Understanding Bradyarrhythmia on ECG

Introduction

Bradyarrhythmia refers to an abnormally slow heart rhythm, typically defined as a heart rate below 60 beats per minute. It can result from issues in the heart's electrical conduction system and is commonly diagnosed using an electrocardiogram (ECG).

Causes of Bradyarrhythmia

Bradyarrhythmia can be caused by:

• Sinus node dysfunction (e.g., sick sinus syndrome)
• Atrioventricular (AV) block (e.g., first, second, or third-degree block)
• Medications (e.g., beta-blockers, calcium channel blockers, digoxin)
• Metabolic disorders (e.g., hypothyroidism, electrolyte imbalances)
• Structural heart disease (e.g., myocardial infarction, cardiomyopathy)

ECG Findings in Bradyarrhythmias

1. Sinus Bradycardia:

• Regular P waves
• Normal PR interval
• Heart rate < 60 bpm

2. Atrioventricular (AV) Blocks:

• First-degree AV block: Prolonged PR (>200ms), all P waves conducted
• Second-degree AV block Type I (Wenckebach/Mobitz I): Progressive PR prolongation until a QRS is dropped
• Second-degree AV block Type II (Mobitz II): Fixed PR interval with occasional non-conducted P waves
• Third-degree (complete) AV block: No association between P waves and QRS complexes

3. Junctional Bradycardia:

• Absent or retrograde P waves
• Narrow QRS complexes

Clinical Significance and Symptoms

• Fatigue, dizziness, syncope (loss of consciousness), and shortness of breath
• Severe cases may require pacemaker implantation if symptomatic or associated with AV block

Treatment Options

Non-Emergent Cases:

• Identifying and stopping offending medications
• Managing underlying conditions (e.g., hypothyroidism)

Emergent Cases:

• Atropine IV for symptomatic bradycardia
• Temporary or permanent pacemaker for severe conduction disturbances

Conclusion

Bradyarrhythmias are often detected through ECG and can be benign or life-threatening. If bradyarrhythmia is symptomatic or due to a severe conduction disorder, medical intervention may be necessary.

Source recommendations

1. American Heart Association Guidelines on Bradyarrhythmia

1. https://www.heart.org/en/health-topics/arrhythmia/about-arrhythmia/bradycardia--slow-heart-rate
2. https://cpr.heart.org/-/media/cpr-files/cpr-guidelines-files/algorithms/algorithmacls_bradycardia_200612.pdf
3. https://www.ahajournals.org/doi/10.1161/CIR.0000000000000628
4. https://cpr.heart.org/en/resuscitation-science/cpr-and-ecc-guidelines/algorithms
5. https://pubmed.ncbi.nlm.nih.gov/30412710/

2. European Society of Cardiology Guidelines on Bradyarrhythmia

1. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines/Cardiac-Pacing-and-Cardiac-Resynchronization-Therapy
2. https://academic.oup.com/eurheartj/article/42/35/3427/6358547
3. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines
4. https://academic.oup.com/eurheartj/article/34/29/2281/401445
5. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines/Ventricular-Arrhythmias-and-the-Prevention-of-Sudden-Cardiac-Death