Effect of pharmacologic agents on the function of the ischemic heart

Effect of cardioselective beta-blockade on heart function and chest pain in acute myocardial infarction

Systolic time intervals and the a/H ratio were recorded in 20 patients with uncomplicated acute myocardial infarction over a period of five days. The initial high heart rate and systolic blood pressure and the short PEP and ICT indicating a sympathetic overactivity were spontaneously normalized during the first week of infarction. LVET was reduced indicating a fall in stroke volume and the a/H ratio was unchanged at the high levels suggestive of elevated preload or LVEDP. In 10 patients with acute myocardial infarction and recurrent chest pain recordings on noninvasive parameters were made before and 30 min after intravenous injection of practolol. In addition, 7 patients with chest pain, classified as acute myocardial infarction, were given practolol. The average dose of practolol was 17.9 mg ranging from 5 to 30 mg. An almost immediate and pronounced relief of pain was observed in all patients and no signs of impaired left ventricular function appeared. The product of systolic blood pressure and heart rate was decreased by practolol and the PEP and the ICT were prolonged to normal values while no changes were seen in LVET and a/H ratio. On 126 occasions practolol was given in dosages ranging from 5 to 30 mg (mean 8 mg) to 75 patients with acute myocardial infarction and recurrent chest pain. A satisfactory pain relief was seen on 108 occasions. It is suggested that an inappropriate sympathetic overactivity is an important factor in provoking recurrent chest pain in acute myocardial infarction. Administration of the beta-adrenergic blocking agent practolol resulted in pain relief due to reduction of heart work and in severity of myocardial ischemia. The beta-blocking agent was well tolerated in the present study. Continuous beta-blockade during the whole hospital stay to patients with acute myocardial infarction seems to be a very attractive therapy in order to preserve the ischemic myocardium and limit the size of infarction.

Factors modifying ischemic injury in the isolated rat heart

The extent of ischemic injury has been studied in the isolated working rat heart utilizing an aortic ball valve that reduces the coronary flow. A number of factors were tested including high heart rate, noradrenaline, acidosis, alkalosis, high afterload, beta-blockade, glucose-insulin-potassium (GIK), palmitate and methylprednisolone. Mechanical performance, myocardial contents of ATP, creatine phosphate, glycogen and lactate and the leakage of creatine phosphokinase (CK) from the myocardium to the perfusion buffer were measured and used for determination of the ischemic injury. Tachycardia, noradrenaline and palmitate are factors that markedly increase the ischemic injury in this preparation. GIK and probably metoprolol decrease the release of CK compared with the controls.

The importance of mechanical performance for development of myocardial infarction in man

In studies using an experimental infarction as a model it has been shown that factors increasing myocardial oxygen consumption will increase the size of infarction, while factors reducing the oxygen consumption have the opposite effect. The presence of catecholamines might be most important. It is suggested that local release of noradrenaline from the sympathetic nerve endings in ischemic myocardium can induce vigorous contractions and deleterious ischemia and result in cellular necrosis. A retrospective study was performed in 81 patients hospitalized in Göteborg in 1964-1965 due to attacks of severe chest pain with no previous documented myocardial infarction. In 31 of these patients definite congestive heart failure was seen at hospitalization or developed later. During 10 years of follow up the mortality was 48 per cent and an acute myocardial infarction was found in 64 per cent of the patients without congestive heart failure. In patients with congestive heart failure the mortality was 42 per cent, and 6.4 per cent had an acute myocardial infarction. The poor mechanical performance and a lower myocardial content of noradrenaline of the failing heart might protect from the acute myocardial infarction and instead be predisposed to a slow degeneration, pump failure, and serious arrhythmias. Severe angina pectoris and congestive heart failure might represent opposite ends of the spectrum of ischemic heart disease with similar degrees of luminal narrowing of the coronary arteries.

Early intravenous administration of metoprolol enhances myocardial salvage by thrombolysis with recombinant tissue-type plasminogen activator after thrombotic coronary artery occlusion in the dog by improvement of the collateral blood flow to the area at risk

OBJECTIVES

We studied the effects of beta 1-adrenergic blockade preceding thrombolysis on hemodynamic variables, myocardial blood flow and infarct size in a canine model of thrombotic occlusion of the left anterior descending coronary artery.

BACKGROUND

Previous work suggested a reduction in infarct size and improvement in left ventricular function by intravenous beta-blockade preceding thrombolysis.

METHODS

Experiments were conducted in 34 anesthetized dogs; 17 received 0.975 mg/kg body weight of metoprolol intravenously starting 15 min after occlusion, and thrombolysis was initiated 60 min after occlusion. Seventeen dogs received saline solution followed by thrombolysis. Coronary blood flow was measured by radioactive microspheres, infarct size by a dye method, hemodynamic variables by catheter-tipped pressure transducers and cardiac output by the thermodilution method.

