New collateral flow increasing early after coronary occlusion prevented myocardial necrosis in dogs

A protective role of early collateral blood flow in patients with ST-segment elevation myocardial infarction

Conflict persists regarding whether the presence of early collateral blood flow to the infarct-related artery has an effective role in reducing infarct size and improving myocardial salvage in patients with ST-segment elevation myocardial infarction (STEMI). We sought to investigate the impact of the collateral circulation on myocardial salvage and infarct size in STEMI patients.

METHODS

In 306 patients who were diagnosed with STEMI and underwent cardiac magnetic resonance within 1 week after revascularization, initial collateral flow to the infarct-related artery was assessed by coronary angiography. Using cardiac magnetic resonance imaging, myocardial infarct size and salvage were measured.

RESULTS

Among 247 patients with preprocedural Thrombolysis in Myocardial Infarction flow 0/1, 54 (22%) patients had good collaterals (Rentrop grade ≥ 2, Collateral Connection Score ≥ 2). Infarct size and area at risk were significantly smaller in patients with good collaterals than those with poor collaterals (infarct size: 17.1 ± 10.1 %LV vs 21.8 ± 10.5 %LV, P = .003, area at risk: 33.8 ± 16.8 %LV vs 38.8 ± 15.5 %LV, P = .039). There was a significant difference of myocardial salvage index between 2 groups (50.9% ± 15.0% vs 43.8% ± 18.5%, P = .005). Poor collateralization was an independent predictor for large infarct size (odd ratio 2.48 [1.28-4.80], P = .007).

CONCLUSIONS

In patients with STEMI, the presence of well-developed collaterals to occluded coronary artery from the noninfarct vessel and its extent were independently associated with reduced infarct burden and improved myocardial salvage. Our results help explain why MI patients with well-developed collateralization have reduced mortality and morbidity.

Reactive oxygen species are critical mediators of coronary collateral development in a canine model

Recent evidence suggests that reactive oxygen species (ROS) promote proliferation and migration of vascular smooth muscle (VSMC) and endothelial cells (EC). We tested the hypothesis that ROS serve as crucial messengers during coronary collateral development. Dogs were subjected to brief (2 min), repetitive coronary artery occlusions (1/h, 8/day, 21 day duration) in the absence (occlusion, n = 8) or presence of N-acetylcysteine (NAC) (occlusion + NAC, n = 8). A sham group (n = 8) was instrumented identically but received no occlusions. In separate experiments, ROS generation after a single 2-min coronary artery occlusion was assessed with dihydroethidium fluorescence. Coronary collateral blood flow (expressed as a percentage of normal zone flow) was significantly increased (71 +/- 7%) in occlusion dogs after 21 days but remained unchanged (13 +/- 3%) in sham dogs. Treatment with NAC attenuated increases in collateral blood flow (28 +/- 8%). Brief coronary artery occlusion and reperfusion caused ROS production (256 +/- 33% of baseline values), which was abolished with NAC (104 +/- 12%). Myocardial interstitial fluid produced tube formation and proliferation of VSMC and EC in occlusion but not in NAC-treated or sham dogs. The results indicate that ROS are critical for the development of the coronary collateral circulation.

Development and evaluation of a new canine myocardial infarction model using a closed-chest injection of thrombogenic material

A new canine myocardial infarction model using thrombi induced by closed-chest injection of thrombin and autogenous blood with fibrinogen into coronary arteries was developed. Occlusive thrombi were formed in all treated animals. Occluded vessels did not spontaneously reperfuse 1 day after occlusion, but did so within 3 days. Infarction was confirmed by increased levels of creatine kinase-MB, glutamate-oxaloacetate transaminase and a-hydroxybutyrate dehydrogenase. Additionally, the left ventricular ejection fraction (LVEF) decreased within 0.5 h after occlusion and had not improved 4 weeks later. After 1 week, extensive transmural anteroinferior myocardial infarction was observed and heart mass had increased. By 4 weeks after occlusion, pulmonary capillary wedge pressure and central venous pressure were increased, and oxygen pressure was decreased. Dropout of nuclei in cardiomyocytes and increased amount of collagen fiber were observed in myocardial infarct regions of hearts excised 4 weeks after occlusion. This canine model may be useful and convenient in evaluating treatment efficacy and the long-term outcome of acute myocardial infarction.

A study to determine if basic fibroblast growth factor (bFGF) reduces myocardial infarct size in acute coronary arterial occlusion

We investigated the angiogenic and myocardial salvage effects of bFGF. Twelve beagles with ligated left anterior descending coronary arteries were divided into two groups: a FGF group administered bFGF intravenously, and a Control group, after CAG immediately post-ligation. One week post-ligation, CAG was repeated. The heart was sliced along the short axis. For each section, the fluorescein Na staining deficit area (DA) and ratio of DA to total area (DAR), TTC staining of the infarct area (IA) and ratio of IA to total area (IAR), and Masson trichrome staining of the fibrosed area (MA) and ratio of MA to total area (MAR), were calculated. The increase in the number of collateral vessels, seen on CAG from post-ligation to 1 week later, was significantly greater in the FGF group. No significant differences in IAR or MAR were seen between the groups. However, DAR and DA/IA were significantly less in the FGF group. In conclusion, bFGF had no effect on infarct size, but stimulated the growth of collateral vessels and improved coronary blood flow in IA.

Myocardial salvage by reperfusion 12 hours after coronary ligation in dogs

It is not clear why late reperfusion therapy in patients with acute myocardial infarction is effective. An investigation was carried out as to whether or not reperfusion conducted 12 h after coronary occlusion causes myocardial salvage in dogs. Coronary arteries were occluded in 11 mongrel dogs and a portion of the occlusion (late reperfusion area; LR area) reperfused 12 h later; the other part was left occluded (permanent occlusion area; PO area). The dogs were maintained for 4 weeks after reperfusion. Regional myocardial blood flow (Qm) was measured by the non-radioactive colored microsphere method. In both areas, the transmurality of necrosis was measured by triphenyl tetrazolium chloride staining, and the amount of viable myocardium and the extent of fibrosis was determined by Azan-Mallory staining. Qm decreased markedly after coronary occlusion to similar levels in both areas until 12 h. Qm transiently increased in the LR area only following reperfusion after 12 h. The transmurality of necrosis in the PO area was 83.8+/-10.5%, but that in the LR area was 58.7+/-21.3%, a significant decrease (p<0.01). In the outer layer, the amount of viable myocardium was significantly greater, and the extent of myocardial fibrosis was significantly less in the LR area. Evaluation in the same heart of dogs confirmed the myocardial salvage effects of late reperfusion (12 h after coronary occlusion).