Comparison between metabolic changes in local venous and coronary sinus blood after acute experimental coronary arterial occlusion

Beta-adrenergic stimulation of reperfused myocardium after 2-hour ischemia

Postischemic myocardium possesses considerable contractile and metabolic reserves, but their mobilization could result in increased cell death. We tested the hypothesis that beta-adrenergic stimulation of reperfused myocardium would increase segment work more than O2 consumption, thereby improving efficiency without increased cell death. In 16 open-chest anesthetized dogs, the left anterior descending coronary artery (LAD) was ligated for 2 h; during the reperfusion period, isoproterenol (ISO; 0.1 microg/kg/min, i.v.) was administered to nine of the animals. Regional myocardial segment length and force were measured in the anterior (LAD) and posterior circumflex coronary artery (CFX) regions of the left ventricular myocardium. Work was calculated as the integrated products of force and shortening for each region. Regional myocardial O2 consumption was obtained from LAD flow and arterial and local venous O2 saturations. Infarct size (tetrazolium) was measured in the treated and untreated hearts at the end of the experiment. In untreated hearts, the first derivative of left ventricular pressure, cardiac output, and external work were significantly depressed during reperfusion; ISO restored all values to preocclusion levels. Regional myocardial work in both LAD and CFX regions was significantly increased by ISO (from 564 +/- 207 to 1,635 +/- 543 g/mm/min in LAD, and from 753 +/- 90 to 1,426 +/- 245 g/mm/min in CFX). Efficiency (work/oxygen consumption) of the reperfused region was similarly increased. LAD flow was significantly increased by ISO, and O2 extraction was unchanged. Infarct size was 28.2 +/- 4.7% in untreated hearts and 29.0 +/- 3.5% in ISO hearts. Thus isoproterenol stimulation significantly improved both regional and global function without subsequent evidence of increased cell death.

Myocardial metabolism during increased work states in the porcine left ventricle in vivo

It is not known whether myocardial energy requirements can be increased to the degree that they exceed myocardial O2 availability in the absence of abnormalities of coronary blood flow or coronary reserve. To determine whether this form of "demand ischemia" occurs, 10 swine were subjected to pressure overload induced by aortic constriction, inotropic and chronotropic stimulation by dobutamine, and the combination of these interventions. In an additional 9 animals, intravenous adenosine was administered during the combination of constriction and dobutamine to determine whether further increases in coronary flow could be achieved and if they would attenuate the metabolic changes. Left ventricular anterior wall transmural blood flow was measured by radioactive microspheres. Energy phosphates were assessed by 31P magnetic resonance spectroscopy using the Fourier series window technique to increase the proportion of signal derived from the subendocardium. Myocardial lactate release was quantified independent of net lactate uptake using an isotopic tracer technique. The three interventions produced 39% to 195% increases in myocardial O2 uptake from control measurements. The phosphocreatine to ATP ratio (PCr/ATP), uncorrected for partial saturation, fell significantly, from 1.39 +/- 0.10 at control conditions to 1.25 +/- 0.10 with dobutamine alone and 1.15 +/- 0.08 with dobutamine plus constriction (P < .05 for both). Myocardial lactate release rose from 0.21 +/- 0.03 mumol.g-1.min-1 at control conditions to 0.45 +/- 0.05 and 0.59 +/- 0.10 mumol.g-1.min-1, respectively (P < .05 for both), with these two interventions. Although transmurally averaged left ventricular blood flow rose from 0.97 +/- 0.09 mL.g-1.min-1 at control conditions to 3.25 +/- 0.47 mL.g-1.min-1 (P < .001) and subendocardial blood flow increased from 1.02 +/- 0.09 to 2.92 +/- 0.45 mL.g-1.min-1 (P < .001) at the highest of the three increased work states, the subendocardial to subepicardial flow ratio declined progressively from 1.13 +/- 0.08 to 0.87 +/- 0.04 (P < .05). With a further increase in aortic constriction, myocardial O2 uptake and subepicardial blood flow rose, whereas subendocardial blood flow did not change, and there was a further decline in PCr/ATP and a rise in lactate release. Although adenosine increased the average myocardial blood flow during high work state from 3.79 +/- 0.91 to 6.29 +/- 1.08 mL.g-1.min-1 (P < .001), the further rise in subendocardial flow from 3.08 +/- 0.62 to 3.78 +/- 0.68 mL.g-1.min-1 was not significant, nor were the accompanying changes in PCr/ATP or lactate metabolism.(ABSTRACT TRUNCATED AT 400 WORDS)

Coronary haemodynamics and myocardial metabolism during weaning from mechanical ventilation in cardiac surgical patients

The present clinical study was undertaken to assess the alterations in myocardial metabolism and coronary haemodynamics during weaning from mechanical ventilation in postoperative cardiac surgical patients. Global and regional myocardial blood flow and metabolism were assessed using a dual port coronary sinus-great cardiac vein thermodilution catheter in 17 patients who had undergone coronary revascularization and who were being weaned from mechanical ventilation. Anaerobic myocardial metabolism, as demonstrated by the production of myocardial lactate, manifested in 8 of 17 patients during at least one of the weaning phases. There were no differences in coronary blood flow between patients who produced myocardial lactate and those who maintained aerobic cardiac metabolism. However, lactate producers exhibited larger changes in systemic vascular resistance and mean arterial pressure than the non-lactate producers. This metabolic manifestation of myocardial ischaemia was not accompanied by electrocardiographic changes of ischaemia, nor presence of chest pain, and may represent another form of silent ischaemia. We conclude that despite coronary revascularization, the myocardium may remain vulnerable to ischaemic anaerobic metabolism in the immediate postoperative period.

