Experimental and clinical observations on the efficacy of esmolol in myocardial ischemia

Effect of esmolol on myocardial protection in pediatrics congenital heart defects

Background:

Although it is accepted that inducing cardioplegia is the gold standard in myocardial protection, there is still no consensus on the exact type of the cardioplegia. There are fewer studies on the type of the cardioplegia in hearts of the children than adults and they are contradictory. The effects of esmolol have been reviewed (a type of ultrashort-acting beta-adrenergic antagonist, i.e., ß-blockers) in conjunction with the cardioplegia due to the effect of the β-blockers in reducing the myocardial ischemia and reperfusion.

Materials and Methods:

The left ventricle ejection fraction (LVEF), systolic blood pressure, central venous pressure (CVP), heart rate, etc., were recorded separately in patients who received the cardioplegia without esmolol (n = 35) and with esmolol (n = 30) and matched for the age and sex.

Results:

The amount of inotrope used in the group without esmolol (100%) was considerably higher than in the group with esmolol (86.7%). Postoperative arrhythmias did not differ significantly between the two groups. There was no significant difference in the duration of cardiopulmonary bypass (CPB), time of the extubation, length of the ICU stay, the first day EF after surgery, and the first week EF after surgery as well. Creatinine kinase-MB (CKMB) was significantly higher in the group without esmolol during operation than in the group with esmolol.

Conclusions:

The patients who received cardioplegia along with esmolol had less inotropic requirement after operation, and increase in EF and cardiac output (CO) 1 week after surgery. In addition, it reduced damage to the heart during surgery, and patients may have greater stability in the cardiac conduction system.

Intracoronary followed by intravenous administration of the short-acting β-blocker landiolol prevents myocardial injury in the face of elective percutaneous coronary intervention

BACKGROUND

Myocardial injury during elective percutaneous coronary intervention (PCI) is associated with higher subsequent cardiac events and mortality. β-Blockers have been used to reduce myocardial injury during ischemia and reperfusion. We investigated whether intracoronary followed by intravenous administration of the short-acting β-blocker landiolol prevents myocardial injury in the face of elective PCI.

METHODS AND RESULTS

Patients undergoing elective PCI (n=70) were randomly assigned to the landiolol (n=35) or control (n=35) group. Landiolol or saline was administered into target vessels through a balloon catheter for 1min before and after first balloon inflation followed by continuous intravenous administration for 6h after PCI. The incidence of myocardial injury defined by cardiac troponin-I (cTnI) >/=0.05 ng/ml was 79% of the patients in the control group compared to 56% in the landiolol group (p=0.04). The cTnI level at 24h after PCI tended to be lower in the landiolol group (0.57 ± 1.14 versus 1.27 ± 2.48 ng/ml; p=0.07), while the CK-MB level was not significantly different between the landiolol and control groups. The incidence of peri-procedural myocardial infarction defined by cTnI >/=0.12 ng/ml was significantly (p=0.02) lower in the landiolol group (41%) compared to the control group (70%). There was no incidence of coronary spasm, hypotension, bradycardia or heart failure during and after PCI in the two groups.

CONCLUSIONS

Brief intracoronary followed by continuous intravenous administration of landiolol is safe and effective for myocardial protection in the face of elective PCI.

Protective effects of a magnesium magnetic isotope (Mg25)-exchanging nanoparticle (25MgPMC16 ) on mitochondrial functional disorders in esmolol-induced cardiac arrest in rats

In cardiac surgery, agents are needed to produce temporary cardiac arrest (cardioplegia). One of these agents is esmolol (ESM) which is a short-acting selective beta-1 adrenergic receptor antagonist and its overdose causes diastolic ventricular arrest. The (25) MgPMC(16) (porphyrin adducts of cyclohexil fullerene-C60) is known as a nanoparticle which has a cardioprotective effect when the heart is subjected to stressful conditions. In this study, we aimed to confirm the deleterious effects of ESM overdose on cardiac mitochondria and identify any protective effects of (25) MgPMC(16) in male Wistar rats. Esmolol 100 mg kg(-1) (LD50 = 71 mg kg(-1) ) was injected intravenously (i.v.) into tail vein to induce cardiac arrest. This dose was obtained from an ESM dose-response curve which induces at least 80% arrest in rats. (25) MgPMC(16) at three different doses (45, 90 and 224 mg kg(-1) ) was injected i.v. as pretreatment, eight hours before ESM injection. (25) MgCl(2) or (24) MgPMC(16) were used as controls. Following cardiac arrest, the heart was removed and the mitochondria extracted. Mitochondrial viability and the adenosine 5'-diphosphate sodium salt hydrate/Adenosine 5'-triphosphate disodium salt hydrate (ADP/ATP) ratio were measured as biomarkers of mitochondrial function. Results indicate that (25) MgPMC(16) caused a significant increase in mitochondrial viability and decrease in ADP/ATP ratio. No significant changes were seen with (24) MgPMC(16) or (25) MgCl(2) . It is concluded that cardiac arrest induced by ESM overdose leads to a significant decrease in mitochondrial viability and their ATP levels, whereas pretreatment by (25) MgPMC(16) can protect mitochondria by increasing ATP level through liberation of Mg into cells and the improvement of hypoxia.

