The functional value of coronary collaterals in myocardial ischemia and therapeutic approach to enhance collateral flow

Comparing effects of lacidipine, ramipril, and valsartan against experimentally induced myocardial infarcted rats

In this study, the effects of lacidipine (LAC), ramipril (RAM), and valsartan (VAL) on biochemical and histopathologic changes in heart tissue were studied in rats with isoproterenol-induced (ISO-induced) myocardial infarction (MI). LAC, RAM, and VAL had been administered via oral gavage at 3, 3, and 30 mg/kg doses, respectively, once per day during a 30-day time period. On days 29 and 30, the drug treatment group and the control group (with the exception of the intact control group, in which no medications were given, and ISO was not administered) were administered 180 mg/kg ISO subcutaneously over an interval of 24 h. After this period, the hearts of the rats were removed and processed for biochemical and histopathologic studies. The antioxidant parameters superoxide dismutase (SOD), catalase (CAT), and malondialdehyde (MDA) were estimated. A diagnosis of MI was confirmed with antioxidant parameters and histopathologic findings. In MI control groups, histopathologic indicators were found to be statistically higher than those in drug groups; an increase in histopathologic indicators of MI correlates with significant decreases in SOD and CAT levels, and an increase in MDA level. Histopathologic grades of MI indicators were significantly higher in MI group that did not receive any cardioprotective medications in comparison with MI groups that received LAC, RAM, and VAL. Each of the three medications favorably modulated most of the biochemical and histopathologic parameters observed. No significant difference existed with regard to any of the estimated parameters in the rat groups that received medications without MI induction. In conclusion, results indicate that LAC, RAM, and VAL significantly reduced myocardial injury and emphasize the cardioprotective nature of these agents.

Branching patterns in coronary artery and ischemic areas induced by coronary arterial occlusion in the CLAWN miniature pig

This study of 28 CLAWN miniature pigs (male 17, female 11, mean weight 29 kg) was undertaken to investigate the coronary arterial branching patterns and the ischemic area induced by surgical occlusion of the left anterior descending artery (LAD) and change in the ischemic area over time. These results were compared with those in dogs, which have frequently been used in myocardial ischemic research. Regarding the coronary arterial branching pattern, there were fewer ventricular branches from the right and left coronary arteries than in dogs. The septal branches arose from only the LAD and the posterior descending artery (PD). The largest septal artery branched from the LAD. There were two types of septal artery branching patterns. In approximately 80% of the CLAWN miniature pigs, the PD arose from the right coronary artery (Right dominance). The peculiarity of the coronary arterial branching pattern in the CLAWN miniature pigs was more similar to human beings than to dogs. The ischemic area induced by occlusion at three-fifths distal section of the LAD was 12.1% to 22.6% (mean 17.1%) of the left ventricle. The ischemic area in all animals that died of global left ventricular malfunction and hemodynamic instability after LAD occlusion was more than 25% of the left ventricle.

Unusual coronary collateral circulation: filling of a totally occluded left anterior descending artery by direct continuity from a left posterior descending artery. A case report

A patient with an unusual coronary collateral circulation is presented. The left anterior descending artery, which was totally occluded proximally, was filled directly by a continuation of the left posterior descending artery. A thallium stress test revealed normal perfusion in the territory of the left anterior descending artery.

Acute effects of nifedipine versus isosorbide dinitrate on exercise tolerance in patients with isolated coronary artery occlusion and collaterals

