Myocardial infarct size. Part 2. Comparison of anti-infarct effects of beta-blockade, glucose-insulin-potassium, nitrates, and hyaluronidase

Effects of high-dose glucose-insulin-potassium on acute coronary syndrome patients receiving reperfusion therapy: a meta-analysis

BACKGROUND

This meta-analysis aimed to assess the efficacy of high-dose glucose-insulin-potassium (GIK) therapy on clinical outcomes in acute coronary syndrome (ACS) patients receiving reperfusion therapy.

METHODS

We searched the PubMed, Web of Science, MEDLINE, Embase, and Cochrane Library databases from inception to April 26, 2022, for randomized controlled trials (RCTs) that compared high-dose GIK and placebos in ACS patients receiving reperfusion therapy. The primary endpoint was major adverse cardiovascular events (MACEs).

RESULTS

Eleven RCTs with 884 patients were ultimately included. Compared with placebos, high-dose GIK markedly reduced MACEs (risk ratio [RR] 0.57, 95% confidence interval [95% CI]: 0.35 to 0.94, P=0.03) and the risk of heart failure (RR 0.48, 95% CI: 0.25 to 0.95, P=0.04) and improved the left ventricular ejection fraction (LVEF) (mean difference [MD] 2.12, 95% CI: 0.40 to 3.92, P=0.02) at 6 months. However, no difference was observed in all-cause mortality at 30 d or 1 year. Additionally, high-dose GIK was significantly associated with increased incidences of phlebitis (RR 4.78, 95% CI: 1.36 to 16.76, P=0.01), hyperglycemia (RR 9.06, 95% CI: 1.74 to 47.29, P=0.009) and hypoglycemia (RR 6.50, 95% CI: 1.28 to 33.01, P=0.02) but not reinfarction, hyperkalemia or secondary reperfusion. In terms of oxidative stress-lowering function, high-dose GIK markedly reduced superoxide dismutase (SOD) activity but not glutathione peroxidase (GSH-Px) or catalase (CAT) activity.

CONCLUSION

Patients with ACS receiving reperfusion therapy exhibited a reduction in MACEs and good oxidative stress-lowering efficacy in response to high-dose GIK. Moreover, with a higher incidence of complications such as phlebitis, hyperglycemia, and hypoglycemia. Furthermore, there were no observed survival benefits associated with high-dose GIK. More trials with long-term follow-up are still needed.

Effect of preinitiated glucose-insulin-potassium strategy for patients with undergoing planned percutaneous coronary intervention: a systematic review and meta-analysis

OBJECTIVES

Whether the glucose-insulin-potassium (GIK) should be used as an adjuvant therapy for ischaemic myocardial disease remains controversial nowadays reperfusion era. This meta-analysis aimed to assess the effects of preinitiated GIK for patients undergoing planned percutaneous coronary intervention (PCI).

DESIGN

Systematic review and meta-analysis.

DATA SOURCES

PubMed, Web of science, MEDLINE, Embase, Cochrane Library and ClinicalTrials.gov were searched through 27 November 2022.

ELIGIBILITY CRITERIA

Only randomised controlled trials involving participants preinitiated with GIK or placebo before planned PCI were included.

DATA EXTRACTION AND SYNTHESIS

Two independent reviewers used standardised methods to search, screen and code included trials. Risk of bias was assessed with the Cochrane tool. Pooled analysis was conducted using random or effects models according to the heterogeneity. Subgroup analyses were carried out for dosage of GIK and if with ongoing myocardial ischaemia.

RESULTS

13 randomised controlled trials (RCTs) including 3754 participants were evaluated. We found patients preconditioned with GIK before PCI showed a significant increase in Thrombolysis in Myocardial Infarction 3 flow events after angioplasty (OR 1.59, 95% CI 1.03 to 2.46, p=0.04), also revealed improved in-hospital left ventricular ejection fraction (weighed mean difference, WMD 1.62, 95% CI 0.21 to 3.03, p=0.02) and myocardial salvage index (WMD 0.09, 95% CI 0.01 to 0.16, p=0.03). Nevertheless, no benefit was observed in all-cause mortality neither on 30-day (OR 0.81, 95% CI 0.59 to 1.11, p=0.18) nor 6 months (OR 1.02, 95% CI 0.42 to 2.46, p=0.97). Furthermore, GIK intervention was associated with higher occurrences of complications such as phlebitis (OR 10.13, 95% CI 1.74 to 59.00, p=0.01) and hypoglycaemia (OR 10.43, 95% CI 1.32 to 82.29, p=0.03), but not hyperkalaemia (OR 9.36, 95% CI 0.50 to 175.27, p=0.13), liquid overload (OR 1.02, 95% CI 0.25 to 4.13, p=0.98) or in-hospital heart failure (OR 0.42, 95% CI 0.06 to 2.96, p=0.39).

