What medications are used to manage abnormal heart rates, such as tachycardia and bradycardia?

Medications for Heart Rate Management

Primary Agents for Tachycardia (Heart Rate >100 bpm)

For acute rate control in supraventricular tachycardias including atrial fibrillation and atrial flutter, beta-blockers (metoprolol, esmolol) and calcium channel blockers (diltiazem) are first-line agents, while for ventricular tachycardia, amiodarone or procainamide should be used instead of beta-blockers. 1, 2

Beta-Blockers for Tachycardia

Metoprolol is highly effective for supraventricular arrhythmias:

• IV dosing: 5 mg slow IV bolus over 1-2 minutes, repeat every 5 minutes up to maximum 15 mg total 1, 3
• Indications: Stable narrow-complex tachycardias unresponsive to adenosine, atrial fibrillation/flutter rate control, certain polymorphic VT with acute ischemia 1
• Efficacy: Achieves heart rate <100 bpm in 46-81% of patients with supraventricular tachyarrhythmias, with mean rate reduction from 134 to 106 bpm within 10 minutes 4, 5
• Oral dosing: 25-100 mg twice daily (tartrate) or 50-400 mg once daily (succinate) for chronic rate control 1

Esmolol offers ultra-short action (2-9 minute half-life):

• Loading dose: 500 mcg/kg (0.5 mg/kg) over 1 minute 1
• Maintenance: 50 mcg/kg/min, titrate up to 300 mcg/kg/min as needed 1
• Advantage: Rapid reversibility if hypotension or bradycardia develops 1

Atenolol for less urgent situations:

• Dosing: 5 mg IV over 5 minutes, repeat once in 10 minutes if needed 1

Propranolol (nonselective):

• Dosing: 0.5-1 mg over 1 minute, up to 0.1 mg/kg total 1

Calcium Channel Blockers for Tachycardia

Diltiazem is superior to metoprolol for rapid rate control in atrial fibrillation:

• Efficacy: 95.8% achieve heart rate <100 bpm by 30 minutes vs. 46.4% with metoprolol, with 50% achieving target in first 5 minutes vs. 10.7% with metoprolol 6
• Dosing: Start 0.25 mg/kg IV bolus, then 5-15 mg/hour continuous infusion 1
• Safety: No increased hypotension or bradycardia compared to metoprolol 6

Verapamil is an alternative:

• Dosing: Similar to diltiazem for rate control 1
• Critical warning: Never use in wide-complex tachycardias (may be ventricular tachycardia) 2

Antiarrhythmic Agents for Tachycardia

Amiodarone (multichannel blocker):

• Indications: Stable irregular narrow-complex tachycardia, pre-excited atrial arrhythmias, hemodynamically stable monomorphic VT, polymorphic VT with normal QT 1
• Dosing: 150 mg IV over 10 minutes, repeat if needed, then 1 mg/min × 6 hours, then 0.5 mg/min (max 2.2 g/24 hours) 1
• Side effects: Bradycardia, hypotension, phlebitis 1

Procainamide (sodium/potassium channel blocker):

• Indications: Pre-excited atrial fibrillation, hemodynamically stable monomorphic VT 1
• Dosing: 20-50 mg/min until arrhythmia suppressed, hypotension occurs, QRS widens 50%, or 17 mg/kg total given 1
• Contraindications: QT prolongation, heart failure 1

Adenosine for narrow-complex regular tachycardias:

• Dosing: 6 mg rapid IV push, then 12 mg if needed 1
• Mechanism: Transiently blocks AV node to terminate reentrant SVT 1

Digoxin (less useful acutely):

• Dosing: 8-12 mcg/kg total loading dose, half initially over 5 minutes, remainder in 25% fractions at 4-8 hour intervals 1
• Limitation: Slow onset renders it less useful for acute arrhythmias 1

Critical Contraindications for Beta-Blockers and Calcium Channel Blockers

Absolute contraindications:

