Experimental Coronary Artery Occlusion Research Articles

17 Cannabidiol as an anti-arrhythmic, the role of the CB1 receptors

Cannabidiol (CBD) has been shown to be anti-arrhythmic (Walsh et al, 2010) and tissue sparing (Durst et al, 2007) in an in vivo rat model of coronary artery occlusion (CAO),...

Eugene Braunwald

In the last issue of Circulation Research ,1 we heard from esteemed cardiologist Eugene Braunwald (Harvard Medical School and Brigham and Women’s Hospital, Boston, MA) about his family’s escape from Nazi-occupied Austria. Braunwald arrived in the United States with his family in 1939, aged 10. He went on to become one of the most influential and highly regarded clinical cardiovascular scientists of the last 50 years. It is safe to say that through his research, Braunwald has contributed to the survival of countless heart attack patients across the globe. In part two of this interview, we learn how Braunwald’s passion for cardiology developed and how at 80 years of age that passion, as well as his work ethic, show no signs of diminishing. ### So, a New Life in Brooklyn Began… Thankfully, we were out of danger, but my parents were now concerned about our future as strangers in a country that, contrary to current belief, was not yet out of the depression. We were as poor as the proverbial church mice, and my father had to figure out how to support us. I don’t know how, but he always managed to put bread on the table. Life was nothing like it had been in Vienna before March 1938. But, my father was a very enterprising, strongly motivated, and hard-working man, and after a few false starts, he managed, with my mother’s help, to create a second successful wholesale clothing business. ### Tell Me About Your School Days in Brooklyn I started in an elementary school and did well. In fact, I was the class Valedictorian, which was quite an honor for a relatively recent arrival. Then, I went off to Brooklyn Technical High School, an elite public high school that required passing a very tough entrance examination. ### You Were Already Leaning Toward the Sciences. At What Point Did You Decide to Study Medicine? I started high school with the desire to become an engineer. It was the “in thing” to do …

Edema as a Very Early Marker for Acute Myocardial Ischemia: A Cardiovascular Magnetic Resonance Study

This study was designed to determine whether imaging myocardial edema would identify acute myocardial ischemia before irreversible injury takes place. Early identification of acute myocardial ischemia is a diagnostic challenge. We studied 15 dogs with serial T(2)-weighted and cine imaging at baseline, during transient coronary occlusion of up to 35 min, and after reperfusion in a 1.5-T magnetic resonance imaging system. Late gadolinium enhancement and troponin measurements were used to assess for the presence of irreversible injury. Myocardial water content was measured to assess myocardial edema. We consistently observed a transmural area of high T(2) signal intensity matching areas with new onset regional akinesia 28 +/- 4 min after experimental coronary artery occlusion. At this time, the contrast-to-noise ratio between the ischemic and remote myocardium had significantly increased from 1.0 +/- 2.0 to 12.8 +/- 9.6 (p < 0.003), which further increased after reperfusion to 15.8 +/- 10.3 (p < 0.004 compared with baseline). Neither myocardial late gadolinium enhancement nor troponin elevation were noted at this time window. Myocardial water content of the ischemic segments was consistently higher (68.9 +/- 2% vs. 67.0 +/- 2%; p < 0.004) than in remote segments and the difference correlated significantly to the contrast-to-noise ratio in T(2) images (p < 0.04). We provide the first evidence that T(2)-weighted cardiovascular magnetic resonance imaging of edema detects acute ischemic myocyte injury before the onset of irreversible injury. T(2)-weighted cardiovascular magnetic resonance imaging may serve as a very useful diagnostic marker in clinical settings such as unstable angina or evolving infarction.

