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Contractile function of heterogeneously perfused myocardium in conscious dogs
1Montreal Heart Institute, University of Montreal, Quebec, Canada.
Insights
Heterogeneously perfused segments (HET) showed reduced contractile function after coronary artery occlusion (CAO), proportional to ischemic myocardium. Function improved over 4 weeks, unaffected by stimulation or afterload changes.
Area of Science:
- Cardiology
- Physiology
- Myocardial Ischemia Research
Background:
- Coronary artery occlusion (CAO) leads to myocardial ischemia, affecting cardiac contractile function.
- Heterogeneously perfused segments (HET) present a complex model for studying regional myocardial dysfunction post-ischemia.
Purpose of the Study:
- To examine the contractile function of heterogeneously perfused segments (HET) in conscious dogs following circumflex coronary artery occlusion (CAO).
- To determine the relationship between the extent of ischemic myocardium and contractile dysfunction in HET.
- To assess the recovery of contractile function in HET over a 4-week period post-CAO.
Main Methods:
- Conscious dogs underwent circumflex coronary artery occlusion (CAO).
- Regional shortening (SH) and regional endocardial blood flow (REBF) were measured using sonomicrometry crystals placed in non-ischemic and ischemic myocardium.
- REBF mapping was performed using serial sections of ventricular rings.
Main Results:
- At 1 hour post-CAO, HET exhibited a 53.2% reduction in SH, directly proportional to the 50% ischemic myocardium.
- Ischemic segments showed paradoxical bulging and severely reduced REBF.
- Over 4 weeks, SH in HET significantly recovered but remained depressed by 26.8%, while function in purely ischemic segments did not improve.
- Contractile responses to inotropic stimulation and afterload changes in HET were preserved before and after recovery.
Conclusions:
- Acute contractile dysfunction in HET is determined by the amount of ischemic myocardium between recording sites.
- Significant functional recovery occurs in HET over 4 weeks post-CAO.
- Preserved responsiveness to interventions suggests adaptive mechanisms in recovering HET myocardium.
Abstract:
The contractile function of heterogeneously perfused segments (HET) after circumflex coronary artery occlusion (CAO) was examined in conscious dogs. At 1 h after CAO, regional shortening (SH) in nonischemic segments did not change from pre-CAO base line, and regional endocardial blood flow (REBF) increased (P less than 0.05) to 1.52 +/- 0.20 from 1.06 +/- 0.08 ml.min-1.g of tissue-1. In ischemic segments, SH was replaced by paradoxical bulging, and REBF averaged 0.07 +/- 0.02 ml.min-1.g of tissue-1. In HET with one crystal of each pair in nonischemic myocardium and the other in severely ischemic myocardium, SH at 1 h after CAO was reduced (P less than 0.01) by 53.2 +/- 3.4%. REBF maps constructed with serial sections of ventricular rings containing the crystals revealed that in HET 50 +/- 5% of the myocardium was ischemic. Therefore, in the acute phase of ischemia, the reductions in SH in HET were proportional to the amount of ischemic myocardium between recording sites. In HET, SH significantly recovered (P less than 0.01) over 4 wk after CAO but remained depressed by 26.8 +/- 5.1%. In contrast, SH in ischemic segments did not improve after CAO. In HET, the effects of inotropic stimulation and changes in left ventricular afterload on SH (as percent of base line) were similar before and at 1-4 wk after CAO. Thus, in HET, the level of dysfunction is acutely determined by the amount of ischemic myocardium between recording sites. Over 4 wk after CAO, SH improved substantially in these segments, and contractile function was not adversely influenced by an inotropic stimulation or an increase in ventricular afterload.