Initial diagnosis of
acute coronary syndrome is based almost entirely on history, risk
factors, and, to a lesser extent, ECG. The symptoms are due to myocardial
ischemia, which has an underlying cause of an imbalance between
supply and demand for myocardial oxygen.
most often develops as a result of reduced blood supply, due to
atherosclerotic plaques, to a portion of the myocardium. The plaques
initially allow sufficient blood flow to match myocardial demand.
These areas of narrowing may become clinically significant and precipitate
angina when myocardial demand increases. Angina that is reproduced
by exercise, eating, and/or stress and is subsequently relieved
with rest and without recent change in frequency or severity of
activity necessary to produce symptoms is called chronic stable
angina. Over time, the plaques may thicken and rupture, exposing
a thrombogenic surface upon which platelets aggregate and thrombi
form. The patient may note a change in symptoms of cardiac ischemia
with a change in severity or of duration of symptoms. This condition
is referred to as unstable angina.
A less common cause of
angina is dynamic obstruction, which may be caused by intense focal
spasm of a segment of an epicardial artery (Prinzmetal angina).
Two other causes include arterial inflammation and secondary unstable
angina. Arterial inflammation may be caused by or related to infection.
Secondary unstable angina occurs when the precipitating cause is
extrinsic to the coronary arterial bed, such as fever, tachycardia,
thyrotoxicosis, hypotension, anemia, or hypoxemia. Most patients
who experience secondary unstable angina have chronic stable angina.
Irrespective of the cause of unstable angina, the result of persistent
ischemia is myocardial infarction (MI).
In the US: Estimates
of frequency and prevalence of angina are of limited accuracy due
to the variable nature of the disease and history-based diagnosis.
Treatment modalities and variations in diagnostic criteria also
Internationally: In Britain, annual incidence of angina is estimated
at 1.1 cases per 1000 males and 0.5 cases per 1000 females aged
31-70 years. In Sweden, chest pain of ischemic origin is thought
to affect 5% of all males aged 50-57 years. In industrialized countries,
annual incidence of unstable angina is approximately 6 cases per
Mortality/Morbidity: When the only treatment for angina was nitroglycerin
and limitation of activity, studies of patients with newly diagnosed
angina indicated 40% incidence of MI and 17% mortality within 3
months of onset. More recent studies show that prognosis of patients
with stable angina pectoris is significantly better due to improvements
in identification, risk stratification, and intervention. Clinical
characteristics associated with a poor prognosis include advanced
age, male sex, prior MI, diabetes, hypertension, and multiple-vessel
or left-mainstem disease.
Incidence is higher in
males in those younger than 70 years. This is due to the cardioprotective
effect of estrogen in females. At 15 years postmenopause, incidence
of angina occurs with equal frequency in both sexes.
Angina becomes progressively
more common, as does the underlying cardiac disease responsible,
with increasing age. In persons aged 40-70 years, angina is diagnosed
more often in men than in women. In persons older than 70 years,
men and women are affected equally.