Elevated heart rate and cardiovascular outcomes in patients with coronary artery disease: clinical evidence and pathophysiological mechanisms

There is an established body of evidence from epidemiological studies which indicates that an elevated resting heart rate is independently associated with atherosclerosis and increased cardiovascular morbidity and mortality, in both the general population and in patients with established cardiovascular disease. Clinical trial data suggest that in patients with coronary artery disease, an elevated heart rate identifies those at increased risk of adverse cardiovascular outcomes, and that lowering of heart rate may reduce major cardiovascular events in patients with an elevated heart rate and symptom-limiting angina. These results suggest that an increased heart rate may have an adverse impact on the atherosclerotic process and increase the risk of a cardiovascular event in patients with coronary artery disease. The precise pathophysiological mechanisms that link heart rate and cardiovascular outcomes have yet to be defined. Possibilities may include indirect mechanisms related to autonomic dysregulation and those due to an increase in heart rate per se, which can increase the ischaemic burden and exert local haemodynamic forces that can adversely impact on the endothelium and arterial wall. For these reasons, heart rate should be considered as a therapeutic target in the treatment of patients with coronary artery disease.

The effect of landiolol on cerebral blood flow in patients undergoing off-pump coronary artery bypass surgery

PURPOSE

To examine the effect of landiolol on cerebral blood flow in patients with normal or deteriorated cardiac function.

METHODS

Thirty adult patients who were diagnosed with angina pectoris and who underwent elective off-pump coronary artery bypass surgery were studied. Patients were divided into two groups, one with a preoperative left ventricular ejection fraction (EF) of 50% or higher (normal EF group; n = 15) and the other with an EF of less than 50% (low EF group; n = 15). The mean cerebral blood flow velocity (Vmca) and pulsatility index (PI) in the middle cerebral artery were recorded using transcranial Doppler ultrasonography (TCD). Individual hemodynamic data were obtained using a pulmonary arterial catheter.

RESULTS

In both groups, landiolol produced a significant decrease in heart rate (HR), which then returned to baseline 15 min after administration was completed. A significant decrease in mean arterial pressure occurred in the low EF group, but the decrease was within 30% of the baseline. In the normal EF group, there was no decrease in cardiac index (CI), whereas in the low EF group, CI significantly decreased along with the decrease in HR. There were no significant differences in Vmca and PI between the two groups.

CONCLUSION

Continuous administration of landiolol at a dose of 0.04 mg/kg/min after 1 min rapid i.v. administration at a dose of 0.125 mg/kg/min decreases HR without causing aggravation of CBF during treatment of intraoperative tachycardia in patients with normal and deteriorated cardiac function.

Comparison of the potassium channel blocker tedisamil with the beta-adrenoceptor blocker esmolol and the calcium antagonist gallopamil in patients with coronary artery disease

BACKGROUND

Tedisamil is a new bradycardic agent proven to exert anti-ischemic and antiarrhythmic effects by blockade of the different cardiac and vascular K+ currents.

HYPOTHESIS

It was the aim of the present study to compare the favorable anti-ischemic effects of tedisamil, with two long established representatives in the treatment of coronary artery disease (CAD), namely, the beta1 blocker esmolol and the Ca2 antagonist gallopamil.

METHODS

The hemodynamic and neurohumoral effects of the new potassium channel blocker tedisamil, an agent with negative chronotropic and class III antiarrhythmic properties, were compared with the ultra-short-acting beta1-selective adrenoceptor blocker esmolol and the calcium antagonist gallopamil. A total of 22 patients with angiographically proven CAD and reproducible ST-segment depression in the exercise electrocardiogram was included in two studies with an almost identical design and inclusion criteria. The investigation was carried out using right heart catheterization and bicycle ergometry. A subgroup of 8 patients receiving 0.3 mg/kg body weight tedisamil intravenously (i.v.) in an open dose-finding study was compared with a group of 14 patients who had received esmolol (i.v. bolus of 500 micrograms/kg, maintenance dose 200 micrograms/kg/min) and gallopamil (initial dose 0.025 mg/kg, maintenance dose 0.0005 mg/kg/h) in a second intraindividual comparison.

RESULTS

Tedisamil and esmolol reduced heart rate at rest by 13% (p < 0.001), and 6% (p < 0.05), and at maximum working levels by 8% (p < 0.01) and 9% (p < 0.05), respectively. Gallopamil increased heart rate at rest by 7% (p < 0.05), with only slight changes occurring during exercise. Corresponding findings for each drug were observed for cardiac output both at rest and during exercise [tedisamil: at rest -10% (NS), max. exercise -8%; esmolol: at rest -14% (NS), max. exercise -18% (NS); gallopamil: no significant changes]. Compared with tedisamil, stroke volume was reduced by esmolol [at rest and max. workload: -9% (NS)] and gallopamil [rest: -6% (NS), max. exercise: -2% (NS)]. Of the indirect parameters of ventricular function, that is, mean capillary wedge pressure (PCWPm) and right ventricular ejection fraction, only PCWPm demonstrated significant differences between tedisamil and gallopamil (+18% and -6% at rest, +17% and -21% during exercise, respectively; p < 0.001). Compared with gallopamil, both tedisamil and esmolol were superior in their effects on rate-pressure product, myocardial oxygen consumption, and ST-segment depression, whereas plasma lactate concentration was more reduced by tedisamil and gallopamil. Tedisamil led to a fall in norepinephrine levels in particular.

