Screening asymptomatic patients with type 2 diabetes: The debates persist
Received Aug
Screening asymptomatic patients with type 2 diabetes: The debates persist
George A. Beller 0 1
Jamieson M. Bourque 0
MHS 0 1
0 Reprint requests: Jamieson M. Bourque MD, MHS, Division of Cardi- ovascular Medicine, Department of Medicine, University of Virginia Health System , Charlottesville, VA
1 Cardiovascular Division, Department of Medicine, University of Virginia Health System , Charlottesville, VA
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During the past decade considerable discussion and
debate pertaining to the clinical value and
cost-effectiveness of imaging asymptomatic patients with Type 2
diabetes to detect functionally important coronary artery
disease (CAD) have transpired. The controversy
continues with two articles published in this issue of the
Journal of Nuclear Cardiology. Petretta et al1 take the
‘‘Pro’’ position, whereas, Gibbons2 takes the ‘‘Con’’
position in this ongoing debate. These authors cite recent
published clinical research studies to bolster their points
of view.
The rationale for screening Type 2 diabetic patients
for CAD stems from data indicating that CAD is the
leading cause of mortality in these patients, accounting
for 65% to 70% of deaths.3 Furthermore, these data
showed that diabetes was associated with a 2 to 4 fold
increased prevalence of CAD, and an increased risk of
dying from CAD, compared to nondiabetic patients.4,5
Other data supported the notion that patients with
diabetes without a prior myocardial infarction (MI) had the
same risk of coronary events as patients without diabetes
and a prior MI.6 This led to the concept of diabetes as a
coronary risk equivalent, which required more
aggressive primary prevention measures such as statin therapy
to reduce LDL cholesterol to below 100 mg/dl. Since
stress perfusion imaging was successful in separating
high and low risk subsets of symptomatic patients, it was
thought that if diabetes is a CAD equivalent, should not
asymptomatic diabetic patients also undergo imaging to
detect CAD and improve outcomes? The concept of
CAD risk equivalency has been recently questioned
following the report of a meta-analysis7 comprising
more than 45,000 patients followed for a mean of
13.4 years. This analysis showed, contrary to the
existing paradigm, that patients with diabetes and no prior MI
had actually a 43% lower risk of future CAD events
compared with patients without diabetes and a prior MI.
This finding and the observation that one-third of
asymptomatic diabetic patients have no evidence of
coronary atherosclerosis by CTA or CAC scoring8 have
led to movement away from considering Type 2 diabetes
as a CAD equivalent.
It should be noted that published studies reporting
the percentage of asymptomatic Type 2 diabetic patients
that have significant CAD have patient populations with
substantial differences in clinical risk profiles. Some of
these diabetic patient populations, despite being
asymptomatic at the time of imaging, have a significant
number of patients with either known CAD, peripheral
vascular disease, renal disease, or an abnormal resting
ECG. These may have been symptomatic in the past and
even may have had a prior MI or revascularization. For
example, in the Mayo Clinic cohort of asymptomatic
diabetic patients, 50% were referred for preoperative
risk assessment, 43% had ECG Q-waves and 28% had
peripheral vascular disease.9 In contrast, other
asymptomatic patient cohorts in published studies were at
lower clinical risk, with no prior history of CAD, no
prior symptoms consistent with CAD, and a normal
resting electrocardiogram. An example of this type of
population is the DIAD study10 which excluded patients
with a history of CAD or those with an abnormal resting
ECG. Both types of asymptomatic diabetic patient
cohorts are included in screening studies, although the
probability of detecting CAD, and determining an
increased risk for future cardiac events, are higher in the
former. This should be kept in mind when reviewing
reports either supporting or negating the concept of
screening for CAD in diabetic patients. Other issues
regarding the value of screening raised by Dr. Gibbons
in his argument against routine screening of
asymptomatic patients is whether it provides incremental
prognostic information to traditional CAD risk factors,
and whether it will lead to changes in treatment that
improves outcomes compared to standard guideline
medical therapy and other primary prevention measures
(e.g., invasive strategies for silent ischemia, even greater
reduction of LDL cholesterol, etc.). To our knowledge,
these benefits of screening have not yet been
demonstrated. Certainly, knowledge of presence of occult
coronary atherosclerosis or significant CAD found by
screening might lead to better compliance with medical
therapy, and better outcomes. This also has not been
definitively demonstrated.
It has been observed that the prevalence of high-risk
CAD and ischemia on stress imaging in diabetic patients
may be decreasing, presumably because of b (...truncated)