RESULTS

Infarct size in metoprolol- and placebo-treated dogs was 23.62 +/- 18.04% and 41.50 +/- 16.03% of area at risk, respectively (p < 0.01). Before occlusion, myocardial blood flow and hemodynamic variables were similar. Sixty minutes after occlusion, cardiac output (1.94 +/- 0.41 vs. 2.32 +/- 0.68 liters/min, p < 0.01) was lower in the metoprolol-treated dogs. Collateral flow to the area at risk (17.27 +/- 7.44 vs. 10.25 +/- 5.33) and to its epicardial (21.68 +/- 8.04 vs. 11.5 +/- 6.10), midmyocardial (14.30 +/- 8.63 vs. 7.35 +/- 4.94) and endocardial (13.18 +/- 8.21 vs. 6.26 +/- 5.34 cm3/min per 100 g) layers was higher (p < or = 0.05) in the metoprolol-treated dogs. The ratio of epicardial flow area at risk/circumflex territory was inversely correlated to infarct size (r = -0.69, p < 0.01). After 5 min of occlusion, collateral flow was comparable in the five dogs of each group; over the next 55 min it remained constant in the metoprolol group but decreased in the placebo dogs.

CONCLUSIONS

Intravenous metoprolol, administered before thrombolysis, enhances infarct size limitation, partly by improvement of collateral flow to area at risk.

Beta 2-mediated changes in central haemodynamics, coronary circulation and myocardial metabolism in canine

The combined effect of terbutaline on systemic and coronary circulation was investigated in dogs to clarify its influence on myocardial oxygen supply and lactate balance. The dogs were anaesthetized and the chest opened. Coronary sinus blood flow and cardiac output were monitored by thermodilution, aortic pressure was measured by tip-transducer and heart rate by RR-interval on ECG, coronary sinus blood were analyzed for lactate, oxygen and carbon dioxide. Terbutaline caused a substantial systemic vasodilation and an increased heart rate, the total external cardiac work increased to a minor degree. Terbutaline increased arterial lactate concentration. Coronary vascular resistance was reduced after terbutaline. Even if myocardial perfusion pressure was reduced and an increased external cardiac work was present, no signs of myocardial distress was observed in lactate metabolism or coronary sinus oxygen content. In fact a tendency to increased myocardial aerobic metabolism was observed, as myocardial lactate consumption increased after terbutaline. Terbutaline seems to be a coronary vasodilator in dogs. However, the demand for oxygen secondary to both an increase in cardiac work and aerobic metabolism can be hazardous to the potentially ischaemic myocardium.

Is inotropic therapy appropriate for patients with chronic congestive heart failure? Or is the digitalis leaf withering?

The appropriateness of inotropic therapy in chronic heart failure was examined by critically reviewing five assumptions upon which this form of therapy has been justified. Only the first, that cardiac performance can be acutely improved by inotropic therapy, has been empirically proven. That such acute improvement is sustained appears to be true with non-catecholamine agents whereas the chronic haemodynamic efficacy of oral catecholamines remains in doubt. That any inotropic agent can improve exercise tolerance, make the patient feel better, or effect a change without deleteriously affecting the myocyte is very much in doubt. Thus, although the prospect of using powerful inotropic therapy in the patient with heart failure is theoretically appealing, its utility remains to be proven.

Hemodynamic advantage of combined administration of oral ibopamine and nitroprusside in patients with ischemic and idiopathic congestive cardiomyopathy

The hemodynamic effects of combined administration of ibopamine (Ib) (150 mg orally) with nitroprusside (NP) (50-150 micrograms/min intravenously) were compared with those of NP alone in 17 patients with severe congestive heart failure due to coronary artery disease (7 patients) or idiopathic cardiomyopathy (10 patients). Hemodynamic measurements were obtained using a Swan-Ganz thermodilution catheter and a bedside thermodilution cardiac output computer. Nitroprusside alone produced a significant decrease (-12.4%) in mean arterial pressure, mean pulmonary arterial pressure (-28.3%), and systemic vascular resistance (-22.6%), and a significant increase in stroke volume index (23.1%). The administration of combined NP and Ib produced a further significant increase of stroke volume index (20.1%) with a concomitant and significant reduction of systemic vascular resistance (-19.4%); heart rate, mean systemic and pulmonary arterial pressures did not change significantly from the values observed with NP alone. Moreover, stroke work index, although not significantly modified with the vasodilator alone, was significantly increased over control values with NP + Ib association. Although NP alone induced similar effects in both the ischemic and idiopathic cardiomyopathies, the association of Ib gave a more favorable, though not significant, hemodynamic response in the subjects with primitive cardiomyopathy than in the ischemic ones. Thus, the association of Ib to NP therapy, in patients with congestive heart failure, further increases stroke volume index and stroke work index with a concomitant reduction of systemic vascular resistance, without any significant change in mean systemic and pulmonary arterial pressures, or heart rate. These results point out the possibility of associating Ib with other orally active vasodilators in the chronic treatment of congestive heart failure.