CONCLUSION

Tedisamil and esmolol showed almost equipotent anti-ischemic effects at the doses administered. Tedisamil acts mainly by reductions in heart rate, and esmolol, though to a lesser degree, also by reductions in systolic blood pressure. The mechanism of gallopamil is to reduce afterload and to improve coronary perfusion. At the doses applied, however, it has lower antianginal potency compared with tedisamil and esmolol.

The effect of landiolol on hemodynamics and left ventricular function in patients with coronary artery disease

STUDY OBJECTIVE

To examine the effect of landiolol (normal dose) on hemodynamics and left ventricular (LV) function.

DESIGN

Prospective, observational, repeated-measures study.

SETTING

University hospital.

PATIENTS

56 adult patients who were diagnosed with angina pectoris and who underwent elective off-pump coronary artery bypass surgery.

INTERVENTIONS

Patients were divided into two groups based on a preoperative LV ejection fraction (EF) 50% or higher (normal EF group, n = 28) and lower than 50% (low EF group, n = 28). Hemodynamics and LV function were recorded using a pulmonary artery catheter and transesophageal echocardiography at three time points (before administration of landiolol, immediately before completion of administration, and 15 minutes after completion of administration).

MEASUREMENTS

Individual hemodynamic data were obtained using a pulmonary artery catheter, and individual parameters were determined from LV short-axis views in transesophageal echocardiography.

MAIN RESULTS

Mean preoperative EFs were 57% +/- 5% and 47% +/- 3% in the normal and low EF groups, respectively. In both groups, landiolol produced a significant decrease in heart rate (HR), which then returned to baseline 15 minutes after completion of administration. A significant decrease in mean arterial pressure occurred in the low EF group, but the decrease was within 30% of baseline. In the normal EF group, there was no decrease in cardiac index, but a significant increase in stroke index, in addition to an increase in stroke volume. In the low EF group, cardiac index significantly decreased along with the decrease in HR, but there was no increase in end-diastolic volume or stroke volume.

CONCLUSIONS

Administration of landiolol using the presently recommended dosage and administration route causes a decrease in HR without aggravation of hemodynamics in patients with normal cardiac function, but in patients with preoperative EF lower than 50%, it may lead to further deterioration of cardiac function due to a decrease in HR.

Efficacy of esmolol as a myocardial protective agent during continuous retrograde blood cardioplegia

OBJECTIVE

Esmolol, an ultra-short-acting beta-blocker, is known to attenuate myocardial ischemia-reperfusion injury. The aim of this study was to compare the effects of esmolol and potassium on myocardial metabolism during continuous normothermic retrograde blood cardioplegia.

METHODS

Forty-one patients operated on for isolated aortic valve stenosis were randomly assigned to continuous coronary infusion with either potassium or esmolol during cardiopulmonary bypass. Myocardial metabolism was assessed by measuring the transmyocardial gradient of oxygen content indexed to left ventricular mass of glucose, lactate, and nitric oxide. To do so, blood samples were simultaneously withdrawn upstream (in the cardioplegia line) and downstream of the myocardium (in the left coronary ostium) 10 and 30 minutes after aortic crossclamping.

RESULTS

Although the cardioplegia flow rate and pressure were similar, esmolol markedly reduced the transmyocardial gradient of oxygen content indexed to left ventricular mass compared with potassium: 13 +/- 6 vs 20 +/- 6 mL of oxygen per liter of blood per 100 g of myocardium, respectively, at 10 minutes and 16 +/- 8 vs 24 +/- 8 mL of oxygen per liter of blood per 100 g of myocardium, respectively, at 30 minutes (P =.009). Coronary glucose and lactate transmyocardial gradients were similar in both groups, indicating adequate myocardial perfusion in all patients at all times. In addition, during retrograde cardioplegia, esmolol showed a lower nitric oxide release compared with that caused by potassium (39 +/- 49 micro mol x L(-1) for potassium vs 14 +/- 8 micro mol x L(-1) for esmolol at 10 minutes and 39 +/- 47 micro mol x L(-1) for potassium vs 6 +/- 8 micro mol x L(-1) for esmolol at 30 minutes, P =.05). However, hemodynamic parameters and plasma troponin I levels remained unchanged postoperatively between the 2 types of cardioplegia.

CONCLUSION

Esmolol provides potent myocardial protection in hypertrophied hearts, at least in part, by reducing myocardial oxygen metabolism.

