Beta-adrenergic blockade in the prevention of myocardial infarction: a new theory

Usefulness of universal beta-blocker therapy in patients after ST-elevation myocardial infarction

The use of beta-blockers (BB) in the context of ST-segment elevation myocardial infarction (STEMI) was a universal practice in the pre-reperfusion era. Since then, evidence of their use for secondary prevention after STEMI is scarce. Our aim is to determine treatment results associated with BB therapy after a STEMI at 1-year follow-up in a contemporary nationwide cohort.A prospective analysis involving 49 national centers, including patients admitted with STEMI, enrolled between October 2010 and September 2019 was conducted. The primary outcome was defined as the composite of all-cause mortality or hospital re-admission for a cardiovascular (CV) cause in the first year after STEMI. The patients were distributed into 2 groups, depending on whether they received therapy with BB at hospital discharge or not (BB and NB group, respectively).A total of 3145 patients were included in the analysis, of which 2526 (80.3%) in the BB group. A total of 12.2% of patients reached the primary outcome. Regarding the univariate Cox regression analysis, the BB group presented lower mortality or re-admission for CV cause at 1-year follow-up [hazard ratio (HR) 0.69, confidence interval (CI) 95% 0.55-0.87, P = .001]. However, after adjustment for significant covariates, this association was lost (HR 0.73, CI 95% 0.51-1.04, P = .081). In patients with preserved (HR 0.73, CI 95% 0.51-1.04, P = .081) and mid-range (HR 1.01, CI 95% 0.64-1.61, P = .959) left ventricular ejection fraction (LVEF), the primary outcome was similar between the 2 groups, while in patients with reduced LVEF, the BB group presented a better prognosis, with fewer patients reaching the primary outcome (HR 0.431, CI 95% 0.262-0.703, P = .001).BB universal therapy after STEMI has not proved useful, but it seems to be beneficial in patients with reduced LVEF.

Effect of beta blockers, particularly carvedilol, on reducing the risk of events after acute myocardial infarction

The morbidity and mortality rates of patients who have had acute myocardial infarctions (AMIs) are high. Clinical guidelines recommend that most survivors of AMIs without contraindications should receive long-term treatment with beta blockade. Beta blockers have been shown to reduce mortality and reinfarction after AMI, but the pharmacologic differences among beta blockers may affect their ability to reduce these adverse events. The beta blocker carvedilol has adjunctive pharmacologic properties, including alpha1-blocking, antioxidant, anti-inflammatory, and antiarrhythmic activities that appear to underlie the outcomes demonstrated in experimental models and clinical trials. In conclusion, this review explores the experimental and clinical evidence supporting the preferential use of carvedilol in post-AMI patients with left ventricular dysfunction.

Esmolol cardioplegia in unstable coronary revascularisation patients. A randomised clinical trial

BACKGROUND

Esmolol has been studied and applied to control hypertension and tachycardia during open heart surgery. Esmolol has been used on a minor scale as a single cardioplegic agent. Little information is available on esmolol as a component of blood cardioplegia. In this prospective, randomised, double-blind clinical study we investigated whether esmolol improves cardioprotection in patients scheduled for an urgent coronary operation.

METHODS

Forty patients with unstable angina were operated using cold blood cardioplegia as the basic cardioprotective method. Cardioplegia was infused intermittently, and esmolol was given into the cardioplegia line (15 mg/min) during cold infusions. Patients with ongoing myocardial infarction were excluded.

RESULTS

The arrest time during the cardioplegic induction or the rate of spontaneous resumption of the heart rhythm did not differ significantly between the groups. The serial measurements of plasma creatine kinase MB-fraction activity (P=0.27), serum creatine kinase MB-fraction mass assay (P=0.16), troponin I (P=0.41) and myoglobin (P=0.14) similarly did not differ between the groups, nor did myocardial lactate extraction (P= 0.12).

CONCLUSION

Esmolol addition to blood cardioplegia did not increase the efficacy of cardioprotection in the present study setting in unstable patients during urgent coronary revascularisation.

Failure of allopurinol to improve left ventricular stroke work after cardiopulmonary bypass surgery

OBJECTIVE

This study examined the effects of allopurinol on global left ventricular function after coronary artery bypass surgery.

DESIGN

A randomized prospective partially blinded study in 52 patients undergoing elective coronary artery bypass surgery.

SETTING

Conducted in a university-affiliated tertiary care facility.

INTERVENTIONS

Participants received 400 mg of allopurinol 18 hours and 400 mg of allopurinol orally 3 hours before surgery or no allopurinol. Patients then received a standard anesthetic technique consisting of target-controlled opiate infusion and inhalation anesthesia. Coronary artery bypass was performed using moderate hypothermia and oxygenated crystalloid cardioplegia.

MEASUREMENTS AND MAIN RESULTS

Global left ventricular function was assessed by means of left ventricular stroke work index (LVSWI) calculated before and after induction of anesthesia and after cardiopulmonary bypass at 15 minutes, 6, 12 and 24 hours. There was no difference in the LVSWI before or after surgery when the two groups were compared.

CONCLUSIONS

In this population sample, the use of preoperative allopurinol did not result in improved left ventricular stroke work after coronary artery bypass surgery.

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.

Absence of beneficial effect of intravenous metoprolol given during angioplasty in patients with single-vessel coronary artery disease

In a double-blind, randomized, placebo-controlled trial, the possible anti-ischemic effect of metoprolol during percutaneous transluminal coronary angioplasty was tested. Electrocardiograms, hemodynamics, and metabolism were studied in 27 patients with a stenosis in the left anterior descending coronary artery. Measurements took place before angioplasty, after each of four 1-minute occlusions and 15 minutes after the last balloon deflation. Patients were randomly given placebo or metoprolol (15 mg as a bolus intravenously, followed by an infusion of 0.04 mg/kg/hr). At the end of the procedure, the rate-pressure product had decreased by 15% (NS) and 23% (p = 0.001) in the placebo and metoprolol groups, respectively, mainly due to similar decreases in heart rate. Metoprolol tended to lower chest pain and reduce precordial ST-segment elevation due to angioplasty, but the effects were not statistically significant. Lactate, hypoxanthine, and urate release immediately after deflation was similar in both groups. Metoprolol reduced arterial plasma hypoxanthine throughout the procedure by about 30% (p < or = 0.02 vs. placebo). Thus, intravenous infusion of metoprolol did not significantly attenuate chest pain and ST-segment elevation, and failed to decrease cardiac lactate and oxypurine release. It did, however, reduce arterial hypoxanthine concentrations during angioplasty, possibly indicating that the beta-blocker inhibits extracardiac ATP catabolism.