The quality of evidence is downgraded by study limitations (unclear allocation concealment and blinding), and by indirectness (differences between the population of interest and those studied).
A Cochrane review [Abstract] 1 included 25 studies with a total of 22 423 subjects (mean age 56.9 years) to assess beta-blockers compared with placebo (21 studies) or no treatment (4 studies) in patients without heart failure and with left ventricular ejection fraction (LVEF) greater than 40% in the non-acute stable phase after myocardial infarction. All studies except 1 included participants younger than 75 years of age. One study included participants with ST-elevation myocardial infarction, and 24 studies included a mixed group of participants with ST-elevation myocardial infarction and non-ST myocardial infarction. Methods used to exclude heart failure were various and were likely insufficient. All patients received usual care; 24 studies were from the pre-reperfusion era (published from 1974 to 1999), and 1 study was from the reperfusion era (published in 2018). Six studies observed participants for up to 12 months, 12 studies observed for 1 to 3 years, and 3 studies observed for 3 years or longer. It was assumed that beta-blockers were administered during these periods.
Beta-blockers reduced the risks of all-cause mortality, cardiovascular mortality, major cardiovascular events (cardiovascular mortality or non-fatal myocardial infarction), and myocardial reinfarction compared to placebo or no intervention, but beta-blockers did not affect the risk of angina pectoris (table T1).
| Outcome | Mean follow-up (range) | Relative effect (CI) | Risk with control | Risk with beta-blockers (CI) | NNTB | Participants (studies) |
|---|---|---|---|---|---|---|
| All-cause mortality | 24.9 months (9 to 60) | RR 0.81,97.5% CI (0.73 to 0.90) | 109 per 1000 | 87 per 1000(81 to 97) | 46 | 22 085 (21) |
| Cardiovascular mortality | 28.8 months (9 to 48 months) | RR 0.73,98% CI (0.61 to 0.88) | 80 per 1000 | 60 per 1000(54 to 68) | 50 | 21 763 (19) |
| Major cardiovascular events* | 26.3 months (9 to 48 months) | RR 0.72,97.5% CI (0.62 to 0.83) | 140 per 1000 | 103 per 1000(97 to 118) | 23 | 14 994 (15) |
| Myocardial infarction | 33.3 months (9 to 48 months) | RR 0.76,98% CI (0.67 to 0.86) | 78 per 1000 | 59 per 1000(54 to 69) | 53 | 19 606 (19) |
| Angina pectoris | 10 months (12 to 47 months) | RR 1.04,98% CI (0.95 to 1.13) | 256 per 1000 | 264 per 1000(238 to 289) | - | 7 715 (5) |
Due to the introduction of reperfusion strategies, and major advancements in medical therapy (antiplatelet therapies, angiotensin-converting enzyme inhibitors/angiotensin-receptor blockers, statins), survival from myocardial infarction has improved. Antiplatelets and statins reduce the risk of reinfarction by reducing atherothrombosis, and ACE inhibitors and ARBs prevent adverse ventricular remodelling and development of severe heart failure. Hence, these therapies, which currently constitute standard care for myocardial infarction, have been shown to have the same positive effects as beta-blockers on pathophysiological consequences following a myocardial infarction. Most of the studies included in this review were conducted between 1974 and 1999 - an era in which the above mentioned therapies were not routinely used. Therefore, the findings of this review may not be compatible with the present management of myocardial infarction in the non-acute phase following acute myocardial infarction.
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