Aren’t long-term beta-blockers necessary for some after an MI?

Beta-blocker treatment beyond 1 year after myocardial infarction (IM) for patients without heart failure or left ventricular systolic dysfunction was not associated with better cardiovascular outcomes in a new analysis of a nationwide cohort of over 40,000 patients.

“The results of our study fill an existing gap in the current evidence and provide insight into optimal long-term secondary prevention strategies for a large proportion of MI survivors, namely patients without heart failure or left ventricular systolic dysfunction who may have longer survival compared to those who develop such complications after MI,” say the authors, led by Divan Ishak, MD, Uppsala University, Sweden.

The study was published online In Heart May 2nd.

The researchers explain that clinical outcomes after MI have improved in recent years, in part due to the use of evidence-based therapies, including timely reperfusion and secondary prevention medications. Thus, more patients survive MI without heart failure or left ventricular systolic dysfunction.

Beta-blockers are an established treatment for patients with heart failure and/or left ventricular systolic dysfunction because they reduce morbidity and mortality. For those without heart failure or left ventricular systolic dysfunction, evidence supports the use of beta-blockers in the early phase after MI, but there is uncertainty as to whether they should be continued beyond the first year in the absence of other clinical indications.

In historic randomized trials, long-term beta-blocker therapy has been shown to reduce mortality rates, but these trials were conducted before the introduction of invasive reperfusion strategies and antithrombotic agents into routine care. of myocardial infarction. More recent studies have been limited by inclusion of a subset of patients with MI, relatively small sample size, or short follow-up, the authors note.

Although more comprehensive randomized trials are underway, the benefit of beta-blockers in the chronic phase beyond the first year may remain unknown and the long follow-up required to draw firm conclusions may be difficult to achieve.

The present study therefore aimed to investigate the association between beta-blocker therapy and cardiovascular outcomes beyond the first year after MI in patients without heart failure or left ventricular systolic dysfunction using real data from the SWEDEHEART registry of patients with coronary disease in Sweden.

The study included all 43,618 patients aged 18 or older with MI, including ST-segment elevation (STEMI) and non-STEMI, who had been hospitalized in one of 74 cardiac care units in Sweden. between 2005 and 2016.

Follow-up began 1 year after hospitalization (index date). Patients with heart failure or left ventricular systolic dysfunction up to the index date were excluded. The patients were divided into two groups according to the beta-blocker treatment. The primary endpoint was a composite endpoint of all-cause mortality, MI, unscheduled revascularization, and hospitalization for heart failure.

The results showed that, overall, 78.5% of patients had received a beta-blocker and 21.5% had not taken a beta-blocker at the index date 1 year after MI. The median age was 64 years and 25.5% were women. The median follow-up was 4.5 years.

In the intent-to-treat analysis, the unadjusted primary outcome rate was lower in patients who received a beta-blocker compared to those who did not (3.8 versus 4.9 events/ 100 person-years, relative risk [HR], 0.76; 95% confidence interval [CI]0.73 to 1.04).

However, after inverse propensity score weighting and multivariate adjustment, the risk of the primary outcome was not different by beta-blocker treatment (RR, 0.99; 95% CI, 0.93 to 1.04). These results were consistent across individual secondary endpoints and across patient subgroups.

The authors say this is the largest study to have evaluated beta-blocker therapy in patients without heart failure or left ventricular systolic dysfunction after MI. Although the design is observational, it includes a large sample of patients, has a median follow-up of 4.5 years, and implements causal inference techniques, they state.

They also point out that the results align with those of a recent study meta-analysis contemporary essays on this issue.

They note that the potential mechanism of beta-blockers in improving cardiovascular outcomes after myocardial infarction is attributed to inhibition of sympathetic overdrive, lowering heart rate and thus reducing consumption of myocardial oxygen.

However, routine and timely coronary reperfusion, along with the use of potent antiplatelet therapy, reduces infarct size, minimizing upregulation of sympathetic activity, particularly in people who do not suffer significant myocardial damage.

Additionally, beta-blockers have been linked to several side effects, including depression and fatigue, so determining whether they are indicated beyond the first year after MI may impact patients’ health-related quality of life, the authors suggest.

In a accompanying editorialTom Evans, MD, and Ralph Stewart, MD, Green Lane Cardiovascular Service, Auckland City Hospital, New Zealand, say the present study raises an important question directly related to quality of care: patients with ventricular ejection fraction normal left benefit from long-term beta-blocker treatment after myocardial infarction?

They note that the study had a number of strengths, including a large sample size, a representative study population, detailed information on the risk markers used for the propensity-adjusted analysis, and an unbiased assessment of the results from administrative datasets up to 12 years after the MI index.

But they caution that the unrecognized potential for confounding is a limitation and therefore more evidence from large randomized clinical trials is needed to answer this question.

This work was supported by grants from the Swedish government.

Heart. Published online May 2, 2023. Full Text, Editorial

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