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Effect of afterload alterations on the functional border zone measured with two-dimensional echocardiography during
K M Kavanaugh1, H M Brenner, K P Gallagher
1Department of Internal Medicine, University of Michigan Medical School, Ann Arbor.
Insights
Altering afterload with phenylephrine or nitroprusside did not change the functional border zone during acute myocardial infarction in dogs. This suggests afterload changes do not impact the extent of left ventricular dysfunction in this model.
Area of Science:
- Cardiovascular Physiology
- Myocardial Ischemia Research
Background:
- Pharmacologic interventions altering afterload are common in acute myocardial infarction.
- The impact of these afterload changes on regional left ventricular function, particularly the functional border zone, remains under-investigated.
Purpose of the Study:
- To investigate the effects of afterload manipulation on circumferential flow-function relationships.
- To determine the impact of afterload changes on the functional border zone during acute myocardial infarction.
Main Methods:
- 16 open-chest, anesthetized dogs underwent left circumflex coronary artery occlusion.
- Animals were infused with phenylephrine (n=8) to increase afterload or nitroprusside (n=8) for afterload reduction.
- Regional subendocardial blood flow and wall thickening were measured.
Main Results:
- Coronary artery occlusion reduced subendocardial blood flow and wall thickening in the ischemic zone.
- The extent of hypoperfusion was similar with or without afterload manipulation.
- The functional border zone, defined as the area where wall thickening was abnormal but flow was not, did not significantly change with either increased or decreased afterload.
Conclusions:
- Circumferential flow-function relationships are not altered by changing afterload during acute coronary artery occlusion.
- The spatial extent of the functional border zone remains unaffected by afterload manipulation in this experimental model.
Abstract:
In the setting of acute myocardial infarction, pharmacologic intervention resulting in afterload changes are common but the effect of these changes on regional left ventricular function, and specifically the functional border zone, has not been fully investigated. Accordingly, we studied the effects of afterload manipulation on circumferential flow-function relationships and the functional border zone in 16 open-chest, anesthetized dogs. During left circumflex coronary artery occlusion, eight animals were infused with phenylephrine to increase afterload; eight others received nitroprusside for afterload reduction. Following coronary artery occlusion, subendocardial blood flow and wall thickening decreased in the ischemic zone (p less than 0.001). The circumferential extent of hypoperfusion did not differ when coronary artery occlusion alone was compared to occlusion in combination with phenylephrine or nitroprusside, but in both groups the circumferential extent of the wall thickening abnormality was consistently greater than the extent of hypoperfusion. When blood pressure was decreased by 33%, the extent of the functional border zone did not change relative to that during coronary artery occlusion (22 +/- 11 degrees vs 36 +/- 16 degrees, p = ns). Similarly, when blood pressure was increased by 47%, the extent of the functional border zone did not change (32 +/- 10 degrees vs 37 +/- 10 degrees). Therefore circumferential flow-function relations and the spatial extent of the functional border zone are not altered by changing afterload during acute left circumflex coronary artery occlusion in this model.