Abrupt propranolol withdrawal in angina pectoris: effects on platelet aggregation and exercise tolerance

Influence of exercise test on platelet function in patients with coronary arterial disease: A systematic review

BACKGROUND

Exercise test (ET) may have adverse effects on platelet function and induce acute thrombotic events in patients with coronary artery disease (CAD). The aim of this study is to investigate the platelet function and evaluate the risk of thrombotic events in CAD patients during ET.

METHODS

Pubmed, Embase, Cochrane Library, and Web of Science were searched for a systematic review from initiation to October 2019. The inclusion criteria were controlled clinical trails as study design; investigating platelet function in CAD patients during ET; with ET carried out by treadmill or bicycle ergometer; written in English. Included articles were screened based on title/abstract and full-text review by 2 independent reviewers. Platelet aggregation (PA), platelet surface expression of CD62p and PAC-1, plasma levels of platelet factor 4 (PF4) and beta-thromboglobulin (β-TG) were evaluated before and after ET.

RESULTS

Eighteen articles were included out of the 427 references initially identified. In most of the studies included ET was terminated because of limited symptoms. Prior to ET, no difference in platelet aggregation was observed in CAD patients compared with healthy controls in majority of the studies, with or without the treatment with Aspirin. Dual anti-platelet therapy suppressed adenosine diphosphate (ADP)-induced platelet aggregation at rest. After ET, platelet aggregation, the serum levels of β-thromboglobulin were found unchanged in majority of studies and platelet factor-4 were found unchanged in half of studies. The expression of platelet surface markers were elevated by ET in a few study.

CONCLUSION

Symptom-limited exercise test did not affect platelet function in patients with coronary artery disease; however exercise to higher intensity may induce platelet activation.

Effect of β-blockers on platelet aggregation: a systematic review and meta-analysis

AIMS

Platelets play an important role in cardiovascular disease, and β-blockers are often prescribed for cardiovascular disease prevention. β-Blockers may directly affect platelet aggregation, because β-adrenergic receptors are present on platelets. There is uncertainty about the existence and magnitude of an effect of β-blockers on platelet aggregation. The aim of this study was to perform a systematic review and meta-analysis of the effect of β-blockers on platelet aggregation.

METHODS

MEDLINE and EMBASE were searched until April 2014. Two reviewers independently performed data extraction and risk of bias assessment. Type of β-blocker, population, treatment duration and platelet aggregation were extracted. Standardized mean differences were calculated for each study and pooled in a random-effects meta-analysis.

RESULTS

We retrieved 31 studies (28 clinical trials and three observational studies). β-Blockers decreased platelet aggregation (standardized mean difference -0.54, 95% confidence interval -0.85 to -0.24, P < 0.0001). This corresponds to a reduction of 13% (95% confidence interval 8-17%). Nonselective lipophilic β-blockers decreased platelet aggregation more than selective nonlipophilic β-blockers.

CONCLUSIONS

Clinically used β-blockers significantly reduce platelet aggregation. Nonselective lipophilic β-blockers seem to reduce platelet aggregation more effectively than selective nonlipophilic β-blockers. These findings may help to explain why some β-blockers are more effective than others in preventing cardiovascular disease.

β-blocker continuation after noncardiac surgery: a report from the surgical care and outcomes assessment program

BACKGROUND

Despite limited evidence of effect, β-blocker continuation has become a national quality improvement metric.

OBJECTIVE

To determine the effect of β-blocker continuation on outcomes in patients undergoing elective noncardiac surgery.

DESIGN, SETTING, AND PATIENTS

The Surgical Care and Outcomes Assessment Program is a Washington quality improvement benchmarking initiative based on clinical data from more than 55 hospitals. Linking Surgical Care and Outcomes Assessment Program data to Washington's hospital admission and vital status registries, we studied patients undergoing elective colorectal and bariatric surgical procedures at 38 hospitals between January 1, 2008, and December 31, 2009.

MAIN OUTCOME MEASURES

Mortality, cardiac events, and the combined adverse event of cardiac events and/or mortality.

RESULTS

Of 8431 patients, 23.5% were taking β-blockers prior to surgery (mean [SD] age, 61.9 [13.7] years; 63.0% were women). Treatment with β-blockers was continued on the day of surgery and during the postoperative period in 66.0% of patients. Continuation of β-blockers both on the day of surgery and postoperatively improved from 57.2% in the first quarter of 2008 to 71.3% in the fourth quarter of 2009 (P value <.001). After adjusting for risk characteristics, failure to continue β-blocker treatment was associated with a nearly 2-fold risk of 90-day combined adverse event (odds ratio, 1.97; 95% CI, 1.19-3.26). The odds were even greater among patients with higher cardiac risk (odds ratio, 5.91; 95% CI, 1.40- 25.00). The odds of combined adverse events continued to be elevated 1 year postoperatively (odds ratio, 1.66; 95% CI, 1.08-2.55).

CONCLUSIONS

β-Blocker continuation on the day of and after surgery was associated with fewer cardiac events and lower 90-day mortality. A focus on β-blocker continuation is a worthwhile quality improvement target and should improve patient outcomes.

