Heart Block (Atrioventricular Conduction Abnormalities)
What is Heart Block?
Heart block is a disorder of the electrical conduction system of the heart. Based on the severity heart blocks are classified into three:
- 1st degree: There is delayed conduction between the atria and ventricles, but all beats are conducted.
- 2nd degree: Some beats from the atria are not conducted to the ventricles. There are two types of 2nd degree AV block.
- 3rd degree: The heart’s electrical impulse does not pass from the heart’s upper to lower chambers at all. The atria and the ventricles beat completely independently of each other. When this occurs, the heart does not beat correctly and cannot effectively pump blood to the body. Complete heart block is the most serious type of AV heart block and needs urgent treatment.
1. Statistics on Heart Block: Acquired and persistent failure of AV conduction is rare in a healthy adult population. First-degree heart block, though common among elderly patients above 70 years, is usually asymptomatic (without obvious signs or symptoms). Higher degrees can be common, particularly in elderly populations and in association with heart disease like coronary artery disease (CAD), cardiomyopathy and infiltrative heart diseases.
2. Risk Factors for Heart Block: Coronary artery disease is one of the important cause of heart block. It may also be caused by degeneration with fibrosis and calcification of the conducting system (Lev’s and Lenegre’s diseases). Other causative factors include drugs that interfere with conduction, electrolyte disturbances, cardiac surgery, pericarditis, myocarditis, cardiomyopathy and rheumatic heart disease and infections like diphtheria, Lyme disease, etc. Congenital heart block may be present in association with congenital heart disease or in structurally normal heart.
3. Symptoms of Heart Block: First degree blocks are never symptomatic and do not require any treatment. Symptoms of second and third degree heart blocks include awareness of the slow heart beat(palpitation), light-headedness, dizziness, sense of fall or near fall (presyncope) and transient loss of consciousness (syncope). Some patients may complain of easy fatigability, chest pain and shortness of breath, others may develop cardiac arrest leading to death.
4. Clinical Examination: The pulse is generally slow. With second-degree heart block, it may be regular or regularly irregular. With third-degree heart block it is usually slow (<50) and regular.
5. How is Heart Block Diagnosed? : Electrocardiography (ECG) is a cheap and simple test to diagnose electrical conduction disturbances of the heart. Holter test (24hrs ECG monitoring) might be required in patients with intermittent conduction disturbances that are not detected with routine ECG. Electrophysiology study (EPS) might be required when a non-invasive test fail to diagnose the cause of syncope. Blood tests should be used to rule out electrolyte disturbances and to detect systemic diseases that cause conduction disturbances. Thyroid function testing to assess levels of thyroid hormones.
6. Prognosis of Heart Block: This depends on the severity of the dysfunction and the nature of the arrhythmia. For first-degree heart block, the outlook is good as most are never symptomatic and require no treatment.
Most cases of second-degree heart block need no treatment, but it is important to check with a specialist as some may need a pacemaker inserted in case it progresses.
Third-degree heart block can cause cardiac arrest thus it should always be treated with a pacemaker.
7. How is Heart Block Treated? : Treatment depends on the severity of the block, and whether or not symptoms are present. Any underlying cause of the heart block should be treated if possible. Temporary cardiac pacing support is lifesaving for initial stabilization of hemodynamically unstable patients with cardiac conduction disturbances. Drugs that interfere with conduction like beta blockers, calcium channel blockers, digoxin to be discontinued. Permanent pacing is the treatment of choice in those with irreversible causes of cardiac conduction disturbances.
Dr. Pranab Deka | Consultant: Interventional Cardiology | Narayana Superspeciality Hospital, Guwahati