Myocardial lactate release during ischemia in swine. Relation to regional blood flow

To determine the relation between regional myocardial blood flow, contractile function, and myocardial lactate release during mild-to-moderate regional myocardial ischemia, nine open-chest swine were instrumented for measurement of regional myocardial blood flow (microsphere method), contractile function (sonomicrometry), and hemodynamics. L-[1-14C]Lactate or L-[U-13C]lactate was infused intravenously using a primed continuous infusion technique to quantify regional myocardial lactate release. D-[U-13C]glucose or D-[6-14C]glucose was simultaneously infused to determine the contribution of exogenous glucose to lactate release. Graded coronary ischemia (two to three levels) was created in the left anterior descending coronary arterial distribution by mechanically constricting the artery in five animals or by decreasing flow through a cannulated left anterior descending artery in four animals. In all nine animals, subendocardial blood flow was 0.99 +/- 0.21 (ml/min)/g during control and 0.34 +/- 0.14 (ml/min)/g during the most severe grade of underperfusion (p less than 0.001) in the left anterior descending coronary arterial distribution. Regional myocardial lactate release was 0.15 +/- 0.09 and 1.19 +/- 0.75 mumols/ml, respectively (p less than 0.003). A highly significant inverse correlation was observed between subendocardial blood flow and myocardial lactate release during the graded reductions in blood flow (r = -0.71, p less than 0.001). Results from sonomicrometry showed a significant reduction in contractile ventricular function in the anterior wall during the graded reductions in blood flow. The regional arterial-venous glucose difference increased significantly with underperfusion in the left anterior descending coronary arterial distribution, from 0.14 +/- 0.15 to 0.56 +/- 0.37 mumols/ml (p less than 0.003). The contribution of exogenous glucose to lactate release also increased significantly; 0.04 +/- 0.03 mumols/ml of the lactate came from exogenous glucose during control compared with 0.64 +/- 0.59 mumols/ml during the most severe underperfusion (p less than 0.02). A significant positive correlation exists between lactate release and lactate from exogenous glucose during graded underperfusion (r = 0.96, p less than 0.001). In summary, these data demonstrate a close inverse relation between regional myocardial lactate release and regional subendocardial blood flow during graded ischemia.

Validation of [1-11C]acetate as a tracer for noninvasive assessment of oxidative metabolism with positron emission tomography in normal, ischemic, postischemic, and hyperemic canine myocardium

Extraction and clearance kinetics of [1-11C]acetate were examined in 65 experiments in 30 open-chest dogs. Twenty-nine studies were performed at control, 13 during ischemia, eight after reperfusion, 13 during dipyridamole-induced hyperemia, and two during alteration of cardiac workload. [1-11C]Acetate was injected directly into the left anterior descending coronary artery, and myocardial tissue-time activity curves were recorded with a gamma probe. The single-pass extraction fraction averaged 64.2 +/- 9.7% in control, 65.3 +/- 9.1% in ischemia, 70.0 +/- 4.4% in reperfusion, and 46.5 +/- 7.4% in dipyridamole-induced hyperemia groups. 11C clearance was biexponential in all cases. The rate constant k1 for the first rapid clearance phase correlated closely with myocardial oxygen consumption (r = 0.94) in control, ischemia, reperfusion, and dipyridamole-induced hyperemia groups. Monoexponential fitting of only the first linear part of the clearance curve yielded the rate constant kmono, which also correlated with myocardial oxygen consumption (r = 0.96). Arterial lactate concentrations and the amount of free fatty acid oxygen equivalents consumed by the myocardium were shown to have a small but statistically significant impact on the relation between [1-11C]acetate clearance rate constants and myocardial oxygen consumption. The fraction of 14CO2 activity contributing to overall 14C activity leaving the myocardium after simultaneous injection of [1-14C]acetate (n = 24) was relatively high in all cases (97.4 +/- 2.5% in control, 89 +/- 2.6% in ischemia, 94.1 +/- 3.5% in reperfusion, and greater than 99% in dipyridamole groups), indicating that externally measured 11C clearance corresponds to CO2 production and thus to tricarboxylic acid cycle activity. In conclusion, the results validate the use of [1-11C]acetate as a tracer of oxidative myocardial metabolism for use with positron emission tomography.

Effects of nitroglycerin on regional O2 supply and O2 consumption in reperfused dog myocardium

This study was designed to assess whether nitroglycerin would improve the relationship between O2 supply and O2 consumption in the reperfused ischemic dog myocardium. In 16 dogs the left anterior descending coronary artery was occluded for 2 h, followed by a 4 h period of reperfusion. In 8 of the 16 dogs, an infusion of 10 micrograms/kg per min of nitroglycerin was begun 10 min prior and continued during 4 h of reperfusion. Small artery and vein O2 saturations obtained microspectrophotometrically were combined with regional blood flow measurements using radioactive microspheres to determine regional myocardial O2 consumption. In both groups, 2 h of occlusion lowered the regional flow to a similar level. In the control group, 4 h of reperfusion returned the blood flow towards normal levels, from 15 +/- 20 ml/min per 100 g (mean +/- S.D.) at the end of occlusion to 57 +/- 39 in the affected area compared to 84 +/- 32 ml/min per 100 g in the nonischemic area. In nitroglycerin treated animals, the flow increase with reperfusion was similar to the control group (12 +/- 10 to 65 +/- 33 ml/min per 100 g). O2 extraction was greater in the reperfused than in the unaffected area in both groups. However, reperfused region O2 extraction was lower in the nitroglycerin treated than control group. There was a greater number of arteries and veins with reduced O2 saturations in the control group reperfused area compared to the nonischemic area. Nitroglycerin decreased the number of low O2 saturation vessels in the reperfusion area. Reperfusion alone does not restore the ratio of O2 supply to O2 consumption to control values, while nitroglycerin significantly improves this ratio. Thus nitroglycerin appears to better match the increased flow during reperfusion with microregional O2 consumption.

Effect of reperfusion on O2 supply/consumption balance in ischemic canine left ventricle

This study was designed to assess the effects of reperfusion on regional O2 supply and O2 consumption of ischemic areas of the myocardium in 15 anesthetized open-chested dogs. The left anterior descending coronary artery (LAD) was occluded for 6 h (n = 8), 2 h (n = 5), 2-h occlusion followed by 4-h period of reperfusion (n = 7), and 10-min occlusion followed by 90-min period of reperfusion (n = 3). Small artery and vein O2 saturations obtained microspectrophotometrically were combined with regional flow measurements using radioactive microspheres to determine regional myocardial O2 consumption. Coronary occlusion for 2 or 6 h significantly reduced mean flow to 15 +/- 8 and 13 +/- 14 ml/min/100 g (mean +/- SD), respectively, in the affected LAD areas as compared to 128 +/- 26 and 113 +/- 46 ml/min/100 g in the non-ischemic areas. In the 4-h reperfusion group, reperfusion increased the average flow (60 +/- 42 ml/min/100 g). O2 extraction was greater in the ischemic area than in the unaffected area after both occlusion and 4-h reperfusion. In the affected area, O2 consumption was reduced by 84% after 6-h occlusion. Reperfusion for 4 h increased O2 consumption toward normal values. Coronary artery occlusion produced an increase in the number of arteries and veins with reduced O2 saturations and this was not affected by reperfusion. Short-term occlusion had no significant O2 supply effects after 90 min of reperfusion. It can be concluded that even though there was an increased O2 consumption as a consequence of reperfusion, O2 consumption still appeared to be flow-limited as indicated by the microregions of low O2 supply and/or high O2 extraction.