Reduction of nonfatal reinfarctions in patients with a history of hypertension by chronic postinfarction treatment with metoprolol

The Stockholm Metoprolol Trial is a prospective double-blind placebo-controlled postmyocardial infarction study of 301 patients treated with metoprolol, 100 mg b.i.d., or matching placebo for three years. From this study we have retrospectively evaluated the outcome in patients with a history of treatment for hypertension prior to the index infarction. There were 41 such patients in the placebo group and 35 in the metoprolol group. Blood pressures during follow-up were nearly identical in the two groups. During the three years 11 patients died in the placebo group and 7 in the metoprolol group. Corresponding figures for nonfatal events such as reinfarction, coronary artery bypass surgery, cerebrovascular events and lower limb amputation were 12 vs. 1 (p less than 0.005), 3 vs. 0, 4 vs. 0 and 1 vs. 0, respectively. The numbers of patients with fatal and nonfatal events were 24 vs. 8 (p less than 0.01). In a retrospective subgroup analysis the results must always be interpreted with caution. The present results may, however, imply that postinfarction treatment with metoprolol reduces nonfatal atherosclerotic complications, especially nonfatal reinfarctions, in patients with a history of hypertension.

Withdrawal syndrome following cessation of antihypertensive drug therapy

In this study, a review of the available information concerning abrupt withdrawal of antihypertensive drug therapy is presented. Abrupt withdrawal of these drugs can produce a syndrome of sympathetic overactivity that includes nervousness, tachycardia, headache, agitation and nausea 36-72 h after cessation of the drug. A withdrawal syndrome may occur after discontinuation of almost all types of antihypertensive drugs, but mostly occurs with clonidine, beta-blockers, methyldopa and guanabenz. Less commonly can produce a rapid increase of the blood pressure to pre-treatment levels or above, or both and/or myocardial ischaemia. Although the exact incidence of the syndrome is not known, it appears to be rare, at least in patients receiving standard doses of the above antihypertensive drugs. The best treatment is prevention. In this study regarding the withdrawal syndrome that follows cessation of antihypertensive drugs therapy, a reference to the abrupt discontinuation of the main categories of antihypertensive drugs is also attempted.

Contraindications to vasoconstrictors in dentistry: Part III. Pharmacologic interactions

This article discusses the relative contraindications to the use of vasoconstrictor in patients currently medicated with tricyclic antidepressants, monoamine oxidase inhibitors, phenothiazines and beta-blockers. It reviews drug interactions and emphasizes potential detrimental systemic effects that epinephrine contained in local anesthetics can have when administered concomitantly with these drugs. Finally, special considerations are expressed concerning patients who abuse illicit drugs such as cocaine.

Metoprolol does not reduce platelet aggregability during sympatho-adrenal stimulation

The possibility that beta-adrenoceptor blockers, especially beta 1-selective agents might inhibit platelet function is of considerable interest, as this might be of pathophysiological importance in cardiovascular diseases. Platelet function, however, is difficult to assess and in vivo related data are scarce. The effect of one week of treatment with metoprolol 200 mg/day on platelet aggregability during mental stress (colour word conflict test; CWT) and low and high dose adrenaline infusions has been evaluated in a double-blind, placebo-controlled, cross-over study in 10 healthy male volunteers. Platelet function in vivo was assessed using ex vivo filtragometry, and the urinary excretions of beta-thromboglobulin (HMW beta-TG) and 11-dehydro-TxB2 (a thromboxane metabolite). Conventional in vitro aggregometry and the urinary levels of 2,3-dinor-6-keto-PGF1 alpha (a prostacyclin metabolite) were also studied. During the interventions there was increased platelet aggregability in vivo, as filtragometry readings were shortened by 41 +/- 11% during high dose adrenaline infusion, urinary HMW beta-TG levels increased and urinary 11-dehydro-TxB2 tended to increase. In contrast, platelet sensitivity to ADP in vitro was reduced. The urinary 2,3-dinor-6-keto-PGF1 alpha levels were increased during the interventions. Despite the cardiovascular and biochemical signs of beta-adrenoceptor blockade at rest and during the interventions, metoprolol failed to influence platelet function in vivo, as measured by ex vivo filtragometry, or urinary HMW beta-TG or 11-dehydro-TxB2 levels. It tended rather to enhance the stress response measured by ex vivo filtragometry. Platelet aggregability in vitro and urinary 2,3-dinor-6-keto-PGF1 alpha levels were not altered by metoprolol.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic hypersensitivity after beta-blocker withdrawal in hypertrophic cardiomyopathy

Withdrawal of beta-blocker therapy has been associated with the development of adrenergic hypersensitivity and adverse clinical effects in patients with coronary artery disease and hypertension. The aim of this study was to establish the occurrence and clinical significance of adrenergic hypersensitivity after abrupt withdrawal of long-term beta blockade in hypertrophic cardiomyopathy. Beta-adrenergic sensitivity was measured using the isoprenaline chronotropic dose25. Symptom assessment chronotropic dose25 calculation, bicycle exercise, echocardiography and Holter monitoring were performed while the patient received beta-blocker therapy and repeated on days 2, 4, 6, 8 (acute withdrawal period) and on day 21 after abrupt withdrawal. The study was terminated after 7 patients had been studied because all patients experienced a marked deterioration in symptoms and several clinical events had occurred. The chronotropic dose25 (mean +/- standard deviation) demonstrated beta 1-adrenergic hypersensitivity with a minimal value of 1.6 +/- 0.8 micrograms during the acute withdrawal period compared with 3.8 +/- 1.7 micrograms on day 21 (p = 0.003). Heart rates during rest and exercise showed an overshoot increase during the acute withdrawal period. The maximal 24-hour ventricular ectopic count was higher during the acute withdrawal period than during day 21 (p = 0.04). Of 3 patients with inducible outflow tract gradients, 2 developed resting gradients greater than 30 mm Hg during the acute withdrawal period. There was an increase in peak late filling velocity of mitral inflow after beta-blocker withdrawal. In conclusion, transient beta-adrenergic hypersensitivity occurs after beta-blocker withdrawal in hypertrophic cardiomyopathy and is associated with significant physiologic changes and adverse clinical consequences.

