BMJ  2007;334:946-949 (5 May), doi:10.1136/bmj.39185.440382.47

Clinical Review

blockers in hypertension and cardiovascular disease

H T Ong Heart Clinic, 251C Burma Road, Penang, Malaysia

This review provides practical pointers on the use of blockers for the non-specialist clinician

blockers are useful in managing angina and reducing mortality after myocardial infarction and in heart failure. They probably reduce cardiovascular events in high risk surgery and retard the progression of atherosclerosis. In younger patients, blockers should remain first line antihypertensives, together with diuretics, calcium channel blockers, angiotensin converting enzymes, and adrenergic receptor binders; choice depends on the individual case.

Not all blockers are equivalent in cardiovascular protective effects, and atenolol seems inferior to other antihypertensive drugs in reducing stroke and total mortality. Recent publications have found that blockers are less effective than other antihypertensive drugs in preventing cardiovascular outcomes in hypertensive patients.^{1 2 3} In interpreting the new data, it is important to integrate these new results with previous trials and meta-analyses.

Sources and selection criteria The references in the ASCOT trial,1 recent meta-analyses of treatment with blockers,2 3 and guidelines of hypertension societies (Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC 7), British Hypertension Society, World Health Organization, European Society of Hypertension–European Society of. Cardiology) were supplemented with a PubMed search using the keywords "clinical trial", "beta-blockers", "hypertension", and "cardiovascular outcomes".

Are blockers less protective in hypertensive patients?

Results of ASCOT-BPLA (the Anglo-Scandinavian cardiac outcomes trial—blood pressure lowering arm) suggest that atenolol may be only marginally inferior to amlodipine.¹ Its main lesson is that blood pressure must be tightly controlled, and patients taking blockers (and diuretics) must be monitored so that cardiovascular risk factors are not adversely altered.

ASCOT-BPLA randomised 19 257 high risk people with hypertension to amlodipine (adding perindopril) or atenolol (adding bendroflumethiazide). After 5.5 years, the primary end point, non-fatal myocardial infarction and cardiovascular death, was similar in the two groups (relative risk 0.90, 95% confidence interval 0.79 to 1.02; P=0.11). Several measures were lower with amlodipine: coronary end point (8% v 9%; 0.87, 0.79 to 0.96; P=0.007), stroke (3% v 4%; 0.77, 0.66 to 0.89; P=0.0003) and mortality (8% v 9%; 0.89, 0.81 to 0.99; P=0.02). Patients taking amlodipine had significantly lower blood pressure, as well as higher HDL (high density lipoprotein) cholesterol, and lower body mass index and concentrations of triglyceride, creatinine, and glucose. Multivariate adjustment for all these differences abolishes the difference in the cardiovascular event rate of the two groups.⁴

Thus, rather than showing the inferiority of atenolol, ASCOT-BPLA shows the importance of rigorously controlling blood pressure and other risk factors to reduce clinical cardiovascular disease. Although statistically significant, the 1% reduction in coronary event, stroke, and total mortality is not inspiring; the number needed to treat (NNT) for a year to prevent one cardiovascular event is 220, and to prevent one death is 650.^w1 With diuretic antihypertensive therapy to prevent heart failure NNT=48, and for the reduction in mortality with blockers after myocardial infarction NNT=25-80.^{w2 w3}

Meta-analyses
Two large meta-analyses also question the value of blockers in cardiovascular protection of hypertensive patients.^{2 3} These show that atenolol is inferior in reducing stroke and mortality, but non-atenolol blockers may be equivalent to other antihypertensive drugs.

Carlberg reviewed the effects of atenolol on cardiovascular outcomes in hypertensive patients aged 52-70 who were followed up for 4.6 years. In four studies comparing atenolol with placebo (6825 patients) there was no difference in total mortality (relative risk 1.01, 0.89 to 1.15), cardiovascular mortality (0.99, 0.83 to 1.18), myocardial infarction (0.99, 0.83 to 1.19), and stroke (0.85, 0.72 to 1.01). In five studies comparing atenolol with other antihypertensive agents (17 671 patients), despite equivalent reduction in blood pressure, atenolol treatment was associated with higher total mortality (1.13, 1.02 to 1.25), cardiovascular mortality (1.16, 1.00 to 1.34), and stroke (1.30, 1.12 to 1.50).