Salutary action of nicorandil, a new antianginal drug, on myocardial metabolism during ischemia and on postischemic function in a canine preparation of brief, repetitive coronary artery occlusions: comparison with isosorbide dinitrate

The effects of two antianginal drugs, nicorandil and isosorbide dinitrate (ISDN), on metabolism and function of the ischemic myocardium were studied in a preparation of multiple coronary occlusions in barbital-anesthetized dogs. The preparation consisted of three 5 min occlusions of the left anterior descending coronary artery interspersed by 30 min of reperfusion. An equihypotensive dose of nicorandil (7.5 micrograms/kg/min) or ISDN (12.5 micrograms/kg/min) was infused 15 min before and during the second occlusion period. Hemodynamics, myocardial segment shortening (%SS), tissue blood flow, and myocardial oxygen consumption were determined throughout. Uptake of free fatty acids (FFA), glucose, and lactate were determined during control and ischemic periods. At the end of the final 30 min reperfusion period, biopsy samples of transmural tissue were taken for analysis of phosphocreatine, adenine nucleotides, and total tissue water content. No major hemodynamic changes were produced by either drug except for a 5 to 10 mm Hg decrease in mean aortic pressure. Compared with untreated and ISDN-treated hearts, hearts of dogs treated with nicorandil exhibited reversal of a significant increase in FFA uptake during recurrent ischemia. This was accompanied by an attenuation of the increase in oxygen extraction and CO2 production in the ischemic zone by nicorandil, but not by ISDN. Nicorandil, but not ISDN, improved %SS during reperfusion. Endocardial ATP and total adenine nucleotides were preserved in both nicorandil- and ISDN-treated hearts. Tissue edema was also attenuated by both compounds. Thus, nicorandil improved both function and metabolism during recurrent myocardial ischemia independent of a hemodynamic effect, whereas ISDN only attenuated the loss of adenine nucleotides and increase in tissue water.

Methods for the metabolic quantification of regional myocardial ischemia

An adequate balance between oxygen supply and demand is a basic requirement for normal cardiac function. When oxygen supply does not meet the demand, progressive cellular damage occurs leading to cardiac dysfunction and, ultimately, tissue death. While traditionally "ischemia" has been defined as decreased oxygen supply secondary to a decrease in blood flow, and "hypoxia" as decreased oxygen supply secondary to a decrease in oxygen tension, this review defines ischemia in its broader sense, namely as a pathophysiologic state in which there is a lack of oxygen relative to the demand for it. In a large number of experimental studies involving the heart, there is need to promptly recognize the ischemic state, to monitor its course in vivo, and to quantify it. Because of cardiac autoregulatory mechanisms, research methods which attempt to quantify supply (e.g., measurement of myocardial blood flow) and/or demand (e.g., measurement of myocardial oxygen consumption) do not necessarily reflect the status of the balance between supply and demand. An imbalance between myocardial supply and demand is more likely to be reflected by metabolic fluxes and by the accumulation of products specific to the ischemic state. Thus, the purpose of this review is to summarize the various methods available to the cardiac surgical investigator today for the metabolic quantification of myocardial ischemia. Due to the complexity of the heart and its inherent regional differences, myocardial ischemic changes are frequently regional in nature. Thus, this review will address metabolic methods for the regional quantification of myocardial ischemia.

Evaluation of acute stress-induced regional myocardial ischemia: comparison of regional contractile and metabolic indices to easily accessible global left ventricular indices

In clinical studies stress-induced myocardial ischemia in patients with coronary artery disease is used to evaluate the severity of this disease. The discussion on the importance of some parameters measured during this intervention is controversial, other parameters are difficult to obtain. On the basis of an experimental model of stress-induced myocardial ischemia, we tried to find an index that reflects best this cardiac state. We therefore compared in eight anesthetized open-chest dogs control conditions with three other hemodynamic states with increasing imbalance between myocardial oxygen demand and oxygen supply: severe stenosis on circumflex coronary artery, 60 s cardiac sympathetic nerve stimulation (CSNS) with a severe stenosis on circumflex coronary artery, and 60 s complete occlusion of circumflex coronary artery. Using a one-way analysis of variance, we found two significantly changed parameters during the stress-induced ischemia: Regional lactate extraction was turned to production (32 +/- 4 vs. -4 +/- 1%) and the ratio of dP/dtmin to dP/dtmax was decreased (1.13 +/- 0.05 vs. 0.67 +/- 0.05; control vs. CSNS with a severe stenosis on circumflex coronary artery). We conclude that the ratio of dP/dtmin to dP/dtmax is an easily accessible, sensitive, and dynamic index for characterization of an stress-induced myocardial ischemia.

