Survival by stress modality in patients with a normal myocardial perfusion study

Abstract

We sought to determine the differential prognosis of patients with a normal single-photon emission computed tomographic (SPECT) perfusion study by type of stress modality. Even with a normal SPECT perfusion study, patients selected for adenosine stress have a worse survival than those selected for exercise stress. In patients who are able, low-level treadmill exercise is commonly performed during adenosine infusion ("walking" adenosine). The adjusted differential prognosis of patients performing walking adenosine is unknown. Our historical cohort underwent adenosine or treadmill stress with SPECT imaging during 2003 and 2004. Adenosine studies were classified as walking or adenosine only (no low-level exercise). Patients with an abnormal single-photon emission computed tomogram or missing demographic information were excluded. All-cause mortality was determined through July 2008. In total 3,479 patients were included, of which 1,451 (41.7%) were stressed with adenosine only, 201 (5.8%) with walking adenosine, and 1,827 (52.5%) with treadmill exercise. Over an average of 4.3 ± 1.0 years of follow-up, 307 (8.8%) died. Mortality was greatest for adenosine only, intermediate for walking adenosine, and least for exercise (p <0.001 by log-rank test), even after accounting for covariates (adjusted hazard ratio for walking adenosine 0.57, p = 0.044). In conclusion, patients with a normal SPECT perfusion scan who are able to undergo an adenosine protocol in conjunction with exercise have an intermediate prognosis between those who cannot perform low-level exercise and patients able to undergo full treadmill exercise. This differential survival remains significant after adjustment, perhaps because of differences in baseline functional capacity.