Value of Repeat Stress Testing in Asymptomatic Patients with Positive CT Calcium Scans
Value of Repeat Stress Testing in Asymptomatic Patients with Positive CT Calcium Scans
Abstract & Commentary
By Michael Crawford, MD
Source: Askew JW, et al. Abnormal electron beam computed tomography results: The value of repeating myocardial perfusion single-photon emission computed tomography in the ongoing assessment of coronary artery disease. Mayo Clin Proc. 2008;83:17-22.
Patients with a positive CT scan for coronary calcium often have a stress test. Askew and colleagues from the Mayo Clinic asked whether such patients should undergo repeat stress testing if the first one is negative or low risk? They identified 69 asymptomatic patients who had a positive coronary CT calcium scan and a normal or low-risk stress myocardial perfusion scan within 90 days and underwent repeat stress testing within four years, without intervening symptom development. These 69 patients were compared to similar patients (216) who did not undergo repeat stress testing. End points were a substantial change in the stress perfusion imaging or a clinical event (death, myocardial infarction, or revascularization).
Results: Only four of the 69 patients (6%) had a substantial change in their stress perfusion results, and all of them had CT calcium scores > 100. Three of these patients were revascularized, and no one died or suffered a MI. The five-year event-free survival was 94%. In comparison to the reference group, the study group had higher calcium scores on average; otherwise, there were no differences. Askew et al concluded that asymptomatic patients with abnormal coronary CT calcium scores and normal or low-risk stress perfusion scans, who remain asymptomatic, are very low risk for subsequent coronary events. Substantial worsening of stress perfusion imaging scores on a subsequent stress test was uncommon (6%) and was not associated with hard clinical events (death or MI).
Commentary
This is a substudy of a previously published study (Am Heart J. 2007;153:807-814) of over 800 patients, of whom 285 had a positive coronary CT calcium score, as well as a negative or low-risk stress perfusion study. This 69-patient subgroup consisted of those who had at least one repeat stress test over four years. In the original cohort, events were only observed in those with a calcium score of > 400; they were infrequent (death 0.4%, death/MI 0.9%, death/MI/revascularization 2.1%). In the repeat testing subgroup, 51% had calcium scores > 400, which was higher than in the group that remained asymptomatic and did not have repeat testing (32%, P = 0.2). Clearly, in this observational study, higher calcium scores were a driver of repeat testing. Despite this, there were no deaths or MIs in the study group. The annual event rate for asymptomatic patients with a positive coronary CT calcium scan and a negative or low-risk stress perfusion scan was < 1%. Thus, performing repeat tests in those who remain asymptomatic does not seem justified.
Even the initial stress study may not always be indicated. These data support the ACC/AHA guideline recommendations that stress testing is not indicated for asymptomatic patients with calcium scores < 100, as they all had negative stress studies and no progression was observed on repeat studies. The guidelines also state that it is appropriate to stress those with scores > 400, but the 100-400 scores remain a grey zone. Individual patient characteristics need to be considered in this group. Perhaps diabetics in the intermediate range should be stress tested, for example. In this study, only 17% of the study group was diabetic, which is low, suggesting that diabetics don't often have negative stress perfusion scans if they have a positive coronary calcium score. Of course, this study is limited by its small size and observational nature, but certainly questions the value of repeat testing within four years of those with initially negative stress perfusion studies who remain asymptomatic.
Patients with a positive CT scan for coronary calcium often have a stress test. Askew and colleagues from the Mayo Clinic asked whether such patients should undergo repeat stress testing if the first one is negative or low risk?Subscribe Now for Access
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