CONCLUSIONS

Our study shows preconditioning GIK exhibits myocardial reperfusion and cardiac function benefits for patients planning to receive PCI intervention, while also some complications such as phlebitis and hypoglycaemia accompany.

PROSPERO REGISTRATION NUMBER

CRD42022326334.

Beneficial Effects of Insulin on Ischemia Reperfusion Injury in Human Skeletal Muscle

PURPOSE

Exaggerated leucocyte activity is a crucial step in the pathophysiology of skeletal muscle ischemia-reperfusion injury (IRI). We tested the hypothesis that insulin, via its' anti-leukocyte activity, attenuates skeletal muscle IRI in humans.

MATERIALS AND METHODS

This randomized, blinded, placebo-controlled trial was conducted in patients with skeletal muscle ischemia who required revascularization. Treatment protocols were similar among them except for the insulin group, which received an infusion of insulin at 2.5 U/h. The degree of endothelial adhesiveness; leukocyte activity and pro-inflammatory status via P-selectin, tumor necrosis factor (TNF)-alpha, and myeloperoxidase (MPO) levels in the venous effluent; and clinical outcomes were measured.

RESULTS

Twenty-four consenting patients were randomized to the insulin or control group. There were no significant differences between the two groups except for the median serum insulin level, which was higher in the insulin group (P<0.01). No serious intervention-related adverse events were observed. P-selectin (55.04-99.86 pg/mL; P<0.001), MPO (110.8-160.6 pg/mL; P<0.001), and TNF-alpha (12.16-36.01 pg/mL; P<0.001) levels demonstrated a significant increase post-reperfusion in the 'control' group, reaching a peak value at 2 hours post-reperfusion. The increase in all three markers from baseline was significantly diminished in the insulin group at the two-hour (P-selectin, P=0.001; MPO, P=0.001; TNF-alpha, P=0.005) and four-hour (P-selectin, P=0.003; MPO, P=0.002; TNF-alpha, P=0.01) intervals. The differences in clinical outcomes between the insulin and control groups were not statistically significant.

CONCLUSION

In clinical practice, insulin has the potential to attenuate the severity of skeletal muscle IRI inhibiting P-selectin, MPO, and TNF-alpha levels.

How to best manage glycemia and non-glycemia during the time of acute myocardial infarction

Acute myocardial infarction (AMI) is common in patients with diabetes. Reasons for this are multifactorial, but all relate to a variety of maladaptive responses to acute hyperglycemia. Persistent hyperglycemia is associated with worse left ventricular function and higher mortality during AMI, but intervention data are far from clear. Although there is a theoretical basis for the use of glucose-insulin-potassium infusion during AMI, lack of outcome efficacy (and inability to reach glycemic targets) in recent randomized trials has resulted in little enthusiasm for this strategy. Based on the increasing understanding of the dangers of hypoglycemia, while at the same time appreciating the role of hyperglycemia in AMI patients, goal glucose levels of 140-180 mg/dL using an intravenous insulin infusion while not eating seem reasonable for most patients and hospital systems. Non-glycemic therapy for patients with diabetes and AMI has benefited from more conclusive data, as this population has greater morbidity and mortality than those without diabetes. For ST-elevation myocardial infarction (STEMI), reperfusion therapy with primary percutaneous coronary intervention or fibrinolysis, antithrombotic therapy to prevent acute stent thrombosis following percutaneous coronary intervention or rethrombosis following thrombolysis, and initiation of β-blocker therapy are the current standard of care. Emergency coronary artery bypass graft surgery is reserved for the most critically ill. For those with non-STEMI, initial reperfusion therapy or fibrinolysis is not routinely indicated. Overall, there have been dramatic advances for the treatment of people with AMI and diabetes. The use of continuous glucose monitoring in this population may allow better ability to safely reach glycemic targets, which it is hoped will improve glycemic control.

High-dose glucose-insulin-potassium has hemodynamic benefits and can improve cardiac remodeling in acute myocardial infarction treated with primary percutaneous coronary intervention: From a randomized controlled study

Objective:

To evaluate the effects of high-dose glucose–insulin–potassium (GIK) solution on hemodynamics and cardiac remodeling in patients with acute myocardial infarction (AMI) treated with primary percutaneous coronary intervention (PCI).