Profile of an ideal antianginal agent

Many antianginal agents are available for the treatment of coronary artery disease. These agents act by influencing the determinants of myocardial oxygen supply and demand. The 3 main classes of agents are the nitrates, beta-adrenergic blocking agents and the calcium entry blockers. Agents from all 3 classes have shown efficacy in treating both symptomatic and asymptomatic myocardial ischaemia. However, some patients cannot be treated with these agents because of side effects or contraindications. An ideal antianginal drug should effectively treat both angina and silent ischaemia. Additionally, it should be free of side effects, allow for maintenance of physical performance and be metabolically neutral. New agents are being developed which strive for this goal.

Beta-adrenergic receptor blockers. Adverse effects and drug interactions

Adverse effects of beta-adrenergic receptor blocking drugs can be divided into two categories: 1) those that result from known pharmacological consequences of beta-adrenergic receptor blockade; and 2) other reactions that do not appear to result from beta-adrenergic receptor blockade. Adverse effects of the first type include bronchospasm, heart failure, prolonged hypoglycemia, bradycardia, heart block, intermittent claudication, and Raynaud's phenomenon. Neurological reactions include depression, fatigue, and nightmares. It is not yet proven whether the beta 1-selective adrenergic blockers or those with partial agonist activity reduce the overall frequency of adverse reactions seen with propranolol. Patient age does not appear, in itself, to be associated with more beta-blocker side effects. Side effects of the second category are rare. They include an unusual oculomucocutaneous reaction and the possibility of oncogenesis. There are also many drugs that interact with beta-blockers, which may increase toxicity. Finally, there are specific patient characteristics where one beta-blocker may be more effective and safer than another.

Regulation by chronic drug administration of neuronal and cardiac calcium channel, beta-adrenoceptor and muscarinic receptor levels

Chronic administration of atropine (40-100 mg/kg, 23 days) produced a 29-33% increase in muscarinic receptors, measured by [3H]quinuclidinyl benzilate binding, in rat brain. Diisopropyl phosphorofluoridate (0.9 mg/kg, 14 days) produced a 35% decrease in muscarinic receptors. Propranolol administration (800 micrograms/kg/hr, 10 days) increased beta-adrenoceptors, measured by [3H]dihydroalprenolol binding, by 69 and 50% in brain and heart respectively. Isoproterenol administration (800 micrograms/kg/hr, 10 days) produced a 50% reduction in cardiac beta-adrenoceptors but did not alter brain receptors. These drug treatments were without effect on binding of the Ca2+ channel ligands, [3H]nimodipine and [3H]nitrendipine, to brain or heart respectively. However, chronic administration of nifedipine for 20 days (36 and 360 micrograms/kg/hr) did produce down-regulation of both cardiac and neuronal Ca2+ channels and a similar down-regulation of beta-adrenoceptors. Co-regulation of Ca2+ channels and neurotransmitter receptors may occur but may not be an automatic consequence of either receptor or channel regulation.

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.

Clinical consequences of abrupt drug withdrawal

Syndromes due to the abrupt withdrawal of drug treatment occur mainly with adrenal corticosteroids and agents with an action on either the cardiovascular system or central nervous system. The abrupt withdrawal of antihypertensive therapy typically results in symptoms of overactivity in the sympathetic nervous system. Clonidine and beta-adrenoceptor antagonists are clinically the most important of these agents, but numerous other drugs have been implicated. Overall, the problem is small when viewed in the context of the huge scale of prescribing of antihypertensive medicines. A more serious problem is the occurrence of crescendo angina following the abrupt withdrawal of beta-adrenoceptor antagonists. Although other factors may be involved, adaptive up-regulation of beta-adrenoceptor density is the most likely cause of crescendo angina, and renders the patient more susceptible to sympathetic nervous stimulation following withdrawal of treatment. Besides leading to a recrudescence of the disease being treated, the withdrawal of corticosteroids can cause a variety of syndromes. In particular, problems can arise as a result of treatment-induced suppression of the hypothalamic-pituitary-adrenal (HPA) axis. Another steroid withdrawal syndrome of unknown aetiology, without significant abnormalities of the HPA axis occurring, has been described. Benign intracranial hypertension may rarely follow steroid withdrawal in children. The syndromes associated with withdrawal of drugs which have an action on the CNS are poorly understood. Withdrawal of neuroleptic drugs can be followed by symptoms that resemble those described following withdrawal of anticholinergic drugs, and those agents with the greatest muscarinic-receptor-blocking properties are those which are most frequently implicated. However, the less common withdrawal dyskinesias are thought to reflect up-regulation of dopaminergic receptors during long term treatment. Gastrointestinal symptoms predominate following the abrupt withdrawal of antidepressants but hypomania and an 'akathisia-like' syndrome have been reported. Barbiturates are no longer recommended as hypnotics because of severe effects of withdrawal and the existence of safer alternatives. Short acting barbiturates can be withdrawn by replacement with either phenobarbitone (phenobarbitol) or diazepam and subsequent gradual reduction in dose. The recognition of dependency on benzodiazepines has been slow because of the similarity of mild withdrawal symptoms to the original problem which led to treatment being offered.(ABSTRACT TRUNCATED AT 400 WORDS)