Lactate metabolism in acute myocardial infarction and its relation to regional ventricular performance

Myocardial metabolism was assessed in 20 patients with acute anterior myocardial infarction using lactate uptake (defined as (aortic lactate - great cardiac venous lactate)/aortic lactate X 100) as an index. The regional ejection fraction of the anterior wall was obtained from left ventriculography. There was a linear relation between lactate uptake and regional ejection fraction (r = 0.79, p less than 0.001). Four patients without total occlusion in the infarct vessel had a higher lactate uptake (19.6 +/- 6.7 versus 4.2 +/- 13.4%, p less than 0.05) and regional ejection fraction (26.3 +/- 7.9 versus 14.9 +/- 7.0%, p less than 0.05) than did 16 patients with total occlusion. The latter group of patients underwent intracoronary infusion of urokinase, which resulted in reperfusion in 13 patients. Lactate uptake before urokinase infusion (sample I), just after reperfusion (sample II), 30 minutes after reperfusion (sample III) and 4 weeks after reperfusion (sample IV) was 5.7 +/- 13.2, -13.9 +/- 14.7, 2.9 +/- 15.2 and 20.2 +/- 11.0%, respectively (sample I versus II and II versus III, p less than 0.01; sample I versus IV and III versus IV, p less than 0.05). The decrease in lactate uptake immediately after reperfusion, which was accompanied by an increase in creatine kinase-MB isoenzyme release into the blood, was considered to be the result of a "washout" effect. Lactate uptake was ameliorated 4 weeks later, accompanied by an improvement (from 15.1 +/- 7.1 to 23.4 +/- 7.2%, p less than 0.01) in the regional ejection fraction. It is concluded that the degree of asynergy was closely related to the extent of metabolic deterioration in myocardial infarction.

Improvement in regional myocardial O2 supply and O2 consumption by nitroglycerin during ischemia

In eight open-chest anesthetized dogs, nitroglycerin (10 micrograms/kg per min) was infused intravenously for 2 h, beginning 10 min following ligation of the left anterior descending coronary artery. Oxygen supply, (radioactive microspheres), extraction (microspectrophotometry) and consumption were determined in subepicardial and subendocardial regions of both ischemic and non-ischemic myocardium, and compared to eight control hearts. In control, coronary occlusion reduced both subepicardial and subendocardial blood flow by 49.5% and 79.5% respectively. In the presence of nitroglycerin, depression of blood flow to the occluded regions was significantly less marked (-79.5% in control and -26.6% in the nitroglycerin group in the subendocardium). O2 extraction was significantly lowered by nitroglycerin in all areas. Regional O2 consumption was significantly lower in the control occluded than non-occluded regions; no regional O2 consumption differences were observed following nitroglycerin. In the occluded regions, nitroglycerin reduced the number of veins with very low O2 saturation. It is concluded that nitroglycerin improves the O2 supply/consumption balance in ischemia by redistribution of blood flow and possibly by alterations in local O2 consumption.

Role of propranolol in improvement of the relationship between O2 supply and consumption in an ischemic region of the dog heart

Several aspects of the myocardial O(2) supply/consumption relationship were determined after coronary artery occlusion and subsequent beta-adrenergic blockade in 16 anesthetized open-chest dogs. Small artery and vein O(2) saturations, and hence extraction, were obtained microspectrophotometrically and combined with radioactive microsphere blood flow determinations to calculate regional myocardial O(2) consumption. Eight dogs remained untreated after coronary artery ligation while another group was given 2 mg/kg propranolol, 10 min after occlusion. Untreated occlusion resulted in decreased arterial and especially venous O(2) saturations, indicating an increased O(2) extraction. Ischemic O(2) consumption was reduced and the subendocardial/subepicardial consumption ratio was reversed (1.26 vs. 0.37) due to the pattern of occluded area flow. Calculated O(2) supply/consumption also decreased. Propranolol produced no significant changes in volume or distribution of flow within the ischemic region while reducing flow, extraction, and consumption in the unoccluded region. The heterogeneity of arterial and particularly venous O(2) saturations within the ischemic region decreased dramatically. Venous O(2) saturations were elevated relative to the control group resulting in a reduced O(2) extraction. The decrease in heterogeneity of arterial and venous O(2) saturations suggest that propranolol eliminates microregions of relatively high O(2) extraction, consumption, and/or a majority of vessels with extremely low flow. This leads to a significant improvement in the O(2) supply/consumption ratio in the ischemic myocardium of the dog. This may be due to a reduction in the heterogeneity and level of beta(1)-adrenergic receptor activity within the heart.

Uptake and turnover of L-(13N)-glutamate in the normal human heart and in patients with coronary artery disease

L-(13N)-glutamate (4-8 mCi) was administered IV to 27 patients with coronary artery disease and to 12 control subjects. Quantitative whole body imaging of the 13N label was performed in 31 individuals at different time intervals following the injection. Initial uptake of the total myocardium was estimated to be 5.0 +/- 0.88% of the dose. Standardized areas of reduced size on the projection plane contained 2.38 +2- 0.41% of the total dose in control subjects and 2.67 +/- 0.49% in coronary patients. Subsequent imaging exhibited significant differences in the dynamic behavior of both groups: 13N activity loss within 10 min was 3.2 +/- 4.2% of the initial value in control subjects and 16.0 +/- 9.8% in coronary patients. In individual cases a high myocardial accumulation of the 13N label was observed in regions of reduced 201Tl uptake. The findings are explained by an augmented extraction efficiency in cases of flow reduction. Glutamate utilization may be involved in metabolic adaptations of the myocardium to chronic or repetitive ischemia and may be worthy of further investigation by positron emission tomography.

Tissue and coronary venous pH in ischemic canine myocardium

The relationship between changes in myocardial tissue pH and local coronary venous pH during and after transient occlusion of the left anterior descending artery was investigated in 6 open chested anesthesized dogs. Tissue pH was recorded with a needle pH electrode, and coronary venous pH with a specially designed catheter tip pH electrode. Myocardial tissue pH fell steadily after coronary occlusion, and had fallen by 0.107 +/- 0.043 pH units (mean +/- SD, n = 12, occlusions) after 150 s. On reperfusion there was a further small fall in tissue pH to 0.138 +/- 0.035 units before tissue pH returned to control. In contrast, the fall of coronary venous pH during ischemia was small (0.15 +/- 0.027 after 150 s, n = 12 occlusions). Within 5 s of reperfusion, a large fall in venous pH occurred, reaching a maximum of 0.150 +/- 0.072 at 20-30 s after reperfusion. During ischemia changes in tissue pH are poorly represented by changes in coronary venous pH. The size of early change of venous pH during the reperfusion washout of retained metabolites is a better estimate of the fall of tissue pH. Measurement of metabolites in the coronary sinus of man during the washout after the end of an ischemic intervention such as a trial pacing is superior to measurements performed during pacing in providing biochemical evidence of myocardial ischemia.

