The relative nature of a “normal” myocardial perfusion SPECT

Abstract

See related article, pp. 999-1008The farther backward you can look, the farther forward you can see.Winston ChurchillWith an array of non-invasive imaging modalities available to diagnose and risk stratify individuals with suspected coronary artery disease (CAD), myocardial perfusion SPECT (MPS) has distinguished itself from others owing to its wealth of prognostic data. This is not only true for patients with greater extent, severity, and reversibility of MPS abnormalities, but also for those with normal MPS findings. 1 The salutatory prognosis of those with a normal MPS test has lead to the implication of a ''warranty period'' following a normal SPECT stress test.While tempting to generalize this ''warranty period'' to all patients undergoing MPS, rates of freedom from adverse cardiac events differ significantly for patients with normal exercise MPS as compared to patients with normal pharmacological MPS. 2 The reasons for these observed differences based on the method of hyperemia induction may seem intuitive; patients who undergo pharmacological MPS tend toward older age, greater numbers of CAD risk factors, increased non-cardiac co-morbidities and reduced functional status, a known powerful predictor of mortality. 3 Nevertheless, because prior studies comparing those undergoing exercise vs pharmacological MPS have not accounted for these clinical differences, it remains unknown whether the prognostic ability of a normal MPS also differs for individuals who can against cannot exercise. To address this question, Rozanski et al 4 undertook an important study evaluating the prognostic differences between normal exercise and normal pharmacological MPS-as defined by a summed stress score B3-among patients with similar clinical profiles.The authors followed 6,069 patients without known CAD for 10.2 ± 1.7 years for rates of all-cause mortality. By propensity score analysis accounting for age, gender, angina typicality, CAD risk factors, medications, and baseline findings at the time of MPS testing (including heart rate, blood pressure, and presence of left ventricular hypertrophy), the authors further compared 1,125 patients with normal exercise MPS (defined by summed stress score B 3) matched to 1,125 patients with normal pharmacological MPS for long-term all-cause mortality, as well as short-term 2.6 ± 2.1 years cardiac death and non-fatal myocardial infarction.Within propensity-matched groups manifesting normal MPS findings, individuals undergoing pharmacological MPS still experienced an annualized mortality rate that was almost twofold that of their exercising counterparts (3.9% vs 1.6%, P \ .0001), a relationship consistently observed across all age groups and independent of smoking status, diabetic state, body mass index, presence of left ventricular hypertrophy, or history of peripheral vascular disease. Even more divergent differences were observed for short-term cardiac outcomes between propensity-matched patients manifesting normal exercise vs normal pharmacological MPS, with a nearly sixfold higher annua...

Prognosis in patients with suspected or known ischemic heart disease and normal myocardial perfusion: Long-term outcome and temporal risk variations

“…Therefore, our data indicate that follow-up should be closer in patients with existing CAD or higher risk equivalents like diabetes or old age-quite in agreement with prior proposals. [8][9][10]15,31,34,35 A scientific basis for timing of repeat testing has been sought after. In the cases of alterations in the patient's symptoms or functional capabilities, re-testing may be considered when risk begins to accelerate.…”