Reducing Myocardial Injury by Minimizing Imbalance between Oxygen Supply and Demand

The purpose of this study was to determine whether hemodynamic and pharmacologic factors can influence the extent and severity of myocardial necrosis produced by coronary occlusion. In 48 dogs, 10 to 14 epicardial leads were recorded on the anterior surface of the left ventricle in the distribution and vicinity of the site of occlusion of a branch of the left anterior descending coronary artery. The average S-T segment elevation for each animal was determined at 5-min intervals after occlusion. This elevation was used as an index of the presence and severity of myocardial ischemic injury. Isoproterenol, ouabain, glucagon, bretylium, and tachycardia given prior to a repeated occlusion each increased the severity and extent of ischemic injury, while propranolol decreased it. Elevation of arterial pressure with methoxamine reduced the occlusion-induced S-T segment elevation, and lowering of the mean arterial pressure by hemorrhage had the opposite effect. In 19 additional experiments, propranolol, isoproterenol, and alterations in arterial pressure produced similar alterations in S-T segment elevation when these interventions were applied as long as 3 hr after ligation. Myocardial creatine phosphokinase (CPK) activity determined 24 hr after coronary artery ligation correlated well with S-T segment elevation at the same sites recorded 15 min after ligation. Moreover, isoproterenol increased and propranolol decreased the area of depression of myocardial CPK activity. We conclude that the hemodynamic status and neurohumoral background at the time of coronary occlusion and for at least 3 hr thereafter can alter the extent and severity of myocardial ischemic injury and myocardial necrosis.

Reduction of the infarcted area with the use of simplified coronary sinus retroperfusion during experimental coronary artery occlusion

This study examined if the use of simplified coronary sinus retroperfusion would lead to any reduction in the infarcted area associated with improved right and left ventricular function. Twelve mongrel dogs were entered in this study. Following anesthesia, a fast response thermistor was placed on the pulmonary artery via the jugular vein and aorta via the left ventricular apex. The left anterior descending artery (LAD) was separated from the vein. A retrograde cardioplegia catheter was inserted into the coronary sinus. Following these procedures, LAD was occluded for a period of 3.5 h. After 30 min ischemia, the aorta-coronary sinus connection was established. The animals were divided into two equal groups. One group was not treated and was considered the control group (six animals). In the remaining group (six animals), retroperfusion was used and was considered the retroperfusion group. At the end of the study, the left ventricular ejection fraction was 65±15% in the retroperfusion group and 48±5% in the control group ( P<0.05). The left ventricular stroke work index was 0.44±0.04 (g m/kg) in the retroperfusion group and 0.31±0.05 (g m/kg) in the control group ( P<0.05). Cardiac output was 1650±75 ml/min in the retroperfusion group and 1250±125 ml/min in the control group. The ratio of the infarct size to the area at risk was 49±5% in the control group and 7±3% in the retroperfusion group. In light of these studies, we conclude that simplified coronary sinus retroperfusion appears to be an effective method that must be taken into consideration.

Insulin-like growth factor-II delays myocardial infarction in experimental coronary artery occlusion.

We have previously shown that short pulses of myocardial ischemia cause increased mRNA expression of the insulin-like growth factor II (IGF-II) gene. The expression of IGF-II precedes the expression of its binding protein 5 (IGFBP-5). The cardioprotective actions of the IGF-II peptide and of its binding protein 5 as well as the underlying mechanisms were investigated in this study. Human recombinant IGF-II (0.25 microgram/ml) was applied by means of direct intramyocardial infusion (IM) for 60 min prior to a 60 min LAD occlusion and 120 min reperfusion. Myocardial infarction, compared to the region at risk, was significantly decreased by IGF-II treatment, whereas infusion of Krebs-Henseleit buffer did not show any protective effect (IGF-II, 78.75 +/- 1.51%; control, 100%; P < 0.005). A comparable degree of cardioprotection was observed after infusion of an equipotent concentration of recombinant human insulin (0.02 IU/ml; 88.25 +/- 1.45%; P < 0.05). Lavendustin A (100 microM), an inhibitor of protein tyrosine kinases, prevented the observed cardioprotection. The protective effect of IGF-II was lost when IGFBP-5 was simultaneously infused. IGF-II, a peptide that binds to the insulin receptor and whose mRNA is rapidly transcribed by cardiac myocytes following ischemic stress, is cardioprotective and mimics ischemic preconditioning. Its observed actions are probably based on its metabolic effects and are mediated by the insulin or the IGF-I receptor. IGFBP-5, whose expression follows IGF-II's expression with a short delay, inhibits the cardioprotection afforded by IGF-II and may thus account for the limited temporal duration of ischemic preconditioning.

