and the prognostic value of normal studies. 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 months period. A subset of 43 subjects subsequently underwent coronary angiography whose results were compared to MPI. Hospital records and the Social Security Death Index were searched to assess all-cause mortality. Results: Of the 433 patients reviewed 139 (32%) had abnormal MPI results and 294 (68%) normal results. Comparing the patients with abnormal MPI results to normal MPI, the average age was 55 ± 12 versus 53 ± 11 years, BMI 46.9 ± 7 versus 47.5 ± 8 kg/m 2, weight 285 ± 58 versus 275 ± 63 lbs, and Tc99m dose of 36.2 ± 4.3 versus 35.3 ± 5.9 mCi (all p=NS). Of the 43 patients who underwent angiography, performed a median of 15 days later, 5 were performed on patients with normal MPI studies and 38 on patients with abnormal studies. Stress MPI had a sensitivity of 95%, specificity of 17%, positive predictive value of 50%, and negative predictive value of 80% for the detection of > 50% epicardial vessel stenosis. At one year of follow-up, 9 of the 295 patients (3.1%) with a normal MPI died during the follow-up (669 ± 307 days) yielding a 96.9% 1 year survival. Of the 139 patients with an abnormal MPI, 9 (6.5%) died during follow-up (719 ± 318 days) yielding a 93.5% 1 year survival. Conclusion: In the morbidly obese population, stress SPECT MPI imaging has high sensitivity and poor positive predictive value when compared to coronary angiography. One year mortality of the morbidly obese with a normal MPI study (3.1%) exceeds published expected mortality of patients with normal MPI results, as well as diabetic patients with normal MPI results.