Lindholm's meta-analysis was more comprehensive, reviewing 13 trials (105 951 patients) comparing blockers with other antihypertensives and seven trials (27 433 patients) comparing blockers with placebo. Overall, blockers were inferior to other antihypertensives in preventing stroke (1.16, 1.04 to 1.30), but the results were different for atenolol and non-atenolol blockers (table 1). Compared with other antihypertensive drugs, atenonol was associated with higher risk of stroke (1.26, 1.15 to 1.38) and total mortality (1.08, 1.02 to 1.14). Non-atenolol blockers were not inferior to other antihypertensives in preventing stroke (1.20, 0.30 to 4.71), myocardial infarction (0.86, 0.67 to 1.11), and total mortality (0.89, 0.70 to 1.12).

View this table: [in this window] [in a new window]   Table 1  Incidence of stroke and myocardial infarction and total mortality in hypertensive patients

 
Atenolol
The different pharmacokinetic properties of atenolol and non-atenolol blockers may account for their different cardiovascular protective effects in older hypertensive patients. Good data now show that atenolol is inferior, but the data are not conclusive enough to require using a substitute in all patients. Before starting or continuing with atenolol, though, a cautious clinician would ask whether another blocker could be used. Atenolol is hydrophilic, has minimal hepatic metabolism, and is excreted in the urine; its long half life allows once daily dosage.^w4 It is inexpensive and has little interaction with drugs that are metabolised in the liver; these features account for its popularity. However, its pharmacokinetic profile can be disadvantageous in older patients with renal impairment, which slows clearance of atenolol.^w5

Do blockers have any role in cardiovascular disease?

Although the value of blocker use in early myocardial infarction is controversial, blockade clearly reduces adverse events in secondary prevention after infarction.^w6 Reviewing 31 trials (24 974 patients), Freemantle found that treatment with blockers after infarction significantly reduced mortality (relative risk 0.77, 0.69 to 0.85).⁵ All blockers did not behave similarly; mortality was reduced with acebutolol (607 patients; 0.49, 0.25 to 0.93), metoprolol (5772 patients; 0.80, 0.66 to 0.96), propranolol (5785 patients; 0.71, 0.59 to 0.85), and timolol (2084 patients; 0.59, 0.46 to 0.77). No mortality reduction was seen with atenolol (1.02, 0.52 to 1.99). The NNT over two years to reduce one death with blockers after infarction is 42; it compares favourably with treatment with antiplatelets (NNT=153) and statins (NNT=94).

Good evidence exists for reduction in symptoms of angina and also for an antiatherosclerotic effect with blockers.⁶ By influencing the pathophysiology of atheroma progression they may improve prognosis. BCAPS (the blocker cholesterol lowering asymptomatic plaque study) studied 793 patients with asymptomatic carotid plaques over 36 months, randomising them to placebo, fluvastatin 40 mg, or long acting metoprolol 25 mg. Progression of atheroma was assessed by measuring carotid intima-media thickness. Compared with placebo, metoprolol significantly reduced the rate of plaque progression over 18 months (difference 0.058 mm/year; P=0.004) and over 36 months (0.023 mm/year; P=0.014). In patients taking metoprolol, total mortality and cardiovascular events were significantly lower than in those not taking blockers (8 v 19; P=0.031).

blockers improve prognosis in patients with all grades of symptomatic heart failure. Recent evidence suggests that blockers are equivalent to angiotensin converting enzyme inhibitors as initial drugs in treating heart failure.^w8 Bisoprolol, metoprolol, and carvedilol all reduce mortality in heart failure.

CIBIS-II (the cardiac insufficiency bisoprolol study II) randomised 2647 patients with ejection fraction <35% and New York Heart Association (NYHA) class III or IV to bisoprolol or placebo, with the primary end point of total mortality.⁷ The trial was terminated after 1.3 years, when it showed that bisoprolol reduced mortality significantly (11.8% v 17.3%; relative risk 0.66, 0.54 to 0.81; P<0.0001). It also significantly reduced total hospitalisation (0.80, 0.71 to 0.91; P=0.0006) and death from cardiovascular causes (0.71, 0.56 to 0.90; P=0.0049).