Dopamine: its potential for inducing ischemic left ventricular dysfunction

As an agent potentially capable of inducing ischemia in patients with coronary artery disease, dopamine administered intravenously was evaluated as a pharmacologic stress agent by supine radionuclide angiography, and the results were compared with ergometer exercise. In a preliminary group of 11 subjects (4 normal subjects and 7 patients with coronary disease), dopamine alone was administered in increments of 2.5 micrograms/kg per min to a maximum of 15 micrograms/kg per min. There were significant differences between exercise and dopamine in maximal stress heart rates, 129.3 +/- 30.0 versus 88.0 +/- 35.8 beats/min (p less than 0.05) in normal subjects and 118.9 +/- 21.1 versus 87.6 +/- 22.6 beats/min (p less than 0.05) in patients with coronary disease, as well as in maximal stress rate-pressure products, 213.3 +/- 51.4 versus 155.0 +/- 52.5 mm Hg/min X 10(2) (p less than 0.02) in normal subjects and 216.0 +/- 45.6 versus 161.0 +/- 48.6 mm Hg/min X 10(2) (p less than 0.003) in patients with coronary disease. As a result, in these patients the ejection fraction response was significantly different: -3.3 +/- 4.5% with exercise versus + 6.3 +/- 4.6% with dopamine (p less than 0.05). In a second group of 41 subjects (9 normal subjects and 32 patients with coronary disease), atropine (0.6 mg) was administered intravenously before and after every second dopamine dose increment. This produced statistically similar maximal stress heart rates as compared with exercise in all subjects, rate-pressure products in normal subjects and slightly higher values with dopamine in patients with coronary disease: 200.3 +/- 47.2 versus 183.1 +/- 43.0 (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Beneficial effects of perfluorochemical artificial blood on cardiac function following coronary occlusion

This study compares the effects of perfluorochemical artificial blood versus whole blood on the systolic and diastolic function of regionally ischemic myocardial preparations. Regional ischemia was produced by ligation of the circumflex coronary artery in isolated, blood-perfused rabbit hearts. Three minutes after occlusion, half the hearts were switched from the blood perfusate to perfluorochemical artificial blood; the other half continued to be perfused with blood. Isovolumic left ventricular (LV) developed pressure, dP/dt and resting pressure were monitored before, and for 2 hours after coronary occlusion. After 90 minutes of regional ischemia, perfluorochemical-treated hearts exhibited significantly greater developed pressure than those perfused with blood (78 +/- 6% versus 61 +/- 5% of preligation values; P less than 0.05). At the end of the experiment, LV dP/dt was 21% greater in the perfluorochemical-perfused group than in the blood-perfused group (74 +/- 8% versus 53 +/- 10%; P less than 0.01). Perfluorochemical perfusion also preserved diastolic function by preventing the 58% increase in left ventricular chamber stiffness (i.e., resting pressure; P less than 0.01) associated with circumflex ligation. Thus, in the present model of regional ischemia, perfluorochemical artificial blood is significantly better than blood at maintaining both systolic and diastolic myocardial function after a major coronary artery has been occluded.

The effect of graded doses of norepinephrine on the O2 supply/consumption balance in ischemic and nonischemic rabbit myocardium

The purpose of this study was to determine the effect of graded doses of norepinephrine on the regional O2 supply/consumption ratio in ischemic rabbit hearts. Open chested, anesthetized rabbits were used and regional flows, O2 extraction, consumption and O2 supply/consumption ratios were determined before and 1 h after occlusion of the left anterior descending coronary artery in controls and animals given 0.1, 1.0 and 10 micrograms/kg per min norepinephrine (NE). After occlusion in controls, mean myocardial blood flow decreased 40% in the occluded region. Blood flow was also depressed in the occluded region for all NE doses compared to their own preocclusion values, but was higher in these regions compared to control animals. O2 extraction was higher in the occluded region compared to the nonoccluded region for all groups; however these values were lower in the NE groups compared to controls. NE increased O2 consumption in the occluded and nonoccluded regions compared to control group values. The O2 supply/consumption ratio was depressed in the occluded region in all groups compared to the nonoccluded region, though no differences were seen between NE and control groups. Thus, increases in the blood flow to the occluded region were proportional to the increases in O2 consumption with infusion of NE, indicating that a reserve exists and can be utilized with NE.