Myocardial protection with oxygenated esmolol cardioplegia during prolonged normothermic ischemia in the rat

OBJECTIVE

We previously showed that arrest with multidose infusions of high-dose (1 mmol/L) esmolol (an ultra-short-acting beta-blocker) in oxygenated Krebs-Henseleit buffer (esmolol cardioplegia) provided complete myocardial protection after 40 minutes of normothermic (37 degrees C) global ischemia in isolated rat hearts. In this study we investigated the importance of oxygenation for protection with esmolol cardioplegia, compared it with that of St Thomas' Hospital cardioplegia, and determined the protective efficacy of multidose esmolol cardioplegia for extended ischemic durations.

METHODS

Isolated rat hearts (n = 6/group) were perfused in the Langendorff mode at constant pressure (75 mm Hg) with oxygenated Krebs-Henseleit bicarbonate buffer at 37 degrees C. The first part of the first study had four groups: (i) multidose (every 15 minutes) oxygenated (95% oxygen/5% carbon dioxide) Krebs-Henseleit buffer during 60 minutes of global ischemia, (ii) multidose deoxygenated (95% nitrogen/5% carbon dioxide) Krebs-Henseleit buffer during 60 minutes of global ischemia, (iii) multidose oxygenated esmolol cardioplegia during 60 minutes of global ischemia, and (iv) multidose deoxygenated esmolol cardioplegia during 60 minutes of global ischemia. The second part of the first study had three groups: (v) multidose St Thomas' Hospital solution during 60 minutes of global ischemia, (vi) multidose oxygenated St Thomas' Hospital solution during 60 minutes of global ischemia, and (vii) multidose oxygenated esmolol cardioplegia during 60 minutes of global ischemia. In the second study, hearts were randomly assigned to 60, 75, 90, or 120 minutes of global ischemia and at each ischemic duration were subjected to multidose oxygenated constant flow or constant pressure infusion of (i) Krebs-Henseleit buffer (constant flow), (ii) Krebs-Henseleit buffer (constant pressure), (iii) esmolol cardioplegia (constant flow), or (iv) esmolol cardioplegia (constant pressure). All hearts were reperfused for 60 minutes, and recovery of function was measured.

RESULTS

Multidose infusion of oxygenated esmolol cardioplegia completely protected the hearts (97% +/- 5%) after 60 minutes of 37 degrees C global ischemia. Deoxygenated esmolol cardioplegia was significantly less protective (45% +/- 8%). Oxygenation of St Thomas' Hospital solution did not alter its protective efficacy in this study (70% +/- 4% vs 69% +/- 7%). Infusion of esmolol cardioplegia at constant pressure provided complete protection for 60, 75, and 90 minutes (104% +/- 5%, 95% +/- 5%, and 95% +/- 3%, respectively), whereas protection with constant-flow esmolol cardioplegic infusion was significantly decreased at ischemic durations longer than 60 minutes. This decrease in efficacy of constant-flow esmolol cardioplegia was associated with increasing coronary perfusion pressure leading to myocardial injury.

CONCLUSIONS

Oxygenation of esmolol cardioplegia (Krebs-Henseleit buffer plus 1.0 mmol/L esmolol) was essential for optimal myocardial protection. Multidose infusion of oxygenated esmolol cardioplegia provided good myocardial protection during extended periods of normothermic ischemia. Esmolol cardioplegia may provide an efficacious alternative to hyperkalemia.

Myocardial protection: the efficacy of an ultra-short-acting beta-blocker, esmolol, as a cardioplegic agent

OBJECTIVE

During myocardial revascularization, some surgeons (particularly in the United Kingdom) use intermittent crossclamping with fibrillation as an alternative to cardioplegia. We recently showed that intermittent crossclamping with fibrillation has an intrinsic protection equivalent to that of cardioplegia. In this study we hypothesized that arrest, rather than fibrillation, during intermittent crossclamping may be beneficial. Because esmolol, an ultra-short-acting beta-blocker, is known to attenuate myocardial ischemia-reperfusion injury, we compared the protective effect of esmolol arrest with that of intermittent crossclamping with fibrillation and conventional cardioplegia (St Thomas' Hospital solution).

METHODS

Isolated rat hearts were Langendorff perfused at either constant flow (14 mL/min) or constant pressure (75 mm Hg) with oxygenated Krebs-Henseleit bicarbonate buffer (37 degrees C), and left ventricular developed pressure was assessed. In study 1 (constant flow perfusion) 8 groups (n = 6 hearts per group) were studied: (1) 40 minutes of global ischemia; (2) 2 minutes of St Thomas' Hospital infusion and 40 minutes of ischemia; (3) multidose (every 10 minutes) infusions of St Thomas' Hospital solution during 40 minutes of ischemia; (4) 2 minutes of esmolol infusion and 40 minutes of ischemia; (5) multidose (every 10 minutes) esmolol infusions during 40 minutes of ischemia; (6) continuous infusion of esmolol for 40 minutes during coronary perfusion; (7) intermittent (4 x 10 minutes) ischemia with ventricular fibrillation; and (8) intermittent (4 x 10 minutes) ischemia preceded by intermittent esmolol administration. All protocols were followed by 60 minutes of reperfusion. Further experiments (study 2) examined the esmolol administration method in hearts perfused by constant pressure.