The acute effects of slow-release nifedipine and isosorbide dinitrate on exercise tolerance were compared in nine patients with isolated total coronary artery occlusion showing retrograde filling via collaterals. All patients had a reproducible positive exercise stress test off medication before the study. Each patient was randomized to 10 mg slow-release nifedipine and 5 mg isosorbide dinitrate in a single-blind, cross-over study. The exercise stress test was performed 30 minutes after drug administration. After nifedipine, three patients had a negative exercise stress test, whereas the test was negative after isosorbide dinitrate only in one patient. A significantly higher exercise tolerance was detected at peak exercise after nifedipine than after isosorbide dinitrate, as shown by a longer exercise time (380 +/- 44 vs. 295 +/- 41 seconds, p less than 0.001), a more increased maximum work load (355 +/- 89 vs. 255 +/- 55 W x min, p less than 0.02), and a higher rate-pressure product (30,300 +/- 2,500 vs. 26,100 +/- 2,700, p less than 0.01). In conclusion, these results seem to suggest that nifedipine may have a vasomotor effect on collaterals, since it elevated the threshold of ischemia more than isosorbide dinitrate did in patients with isolated coronary artery occlusion, showing retrograde filling via collaterals.

Coronary collateral regression in conscious dogs

To study the effect of long-term coronary reperfusion on regression of newly developed collateral vessels, the authors reoccluded the coronary artery for ten minutes following one to fifteen weeks of reperfusion. They repeated one- or two-minute occlusions of the left circumflex coronary artery (LCCA) in 8 conscious dogs. After 401 +/- 202 (SD) minutes of total LCCA occlusion time (35 +/- 19 days), The LCCA occlusion produced no sustained reduction in regional myocardial shortening and negligible reactive hyperemia. Upon reocclusion following a long-term reperfusion, the subendocardial segment shortening in the region at risk deteriorated markedly. At two minutes of occlusion, percent systolic shortening showed minimal values and thereafter gradually returned to the preocclusion resting levels within six to eight minutes of occlusion. In the presence of a resting heart rate similar to that at the time of functional recovery during the LCCA occlusion, long-term reperfusion did not modify the time course of regional functional response to the prolonged coronary occlusion. It is concluded that the newly developed collateral vessels still serve as significant blood-conveying conduits following a considerable period of reperfusion, and it requires approximately six to eight minutes to restore regional myocardial function in the collateral dependent zone following coronary reocclusion.

Changes in cardiac neuropeptide Y after experimental myocardial infarction in rat

We have investigated the hypothesis that neuropeptide Y (NPY) is released from noradrenergic sympathetic nerves during experimentally induced myocardial infarction. A left thoracotomy was performed, the left main coronary artery ligated, and the animals sacrificed 4 or 48 h later. NPY levels in heart tissue from these rats and sham-operated controls were measured with radioimmunoassay. Levels of NPY in the right atrium were greater than other regions of the rat heart. After ligation of the left coronary artery, the concentration of NPY in the infarcted area of the left ventricle was reduced at 4 and 48 h when compared to a similar area in sham-operated rats. NPY levels in the septum were unchanged. The results suggest that during myocardial infarction, NPY is released from nerves in the infarcted region and may deleteriously affect increased collateral blood flow surrounding the infarcted tissue.

Septal collateralization: demonstration of canine intramyocardial collaterals

The anatomical distribution of intramyocardial collateral arteries that develop from the septal to the other major coronary arteries was studied in dogs following gradual Ameroid occlusion of the circumflex artery. The septal artery was cannulated and injected with Batson's plastic compound resulting in a cast of the coronary circulation. Collateral vessels radiated from the septal vascular bed to both the circumflex and anterior descending arteries. The collaterals developed from the entire base-to-apex extent of the septal artery and were found on both the right and left sides of the septum. Collateral growth appeared to be more concentrated at the apex of the heart. The anatomical details of septal collateral circulation illustrate the importance of intramyocardial collateralization in the dog, which was thought to exhibit primarily epicardial collaterals.

