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33
MEDICC Review, January 2013, Vol 15, No 1 Peer Reviewed
Perspective
INTRODUCTION
In 2000, global estimates indicated 171 million people had diabe-
tes mellitus (DM), projected to reach 366 million by 2030.[1] As
DM evolves, it produces endothelial dysfunction and changes in
energy metabolism that lead to atherosclerosis in medium- and
large-caliber arteries, creating lesions in coronary, cerebrovas-
cular and peripheral arteries. In diabetics, atherosclerotic plaque
tends to develop earlier, evolve more quickly and be more dif-
fuse. All these factors contribute to DM patients having two to four
times greater risk of a cardiovascular event than nondiabetics,
with cardiovascular disease (CVD) being the main cause of death
in these patients.[2] In 2008, WHO reported a combined mortality
rate from CVDs and DM of 245 per 100,000 population for adults
aged 30 to 70 years.[3]
Cardiac mortality for diabetics with no known coronary disease is
the same as that for non-diabetics with a history of acute myocar-
dial infarction, which is why clinical guidelines consider diabetics
at high risk for CVD.[2]
Presence of cardiac autonomic dysfunction, common in diabet-
ics,[4] is a factor that infl uences the frequently silent appearance
of myocardial ischemia. Hence the importance of identifying
individuals with high risk for cardiovascular events, even prior to
symptom onset. DM also affects vascular endothelium, causing
endothelial dysfunction.[5] The American Diabetes Association[6]
therefore recommends performing stress tests on asymptomat-
ic diabetics who present a minimum of two additional risk fac-
tors (such as hypertension, dyslipidemia and smoking). This
approach, however, is still controversial.
How can silent ischemia be detected in diabetics? The fi rst
step in diagnosing silent ischemia in asymptomatic DM with two
or more additional risk factors is a stress test,[7] whether with a
treadmill or bicycle ergometer.
Ergometry provides valuable functional results—not only for
detecting ischemia, but also for assessing functional capac-
ity, as well as behavior of arterial pressure and arrhythmia on
exertion.[7] Its availability and utility make it the fi rst option for
patients without diabetic neuropathy who are able to do physical
exercise.
In patients with low functional capacity, imaging techniques such
as echocardiography or myocardial perfusion scintigraphy (MPS)
are more helpful, since they have acceptable sensitivity and spec-
ifi city, and allow pharmacological stressors (dobutamine in echo-
cardiogram; dipyridamole or dobutamine in MPS) to substitute
for physical exercise.[8–12] An alternative for patients able to do
physical exercise would be a stress MPS, which combines data
from a stress ECG and functional capacity with that from an MPS.
MPS with single-photon emission-computed tomography
(SPECT) is a validated nuclear medicine technique for obtaining
functional information about the heart by demonstrating myocardi-
al ischemia. If images are synchronized with ECG (gated SPECT
or gSPECT), a single study can provide data on myocardial perfu-
sion as well as intraventricular synchronism and ventricular func-
tion (left ventricular ejection fraction and systolic wall thickening,
which permit assessment of segmental wall-motion abnormali-
ties).[10] gSPECT can be extremely useful in diagnosis and risk
stratifi cation in patients with CVD. Nuclear cardiology techniques
have been used in Cuba since the 1980s and are currently avail-
able free of cost to patients in several tertiary care centers.
Two other imaging techniques, although not used in the same
way as echocardiography and MPS to detect ischemia, provide
complementary data useful for diagnosis. The fi rst is the coro-
nary calcium score obtained through computed axial tomogra-
phy (CAT);[11,12] it quantifi es calcium in coronary arteries and is
therefore an indicator of CVD, although since it provides structural
rather than functional information, it cannot detect ischemia. The
second method is measurement of endothelial function, which
can be assessed in the brachial artery by using ultrasound to
measure fl ow-mediated endothelium-dependent vasodilation, as
described by Celermajer.[13] Marcus[14] found that impairment
of endothelium-dependent vasodilation in coronary resistance
vessels (<450 μm in diameter) may be associated with perfusion
abnormalities in diabetics, even in the absence of stenotic lesions
in epicardial coronary arteries, suggesting the presence of micro-
vascular CVD. This test is more widely available, since it requires
only ultrasound equipment and an echocardiographer trained in
the technique.
