From the Guidelines
Beta blockers are generally recommended for Type 1 NSTEMI but should be used with caution in Type 2 NSTEMI, as they may worsen the underlying condition by exacerbating the supply-demand mismatch. For Type 1 NSTEMI (caused by plaque rupture and thrombosis), beta blockers like metoprolol (25-50mg orally twice daily) or carvedilol (3.125-25mg twice daily) should be started within 24 hours of presentation if there are no contraindications, as they reduce myocardial oxygen demand, decrease heart rate and blood pressure, and have been shown to reduce mortality and reinfarction rates 1. The use of beta blockers in Type 1 NSTEMI is supported by evidence from the 2017 AHA/ACC clinical performance and quality measures for adults with ST-elevation and non-ST-elevation myocardial infarction, which recommends oral beta blockers for all patients with MI without contraindications 1.
Some key points to consider when using beta blockers in NSTEMI include:
- Contraindications for beta blocker use, such as heart failure or risk for cardiogenic shock, bradycardia, hypotension, heart block, or active bronchospasm, or acute cocaine ingestion 1
- The potential harm of administering intravenous beta blockers in patients with NSTE-ACS who have risk factors for shock, such as age >70 years, heart rate >110 beats per minute, systolic BP <120 mm Hg, and late presentation 1
- The importance of using beta blockers without intrinsic sympathomimetic activity, and selecting beta-1 blockers such as sustained-release metoprolol succinate, bisoprolol, or carvedilol, which have been shown to have a mortality benefit in patients with heart failure and systolic dysfunction 1
In Type 2 NSTEMI (caused by oxygen supply-demand mismatch without plaque rupture), the primary approach should be treating the underlying cause (anemia, hypotension, tachyarrhythmia, etc.) rather than automatically starting beta blockers. If beta blockers are used in Type 2 NSTEMI, start with lower doses and monitor closely for signs of hemodynamic compromise. The different approach is necessary because the pathophysiology differs significantly between the two types - Type 1 involves actual plaque disruption where reducing cardiac workload is beneficial, while Type 2 often involves conditions where beta blockade might exacerbate the supply-demand mismatch 1.
From the FDA Drug Label
Myocardial Infarction The precise mechanism of action of metoprolol in patients with suspected or definite myocardial infarction is not known.
The FDA drug label does not answer the question.
From the Research
Role of Beta Blockers in NSTEMI
- Beta blockers play a crucial role in the management of Non-ST-Elevation Myocardial Infarction (NSTEMI) by reducing myocardial oxygen demand and improving outcomes 2, 3.
- The use of beta blockers in NSTEMI has been associated with lower in-hospital mortality and improved clinical outcomes in various patient subgroups 2, 3.
NSTEMI Type 1 vs Type 2
- Type 1 NSTEMI is characterized by intracoronary atherothrombosis, while type 2 NSTEMI is caused by a myocardial oxygen supply-demand imbalance unrelated to acute coronary atherothrombosis 4.
- Most NSTEMI cases (65%-90%) are type 1 MI, and patients with type 2 MI often have multiple comorbidities and non-cardiovascular causes of in-hospital mortality 4.
- The distinction between type 1 and type 2 NSTEMI is important for guiding treatment, as the underlying pathophysiology and prognosis differ between the two types 4.
Beta Blocker Therapy in NSTEMI
- Early beta blocker therapy has been shown to improve in-hospital mortality in patients with NSTEMI, with a reduction in odds ratio of 0.43 [0.36-0.51] 3.
- Beta blockers are effective in reducing myocardial oxygen demand and improving outcomes in patients with NSTEMI, and their use is recommended in current guidelines 2, 5, 3.
- The benefits of beta blocker therapy in NSTEMI are thought to be similar to those seen in ST-elevation myocardial infarction (STEMI) patients, with improved outcomes and reduced mortality 3.