• Decompensated heart failure or signs of low output state 1, 3
• Second or third-degree AV block without pacemaker 1
• Active asthma or severe reactive airway disease 1
• Systolic BP <100-120 mmHg (depending on clinical context) 1, 3
• Pre-excited atrial fibrillation (WPW syndrome) - these agents can accelerate ventricular rate and cause ventricular fibrillation 1, 3

Relative contraindications:

• Heart rate <60 bpm or >110 bpm in acute MI setting 1, 3
• PR interval >0.24 seconds 1
• Age >70 years with multiple risk factors in acute MI 3

Target Heart Rates for Rate Control

Atrial fibrillation/flutter:

• Resting: 60-80 bpm (strict control) or <110 bpm (lenient control) 1, 3
• Moderate exercise: 90-115 bpm 1

General tachycardia: Target <100 bpm, though symptoms unlikely to be primarily from tachycardia if rate <150 bpm unless impaired ventricular function present 1

Primary Agents for Bradycardia (Heart Rate <60 bpm with symptoms)

For symptomatic bradycardia, atropine is first-line pharmacologic therapy, followed by transcutaneous pacing if atropine fails, with transvenous pacing for definitive management. 1

Atropine (First-Line)

• Dosing: 0.5-1 mg IV every 3-5 minutes, maximum 3 mg total 1, 7
• Mechanism: Blocks vagal effects on SA and AV nodes 1
• Efficacy: Rapidly effective for bradycardia due to excessive vagal tone or AV block 1

Transcutaneous Pacing (TCP)

• Indication: Unstable patients not responding to atropine 1
• Limitation: Painful in conscious patients, may not achieve consistent capture 1
• Bridge: Prepare for transvenous pacing while using TCP 1

Chronotropic Infusions (if atropine/pacing unavailable)

Dopamine:

• Dosing: 2-10 mcg/kg/min infusion, titrate to effect 1

Epinephrine:

• Dosing: 2-10 mcg/min infusion, titrate to effect 1

Isoproterenol (use cautiously):

• Indication: Bradycardia refractory to atropine, particularly in heart transplant patients 7
• Caution: May worsen ischemia in coronary disease 7

Calcium for Beta-Blocker/Calcium Channel Blocker Overdose

For bradycardia and hypotension from beta-blocker or calcium channel blocker toxicity:

• Dosing: 1 g calcium chloride or 3 g calcium gluconate IV over 5 minutes, repeat every 10-20 minutes as needed 7
• Alternative: Continuous infusion 2 g/hour for up to 24 hours 7
• Effectiveness: Inconsistent but may make bradycardia more responsive to atropine 7
• Monitoring: Watch for hypercalcemia 7

Common Pitfalls and Critical Warnings

Tachycardia Management Pitfalls

1. Never give AV nodal blockers (beta-blockers, calcium channel blockers, digoxin, adenosine) in pre-excited atrial fibrillation (WPW) - can cause ventricular fibrillation by facilitating accessory pathway conduction 1, 3

2. Never assume wide-complex tachycardia is SVT with aberrancy - most are ventricular in origin; avoid metoprolol IV and use amiodarone or procainamide instead 1, 2

3. Never give full 15 mg metoprolol as single rapid bolus - significantly increases hypotension/bradycardia risk; give 5 mg increments over 1-2 minutes 3

4. Avoid IV metoprolol in acute MI with signs of heart failure - COMMIT trial showed 30% increased cardiogenic shock risk, particularly in patients >70 years, SBP <120 mmHg, HR >110 or <60 bpm 3

5. Combinations of rate-controlling agents increase bradycardia risk - particularly beta-blockers with digoxin, diltiazem, verapamil, or amiodarone 1

Bradycardia Management Pitfalls

1. Never abruptly discontinue beta-blockers - causes 2.7-fold increased 1-year mortality, severe angina exacerbation, MI, and ventricular arrhythmias with 50% mortality in one study 3

2. Reduce dose by 50% rather than stopping completely for symptomatic bradycardia on beta-blockers, unless severe hypotension with hypoperfusion present 3

3. Rule out secondary causes before treating bradycardia - infection, hypothyroidism, increased intracranial pressure, drug interactions 3

4. Transcutaneous pacing is temporizing only - arrange for transvenous pacing in refractory cases 1