From the Guidelines
Bradycardia is most commonly caused by factors such as certain medications, underlying heart conditions, hypothyroidism, electrolyte imbalances, sleep apnea, increased vagal tone, hypothermia, and severe infections, as outlined in the 2019 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay 1.
Causes of Bradycardia
The causes of bradycardia can be diverse and multifactorial. Some of the key causes include:
- Certain medications like beta-blockers (metoprolol, propranolol), calcium channel blockers (diltiazem, verapamil), and digoxin, which can intentionally slow heart rate 1
- Underlying heart conditions such as sick sinus syndrome, heart block, or damage from heart attacks that can disrupt normal electrical conduction
- Hypothyroidism, which reduces metabolic rate and slows heart function
- Electrolyte imbalances, particularly high potassium or low sodium, that can interfere with cardiac electrical activity
- Sleep apnea, increased vagal tone (often in athletes), hypothermia, and severe infections that can trigger bradycardia
Importance of History and Physical Examination
A thorough history and physical examination are essential in identifying the underlying cause of bradycardia, as emphasized in the 2019 ACC/AHA/HRS guideline 1. This includes outlining the frequency, timing, duration, severity, longevity, circumstances, triggers, and alleviating factors of symptoms suspicious for bradycardia or conduction disorders. A comprehensive review of prescription and over-the-counter medications is also crucial, as some medications can elicit or exacerbate bradyarrhythmias.
Management of Bradycardia
Management of bradycardia depends on identifying the underlying cause, which may involve medication adjustment, thyroid hormone replacement, electrolyte correction, or in severe cases, pacemaker implantation. Symptomatic bradycardia (causing dizziness, fatigue, or syncope) requires prompt medical evaluation. It is essential to prioritize the identification and treatment of the underlying cause of bradycardia to improve morbidity, mortality, and quality of life outcomes 1.
From the FDA Drug Label
Because digoxin slows sinoatrial and AV conduction, the drug commonly prolongs the PR interval. The drug may cause severe sinus bradycardia or sinoatrial block in patients with pre-existing sinus node disease and may cause advanced or complete heart block in patients with pre-existing incomplete AV block If the rhythm disturbance is a symptomatic bradyarrhythmia or heart block, consideration should be given to the reversal of toxicity with DIGIBIND® [Digoxin Immune Fab (Ovine)] High doses of digoxin may produce a variety of rhythm disturbances, such as first-degree, second-degree (Wenckebach), or third-degree heart block (including asystole); atrial tachycardia with block; AV dissociation; accelerated junctional (nodal) rhythm; unifocal or multiform ventricular premature contractions (especially bigeminy or trigeminy); ventricular tachycardia; and ventricular fibrillation. In children, the use of digoxin may produce any arrhythmia The most common are conduction disturbances or supraventricular tachyarrhythmias, such as atrial tachycardia (with or without block) and junctional (nodal) tachycardia. Ventricular arrhythmias are less common. Sinus bradycardia may be a sign of impending digoxin intoxication, especially in infants, even in the absence of first-degree heart block
The causes of bradycardia include:
- Pre-existing sinus node disease
- Pre-existing incomplete AV block
- High doses of digoxin
- Digoxin toxicity
- Conduction disturbances 2, 2, 2
From the Research
Causes of Bradycardia
- Bradycardia can be caused by various factors, including the use of certain medications such as beta-blockers and calcium-channel blockers 3, 4, 5, 6, 7
- Beta-blocker and calcium-channel blocker overdoses are associated with severe morbidity and mortality, and can cause bradycardia and hypotension 4
- The use of calcium-channel blockers, particularly non-dihydropyridine calcium channel blockers, can be associated with a lower risk of bradycardia during sinus rhythm compared to beta-blockers 5
- However, the combination of non-dihydropyridine calcium channel blockers and beta-blockers can lead to severe bradycardia due to their synergistic negative chronotropic action 7
- Other factors, such as hypocalcemia or excess calcium-channel blockers, can also contribute to the development of bradycardia 3