Silent myocardial ischaemia: prevalence, pathophysiology and significance

It is now generally accepted that in many individuals with ischaemic heart disease the bulk of transient 'ischaemic activity' is asymptomatic or silent. Moreover, a substantial proportion of acute myocardial infarctions occur without symptoms. Transient episodes of silent ischaemia (SI) may often occur in the absence of any evidence of an increase in myocardial demand. In line with this is the fact that they are usually associated with periods of normal, low levels of, physical activity and may occur at rest and during sleep. These findings imply that myocardial oxygen supply, mediated largely by coronary vasomotion, may be an important factor in the aetiology of SI: although in many instances myocardial demand is also important. Ischaemic activity in patients with coronary heart disease exhibits a circadian variation, with a peak in the morning and a smaller secondary peak in the early evening. This rhythm may also reflect, in part, an underlying variation in coronary artery tone. The prognostic significance of SI has still to be fully determined. Its frequency in daily life in individuals with proven coronary heart disease is related to recognised prognostic indicators on standard exercise testing, indicating potential prognostic importance. There is reasonably substantial evidence that the frequency and duration of SI in some patients with unstable angina, despite full medical treatment, is an important determinant of short- and long-term outcome. Limited data indicate that the frequency of SI during ambulant activity may also be of prognostic importance in some survivors of myocardial infarction. In patients with stable coronary heart disease, SI during exercise testing carries the same adverse prognosis as symptomatic ischaemia.(ABSTRACT TRUNCATED AT 250 WORDS)