Coronary heart disease: Overview

Coronary heart disease: Overview

Myocardial contrast echocardiography in experimental coronary artery occlusion with a new intravenously administered contrast agent

A new intravenously administered ultrasound contrast agent was studied in eight dogs during intermittent coronary artery occlusion. The area of the myocardial contrast defect was compared with that of the acute wall motion abnormality induced by coronary occlusion. A close correlation was found between these two independent measures of acute myocardial ischemia. The peak change in myocardial intensity during coronary occlusion was significantly less than for the same segment before ischemia and for a remote nonischemic segment. This new, intravenously administered ultrasound contrast agent can be used to evaluate the spatial distribution of hypoperfused myocardium and should therefore prove valuable in the clinical evaluation of ischemic syndromes.

The failure of retrograde continuous warm-blood cardioplegia to resuscitate cardiac function in experimental acute coronary artery occlusion and reperfusion.

The effects of retrograde continuous warm-blood cardioplegia (RCWBC) on myocardial preservation during surgical revascularization for acute coronary artery occlusion were investigated using an isolated in-situ dog heart model. The left anterior descending artery (LAD) was occluded for 60 minutes followed by 60 minutes of cardioplegic arrest and reperfusion after release of the coronary artery occlusion. Thirty one animals were divided into 3 groups according to the manner of cardioplegic arrest. The first group of animals (n=10) received multiple doses of cold St. Thomas' Hospital solution delivered antegradely through the aortic root. The second group of animals (n=11) received the same dose of the crystalloid solution delivered retrogradely through the coronary sinus. The third group of animals (n=10) received RCWBC through the coronary sinus. In the animals which were capable of supporting the working mode after reperfusion (8 hearts in each group), regional myocardial function in the occluded LAD distribution measured by sonomicrometer as well as global myocardial function evaluated by left-ventricular stroke-work index were not significantly improved during reperfusion by RCWBC. Corresponding to the functional data, myocardial pH in the occluded LAD distribution was not significantly increased by RCWBC. Although RCWBC maintained myocardial pH in the circumflex artery distribution at a significantly higher level than the other two groups of hearts undergoing cold crystalloid cardioplegia, RCWBC resulted in a substantial decline of myocardial pH in the right-ventricular free wall. These results suggest that RCWBC after 60 minutes of LAD occlusion may not provide a significant benefit in myocardial preservation compared to cold crystalloid cardioplegia delivered through either an antegrade or retrograde manner.

ST Segment Alternans During Balloon Occlusion in Elective Percutaneous Transluminal Coronary Angioplasty: Case Report and Review of the Literature

ST segment alternans has been described in experimental coronary artery occlusion and in patients with variant angina. It is also seen during coronary angioplasty and may represent a continuum of the ST segment changes secondary to transmural myocardial ischemia. Its presence has been associated with ventricular arrhythmias and its relative infrequency attributed to the coexistent use of calcium channel blockers in patients undergoing elective angioplasty. We describe a patient with this phenomenon during balloon angioplasty of the left anterior descending coronary artery with a review of the literature. (J Interven Cardiol 1993; 6:231–234)

Early Detection and Measurement of Experiment Myocardial Infarcts with Horseradish Peroxidase

Current methods of experimental infarct size measurement require tisue analysis several hours after the ischemic event. Electron microscopy identifies irreversibly injured myocytes early after ischemia, but cannot be used to measure myocardial infarct size. Horseradish peroxidase (HRP), a tracer protein that permeates the disrupted sarcolemma of injured myocytes, was used to determine infarct size. New Zealand White rabbits ( n = 15) were subjected to 30 min coronary artery occlusion and 24 h reperfusion. Prior to euthanasia, HRP was administered intravenously. The hearts were excised, perfused with triphenyl tetrazolium chloride (TTC), and perfusion fixed. A frozen section was cut from left ventricular slices, and the brown HRP reaction product was developed with 3,3′-diaminobenzidine tetrahydrochloride and H 2O 2. The areas delineated by intramyocyte HRP (as a percent of the left ventricle) closely correlated with infarct size determined by conventional hematoxylin-eosin (H&E) stain and TTC (means ± S.E.M.): 29.5 ± 3.0.% vs 27.6 ± 2.9% vs 28.6 ± 2.6%, respectively. The coefficient of correlation between HRP and H&E was 0.94. This method was tested for early infarct detection in rabbits subjected to 30 min coronary occlusion followed by intravenous injection of HRP and sacrifice. HRP-delineated infarcts measured 21.4 ± 3.7% of the left ventricle, and electron microscopic examination from ischemic and non-ischemic areas was used to confirm that cells containing HRP were irreversibly injured. Thus, HRP can be used to accurately measure myocardial infarct size in experimental coronary artery occlusion and reperfusion in infarcts as early as 30 min after coronary occlusion or following 24 h of reperfusion.

