ST-segment analysis in ambulatory ECG (AECG or Holter) monitoring in patients with coronary artery disease: Clinical significance and analytic techniques

Asymptomatic ischemia is common in patients with stable coronary disease during routine daily activities. The perception of ischemic pain (angina) may in part be related to modulation of pain sensation by peripheral neuropathic changes or modulation of central processing of afferent stimuli by physiologic and psychological influences. Since asymptomatic ischemia is not associated with any symptoms or discomforts, the detection of ischemia by AECG monitoring would only be of clinical significance if its presence was independently associated with an adverse prognosis. Observational studies and small-scale randomized clinical trials suggest that more aggressive and thorough treatment of ischemia would lead to an improved outcome, but a more definitive large-scale study is necessary to confirm this relationship. The incidence of ischemia in patients with unstable angina has declined dramatically with use of aspirin, heparin, and the more powerful antithrombotic agents. Identification of ischemia by continuous ECG monitoring in unstable angina patients indicates high risk, but the unique contribution of continuous ECG monitoring to identify high risk may be quite low. Other risk stratifying tests such as exercise testing or exercise perfusion scintigraphy may be more appropriate than continuous ECG monitoring for widespread clinical use. In patients with acute MI, continuous ECG monitoring is valuable both to identify patients at high risk, based on the presence of recurrent ischemia, and to gauge efficacy of treatment, based on the characteristics of resolution of ST-segment elevation. The technical analysis of ST-segment changes indicative of ischemia require careful attention to detail both in the setup of the patient prior to the recording session and in the analysis of the recording itself. Careful preparation will allow for a clear QRS-T signal that lends itself to proper interpretation. Identification of ischemic episodes can be accomplished accurately with close scrutiny of both baseline QRS-T morphology and episodic deviations in morphology. Such analyses provide accurate identification and characterization of the high-risk patient with coronary artery disease.