What beta blocker to use in Non-ST-Elevation Myocardial Infarction (NSTEMI)?

Beta Blocker Selection in NSTEMI

Oral beta blockers should be initiated within the first 24 hours in NSTEMI patients without contraindications, and the specific agent chosen (metoprolol, atenolol, carvedilol, or bisoprolol) matters less than ensuring appropriate dosing and avoiding intravenous administration in hemodynamically unstable patients. 1

Route of Administration: Oral First-Line

• Oral beta blockers are the preferred initial route for most NSTEMI patients, as they reduce mortality without the increased risk of cardiogenic shock associated with intravenous administration 1
• Intravenous beta blockers may be considered only for specific indications such as hypertension in hemodynamically stable patients, but should be avoided in those with heart failure, low-output state, or increased shock risk 1
• Recent evidence from the GRACE registry showed that early IV beta blocker use was associated with increased in-hospital mortality (adjusted OR 1.41), while oral administration was protective 2

Specific Beta Blocker Agents

The ACC/AHA guidelines do not mandate a specific beta blocker, but provide a table of acceptable agents with their dosing 1:

• Metoprolol (beta-1 selective): 50-200 mg twice daily orally; if IV needed, 5 mg increments over 1-2 minutes up to 15 mg total, then oral 25-50 mg every 6 hours for 48 hours, followed by 100 mg twice daily 1
• Atenolol (beta-1 selective): 50-200 mg daily 1
• Carvedilol (non-selective with alpha blockade): Starting dose 6.25 mg twice daily, titrated to target of 25 mg twice daily over 3-10 days in post-MI patients 3
• Bisoprolol (beta-1 selective): 10 mg daily 1
• Propranolol (non-selective): 20-80 mg twice daily 1

Comparative Evidence

• A head-to-head trial comparing carvedilol versus metoprolol in acute MI patients undergoing PCI found no significant differences in ejection fraction improvement, infarct size reduction, or cardiac biomarker kinetics between the two agents 4
• Both beta-1 selective agents (metoprolol, atenolol, bisoprolol) and non-selective agents with additional properties (carvedilol) are acceptable choices 1

Absolute Contraindications to Beta Blockers

Do not administer beta blockers if any of the following are present 1, 5:

• Signs of heart failure or pulmonary congestion
• Evidence of low-output state
• High risk for cardiogenic shock defined as: age >70 years, systolic BP <120 mmHg, heart rate >110 or <60 bpm, or prolonged time since symptom onset 1
• PR interval >0.24 seconds, second- or third-degree heart block 1
• Active asthma or reactive airway disease 1
• Systolic blood pressure <100 mmHg 1

Clinical Evidence Supporting Beta Blocker Use

• In the CRUSADE registry of 72,054 NSTEMI patients, acute beta blocker therapy was associated with significantly lower in-hospital mortality (adjusted OR 0.66,95% CI 0.60-0.72) 6
• The Global Registry of Acute Coronary Events showed that early oral beta blocker use in NSTEMI reduced hospital mortality (OR 0.58) and 6-month mortality (OR 0.75), with particular benefit in patients with Killip class II/III heart failure (OR 0.39) 7
• However, the ACTION Registry demonstrated that very early emergency department administration increased shock risk compared to treatment later within 24 hours, supporting a measured approach 8

Practical Algorithm for Beta Blocker Initiation

Step 1: Assess for contraindications (heart failure signs, hypotension, bradycardia, heart block, asthma) 1

Step 2: If no contraindications present, initiate oral beta blocker within first 24 hours 1, 5

Step 3: Choose any beta-1 selective agent (metoprolol, atenolol, bisoprolol) or carvedilol based on:

• Metoprolol or atenolol for straightforward cases 1
• Carvedilol if post-MI left ventricular dysfunction is documented (LVEF ≤40%), as it has specific FDA approval and trial data for this indication 3

Step 4: Start with conservative dosing and titrate based on heart rate and blood pressure response 1, 3

Common Pitfalls to Avoid

• Do not use intravenous beta blockers routinely - reserve only for hypertensive patients without shock risk factors, as IV administration increases cardiogenic shock risk 1, 2
• Do not delay oral beta blocker initiation - failure to start within 24 hours is associated with lower rates of subsequent beta blocker therapy and worse outcomes 7, 6
• Do not use immediate-release dihydropyridine calcium channel blockers as alternatives without adequate beta blockade first 1
• Recognize that patients with multiple shock risk factors (elderly, hypotensive, tachycardic) had increased complications with early beta blocker use in the ACTION Registry 8