Beta-adrenergic blocker withdrawal

Abrupt withdrawal of long-term beta-blocker therapy in patients with angina may be associated with unstable angina and myocardial infarction. It appears that an "overshoot" in heart rate from pretreatment values occurs, which increases myocardial oxygen demand. This increase in heart rate may be secondary to increased beta receptor numbers or increased receptor sensitivity. Another possible mechanism for the increased risk of myocardial infarction after beta-blocker withdrawal is increased platelet aggregability. Withdrawal reactions may be less severe with beta blockers that have partial agonist activity. In patients undergoing coronary artery bypass surgery, beta-blocker withdrawal reactions have also been observed. Maintenance of beta-blocker therapy on the morning of surgery appears to reduce this risk. Gradual withdrawal regimens in outpatients with angina may be associated with lower risk for a beta-blocker withdrawal reaction. The gradual withdrawal of beta blockers in hypertensive patients requires further study.

Antiplatelet effects of fenflumizole, a new anti-inflammatory drug, in dogs

Fenflumizole (2-(2,4-difluorophenyl)-4,5-bis(4-methoxyphenyl) imidazole) was given to dogs in a single oral dose of 3 or 10 mg/kg. The plasma concentrations of fenflumizole and the two metabolites (mono- and di-demethyl forms) attained to the peak level 1-2 hr after dosing of fenflumizole, returning to near the predose levels 8 hr after the dosing. Fenflumizole (10 mg/kg) given orally significantly inhibited collagen- and ADP-induced platelet aggregations ex vivo over 4 hr after the dosing. Fenflumizole effectively inhibited in vitro collagen-induced platelet aggregation, but failed to prevent ADP-induced aggregation. The mono-demethyl form of fenflumizole inhibited in vitro ADP- and collagen-induced aggregations, but the di-demethyl form was ineffective in inhibiting them.

Abrupt withdrawal of beta-blockade therapy in patients with myocardial infarction: effects on infarct size, left ventricular function, and hospital course

The effects of abrupt withdrawal or continuation of beta-blockade therapy during acute myocardial infarction were evaluated in 326 patients participating in the Multicenter Investigation of the Limitation of Infarct Size (MILIS). Thirty-nine patients previously receiving a beta-blocker and randomly selected for withdrawal of beta-blockers and placebo treatment during infarction (group 1) were compared with 272 patients previously untreated with beta-blockers who were also randomly assigned to placebo therapy (group 2). There were no significant differences between the two groups in MB creatine kinase isoenzyme (15.8 +/- 10.9 vs 18.2 +/- 14.4 g-eq/m2, respectively) estimates of infarct size, radionuclide-determined left ventricular ejection fractions within 18 hr of infarction (0.44 +/- 0.15 vs 0.47 +/- 0.16) or 10 days later (0.42 +/- 0.14 vs 0.47 +/- 0.16), creatine kinase-determined incidence of infarct extension (13% vs 6%), congestive heart failure (43% vs 37%), nonfatal ventricular fibrillation (5% vs 7%), or in-hospital mortality (13% vs 9%). Patients in group 1 had more recurrent ischemic chest pain (p = .002) within the first 24 hr after infarction, but not thereafter. However, this did not appear to be related to a rebound increase in systolic blood pressure, heart rate, or double product. In a separate analysis, 20 propranolol-eligible group 1 patients randomly selected for withdrawal of beta-blockade (group 3) were compared with 15 patients randomly selected for continuation of prior beta-blockade therapy (group 4). This comparison yielded similar results. These data indicate that the beta-blockade withdrawal phenomenon is not a major clinical problem in patients with acute myocardial infarction. beta-Blockade therapy can be discontinued abruptly during acute myocardial infarction if clinically indicated.

Does left ventricular aneurysmectomy improve ventricular function in patients undergoing coronary bypass surgery?

Fourteen consecutive patients undergoing left ventricular aneurysmectomy and coronary artery bypass grafting were studied by multiple gated ventricular scintigraphy at rest and during exercise before and at six weeks and six months after surgery. All had congestive heart failure and 12 angina pectoris. Before operation left ventricular ejection fraction fell significantly with exercise, as did the regional wall motion score. Six weeks after surgery all surviving patients were free of angina, with an improvement in functional class; the total exercise workload improved significantly, but resting left ventricular ejection fraction was unchanged; the regional wall motion score improved in both the anterior and left anterior oblique projections, although extensive areas of abnormal contraction persisted. Exercise left ventricular ejection fraction improved significantly after operation at six weeks, and previous exercise induced abnormalities of regional contraction were abolished. Six months after operation angina pectoris had recurred in one patient, but there was no further change in ventricular function in the remainder. Although resting ejection fraction is not improved, symptoms, exercise workload, and exercise ventricular function can be improved by aneurysmectomy and coronary artery bypass grafting, but the respective contribution of these two procedures remains uncertain.