Effect of hyaluronidase on substrate exchange and blood flow in the ischaemic myocardium of the dog

The mechanism for reduced myocardial ischaemic injury by hyaluronidase was studied in open chest anaesthetized dogs. Repeated coronary artery occlusions were performed and the effect of hyaluronidase (225 NF units per kg) was studied during infusion of noradrenaline 0.125 mg/kg . min. Ischaemic injury was measured as the sum of ST-segment elevations (sigma ST) at 10-15 sites. Regional myocardial blood flow was determined by tracer microspheres. Blood for metabolic studies was sampled from a local coronary vein draining ischaemic tissue and from the coronary sinus draining predominantly non-ischaemic tissue. Hyaluronidase reduced sigma ST and increased subepicardial and transmural blood flow in ischaemic myocardium, but flow was not significantly changed in the ischaemic subendocardium or in non-ischaemic myocardium. Hyaluronidase had no significant effect on arterio-local venous differences of oxygen, glucose, lactate or free fatty acids across the ischaemic myocardium. In conclusion, reduction of myocardial ischaemic injury by hyaluronidase can be explained by increased collateral blood flow and not by an effect on fluxes of substrates across the ischaemic myocardium.

Lactate metabolism as a prognostic index in unstable angina

Fifty patients evaluated because of unstable angina were followed up for a mean period of 63.7 months. Analysis of transmyocardial lactate metabolism was performed in all patients in addition to coronary angiography and ventriculography. All patients had at least one coronary lesion of great than 75%. Although technically feasible, aortocoronary bypass surgery was not performed on initial hospitalization and all patients were treated medically. Patients were divided into two groups on the basis of lactate metabolism; group A lactate production great than 15%, group B lactate production less than 15% or lactate extraction. There was no difference in left ventricular end-diastolic pressure or ejection fraction between the two groups. A coronary score index was higher in group A than group B (5.45 +/- 2.2 vs 3.13 +/- 1.2) (p less than 0.05). The incidence of myocardial infarction was higher in group A than group B in hospital (44.4% vs. 4.3%, p less than 0.05), and long term (70.3% vs. 17.3%, p less than 0.05). Mortality was higher in group A than group B in hospital (25.9% vs. 0%, p less than 0.05) and long term (66.7% vs. 13%, p less than 0.05). Analysis of lactate metabolism thus provides a prognostic index in unstable angina which complements information obtained by coronary angiography and ventriculography.

The effect of elevated arterial free fatty acid concentrations on hemodynamics and myocardial metabolism and blood flow during ischemia

In the present investigation the effect of elevated arterial free fatty acid (FFA) concentrations on regional myocardial blood flow (MBF), myocardial metabolism and hemodynamics during ischemia was studied in anesthetized dogs. Ischemia was induced by stenosis of the left interventricular coronary artery. Mean poststenotic coronary artery pressure was kept constant during ischemia. FFA concentrations were elevated by intravenous injection of heparin (group I), intralipid (group II) or both substances (group III). After elevation of FFA concentrations by heparin alone or together with intralipid, heart rate gradually increased, while aortic pressure tended to decrease. Slight elevation of arterial FFA levels (up to 0.30 mM, group I, and up to 0.53 mM, group II) had no significant effect on total MBF and uptake of glucose, FFA, and oxygen or release of lactate in the ischemic myocardium. However, elevating arterial FFA levels up to 0.81 mM (Group III), significantly decreased total MBF (6%), endo/epicardial blood flow ratio (13%), and oxygen uptake (34%) in the ischemic myocardium and resulted in release of lactate from this area. The release of potassium, inorganic phosphate and H+ as well as plasma CO2 concentration were not influenced. Neither was the uptake of glucose and FFA. These findings suggest that elevated arterial FFA concentrations can decrease MBF and augment lactate production in the ischemic myocardium.

Effect of myocardial ischaemia and antilipolytic agents on lipolysis and fatty acid metabolism in the in situ dog heart

Myocardial metabolism was studied in open-chest dogs before and during induction of myocardial ischaemia by coronary artery occlusion. Blood was sampled from a local coronary vein draining ischaemic tissue and from coronary sinus draining predominantly nonischaemic tissue. In the basal state, induction of myocardial ischaemia stimulated myocardial lipolysis as shown by release of glycerol from the ischaemic zone. During isoprenaline infusion, free fatty acids (FFA) extraction across the ischaemic myocardium was substantially increased, but no glycerol release occurred. Pretreatment with nicotinic acid or sodium salicylate markedly depressed FFA extraction across ischaemic myocardium, both during basal and isoprenaline stimulated lipolysis and nicotinic acid most likely inhibited lipolysis in the ischaemic zone. Thus, reduced severity of acute ischaemic injury by antilipolytic treatment might be due to a combination of inhibited myocardial lipolysis and reduced FFA extraction.

Myocardial release of lactate, inosine and hypoxanthine during atrial pacing and exercise-induced angina

The coronary venous efflux of lactate, inosine and hypoxanthine during pacing-induced angina has been compared with myocardial extraction of the catabolites during exercise-induced angina. Inosine and hypoxanthine were analyzed by enzyme assay after separation by column chromatography. Myocardial lactate extraction at rest (15 +/- 9%, mean +/- SD) was converted to production levels (-34 +/- 26%) during pacing-induced angina (p less than 0.0005) and increased (24 +/- 13%) during exercise (p less than 0.05). The arterial values at rest (850 +/- 330 mumol/1) were unchanged during pacing and increased five-fold during exercise (4380 +/- 1860 mumol/1). The mean myocardial inosine extraction at rest (33 +/- 10%) was transformed to release values (-41 +/- 30%) during pacing (p less than 0.0005) as well as during exercise (-20 +/- 27%) (p less than 0.0005). The hypoxanthine extraction at rest (25 +/- 11%) decreased during pacing (-7.8 +/- 29%) (p less than 0.0025) and exercise (10 +/- 25%) (NS). The slight increase of arterial inosine and hypoxanthine values was not significant. Myocardially produced lactate, a sensitive marker of pacing-induced ischemia, was obscured by elevated arterial concentrations during exercise. However, inosine significantly correlated with lactate during pacing, and was useful in detecting ischemic myocardial energy deficiency during exercise-induced angina.

