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

Pathophysiology of Myocardial Infarction

Myocardial infarction is defined as sudden ischemic death of myocardial tissue. In the clinical context, myocardial infarction is usually due to thrombotic occlusion of a coronary vessel caused by rupture of a vulnerable plaque. Ischemia induces profound metabolic and ionic perturbations in the affected myocardium and causes rapid depression of systolic function. Prolonged myocardial ischemia activates a "wavefront" of cardiomyocyte death that extends from the subendocardium to the subepicardium. Mitochondrial alterations are prominently involved in apoptosis and necrosis of cardiomyocytes in the infarcted heart. The adult mammalian heart has negligible regenerative capacity, thus the infarcted myocardium heals through formation of a scar. Infarct healing is dependent on an inflammatory cascade, triggered by alarmins released by dying cells. Clearance of dead cells and matrix debris by infiltrating phagocytes activates anti-inflammatory pathways leading to suppression of cytokine and chemokine signaling. Activation of the renin-angiotensin-aldosterone system and release of transforming growth factor-β induce conversion of fibroblasts into myofibroblasts, promoting deposition of extracellular matrix proteins. Infarct healing is intertwined with geometric remodeling of the chamber, characterized by dilation, hypertrophy of viable segments, and progressive dysfunction. This review manuscript describes the molecular signals and cellular effectors implicated in injury, repair, and remodeling of the infarcted heart, the mechanistic basis of the most common complications associated with myocardial infarction, and the pathophysiologic effects of established treatment strategies. Moreover, we discuss the implications of pathophysiological insights in design and implementation of new promising therapeutic approaches for patients with myocardial infarction.

β1-Adrenergic blockade during cardiopulmonary resuscitation improves survival

OBJECTIVE

The short-acting beta1-selective adrenergic blocking agent, esmolol, was administrated during cardiopulmonary resuscitation with the hypothesis that initial resuscitation and postresuscitation survival would be improved.

DESIGN

Prospective, randomized, controlled study.

SETTING

Animal research laboratory.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Ventricular fibrillation was induced in 18 male Sprague-Dawley rats, which were then left untreated for 6 mins before attempted resuscitation with precordial compression, mechanical ventilation, and electrical defibrillation. Animals were randomized to receive 300 microg/kg esmolol in a volume of 200 microL or an equivalent volume of saline placebo during cardiopulmonary resuscitation. Electrical defibrillation was attempted after 12 mins of ventricular fibrillation.

MEASUREMENTS AND MAIN RESULTS

Esmolol-treated animals required a significantly smaller number of electrical shocks before resuscitation. Each of the esmolol-treated but only five of nine placebo-treated animals were successfully resuscitated. Postresuscitation contractile and left ventricular diastolic functions of resuscitated animals were significantly better after esmolol administration and duration of survival was significantly increased.

CONCLUSIONS

A short-acting beta1-selective adrenergic blocking agent, when administered during cardiopulmonary resuscitation, significantly improved initial cardiac resuscitation, minimized postresuscitation myocardial dysfunction, and increased the duration of postresuscitation survival.

Beta-adrenergic blockade during severe ischemia

OBJECTIVE

To examine the effect of acebutolol, a beta-adrenergic-receptor blocker, on severe regional myocardial ischemia, specifically the effects on regional myocardial function and metabolism.

DESIGN

Randomized study.

SETTING

Animal laboratory of the Department of Anesthesiology and Critical Care, University of Stellenbosch Medical School.

PARTICIPANTS

Anesthetized open-chest pig model (n = 18).

INTERVENTIONS

Regional left ventricular function and metabolism were evaluated. Severe stenosis was applied to the left anterior descending coronary artery. After establishing regional myocardial ischemia, acebutolol was administered intravenously, and results were compared with controls who did not receive acebutolol. Animals were prospectively randomized to 1 of the groups.

MEASUREMENTS AND MAIN RESULTS

Regional myocardial function and metabolism were assessed by end-systolic pressure relationship, regional systolic shortening, postsystolic shortening, regional myocardial oxygen consumption, and lactate dynamics. Coronary blood flow was determined with a Doppler flow probe. Results indicated that acebutolol increased regional myocardial blood flow, and this resulted in less severe regional myocardial ischemia, improved function, and an increase in regional myocardial oxygen consumption.

CONCLUSION

The beta-Adrenergic-receptor antagonist was successful in reducing regional myocardial ischemia in this model. This reduction was achieved by an increase in coronary blood flow, which resulted in an improvement in regional mechanical function and an increase in oxygen consumption.

Alpha-human atrial natriuretic peptide, carperitide, reduces infarct size but not arrhythmias after coronary occlusion/reperfusion in dogs

Carperitide, a recombinant form of alpha-hANP, possesses potent diuretic, natriuretic, and vasodilatory activity, and inhibits the renin-aldosterone system and sympathetic nervous activity. However, its beneficial effects on ischemic myocardium have not been studied fully. We examined carperitide's effects on infarct size, hemodynamics, and arrhythmia frequency in anesthetized dogs (n = 20) subjected to a 90-min coronary artery occlusion/6-h reperfusion protocol. Intravenous infusion of carperitide (0.2 microg/kg/min) commenced 15 min after occlusion and continued during occlusion/reperfusion. Ventricular fibrillation developed in two of 10 control versus three of 10 treated dogs (p = NS). Hemodynamics, collateral blood flow to the ischemic wall measured 10 min after occlusion, and extent of area at risk were comparable for the two groups. Infarct size/area at risk was smaller in treated than in control dogs (4.5 +/- 2.1% vs. 27.8 +/- 7.8%, respectively; p < 0.05). During occlusion, carperitide tended to increase collateral blood flow (+39%) and significantly decreased left ventricular systolic pressure (-13%) and end-diastolic pressure (-40%) compared with baseline. In control dogs, collateral blood flow tended to decrease (-8.3%), whereas most hemodynamic parameters did not change significantly with respect to baseline. The number of arrhythmias recorded during occlusion/reperfusion was similar in the two groups. Intravenous administration of carperitide limited infarct size, but did not reduce incidence of ventricular arrhythmias after 90-min coronary occlusion/6-h reperfusion in anesthetized dogs. Although the beneficial effects of carperitide may be attributable to concomitant changes in hemodynamics and collateral blood flow, the precise mechanisms require further investigation.