Enhancement of the antiaggregatory activity of prostacyclin by propranolol in human platelets

The beta-adrenergic antagonist propranolol has been found to inhibit platelet aggregation. We investigated the possibility that propranolol exerts this action by stimulating the synthesis or enhancing the antiaggregatory activity of prostaglandin (PG) I2. The media from cultures of human endothelial cells inhibited thrombin-induced platelet aggregation, an effect attributed to PGI2 production by the cells. When endothelial cells were incubated with dl- or d-propranolol, the media had two to three times the inhibitory activity of control media. However, this increased activity was not due to increased synthesis of PGI2 because control and propranolol-treated cultures synthesized similar amounts of the PGI2 metabolite, 6-keto-PGF1 alpha. Instead, propranolol enhanced the antiaggregatory activity of PGI2. Propranolol (1 microM) and PGI2 (0.05 nM), when tested separately, inhibited aggregation by 19% and 13%, respectively, whereas the combination inhibited aggregation by 51%. PGI2 inhibited platelet aggregation and thromboxane (Tx) B2 production but stimulated cyclic AMP formation. The adenyl cyclase inhibitor 2',5'-dideoxyadenosine (DDA) had no effect of its own on these parameters, but blocked the actions of PGI2. Propranolol inhibited aggregation and TxB2 synthesis without changing cyclic AMP levels. Unlike PGI2, propranolol's effects were not altered by DDA. While the combination of propranolol and PGI2 inhibited aggregation to a greater extent than either agent alone, this enhanced effect with the combination did not extend to TxB2 or cyclic AMP production. Propranolol, PGI2, and the combination inhibited TxB2 synthesis to a similar extent, and PGI2 produced a similar increase in cyclic AMP in the presence and absence of propranolol. These findings indicate that propranolol and PGI2 inhibit platelet aggregation through cyclic AMP-independent and dependent mechanisms, respectively. While propranolol does not alter the synthesis of PGI2, it enhances the inhibition of aggregation by PGI2, and this may contribute to its antiplatelet effect.

Rebound phenomena following gradual withdrawal of chronic metoprolol treatment in patients with ischemic heart disease

Metoprolol or placebo was gradually withdrawn during 1 week in 115 patients participating in a 3-year, double-blind, postinfarction study. During the first month after withdrawal mental symptoms and increased cardiac symptoms occurred significantly more frequently in the metoprolol group. Disabling symptoms requiring reinstitution of treatment were seen in 14 of 58 in the metoprolol group vs 4 of 57 in the placebo group (p less than 0.05). In the metoprolol group, there was a rebound increase of basal heart rate and of the heart rate response to orthostatic testing during 3 weeks after withdrawal, when compared to values obtained 6 months later. In 27 patients plasma catecholamine levels were analyzed during repeated exercise tests and orthostatic provocations. Plasma norepinephrine and epinephrine responses to exercise were reduced 1 week after completion of withdrawal. At this time norepinephrine levels tended to be lower in relation to heart rate at all work loads. Our laboratory findings may be related to increased beta-adrenoceptor responsiveness, but unmasking of ischemic symptoms probably contributed to the clinical findings.

Nadolol compared to propranolol for treating chronic stable angina pectoris

In order to determine the relative efficacy and dose equivalency of propranolol four times a day and nadolol once daily for the treatment of stable angina pectoris, ten patients were studied in a double blind randomized placebo controlled crossover study. Total daily doses of propranolol and nadolol were determined by titrating until an equivalent degree of reduction in the heart rate response to exercise was achieved. At these doses, the treadmill exercise time to 0.1 mV of electrocardiographic ST-segment depression was increased from 248 +/- 75 seconds on placebo to 405 +/- 56 seconds on propranolol (p less than 0.05) and 471 +/- 46 seconds on nadolol (p less than 0.01). Also, the mean frequency of angina decreased from eight attacks per week on placebo to three on propranolol and nadolol (both p less than 0.05). In six of the ten patients, the effective total daily dose of propranolol and nadolol was identical, and the dose ratio for all ten patients was 1.17:1, propranolol to nadolol. However, individual dose titration is recommended when switching from propranolol four times a day to nadolol once daily because of the dosage variability noted in 40 percent of the patients.

Alpha- and beta-blockade in angina pectoris

Angina pectoris encompasses a clinically diverse group of syndromes in which the common factor is myocardial ischaemia resulting from an imbalance between oxygen requirement and delivery. Anginal pain is most frequently precipitated by exercise, but may occur without any apparent cause at rest. Fixed obstructions in the coronary vessels, often attended by thickening of the overlying coronary artery media, are the most frequent cause of ischaemic cardiac pain. The resulting myocardial fibrosis impairs efficient filling and emptying of the ventricles, further aggravating the functional embarrassment resulting from the reduced coronary blood flow. In stable coronary heart disease the increased energy demands during exercise are associated with the rapid development of a haemodynamic profile characteristic of acute left ventricular failure. This results in further substantial increases in pressure work, wall stress and oxygen consumption of the left ventricle. The reflex sympathoadrenal consequences of these primary haemodynamic changes lead to further mechanical and electrical embarrassment of the ischaemic heart. Increased stimulation of beta 1- and beta 2-receptors in the heart increases heart rate and contractility and thereby myocardial oxygen demand. Increased stimulation of alpha-receptors in the peripheral veins and arteries indirectly increases left ventricular oxygen demand still further by increasing preload and afterload, respectively. The reduced blood flow to the endocardium enhances its sensitivity to increased sympathoadrenal stimulation and facilitates initiation of arrhythmias. Blockade of all adrenergic activity, particularly in the myocardium, coronary arteries and peripheral blood vessels should, therefore, help alleviate the myocardial ischaemia. There is a rational argument for the use of alpha-blockade in coronary heart disease, particularly in conjunction with beta-blockade. Attenuation of the risk of coronary spasm and ventricular arrhythmias and reduction of pressure work and left ventricular afterload are amongst the potential attributes of alpha-blockade. Alone, however, their utility is severely limited by the risks of hypotension and reduction in coronary perfusion pressure and reflex oxygen-wasting tachycardia. Alone, alpha-adrenoceptor antagonists have no place in the treatment of angina pectoris. beta-Adrenoceptor blocking drugs competitively inhibit catecholamines at both cardiac and peripheral vascular beta-adrenergic receptors. Their main advantage is that they reduce many of the important determinants of myocardial oxygen consumption, particularly by reducing the heart rate during exercise.(ABSTRACT TRUNCATED AT 400 WORDS)