MERIT-HF (metoprolol CR/XL randomised intervention trial in congestive heart failure) involved 3391 patients (NYHA classes II to IV, ejection fraction <40%).⁸ When the trial was terminated after one year, metoprolol clearly reduced total mortality (7.2% v 11.0%; 0.66, 0.53 to 0.81; P<0.0001) as well as cardiovascular mortality (0.62, 0.50 to 0.78), sudden death (RR 0.59, 0.45 to 0.78), and death from heart failure (0.51, 0.33 to 0.79). A carvedilol trial involving 1094 patients also showed highly significant reduction in total mortality (3.2% v 7.8%; 0.35, 0.20 to 0.61; P<0.001).^w7

More impressive was COPERNICUS (the carvedilol prospective randomised cumulative survival study), which enrolled 2289 ill patients (NYHA class IV, ejection fraction <25%).⁹ After 10.4 months, carvedilol markedly reduced overall mortality (130 v 190 deaths; 0.65, 0.52 to 0.81; P=0.0014), as well as death or admission to hospital (0.76, 0.67 to 0.87; P<0.001).

Is treatment outcome affected by type of blocker used or age profile of patient?

blockers do not all produce the same outcome when used in the same clinical condition. A study similar to COPERNICUS but using bucindolol produced results different from those with carvedilol.¹⁰ In 2708 patients (NYHA class III or IV, ejection fraction <35%) after two years, total mortality was not significantly affected by bucindolol (33% with placebo, 30% with bucindolol; 0.90, 0.78 to 1.02; P=0.10). Although many reasons were postulated, the practical message is that some, but not all, blockers reduce mortality in heart failure.^w9 Thus, in treating heart failure, clinicians should choose only those blockers that have been shown to be useful. Similarly, in hypertension, myocardial ischaemia, or after myocardial infarction, only those blockers with good evidence favouring their value should be used.

Older people with hypertension may have a different profile from younger ones.¹³ Khan and McAlister reviewed cardiovascular events (stroke, myocardial infarction, and death) in 145 811 patients from 21 hypertension trials (table 2). Among patients under 60 years, blockers reduced cardiovascular outcomes compared with placebo (19 414 patients; relative risk 0.86, 0.74 to 0.99) and were equivalent to other antihypertensive drugs (30 412 patients; 0.97, 0.88 to 1.07). In patients aged 60 and over, blockers were equivalent to placebo (8019 patients; 0.89, 0.75 to 1.09) and were less effective in reducing cardiovascular outcomes than other antihypertensive drugs (79 775 patients; 1.06, 1.01 to 1.10). These results are clinically reasonable, since the pathophysiology of hypertension is different in younger and older patients.^{14 15}

blockers may be more useful in younger people with hypertension who have a higher sympathetic drive but essentially normal vascular resistance.¹⁶ Rather than pointing to "the end of blockers in uncomplicated hypertension," the evidence today suggests that blockers are efficacious in cardiovascular protection of younger people with hypertension.^w14

View this table: [in this window] [in a new window]   Table 2  Relative risk of cardiovascular outcomes (death, stroke, or myocardial infarction) in hypertensive patients treated with blockers

 

Which blocker should we use? Strong evidence from clinical trials shows that bisoprolol, carvedilol, and metoprolol improve prognosis in heart failure, and acebutolol, metoprolol, propranolol, and timolol reduce mortality after myocardial infarction5 7 8 9 Metoprolol and bisoprolol may improve prognosis in patients with coronary artery disease, as some randomised trials have shown they reduce adverse events in stable patients and patients at high risk6 19 20 Atenolol has been shown in clinical trials to be inferior to other antihypertensive agents in reducing cardiovascular outcomes (especially strokes); no evidence from clinical trials supports its use after a myocardial infarction or in heart failure2 3 11 12w10-w14

How should blockers be used?