Patients and Methods:

We observed the changes in the hemodynamic parameters in 26 patients with AMI. All patients received primary PCI before entering the study. All patients in the study were randomized into the GIK group (n = 14) or the control group (n = 12). Patients in the GIK group received high-dose GIK solution (25% glucose, 80 mmol/L KCl and 50 IU/L insulin; 1.5 ml/kg/h) over 24 h. Patients in the control group received standard therapy. We monitored the hemodynamic parameters at baseline and after 6 h, 12 h, 18 h and 24 h, respectively. Then, we followed-up the cardiac function with echocardiography after 7 days, 1 month and 6 months.

Results:

The basic clinical data was similar between the groups. Primary PCI was performed successfully in 25 patients. The two groups were indistinguishable in all factors measured. GIK solution did not have a deleterious effect on the hemodynamic parameters. The pulmonary capillary wedge pressure increased during the first 12-h period and then decreased smoothly (F = 3.75, P = 0.02). The trends were similar between the two groups. The system vascular resistance index (SVRI) and pulmonary vascular resistance index (PVRI) decreased during the first 12 h in the GIK group but increased in the control group. The GIK solution significantly influenced SVRI (F = 4.71, P = 0.02). GIK solution improved the cardiac function measured by stroke volume (F = 4.11, P = 0.03) and cardiac index (F = 4.40, P = 0.02). In the 6-month follow-up, GIK improved cardiac remodeling (left ventricular diastolic diameter: 49.2 ± 2.89 vs. 53.9 ± 2.48, P < 0.001; left ventricular systolic diameter: 32.9 ± 2.24 vs. 35.9 ± 2.78, P < 0.01).

Conclusion:

High-dose GIK solution had no adverse effects on the hemodynamics in AMI patients treated with primary PCI. It can improve cardiac function by lowering SVRI. In the 6-month follow-up, it improved cardiac remodeling.

Prophylactic furosemide treatment in acute myocardial infarction

Prophylactic diuretic therapy in acute myocardial infarction (AMI) was evaluated in 83 consecutive patients without severe left ventricular failure (LVF) on admission. A high dose group (HDG) received 120-160 mg and a low dose group (LDG) 20-40 mg furosemide daily for six weeks. Mortality and reinfarction rates did not differ between the groups. One HDG patient and five LDG patients developed severe LVF. Four HDG patients developed severe dehydration. Serum enzyme activities and electrolytes were similar in both groups. The increased diuresis in the HDG was accompanied by a 4% hemoconcentration, smaller radiological heart volumes, higher heart rates, a higher demand for nitroglycerin and higher ratings of thirst. Exercise tests yielded similar results in both groups. Later blood volumes and transthoracic electrical impedance were similar in both groups. It is concluded that liberal prophylactic furosemide treatment in AMI offers no major clinical advantage.

The effects of a highly purified hyaluronidase preparation on experimental myocardial infarction in the rat

Several substances have been claimed to be effective in reducing the area of necrosis in acute myocardial infarction. The effects of a highly purified hyaluronidase preparation (Hyalas) on experimental myocardial infarction in the rat have been evaluated in this study. In the first series, one group of rats was treated with hyaluronidase 1 500-2 000 IU/kg injected intravenously 2, 4, 18, 24, 28 and 42 hours after induction of infarction by coronary artery occlusion. Another group was treated with NaCl solution. The infarction size was evaluated by serum lactate dehydrogenase and weight of infarcted myocardium. In a second series, the substances were administered immediately after the occlusion. In this experiment, the infarction size was estimated by planimetry. The percentage of salvaged myocardium in the hyaluronidase-treated groups was within the range of 20%. It seems reasonable to suggest that the use of highly purified hyaluronidase may be of clinical value for reduction of the myocardial infarction size.

Metabolic aspects of rhythm disturbances

[Profound alterations in metabolism occur within the first few minutes of myocardial ischaemia which may induce or modulate myocardial electrophysiological abnormalities and arrhythmogenesis, Fatty acid oxidation is inhibited with accumulation of long-chain acyl CoA esters and glycolysis is stimulated but later inhibited. This may be worsened by a peripheral sympathetic response. In particular regional variations in glycolytic ATP productions which can modulate "slow channel" ion flux and hence slow conducting "slow response" potential activity, could influence patterns of slow conduction in ischaemic myocardium of importance in generating early re-entrant arrhythmias. This possibility has been examined in open chest anaesthetised dogs following experimental coronary occlusion by detailed computer aided analysis and construction of three dimensional maps of regional metabolism, blood flow and epicardial activation patterns at the time of early ventricular arrhythmias. Activation patterns were obtained using an electronic multiplexing system, flow using tracer microspheres and metabolic changes by analysis of multiple tissue samples for lactate and indices of glycolytic activity after rapid excision and freezing of the heart. Marked spacial inhomogeneities in flow, lactate and glycolytic activity were associated with delayed and fragmented activation in the central ischaemic region. Within the border region of flow, however, glycolytic activity was enhanced and conduction generally little impaired. It is suggested that transient changes in the homogeneity of myocardial metabolism and flow are critical in determining patterns of conduction and hence arrhythmogenesis. This may provide a basis for understanding anti-arrhythmic effects of metabolic interventions.