RESULTS

An optimal arresting dose of 1.0 mmol/L esmolol was established. In study 1 recovery of left ventricular developed pressure (expressed as percentage of preischemic value) was 7% +/- 4%, 28% +/- 8%, 70% +/- 5%, 8% +/- 1%, 90% +/- 4%, 65% +/- 3%, 71% +/- 5%, and 76% +/- 5% in groups 1 to 8, respectively. Intermittent esmolol arrest with global ischemia provided equivalent myocardial protection to intermittent crossclamping with fibrillation, continuous esmolol perfusion, and multidose St Thomas' Hospital solution. Surprisingly, multidose esmolol infusion was more protective than all other treatments. In further experiments (study 2) optimal recovery was obtained with multiple esmolol infusions (by constant flow or constant pressure), but continuous esmolol infusion (at constant flow) was less effective than constant pressure infusion.

CONCLUSIONS

Intermittent arrest with esmolol did not enhance protection of intermittent crossclamping with fibrillation; however, multiple esmolol infusions during global ischemia provided improved protection. Administration (constant flow or constant pressure) of arresting solutions influenced outcome only during continuous infusion. Multidose esmolol arrest may be a beneficial alternative to intermittent crossclamping with fibrillation or conventional cardioplegia.

Ischemic preconditioning, myocardial stunning and anesthesia

Brief periods of ischemia have been shown to protect the heart against a subsequent prolonged ischemic insult, a phenomenon known as ischemic preconditioning. The protective effects of preconditioning markedly reduce myocardial ischemic injury in vivo. Volatile anesthetics have been shown to protect myocardium against infarction by a mechanism similar to that of ischemic preconditioning. Contractile dysfunction occurs after a brief period of myocardial ischemia, despite restoration of coronary blood flow in the absence of tissue necrosis. This process is known as myocardial stunning and has important clinical ramifications. Evidence indicates that adenosine triphosphate-regulated potassium channel function plays a central role in ischemic preconditioning, stunned myocardium, and in anesthetic-induced protection against ischemic injury.

Esmolol and percutaneous cardiopulmonary bypass enhance myocardial salvage during ischemia in a dog model

Despite recent advances in techniques of reperfusion for acute myocardial ischemia, myocardial salvage remains suboptimal. Beta-blockers have been shown to limit infarct size during acute ischemia, but their negative inotropic properties have limited their use. Cardiopulmonary bypass is an attractive technique for cardiac resuscitation because it can stabilize a hemodynamically compromised patient and potentially reduce myocardial oxygen consumption. In an attempt to maximize myocardial salvage in the setting of acute ischemia, the combination of esmolol, an ultrashort-acting beta-blocker, with percutaneous cardiopulmonary bypass was evaluated. Four groups of instrumented dogs underwent 2 hours of myocardial ischemia induced by occlusion of the proximal left anterior descending coronary artery, followed by 1 hour of reperfusion. Throughout the period of ischemia and reperfusion, esmolol plus percutaneous cardiopulmonary bypass was compared with esmolol alone, percutaneous cardiopulmonary bypass alone, and control conditions. After the reperfusion period, the extent of infarction of the left ventricle at risk was determined. Four animals had intractable arrhythmias: one in the esmolol plus bypass group, one in the esmolol group, and two in the control group. The extent of infarction of the left ventricle at risk was significantly reduced in the esmolol plus bypass group (30%) compared with bypass alone (52%), with esmolol alone (54%), and with the control groups (59%; p < 0.05). We conclude that in this experimental model the combination of esmolol with bypass improves myocardial salvage after ischemia and reperfusion.

Comparative effects of esmolol and labetalol to attenuate hyperdynamic states after electroconvulsive therapy

We studied 18 patients (age range, 53-90 yr) with at least one cardiovascular risk factor who were treated with electroconvulsive therapy (ECT) and compared effects of five pretreatments: no drug; esmolol, 1.3 or 4.4 mg/kg; or labetalol, 0.13 or 0.44 mg/kg. Each patient received all five treatments, during a series of five ECT sessions. Pretreatment was administered as a bolus within 10 s of induction or anesthesia. Doses of methohexital and succinylcholine were constant for the series of treatments and the assignment to no drug or to drug and dose was determined by randomized block design. Measurements of systolic and diastolic blood pressure (SBP, DBP) and heart rate (HR) were recorded during the awake state and 1, 3, 5, and 10 min after the seizure. The deviation of ST segments from baseline was measured by an electrocardiogram (ECG) monitor equipped with ST-segment analysis software. The results (mean +/- SEM) show that without pretreatment, there were significant (P < 0.05) peak increases in SBP and HR (55 +/- 5 mm Hg and 37 +/- 6 bpm, respectively), recorded 1 min after the seizure. Comparable reductions (by approximately 50%) in these peak values were achieved after esmolol (1.3 mg/kg) or labetalol (0.13 mg/kg), and cardiovascular responses were nearly eliminated after the same drugs in doses of 4.4 and 0.44 mg/kg, respectively. The deviation of ST-segment values from baseline in any lead was not measurably influenced by either antihypertensive drug. SBP values were lower after labetalol 10 min after the seizure, but not after esmolol. Asystolic time after the seizure was not significantly longer with either drug.(ABSTRACT TRUNCATED AT 250 WORDS)

Is esmolol cardioprotective? Tolerance of pacing tachycardia, acute afterloading and hemodilution in dogs with coronary stenosis

OBJECTIVES

The aim of this study was to determine whether esmolol, an ultrashort-acting beta-adrenergic antagonist, possesses cardioprotective properties unrelated to a concomitant decrease in heart rate.

