ACHIEVING BEST PRACTICE
SA JOURNAL OF DIABETES & VASCULAR DISEASE
78
VOLUME 7 NUMBER 2 • JUNE 2010
CAD. The prevalence of ED in diabetic patients with silent CAD
was 33.8% versus 4.7% in those without silent ischaemia. ED was
shown to be a more efficient predictor of silent CAD than smoking,
microalbuminuria and low-density lipoprotein concentrations.
56
Conventional risk factors
By convention, smoking, hypertension, hypercholesterolaemia,
family history and microalbuminaemia have been considered the
key risk factors in the development of atherosclerosis in diabetic
patients. However, their value in predicting silent ischaemia has
been widely questioned: including in recent guidelines from the
American Diabetes Association.
46
In diabetic patients, the DIAD
study found they were not a good predictive marker for the
presence of silent ischaemia.
57
This finding was confirmed by
Scognamiglio,
et al.
17
in a study of 1 899 asymptomatic patients
with type 2 diabetes. However, the same group also showed that
subjects with two or more risk factors were more likely to have
prognostically significant disease.
17
Diabetic patients with such
disease require revascularisation, and if conventional risk factors
can indeed bring these patients to our attention then they still have
an important role.
Conclusion: an algorithm for diagnosis and
management of silent ischaemia
On the basis of the above discussion we have formulated an
algorithm describing one possible approach to the diagnosis and
management of silent ischaemia in the diabetic population. It is
summarised in Fig. 2.
Population screening is not feasible but diabetic patients at
high risk of silent ischaemia should be identified and investigated
further. We have proposed a system based around the presence
of hard clinical markers that are associated with a high predictive
value for silent ischaemia. The markers selected are as follows: ED,
PVD, CAN and an ischaemic resting ECG.
We feel that the presence of one of these factors increases the
risk of silent ischaemia sufficiently to warrant further investigation.
They can all be quickly identified in the outpatient clinic. Patients
can be asked about erectile function and intermittent claudication.
Examination may reveal the presence of a postural drop (as evidence
of CAN) carotid bruits or absent pulses. An ECG can finally be
performed to look for ischaemic changes at rest.
Breathlessness on exertion and presence of conventional risk
factors are important in risk stratification. However, both have their
limitations and we have not included them in their own right. We
feel that breathlessness is too common a symptom with too wide a
differential diagnosis to merit investigation without other markers
of risk.
Conflicting results have been reported in the literature regarding
the value of conventional risk factors in predicting silent ischaemia.
One trial has suggested that the presence of two or more risk factors
can predict prognostically important disease. However, all diabetic
patients with the metabolic syndrome will have two risk factors and
it is not practical to screen all these patients. We have therefore
suggested that conventional risk factors and breathlessness on
exertion should be considered as part of an overall impression for
the risk of silent ischaemia. If this is felt to be high then patients
should be investigated. Other factors should also be considered in
this impression. For example, BNP release has been shown to be
elevated in patients with CAD as well as heart failure. Rana,
et
al.
58
showed that BNP was of value in predicting silent ischaemia in
asymptomatic type 2 diabetic subjects.
We have based diagnostic investigation around the ETT, which
is the most widely available and used test in the UK. Given the
predictive power of our clinical markers, confirmation with stress
echo or myocardial perfusion imaging will not usually be necessary.
They may be used as an alternative investigation: if patients
are unable to exercise or if ECG changes will interfere with ETT
interpretation. If the ETT is clearly positive for silent ischaemia (
>
2
mm of flat or down-sloping ST depression in two or more adjacent
leads) then patients require aggressive risk factor modification, a
beta-blocker to reduce the ischaemic load, and an angiogram to
establish the nature of their CAD. Prognostically important disease
should be treated with revascularisation.
If the ETT is clearly negative then patients require risk factor
modification but no other treatment. If the ETT result is equivocal
then confirmation should be sought with either stress echo or
myocardial perfusion imaging, before deciding on whether the
positive or negative test pathways should be followed.
Acknowledgements
This review is based upon a dissertation submitted to Bute Medical
School, University of St Andrews, by Douglas Miller.
References
Deedwania PC, Carbajal EV. Silent myocardial ischaemia: a clinical perspective.
1.
Arch Intern Med
1991;
151
: 2373–82.
Sajadieh A, Nielsen OW, Rasmussen V,
2.
et al
. Prevalence and prognostic
significance of daily-life silent myocardial ischaemia in middle-aged and elderly
subjects with no apparent heart disease.
Eur Heart J
2005;
26
: 1402–09
Dweck M, Miller D, Campbell I, Francis C. Mechanisms of silent myocardial
3.
ischaemia: with particular reference to diabetes mellitus.
Br J Diabetes Vasc Dis
2009;
9
: 99–102.
Cohn PF, Fox KM, Kaly C. Silent myocardial ischaemia.
4.
Circulation
2002;
108
:
1263–77.
Gottlieb SO, Gottlieb SH, Achuff SC,
5.
et al
. Silent ischaemia on Holter monitoring
predicts mortality in high-risk post infarction patients.
J Am Med Assoc
1988;
259
: 1030–5.
Tzivoni D, Gavish A, Zin D,
6.
et al
. Prognostic significance of ischaemic episodes in
patients with previous myocardial infarction.
Am J Cardiol
1988;
62
: 661–4.
Gottlieb SO, Weisfeldt ML, Ouyant P,
7.
et al
. Silent ischaemia as a marker for early
unfavourable outcomes in patients with unstable angina.
N Engl J Med
1986;
314
: 1214–19.
Langou RA, Huang EK, Kelley MK,
8.
et al
. Predictive accuracy of coronary
artery calcification and abnormal exercise test for coronary artery disease in
Key messages
Silent myocardial ischaemia:
is common especially in the diabetic population
•
is a marker of significant
•
caD
is associated with an adverse prognosis
•
is diagnosed by a positive
•
eTT, myocardial perfusion scan or
stress echo
high-risk markers in diabetes are abnormal resting
•
ecg;
peripheral vascular disease; erectile dysfunction and can
requires intensive risk factor modification
•
requires coronary revascularisation in prognostically
•
important disease.