Effect of esmolol given during cardiopulmonary bypass on fractional area of contraction from transesophageal echocardiography

The infusion of esmolol during hypothermic cardiopulmonary bypass (CPB) has no negative myocardial effects after CPB, despite increased esmolol levels during CPB due to hypothermia. The purpose of this randomized, double-blind, prospective study was to measure the effects of esmolol infused during CPB on cardiac function as measured by calculated indices of cardiac work and by transesophageal echocardiography (TEE). Patients scheduled for CPB were randomized to receive intravenous esmolol (300 micrograms.kg-1.min-1 during CPB after bolus of 2 mg/kg prior to CPB) or placebo. Infusion was stopped at 10 min after release of aortic cross-clamp. Hemodynamics and TEE were recorded during the procedure. Fractional area of contraction (FAC), an approximation of left ventricular ejection fraction, was calculated from end-diastolic and end-systolic areas. Esmolol was administered to 15 patients and placebo to 14. Heart rates in the esmolol group were lower during infusion and prior to CPB (P < 0.05). Stroke volume index and left ventricular stroke work index were higher in the esmolol group at 15 min post-CPB (P < 0.05). FAC was higher in the esmolol group at 15 and 30 min post-CPB (P < 0.05), but no difference was observed between groups at 1 h post-CPB. Esmolol infused during CPB in this series of patients was associated with better left ventricular function during the first 0.5 h post-CPB.

The effect of esmolol given during cardiopulmonary bypass

beta-Adrenergic antagonism decreases the size of myocardial infarction and provides myocardial protection during hypothermic arrest for cardiac surgery. However, concern regarding the negative inotropic and chronotropic effects of beta-adrenergic antagonism persisting after cardiopulmonary bypass (CPB) has impeded the use of esmolol for this purpose during cardiac surgery. This is a randomized, double-blind prospective study of the effects of esmolol infused during CPB and the effects of hypothermic CPB on esmolol. Patients scheduled for CPB were randomized to receive intravenous esmolol (300.micrograms.kg-1.min-1 during CPB after a bolus of 2 mg/kg prior to CPB) or placebo. Infusion was stopped at 10 min after release of aortic cross-clamp. Hemodynamics were measured, as well as serum esmolol, catecholamines, lactate, and potassium. Postoperative variables measured included electrocardiographic changes, creatine kinase (CK)-MB fractions, post-CPB dysrhythmias and drugs, hospitalization time and cost, and mortality. Esmolol was administered to 16 patients and placebo to 14. Esmolol levels reached a high of 10.5 +/- 0.9 micrograms/mL during CPB, but decreased to 0.1 +/- 0.02 microgram/mL within 30 min after stopping infusion. Cardiac indices (cardiac index, stroke volume index, left cardiac work index, left ventricular stroke work index, right cardiac work index, and right ventricular stroke work index) were higher in the esmolol group for the first hour post-CPB (P < 0.05). Systemic arterial lactate and coronary sinus lactate were lower in the esmolol group after CPB (P < 0.05), but myocardial lactate extraction was not significantly different between groups. After CPB, hemoglobin was lower in the esmolol group (P < 0.05) due to longer CPB and aortic cross-clamp time (P < 0.05), but oxygen consumption was less than in the control group (P < 0.05). Post-CPB serum potassium was higher in the esmolol group (P < 0.05). Results are confounded by more chronically beta-adrenergically blocked patients randomized to the esmolol group (P < 0.05). Esmolol infused during CPB in this series of patients was associated with high concentrations during CPB but did not result in any adverse clinical effects after CPB.

