Complete Heart Block (CHB) on ECG

Introduction

Complete heart block (CHB), also known as third-degree atrioventricular (AV) block, is a serious cardiac condition in which electrical signals from the atria do not reach the ventricles. This results in independent atrial and ventricular electrical activity, leading to slow heart rates and potential circulation problems.

ECG Features of CHB

Identifying CHB on an electrocardiogram (ECG) involves recognizing the following characteristics: - P waves and QRS complexes are independent: Electrical impulses from the atria (P waves) do not conduct to the ventricles. - Regular P-P intervals and R-R intervals: The atrial and ventricular rhythms are both regular, but they are not synchronized. - Bradycardia (slow heart rate): The ventricular rate is typically much slower than the atrial rate. - Wide or narrow QRS complexes: If the block occurs above the His bundle, QRS complexes tend to be narrow; if the block is lower, the QRS can be wide due to ventricular pacing.

Causes of Complete Heart Block

CHB can result from various conditions, including: - Ischemic heart disease (e.g., heart attack affecting the conduction system) - Age-related degeneration of the conduction system - Congenital heart diseases - Medications (e.g., beta-blockers, calcium channel blockers, digoxin toxicity) - Electrolyte imbalances and myocarditis

Symptoms and Clinical Presentation

A patient with CHB may experience: - Fatigue and dizziness due to inadequate cardiac output - Fainting (syncope), which can be dangerous - Shortness of breath - Chest discomfort in cases related to ischemia - Palpitations or irregular heartbeat sensations

Management of CHB

Immediate Management:

• Emergent temporary pacemaker placement if the patient is hemodynamically unstable.
• Atropine may be attempted, but it is usually ineffective in CHB.

Long-term Management:

• Permanent pacemaker implantation is usually necessary to restore reliable ventricular conduction and prevent complications like sudden cardiac arrest.
• Managing underlying causes, such as stopping medications that contribute to the block.

Conclusion

Complete heart block is a critical condition that requires prompt diagnosis and management. ECG interpretation plays a vital role in recognizing CHB, and timely pacemaker placement can significantly improve patient outcomes.

Source recommendations

1. American Heart Association Guidelines on Bradycardia and Conduction Disorders

1. https://www.heart.org/en/health-topics/arrhythmia/about-arrhythmia/conduction-disorders
2. https://www.ahajournals.org/doi/10.1161/CIR.0000000000000628
3. https://www.heart.org/en/health-topics/arrhythmia/about-arrhythmia
4. https://www.ahajournals.org/doi/10.1161/CIR.0000000000000627
5. https://pubmed.ncbi.nlm.nih.gov/30412709/

2. European Society of Cardiology Guidelines on Cardiac Pacing and Resynchronization Therapy

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://pubmed.ncbi.nlm.nih.gov/34455430/
4. https://academic.oup.com/eurheartj/article/34/29/2281/401445
5. https://pubmed.ncbi.nlm.nih.gov/23801827/