Types of Bradyarrhythmias

Introduction

Bradyarrhythmias are a group of heart rhythm disorders characterized by a slower than normal heart rate, typically below 60 beats per minute. While mild cases may not cause noticeable symptoms, severe bradyarrhythmias can lead to dizziness, fainting, fatigue, and even life-threatening complications.

Classification of Bradyarrhythmias

Bradyarrhythmias can be classified based on the underlying mechanism and the part of the heart affected:

1. Sinus Node Dysfunction (Sick Sinus Syndrome)

• The sinus node, the heart’s natural pacemaker, fails to generate regular impulses.
• Types include sinus bradycardia, sinus pauses, sinoatrial block, and tachy-brady syndrome (alternating fast and slow rhythms).
• Common causes: aging, ischemic heart disease, infiltrative diseases, and certain medications (e.g., beta-blockers, calcium channel blockers).

2. Atrioventricular (AV) Block

AV block occurs when electrical impulses are delayed or blocked from reaching the ventricles. - First-degree AV block: Prolonged PR interval but all impulses are conducted. - Second-degree AV block: - Mobitz Type I (Wenckebach): Progressive PR interval prolongation before a dropped beat. - Mobitz Type II: Sudden dropped beats without progressive PR prolongation (more serious). - Third-degree (Complete) AV Block: No electrical signals pass from atria to ventricles, leading to a slow escape rhythm.

3. Junctional Bradycardia

• The AV junction can take over as a pacemaker when the sinus node fails, leading to slow heart rates.
• This can be seen in conditions like myocarditis, medication effects, or after heart surgery.

4. Bradyarrhythmias Due to Metabolic or Toxic Causes

• Conditions like hypothyroidism, hyperkalemia, or drug toxicity (e.g., digoxin, beta-blockers) can lead to bradyarrhythmias.
• Addressing the underlying cause is crucial for management.

Symptoms of Bradyarrhythmias

• Fatigue
• Dizziness or lightheadedness
• Fainting (syncope)
• Shortness of breath
• Exercise intolerance

Diagnosis and Management

• ECG (Electrocardiogram): Helps identify rhythm disturbances.
• Holter Monitoring: Useful for intermittent bradyarrhythmias.
• Electrophysiological Studies: Occasionally needed for complex cases.
• Treatment: Depends on the underlying cause (medication withdrawal, pacemaker implantation for severe cases).

Conclusion

Bradyarrhythmias can range from mild sinus bradycardia to life-threatening complete heart block. Identifying the cause and determining whether intervention is necessary is key to effective management.

Source recommendations

1. 2023 ESC Guidelines on Cardiac Pacing and Cardiac Resynchronization Therapy

1. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines/Cardiac-Pacing-and-Cardiac-Resynchronization-Therapy
2. https://www.heartrhythmjournal.com/article/S1547-5271(23)02026-X/fulltext
3. https://academic.oup.com/eurheartj/article/42/35/3427/6358547
4. https://pubmed.ncbi.nlm.nih.gov/34455430/
5. https://academic.oup.com/eurheartj/article/34/29/2281/401445

2. 2024 AHA/ACC/HRS Guidelines for the Evaluation and Management of Bradyarrhythmias

1. https://www.ahajournals.org/doi/10.1161/CIR.0000000000000628
2. https://www.jacc.org/doi/abs/10.1016/j.jacc.2018.10.044
3. https://www.ahajournals.org/doi/10.1161/CIR.0000000000001250
4. https://www.jacc.org/guidelines/bradycardia
5. https://www.heartrhythmjournal.com/article/S1547-5271(18)31127-5/fulltext