The effect of nitroglycerin on myocardial release of inosine, hypoxanthine and lactate during pacing-induced angina

The efficacy of nitroglycerin as an antianginal drug has been evaluated by calculation of myocardial extraction and production values of lactate and the adenosine triphosphate (ATP) catabolites inosine and hypoxanthine. Coronary venous and arterial blood was sampled at rest, during pacing-induced angina and 4--6 min after nitroglycerin at identical paced heart rates for enzymatic assay of inosine and hypoxanthine after separation by column chromatography and for determination of lactate. Sublingual nitroglycerin given to 10 patients with coronary artery disease decreased coronary venous lactate values from 1175 +/- 320 mumol/l during pacing-induced angina to 950 +/- 240 mumol/l (p less than 0.05). The calculated myocardial lactate production during angina (-31 +/- 19%) diminished after nitroglycerin (-1.7 +/- 22%) (p less than 0.0025). Coronary venous inosine values during angina (1275 +/- 865 nmol/l) decreased after nitroglycerin (795 +/- 555 nmol/l) (p = n.s.), the arterial values (885 +/- 610 nmol/l) increased (960 +/- 580 nmol/l) (p = n.s.), the myocardial inosine release (-26 +/- 20%) changed to extraction values (19 +/- 19%) (p less than 0.0005). Coronary venous hypoxanthine values during angina (1540 +/- 1035 nmol/l) were reduced (1110 +/- 675 nmol/l) (p = n.s.); the arterial values (1625 +/- 1050 nmol/l) decreased (1510 +/- 935 nmol/l) (p = n.s.), the myocardial hypoxanthine extraction (0.3 +/- 29%) with a wide individual variability increased after nitroglycerin (24 +/- 13%) (p less than 0.025). The myocardial release of inosine and lactate during severe angina with significant positive correlation (r = 0.66, p less than 0.0025) demonstrates that anaerobic glycolysis is accompanied by ATP breakdown. The unchanged myocardial inosine and hypoxanthine extraction after nitroglycerin indicates that nitroglycerin is capable of attenuating this effect. In spite of reduced mean myocardial lactate production after nitroglycerin ischemic myocardial energy deficiency may be less marked. Thus, the enhanced myocardial inosine uptake may be one factor contributing the beneficial effects of nitroglycerin including the improvement of myocardial oxygen balance.

Early changes in regional and global left ventricular function induced by graded reductions in regional coronary perfusion

To determine the sequence of changes in segmental myocardial function, regional lactate metabolism and global left ventricular function induced by mild regional ischemia, blood flow in the left anterior descending coronary artery of 10 dogs was reduced by 10 percent decrements with use of a screw clamp. At each level of flow, segmental mechanical function and regional metabolism were assessed, the former with use of a mercury-in-Silastic length gauge and the latter with transmyocardial lactate balance measurements obtained with sampling from the anterior interventricular vein. Coronary arterial flow at the onset of regional lactate production was 48 +/- 4 percent (mean +/- standard error of the mean) of the control value. The onset of segmental mechanical dysfunction coincided with the onset of lactate production. Epicardial S-T segment abnormalities over the ischemic zone usually could not be detected until coronary flow was further reduced. After the onset of regional ischemia there was a linear correlation between coronary arterial flow and regional lactate production. At the onset of mild regional ischemia, defined as the onset of regional lactate production, no significant or directionally consistent changes were noted in standard measurements of global left ventricular performance, including heart rate, mean aortic pressure, left ventricular end-diastolic pressure, cardiac output, stroke volume, stroke work and peak positive dP/dt (maximal rate of rise of pressure). However, peak negative dP/dt (maximal rate of pressure decrease) decreased from 99 +/- 2 to 89 +/- 3 percent of the control value (P less than 0.0005) coincident with the onset of ischemia. It is hypothesized that dyssynchronous wall motion in the ischemic zone during isometric relaxation accounts for this decrease in peak negative dP/dt.

Alterations of myocardial amino acid metabolism in chronic ischemic heart disease

Arteriovenous differences (A-V) of all naturally occurring amino acids, lactate, and oxygen were measured simultaneously with coronary sinus blood flow (CSBF) in 8 normal subjects and 11 patients with coronary artery disease at rest and during pacing stress. Mean values for CSBF and myocardial oxygen consumptions (MVO2) for the two groups were similar at rest and during pacing, although mean CSBF and MVO2 increased significantly in both groups in the paced as compared to the rest state. Alanine (ala) was the only amino acid released by the myocardium, while only glutamic acid(glu) demonstrated uptake. Mean A-V ala was negative at rest in the control and coronary disease groups (-4.8+/-3.8 vs. -22.0+/-3.0 nmol/ml, respectively), but was significantly more negative in the coronary group (P less than 0.001) and not statistically different than zero in the normals. A-V ala became significantly negative with pacing in the normals (-10.0+/-4.3 nmol/ml), remained unchanged in the coronary group (-23.0+/-2.9 nmol/ml), and was significantly more negative in the coronary group (P less than 0.05). Calculation of data on the basis of net ala flux ([A-V] X [CSBF X hematocrit]) yielded similar results as that obtained with A-V differences. A-V glu was significantly positive in normals (27.7 +/- 8.9 nmol/ml, P less than 0.01) and coronary patients (59.9 +/- 8.9 nmol/ml, P less than 0.01) at rest but significantly greater in the latter group (P less than 0.001). With pacing, A-V glu remained significantly greater than zero in coronary patients (35.3 +/- 6.3 nmol/ml) and decreased to zero in the normals (4.3 +/- 11.8 nmol/ml). Calculation of net glu flux (nmol/min) at rest yielded data similar to that based on A-V difference. With pacing, net glu flux in the coronary patients did not decrease due to the augmentation of CSBF. No relation between A-V glu or ala and CSBF, MVO2 or A-V lactate was noted. The data demonstrate that specific alterations of myocardial amino acid metabolism characterize patients with chronic ischemic heart disease.

