Localization of maximal ST segment displacement in various ischemic settings by orthogonal ECG: Implications for lead selection and the mechanism of ST shift.
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.


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).


CONCLUSIONS
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.
Nasmith
J B
JB
Faculty of Medicine, Université de Montréal and Research Centre, Hôpital du Sacré-Coeur de Montréal, Montréal, Canada. J-nasmith@crhsc.umontreal.ca
Pharand
C
C
Dubé
B
B
Matteau
S
S
LeBlanc
A
A
Nadeau
R
R
D000789:Angina, Unstable / Q000503:physiopathology; D015906:Angioplasty, Balloon, Coronary; D004562:Electrocardiography / Q000379:methods*; D006801:Humans; D009203:Myocardial Infarction / Q000188:drug therapy / Q000503:physiopathology; D017202:Myocardial Ischemia / Q000503:physiopathology*; D012815:Signal Processing, Computer-Assisted; D015912:Thrombolytic Therapy