Increased platelet adhesion and aggregation in hypertensive patients: effect of atenolol

Fourteen patients with established hypertension followed a double-blind crossover-styled trial to study the effects of 100 mg/day atenolol compared to placebo. Atenolol was found to be an effective antihypertensive agent, reducing both systolic and diastolic blood pressure. Hypertensive patients appear to have increased in vitro platelet adhesion and aggregation. Atenolol significantly reduced platelet adhesion, but had little effect on aggregation. This may be important in contributing towards the now-recognised cardio-protective effect of the beta-adrenoceptor blocking agents. Blood chemistry and haematological parameters were unchanged; but whereas plasma cholesterol and plasma triglyceride levels remained normal, there was a significant fall in plasma high-density lipoprotein cholesterol levels. Side effects were very few.

Intrinsic sympathomimetic activity: clinical fact or fiction?

The therapeutic importance of the ancillary pharmacologic property of partial agonist activity, or intrinsic sympathomimetic activity (ISA), of a beta-adrenoceptor antagonist is controversial. Its pharmacologic definition and accepted physiologic potential are now joined by convincing evidence that ISA may have important therapeutic implications. The ability to support basal cardiac functions while preventing the potential hazards of random sympathetic stimulation is an important attribute of this property, particularly in the damaged heart. The beneficial effects of ISA on peripheral blood flow, systemic vascular resistance and left ventricular afterload are established. Although all beta-blocking drugs are contraindicated in patients with asthma, ISA appears to be at least as important as cardioselectivity in offsetting some of the increase in airway resistance that results from beta blockade alone both at rest and during exertion. These pharmacodynamic consequences of ISA may explain the lesser reduction in exercise tolerance afforded by beta-blocking drugs with ISA than by those without. ISA may also enhance the primary oxygen-sparing effects of beta blockade in the ischemic myocardium by reducing coronary resistance, enhancing coronary blood flow, and reducing anaerobic metabolism. The adverse effects of beta-blocking drugs on blood lipids and carbohydrate metabolism also appear to be largely negated in drugs with ISA. The risks of rebound effects from abrupt withdrawal are significantly less in drugs with ISA than in those without.

Effects of coronary artery bypass grafting on left ventricular function assessed by multiple gated ventricular scintigraphy

The effect of coronary artery bypass grafting on global left ventricular ejection fraction and regional contraction was studied in 56 consecutive patients with chronic stable angina pectoris by means of multiple gated ventricular scintigraphy at rest and during dynamic supine exercise before and six weeks after myocardial revascularisation. Before operation, exercise induced a significant fall in ejection fraction and regional wall motion score. Six weeks after operation 52 patients were symptomless. Resting ejection fraction and regional wall motion score were unchanged but during exercise ejection fraction increased significantly, and the previous exercise induced regional wall motion abnormalities were abolished. All four patients with persisting angina showed the same pattern as before operation, with a fall in left ventricular ejection fraction and regional wall motion score during exercise. Multiple gated ventricular scintigraphy affords a safe, objective, reproducible, and non-invasive means of assessing serial ventricular function at rest and during exercise in patients with ischaemic heart disease. The technique confirms that coronary bypass surgery abolishes exercise induced abnormalities of left ventricular function, but has no influence on resting function.

Effects of propranolol in vitro and in vivo on platelet function and thromboxane formation in normal volunteers

In vitro and ex vivo effects of propranolol on platelet aggregation, formation of thromboxane B2 (TXB2) and platelet sensitivity to prostacyclin were studied in healthy men. Propranolol, added in vitro to platelet rich plasma (PRP) inhibited platelet aggregation and TXB2 formation induced by ADP, 1-epinephrine, collagen and arachidonic acid. Concentrations of 20-100 microM propranolol were effective when ADP, 1-epinephrine and collagen were used as stimuli. Higher concentrations (250-500 microM) were needed to inhibit aggregation induced by arachidonic acid. Oral administration of propranolol either as a single dose (120 mg) or for one week (3 x 40 mg/day) did, however, not affect platelet aggregation, thromboxane formation and platelet sensitivity to prostacyclin. In addition, withdrawal of propranolol was without effect on these parameters. Although propranolol has potent effects on platelet function in vitro, it seems that the blood levels achievable by oral administration of propranolol are too low to affect platelet aggregation and TXB2 formation.

Beta-receptor blocker withdrawal. A preoperative problem in general surgery?