DIAGNOSTIC APPROACH TO DETECTING SILENT
ISCHEMIA IN DIABETICS
There are several different algorithms for detection of silent isch-
emia in diabetic patients. The experience of our working group at
Cuba’s cardiology and endocrinology institutes is reviewed below.
All data have been published previously as cited.
As part of multicenter research coordinated with the International
Atomic Energy Agency, we studied a group of 59 diabetic patients,
Usefulness of Nuclear Cardiology Techniques
for Silent Ischemia Detection in Diabetics
Amalia Peix MD PhD DrSc
ABSTRACT
Cardiovascular disease is the main cause of death for diabetics,
and in many cases its presence is silent due to cardiac autonomic
neuropathy. Thus, early diagnosis of coronary disease is essen-
tial, permitting proper risk stratifi cation and appropriate therapy.
This paper examines the usefulness of several noninvasive imag-
ing techniques to study cardiovascular diseases in individuals
with diabetes mellitus, with emphasis on nuclear cardiology, and
proposes a diagnostic algorithm for detection of silent ischemia.
Keywords Myocardial perfusion scintigraphy, myocardial perfu-
sion imaging, radionuclide imaging, diabetes mellitus, silent myo-
cardial ischemia, Cuba
MEDICC Review, January 2013, Vol 15, No 1
34
Perspective
comparing them with a control group of 42
participants (who were not diabetic but
had coronary risk factors) to detect silent
ischemia through MPS, coronary calcium
score and endothelial function assess-
ment.[15]
We found that 69% of DM patients with
stress-induced ischemia in MPS had
impaired endothelium-mediated vaso-
dilation, which can be interpreted as a
manifestation of endothelial dysfunc-
tion. However, only 43% of nondiabetic
patients with other atherosclerotic risk
factors had involvement of endothelium-
mediated vasodilation.[15]
These results are supported by the fi ndings
of Papaioannu,[5] who used ultrasound
to measure endothelium-dependent and
independent vasodilation in the brachial
artery in a subgroup of 75 asymptomatic
diabetics in the Detection of Ischemia in
Asymptomatic Diabetics (DIAD) study; it
was determined that ≥8% endothelium-
dependent vasodilation had a negative
predictive value of 93% for CVD.
Perfusion abnormalities have been
detected in a relatively high percentage
(25%–50%) of asymptomatic diabetics in
different series.[16,17] Two studies have
been conducted in Cuba to date using
gSPECT: one by Peña,[18,19] which
included 220 patients and found ischemia
in 29.1%; and the second by Peix,[15] that
found 33% of patients with DM had isch-
emia versus 16% of those without (p = 0.04). Figure 1 presents
an example of a diabetic patient with silent myocardial ischemia
diagnosed by gSPECT.
To date, MPS has been used in only two other studies to exam-
ine prevalence of ischemia in asymptomatic diabetics: the DIAD
study[4] and that of Scholte,[20] which detected ischemia in
approximately 20% and 33% of cases, respectively, independent
of the number of risk factors. However, unlike the Peix study, nei-
ther of these used physical exercise as a stressor or had control
groups.[15]
Presence of coronary calcium is associated with risk of cardiac
events, with 1–99 Agatston units indicating low risk; 100–400,
moderate risk; and >400, high risk.[21] A prospective study by
Anand[11] followed a two-stage strategy: a calcium score was
derived for all patients through multislice CAT scan, followed
by gSPECT for those who scored >100 Agatston units and for
a random sample of those with scores of ≤100. Some 32% of
MPS showed perfusion abnormalities corresponding to ischemia.