Effect of hypertrophy induced by pressure overload or volume overload on reperfusion induced arrhythmias in anaesthetised rats

The aim was to determine the effect of myocardial hypertrophy on the incidence and severity of arrhythmias following reperfusion after experimental coronary artery occlusion, and to establish if the effect differed between pressure overload hypertrophy and volume overload hypertrophy. The experiments were performed in rats. Pressure overload hypertrophy was induced by aortic banding, and volume overload hypertrophy by perforation of the aortic valve. Four weeks after surgery, coronary artery occlusion and reperfusion experiments were performed. Both pressure and volume overloaded hearts exhibited a similar degree of left ventricular hypertrophy of about 45% weight gain compared to control animals. The total number of ventricular premature beats during reperfusion was not significantly increased in either model of hypertrophy. In contrast to volume overload, the incidence of reperfusion induced ventricular fibrillation was significantly increased in pressure overloaded hearts. Furthermore, there was a significant correlation between number of ventricular premature beats and degree of left ventricular hypertrophy, as well as between duration of ventricular tachycardia and degree of hypertrophy in the pressure overloaded group. Such correlations were not observed in hypertrophy due to volume overload. Neither volume nor pressure overload hypertrophy significantly increased mortality from ventricular fibrillation. An increase in cardiac mass per se does not necessarily aggravate reperfusion arrhythmias. The susceptibility to arrhythmias in this model seems to be critically dependent on the nature of the stimulus triggering left ventricular hypertrophy.

Antifibrillatory effects of α1-adrenoceptor blocking drugs in experimental coronary artery occlusion and reperfusion

The myocardium of animals and man possesses alpha 1-adrenoceptors in addition to beta-adrenoceptors. Ischemia increases sympathetic tone, and ventricular arrhythmias can occur by beta- and alpha 1-adrenoceptor stimulation. I believe that alpha 1-adrenoceptor blocking drugs have antifibrillatory effects and will review the data that support this condition. The effect of alpha 1-adrenoceptor blocking drugs on the incidence of ventricular fibrillation in acute coronary artery occlusion and (or) reperfusion has been determined in 24 studies in conscious and anesthetized dogs and rats, anesthetized cats and pigs, and rat and guinea-pig isolated hearts. The drugs reduced the incidence of fibrillation from 35 to 24% in coronary occlusion and from 61 to 29% in reperfusion.

Enzyme and immunohistochemical assessment of myocardial damage after ischaemia and reperfusion in a closed-chest pig model.