Abnormality of left ventricular sympathetic nervous function assessed by (123)I-metaiodobenzylguanidine imaging in patients with COPD

BACKGROUND

Cardiac and systemic autonomic nervous function may be impaired in patients with COPD. Few reports, however, have described sympathetic nervous function of the left ventricle (LV) in COPD patients.

STUDY OBJECTIVE

To assess the LV sympathetic nervous function in patients with COPD using (123)I-metaiodobenzylguanidine (MIBG) imaging of the heart.

DESIGN

Prospective comparison of (123)I-MIBG imaging results in COPD patients and normal subjects.

PARTICIPANTS

Twenty-eight patients with COPD without manifest right ventricular overload and 7 volunteers without cardiopulmonary disease (control subjects).

MEASUREMENTS

(123)I-MIBG imaging results and plasma norepinephrine concentration were compared between the COPD and control groups. In the COPD group, pulmonary function tests were performed and all subjects were interviewed about their symptoms.

RESULTS

(123)I-MIBG uptake, assessed as the cardiac to mediastinal activity ratio in the delayed image, was significantly lower in the COPD group than in the control group (p < 0.05). (123)I-MIBG turnover, expressed as the washout rate (WR) of (123)I-MIBG from 15 to 240 min, was significantly higher in the COPD group than in the control group (p < 0.01). In the COPD group, patients with dyspnea showed lower cardiac to mediastinal activity ratios and higher WRs compared with patients who had mild dyspnea. The WR correlated negatively with the vital capacity/predicted value ratio, correlated negatively with the maximal voluntary ventilation volume/predicted value ratio, and correlated positively with the residual volume/total lung capacity ratio in the COPD group. The plasma norepinephrine concentration in COPD patients was higher than that in the control subjects.

CONCLUSION

Patients with COPD have significant sympathetic nervous impairment of the LV myocardium as a result of generalized sympathetic overactivity.

Pharmacokinetics and pharmacodynamics of propranolol in hypertensive patients after sublingual administration: systemic availability

The bioavailability of propranolol depends on the degree of liver metabolism. Orally but not intravenously administered propranolol is heavily metabolized. In the present study we assessed the pharmacokinetics and pharmacodynamics of sublingual propranolol. Fourteen severely hypertensive patients (diastolic blood pressure (DBP) > or = 115 mmHg), aged 40 to 66 years, were randomly chosen to receive a single dose of 40 mg propranolol hydrochloride by sublingual or peroral administration. Systolic (SBP) and diastolic (DBP) blood pressures, heart rate (HR) for pharmacodynamics and blood samples for noncompartmental pharmacokinetics were obtained at baseline and at 10, 20, 30, 60 and 120 min after the single dose. Significant reductions in BP and HR were obtained, but differences in these parameters were not observed when sublingual and peroral administrations were compared as follows: SBP (17 vs 18%, P = NS), DBP (14 vs 8%, P = NS) and HR (22 vs 28%, P = NS), respectively. The pharmacokinetic parameters obtained after sublingual or peroral drug administration were: peak plasma concentration (CMAX): 147 +/- 72 vs 41 +/- 12 ng/ml, P < 0.05; time to reach CMAX (TMAX): 34 +/- 18 vs 52 +/- 11 min, P < 0.05; biological half-life (t1/2b): 0.91 +/- 0.54 vs 2.41 +/- 1.16 h, P < 0.05; area under the curve (AUCT): 245 +/- 134 vs 79 +/- 54 ng h-1 ml-1, P < 0.05; total body clearance (CLT/F): 44 +/- 23 vs 26 +/- 12 ml min-1 kg-1, P = NS. Systemic availability measured by the AUCT ratio indicates that extension of bioavailability was increased 3 times by the sublingual route. Mouth paresthesia was the main adverse effect observed after sublingual administration. Sublingual propranolol administration showed a better pharmacokinetic profile and this route of administration may be an alternative for intravenous or oral administration.

Effect of angina pectoris on myocardial protection in patients with reperfused anterior wall myocardial infarction: retrospective clinical evidence of "preconditioning"

OBJECTIVES

We examined whether angina pectoris occurring shortly before the onset of acute myocardial infarction can actually preserve postischemic left ventricular function in humans.

BACKGROUND

Experimental studies indicate that brief, transient episodes of ischemia render the heart very resistant to infarction from a subsequent sustained ischemic insult, an effect termed ischemic preconditioning. However, no clinical data are available concerning the implications of angina pectoris shortly before the onset of infarction in humans.

METHODS

We studied 84 patients with an acute anterior myocardial infarction. All patients had total occlusion of the proximal or medial portion of the left anterior descending coronary artery and achieved reflow within 6 h of onset. Patients were classified into three groups on the basis of duration of antecedent angina pectoris: group 1 = no angina (37 patients); group 2 = new angina pectoris occurring < or = 7 days of onset of infarction (22 patients); group 3 = angina pectoris beginning > 7 days before onset of infarction (25 patients). All patients underwent left ventriculography on the day of, and 28 days after, onset of infarction to determine ejection fraction and regional wall motion in the territory of the left anterior descending coronary artery by the centerline method.

RESULTS

Angiographic collateral flow grade was higher in group 3 than in groups 1 and 2 ([mean +/- SD] group 1 = 0.08 +/- 0.7, group 2 = 0.7 +/- 0.7, group 3 = 1.5 +/- 0.8). Although there were no differences in baseline ejection fraction and regional wall motion among the three groups, the degree of improvement was significantly greater in groups 2 and 3 than in group 1 (late minus baseline ejection fraction: group 1 = 0 +/- 8%, group 2 = 7 +/- 10% group 3 = 6 +/- 10% [p < 0.05 group 1 vs. groups 2 and 3]; late minus baseline regional wall motion: group 1 = 0.2 +/- 0.4, group 2 = 0.6 +/- 0.5, group 3 = 0.5 +/- 0.6 SD/chord [p < 0.05, group 1 vs. group 2]). When the study was limited to those patients with no or poor collateral flow (31 in group 1, 19 in group 2, 10 in group 3), only group 2 patients had a significant improvement in wall motion. Angina pectoris within 24 h before onset of infarction was more frequent in group 2 (82%) than group 3 (28%, p < 0.05).