Effects of coronary occlusion on transmural distribution of blood flow in the interventricular septum and left ventricular free wall

Collateral flow to the interventricular septum in the dog was measured after septal artery ligation (N = 8) and compared to that in the left ventricular free wall after occlusion of the left anterior descending coronary artery (N = 10) in other animals. Flow was quantitated by radiolabelled microsphere injection before, and 90 s, 2 h and 4 h after occlusion. Perfusion territory size was measured after colored dye infusion; the septal artery bed occupied 21.74 +/- 5.44% of the left ventricle and was significantly smaller than the anterior descending artery zone (40.72 +/- 7.56%). Regional blood flow prior to occlusion was equal in both beds and symmetric across the ventricular wall; endocardial/epicardial and left/right ratios in the anterior descending and septal artery beds were 0.97 +/- 0.14 and 1.14 +/- 0.17, respectively. 90 s after occlusion, left and right septal and endocardial and epicardial anterior descending flows were significantly (p less than 0.05) reduced. Right septal flows exceeded left sided flows to produce a transseptal gradient. However, right septal flow was significantly greater than epicardial anterior bed values, and free wall endocardial/epicardial was significantly lower than septal left/right ratios. By 2 h after occlusion, left and right septal flows were no longer significantly different from preocclusion values, whereas anterior descending flows remained significantly below control for the full 4-h period. Thus, significant differences between the two beds exist, with greater acute collateral flows and more rapid correction of flow deficits in the septum than in the free wall.

Comparative study of coronary flow reserve, coronary anatomy and results of radionuclide exercise tests in patients with coronary artery disease

A comparative assessment of regional coronary flow reserve, quantitative percent diameter coronary stenosis and exercise-induced perfusion and wall motion abnormalities was performed in 39 patients with coronary artery disease. Coronary flow reserve was determined by a digital angiographic technique utilizing contrast medium as the hyperemic agent. Percent diameter stenosis was calculated by an automated quantification program applied to orthogonal cineangiograms. Thallium-201 scintigraphy and radionuclide ventriculography were used to assess regional perfusion and wall motion abnormalities, respectively, at rest and during exercise. In Group A, 19 patients without transmural infarction or collateral vessels, coronary flow reserve was inversely related to percent diameter stenosis (r = -0.61, p less than 0.0001), and scintigraphic abnormalities occurred only in vascular distributions with a coronary flow reserve of less than 2.00. There was a strong relation among abnormal regional exercise results, stenoses greater than 50% and reactive hyperemia of less than 2.00. Patients with multivessel disease, however, often had normal exercise scintigrams in regions associated with greater than 50% stenosis and low coronary flow reserve when other regions had a lower coronary flow reserve or higher grade stenosis, or both. In Group B, 20 patients with angiographically visible collateral vessels, 12 of whom had prior myocardial infarction, coronary flow reserve correlated less well with percent diameter stenosis than in Group A (r = -0.47, p less than 0.004). As in Group A patients, there was a significant relation between abnormal exercise test results and stenoses greater than 50%. However, reactive hyperemia values were generally lower than in Group A, and positive exercise stress results were strongly correlated only with highly impaired flow reserves of 1.3 or less. In Group B patients, the coronary flow reserve of vessels with less than 50% stenosis was significantly lower than that of similar vessels in Group A patients (2.40 +/- 0.79 versus 1.56 +/- 0.43; p less than 0.0002). It is concluded that: there is a general relation between quantitative percent diameter stenosis and reactive hyperemia that is not of sufficient precision to allow accurate prediction of coronary flow reserve in individual cases; exercise scintigraphic abnormalities are usually associated with low coronary flow reserve, and the relation between these two functional tests is stronger than the relation between exercise test results and quantitative percent diameter stenosis.(ABSTRACT TRUNCATED AT 400 WORDS)

Collateral circulation in coronary artery disease

The coronary arteriograms and left ventriculograms of 202 consecutive patients were reviewed. All had at least 75% diameter reduction of 1 or more major coronary arteries. In 127 patients (63%), at least 1 major branch was totally occluded. Collateral circulation was seen in 125 of these 127 patients (190 of 192 totally occluded arteries). Of the 75 patients without total occlusion, only 2 with 99% (or near-total) occlusion had demonstrable collateral circulation (2 of 208 arteries). In no patient with 75 to 98% diameter narrowing was collateral circulation demonstrated (0 of 164 arteries). An analysis was made of the relation between left ventricular (LV) segmental wall motion and the quality of collateral circulation in 190 totally occluded arteries among 125 patients. Of 126 arteries with good collateral circulation, LV contraction was normal in 21%, hypokinetic in 48% and akinetic/dyskinetic in 29%. Of 64 arteries with poor collateral circulation, LV contraction was normal in 23%, hypokinetic in 55% and akinetic/dyskinetic in 20%. There was no statistically significant difference between the effect of good or poor collateral circulation on LV function. These data indicate that collateral circulation cannot be seen angiographically unless there is total or near-total occlusion, and that the presence of collateral circulation does not correlate with LV wall motion abnormalities, i.e., akinetic area, despite good collateral flow or normal wall motion despite absent or poor collateral flow.