Effects of propranolol on resting and postextrasystolic potentiated left ventricular function in patients with coronary artery disease

The effect of propranolol on global and segmental left ventricular function at rest and after postextrasystolic potentiation was studied in 12 patients with chest pain. Heart rate was controlled with atrial pacing, and left ventricular cineangiograms were performed before and after 0.15 mg/kg of propranolol. During each ventriculogram a premature ventricular stimulus was introduced by means of a programmed stimulator. Propranolol decreased global left ventricular ejection fraction from 64 +/- 4.5 to 58 +/- 4.6 (p less than 0.03). Postextrasystolic potentiated global ejection fraction was not affected by propranolol (78 +/- 3.5 vs 73.6 +/- 3.4; p = NS). The area ejection fraction of the anteroapical region was decreased after propranolol (64 +/- 4.8 vs 52 +/- 6.5; p less than 0.01); however, the postextrasystolic potentiated area ejection fraction was not affected by propranolol (78 +/- 2.6 vs 71 +/- 4.6; p = NS). Frame by frame analysis of the ventriculograms demonstrated that propranolol depressed global and segmental left ventricular function by affecting the second one-third ejection fraction without influencing the first or third one-third ejection fraction. Propranolol has a small depressant effect on global and segmental left ventricular function in patients with coronary artery disease. Postextrasystolic potentiated global and segmental left ventricular function and early systolic ejection phase indices are not altered by propranolol and therefore may be useful in assessing left ventricular function in patients with coronary artery disease who are taking propranolol.

Role of beta-adrenergic blockade in the therapy of patients with myocardial infarction

Beta-adrenergic blockade appears to have beneficial effects on ischemic myocardium, both in experimental animals and in patients. There is substantial evidence that beta blockade, when induced promptly after coronary occlusion, is capable of limiting the size of experimentally produced infarcts. Although many mechanisms of action have been proposed, the bulk of available evidence suggests that beta blockade reduces the severity of myocardial ischemia by reducing myocardial oxygen demands. Intravenous and oral therapy with beta-blockers is safe when patients are carefully selected and observed. Invasive hemodynamic monitoring is not usually necessary for safe use of these drugs. Preliminary reports based on studies with several beta-blockers indicate that early intervention might limit infarct size or even prevent its occurrence, particularly in patients with evidence of increased sympathetic activity. However, before early beta blockade can be recommended as standard therapy for uncomplicated myocardial infarction, these findings should be confirmed in rigorously controlled clinical trials utilizing several techniques for assessment of infarct size. The most significant finding with beta-blockers in patients with myocardial infarction has been that these drugs can improve survival when administered to patients on a long-term basis after infarction. Although the mechanism of this protective effect is not yet understood, the results are clear enough to warrant the routine administration of a beta-blocker to patients who have had infarction and who have no contraindications to such therapy.

Impaired beta-adrenergic stimulation in the uninvolved ventricle post-acute myocardial infarction: reversible defect due to excessive circulating catecholamine-induced decline in number and affinity of beta-receptors

Left ventricular infarction (AMI) was produced in experimental animals and the contractile response to isoproterenol was tested in the isolated perfused heart preparation. Adenylate cyclase activity, phosphodiesterase activity, and beta-receptor binding characteristics were determined in a sarcolemmal preparation of the right ventricle of the same hearts. Three days post-AMI the dose-response curve for isoproterenol of right ventricular dP/dtmax was significantly depressed, while the inotropic effect of histamine was not impaired. Stimulation of adenylate cyclase activity by isoproterenol was reduced by 70% in the membrane preparation, whereas histamine and NaF stimulation rates were unaltered; phosphodiesterase activity was unchanged. In contrast, beta-receptor binding studies with [3H]-DHA1 indicated 74% loss and 10 times lowered affinity (KD) of the remaining beta-receptors, while specific [3H]-QNB1 binding was unchanged. All of the above alterations were prevented by pretreatment with reserpine or metoprolol. It is concluded that these abnormalities in the nonischemic surviving myocardium post-AMI are the result of specific reversible damage of sarcolemmal beta-receptors due to excessive levels of circulating catecholamines.

Effect of oral propranolol on rest, exercise and postexercise left ventricular performance in normal subjects and patients with coronary artery disease

The effect of beta-adrenergic blockade with oral propranolol on resting, exercise and postexercise ventricular performance was evaluated using multiple-gated equilibrium cardiac blood and pool images in normal volunteers and patients with coronary artery disease. Propranolol produced no detectable effect on basal left ventricular function in normal subjects at doses producing intermediate (160 mg propranolol/day) and maximal (434 +/- 99 mg propranolol/day) beta blockade and in patients with coronary artery disease at clinically effective antianginal doses (162 +/- 47 mg propranolol/day). During exercise, a dose-related, negative inotropic effect was observed in normal subjects: 160 mg propranolol/day produced a small but statistically insignificant decline in exercise left ventricular performance, whereas maximal beta blockade significantly depressed the left ventricular response to exercise. In patients with coronary artery disease, propranolol's effect on exercise ventricular performance depended on the presence or absence of ischemic dysfunction during exercise. In patients with an ischemic functional response to exercise, propranolol significantly improved regional and global performance during and after exercise; in coronary artery disease patients with a normal response to exercise, propranolol had no significant effect on exercise and postexercise ventricular function. These results imply increased sensitivity to the effects of beta blockade in ischemic myocardium. In coronary artery disease patients with an abnormal response to exercise and in normal volunteers during beta blockade, propranolol's effect on exercise left ventricular performance was independent of changes in ventricular preload and after load related to heart rate and blood pressure.