A prospective randomized study was performed in 91 patients scheduled for general surgery on 99 occasions. The patients were chronically (greater than 3 months) treated with beta-receptor blockers because of ischaemic heart disease and/or hypertension and the beta-receptor blockade was either gradually withdrawn (n = 51) during 4 days preoperatively or continued until surgery (n = 48). The effects on arterial blood pressure (BP), heart rate (HR) and rate-pressure product (RPP) at rest and the incidence of chest pain during daily activities were registered. A withdrawal of the beta-receptor blockade was associated with increases of HR (in eight patients greater than 30 beats min-1) and RPP and in patients treated for hypertension there were also increases of systolic and diastolic BP (in five patients greater than or equal to 30/15 mmHg). Patients who continued the beta-receptor blockade until surgery showed no changes. Nine out of 23 patients with a previous history of ischaemic heart disease had an increase of chest pain after withdrawal of the beta-receptor blockers, whereas none of the corresponding 25 patients who continued the therapy suffered from an increased chest pain. Due to the severity of symptoms after beta-receptor blocker withdrawal, surgery had to be postponed in 4 patients. The observations suggest that a 4-day preoperative withdrawal of long-term beta-receptor blockade is potentially hazardous in ischaemic and/or hypertensive patients.

Comparative effects of abrupt withdrawal of propranolol and verapamil in angina pectoris

The potential hazards of abrupt withdrawal of propranolol have been described in patients with angina pectoris; however, the effects of abrupt withdrawal from long-term therapy with verapamil have not previously been investigated. The comparative effects of withdrawal from long-term treatment with propranolol and verapamil were assessed in a placebo-controlled double-blind randomized crossover study of 20 patients received placebo for 2 weeks, then increasing doses of propranolol (60 to 320 mg/day) or verapamil (240 to 480 mg/day) for 3 weeks. Patients were then abruptly withdrawn from drug onto placebo for 1 week, followed by crossover to the other drug treatment and a second withdrawal period. All 20 patients were withdrawn from verapamil without evidence of a rebound increase in frequency of anginal attacks, blood pressure, heart rate, or rate-pressure product and without a rebound deterioration in exercise tolerance. In contrast, with propranolol withdrawal, 2 patients (with the highest baseline angina attack rate) had a severe exacerbation of their anginal syndrome and could not undergo formal exercise testing; the other 18 patients were withdrawn from propranolol without incident. Plasma catecholamines were increased during exercise compared with rest during all treatments; however, the levels of catecholamines during exercise were significantly higher with propranolol than with verapamil and placebo (p less than 0.05). Levels of exercise catecholamines returned to placebo baseline values after withdrawal of propranolol.

Withdrawal of beta-blocking drugs

Our early observations indicated that when treatment was changed from propranolol to placebo, anginal patients experienced a higher incidence of chest pain during the first week of placebo treatment compared to the second week. Since then, there have been several reports of myocardial infarction and sudden death occurring when propranolol therapy has been stopped. However, more formal hospital studies have indicated that ischemia from propranolol withdrawal is relatively infrequent. Studies in normal subjects and hypertensive patients have shown an increase in beta-receptor sensitivity as suggested by increased responsiveness to isoprenaline after propranolol withdrawal. Some investigators have found an increase in free triiodothyronine levels. Catecholamine levels do not appear to be raised. Other relevant factors in ischemic patients might be a reversal of the favorable rightward shift of the oxyhemoglobin dissociation curve or a reversal of reduced platelet aggregation produced by propranolol. Last, propranolol withdrawal in patients who have received the drug for a considerable period might unmask a withdrawal in patients who have received the drug for a considerable period might unmask a progression of the disease process, so that in the absence of beta blockade oxygen supply is inadequate to meet the requirements of relatively ischemic areas even at rest. Whether all beta blockers are similar to propranolol in this regard is unknown. We are examining, in normal volunteers, the sensitivity of the beta receptor after the withdrawal of atenolol, pindolol, or propranolol, administered for at least 2 weeks after final dose adjustment to levels sufficient to produce maximum inhibition of exercise tachycardia. The sensitivity of the beta receptor is being assessed by the response of bolus injections of isoprenaline and the response to exercise tachycardia.

Prevention of propranolol withdrawal mechanism by prolonged small dose propranolol schedule

Abrupt withdrawal of propranolol may be followed by a "propranolol withdrawal syndrome "due, at least in part, to enhanced beta adrenergic sensitivity. Tapering propranolol dosage is frequently used in the hope of preventing adverse withdrawal events but the success of such a maneuver has not been shown. The rationale for the dose tapering schedule in this study was based on earlier observations after abrupt withdrawal of propranolol. Nine hypertensive patients were gradually withdrawn from long-term propranolol therapy, either by serial dose reduction for 6 to 9 days (n = 3) or by reduction to a prolonged small dose (30 mg daily) for 2 weeks before complete withdrawal (n = 6). During dose reduction of propranolol and for 2 additional weeks of placebo therapy, serial measurements were made of cardiac sensitivity to isoproterenol, heart rate at rest, blood pressure, plasma catecholamines, serum thyroxine (T4) and triiodothyronine (T3) and symptoms. Serial dose reduction decreased but did not prevent cardiac hypersensitivity in two of three patients. The prolonged small dose therapy largely prevented cardiac hypersensitivity and overshoot in heart rate, blood pressure and plasma catecholamines and symptoms. Serum T4 decreased significantly and T3 tended to increase during and after prolonged small dose treatment. These results indicate that prolonged administration of small dose propranolol before complete withdrawal in hypertensive patients prevents enhanced cardiac beta adrenergic sensitivity and other adverse events.

