From the Guidelines
Bradycardia can be caused by various medical conditions, including sinus node dysfunction, atrioventricular block, and certain medications, and the most effective treatment approach is to address the underlying cause, as recommended by the 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay 1.
Medical Causes of Bradycardia
The medical causes of bradycardia can be categorized into several groups, including:
- Sinus node dysfunction, which can be caused by aging, heart disease, or scarring
- Atrioventricular block, which disrupts electrical signal transmission between the atria and ventricles
- Certain medications, such as beta-blockers (metoprolol, propranolol), calcium channel blockers (diltiazem, verapamil), and antiarrhythmic drugs (amiodarone, digoxin)
- Hypothyroidism, which slows metabolism and heart rate
- Electrolyte imbalances, particularly hyperkalemia (high potassium) and hypocalcemia (low calcium), which can impair cardiac conduction
- Sleep apnea, increased intracranial pressure, and vasovagal responses, which can trigger bradycardia
- Infectious diseases, such as Lyme disease and endocarditis, which can affect the heart's electrical system
Treatment Approach
The treatment approach for bradycardia depends on the underlying cause and symptom severity, ranging from medication adjustments to pacemaker implantation in severe cases. According to the 2018 ACC/AHA/HRS guideline, patients presenting with symptomatic sinus node dysfunction secondary to a reversible cause should first be managed by directing therapy at eliminating or mitigating the offending condition 1. This may involve discontinuing or reducing the dosage of offending medications, treating underlying medical conditions, or addressing physiological disturbances. In some cases, medications such as theophylline or aminophylline may be used to increase heart rate and improve symptoms 1.
From the FDA Drug Label
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)] Digoxin produces PR prolongation and ST segment depression which should not by themselves be considered digoxin toxicity. Cardiac toxicity can also occur at therapeutic doses in patients who have conditions which may alter their sensitivity to digoxin Disopyramide is a Type I antiarrhythmic drug with potent negative inotropic and chronotropic effects. Disopyramide has been associated with severe bradycardia, asystole and heart failure when administered with beta-blockers. Both digitalis glycosides and beta-blockers slow atrioventricular conduction and decrease heart rate. Concomitant use can increase the risk of bradycardia Clinically significant bradycardia has been reported in breastfed infants.
Medical causes of bradycardia include:
- Digoxin toxicity: can cause symptomatic bradyarrhythmia or heart block 2
- Concomitant use of digitalis glycosides and beta-blockers: can increase the risk of bradycardia 2 3
- Disopyramide: can cause severe bradycardia, asystole, and heart failure when administered with beta-blockers 3
- Beta-blocker therapy: can cause bradycardia, especially in breastfed infants 3
From the Research
Medical Causes of Bradycardia
The medical causes of bradycardia can be attributed to various factors, including:
- Pathology within the sinus node, atrioventricular (AV) nodal tissue, and the specialized His-Purkinje conduction system 4
- Intrinsic causes such as degenerative fibrosis, ion channel dysfunction, and remodeling of the sinoatrial node, which can lead to sick sinus syndrome 5
- Extrinsic factors, including pharmacologic, metabolic, or autonomic factors, which can exacerbate or mimic sick sinus syndrome 5
- Beta blockade, which can increase the corrected sinus node recovery time in patients with sick sinus syndrome and intrinsic slow heart rate 6
- Autonomic nervous system blockade, which can affect the sinus node function and recovery time 6
Specific Conditions
Certain conditions can also contribute to bradycardia, such as:
- Sick sinus syndrome, which refers to a collection of disorders marked by the heart's inability to perform its pacemaking function 5
- Carotid sinus syncope, which can cause bradycardia and syncope 6
- Tachy-brady syndrome, which is characterized by alternating bradycardia and tachycardia 5
Diagnosis and Treatment
Diagnosis of bradycardia and underlying conditions can be challenging, but can be made through electrocardiographic identification of the arrhythmia in conjunction with the presence of symptoms 5. Treatment may include removing extrinsic factors, pacemaker placement, and other management strategies to alleviate symptoms and improve quality of life 4, 5