A possible role of noradrenaline in the development of myocardial infarction: an experimental study in the isolated rat heart

Isolated rat hearts were perfused with buffer containing noradrenaline 10(-7) to 10(-4) M. A dose-dependent depletion of glycogen and ATP were seen together with a leakage of ASAT and creatine phosphokinase (CK). The damage induced by noradrenaline could be prevented by addition of a beta-blocker (metoprolol), verapamil, or lidocaine to the perfusion medium. When the endogenous myocardial stores of noradrenaline are rapidly depleted by perfusion with tyramine a similar cell damage was demonstrated. Electron micrographs from hearts subjected to noradrenaline showed three different types of cell damage that could be correlated to earlier described findings. The importance of noradrenaline for the ischemic injury was demonstrated. It was hypothesized that acute myocardial infarction may start because of a sudden release of endogenous noradrenaline.

Some aspects of the cardiovascular pharmacology of UK 14,275 in patients with coronary artery disease

1. A phosphodiesterase inhibitor, UK 14,275 (Pfizer) was administered intravenously to six patients with suspected coronary artery disease under-going diagnostic cardiac catheterisation to assess its inotropic activity. 2. Intracardiac haemodynamic measurements included pulmonary and systemic arterial pressure. Left ventricular end diastolic pressure and left ventricular dP/dtmax were also measured, in addition to cardiac output using the indocyanine green dye technique. 3. UK 14,275 resulted in a significant increase in LV dP/dtmax and cardiac output. 4. No chronotropic action was observed using this agent. 5. This agent may have potential therapeutic value in the management of cardiovascular failure associated with low cardiac output.

Comparative haemodynamic effects of dobutamine and isoproterenol in man

Dobutamine was infused at a rate of 8 mcg/kg/min in 17 patients with or without congestive heart failure. Cardiac output increased from an average 2.92 to 4.45 1/min/m2(p less than 0.001) with no change in mean aortic pressure (93.4 to 97.8 mmHg) and only a slight increase in heart rate (78 to 87 beats/min). Left ventricular end-diastolic pressure decreased from an average 19 to 13.7 mmHg (p less than 0.01). Peak left ventricular dp/dt was doubled (1147 to 2370 mmHg/sec, p less than 0.001) and Vmax increased from 1.08 to 2.18 circ/sec (p less than 0.001). In 10 patients given equi-inotropic doses (100 per cent increase in peak dp/dt) Isoproterenol produced a greater increase in cardiac output (71 percent) than Dobutamine /51 percent). Isoproterenol caused mean aortic pressure to fall significantly (8 percent) while no change was noted with Dobutamine. Accordingly, peripheral vascular resistances were reduced to a greater extent with Isoproterenol than with Dobutamine (p less than 0.05). Mean pulmonary arterial pressure decreased significantly (25 +/- 5.9 to 22 +/- 5.7 mmHg, p less than 0.05) with Isoproterenol infusion and remained unchanged with Dobutamine infusion. Dobutamine increased both stroke work (57 percent) and minute work (83 percent). With Isoproterenol however, only minute work was significantly increased (90 percent). Dobutamine therefore is a potent inotropic drug, with mild chronotropic and peripheral vascular effect and may be valuable in the management of severe heart failure not associated with hypotension.

The effect of verapamil on experimental myocardial ischaemia with a particular reference to regional myocardial blood flow and metabolism

The effects of verapamil on epicardial ST segment elevation, regional myocardial metabolism and collateral blood flow were studied in open-chest anesthetized dogs following left anterior descending coronary artery occlusion. Collateral blood flow was measured by radioactive microspheres (15 +/- 5 micron diameter) and regional metabolism was studied by measuring lactate concentration in venous blood draining the infarcting myocardium. Verapamil (0-2 mg/kg intravenously) produced a significant reduction (50-60%) in the epicardial ST elevation when it was given before coronary occlusion; when administered 15 minutes after coronary occlusion and infusion continued for two hours, it minimized (30-40%) ST segment elevation, and prevented the fall in cardiac index and rise in systemic resistance found in the untreated animals in which the ST segment remained persistently elevated. Changes in epicardial ST segment occurred without alterations in the QRS duration. Verapamil had no effect on either the total collateral blood flow or the relative distribution of flow to the endocardial and epicardial halves of the ischemic ventricular myocardium. No significant differences were found between the levels of lactate in blood sampled from small epicardial veins at the center of the infarct when the control animals were compared with those treated with verapamil.

Protective action of timolol in acute myocardial ischemia

Timolol, a beta-adrenoceptor blocking agent with little or no cardiodepressant activity, was studied in acute myocardial ischemia in cats. Timolol, at a dose of 25 mug/kg, blocked 75 to 80% of the cardiac response to isoproterenol. This dose also significantly reduced heart rate in cats subjected to acute myocardial ischemia by ligation of the left coronary artery. Timolol significantly prevented the spread of ischemic damage in the myocardium as assessed by (a) curtailing the increase in plasma creatine phosphokinase (CPK) activity, (b) preventing the loss of CPK from the ischemic portion of the myocardium, and (c) restoring the elevated S-T segment of the electrocardiogram toward normal. Timolol did not significantly retard the increase in fragility of lysosomes in ischemic myocardial tissue. The mechanism of the protective effect to timolol on the ischemic myocardium appears to be via reducing myocardial oxygen demand by decreasing heart rate.

