ACHIEVING BEST PRACTICE
SA JOURNAL OF DIABETES & VASCULAR DISEASE
74
VOLUME 7 NUMBER 2 • JUNE 2010
Clinical aspects of silent myocardial ischaemia: with
particular reference to diabetes mellitus
Marc dweck,
ian w campbell, douglas miller, c mark francis
Abstract
S
ilent ischaemia is a common, under-recognised
condition that is associated with an adverse prognosis.
It is a marker of significant underlying coronary
artery disease and therefore of future cardiovascular
events. It is more prevalent in the diabetic population and
diagnosis is usually made by a positive exercise tolerance
test, positive myocardial perfusion scan or stress echo. The
basis of treatment, in diabetic and non-diabetic subjects,
is risk factor modification and coronary revascularisation
of prognostically important coronary disease. Diabetic
patients should receive risk factor modification even in
the absence of ischaemia. Detection of silent ischaemia
allows patients with prognostically important disease to
be offered further treatment. The difficulty lies in deciding
who to investigate further for this surreptitious disorder. The
following clinical markers are of predictive use in this regard:
electrocardiographic changes; erectiledysfunction; peripheral
vascular disease and cardiac autonomic neuropathy. Their
presence should prompt further investigation for silent
ischaemia. Conventional risk factors and breathlessness on
exertion may also be helpful. We have proposed an algorithm
for the detection, investigation and management of silent
myocardial ischaemia in diabetic patients.
Keywords:
diabetes, infarction, myocardial ischaemia, silent.
Introduction
Angina pectoris has been considered the cardinal symptom of
myocardial ischaemia for over 200 years. The concept of silent
ischaemia came to the fore in the 1980s with the advent of
24-h ambulatory (Holter) monitoring.
1,2
This allowed the ECG to
be monitored for signs of ischaemia during everyday life. It was
soon established that patients were frequently having episodes
of myocardial ischaemia without experiencing angina. In fact, it is
now recognised that the most common manifestation of CAD is
silent ischaemia and not angina.
1
At the most severe end of the
spectrum, MI can also be silent in nature. Both silent myocardial
ischaemia and infarction are more common in diabetic patients.
The mechanisms of silent myocardial ischaemia are discussed
herein
3
and in previous reviews.
4
The aim of this review is to discuss
the prevalence, prognosis, diagnosis and treatment of this important
condition. There is evidence that silent ischaemia is associated with
an adverse prognosis and that treatment in the form of risk factor
modification and revascularisation results in clinical benefit. Silent
myocardial ischaemia is therefore an important issue in the care of
diabetic and non-diabetic patients, and because of its surreptitious
nature, a high index of suspicion is required for its detection.
Prevalence
Known coronary artery disease
Studies in the 1980s showed for the first time that silent ischaemia
was the most common manifestation of cardiac ischaemia.
1
Among
patients with known CAD, the prevalence of silent ischaemia
is quite high. It has been reported that 15–30% of MI survivors
have silent ischaemia,
5,6
as do 30–40% of patients with unstable
angina despite optimal medical therapy.
1,7
In patients with stable
angina, it is estimated that up to two-thirds of ischaemic episodes
are silent.
1,8,9
Asymptomatic non-diabetic patients
In asymptomatic, non-diabetic men, aged 40–59 years, with no
previous history of CAD, an Italian group estimated the prevalence
of silent ischaemia (confirmed by coronary angiography) to be
0.89%.
10
Other studies have suggested a prevalence of 1–4%.
11,12
This incidence increases with coronary artery calcification, identified
on CT scanning,
13
and with the number of risk factors – approaching
10% in patients with two or more risk factors.
14
Asymptomatic diabetic patients
Diabetes mellitus appears to confer a dramatic increase in the risk
of silent ischaemia, with most studies suggesting a prevalence
of 10–20%.
15,16
Although in one report of 1 900 asymptomatic
patients with type 2 diabetes, the prevalence of silent ischaemia, as
confirmed by stress echo and angiography, was around 60%.
17
The
increased prevalence of silent ischaemia in diabetes is likely to be
due to an increased prevalence of coronary atherosclerosis in this
group in combination with the presence of can.
3
Prognosis
Silent ischaemia is associated with an adverse clinical outcome
across a range of patient groups. The MRFIT trial of 12 866
asymptomatic diabetic and non-diabetic men with two or more risk
factors showed a significant relationship between silent ischaemia
and mortality.
18
Diabetic patients
Silent ischaemia appears to be an especially important prognostic
factor in patients with diabetes. In a study by Rutter,
et al.
,
19
silent
ischaemia was significantly related to future coronary events
Mark Dweck, Department of Cardiology, Victoria Hospital, Kirkcaldy, UK.
Ian W Campbell, Douglas Miller, University of St Andrews, St Andrews, UK.
Correspondence to: Dr C Mark Francis
Department of Cardiology, Victoria Hospital, Kirkcaldy, Fife KY2 5AH, UK.
Tel: + 44 (0)1592 643355
Fax: + 44 (0)1592 648058
E-mail:
S Afr J Diabetes Vasc Dis
2010;
7
: 74–79.