CONCLUSIONS

Episodes of angina pectoris occurring shortly before the onset of infarction may preserve myocardial contractile function in reperfused myocardial infarction despite less support from collateral flow channels, although these are suggestive results in a limited number of patients.

Sudden cardiac death and the potential role of beta-adrenoceptor-blocking drugs

Sudden cardiac death is a major health problem in the industrially developed countries. The risk of sudden cardiac death may be reduced by early detection of coronary heart disease, elimination of the risk factors, treatment of the ischaemia in patients known to have coronary heart disease and suppression of ventricular arrhythmias. Of all the therapeutic measures currently available to reduce the risk of sudden cardiac death, beta-adrenoceptor-blocking drugs (beta blockers) appear to be the most effective. In this paper their actions are reviewed and evidence for their efficacy is presented.

Can intravenous beta blockade predict long-term haemodynamic benefit in chronic congestive heart failure secondary to ischaemic heart disease? A comparison between intravenous and oral carvedilol

Several studies in the past have shown the long-term beneficial effects of beta-blockers in congestive heart failure. Despite the interest in this mode of therapy, their clinical application has been limited due to their negative inotropic effect. A subset of the heart failure patients do not show any improvements with standard beta-blocker therapy. Carvedilol, a new, non-selective beta-blocking agent with concurrent alpha-blocking properties, was evaluated in 17 patients with chronic heart failure secondary to ischaemic heart disease. All had resting left ventricular ejection fraction less than or equal to 45% and were maintained on diuretic therapy. Acute haemodynamic measurements were made after intravenous carvedilol (2.5-7.5 mg) and also after chronic therapy for 8 weeks (carvedilol 12.5-50 mg b.d.). Radionuclide ventriculography, ambulatory intra-arterial blood pressure monitoring and right heart catheterization were performed before and after 8 weeks of chronic therapy. Twelve patients completed the study and 5 were withdrawn. Symptomatic and haemodynamic improvement was demonstrated in 11 of the 12 patients after 8 weeks of therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Significance of preinfarction angina for preservation of left ventricular function in acute myocardial infarction

The effect of preinfarction angina on the preservation of left ventricular function was evaluated with the use of cineventriculography in 37 patients who had either total or subtotal occlusion of the proximal left anterior descending coronary artery during the convalescent period of myocardial infarction. In 15 patients who had preinfarction angina more than 1 week before the onset of acute myocardial infarction (group A), the global left ventricular ejection fraction was 54 +/- 3% (SEM) and regional wall motion in the infarct area was 10 +/- 3%. In 10 patients who had preinfarction angina occurred within 1 week before the onset of acute myocardial infarction (group B), the left ventricular ejection fraction and regional wall motion in the infarct area were 42 +/- 3% and 1 +/- 2%, respectively. In 12 patients without preinfarction angina (group C), the left ventricular ejection fraction and regional wall motion in the infarct area were 38 +/- 3% and -1 +/- 2%, respectively. In groups B and C, both the left ventricular ejection fraction and regional wall motion in the infarct area were lower than those in group A (p less than 0.05). The collateral circulation at the onset of acute myocardial infarction was better in group A compared with groups B and C (p less than 0.05). Thus the collateral circulation, promoted by repetitive anginal episodes indicative of myocardial ischemia, causes the preservation of myocardial function.

Value of carvedilol in congestive heart failure secondary to coronary artery disease

Despite considerable interest in the use of beta-blocking agents in congestive heart failure (CHF), their clinical application is limited because of their negative inotropic effects. Beta blockers with vasodilating properties may have the advantage of overcoming this, however. Carvedilol, a beta-blocking agent with vasodilating properties, was evaluated in 17 patients with chronic CHF secondary to ischemic heart disease with a resting left ventricular ejection fraction less than or equal to 45%, who were being maintained on diuretics. Exercise testing, radionuclide ventriculography, and right-sided cardiac catheterization were performed and intraarterial blood pressure measured before and after 8 weeks of carvedilol therapy in a dosage of 12.5 to 50.0 mg twice a day. Twelve patients completed the study and 5 withdrew. Symptomatic and hemodynamic improvement was demonstrated in 11 of the 12 patients. Heart rate and intraarterial blood pressure were both reduced by chronic therapy. Mean +/- standard deviation exercise time improved from 4.3 +/- 1.6 to 7.1 +/- 2.7 minutes (p less than 0.0001), as did resting left ventricular ejection fraction, from 27 +/- 9 to 31 +/- 11% (p less than 0.02). Pulmonary arterial wedge pressure fell from 19 +/- 7 mm Hg to 12 +/- 5 mm Hg (p less than 0.001) and total systemic vascular resistance from 1,752 +/- 403 to 1,497 +/- 310 dynes/s/cm-5/m2 (p less than 0.02). Stroke volume index improved also, from 31 +/- 6 ml to 40 +/- 6 ml (p less than 0.0005). These hemodynamic changes were mediated partly by vasodilation, diminished myocardial oxygen demand and reduction of sympathetic overactivity in the failing heart. These data suggest that carvedilol may have beneficial effects in patients with chronic CHF secondary to coronary artery disease.

The effects of propranolol on regional cardiac metabolism during ischemia and reperfusion assessed by magnetic resonance spectroscopy

Sixteen anesthetized New Zealand white rabbits were subjected to thoracotomy, and a reversible snare occluder was attached around a large branch of the left circumflex coronary artery. A 1.3 cm. diameter nuclear magnetic resonance (NMR) surface coil was placed adjacent to the myocardium perfused by this vessel. The animals were divided into two groups of eight animals each, treatment and control. The rabbits were studied using a 2.0 T magnetic resonance (MR) spectrometer, and baseline spectra were acquired. The treatment animals then received intravenous propranolol (1.5 mg/kg) and the control animals received an equal volume of saline. Spectra were then acquired during a 20-minute occlusion period and during subsequent reperfusion. Animals in both groups showed expected decreases in phosphocreatine and adenosine triphosphate and an increase in inorganic phosphate during occlusion; these changes reverted toward baseline values with reperfusion. There were no significant differences between the two groups. The myocardium became acidotic during occlusion in both groups, but significantly more so in the control animals: during the first 10 minutes of occlusion pH was 7.30 +/- 0.41 in the treatment group versus 6.55 +/- 0.24 for controls (p = 0.0005). During the second 10 minutes of occlusion pH was 7.05 +/- 0.65 in the treatment group versus 6.24 +/- 0.25 in controls (p = 0.0053). We conclude that attenuation of intracellular acidosis by propranolol during myocardial ischemia was evident by MR spectroscopy in this animal model.