Scintigraphic abnormalities diagnostic of ischemia were present
in 23% of patients with Agatston scores of >100, 48% of those
with scores of >400 and 71% of those with scores of >1000. The
authors found that the more diffuse the ischemia the worse the
clinical evolution; that the calcium score was better than estab-
lished risk factors at predicting silent ischemia and cardiac events
in persons with DM; and that a coronary calcium score of 0 to
10 Agatston units was associated with normal scintigraphy and
excellent prognosis.[11]
In the Peix study, coronary calcium levels in diabetic patients aver-
aged 74 Agatston units compared to 5 in controls (p = 0.01).[15]
Eight diabetics had calcium scores of >100, which in only three
cases coincided with presence of perfusion abnormalities on MPS.
In two studies in Japan and Israel using CAT scans to compare
asymptomatic diabetic with nondiabetic patients,[22,23] prevalence
of coronary plaques was 80% to 93% in asymptomatic diabetics,
and signifi cant coronary stenosis was more prevalent in diabetics
than in the control group. Scholte[24] found that 41% of plaques
were not calcifi ed, thus undetectable by calcium scoring, while
Raggi[12] found coronary artery calcifi cation in 40% of diabetics.
An appropriate approach for these patients could be the combina-
tion of both tests: coronary calcium score and myocardial perfusion
scintigraphy, thus providing important complementary data.
The two-stage strategy (calcium score followed by perfusion scin-
tigraphy for patients with scores of >100) combines both types of
data: structural (through coronary calcium) and functional (through
MPS-detected ischemia). However, even this should be viewed
with caution because, while more useful in cases of calcifi ed epi-
Figure 1: Myocardial perfusion scintigraphy with Tc-99m MIBI in a two-day protocol for
patient with type 2 diabetes and hypertension
No chest pain reported. Physical stress on treadmill applied: duration of exercise: 9 minutes; 7.7 METS (metabolic
equivalent of task); 90% maximum rate reached, without ECG alteration. The image shows slices along three dif-
ferent axes: short, long vertical and long horizontal. The fi rst four rows present the short axis (from heart apex to
base); the fi fth and sixth rows, long vertical; and the last two rows, long horizontal. In each pair of rows, the top
one presents a stress image and the lower one a rest image. In the vertical short and long axes, arrows indicate a
perfusion abnormality in the inferior segment of the myocardial wall on exertion, which disappears in repose (sign
of ischemia).
Source: Nuclear Medicine Department, Cardiology and Cardiovascular Surgery Institute, Havana, Cuba
(Available in color online at www.medicc.org/mediccreview/peix.html. The color scale appears at the right of the
image. The top of the scale represents 100% radiopharmacological uptake.)
Peer Reviewed
35
MEDICC Review, January 2013, Vol 15, No 1
Perspective
Peer Reviewed
cardial coronary lesions, this approach could miss noncalcifi ed
soft plaques and microvascular angina. Microvascular angina is a
diagnosis of exclusion once ischemia is detected in a patient with
typical angina and normal epicardial coronary arteries. Missing
the presence of noncalcifi ed soft plaques, and so excluding MPS,
would be a drawback of this strategy. Presence of DM in addi-
tion to peripheral vascular diseases, carotid disease, peripheral
neuropathy, autonomic dysfunction, family history of CVD or renal
insuffi ciency confers additional risk and reinforces the need for
testing to detect ischemia; we therefore recommend performing
MPS in such cases, even if the calcium score is less than 100.
Peña[18,19] found that alterations in lipids, fasting blood sugar,
hypertension, smoking and family history of heart disease
increased risk of a positive gSPECT two- to fi ve fold. An LDL level
of ≥100 mg/dL was the variable conferring greatest estimated
risk, while an HDL level of <44 mg/dL was the most important
standardized variable when several factors were present.
In the Peix series, DM was the only signifi cant risk factor
associated with perfusion abnormalities (p = 0.03). How-
ever, coronary calcium of >100 Agatston units, abnormal
endothelium-dependent vasodilation (<5%) and a cholesterol/
HDL index of >4 were associated with perfusion abnormalities
in asymptomatic diabetics.[15]
Another interesting aspect that can be evaluated through nuclear
techniques is cardiac autonomic innervation, which is frequently
impaired in individuals with DM; such impairment constitutes an
independent marker of poor
prognosis, probably due
to increased rates of sud-
den death from malignant
ventricular arrhythmia. The
most common method is
SPECT scintigraphy with
metaiodobenzylguanidine,
a norepinephrine analogue,
labeled with iodine-123 (123I).