BACKGROUND

Previous studies have demonstrated beneficial effects of beta-adrenergic blocking agents with unchanged heart rates.

METHODS

The effect of esmolol (100 micrograms/kg per min) on the response of global cardiovascular and regional myocardial contractile function (sonomicrometry) to pacing-induced tachycardia and acute left ventricular afterloading was assessed in dogs with a critical stenosis of the left anterior descending coronary artery (LAD). These responses were observed at the baseline hemoglobin level (12.5 +/- 0.3 g/100 ml) as well as after hemodilution-induced mild regional contractile dysfunction (7.4 +/- 0.4 g/100 ml) in the area supplied by this artery (LAD area). Data were analyzed by using a repeated measures multivariate analysis of variance with complete block design treating pacing rate and afterloading, respectively, as the repeated measure.

RESULTS

Esmolol decreased the maximal first derivative of left ventricular pressure (dP/dtmax); global cardiovascular and regional myocardial contractile function were otherwise unchanged. Esmolol did not alter the response of global cardiovascular or regional myocardial function to pacing-induced tachycardia or to acute left ventricular afterloading, both at the baseline hemoglobin level as well as during mild hemodilution-induced LAD area contractile dysfunction.

CONCLUSIONS

At an infusion rate of 100 micrograms/kg per min we were unable to demonstrate cardioprotective esmolol effects in a canine model of critical coronary stenosis with controlled heart rate and identical loading conditions.

Esmolol and ventilatory function in cardiac patients with COPD

To assess the effects of acute cardioselective beta blockade on ventilatory function in patients with COPD and active cardiac disorders, 50 patients were studied during intravenous infusion of esmolol. All patients had an obstructive ventilatory component on baseline pulmonary function testing, and 58 percent had a significant bronchodilator response to inhaled albuterol. Esmolol infusion (8 to 24 mg/min) produced large decreases in heart rate (84 +/- 2 to 69 +/- 2 beats/min, p less than 0.01) and SBP (124 +/- 3 to 106 +/- 3 mm Hg, p less than 0.01). Despite this marked hemodynamic response, there was no significant group effect of beta blockade on pulmonary function. No patient experienced dyspnea or wheezing with acute esmolol infusion; however, three patients (6 percent) developed asymptomatic decreases of FEV1. It is concluded that acute beta blockade with esmolol can be achieved in patients with COPD and cardiac disorders with little risk of bronchospasm.

Effect of the ultrashort-acting beta-blocker Brevibloc on free-radical-mediated injuries during the early reperfusion state

The left descending coronary artery (LAD) was ligated for 45 min or 90 min followed by 1-h reperfusion. During experiments the animals in Group I (15 dogs) received saline infusion, in Group II (20 dogs) they received the ultrashort-acting beta-blocker Brevibloc (esmolol HCl). The marker of lipid peroxidation the malondialdehyde (MDH) as well as endogen scavengers, the glutathione (GSH), and superoxide dismutase (SOD) were measured in the heart tissue homogenates. In blood and heart tissue samples the 6-keto-prostaglandin F1 alpha (PGF1 alpha) and thromboxane B2 (TXB2) were determined. Biochemical measurements revealed that esmolol HCl has beneficial effect on the free-radical-meduated-damage reducing the MDA content in the ischemic area. In Group I the value of MDA after 90 min of LAD ligature was 138 +/- 5.6%, in Group II the elevation was only 107.4 +/- 3.2%. After treatment with Brevibloc the GSH content of ischemic-reperfused areas decreased slightly (81.75 +/- 3.5% of the normal value), moreover, in Group I the depletion of GSH was considerable (64.5 +/- 4.2%). Coronary reperfusion caused the release of eicosanoids in both groups, mainly in the first 10 min. The highest value of thromboxane in blood samples could be measured in Group I after 90 min of LAD ligature (24.8 +/- 3.6 pmol/ml; the normal value 8-12 pmol/ml). In Group II during the same period of experiments the TXB2 in the blood was 14 +/- 3.7 pmol/ml. In heart tissue samples the amount of endoperoxides increased in ischemic and non-ischemic areas of Group I and II. Nevertheless, the calculated ratio of PGF1 alpha and TXB2 was near to the normal after Brevibloc treatment (0.85-0.9; the normal values were 1-1.2). These results indicate that esmolol HCl can modulate both the free-radical-mediated reaction and arachidonic acid metabolism.