Effect of glucose-insulin-potassium infusions on arteriovenous differences of glucose of free fatty acids and on tissue metabolic changes in dogs with developing myocardial infarction

Glucose-insulin-potassium infusions were given to dogs for 6 hours, starting 30 minutes after ligation of the left anterior descending coronary artery. Effects on substrate arteriovenous differences, indexes of ischemic damage and other tissue metabolic changes were compared with changes in dogs with comparable ligations but no infusions. Glucose-insulin-potassium increased the arteriovenous difference of glucose, decreased that of free fatty acid and decreased the arterial free fatty acid/albumin molar ratio. Glucose-insulin-potassium accelerated the rate of fall of the epicardial S-T segment in the infarct zone and prevented the small rise in S-T segment found in the perlinfarct and nonischemic zones. Glucose-insulin-potassium increased the tissue content of glycogen in peripheral infarct, periinfarct and nonischemic zones; increased tissue potassium ion/sodium ion ratios in epicardial infarct zones and in the periinfarct zone; increased adenosine triphosphate in the endocardial infarct zone; decreased inorganic phosphate in the periinfarct and nonischemic zones and in the endocardial infarct zone; and increased lactate in the central infarct and nonischemic zones. The phosphate potential increased in the periinfarct and nonischemic zones. Thus, many glucose-insulin-potassium effects were greater in the peripheral infarct and especially the periinfarct zones. Although increased anaerobic metabolism with lactate production could not be excluded as a mode of action of glucose-insulin-potassium, estimated rates of anaerobic glycolysis were very low, suggesting that other effects such as increased aerobic glycolysis decreased extraction of free fatty acid by the heart, increased tissue glycogen or a "membrane" effect might be of major importance.

Prinzmetal's angina with coronary artery spasm. Angiographic, pharmacologic, metabolic and radionuclide perfusion studies

We studied the effects of coronary artery spasm on perfusion of the microvasculature in a patient with Prinzmetal's angina. Intracoronary injections of 99mTc and 131I-labelled macroaggregated human serum albumin were performed (1) at rest, (2) during spontaneous angina, (3) after the administration of nitroglycerin and (4) during pacing-induced spasm and the resultant scans compared. The resting scan was normal. Pain and spasm were associated with a perfusion defect that was localized to the anterior and inferior walls of the left ventricle. The localization of the perfusion defect corresponded with angiographically demonstrated spasm involving left anterior descending and distal circumflex coronary arteries. A subsequent myocardial infarction was localized by 43K scanning to the same perfusion area. Metabolic and parasympathetic stimulation studies were performed but were inconclusive. The patient's recurrent pains were ultimately controlled with large oral doses of isosorbide dinitrate.

Beneficial metabolic effects of methylprednisolone sodium succinate in acute myocardial ischemia

The metabolic and hemodynamic effects of methylprednisolone sodium succinate (40 mg/kg body weight) after acute myocardial ischemia were determined in 24 heparinized mongrel dogs. Myocardial ischemia was produced by ligation of the left anterior descending coronary artery. Catheters in the coronary sinus and the vein draining the left anterior descending coronary arterial area were used to collect blood samples from nonischemic and ischemic myocardium. Lactate, pyruvate, glucose, free fatty acids and oxygen were measured in arterial and venous blood from ischemic and nonischemic areas before and 3, 30 and 60 minutes after myocardial ischemia in animals with (Group II) and without (Group I) steroid treatment. In both Groups I and II glucose, lactate, free fatty acids, oxygen and coronary blood flow in nonischemic areas were not significantly changed, whereas glucose uptake in ischemic areas was significantly increased with myocardial ischemia and remained elevated. In Group I lactate uptake in ischemic areas became negative after coronary arterial ligation and remained so; in Group II, it increased after 30 (70%) and 60 (111%) minutes. Free fatty acid uptake in ischemic areas was reduced after myocardial ischemia in Group I, but in Group II it increased after 30 (224%) and 60 minutes (173%), and there was a concomitant increase in oxygen uptake. Pyruvate uptake in nonischemic areas decreased after 60 minutes in Group I, whereas it was reduced after 30 (68%) and 60 minutes (513%) in Group II. The changes were similar in ischemic myocardium. There were no significant changes in hemodynamic indexes. Coronary blood flow in ischemic areas decreased in Group I after myocardial ischemia and further after 30 and 60 minutes, but in Group II it increased after 30 (82%) and 60 minutes (53%). The data indicate that administration of methylprednisolone results in improved collateral blood flow into the infarcted area and a significantly improved metabolic response of ischemic myocardium. The glucocorticoid may also have a direct benefical effect on carbohydrate metabolism and cause the increased pyruvate neccesary to maintain the generation of energy-producing substrates. The results also suggest that methylprednisolone increases cell survival time and results in greater salvage of ischemic myocardium.

Influence of vasodilators upon function and metabolism of ischemic myocardium

Although the systemic hemodynamic effects of vasodilators such as nitroprusside, phentolamine and nitrates are well known, relatively little information is available regarding their effects upon the function and metabolism of ischemic myocardium. Experimental and clinical studies indicate that vasodilators improve the mechanical performance of regional ischemic myocardium, probably by simultaneous reduction of peripheral resistance and reduction of the degree of ischemia. The majority of evidence, although still controversial, seems to indicate that myocardial perfusion can also be increased, particularly when coronary collateral vessels are present. Concomitant reduction in preload contributes to reduced oxygen demand, as evidenced by findings of reduced oxygen extraction. Thus, the balance of the oxygen supply and demand may be improved as indicated by decreases in lactate production. In addition, limited evidence in experimental animals and man suggests that vasodilators may also reduce the extent of myocardial injury as measured by S-T segment mapping and the creatine phosphokinase (CPK) release technique. However, these effects are contingent upon the arterial pressure response, and directionally opposite results may be anticipated if hypotension occurs. Since the mechanism of action of vasodilators is reasonably well understood, vasodilator therapy can be administered safely in anticipation of both improvement in total cardiac performance and a decrease in severity of ischemia.

Characterization of the ischemic process by regional metabolism

The myocardial cell requires energy for contractile activity and for the work of internal maintenance. With the onset of ischemia mechanical performance is compromised. If the ischemia is severe and persistent, the energy necessary to maintain the internal millieu proves inadequate and cell death ensues. Ischemic heart disease is a regional phenomenon with normal and abnormal cell metabolism occurring side by side. The ischemic cell demonstrates hemodynamic, electrical and biochemical instability; its passage from a state of reversible to irreversible injury may persist for as long as 7 days and offers an opportunity to introduce interventions that may protect it and reduce ultimate infarct size. There is as yet no adequate objective means for predicting the mass of infarcted tissue. However, studies of regional metabolism, if properly conducted, may help define the adequacy of coronary vascular reserve and characterize the ischemic process. Current techniques utilize a myocardial pacing stress to induce an ischemic response. Although virtually every metabolic pathway is disrupted by severe ischemia, the assay of selected metabolities in arterial and coronary venous blood samples has provided information of diagnostic significance.

