Cardiovascular Disease

Acute Coronary Syndrome

Background:

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.

Pathophysiology:

Myocardial ischemia 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).

Frequency:

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 affect prevalence.
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 10,000 people.
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.

Sex:

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.

Age:

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.

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