Influence of propranolol on high energy phosphate and tissue acidosis in regional ischemic myocardium of pigs: assessment with arterial pressure and respiration gated in vivo 31-phosphorus magnetic resonance spectroscopy

In an attempt to define the metabolic abnormalities of the ischemic myocardium, the changes in high energy phosphates, inorganic phosphate and intracellular pH were serially and quantitatively evaluated in ischemic porcine hearts having no collateral circulation, using arterial pressure and respiration gated in vivo 31P magnetic resonance spectroscopy. The protocol was also modified for propranolol pretreatment (0.6 mg/kg intravenously) to define its effect on the metabolism of ischemic myocardium. In the non-treated group, creatine phosphate was rapidly depleted by 10 minutes after ischemia; by 40 minutes, ATP and intracellular pH gradually decreased to 10 +/- 11% of control and to 5.90 +/- 0.26, respectively, and inorganic phosphate rose to 303 +/- 43% of control. In the propranolol treated group, the concentrations of creatine phosphate and ATP were higher, and those of inorganic phosphate and tissue pH were similar compared with controls during 40 minutes of ischemia. This suggests that the beneficial effect of propranolol on the ischemic myocardium is due to the preservation of ATP, an essential energy resource for numerous enzymatic reactions in viable myocardium.

Nonthrombolytic intervention in acute myocardial infarction

Alternative interventions are available for patients in whom thrombolytic therapy is inappropriate after an acute myocardial infarction. Administration of a beta blocker within the first 24 hours of the patient's admission to the coronary care unit can reduce overall morbidity and mortality within the first 7 days by about 15%. Maintenance therapy with an oral beta blocker can reduce mortality within the succeeding 3 years by about 25%. Esmolol, a unique cardioselective beta 1-adrenergic receptor blocker with a half-life of 9 minutes, can enable some patients with relative contraindications to beta blockers to nevertheless benefit from early beta-blocking therapy. It also is useful in screening patients for subsequent therapy with beta blockers. Those who tolerate the esmolol infusion can be given a long-acting beta blocker. For patients who exhibit intolerance to esmolol, the infusion can be terminated with rapid return to baseline hemodynamics.

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)

The effect of chronic timolol in an animal model for myocardial infarction

The effect of no drug or timolol (5 mg/kg, PO, for 1, 2, or 8 weeks on postganglionic cardiac sympathetic neural discharge, blood pressure, heart rate and beta-receptor density after acute coronary occlusion of the left anterior descending artery was compared. Beta-receptor density, determined by binding of 3H-dihydroalprenolol, was examined in the myocardium (LA = left atrium, RA = right atrium, LV1 = proximal and LV2 = distal left anterior descending artery distribution, LV3 = posterior left ventricle, S = septum, and RV = right ventricle). In control cats (no coronary occlusion or timolol) beta-receptor density of LV2 and LV3 was greater (P less than .05) than LA, RA, LV1, and RV. LV3 was greater (P less than .05) than S and RA, and LA was less than S. Longer treatment with timolol increased beta-receptor density. When compared with no timolol, beta-receptor density was greater in RA after 8 weeks and in LV1 after 2 weeks and not different in LV2 and S. Beta-receptor density and LV3 and RV were greater after 8 weeks than after 1 week or no timolol. Spearman rank correlation coefficients between dose and beta-receptor density revealed an increase (P less than .05) for all heart areas. Heart rate did not vary before timolol and was decreased after all doses of timolol. Timolol increased the mean times to coronary occlusion-induced death although the increase was not statistically significant. Timolol did not prevent postganglionic cardiac sympathetic neural discharge associated with arrhythmia. Timolol may increase beta-receptor density and decrease synaptic norepinephrine, causing a decreased release per cardiac sympathetic nerve impulse. Alternatively, molecules of timolol may accumulate in nerve endings and be released in greater concentrations at the receptors. This could explain the protection against coronary occlusion-induced arrhythmia and death.

Controlled beta-receptor blockade with esmolol and flestolol

Beta-receptor-blocking agents are commonly used in the management of various cardiovascular diseases. Recently, esmolol, a pharmacokinetically novel cardioselective beta-receptor-blocking agent, has been introduced for use in the treatment of critically ill patients. It is devoid of intrinsic sympathomimetic activity and in doses used clinically, it has no direct depressant effect on the heart. Esmolol is an ester and is metabolized by choline-esterase to ASL 8123, an inactive molecule. Esmolol has an elimination half-life of nine minutes which accounts for its ultrashort duration of action. This unique pharmacokinetic property provides two advantages over other longer-acting beta-receptor-blocking agents. First, the magnitude of beta-receptor blockade can be titrated to a desired level. Second, if adverse effects are experienced, reducing the dosage or terminating the infusion results in rapid reversal of its pharmacological effects. Another ultrashort-acting, non-cardioselective beta-receptor blocking agent, flestolol is undergoing clinical evaluation. Esmolol has been approved for the management of supraventricular tachycardia. The clinical safety of these novel drugs will expand the use of beta-receptor-blocking agents in the management of cardiovascular diseases in critically ill patients.

Secondary prevention after myocardial infarction: effects of beta blocking agents and calcium antagonists

Therapeutic interventions in patients with myocardial infarction, whether during the first hours after coronary occlusion or several days later, aim to reduce mortality and morbidity by several mechanisms: Prevention of fatal ventricular fibrillation, limitation of infarct size, and inhibition of platelet aggregation are some examples of such mechanisms. Results from early intervention trials with beta blocking agents, particularly from ISIS-I, suggest that 1-year mortality is significantly lower in selected patients randomized to active treatment. Late intervention studies also suggest a significant reduction in coronary mortality and morbidity with beta blockade, particularly when data are pooled. Studies with the calcium channel blockers nifedipine and verapamil were unable to demonstrate any beneficial effects of these drugs on mortality or reinfarction. In this review article, attention will be directed to the most recent information about the preventive value of beta adrenergic blocking drugs and slow calcium channel inhibitors.