Patients with DM and car-
diac autonomic neuropathy
have reduced myocardial
metaiodobenzylguanidine
uptake, which has been asso-
ciated with long-term adverse
cardiovascular events.[25]
After completion of the DIAD
study and publication of its
fi ve-year results,[4,26,27] al-
though screening did not have
an impact on adverse cardiac
events overall, it was use-
ful in classifying patients as
high risk (moderate-to-severe
abnormalities and ischemia
on stress ECG) and low risk
(small defects or normal per-
fusion). Hence it would be
preferable to test for ischemia
more selectively rather than
testing all diabetics.
We suggest that asymptomatic patients who have had DM
for at least five years and are able to do physical exercise
take an ergometric test every two years to detect silent
ischemia. For those with inconclusive ergometry and two
risk factors in addition to DM, we suggest including an
endothelium-dependent vasodilation test and coronary
calcium score prior to performing an imaging stress test
(either stress echocardiography or MPS).
In patients who are unable to do physical exercise, an alter-
native to consider is pharmacological stress with dobutamine
or dipyridamole (either echocardiography or MPS). Figure 2
presents an overview of this algorithm proposed for diagnos-
ing silent ischemia in diabetics.
Interestingly, in 79% of patients in the DIAD study with ischemia
on initial MPS, ischemia resolved in the third year.[26] This pat-
tern was associated with intensifi ed treatment using aspirin,
statins and angiotensin-converting enzyme inhibitors. However,
the authors point out that since the study was not designed as a
treatment trial, this association cannot be considered evidence of
a causal relation.
Our working group is currently conducting a third-year assess-
ment of the diabetic group studied. To date, we have observed
resolution of ischemia in 71% of cases, also coinciding with inten-
sifi ed medical treatment and more aggressive control of coronary
risk factors (Peix A, Cabrera LO, Castillo I, Heres F, Rodríguez L,
Padrón K, Valiente J, Llanes R, Mendoza V, Licea M, Gárciga F,
Figure 2: Proposed algorithm for detecting silent ischemia in asymptomatic diabetic patients
DM ≥5 years
Ergometry every 2 years
Negative
Coronary
angiography
Positive Inconclusiveb + 2 additional CRFs
Medical treatment and
CRF control
MPS
Extensive
defects
(≥10% of myocardium)
Small–moderate
defects
(<10% of myocardium)
Endothelial-dependent
vasodilationc
CRF control
Able to perform physical exercisea
>100
Agatston units
Coronary calcium
score
≤100
Agatston units
DM: diabetes mellitus CRF: coronary risk factors
MPS: myocardial perfusion scintigraphy
a If patients cannot perform exercise, pharmacological stress can be applied with dobutamine or dipyridamole
(with echocardiogram or MPS)
b When patient does not reach submaximal heart rate: 85% of maximum (220 minus age)
c Altered endothelium-dependent vasodilation provides information on endothelial function to better orient treatment
MEDICC Review, January 2013, Vol 15, No 1
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THE AUTHOR
Amalia Peix (peix@infomed.sld.cu), cardio-
logist. Full professor and senior researcher,
Cardiology and Cardiovascular Surgery Insti-
tute, Havana, Cuba.
Submitted: May 30, 2012
Approved for publication: December 27, 2012
Disclosures: None
Dondi M; unpublished data), similar to the DIAD results. This line
of inquiry requires more extensive prospective studies, empha-
sizing the need for early diagnosis of ischemia in these patients
through diagnostic techniques available in Cuba and described
above. Early detection of ischemia will support customized indi-
vidual treatment with both medications and appropriate manage-
ment of behavioral risk factors.
CONCLUSIONS
Noninvasive imaging techniques have been shown to be extreme-
ly useful in diagnostic and prognostic assessment of coronary dis-
ease in individuals with DM, but such techniques must always be
judiciously applied and in combination with clinical examination,
evaluating atherosclerotic risk factors and applying an appropri-
ate diagnostic algorithm.
Perspective
REFERENCES
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