Possible survival benefit from concomitant beta-but not calcium-antagonist therapy during reperfusion for acute myocardial infarction

To test the hypothesis that long-term beta- or calcium-antagonist therapy begun before the time of myocardial infarction and coronary reperfusion might improve patient in-hospital survival compared with reperfusion alone, 424 consecutive patients successfully reperfused with coronary angioplasty within 12 hours of infarct symptom onset were carefully and retrospectively characterized. Forty-seven patients (11%) were taking beta antagonists and 74 patients (17%) were taking calcium antagonists at the time of infarction. Patients receiving beta antagonists had a more frequent history of hypertension (p less than or equal to 0.001) and prior infarction (p less than or equal to 0.01) than those not so treated and patients receiving calcium antagonists had a more frequent history of prior infarction, prior angina, hypertension and diabetes (all p less than or equal to 0.001) than their nontreated counterparts. Stepwise logistic regression analysis found significant independent correlations between in-hospital death and the following variables: recurrent ischemia (p less than or equal to 0.001); proximal left anterior descending coronary infarct (p less than or equal to 0.001); 3-vessel disease (p = 0.002); patient age (p = 0.004); and initial total occlusion of the infarct artery (p = 0.022). After adjustment for these factors, beta antagonist use (mortality = 0 vs 8% without treatment) was still significantly correlated with improved survival (p = 0.048), whereas calcium-antagonist therapy made no difference in survival. Heart rate and left ventricular end-diastolic pressure upon presentation were significantly lower in patients treated with beta antagonists. Thus, beta-antagonists therapy, but probably not calcium-antagonist therapy, taken before reperfusion for acute myocardial infarction, may improve early survival compared to reperfusion alone. Larger studies will be required to confirm or refute these observations.

Bolus administration of esmolol for the treatment of intraoperative myocardial ischaemia

We report the successful treatment with esmolol of intraoperative myocardial ischaemia associated with concurrent hypertension and tachycardia, in a patient with risk factors for coronary artery disease undergoing peripheral vascular surgery. The pathophysiology of myocardial ischaemia, and the therapeutic role of beta blocking drugs are briefly reviewed. Esmolol, a short-acting cardioselective beta blocking drug, was administered in a bolus of 1.5 mg.kg-1, and resulted in prompt resolution of the haemodynamic abnormalities, with concomitant restitution of the ST segments to isoelectric baseline. We conclude that bolus administration of esmolol is practical and can be effective for the treatment of intraoperative myocardial ischaemia.

Is "stunned myocardium" a protective mechanism? Effect of acute recruitment and acute beta-blockade on recovery of contractile function and high-energy phosphate stores at 1 day post-reperfusion

There is little doubt that the "stunned myocardium" is amenable to therapeutic intervention, as a host of diverse pharmacologic agents have all been shown to improve short-term contractile function of viable, previously ischemic myocardium. However, few studies have addressed the question: Should the stunned myocardium be forced to contract? If the stunned myocardium is a protective mechanism, then acute recruitment could have later deleterious consequences on recovery of contractile function and high-energy phosphate stores. Conversely, acutely "resting" the heart (i.e. by beta-adrenergic blockade) could conceivably enhance or accelerate recovery of the stunned, postischemic tissue. We therefore sought to assess the immediate and longer-term effects of acute recruitment and acute beta-blockade on regional wall thickening (WT: using two-dimensional echocardiography) and adenosine triphosphate (ATP) content in the canine model of the stunned myocardium. Anesthetized open-chest dogs underwent 15 minutes of transient coronary artery occlusion. At 30 minutes following reperfusion, the dogs acutely received either: the ultrashort-acting beta-blocker esmolol, the afterload reducing and cardiostimulatory agent hydralazine, or saline. As anticipated, hydralazine enhanced contractile function of the stunned tissue in the short term: WT at 2 hours after treatment was 53.7 +/- 6.9% versus 7.1 +/- 6.5% in treated versus saline controls (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Safety and efficacy of esmolol for unstable angina pectoris

Esmolol is a rapidly metabolized cardioselective beta-adrenergic blocker that provides steady state beta-adrenergic blockade when administered by continuous intravenous infusion. To determine the efficacy of esmolol in the management of unstable angina, 23 patients with known coronary artery disease, who averaged 3.7 +/- 2.7 daily episodes of chest pain at rest, were randomized to receive either a continuous infusion of esmolol (n = 12) or oral propranolol (n = 11), as an adjunct to concomitant antianginal therapy. Patients with systolic blood pressure less than 110 mm Hg, heart rate less than 60 beats/min or known contraindications to beta blockade were excluded. Esmolol was titrated in a step-wise fashion from 2 to 24 mg/min at 5-minute intervals up to a 30% reduction in heart rate and systolic blood pressure double-product. The propranolol dose was increased every 6 hours by 50 to 100% to achieve a similar reduction in heart rate and blood pressure. When compared with their 24-hour baseline periods, both groups achieved a significant reduction in episodes of chest pain, from 4.6 +/- 3.3 to 1.4 +/- 1.5 in the esmolol group (p less than 0.02) and 2.6 +/- 1.4 to 1.0 +/- 1.5 in the propranolol group (p less than 0.02) during the subsequent study period. The cardiac event rate and incidence of drug side effects were similar between the 2 groups; however, side effects seen with esmolol did not require treatment after drug discontinuation. Thus, maximally tolerated beta blockade is an effective therapy for unstable angina.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of an ultrashort-acting beta-receptor blocker (esmolol) in patients with acute myocardial ischemia and relative contraindications to beta-blockade therapy