Hemodynamic effects of flestolol, a titratable short-acting intravenous beta-adrenergic receptor blocker

The hemodynamic effects of flestolol were evaluated in 30 patients undergoing routine cardiac catheterization. Hemodynamic measurements were obtained during baseline (prior to flestolol), at steady state during IV flestolol infusion (1, 5, and 10 micrograms/kg/min) and at 20 to 30 minutes after discontinuation (postinfusion). Flestolol-induced hemodynamic changes were similar to those induced by other beta blockers without intrinsic sympathomimetic activity. Significant dose-dependent reduction in heart rate, rate pressure product, and increase in peripheral vascular resistance were seen. Flestolol produced clinically insignificant decrease in myocardial contractility as shown by slight decrease in LVdp/dt, CI, and LVEF. Hemodynamic data from patients with paced heart rate, further confirms a direct mild cardiac depressant effect of flestolol, a finding common to other beta blockers. Consistent with the short elimination half-life of flestolol (t1/2 = 6.5 minutes), most of the hemodynamic changes rapidly returned to preinfusion level within 20 to 30 minutes following its discontinuation. Thus flestolol, with its unique pharmacokinetic profile and titrability, may be beneficial in the treatment of critically ill patients.

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.

Beta-adrenergic blockers

beta-Adrenergic blocking drugs have been available for several years to treat ischemic heart disease and other cardiovascular and noncardiovascular disorders. There are multiple drugs in this class with various pharmacodynamic and pharmacokinetic properties that may be important in specific clinical situations and in avoiding certain adverse reactions. These drugs have been shown to be efficacious in relieving anginal symptoms and prolonging exercise tolerance, in reducing high blood pressure, for treating various arrhythmias, in therapy of hypertrophic cardiomyopathy, and for prolonging life in many survivors of acute myocardial infarction.

Esmolol: a titratable short-acting intravenous beta blocker for acute critical care settings

Esmolol (Brevibloc) is an intravenous, short-acting, titratable, cardioselective beta blocker with a very rapid onset and offset of action (t1/2 = 9.2 minutes). Esmolol-induced beta blockade can be maintained as long as infusion is continued. It exhibits neither intrinsic sympathomimetic activity nor significant membrane-stabilizing activity. It is rapidly metabolized by an esterase in the erythrocyte cytosol to an inactive acid metabolite. Its hemodynamic and electrophysiologic effects are similar to those of other beta blockers. Unlike the effects of other beta blockers, however, the effects of esmolol dissipate rapidly to baseline within 30 minutes after its discontinuation. Evidence obtained from clinical studies indicates that esmolol is effective and safe in reducing the ventricular rate in patients with supraventricular tachyarrhythmias, and in reducing the heart rate in patients with acute myocardial infarction and/or unstable angina. Esmolol has also been shown to be effective and safe in attenuating the tachycardia and hypertension seen during the intraoperative period. Data from postoperative patients indicate that esmolol is ideal as sole-agent therapy for the treatment of moderate postoperative hypertension associated with a hyperdynamic state. The short duration of action and titratability of esmolol make it an ideal drug for use in patients in whom the clinical need for beta blockade is limited in duration, and it offers additional safety in patients in whom beta blockade is beneficial; however, it might be precluded because of coexisting contraindications. To date, experience with esmolol in over 1200 patients has been gathered, and the adverse effect profile is basically similar to that reported here.

Beneficial effects of timolol on infarct size and late ventricular tachycardia in patients with acute myocardial infarction

This investigation was undertaken to study the effects of beta-adrenergic blockade with timolol on infarct size and on the incidence of late ventricular tachycardia in patients with acute myocardial infarction of less than 6 hr of evolution. Patients were assigned randomly either to a placebo-treated group (98 patients) or to a timolol-treated group (102 patients). The patients were treated with 5.5 mg iv timolol (or matched placebo) as a bolus divided into four doses during the first 2 hr followed by 10 mg orally twice daily for 1 month. Cumulative total creatine kinase (CK) release, which reflects the amount of myocardial necrosis was 1677 +/- 132 IU/liter in the placebo group (n = 83) and 1274 +/- 73 IU/liter in the timolol group (n = 81, p less than .01), a 24% reduction. Cumulative release of CK-MB was 138 +/- 8 IU/liter in the placebo group and 106 +/- 8 IU/liter in the timolol group (p less than .01), a 23% reduction. Twenty-four hour Holter electrocardiograms were obtained on days 7, 14, 21, and 28 after the onset of the acute myocardial infarction in 80 patients in the placebo group and 82 patients in the timolol group. The incidence of ventricular tachycardia was lower in the timolol than in the placebo group (7 vs 16 patients, p = .05). We conclude that early administration of intravenous timolol followed by oral treatment in patients with acute myocardial infarction reduces infarct size as assessed by CK and CK-MB serum activity, and decreases the occurrence of late ventricular tachycardia.

Therapeutic trends in the management of patients with acute myocardial infarction (1975-1984): the Worcester Heart Attack Study

As part of an ongoing community-wide study of time trends in the incidence and case-fatality rates of patients hospitalized with acute myocardial infarction (MI) in all 16 Worcester, Massachusetts, metropolitan hospitals during the years 1975, 1978, 1981, and 1984, changes over time in the therapeutic management of 3263 patients with validated acute myocardial infarction were examined. Beta-blocker (21%, 1975; 52%, 1984) and nitrate (56%, 1975; 93%, 1984) therapy use increased dramatically over time. Use of antiplatelet agents was inconsistent over time, while use of digoxin remained stable, being used in approximately 40% of all patients over the four periods studied. Use of antiarrhythmic medications other than lidocaine decreased consistently over time (31%, 1975; 22%, 1984). Lidocaine use increased between 1975 (31%) and 1978 (52%) and then leveled off to being used in approximately 45% of hospitalized patients with acute MI in 1981 and 1984. A variety of demographic (e.g., age, sex, teaching hospital) and clinical characteristics (e.g., MI order, MI type, MI location, peak CPK findings, occurrence of acute clinical complications) were also associated with the use of these therapies for the combined study periods. The results of this population-based study suggest considerable changes over time in the therapeutic management of patients hospitalized with acute myocardial infarction and of numerous patient demographic and clinical factors associated with their use.

