Distinction between myocardial ischemia and postural changes in continuous ECG monitoring based on ST-segment amplitude and vector orientation--preliminary results.

Background: Myocardial ischemia, commonly defined as ST-segment elevation or depression on the electrocardiogram (ECG), is plagued by a large number of false positive events.

Objectives: To present a new method that attempts to distinguish between 'highly probable ischemia' and positional changes.

Methods: Continuous three-lead orthogonal ECG monitoring was performed in three groups of subjects: 16 healthy volunteers undergoing a body position change protocol, 22 patients undergoing percutaneous transluminal coronary angioplasty (PTCA) and 17 patients with acute coronary syndromes (ACS). For each event (ischemic or postural), the change in ST-segment amplitude was calculated, as well as the angle between the ST-segment vector of the reference beat and the beats demonstrating ST-segment elevation or depression. Angles and ST-segment amplitude changes from well-documented ischemic events obtained from the PTCA patients and from the healthy volunteers in six different body positions were compared.

Results: Using both ST-segment amplitude and vector angle changes, ischemic events could be detected and differentiated from a postural change with a sensitivity of 91% and a specificity of 96%. Finally, the approach was blindly applied to continuous ECG recordings of ACS patients. The method allowed the classification of 37% of all ST-segment changes detected as highly probable ischemic events as opposed to only 7% using the standard 100 microV threshold.

Conclusion: The current approach showed that highly probable ischemic events could be better distinguished from positional changes with objective criteria using ST-segment amplitude and vector orientation.