Regional differences in lactate concentration in experimental myocardial infarction

Lacate concentrations were measured in blood from (a) coronary veins within ischaemic myocardium and (b) veins nearer to the coronary vein, for periods of up to 2 1/2 hours after ligation of the left anterior descending artery in dogs. Concentrations at (a) were three to four times higher than at (b), while blood sampled simultaneously from two veins at (a) yielded similar concentrations of lactate. At 2 1/2 hours after ligation the veno-arterial difference of lactate concentration in blood from (a) was about one half of the difference at 15 minutes. Lactate concentration at (a) was approximately twice as great when the area of ischaemic myocardium drained by the vein was large (18 not equal to 1% of heart weight) than when it was small (6 not equal to 1% of heart weight). No close correlation was apparent between the height of epicardial ST-segment elevation and the level of lactate release. These experiments extend previous observations that changes in lactate concentration at a given site may reflect changes in venous dilution, rather than in the rate of production of lactate, and emphasize that caution is necessary in interpretation of changes in concentrations of metabolites in coronary sinus blood after acute myocardial infarction in man.

Metabolism of free fatty acids, glucose and catecholamines in acute myocardial infarction. Relation to myocardial ischemia and infarct size

The myocardial metabolism of free fatty acids, glucose and catecholamines is reviewed in relation to current trends in the therapy of experimental myocardial infarction. Major modifications in the metabolism of free fatty acids, glucose and catecholamines have already been found after acute myocardial infarction in man, and animal experimental data suggest that such metabolic changes might play a role in the modification of infarct size and sometimes in the development of arrhythmias. However, animal experiments often represent extreme situations and the therapeutic use in man of agents to modify the metabolism of free fatty acids, glucose or catecholamines after myocardial infarction needs intensive investigation before general application. The sum total of the evidence from animal experiments suggests that increased circulating concentrations of free fatty acids and catecholamines, if sufficiently high, may be harmful rather than helpful to the outcome of acute myocardial infarction, and that increased provision of glucose (as glucose, insulin and potassium) may be beneficial. Reservations to these conclusions are that the concentrations used appear to be important factors in catecholamine and free fatty acid effects, and that the mechanism of action of glucose-insulin-potassium is more complex than originally thought.

Changes in coronary venous inosine concentration and myocardial wall thickening during regional ischemia in the pig

Correlations between local mechanical and metabolic events were studied during a partial decrease in flow in the left anterior descending coronary artery in 14 open-chest pigs. A decrease in flow to 28% (19-39%) of the control value was achieved with an adjustable screw clamp. A flow probe was placed around the artery. Blood samples were taken from the regional anterior coronary vein and the femoral artery. Myocardial wall thickening was measured with a harpoon type of mercury strain gauge. During ischemia, systolic myocardial wall thickening decreased to 44.5 ± 5.1% ( SE ) of its control value ( P < 0.001). The mean concentrations of plasma potassium and whole blood inosine, hypoxanthine, and lactate in three serial 2-minute samples obtained during a 6-minute control period were compared with those obtained during a 6-minute period of partial occlusion. During ischemia, venous inosine concentration increased from 10.9 ± 0.7 µ M to 18.5 ± 1.8 µM ( P < 0.005), venous hypoxanthine concentration increased from 28.5 ± 1.4 µ M to 33.0 ± 1.5 µ M ( P < 0.005), venous potassium concentration increased from 3.77 ± 0.10 m M to 4.08 ± 0.13 m M ( P < 0.001), and venous lactate concentration increased from 1.04 ± 0.19 m M to 1.52 ± 0.17 m M ( P < 0.001). The arterial level of potassium increased very little. The arterial concentration of the other compounds did not change significantly during the 6-minute period of ischemia. Myocardial lactate extraction changed from a control value of 42.6 ± 6.7% to -4.6 = 12.5% ( P < 0.05). A negative correlation ( r s = -0.79, P < 0.01) was observed between venous inosine concentration and myocardial wall thickening (percent of control) during ischemia. This study indicates that the local venous inosine concentration is a sensitive indicator of regional myocardial ischemia in the pig.

Myocardial balance of inorganic phosphate and enzymes in man. Effects of tachycardia and ischemia

The effects of atrial pacing on the cardiac balance of inorganic phosphate (P i ) were studied during control, atrial pacing, and recovery periods in 29 patients. Group A (n = 18) who had roentgenographically demonstrated coronary artery disease (CAD) developed angina during pacing, and showed mean myocardial lactate (L) production, abnormal left ventricular end-diastolic pressure (LVEDP) and ST segment depression. Group NA (n = 11), composed of six patients with CAD and five subjects with no demonstrable cardiac disease, had normal lactate metabolism, LVEDP, and ST segments during pacing. In addition, blood levels of two enzymes were determined: creatine phosphokinase (CPK) in nine patients of Group A and six patients of Group NA, and glutamic oxaloacetic transaminase (GOT) in eight patients of each group.

During control, small uptake of P i was observed in both groups. During pacing, Group A showed first a fall and then abolition of mean P i uptake, and during the early recovery period, a small loss of this ion was observed. Although there was a good correlation between L and P i uptakes ( r = 0.86, P < 0.001) throughout the study, P i loss, which occurred in 55% of patients in Group A, appeared to be a less reliable index of myocardial anaerobiosis than L production, which occurred in 72%. No consistent changes in P i balance were observed in Group NA. The only significant enzymatic change was the small but sudden and significant rise of mean CPK levels in coronary sinus (CS) blood above the arterial levels in five patients of Group A during the first 6 min of pacing. These data show that during pacing-induced angina the human heart loses P i . In addition, these preliminary observations on the CS CPK levels during pacing in the angina patients suggest that the stress of tachycardia and ischemia may facilitate the escape of this enzyme from the heart.