Background: The association between silent myocardial ischemia (SMI) and coronary artery disease (CAD) risk factors in asymptomatic patients with no prior history of CAD referred for stress myocardial perfusion imaging (MPI) is unknown.
Methods: We retrospectively evaluated patients who underwent MPI over a 3.4-year period to identify those who did not have chest pain, dyspnea, or known CAD. The presence of risk factors was categorized as none, 1-2, 3-4, and ≥5. MPI was performed using a rest thallium-201/stress Tc-99m sestamibi protocol, and read using a standard five-point perfusion score (0 = normal to 4 = absent) and a 17-segment left ventricular model. Summed stress score and summed rest score were derived as the sum of individual segmental scores at stress and rest, respectively. SMI was diagnosed if the summed differences score (SDS) was ≥2. Prognostically significant ischemia was defined by a SDS ≥ 8.
Results: Among 1,354 asymptomatic patients, SMI was present in 97 (7.2%) and prognostically significant in 60 (4.4%). The prevalence, but not severity, of SMI increased with increasing CAD risk factors--0 for none, 4.1% for 1-2, 8.8% for 3-4, and 12% for those with ≥5 CAD risk factors (P value for trend = .001), in patients <74 years of age. Of the 59 (4.4%) patients who underwent coronary angiography, only 31 (2%) had significant anatomical CAD.
Conclusions: The prevalence of SMI and prognostically significant ischemia is low in asymptomatic patients without known CAD, and is related to the number of CAD risk factors in patients younger than 74 years of age.