The influence of CLS 2210 on the course of myocardial infarction: a pilot study in man

To assess the effect of CLS 2210 (a new formulation of calcium dobesilate) on the evolution of acute myocardial infarction, 100 patients presenting their first infarct were distributed, according to their sequential admissions to the hospital, into CLS 2210-treated group (50 patients) or a comparison group (50 patients not receiving CLS 2210). The two groups were similar in age, sex, predisposing factors, and site of infarction. Intravenous infusion of CLS 2210 was begun within six hours of onset of chest pain and continued for seventy-two hours. Thereafter, it was given, as oral capsules, in a dose of 1,000 mg every eight hours throughout the hospitalization. Before and during the trial, blood samples were drawn for the measurements of serum concentrations of creatine kinase (CK), and twelve-lead electrocardiograms (ECGs) were obtained serially in each patient. All objective data were analyzed on a coded basis without reference to the treatment. In the comparison group, thirty-six to forty-eight hours was required for CK to fall to 50% of the baseline value, whereas in the CLS 2210-treated group it reached 50% of the baseline in eighteen to twenty-four hours. For each infarction site, a statistically significant fall was reached earlier in the CLS 2210 group. CK, the ECG index, and the sum of the ST segments showed earlier and more rapid improvement in the CLS 2210 group than in the comparison group. The consumption of narcotic analgesic agents and nitroglycerin was substantially less in the CLS 2210 group than in the comparison group.(ABSTRACT TRUNCATED AT 250 WORDS)

Beta-adrenergic blockade and calcium channel blockade in myocardial infarction

Because of their hemodynamic and antiarrhythmic actions, beta-adrenergic blockers and calcium-entry blockers have been suggested for use in patients with myocardial infarction (MI) for reducing infarct size, preventing ventricular ectopy, and for prolonging life in survivors of acute MI. Experimental studies have suggested their usefulness in these areas. Clinical studies have demonstrated a role for beta-blockers in the hyperacute phase of MI, and in longterm treatment of infarct survivors. Calcium channel blockers appear to have somewhat less utility in patients with Q wave MIs, but may have an important role in therapy of the non-Q wave infarct.

Comparison of different pharmacological interventions on enzymatic parameters during acute myocardial infarction

The concept that acute myocardial infarction is a dynamic event and that different interventions can modify the extent of the necrosis, has led to renewed interest in early pharmacological and surgical treatments designed to reduce the ischemic injury. To evaluate the effects of different pharmacological interventions aimed to reduce the extent of necrosis, we studied 166 patients (138 male and 28 female, mean age of 59.4 +/- 11.3 years) admitted within 6 h after chest pain and treated with a single therapy during the first 72 h. Enzymatic infarct size (IS) was calculated by serial creatine kinase isoenzyme MB determinations using a compartmental model. Six groups of patients were evaluated: 33 patients were treated only with antiplatelet drugs, 38 with anticoagulants, 34 with intravenous thrombolytic therapy, 20 with calcium channel blockers, 25 with nitrates, and 16 with beta-blockers. Estimated IS (gEq/m2) and elimination constant (Kd, U/L/h) did not differ in the six groups, but patients treated with streptokinase had higher release constant (Ka, U/L/h) and shorter time to peak CK-MB value. Early treatment (less than or equal to 2 h after chest pain) had a favourable effect on the enzymatic IS only in patients treated with calcium channel blockers (p less than 0.005).

The effect of tricyclic antidepressants on ventricular fibrillation and collateral blood supply following acute coronary occlusion

In previous studies, we showed that dibenzepin HCl (D) and other tricyclic antidepressants (TCAD), given either before or during occlusion of the left anterior descending artery (LAD), decreased the incidence of ventricular fibrillation (VF) following occlusion and reperfusion. Moreover, once VF develops in treated animals, it changes into a transient type, reverting spontaneously to a sinus rhythm. In the treated cats, retrograde perfusion of the occluded coronary artery was observed, most likely as a result of increased collateral blood flow. This latter effect is the subject of the present study. The LAD was occluded at its origin in 43 cats, 28 of which were treated either with D or with 5-iminodibenzyl HCl; the remaining 15 were untreated controls. Two hours after the occlusion, methylene blue was injected into the left atrium to determine color demarcation between the perfused and unperfused myocardium, and the cat was then killed. After fixing for 2 or 3 days in 4% formaldehyde, the hearts were sectioned transversely. The results showed that in the 15 control cats, the blood-supplied (blue) area ranged between 16% and 56% of the left ventricular muscle (mean 39%), while in the 28 treated cats the blue area was between 44% and 83% (mean 66%). These results clearly indicate the beneficial effect of TCAD on the blood supply of the occluded area and can explain, in part, the ability of these drugs to prevent VF even if infused after the coronary occlusion, and their protective effect against VF following reperfusion. No other antiarrhythmic drugs have been shown to possess this latter action.(ABSTRACT TRUNCATED AT 250 WORDS)