Effects of the non-selective beta-adrenoceptor blocking agent, carteolol, on platelet function, blood coagulation and viscosity

We have studied the effect of a new beta-adrenergic blocker, carteolol, on platelet function, blood coagulation and viscosity in 10 healthy male volunteers. Following carteolol (5 mg orally) we were able to demonstrate significant inhibition of platelet aggregation to ADP (p less than 0.05) and adrenaline (p less than 0.01) after 5 hours, but not at 2 or 24 hours. This maximum inhibition of platelet aggregation corresponded to peak plasma concentrations of carteolol measured. The platelet release reaction, as measured by plasma levels of the platelet specific protein beta-thromboglobulin (BTG) was unaltered and there was no significant effect on a panel of coagulation tests or on blood viscosity.

Lack of beta-adrenoreceptor hypersensitivity after abrupt withdrawal of long-term therapy with oxprenolol

The possibility of beta-adrenoreceptor hypersensitivity after abrupt withdrawal of long-term therapy (8-18 months) with the slow-release (SR) formulation of oxprenolol (160-320 mg/day) was assessed in six patients with uncomplicated essential hypertension. The chronotropic dose 25 of isoproterenol (the dose that increases the resting heart rate by 25 beats/min), plasma concentration of catecholamines, triiodothyronin and thyroxin, plasma renin activity and aldosterone, hemoglobin, hematocrit and oxyhemoglobin dissociation were measured on the last day of oxprenolol SR intake and 1, 2, 3, 6 and 13 days after abrupt replacement by identical placebo tablets. The chronotropic dose 25 of isoproterenol (microgram/m2), which was greater than 25.6 in all patients on the last day of oxprenolol SR, fell to 4.83 +/- 2.03 on the second day and to 3.50 on the third day after its abrupt withdrawal and reached a minimal value on the thirteenth day (2.78 +/- 0.30). Throughout the study, plasma concentrations of catecholamines, triiodothyronin and thyroxin and oxyhemoglobin dissociation remained unchanged. Plasma renin activity and plasma aldosterone, which were suppressed during oxprenolol administration, rose significantly during placebo, coinciding with a significant fall in hematocrit and hemoglobin. No major subjective symptoms were reported by the patients. Thus, hypersensitivity of beta-adrenoreceptor-mediated responses was not demonstrated after sudden withdrawal of oxprenolol SR.

Adrenergic hypersensitivity after beta-blocker withdrawal

We investigated the possibility of a rebound increase in sympathetic response after stopping beta-blocker treatment by measuring heart rate under conditions of increased sympathetic drive, as provided by standing with vasodilatation, or the Valsalva manoeuvure. Significant rebound increases in heart rate were observed after stopping propranolol given for one or more weeks but not when given for only four days. The amplitude of the rebound heart rate relative to the control heart rate off beta-blockers was similar after propranolol, atenolol, oxprenolol, or acebutolol, and in hyperthyroid subjects.

Limitation of myocardial infarct size in patients less than 66 years treated with alprenolol

Two hundred and eighty-two patients less than 66 years of age admitted with suspected or definite myocardial infarction were allocated in a random fashion to treatment with alprenolol or placebo. Treatment was started immediately upon admission with 5-10 mg alprenolol or placebo intravenously, followed by 200 mg alprenolol or placebo orally twice a day for one year. In 178 patients a definite myocardial infarction was diagnosed. Myocardial infarct size could be estimated from serial determinations of serum total creatine kinase in 42 patients treated with alprenolol and 43 patients receiving placebos. Median infarct size was 20.6 CK g Eq/m2 body surface in the alprenolol group, the corresponding figure in the placebo group being 34.4 CK g Eq/m2 body surface. Median rate of release of creatine kinase from the ischaemic myocardium was 27.7 U/1 per hour and 48.0 U/1 per hour after alprenolol and placebo, respectively. Alprenolol limited infarct size significantly provided the treatment was started within 12 hours of the onset of symptoms.

Effect of long-term beta-blockade with alprenolol on platelet function and fibrinolytic activity in patients with coronary heart disease

In 14 patients with coronary heart disease the effect of long-term treatment (mean 16 months, range 12-33) with alprenolol on platelet function and fibrinolytic activity was studied. While on the beta-blocker and two weeks after gradual withdrawal of it, the patients performed a bicycle-ergometer test and blood samples were obtained before and following exercise. Pre-exercise fibrinolytic activity, assessed by the euglobulin clot lysis time, was 183 +/- 27 min (mean +/- SEM) while on alprenolol as compared to 111 +/- 18 min (p less than 0.01) after its withdrawal. Activation of fibrinolysis following exercise was not significantly influenced by alprenolol. In patients treated with alprenolol, the pre-exercise threshold level of ADP, producing platelet aggregation was 3.3 muM (geometric mean) and 5.1 muM after stopping treatment (p less than or equal to 0.05). In patients receiving the beta-blocker, the ADP- threshold value dropped from 3.3 muM before exercise to 2.3 muM immediately after exercise (not significant). The corresponding values after withdrawal of alprenolol were 5.1 muM and 2.7 muM (p less than or equal to 0.02). Adrenaline - stimulated aggregation was not significantly influenced by alprenolol. Serotonin release from platelets following maximal ADP- and adrenaline stimuli was not significantly changed by exercise in patients on beta-blockade. After stopping treatment, ADP-induced serotonin release was 22 +/- 4.1% before and 15 +/- 4.7% after exercise (p less than 0.02). the corresponding values using the adrenaline stimulus were 29 +/- 5.7% and 17 +/- 4.7% (p less than 0.05). It is suggested that during physical stress alprenolol may protect platelets against aggregatory stimuli.