Mortality in the beta blocker heart attack trial: circumstances surrounding death

In the Beta Blocker Heart Attack Trial, a double blind, randomized, controlled study, patients taking propranolol (180 or 240 mg/day) initiated 5-21 days post myocardial infarction had 26% fewer deaths than those taking placebo over a 25 month (mean) followup. Detailed analysis of the circumstances surrounding the BHAT deaths failed to reveal any striking difference between propranolol and placebo in the type of clinical event preceding death, the incidence and type of acute and prodromal signs and symptoms, the location of death, the activity preceding death or the percentage of deaths that were sudden or instantaneous, suggesting that propranolol may exert an "across the board" effect and improve survival by a combination of mechanisms. An unexpected finding was that the protective effect of propranolol appeared to occur during the hours of 10 p.m. to 7 a.m.

Management of acute myocardial infarction

This article presents plans of therapy based on current knowledge of pathophysiologic mechanisms, taking into consideration the rapid changes in availability of new drugs (or new experiences with old drugs) and new therapeutic interventions. Persistence of ischemic pain in the acute phase, or its recurrence during early convalescence, is a signal of a high-risk state for additional coronary events, and aggressive measures are required to prevent them. The indications, and the role of invasive hemodynamic monitoring in the treatment of left ventricular failure and/or hypotension, are discussed.

The use of beta-adrenergic blockers in the treatment of angina and hypertension

During the past decade, beta-adrenoreceptor blocking agents have proved to be valuable assets in our therapeutic armamentarium for management of both angina pectoris and essential hypertension. In ischemic heart disease, these agents reduce myocardial oxygen requirements by decreasing the force of myocardial contraction and by reducing heart rate. Consequently, decreased blood supply to portions of the myocardium is tolerated better. The beta-blockers are effective in reducing the frequency and severity of episodes of angina pectoris and in extending exercise tolerance. If needed, additional benefit may be gained by adding long-acting nitrates, or calcium-channel blockers or both.

Effect of propranolol after acute myocardial infarction in patients with congestive heart failure

The incidence of congestive heart failure was studied in the Beta Blocker Heart Attack Trial in which postmyocardial infarction patients between the ages of 30 and 69 years, with no contraindication to propranolol, were randomly assigned to receive placebo (n = 1921) or propranolol 180 or 240 mg daily (n = 1916) 5 to 21 days after admission to the hospital for the event. Survivors of acute myocardial infarction with compensated or mild congestive heart failure, including those on digitalis and diuretics, were included in the study. A history of congestive heart failure before randomization characterized 710 (18.5%) patients: 345 (18.0%) in the propranolol group and 365 (19.0%) in the placebo group. The incidence of definite congestive heart failure after randomization and during the study was 6.7% in both groups. In patients with a history of congestive heart failure before randomization, 51 of 345 (14.8%) in the propranolol group and 46 of 365 (12.6%) in the placebo group developed congestive heart failure during an average 25 month follow-up. In the patients with no history of congestive heart failure, 5% in the propranolol group developed congestive heart failure and 5.3% in the placebo group developed congestive heart failure. Baseline characteristics predictive of the occurrence of congestive heart failure by multivariate analyses included an increased cardiothoracic ratio, diabetes, increased heart rate, low baseline weight, prior myocardial infarction, age, and more than 10 ventricular premature beats per hour.(ABSTRACT TRUNCATED AT 250 WORDS)

Initial therapy for mild hypertension

The treatment of mild hypertension has been a subject of controversy because its benefits versus risks are not as well established as they are for moderate to severe hypertension. Results of several studies, however, now show that treatment reduces the frequency of stroke in those with milder blood pressure elevations. New guidelines published by the Joint National Committee recommend that treatment of mild hypertension begin with either a diuretic or a beta blocker. The effect on the most common complication of mild hypertension, that is, coronary heart disease (myocardial infarction and sudden cardiac death), has, however, not been encouraging in studies in which diuretics have been used as first-line treatment. Two large-scale primary preventive studies compared the efficacy of diuretics and beta blockers in reducing coronary heart disease in hypertensive patients; results were in favor of beta blocker regimens in men. So far there is some evidence, but no hard scientific proof, that certain beta blockers offer advantages over diuretics in preventing myocardial infarction and sudden cardiac death in hypertensive patients. A major concern with the use of diuretics is the risk of hypokalemia; this can be reduced when they are combined with beta blockers.

Clinical experience with esmolol, a short-acting beta-adrenergic blocker in cardiac arrhythmias and myocardial ischemia

The efficacy and safety of esmolol, an ultra-short-acting beta-adrenergic blocking agent (elimination half-life, 9 min), was investigated in 358 patients with supraventricular tachyarrhythmias (SVTs) in three multicenter studies (placebo-controlled, propranolol-controlled, and open-label baseline-controlled) and in 19 patients with myocardial ischemia (acute myocardial infarction or unstable angina) in a single-center, open-label study. Esmolol was infused intravenously in doses ranging from 25 micrograms/kg/min to 300 micrograms/kg/min. In SVT studies, efficacy was judged by one or more of the following: a reduction of at least 15% to 20% from the average baseline heart rate, heart rate less than 100 beats/min, or conversion to normal sinus rhythm (NSR). Results revealed that esmolol was superior to placebo and equal to propranolol in controlling heart rate in SVT patients. Conversion to NSR was comparable in patients treated with esmolol (14%) and in those treated with propranolol (16%). The majority of patients achieved therapeutic response at esmolol doses of 200 micrograms/kg/min or less. Among esmolol-treated patients, recovery from beta blockade (i.e., heart rate approaching baseline levels) was achieved within ten minutes after discontinuation of infusion, indicating a brief duration of action of esmolol. In contrast, beta blockade persisted 4.5 hours after discontinuation of propranolol. In patients with myocardial ischemia, esmolol effectively reduced heart rate and blood pressure, thereby decreasing rate-pressure product. The most frequent adverse effect in patients treated with esmolol was hypotension. No clinically significant laboratory abnormalities were reported in esmolol-treated patients. Esmolol was well tolerated in patients infused for durations of up to 24 hours and in patients with conditions for which treatment with beta blockers is inappropriate. These results suggest that esmolol effectively and rapidly controls the heart rate in patients with SVT and in patients with acute myocardial ischemia. Furthermore, because of its short half-life, esmolol offers excellent benefits as compared with the currently available beta-adrenergic blockers in the treatment of critically ill patients. Esmolol was well tolerated by patients for whom beta blockers in general would be unsuitable.