The usefulness of different enzyme and immunohistochemical stains to distinguish reversible and irreversible myocardial cell injury after experimental coronary artery occlusion of varying duration and reperfusion with or without superoxide dismutase as adjunct was investigated. Biopsies or parts of the infarcted and non-infarcted area were rapidly frozen and sectioned in series for enzyme and immunohistochemical evaluation. Sections were stained for the demonstration of phosphorylase, myofibrillar ATPase and mitochondrial oxidative enzymes and also with periodic acid-Schiff, alizarin red S and routine histological stains. Other sections in series were stained with antibodies against fibronectin and the intermediate filament proteins desmin and vimentin. In 49 biopsies a blind quantitative estimation of the area stained for fibronectin, phosphorylase and alizarin red S was performed and evaluated statistically. Phosphorylase, periodic acid-Schiff, fibronectin and alizarin red S allowed delineation of affected myocardium after 30 min of ischaemia followed by reperfusion whereas with the other stains, affected myocardium was readily detectable only after 60 or 90 min of ischaemia followed by reperfusion as well as after 24 h of ischaemia without reperfusion. The immunostaining for fibronectin was very distinct and inversely related to the phosphorylase activity. We show that fibronectin is an excellent marker for damaged cells and that these positively stained myocytes are necrotic as confirmed ultrastructurally. Using alizarin red S as a marker of calcium accumulation in myocytes, a marked discrepancy was observed between the area of fibronectin-containing myocytes and that of myocytes stained by alizarin red S. Calcium accumulation in mitochondria is thus not a prerequisite for myocyte necrosis but does occur only in some of the irreversibly damaged cells. Of special interest is the finding that there was a significant reduction of intracellular calcium in pigs where superoxide dismutase had been used as an adjunct at reperfusion, thus supporting the theory that free radicals do play a role during reperfusion of ischaemic myocardium.

A Study on the Changes in Left Ventricular Function by Experimental Coronary Artery Occlusion and Reperfusion

A Study on the Changes in Left Ventricular Function by Experimental Coronary Artery Occlusion and Reperfusion

Controlled versus hyperemic flow during reperfusion of jeopardized ischemic myocardium

Controlled versus uncontrolled reperfusion of ischemic myocardium after experimental coronary artery occlusion was studied to determine the effect on regional ventricular wall motion and associated blochemical alterations. Fourteen pigs underwent coronary artery occlusion for 1 hour followed by 2 hours of reperfusion. In seven animals uncontrolled reperfusion was achieved by complete release of the arterial occlusion resulting in hyperemic flow. In seven other animals coronary flow during reperfusion was controlled at baseline levels eliminating hyperemic flow. Our results show that controlled reperfusion lessens end-diastolic wall thickness, reduces myocardial calcium deposition, increases the rate of mitochondrial oxidative phosphorylation, and preserves cellular high-energy phosphate stores in the ischemic-reperfused myocardium when compared to the uncontrolled reperfusion state. These data suggest that the magnitude of flow at an early stage of reperfusion is one of the important determinants in the outcome of ischemic myocardium.

Reduction in infarct size by the prostacyclin analogue iloprost (ZK 36374) after experimental coronary artery occlusion-reperfusion

In this study we attempted to determine whether administration of iloprost (ZK 36374), a chemically stable prostacyclin analogue, would reduce infarct size after experimental coronary artery occlusion and reperfusion. One hour of coronary artery occlusion was performed in 28 open-chest, anesthetized rabbits, followed by 5 hours of reperfusion. Two minutes after occlusion, 99mTc-labeled albumin microspheres were injected into the left atrium for later assessment of the area at risk of infarction. Fifteen minutes after occlusion animals were randomly assigned to either the treatment group (iloprost, 1.2 μg/kg/min intravenously for 6 hours; n = 14) or the control group (n = 14). In vitro platelet aggregation was inhibited in rabbits receiving iloprost. In 10 rabbits (five treated and five control) regional myocardial blood flow was also measured by means of differentially labeled radioactive microspheres. Infarct size was significantly smaller in treated rabbits (53.6 ± 4.1% of the risk zone vs 89.4 ± 3.8% in control rabbits; p < 0.001). Flow to the nonischemic myocardium was higher in treated animals, that is, 1.87 ± 0.20 ml/min/gm of tissue 50 minutes after occlusion and 1.90 ± 0.20 ml/min/gm of tissue 4 hours after reperfusion, compared with 1.54 ± 0.20 and 1.64 ± 0.30 ml/min/gm of tissue, respectively, in control rabbits ( p < 0.01). Collateral flow to the ischemic region was not affected by the drug. Mean arterial blood pressure, heart rate, and pressure-rate product in treated rabbits were not significantly different from values in control rabbits. In conclusion, administration of iloprost reduced myocardial infarct size in this model of myocardial ischemia and reperfusion in absence of major hemodynamic effects.