We must be cautious and objective in interpreting the data on use of blockers in hypertensive patients. The preference for new drugs sometimes results in an increase in clinical disease, as the COX-2 experience shows.^{17w15 w16} Diuretics were once thought to be unsafe antihypertensives because of the metabolic changes they induce,^{w17 w18} but ALLHAT (the antihypertensive and lipid lowering treatment to prevent heart attack trial) showed that their cardiovascular protection in hypertension equals or surpasses that conferred by newer drugs.¹⁸ Diuretics are especially useful in stroke prevention, and a meta-analysis by Psaty (42 clinical trials, 192 478 patients) found that all antihypertensive drugs are inferior to diuretics in reducing cardiovascular events.^{w19 w20}

The need to choose the correct blocker for the clinical situation must be borne in mind when interpreting the comparative trials of antihypertensive drugs involving blockers. That blockers relieve angina has been known since the 1960s.^w21 blockers clearly reduce mortality in secondary prevention after myocardial infarction.⁵ They also reduce cardiovascular events in the preoperative management of high risk ischaemic patients before major vascular surgery.¹⁹ Continuation of bisoprolol for two years after surgery further reduces cardiac death and myocardial infarctions.²⁰ Metoprolol's antiatherosclerotic effect provides a pathophysiological rationale for the improved prognosis with blockers in myocardial ischaemia.⁶

blockers reduce mortality in all classes of heart failure,^w22 but not all blockers are the same: bucindolol does not produce the same mortality reduction as carvedilol in similar patients.¹⁰ Although blockers have clear benefit in secondary prevention, they do not affect prognosis when used in early myocardial infarction; the reduction in re-infarction and sudden death is balanced by the increase in heart failure and shock.^{5w6 w23}

The data from trials of atenolol in hypertension are not reassuring. As well as the results of ASCOT-BPLA, atenolol was also shown to be inferior to losartan in the LIFE (losartan intervention for end point reduction in hypertension) study, which found that angiotensin receptor blockers are especially useful in stroke prevention.^21w24 Yet, for preventing stroke, an angiotensin receptor blocker was equivalent to a calcium channel blocker in VALUE (the valsartan antihypertensive long-term use evaluation trial), while the angiotensin converting enzyme inhibitor was inferior to diuretic in ALLHAT.^{18 22} As there is no evidence that angiotensin antagonists are better at preventing stroke, the results of LIFE must be due to the inferiority of atenolol.

The meta-analysis showing atenolol to be inferior to comparative antihypertensive drugs but non-atenolol blockers to be equivalent to comparator drugs, is further evidence cautioning against atenolol use in hypertension.³ The review suggesting that blockers reduce cardiovascular outcomes in younger but not in older people with hypertension makes a logical point.¹³ Younger people with hypertension tend to have a higher sympathetic tone and thus may better respond to blockade. In older people, blockers should be avoided unless another clinical condition necessitates their use.

What is still controversial? Are non-atenolol blockers (especially metoprolol and bisoprolol) superior to atenolol in preventing adverse cardiovascular outcomes in hypertensive patients? Are blockers equivalent to other classes of antihypertensive agents in reducing clinical events in younger patients? Can blockers reduce clinical events and improve prognosis in patients with coronary disease? Will perioperative use of blockers reduce postoperative cardiovascular morbidity and mortality?

Additional educational resources For healthcare professionals National Collaborating Centre for Chronic Conditions. Hypertension: management of hypertension in adults in primary care: partial update. London: Royal College of Physicians, 2006. www.nice.org.uk/CG034guidance World Health Organization, International Society of Hypertension Writing Group. World Health Organisation (WHO)/International Society of Hypertension (ISH) statement on management of hypertension. J Hypertens 2003;21:1983-92. Guidelines Committee. European Society of Hypertension-European Society of Cardiology guidelines for the management of arterial hypertension. J Hypertens 2003;21:1011-53. Chobanian AV, Bakris GL, Black HR, et al and the National High Blood Pressure Education Program Coordinating Committee. Seventh report of the National Committee on prevention, detection, evaluation, and treatment of high blood pressure. Hypertension 2003;42:1206-52. Information for patients NICE. Hypertension—information for the public (www.nice.org.uk/CG034publicinfo) British Blood Pressure Association (www.bpassoc.org.uk) American Heart Association (www.americanheart.org) National Heart Lung and Blood Institute (www.nhlbi.nih.gov/health/index.htm)

Summary points blockers reduce mortality after a myocardial infarction and improve prognosis in patients with systolic heart failure They reduce adverse outcomes in perioperative management of high risk patients In younger hypertensive patients (aged under 60 years), blockers are equivalent to other antihypertensive agents blockers may improve prognosis and favourably retard disease progression in coronary artery disease Atenolol may be less useful than other blockers, and other antihypertensive drugs, in reducing cardiovascular disease in hypertensive patients

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References w1-w24 are on bmj.com

Contributors: HTO is sole contributor.