Failure of hyaluronidase to alter the early course of acute myocardial infarction in pigs

The effect of hyaluronidase on the early course of acute myocardial infarction was evaluated in closed chest anesthetized pigs. One hour after balloon catheter occlusion of the left anterior descending coronary artery, hyaluronidase (500 units/kg body weight) was rapidly infused in 10 animals while 9 received no treatment. The animals were than observed over the next 4 hours. Cardiac output, heart rate, mean arterial pressure and left atrial pressure were not significantly affected by treatment. Heart rate increased and arterial pressure decreased in each group to a comparable degree of 5 hours, but left atrial pressure and cardiac output were unaffected. Precordial S-T segment mapping revealed no significant difference between the two groups. S-T segments rose to a comparable degree in each group and peaked before 1 hour. Hyaluronidase had no acute effects on the S-T segment map in the first 30 minutes after infusion or during the subsequent return of the map toward control level. Slightly lower S-T segments in the hyaluronidase-treated group at 5 hours was of borderline significance but was attributed to factors other than the drug intervention. Changes in ventricular wall motion were assessed angiographically, and all animals manifested akinetic or dyskinetic segments. A significant reduction in shortening fraction of involved segments was seen after occlusion, but no difference was observed between the two groups at 5 hours. Shortening fraction of the combined anterior and anteropical segments decreased from 66 +/- 10 to 20 +/- 6 percent at 5 hours in the hyaluronidase group (no. = 7) whereas in the control group (no. = 6) it decreased from 68 +/- 6 to 28 +/- 9 percent. Comparable increases in end-diastolic volume were also present at 5 hours in each group. Volumes increased from 80.6 +/- 5.1 to 97.5 +/- 6.4 ml3 at 5 hours (P less than 0.05) in the hyaluronidase-treated group (no. = 10) compared with 86.9 +/- 8.9 to 104.8 +/- 11.0 ml3 (P less than 0.05) in the control group (no. = 8). Hyaluronidase did not alter the early course of acute myocardial infarction in pigs. Species differences may contribute to different results reported to date.

Effects of perhexiline maleate on coronary flow distribution in the ischemic canine myocardium

Intravenous perhexiline maleate in a canine preparation with fixed coronary flow increases coronary diastolic pressure. It also redistributes coronary flow so as to preserve endocardial flow. Myocardial oxygen consumption was reduced and lactate uptake enhanced by the drug. It had no effect upon the threshold for ischemic-induced left ventricular failure.

Effects of coronary artery bypass grafting on resting and exercise hemodynamics in patients with stable angina pectoris: a prospective, randomized study

In this prospective randomized study, resting and exercise hemodynamics were determined in the nonmedicated state before ("entry") and 1 year after coronary bypass surgery in 38 patients, and at entry and 1 year in 40 patients treated medically. The surgical group showed a significant decrease in mean pulmonary arterial wedge pressure during exercise (entry 23.5 +/- 6.1 [standard error of the mean] mm Hg, 1 year 18.9 +/- 1.0, P less than 0.02); an increase in cardiac index during exercise (entry 4.3 +/- 0.1 liter/min per m2, 1 year 4.6 +/- 0.1, P less than 0.05); an increase in resting mean arterial pressure (entry 94.5 +/- 2.2 mm Hg, 1 year 100.2 +/- 2.2, P less than 0.02); and an increase in resting heart rate (entry 68.5 +/- 1.9 beats/min, 1 year: 76.0 +/- 2.0, P less than 0.01). Maximal treadmill exercise performance also improved significantly in the surgical group of patients (entry 285 +/- 24 seconds, 1 year 382 +/- 24, P less than 0.002). There were no significant changes in these variables in the medically treated "control" group. The improvement in pulmonary arterial wedge pressure during exercise and in maximal treadmill exercise time in the surgical group as a whole was due to striking improvement in these variables in a subgroup of 16 surgical patients who had a more than 10 mm Hg increase in pulmonary arterial wedge pressure during exercise in their entry study. In this subgoup, considered to contain those patients with marked "ischemicdysfunction," pulmonary arterial wedge pressure during exercise fell from 31.4 +/- 1.5 mm Hg (entry) to 19.l +/- 1.8 (1 year) (P less than 0.0001) and treadmill time increased from 217 +/- 24 seconds (entry) to 357 +/- 37 (1 year) (P less than 0.001). Thus, hemodynamic evidence of ischemic left ventricular dysfunction during stress may identify those patients who will show objective improvement in ventricular performance after bypass graft surgery.