Management of acute myocardial infarction with natural physiological agents

A number of natural physiological agents deserve evaluation in the treatment of acute myocardial infarction. Prostacyclin and magnesium dilate large coronary arteries and could promote collateral circulation to ischemic regions, especially if used in conjunction with alpha-agonists to prevent a drop in coronary perfusion pressure. In addition, prostacyclin has anti-aggregatory and de-aggregatory effects on platelets and a stabilizing action on hypoxic tissue, while magnesium has anti-arrhythmic, potassium-retaining, and fibrinolytic effects, all of which could improve the outcome in acute MI. Adenosine or ribose infusion could be used to promote rapid repletion of adenine nucleotides in reperfused tissue, but unfortunately arteriolar vasodilation by adenosine might reduce collateral perfusion by "coronary steal". High-dose insulin has positive-inotropic (at minimal oxygen cost) and potent anti-arrhythmic actions that have not been adequately tested in previous clinical trials of "polarizing solutions". Carnitine infusion could improve the bioenergetics of ischemic myocardium by relieving inhibition of mitochondrial adenine nucleotide translocase.

Reduced resistances of septal artery collateral channels after cardiac sympathectomy

We have shown that chronic cardiac sympathectomy reduces coronary collateral resistances. The present experiments in isolated dog hearts delineated the role of intramyocardial collateral channels from the septal (SEP) to the circumflex (CIRC), left anterior descending (LAD), and right (RT) coronary arteries in this phenomenon. In 11 controls and 8 2-wk sympathectomized hearts, a retrograde flow technique was used to determine collateral resistances between the epicardial arteries (CIRC, LAD, RT). Collateral resistances between the CIRC and LAD and between the LAD and RT were 42-68% less in sympathectomized hearts (P less than 0.05). Collateral resistances from the SEP to each epicardial artery were determined from retrograde flows simultaneously collected on each epicardial artery when the SEP was the only vessel perfused. Collateral resistances from the SEP to the CIRC and LAD were 51-59% less in the sympathectomized hearts (P less than 0.05). Thus, intramyocardial channels from the SEP to the left coronary arteries show reduced resistances after sympathectomy and can provide a substantial portion of the increased collateral flow to these vessels.

Myocardial infarction in dogs with acute and gradual occlusion of the circumflex or right coronary arteries

This study was designed to quantitate and describe the incidence and magnitude of myocardial infarction in the canine heart following acute and gradual occlusion of the circumflex or right coronary arteries. In animals with acute occlusion, the circumflex artery was ligated just distal to the bifurcation of the left coronary artery for 4 hr (seven dogs). Gradual occlusion was produced by placing an Ameroid occluder on the circumflex artery for 1 month (nine dogs), 3 months (nine dogs), and 5 months (eight dogs) and on the right coronary artery for 3 months (nine dogs). Ten dogs served as controls. At the end of the experiments the dogs were sacrificed, and identification of myocardial infarction was made with an enzyme-mapping technique in dogs with acute occlusion and with histological methods in dogs with gradual occlusion. The volume of ventricular infarction was determined with the use of an Apple II Computer and graphics tablet. After 3 months, gradual occlusion of the right coronary artery produced a 22% incidence of infarction which was significantly less (P less than .01, chi 2) than the 67% incidence observed with 3 months of gradual circumflex occlusion. The average infarct volume produced by gradual right coronary occlusion was 0.94 + 0.69%. The average volume of left ventricular infarction in animals with circumflex acute occlusion was 15.6% + 6.6 and the incidence of infarction was 100%. With gradual occlusion of the circumflex artery for 1, 3, and 5 months, average left ventricular infarction was 2.02 +/- 1.01%, 3.13 +/- 1.53%, and 2.96 +/- 1.35%, respectively. There were no significant differences in the amount of damage observed among the three groups with gradual occlusion, and the average incidence of infarction for these three groups was 76%. In the 1-, 3- or 5-month animals with circumflex occlusion, no additional areas of necrosis subsequent to the original damage were found, indicating that infarction is a single event in this model of gradual occlusion. These results suggest that infarct size is determined primarily by factors at the time of total occlusion and that gradual occlusion allows sufficient time for collateral growth, thereby limiting the extent of myocardial injury.