Use of beta-adrenergic blocking agents after myocardial infarction

Long-term clinical trials have been carried out to evaluate the effectiveness of beta-adrenergic blocking agents in modifying the natural history of myocardial infarction (MI). In most of these studies, a lower mortality rate was documented in patients receiving a beta-blocker than in those receiving placebo. The drugs may have both antiarrhythmic and antiischemic effects. In patients without contraindications to beta-blocker treatment, a relative reduction in mortality of 25% can be expected for at least one to two years, with the reduction higher in older patients or patients having complications at infarction. Study results indicate benefit from starting beta-blocker therapy early after infarction, and some benefit from starting late seems a reasonable assumption. Evidence also points to a benefit from prolonged therapy. Beta-blockers are well tolerated in most patients; those major side effects that do occur are often cardiovascular.

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

Beta blockers reduce myocardial oxygen demand and are therefore useful in ischemic states. They reduce angina pectoris and reduce the risk of death when administered long-term after acute myocardial infarction. Some studies suggest that when administered early after coronary occlusion they can reduce myocardial infarct size. Relative contraindications to beta blockers, such as a history of congestive heart failure, chronic obstructive lung disease, atrioventricular conduction defects and low blood pressure, limit their use. Conventional beta blockers have a relatively long duration of action and are either contraindicated or must be used with particular caution in patients with these contraindications. Esmolol is an ultrashort-acting beta blocker with a biologic half-life of 9 minutes. Therefore, such an agent may be useful in patients with ischemic heart disease in whom reducing heart rate would be beneficial but in whom there is concern that beta blockers might not be tolerated. Esmolol reduced myocardial infarct size in 2 experimental studies of coronary occlusion followed by reperfusion, and improved the recovery of the stunned myocardium when administered during experimental myocardial ischemia. Esmolol's brief duration of action may make it safer than conventional beta blockers for the management of patients with unstable angina or myocardial infarction.

Use of an ultra short-acting beta-blocker in patients with acute myocardial ischemia

Esmolol is a new ultra short-acting (half-life [t1/2] beta 9 min) beta 1-adrenergic-receptor antagonist reported to have no intrinsic sympathomimetic activity. The safety and efficacy of esmolol in lowering the ventricular rate and rate-pressure product in patients with acute myocardial infarction (n = 5), postmyocardial infarction angina (n = 10), or acute unstable angina (n = 4), and without cardiogenic shock were studied. After a 30 min observation period, esmolol was titrated to a maximum dose of 300 micrograms/kg/min and infused for up to 420 min. The ventricular rate fell from 92 +/- 11 (mean +/- SD) to 77 +/- 13 beats/min (p less than .01) and the systolic arterial pressure decreased from 120 +/- 13 to 97 +/- 11 mm Hg (p less than .01) during the initial 30 min titration period. There was no significant change during the maintenance phase, and both the ventricular rate and arterial pressure returned rapidly toward baseline values within 30 min of termination of the infusion. The cardiac index fell from 2.8 +/- 0.6 to 2.2 +/- 0.6 liters/min/m2 (p less than .01) during the same period, and also returned to the baseline level 30 min after termination of the infusion. There was no significant change in the pulmonary capillary wedge pressure, respiratory rate, or PR interval. Five patients required termination of infusion because of hypotension and all recovered uneventfully within 30 min of stopping the esmolol. One patient required a brief infusion of dopamine to restore hemodynamic stability.(ABSTRACT TRUNCATED AT 250 WORDS)

Prediction of mortality during the first year after acute myocardial infarction from clinical variables and stress test at hospital discharge

The predictive value of a predischarge symptom-limited stress test was studied in 405 consecutive survivors of acute myocardial infarction (AMI). Three hundred patients performed bicycle ergometry; 105 could not perform it. Among these latter 105 patients, the stress test was contraindicated in 43 because of angina or heart failure and in 62 because of noncardiac limitations. One-year survival was 44% in the "cardiac-limited" group (19 of 43) and 92% in the "non-cardiac-limited" group (57 of 62). One-year survival among the patients who performed an exercise test at discharge was 93% (280 out of 300). The best stress test predictor of mortality by univariate analysis was the extent of blood pressure (BP) increase: 42 +/- 24 mm Hg in 280 survivors vs 21 +/- 14 mm Hg in 20 nonsurvivors (p less than 0.001). Among the 212 patients in whom BP increased 30 mm Hg or more, mortality was 3% (n = 6), while it was 16% (n = 14) among the 88 patients in whom BP increased less than 30 mm Hg. Angina, ST changes and arrhythmias were not as predictive. Stepwise discriminant function analysis showed inadequate BP increase to be an independent predictor of mortality. A high-risk group can be identified at discharge on clinical grounds in patients unable to perform a stress test, whereas intermediate- and low-risk groups can be identified by the extent of BP increase during exercise.

Acebutolol: ten years of experience

During 10 years of clinical use involving almost 3 million patient-years, acebutolol has become established as a remarkably safe and well-tolerated beta-blocking agent, effective in treating essential hypertension and cardiac arrhythmias. The existence of a long-lived active metabolite (diacetolol) confers a 24-hour duration of action, which permits effective use of a once-daily regimen, particularly for hypertension. Acebutolol has low lipid solubility and low protein binding; the former property reduces the risk of central side effects, and the latter means that displacement interactions with other drugs are unlikely. Because acebutolol and its metabolite normally have both renal and hepatic excretion pathways, an alternative pathway is available should either be compromised through disease. Acebutolol is cardioselective, and clinical use has borne out the low incidence of bronchospasm in patients with impaired lung function. The possession of intrinsic sympathomimetic activity (ISA) leads to only modest reductions in cardiac output, which in turn reduces the chance of excessive bradycardia and the likelihood of precipitating heart failure. A combination of selectivity and ISA may be responsible for the low incidence of tiredness and cold extremities observed with acebutolol compared with other beta blockers. The unique pharmacologic and pharmacokinetic profile of acebutolol confers several therapeutic advantages and may be responsible for the generally low level of side effects experienced in clinical use.