Effects of isoproterenol on regional myocardial function, electrogram, and blood flow in conscious dogs with myocardial ischemia

The effects of coronary occlusion and of subsequent isoproterenol infusion were examined in conscious dogs. Left ventricular (LV) function was assessed by measurements of LV diameter, pressure, velocity and dP/dt/P, and regional myocardial function was assessed by measurements of segment length (SL) and velocity of SL shortening in normal, border, and ischemic zones. Regional myocardial function was measured from the same sites, along with intramyocardial electrograms and regional myocardial blood flow as determined by radioactive microspheres. Coronary occlusion resulted in graded loss of function from the normal to severely ischemic zones with graded flow reductions and graded increases in ST segment elevation. Isoproterenol improved overall LV function, and function in the normal zone. Isoproterenol also improved function in 19 of 21 border-zone segments and in all moderately ischemic segments, while elevating further the ST segments. These changes were accompanied by increases in myocardial blood flow. In contrast, in severely ischemic segments, isoproterenol resulted in a deterioration of function, in that paradoxical motion occurred in segments previously akinetic during systole, while paradoxical motion was intensified in those segments in which it was already present. These changes were accompanied by further ST segment elevation but not by concurrent increases in blood flow. In addition, in 2 of 21 border zone segments, myocardial blood flow fell and these segments responded to isoproterenol with complete loss of function; paradoxical motion developed. Thus, in the conscious dog, a strong inotropic agent can improve function, even in the ischemic myocardium, as long as the required additional blood flow can be provided wither through primary or collateral channels.

Hemodynamic effect of dobutamine in patients with severe heart failure

Dobutamine, a derivative of dopamine, was infused at a rate of 10 mug/kg per min in 15 patients with severe congestive heart failure. Cardiac output increased from an average of 3.1 to 5.6 liters/min (P less than 0.001) with no change in mean arterial pressure (93.3 to 98.2 mm Hg) and only a slight increase in heart rate (98.5 to 105.2 beats/min) (P less than 0.02). Pulmonary wedge pressure was decreased from an average of 27.4 to 21.1 mm Hg (P less than 0.001). In seven patients a dose of 5 mug/kg per min also produced a significant increase in cardiac output but the effect was less than with the 10 mug/kg per min dose. No side effects were observed during the infusion. Dobutamine therefore is a potent inotropic drug with limited chronotropic and peripheral vascular effects and deserves therapeutic trial in the short-term management of low output heart failure.

Left ventricular wall motion response to intravenous propranolol

The effects of intravenous propranolol on left ventricular wall motion and hemodynamics were studied in 16 patients, 12 with significant coronary artery disease and four with chest pain but no coronary disease. Eight patients received 0.10 mg/kg and eight received 0.15 mg/kg of propranolol intravenously. All underwent atrial pacing at a constant rate. Left ventricular angiograms were performed before and 20 minutes after propranolol. At both doses, propranolol caused no significant change in left ventricular systolic or diastolic pressures, either before or immediately following ventriculography. Cardiac index fell significantly (3.4 plus or minus 0.2 [SEM] to 2.6 plus or minus 0.1 L/min/m-2) with the higher dose only. Of the ten patients with coronary artery disease and adequate ventriculograms, one patient had a normal left ventricle, two had regional hypokinesis, only three had areas of hypokinesis and akinesis, two had dyskinetic and akinetic areas, and two had areas of hypokinesis, akinesis and dyskinesis. No changes in regional contractility occurred with propranolol except for a minimal increase in hypokinesis in one patient at each dosage and equivocal development of a new area of slight hypokinesis in one patient and minimal apex of dyskinesis in another at the higher dosage. Of the four patients without coronary artery disease, two were affected by propranolol, one with initial regional akinesis and dyskinesis had slight worsening with propranolol and one with regional hypokinesis developed a definite new area of hypokinesis. Therefore, propranolol, even in large intravenous doses, resulted in no significant change in left ventricular wall motion in patients with coronary artery disease.

Evaluation of haemodynamic effects of intravenous propranolol at low dosage (1 and 2 mg) in acute myocardial infarction

The haemodynamic effects of intravenous propranolol at low dosage (1 and 2 mg) have been evaluated on 14 patients in the acute stage of myocardial infarction. The first 1 mg propranolol was not followed by any significant variation in the variables measured. After the second 1 mg propranolol, the heart rate, cardiac index, and stroke index decreased significantly but moderately. Changes in pulmonary wedge pressure were not significant. It is concluded that intravenous propranolol in the small dosage of 1 or 2 mg, at which antiarrhythmic effect is still produced, has only a negligible depressant myocardial effect.