Tiapamil, a new calcium antagonist: hemodynamic effects in patients with acute myocardial infarction

The afterload reduction and myocardial oxygen sparing that results after administration of calcium antagonists suggests a possible role for these drugs in intervention after onset of acute myocardial infarction, but their use in this setting is limited by the possibility that left ventricular failure will develop. Tiapamil is a new verapamil congener. The hemodynamic effects of this drug (1 mg/kg followed by 25 micrograms/kg/min over 36 hr) were studied in 30 patients randomly assigned in a double-blind manner to a tiapamil or control group within 12 hr of the onset of acute myocardial infarction as diagnosed by Swan-Ganz catheterization and gated blood pool scans. Tiapamil reduced heart rate from 83 +/- 20 beats/min (mean +/- SD) before to 74 +/- 19 beats/min after drug (over an average 36 hr), arterial pressure from 128 +/- 22/87 +/- 14 to 118 +/- 16/74 +/- 11 mm Hg, rate-pressure product from 10,695 +/- 3492 to 8800 +/- 2550 units, and systemic vascular resistance from 1732 +/- 351 to 1400 +/- 350 dynes X sec X cm-5. Tiapamil also increased stroke volume index from 34.7 +/- 12.1 to 41.6 +/- 12.0 ml/m2, left ventricular ejection fraction from 50.1 +/- 14.8% to 56.4 +/- 17.4% (at 24 hr), left ventricular end-diastolic volume index from 71.3 +/- 23.1 to 80.5 +/- 23.7 ml/m2, and peak diastolic filling rate (an index of diastolic relaxation) from 2.1 +/- 0.9 to 2.6 +/- 0.8 end-diastolic volumes/sec (p less than .05 for all changes). Cardiac index, wedge pressure, left ventricular end-systolic volume, and PR interval remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Myocardial protection: heparin-induced free fatty acid elevation during cardiopulmonary bypass and its prevention

Elevated serum free fatty acids (FFA) adversely affect the hypoxic or ischemic myocardium by impairing cardiac function, decreasing contractility, and increasing arrhythmogenicity . Heparin, an anticoagulant used routinely in cardiac surgery, elevates circulating FFA. The purpose of this study was to determine the magnitude of FFA elevation in cardiac surgery patients and to establish, in dogs, a dose-response of FFA to heparin and to test whether glucose-insulin-potassium (GIK) solution could prevent heparin-induced rise in FFA. In 52 patients undergoing cardiopulmonary bypass (CPB), serial blood samples were obtained for FFA determination before and after heparin (300 IU/kg) administration. Then in seven normal dogs, heparin at a dose of 80 or 300 IU/kg was given. In another group of five dogs either GIK solution or NaCl were infused, while intravenous heparin (300 IU/Kg) injection was given. Each dog acted as its own control. It was found that there was a twofold increase in circulating serum FFA after heparin administration during cardiac surgery in patients, reaching the toxicity level of greater than 0.80 meq/liter. One-third of these patients had elevations of FFA level above the arrhythmogenic threshold of greater than 1.20 meq/liter. In the canine experiments low-dose heparin (80 IU/Kg) resulted in milder elevations of FFA for a shorter duration. Dogs given saline and high-dose heparin (300 IU/Kg) had responses similar to those seen in human patients undergoing cardiac surgery, while GIK abolished the elevation of serum FFA in response to high-dose heparin, eventually reducing FFA to below preheparin levels.

Hemodynamic effects of sublingual nifedipine in acute myocardial infarction

Twenty-six patients with acute myocardial infarction (mean delay time 6 hours after onset of symptoms) were randomized to control or nifedipine treatment (10 mg sublingually, followed by 10 mg every 6 hours for a total of 24 hours). Nifedipine reduced arterial blood pressure from 127/78 to 115/70 mm Hg at 30 minutes (p less than 0.001) and continued to reduce the blood pressure significantly for 12 to 18 hours. Nifedipine also reduced systemic vascular resistance and the rate-pressure product. Cardiac output increased from 4.9 liters/min before nifedipine to 5.4 liters/min at 60 minutes (p less than 0.05 vs controls). In patients with high initial pulmonary wedge pressures, sublingual nifedipine decreased the wedge pressure (p less than 0.001) more effectively than did 80 mg of furosemide given intravenously. Thus, nifedipine may be useful in patients with early myocardial infarction and left ventricular failure.

