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Localization of maximal ST segment displacement in various ischemic settings by orthogonal ECG: Implications for lead
J B Nasmith1, C Pharand, B Dubé
1Faculty of Medicine, Université de Montréal and Research Centre, Hôpital du Sacré-Coeur de Montréal, Montréal, Canada. J-nasmith@crhsc.umontreal.ca
Insights
ST segment depression in acute coronary syndromes localizes to the left thorax, irrespective of lesion site. ST elevation vectors, however, align with the occluded artery
Area of Science:
- Cardiology
- Biomedical Engineering
- Electrocardiography
Background:
- ST segment deviation is critical for diagnosing and managing acute coronary syndromes (ACS).
- Understanding the origins of different ST shift polarities and optimal lead placement for ischemic monitoring remains incomplete.
Purpose of the Study:
- To investigate the spatial orientation of ST elevation and ST depression vectors during ACS.
- To correlate vector orientation with coronary lesion location and guide lead placement for monitoring.
Main Methods:
- Continuous orthogonal XYZ lead recordings in 103 patients with MI, PTCA, or unstable angina.
- Analysis of ST segment shifts and vector angles (phi, theta) using polar plots.
- Correlation of ST vector orientation with coronary angiographical data.
Main Results:
- ST depression vectors consistently localized to a lateral cardiac region, independent of coronary lesion location.
- ST elevation vectors demonstrated orientation corresponding to the specific territory of the occluded artery (P<0.002).
Conclusions:
- ST depression in ACS appears to have a consistent spatial pattern over the left thorax, suggesting an incompletely understood mechanism.
- For ambulatory monitoring focused on ST depression, a lateral lead placement may be sufficient.
Background:
ST segment deviation conveys crucial information concerning diagnosis, therapy and prognosis during acute coronary syndromes, but the understanding of the genesis of different ST shift polarities and the rationale for optimal lead placement during ischemic monitoring are incomplete.
Patients And Methods:
Ninety-nine continuous recordings were made with orthogonal X, Y and Z leads in 35 patients during ST elevation myocardial infarction (MI), in 30 patients during single vessel, elective coronary angioplasty (PTCA), and in 34 patients with unstable angina or acute non-Q wave MI. Each lead was sampled at 500 Hz, and dominant QRS-T complexes were averaged every 47 s. In PTCA, 10 s averages were analyzed. Trend plots of ST + 60 ms for each lead and ST vector angles phi and theta were constructed and edited. ST shift polarity (depression or elevation) and vector orientation (phi and theta) were noted for the greatest ST shift 50 microV or greater on any lead for each patient. Coronary angiographical data were consulted when available.
Results:
By constructing polar plots of phi and theta, it was evident that ST depression vectors were confined to a small, lateral cardiac region despite a variety of coronary lesions, while ST elevation vectors were oriented according to the territory of the occluded artery (difference of direction means, P<0.002).
Conclusion:
ST depression in acute coronary syndromes is maximal over the left thorax regardless of coronary lesion location, indicating that the mechanism of ST depression is not fully understood. In ambulatory monitoring where ST depression is expected, a lateral lead may suffice.