The effect of hypoglycemia on myocardial ischemic injury during acute experimental coronary artery occlusion

To determine the effect of hypoglycemia on myocardial ischemic injury following coronary artery occlusion epicardial electrograms were recorded 15 minutes after two 20-minute coronary artery occlusions in seven anesthetized dogs. The first occlusion was a control (blood glucose 85 plus or minus 5(sd) mg per cent). Before the second occlusion hypoglycemia was induced (blood glucose 40 plus or minus 5 mg per cent) by the intravenous administration of insulin (2 units/kg). The average ST-segment elevation in leads during control was 3.5 plus or minus 1.0 mV which rose to 6.1 plus or minus 1.4 mV during the second occlusion (P smaller than 0.05). The number of sites showing ST-segment elevation exceeding 2 mV increased from 7.6 plus or minus 1.6 during control to 10.6 plus or minus 1.4 (P smaller than 0.05) during the occlusion with hypoglycemia. In other dogs, a coronary artery was occluded for 24 hours. Epicardial ST-segment elevations were compared to creatine phosphokinase (CPK) activity and histological appearance from the same sites. CPK activity in sites with normal ST segments (0-2 mV) was 33.1 plus or minus 6.0 IU/mg protein. Six additional dogs received insulin following the 15 minute epicardial map and blood sugar was maintained at a level of 46 plus or minus 6 mg per cent for the 24 hours. These dogs showed more myocardial necrosis than predicted by the ST-segment elevation prior to insulin administration. Forty-six percent of sites, which in control dogs would have been expected to have normal CPK and histological appearance, showed depressed CPK activity and histological evidence of early myocardial necrosis. Thus, hypoglycemia increases myocardial damage, as reflected by enzymatic and histological analyses.

Effects of catecholamines, exercise, and nitroglycerin on the normal and ischemic myocardium in conscious dogs

The effects of isoproterenol, norepinephrine, dobutamine, exercise, and nitroglycerin on left ventricular diameter, pressure, velocity of shortening, dP/dt, dP/dt/P, arterial pressure, left circumflex coronary blood flow, and coronary vascular resistance were examined in healthy conscious dogs with normal coronary perfusion and in the same animals after moderate global ischemia had been induced by partial occlusion of the left main coronary artery. In the normal nonischemic heart, all interventions improved left ventricular performance, as evidenced by increases in dP/dt/P and velocity at the same or lower left ventricular end-diastolic diameter. Interventions, which in the normal heart caused large increases in heart rate and myocardial contractility, e.g. isoproterenol and exercise, or which decreased coronary perfusion pressure, e.g. nitroglycerin or isoproterenol, elicited paradoxical responses in moderate global ischemia, i.e., left ventricular enddiastolic diameter and pressure rose, and dP/dt/P and velocity fell substantially. On the other hand, norepinephrine, which increased coronary perfusion pressure along with myocardial contractility but did not increase heart rate, improved left ventricular function. Dobutamine, which did not alter heart rate or arterial pressure substantially while improving myocardial contractility, produced an intermediate response between that of norepinephrine and isoproterenol in the presence of moderate global myocardial ischemia. Thus, interventions that increase myocardial O(2) requirements, by increasing heart rate and myocardial contractility without augmenting coronary perfusion pressure, can produce a paradoxical depression of ventricular function in the presence of global myocardial ischemia.

Effects of dobutamine on left ventricular performance, coronary dynamics, and distribution of cardiac output in conscious dogs

The effects of dobutamine ([+/-]-4-[2-[[3-(p-hydroxyphenyl)-1-methyl propyl] amino] ethyl] pyrocatechol hydrochloride), a new synthetic cardioactive sympathomimetic amine, were examined on direct and continuous measurements of left ventricular (LV) diameter (D), pressures (P), velocity of shortening (V), dP/dt, dP/dt/P, arterial pressure, cardiac output, and regional blood flows in the left circumflex coronary, mesenteric, renal, and iliac beds in healthy, conscious dogs. At the highest dose of dobutamine examined, 40 mug/kg/min, the drug increased dP/dt/P from 65+/-3 to 128+/-4 s(-1) and isolength velocity from 72+/-4 to 120+/-7 mm/s without affecting LV end diastolic D significantly. Mean arterial P rose from 92+/-2 to 104+/-3 mm Hg and heart rate from 78+/-3 to 111+/-7 beats/min, while LV end systolic D fell from 24.1+/-1.4 to 19.9+/-1.8 mm, reflecting a rise in stroke volume from 30+/-4 to 42+/-3 ml. Cardiac output rose from 2.41+/-0.23 to 4.35+/-0.28 liter/min, while calculated total peripheral resistance declined from 0.042+/-0.005 to 0.028+/-0.003 mm Hg/ml/min. The greatest increases in flow and decreases in calculated resistance occurred in the iliac and coronary beds, and the least occurred in the renal bed. Propranolol blocked the inotropic and beta(2) dilator responses while vasoconstricting effects mediated by alpha adrenergic stimulation remained in each of the beds studied. When dobutamine was infused after a combination of practolol and phentolamine, dilatation occurred in each of the beds studied. These observations indicate that dobutamine is a potent positive inotropic agent with relatively slight effects on preload, afterload, or heart rate, and thus may be a potentially useful clinical agent. The one property of this drug which is not ideal is its tendency to cause a redistribution of cardiac output favoring the muscular beds at the expense of the kidney and visceral beds.