Quantification of ischemic stress during repeated coronary artery occlusion in the dog. A method for validation of therapeutic effects. I. Estimation of O2-debt and O2-repayment

In 9 open-chest mongrel dogs 4-6 intermittent 3-min occlusions of the LAD artery were performed with time intervals of about 45 min. Using a mu-computer, the following variables were calculated online: energy demand according to the Bretschneider equation (Et) from digitized hemodynamic data; myocardial oxygen consumption (MVO2) from fiberoptically measured coronary sinus oxygen saturation and coronary sinus blood flow. Coronary occlusion led to a decrease in MVO2 in comparison to Et. The integral of the difference between MVO2 and Et over the entire occlusion time yielded a total O2-deficiency (DO2) of 76 (+/- 12%) microliter O2/g ischemic tissue and a correlation coefficient with the weights of the intravitally stained ischemic areas of r = 0.96. Additional O2-uptake in relation to Et during the early perfusion period yielded a correlation to the size of the ischemic area of r = 0.95 and an average O2-repayment (RO2) of 32 (+/- 14%) microliter O2/g ischemic tissue. The determination of total myocardial O2-deficiency during ischemic stress as well as determination of O2-repayment during the early reperfusion period could be used to estimate the extent of ischemic stressed myocardium. Subsequently, the evaluation of pharmacological effects on myocardial ischemia should be possible.

Temporal and spatial characteristics of evolving cell injury during regional myocardial ischemia in the dog: the "border zone" controversy

An open chest dog heart with multiple coronary ligations was used to define the temporal and spatial characteristics of injury evolving during regional ischemia. With the use of a multiple (40 sample) biopsy device, adjacent transmural biopsy specimens were obtained from the transition zone between normal and ischemic tissue after 5, 30, 45, 60 and 120 minutes of ischemia. The first 1.8 mm of epicardial tissue was taken for the analysis of flow and metabolites. The results confirmed the existence of a sharp interface of flow and metabolism in the epicardial lateral plane at the boundary of the ischemic zone. There was no significant zone of intermediate injury (flow and metabolism being depressed uniformly throughout the ischemic area). Comparison of the distribution of flow determined by radiolabeled gadolinium-153 at onset of ischemia with that indicated by radiolabeled tin-113 microspheres given at the end of various periods of ischemia revealed no change in the position or steepness of the flow interface at any time during the first 2 hours of ischemia. This observation, together with the absence of any major redistribution or enhancement of residual flow to the ischemic zone, indicated that there was little or no significant collateralization between 5 and 120 minutes. Analysis of the adenosine triphosphate (ATP) content revealed a rapid depletion during the first 5 minutes of ischemia; the content then remained essentially unchanged until 30 minutes, after which time a second phase of accelerated ATP depletion was observed until 45 minutes. ATP content then remained relatively constant up to 2 hours.

Effects of prostaglandin E2, propranolol and nitroglycerine with halothane, pethidine or pentobarbitone anaesthesia on arrhythmias and other responses to ligation of a coronary artery in rats

The effects of various cardiovascular drugs (prostaglandin E2 (PGE2), propranolol and nitroglycerine) and anaesthetic regimens (halothane, pethidine and pentobarbitone), upon the outcome of coronary artery ligation in acutely prepared rats were determined. Effects upon arrhythmias, blood pressure, heart rate, mortality, ECG and the size of the occluded zone were determined for each drug in the presence of each anaesthetic. PGE2 and nitroglycerine had no statistically significant effects on the outcome of ligation whatever the anaesthetic. Propranolol had limited antiarrhythmic actions. The anaesthetic used had major effects upon the outcome of ligation, regardless of the cardiovascular drugs administered. Pentobarbitone anaesthesia resulted in the highest mortality, and most arrhythmias. Pethidine-N2O anaesthesia was associated with fewer arrhythmias. Halothane-N2O anaesthesia markedly decreased the incidence and severity of arrhythmias, independent of the cardiovascular drug. It was concluded that the anaesthetic used can have a major influence on ligation-induced arrhythmias in acutely prepared anaesthetized rats.