Competing interests: None declared.

Provenance and peer review: Non-commissioned and externally peer reviewed.

References

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2. Carlberg B, Samuelsson O, Lindholm LH. Atenolol in hypertension: is it a wise choice? Lancet 2004;364:1684-9.[CrossRef][ISI][Medline]
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9. Packer M, Coats AJS, Fowler MB, et al for the Carvedilol Prospective Randomised Cumulative Survival Study Group. Effect of carvedilol on survival in severe chronic heart failure. N Engl J Med 2001;344:1651-8.[Abstract/Free Full Text]
10. Beta-Blocker Evaluation of Survival Trial Investigators. A trial of the beta-blocker bucindolol in patients with advanced chronic heart failure. N Engl J Med 2001;344:1659-67.[Abstract/Free Full Text]
11. MRC Working Party. Medical Research Council trial of treatment of hypertension in older adults: principal results. BMJ 1992;304:405-12.[ISI][Medline]
12. First International Study of Infarct Survival Collaborative Group. Randomised trial of intravenous atenolol among 16,027 cases of suspected acute myocardial infarction: ISIS1. Lancet 1986;2:57-67.[Medline]
13. Khan N, McAlister FA. Re-examining the efficacy of beta-blockers for the treatment of hypertension: a meta-analysis. CMAJ 2006;174:1737-42.[Abstract/Free Full Text]
14. Benetos A, Waeber B, Izzo J, et al. Influence of age, risk factors, and cardiovascular and renal disease on arterial stiffness. Am J Hypertens 2002;15:1101-8.[CrossRef][ISI][Medline]
15. Franklin SS, Gustin W 4th, Wong ND, Larson MG, Weber MA, Kannel WB, et al. Hemodynamic patterns of age-related changes in blood pressure. The Framingham heart study. Circulation 1997;96:308-15.[ISI][Medline]
16. Resnick LM, Lester MH. Differential effects of antihypertensive drug therapy on arterial compliance. Am J Hypertens 2002;15:1096-100.[CrossRef][ISI][Medline]
17. Topol EJ. Arthritis medicines and cardiovascular events—"House of Coxibs". JAMA 2005;293:366-8.[Free Full Text]
18. ALLHAT Officers and Coordinators for the ALLHAT Collaborative Research Group. Major outcomes in high-risk hypertensive patients randomized to angiotensin-converting enzyme inhibitor or calcium channel blocker vs diuretic: the antihypertensive and lipid-lowering treatment to prevent heart attack trial (ALLHAT). JAMA 2002;288:2981-97.[Abstract/Free Full Text]
19. Poldermans D, Boersma E, Bax JJ, Thomson I, van de Ven L, Blankensteijn J, et al. The effect of bisoprolol on perioperative mortality and myocardial infarction in high risk patients undergoing vascular surgery. Dutch echocardiographic cardiac risk evaluation applying stress echocardiography study group. N Engl J Med 1999;341:1789-94.[Abstract/Free Full Text]
20. Poldermans D, Boersma E, Bax JJ, Poldermans D, Boersma E, Bax JJ, et al. Dutch echocardiographic cardiac risk evaluation applying stress echocardiography study group. Bisoprolol reduces cardiac death and myocardial infarction in high risk patients as long as 2 years after successful major vascular surgery. Eur Heart J 2001;22:1353-8.[Abstract/Free Full Text]
21. Dahlof B, Devereux RB, Kjeldsen SE, Devereux RB, Beevers G, de Faire U, et al for the LIFE study group. Cardiovascular morbidity and mortality in the losartan intervention for endpoint reduction in hypertension study (LIFE): a randomized trial against atenolol. Lancet 2002;359:995-1003.[CrossRef][ISI][Medline]
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(Accepted 27 March 2007)

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