Comparison of clinical variables and variables derived from a limited predischarge exercise test as predictors of early and late mortality after myocardial infarction

An exercise test limited to 5 METS or 70% of age-predicted maximal heart rate was performed 1 day before hospital discharge by 225 survivors of acute myocardial infarction, all of whom were subsequently followed up for at least 5 years. The mortality rate was 11.1% during the first year, but averaged only 2.9% per year from the second to fifth year. Over the entire follow-up period, the five variables that predicted mortality by multivariate analysis were QRS score, an exercise-induced ST segment shift, previous infarction, failure to achieve target heart rate or work load and ventricular arrhythmia during the exercise test. Because mortality differed markedly before and after 1 year, Cox regression analyses were performed separately for both of these periods. The factors that were predictive of mortality during the first year were an exercise-induced ST shift (p less than 0.0001, relative risk 7.8), failure to increase systolic blood pressure by 10 mm Hg or more during exercise (p = 0.0039, relative risk 4.3) and angina in hospital 48 hours or longer after admission (p = 0.0046, relative risk 3.4). None of these three variables was predictive of mortality after 1 year. Previous infarction (p = 0.0007), QRS score (p = 0.0042) and ventricular arrhythmia during the exercise test (p = 0.016) were predictive of mortality after the first year. Thus, clinical and exercise test variables are complementary predictors of mortality after myocardial infarction. An abnormal ST segment response during an early limited exercise test and angina in the hospital are common strong predictors of mortality to 1 year, but not thereafter. Late mortality correlates with markers of poor left ventricular function.

Beta-blocking drugs for arrhythmias, hypertension, and ischemic heart disease

Beta-blocking drugs have provided significant improvement in the medical therapy of many types of heart disease. They are more effective in treating young hypertensive patients than elderly hypertensive patients. These drugs reduce the ventricular rate seen in atrial flutter and fibrillation, and they also reduce the frequency of ventricular ectopy. Beta blockers are important adjuncts for control of angina pectoris. When these drugs are given for a period of 1 to 3 years after myocardial infarction they reduce the incidence of reinfarction and the frequency of sudden death as well as reduce the overall mortality rate. Factors that may contribute to the overall decreased mortality include the reduction in the reinfarction rate and an increased threshold for ventricular fibrillation as well as those mechanisms that reduce myocardial oxygen utilization.

Identification of patients who do not require beta antagonists after myocardial infarction

Recent results obtained from large clinical trials demonstrate that long-term administration of beta-adrenergic antagonists to patients following myocardial infarction reduces the incidence of death for as long as two years. Therefore, it has been recommended that, in the absence of contraindications, all patients be given beta antagonists after infarction. A review of the literature regarding prognosis after infarction demonstrates that patients who have had only one infarction and who have good ventricular function, no complex ectopy, no angina, and negative results of stress testing have a mortality rate no greater than 0.6 percent per year. For a person in this category, the probability that beta blockade will preclude death is exceedingly low (approximately 1 in 700). Both the commonly described side effects, as well as the recent observation that beta-adrenergic antagonists lower the concentration of serum high-density lipoproteins, potentially reducing the protection against atherosclerosis thought to be conferred by high-density lipoproteins, suggest that it may be unwise to use beta antagonists in patients who have a very low probability of benefit.

Pharmacology of combined alpha-beta-blockade. II. Haemodynamic effects of labetalol

The cardinal haemodynamic disturbance in established hypertension is an increased total peripheral resistance and a subnormal blood flow, particularly during exercise. The spontaneously occurring changes in central haemodynamics have been followed in young males with essential hypertension over a 17-year period: a gradual increase in total peripheral resistance and blood pressure, and a gradual fall in cardiac output and stroke volume, have been demonstrated. Labetalol is a unique antihypertensive agent which induces both alpha- and beta-blockade. Numerous studies have shown that when labetalol is given intravenously to patients with mild to moderate essential hypertension, blood pressure falls within a few minutes-partly due to reduction in cardiac output and heart rate and partly due to reduction in total peripheral resistance. In most series the average reduction in blood pressure was 17 to 22%, the reduction in total peripheral resistance 11 to 14%, and the reduction in cardiac output 2 to 10%. Thus, the reduction in cardiac output with labetalol is less than that seen after single-dose injection of beta-blockers without intrinsic sympathomimetic activity. After intravenous injection, the blood pressure-lowering effect is most marked in the upright position and during muscular exercise when cardiac output is usually significantly reduced. Labetalol reduces blood pressure in severe hypertension. Intravenous doses of 0.2 to 0.8 mg/kg bodyweight reduce blood pressure by approximately 20%. This hypotensive effect is partly due to a reduction in total peripheral resistance and partly due to a fall in cardiac index. When the reduction in blood pressure is gradual and moderate (less than 20%), it is mainly produced by a reduction in total peripheral resistance. During long term use labetalol induces haemodynamic changes rather similar to those seen after bolus injection. However, during prolonged use there is a tendency to normalisation in cardiac output and stroke volume; the sustained decrease in blood pressure is mainly due to a reduction in total peripheral resistance. In a recent 6-year follow-up study where 15 patients were studied before treatment and after 1 and 6 years on long term labetalol treatment, a tendency to normalisation of central haemodynamics was found. Over the years total peripheral resistance was gradually reduced by 15 to 20% at rest as well as during exercise. Stroke volume gradually increased and after 6 years of treatment was approximately 10% higher than the pretreatment value. This compensated for the reduced heart rate and no significant reduction in cardiac output was seen either during exercise or at rest.(ABSTRACT TRUNCATED AT 400 WORDS)