From the Guidelines
Bradycardia is caused by several factors that slow the heart rate below 60 beats per minute, including certain medications, medical conditions affecting the heart's electrical system, hypothyroidism, electrolyte imbalances, and increased vagal tone. The causes of bradycardia can be categorized into several groups:
- Medications: certain medications like beta-blockers (metoprolol, propranolol), calcium channel blockers (diltiazem, verapamil), and digoxin, which are prescribed for heart conditions but can excessively slow heart rate 1.
- Medical conditions: conditions that affect the heart's electrical system, such as sick sinus syndrome, heart block, and damage from heart disease or heart attack 1.
- Hypothyroidism: slows metabolism and heart rate 1.
- Electrolyte imbalances: particularly high potassium levels, disrupt normal cardiac conduction 1.
- Increased vagal tone: from activities like meditation or vomiting can temporarily slow the heart 1.
- Severe infections: particularly sepsis, may cause bradycardia in advanced stages 1. Treatment depends on the underlying cause and whether symptoms like dizziness, fatigue, or fainting are present, ranging from medication adjustments to pacemaker implantation for severe cases 1. Some key recommendations for managing bradycardia include:
- Identifying and treating reversible causes, such as medication side effects or hypothyroidism 1.
- Using temporary transvenous pacing if necessary, before determining the need for permanent pacing 1.
- Considering pacemaker implantation for severe cases, such as those with symptomatic second-degree or third-degree atrioventricular block 1.
From the FDA Drug Label
Bradycardia, including sinus pause, heart block, and cardiac arrest have occurred with the use of metoprolol. Patients with first-degree atrioventricular block, sinus node dysfunction, or conduction disorders may be at increased risk. The cause of bradycardia in patients taking metoprolol may be related to the use of the medication itself, particularly in those with pre-existing conduction disorders or sinus node dysfunction.
- Key factors that may contribute to bradycardia in these patients include:
- First-degree atrioventricular block
- Sinus node dysfunction
- Conduction disorders 2
From the Research
Causes of Bradycardia
- Intrinsic cardiac disorders, such as sick sinus syndrome or inferior myocardial infarction 3
- Metabolic and environmental causes, including hypothyroidism and electrolyte disorders 3
- Medications, such as beta-blockers and amiodarone 3, 4
- Infection, including myocarditis 3
- Increased intracranial pressure 3
- Toxic exposure 3
- Renal failure, which can cause accumulation of potassium and beta blockers, leading to bradycardia and hypotension 4
- Hyperkalemia, which can contribute to bradycardia in combination with other factors such as renal failure and beta blocker use 4
- Complete heart block, which can cause altered mental status and require treatment with pacing devices 5
Reversible Causes of Bradycardia
- Electrolyte abnormalities, which can be treated by correcting the underlying imbalance 6, 3
- Hyperthyroidism, which can be treated with medication or other therapies 6, 3
- Stimulant drug use, which can be treated by discontinuing the offending drug 6
- Bradycardia-causing drugs, which can be treated by discontinuing the drug if possible 6
Treatment of Bradycardia
- Atropine, which can be used to increase heart rate in unstable patients 6, 7
- Pacing devices, which can be used to treat bradycardia in patients who are unresponsive to medical therapy 5, 7
- Beta blockers, which can be used to treat symptomatic premature atrial contractions (PACs) and premature ventricular contractions (PVCs) 6
- Nondihydropyridine calcium channel blockers, which can be used to treat PVCs 6
- Antiarrhythmics, which can be used to treat PVCs and other arrhythmias 6, 7