Histochemical and Fluorescent Techniques for Detection of Early Myocardial Ischemia Following Experimental Coronary Artery Occlusion: A Comparative and Quantitative Study

Several workers have used histochemical, enzymatic, and fluorescent methods to diagnose early myocardial ischemia, but the problem of unequivocal detection of early ischemia still remains an enigma to pathologists. In the present study, the left coronary artery was ligated in an animal model, rat, in order to produce myocardial ischemia at different time intervals, from five minutes to six hours. Fluorescent techniques and tetrazolium staining of myocardial succinic dehydrogenases have been used to detect onset of ischemia with the purpose of identifying a sensitive technique for use in routine pathologic specimens. Nitroso-blue tetrazolium and triphenyl tetrazolium chloride staining of myocardium showed loss of dehydrogenases within five to twenty minutes of ligation of the coronary artery. This loss was consistent and progressively increased at longer time intervals, the mean ischemic area mapped being 25.74 mm2 and 66.87 mm2 at five to twenty minutes and six hours respectively. Such comparison of ischemic area of myocardium at different time intervals has not been reported earlier. Autofluorescence in formalin-fixed, hematoxylin and eosin-stained sections showed positive fluorescence only after fifty to seventy-five minutes of ischemia and was patchy in distribution in the left ventricular wall even up to six hours of ligation. Examination of myocardium under fluorescent light after acridine orange staining proved to be more sensitive than autofluorescence for detecting ischemia. At five to twenty minutes, the mean ischemic area was 18.67 mm2 and by six hours it increased to 27.48 mm2.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics of calcium dobesilate in beagle dogs after repeated administration.

Many pharmacological findings suggest that repeated intravenous administration of calcium dobesilate improves myocardial lymphatic drainage, accelerates removal of degradation products and other toxic substances by increasing the number of functioning lymphatics and thus limits infarct size after experimental coronary artery occlusion. The aim of the present study was to investigate the relationship between the blood levels of calcium dobesilate and the pharmacological effect described above using the same dosage schedule. During the first six hours after intravenous administrations, at one hour interval, of three doses each of 100 mg/kg of calcium dobesilate, the average plasma level ranged from 414 micrograms/ml to 95 micrograms/ml with a plateau between the second and fourth hour. During this period, which is the most crucial for the ischemic myocardium, the effect of calcium dobesilate attained its optimum as evidenced by a statistically significant increase in the number of lymphatics visualized by lymphangiography and the reduction of infarct size measured by planimetry, by weight or by tomography. The plasma levels before the 18th hour were still higher than 10 micrograms/ml but no measurable calcium dobesilate was detected in the plasma at the 20th hour which indicates total elimination of the drug from the blood and thus precluding any risk of accumulation. The present results confirm that the doses of calcium dobesilate used in the pharmacological studies correspond to an adequate blood level.

A biochemical method for the quantitation of myocardial scarring after experimental coronary artery occlusion

The histologic examination and planimetric evaluation of tissue slices has been so far the only available technique for studying the extent of experimental myocardial infarcts in long-term studies; however, this approach is rather time-consuming when the sample size is large. This study describes a new biochemical method for the quantitation of myocardial scarring, based on the determination of left ventricular hydroxyproline, and collagen content at the end of the healing process. Accordingly, several modifications were introduced into previously existing methods for the assay of hydroxyproline: our method allows a linear estimation of hydroxyproline in the range from 0.5 to 5 micrograms, with a precision of +/- 6.1% and a day-to-day variation of +/- 10.5%. The reliability of this approach for studying infarct size has been verified in rats with coronary artery occlusion divided into a control group and in a treated group receiving nitroglycerin. The animals were killed 21 days after coronary ligation and randomly assigned for infarct size evaluation either to the histologic or the collagen method. By histology infarct size averaged 30.6 +/- 4.8% (mean +/- S.E.M.) of left ventricle (LV) in control rats and 16.2 +/- 5.8% of LV in nitroglycerin-treated animals; by the proposed alternative method left ventricular collagen content was 26.8 +/- 1.0 micrograms/mg of dry weight in control rats and 19.5 +/- 1.2 micrograms/mg of dry weight in nitroglycerin-treated animals; infarct size calculated from collagen content by a simple formula, was 37.4 +/- 2.6% of LV and 22.3 +/- 2.6% of LV, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)