The hemodynamic responses to esmolol, an ultrashort-acting (t1/2 = 9 min) beta 1-adrenergic receptor antagonist, were examined in 16 patients with myocardial ischemia and compromised left ventricular function as evidenced by a mean pulmonary capillary wedge pressure of 15 to 25 mm Hg. Esmolol was infused intravenously to a maximal dose of 300 micrograms/kg body weight per min for less than or equal to 48 h in 16 patients: 9 with acute myocardial infarction, 6 with periinfarction angina and 1 with acute unstable angina. The sinus rate and systolic arterial pressure declined rapidly in all patients from baseline values of 99 +/- 12 beats/min and 126 +/- 19 mm Hg to 80 +/- 14 beats/min (p less than 0.05) and 107 +/- 20 mm Hg (p less than or equal to 0.05) during esmolol treatment. Rate-pressure product decreased by 33% and cardiac index by 14% during esmolol treatment, but pulmonary capillary wedge pressure was not significantly altered by drug infusion (19 +/- 3 mm Hg at baseline versus 19 +/- 5 during treatment, p = NS). In all patients there was a rapid return toward baseline hemodynamic measurements within 15 min of stopping administration of esmolol, and virtually complete resolution of drug effect was evident within approximately 30 min. During infusion of esmolol, four of nine patients receiving intravenous nitroglycerin required downward adjustment of nitroglycerin infusion rate to maintain systolic blood pressure greater than 90 mm Hg.(ABSTRACT TRUNCATED AT 250 WORDS)

Ultra-short-acting beta-adrenergic blockers

The ultra-short-acting beta-adrenergic blockers are parenteral agents that can be rapidly titrated in clinical situations where immediate beta-adrenergic blockade is warranted. The effects of those drugs rapidly dissipate after termination of treatment, providing an important safety feature. Esmolol, the prototype drug of this class, is approved for treatment of supraventricular tachyarrhythmias but also has potential use in treatment of patients with perioperative hypertension and acute myocardial ischemia.

Newer antiarrhythmic drugs

The effective management of cardiac arrhythmias remains a major challenge in cardiovascular therapeutics. The management of arrhythmias encompasses a wide spectrum of supraventricular and ventricular tachyarrhythmias occurring in patients with various cardiac diagnoses and different degrees of myocardial dysfunction. A number of the newer antiarrhythmic drugs that have either recently been released or appear promising are reviewed in this article. Drugs are described with respect to their basic pharmacology, electrophysiologic actions, pharmacokinetics and metabolism, hemodynamics, antiarrhythmic effects, side effects, interactions, indications, and dosage.

Time course of recovery of "stunned" myocardium following variable periods of ischemia in conscious and anesthetized dogs

Persistence of regional contractile dysfunction after restoration of blood flow to transiently ischemic myocardium has been well described. To date, most studies have been performed in anesthetized animals. The present investigation compared the time course of recovery of regional segment shortening (percentage of segment shortening) in anesthetized versus conscious dogs subjected to a brief period of total occlusion of the left anterior descending coronary artery. Periods of occlusion lasting 5, 10, and 15 minutes were followed by 3 hours of reperfusion. Dogs anesthetized with sodium pentobarbital (30 mg/kg intravenously) had a significantly higher heart rate and blood pressure and lower dP/dt than conscious dogs. Coronary artery occlusion resulted in similar degrees of regional dyskinesis or akinesis, indicative of severe myocardial ischemia, in all experiments. During reperfusion, a gradual return of contractile function toward baseline was observed. At the end of the first 15 minutes of reflow, dogs subjected to 5 minutes of coronary occlusion demonstrated approximately 70% of control segment shortening in the previously ischemic zone. Animals subjected to 10- and 15-minute periods of coronary artery occlusion showed approximately 60% and 40% of control segment shortening at the same time point, respectively. The remainder of the 3-hour reperfusion period was characterized by a more gradual recovery of regional segment function. No differences were observed between anesthetized and conscious animals. It is concluded that the time course of functional recovery of postischemic reperfused myocardium is directly related to the duration of coronary occlusion and is similar in conscious and anesthetized dogs.

Esmolol: a novel cardioselective, titratable, intravenous beta-blocker with ultrashort half-life

Esmolol is an ultrashort-acting, cardioselective, intravenous beta-blocker with an elimination half-life of about nine minutes. After administration of a loading dose, its full therapeutic effect is evident within five minutes. Its efficacy in treating supraventricular arrhythmias is equal to that of propranolol, but unlike propranolol, the action of esmolol is titratable and is largely reversed within 10 to 30 minutes after stopping its administration. Esmolol is also effective in attenuating life-threatening perioperative tachycardia and hypertension caused by adrenergic stimulation in high-risk patients.

New therapeutic modalities for the treatment of elderly patients with ischemic heart disease

In developing a treatment plan for elderly patients with ischemic heart disease, it is important to appreciate that the pathophysiologic process and aging influence the type of response produced by various drugs. The aging process also alters the way drugs are absorbed, distributed, and eliminated. Each of these variables must be considered in deciding which drugs should be used and how they should be administered.