Immediate appearance of coronary collaterals during ergonovine-induced arterial spasm

Angiographically demonstrable collateral flow occurred immediately when coronary arterial spasm was induced by ergonovine in two patients with angina who had organic stenosis of less than 40 percent. These findings suggest that coronary collaterals may develop in response to intermittent brief myocardial ischemia in man, and that collaterals may be preserved even if they are closed at rest and can immediately function when a coronary artery is acutely occluded.

Coronary artery narrowing without irreversible myocardial damage or development of collaterals. Assessment of "critical" stenosis in a human model

Postinfarction cardiac rupture is the result of thrombotic occlusion of a functional end artery with no previous myocardial damage in the perfusion area of the occluded artery. The pre-existing atherosclerotic stenosis at the site of thrombosis is thus"non-critical" in relation to development of collateral vessels and/or irreversible myocardial damage. Eleven cases of postinfarction cardiac rupture were studied by microscopy of cross-sections of the thrombosed segments. At the site of the thrombosis, pre-existing atherosclerosis had narrowed the lumen to 11% or less of its normal cross-sectional area. Maximal pre-existing narrowing of the proximal left anterior descending artery was found in a case with 97% stenosis (histologically measured cross-sectional area reduction) and an estimated residual lumen of 0.71 mm2. The prestenotic luminal area which is usually considered angiographically as "normal" was in all cases shown histologically to be severely narrowed by a diffuse intimal thickening. It is concluded that organic coronary stenosis must be far greater than 75% to be responsible for the development of collateral vessels and/or irreversible myocardial damage.

Determinants of arrhythmic death due to coronary spasm: effect of preexisting coronary artery stenosis on the incidence of reperfusion arrhythmia

Coronary spasm can occur in the presence or absence of coronary artery disease. We therefore determined the effect of preexisting coronary stenosis on the incidence of ventricular fibrillation during reperfusion after circumflex artery (CFX) occlusion. Twenty dogs underwent a 30-minute open-chest CFX occlusion. During reperfusion, CFX blood flow was restricted by a partial occluder. In dogs that survived reperfusion, peak CFX flow was 91 +/- 44% of baseline (mean +/- SD) compared with 163 +/- 68% in dogs that died of ventricular fibrillation (p less than 0.02). In another 17 dogs, the left anterior descending coronary artery was gradually occluded by an ameroid constrictor. After 17-39 days, the CFX was acutely occluded for 30 minutes and then reperfused. Collateral flow to the CFX, measured by microspheres, was 27.6 +/- 28.3 ml/min . 100 g-1 in dogs that died of reperfusion ventricular fibrillation, compared with 64.4 +/- 27.2 ml/min . 100 g-1 in surviving dogs (p less than 0.02). Thus, the risk of reperfusion ventricular fibrillation is greater in dogs with normal coronary arteries than in dogs with a flow-limiting partial stenosis of the artery undergoing transient occlusion, or chronic stenosis of a second coronary artery inducing collateralization to the artery subsequently undergoing transient occlusion. These results suggest that the risk of ventricular fibrillation during release of coronary spasm may be greater in patients without than in those with coronary artery disease.

