Effects of ischemic preconditioning and arterial collateral flow on ST-segment elevation and QRS complex prolongation in a canine model of acute coronary occlusion.
BACKGROUND
During acute myocardial infarction, both ST elevation and QRS distortion on the initial electrocardiogram (ECG) have been correlated with poorer prognosis. Studies in dogs and humans suggest that these ECG markers provide information about myocardial protection from both collateral blood flow and ischemic preconditioning.


METHODS
In a protocol designed to precondition the heart with ischemia, we examined both ST-segment elevation and QRS complex prolongation in lead II of the ECG in 23 mongrel dogs during the first and fourth episode of 5 minutes of left circumflex artery occlusion. Myocardial collateral flow was measured during each of these episodes by injection of radioactive microspheres 2.5 minutes into the episode of ischemia.


RESULTS
During ischemia, the degree of elevation of the ST segments was reduced markedly in hearts preconditioned with ischemia and/or in hearts with the greatest amounts of collateral arterial flow. During the first episode of ischemia, the ST segments increased to a similar extent in severe and moderate ischemia, but less in hearts in which the ischemia was mild. However, marked QRS prolongation was present only in hearts with severe ischemia, and decreased when the hearts were preconditioned. In addition, large ischemic beds exhibited the most marked QRS prolongation, whereas small but even severely ischemic beds showed little or no change in QRS duration.


CONCLUSIONS
Both ST elevation and QRS prolongation are reduced by the presence of collateral flow and ischemic preconditioning. The QRS complex merits further study as an important marker of the degree of myocardial protection during human acute myocardial ischemia/infarction.
Floyd
James S
JS
Duke University School of Medicine, Durham, NC, USA.
Maynard
Charles
C
Weston
Patrick
P
Johanson
Per
P
Jennings
Robert B
RB
Wagner
Galen S
GS
D054058:Acute Coronary Syndrome / Q000175:diagnosis* / Q000503:physiopathology*; D000818:Animals; D003097:Collateral Circulation; D054059:Coronary Occlusion / Q000175:diagnosis* / Q000503:physiopathology*; D004195:Disease Models, Animal; D004285:Dogs; D004562:Electrocardiography / Q000379:methods*; D006339:Heart Rate; D006801:Humans; D019157:Ischemic Preconditioning, Myocardial / Q000379:methods*