Sustained limitation of myocardial necrosis 24 hours after coronary artery occlusion: verapamil infusion in dogs with small myocardial infarcts

Studies were undertaken to ascertain whether verapamil infusion affords a sustained limitation of myocardial injury in the dog after a 24-hour period of coronary artery occlusion. Regional myocardial ischemia was induced by an embolization procedure which did not involve thoracotomy. Immediately after embolization radioactive microspheres were administered intraventricularly to define any area of myocardial underperfusion (zone at risk of infarction). Verapamil (0.005 mg/kg/min) was then administered and maintained for 24 hours during which time the dogs were allowed to recover from anesthesia. The control group received a corresponding infusion of saline solution. After 24 hours the dogs were killed and transverse myocardial sections (3 mm) were prepared. The resulting area of necrosis was visualized by tetrazolium staining, and risk zones were visualized by autoradiography. In the control heart, 62 +/- 7% of the zone at risk deteriorated to necrotic tissue, whereas in the verapamil-treated group only 18 +/- 4% of the tissue in the zone at risk became necrotic. Verapamil appeared to exert a significant (p less than 0.001) tissue-sparing effect that was sustained for at least 24 hours after the onset of ischemia.

Comparison of ASAT, CK, CK-MB, and LD for the estimation of acute myocardial infarct size in man

The purpose of this study was to set up a simple and reliable procedure for estimating acute myocardial infarct (AMI) size by measuring serum enzymes in a few daily blood samples. Peak enzyme values and estimated infarct size from one, two, or three daily samples of aspartate aminotransferase (ASAT), creatine kinase (CK), CK-MB, and lactate dehydrogenase (LD) were compared with the extent of myocardial necrosis measured at autopsy in 22 patients who died from AMI. The correlation between the extent of the necrosis measured and peak serum enzymes from one daily blood sample was highest for CK-MB (r = 0.78) and LD (r = 0.73) compared to CK (r = 0.68) and ASAT (r = 0.67). To obtain a significant correlation, however, two patients had to be excluded from the ASAT and LD analyses. No significant improvement was obtained by more frequent blood sampling. Estimation of infarct size did not improve the correlation significantly for any enzyme, although the coefficient of correlation for CK-MB increased slightly (r = 0.83). Serum CK-MB determination provides a semiquantitative estimate of infarct size, but the other enzymes may give erroneous estimates owing to lesser cardiospecificity.

Ventricular performance and biochemical alteration of regional ischemic myocardium after reperfusion in the pig

Reperfusion of acutely ischemic myocardium may cause profound alterations in left ventricular wall performance and metabolism. This study evaluates regional left ventricular wall thickness, analyzes metabolic and biochemical alterations, and examines tissue hemorrhage during 15, 30, and 120 minutes of myocardial ischemia, each followed by 120 minutes of reperfusion. Reperfusion after 15 minutes of ischemia showed nearly normal ventricular wall thickening and motion, intact metabolic and biochemical function, and no tissue hemorrhage. However, reperfusion after 30 and 120 minutes of ischemia was associated with ventricular wall thickening and failure to resume systolic and diastolic wall motion. Furthermore, adverse metabolic and biochemical alterations and reperfusion zone hemorrhaging increased proportionally with the duration of ischemia. These findings suggest critical myocardial damage occurring between 15 and 30 minutes of ischemia in an animal model without preexisting coronary collateral circulation. The observed metabolic and biochemical changes are consistent with irreversible cell membrane defects, allowing calcium ion accumulation and thus adversely affecting diastolic relaxation and systolic thickening.

Nitroglycerin intravenous infusion

The treatment of various cardiovascular problems with intravenous nitroglycerin is widely practiced though unapproved. The uses of iv nitroglycerin include improvement of the hemodynamics of left ventricular failure and cardiogenic shock associated with infarction, control of hypertension during coronary artery surgery, and possibly, reduction of acute myocardial infarct size. The popularity of this treatment in the absence of an FDA-approved commercial product has forced some hospitals to prepare the drug extemporaneously, and the advantages and disadvantages of preparation and storage techniques are presented.

Effect of halothane on myocardial infarct size in rats

The effect of halothane on myocardial infarction caused by ligation of the left descending coronary artery was studied in rats. The extent of infarction was quantified 48 hours after ligation of the artery by planimetric measurement of left ventricular slices stained with nitrobluetetrazolium. Animals exposed to halothane one per cent for three hours after the coronary ligation were compared with a control group which received halothane for only 5-7 minutes during surgery. It was found that halothane caused a small increase in infarction size (31.3 +/- 1.5 per cent of the left ventricle compared to 25.7 +/- 2.3 per cent, p less than 0.05). This effect was accompanied by a decrease in systolic blood pressure (91 +/- 2 mmHg compared to 113 +/- 3 mmHg, p less than 0.001). Heart rate did not change significantly. Analysis of our results in comparison to previously reported data on the effect of halothane on myocardial ischaemia in different experimental conditions shows that halothane may produce beneficial as well as detrimental effect on ischaemic injury to the myocardium. The latter can result when the drug causes marked hypotension in the absence of a significant decrease in heart rate.