Myocardial infarct size and location in relation to the coronary vascular bed at risk in man

Recent infarcts were compared with the anatomic boundaries of the involved vascular bed in human hearts to determine the amount and location of necrosis in relation to the myocardium at risk. The coronary arteries were injected with BaSO4 in 18 human hearts with 3-16-day-old infarcts. Thin (3-4 mm) slices were cut at 10-15 mm intervals, photographed, x-rayed and used for histologic analysis. Infarct outlines were traced from gross photographs using histologic confirmation of infarct boundaries, and the vascular bed was independently traced from the x-rays. Ischemic bed size and infarct size were then calculated by computerized planimetry. Infarct size ranged from 13-72% of the left ventricle (mean 30 +/- 3.6%) and was linearly related to the size of the occluded vascular bed (r = 0.93). However, the infarcts were always smaller than the occluded beds. They involved 50-88% of the ischemic bed (mean 69 +/- 3.0%) due to variation in the transmural extent of necrosis. A lateral zone of viable muscle within the ischemic bed was present but was consistently narrow (mean 1.7 +/- 0.3 mm) so that the infarcts involved 93 +/- 2.3% of the width of the bed at risk. Thus, ischemic bed size is a major determinant of infarct size in fatal human infarcts. When natural limitation of infarct size occurs, it is due primarily to limitation of the transmural extent of necrosis.

Coronary collateral response and myocardial function

Two hundred and twelve patients with recognizable coronary artery block and no other pathology were selected using an interactive computer data retrieval system. The relationship of coronary artery collaterals to left ventricular (LV) dysfunction was investigated. Analysis revealed the significant role of the left anterior descending (LAD) coronary artery and collateral development to the preservation of LV function. This study underlies the value of radiological observation when subject to statistical scrutiny.

Effect of Coronary Collateral Vessels on Regional Myocardial Blood Flow in Patients With Coronary Artery Disease

The effect of radiographically graded coronary collateral vessels on regional myocardial blood flow was evaluated with intracoronary injection of xenon-1233 at rest and during contrast agent-induced coronary hyperemia in 24 patients with coronary artery disease. Eleven patients had no coronary collateral vessels demonstrated radiologically, whereas 13 had such vessels. In 7 of the 13 these were high grade and noncompromised, whereas in 6 they were of lesser grade. Regional myocardial blood flow at rest in patients with and without collateral channels was similar and increased during hyperemia. However, the increase in flow was significantly greater in the patients with high grade noncompromised collateral vessels than in those with lesser grade collateral vessels (80 +/- 16 versus 31 +/- 9 plercent, p < 0.05). To evaluate the functional significance of the high grade noncompromised collateral vessels against that of vessels of lesser grade, various indexes of global and regional ventricular function were compared in the 13 patients in the present study, as well as in 24 patients whose collateral vessels had been subjected to similar grading systems in previous studies of regional myocardial blood flow. There were no significant differences in degree of regional asynergy, ejection fraction or left ventricular end-diastolic pressure between the patients with high and lower grades of collateral vessels. Thus, high grade noncompromised collateral vessels do not appear to have a beneficial effect on resting left ventricular function despite their enhanced vasoldilatory reserve.

Thallium-201 scintigraphy for diagnosis of old myocardial infarction: comparison with electrocardiographic, ventriculographic, and coronary arteriographic findings

Myocardial scintigraphy with 201Tl was performed at rest in a selected group of 36 patients with unequivocal clinical and electrocardiographic evidence of old myocardial infarction. The scintigraphic findings were correlated with electrocardiographic pattern, and with regional left ventricular wall motion and the severity of coronary artery disease defined by contrast angiography. Detection was dependent on the extent of the infarct but was independent of QRS morphology and of the severity of coronary disease. When positive, 201Tl scintigraphy was often a more precise method than the electrocardiogram for localising and delineating the extent of the infarct. Furthermore, the perfusion defect corresponded in location and extent to abnormalities of left ventricular wall motion. The site or severity of coronary artery disease could not be determined from the 201Tl scintigram.