In a patient with Acute Coronary Syndrome (ACS) and unknown left ventricular ejection fraction (LVEF), which is safer for PRN hypertension management, labetalol or hydralazine, and should metoprolol be initiated prior to catheterization?

Beta-Blocker Management in ACS with Unknown Ejection Fraction

Start oral metoprolol now at a low dose (25 mg twice daily) and use labetalol for PRN hypertension control in this ACS patient with unknown ejection fraction. 1

Immediate Beta-Blocker Initiation

Early oral beta-blocker therapy (within 24 hours) is strongly recommended for ACS patients without contraindications to reduce reinfarction and ventricular arrhythmias. 1 The 2025 ACC/AHA guidelines emphasize that low-dose oral beta blockers should be initiated early after ACS diagnosis with slow dose escalation as blood pressure and heart rate permit. 1

Metoprolol Dosing Strategy

• Start with metoprolol tartrate 25 mg orally every 6 hours (or 50 mg twice daily if hemodynamically stable) 2
• Avoid high initial doses—the COMMIT trial showed that early high-dose metoprolol (up to 15 mg IV then 200 mg daily) increased cardiogenic shock risk, particularly in the first 24 hours 1
• Metoprolol succinate 50 mg once daily is an alternative starting dose with better evidence for mortality reduction in heart failure 1
• Titrate upward gradually based on heart rate, blood pressure, and clinical response 2

Critical Contraindications to Monitor

Do not give beta blockers if the patient has: 1, 2

• Acute heart failure (Killip class II-IV)
• Evidence of low cardiac output or cardiogenic shock risk (age >70 years, heart rate >110 bpm, systolic BP <120 mmHg)
• Severe bradycardia or heart block (PR interval >0.24 seconds, second- or third-degree block without pacemaker)
• Active bronchospasm

Reassess after 24 hours if initial contraindications exist. 1

PRN Hypertension Management: Labetalol vs Hydralazine

Labetalol is the safer choice for PRN hypertension in ACS with unknown ejection fraction. 1

Why Labetalol is Preferred

• Labetalol provides combined alpha- and beta-blockade (7:1 beta:alpha ratio) with minimal effects on cardiac output 3, 4
• Reduces blood pressure without reflex tachycardia, which is beneficial in ACS 3, 4
• Dosing: 200-800 mg orally twice daily for chronic use; can be given IV for acute control 1
• Does not increase myocardial oxygen demand 4

Why Hydralazine Should Be Avoided

Hydralazine causes reflex tachycardia and increased myocardial oxygen demand—both harmful in ACS. 1 The ACC/AHA hypertension guidelines explicitly state that hydralazine is "associated with sodium and water retention and reflex tachycardia; use with a diuretic and beta blocker." 1 In ACS, increasing heart rate and contractility worsens myocardial ischemia.

Unknown Ejection Fraction Considerations

The unknown LVEF status makes beta-blocker initiation even more important, as you may be treating undiagnosed reduced ejection fraction. 5, 6

• Recent registry data (2025) shows beta blockers reduce 1-year mortality primarily in patients with LVEF ≤40% (5.9% vs 14% mortality with vs without beta blockers), with minimal benefit in preserved EF 5
• However, 84.5% of ACS patients with LVEF ≤40% receive beta blockers at discharge in contemporary practice 5
• Lower in-hospital LVEF is strongly associated with increased 1-year mortality (HR 1.26 per 5% LVEF reduction) 6
• Beta blockers should be continued for at least 3 years in all ACS patients with normal LV function 1

Pre-Catheterization Algorithm

Before catheterization tomorrow:

1. Initiate metoprolol tartrate 25 mg PO every 6 hours (or 50 mg twice daily if BP and HR stable) 2
2. Monitor for signs of heart failure or cardiogenic shock (rales, hypotension, tachycardia) 1, 2
3. Use labetalol 200-400 mg PO for PRN hypertension (avoid hydralazine) 1
4. Target heart rate 50-60 bpm and systolic BP 110-140 mmHg 1
5. Obtain echocardiogram urgently if not already done to guide further beta-blocker dosing 6

Post-Catheterization Management

• If LVEF <40% is discovered: continue beta blocker indefinitely (use carvedilol, metoprolol succinate, or bisoprolol for mortality benefit) 1
• If LVEF >40%: continue beta blocker for minimum 3 years 1
• Add ACE inhibitor if LVEF <40%, hypertension, diabetes, or chronic kidney disease 1

Common Pitfalls

• Avoid IV beta blockers in the acute setting—oral administration is safer and equally effective 1
• Do not use high initial doses—start low and titrate up 2
• Never abruptly discontinue beta blockers in coronary artery disease patients—risk of rebound ischemia, MI, and arrhythmias 2
• Hydralazine monotherapy worsens ACS outcomes through reflex tachycardia 1