Complete heart block – CHB
When electrical signals from the upper chambers of the heart (atria) of the heart fail to reach the lower chambers (ventricles), it is known as complete heart block. The heart has a natural pacemaker known as sinus node or sinoatrial node (SA node). It is located in the upper part of right atrium. It produces regular electrical signals which initiates the heart beats. Signals are conducted to a relay station known as the atrioventricular node (AV node) located at the junction of the upper and lower chambers (AV Junction). A conduction bundle called bundle of His originates from it and travels to the lower chambers (ventricles). It divides into two branches – left and right bundle branches which take the signals to the respective ventricles. They give the signals for the heart to contract in a synchronized fashion. In complete heart block, the signals are blocked either at the AV junction or below it. If the block is above the bundle of His, it is known as supra Hisian complete heart block. If it is below, it is known as infra Hisian complete heart block. Infra Hisian block is more dangerous than supra Hisian block. Supra means above and Infra means below, in medical terminology.
What symptoms occur in CHB?
Heart rate becomes very low in CHB and the person may feel dizzy or even may become unconscious for a short period. Sometimes they can develop life threatening rhythm disorders of the ventricle which can result in cardiac arrest and death.
What causes CHB?
CHB can be occur as birth defect. Then it is called congenital complete heart block. Congenital CHB is associated with connective tissue disease in mother like systemic lupus erythematosus (SLE), also called Lupus. In this condition, antibodies cross over to the baby in the womb and cause damage to the conduction system of the heart.
CHB can occur in association with other birth defects of the heart like ventricular septal defect. Several acquired diseases like heart attack, certain bacterial diseases like Lyme disease, infections involving the aortic valve and degenerative changes in the conduction system can cause CHB. Severe calcification of the aortic valve in aortic stenosis can extend to the nearby conduction system and lead to CHB.
How is CHB recognized?
CHB is usually recognized in the ECG. Electrical activity of the upper chambers will be more frequent than that of the lower chambers. CHB in the baby within the mothers womb is noted by ultrasound study (fetal echocardiography). Contraction of the lower chambers will be slower than that of the upper chambers. Getting an ECG of the baby in the womb (fetus)is near to impossible. A novel investigation for documenting CHB in a fetus is magnetocardiography. But magnetocardiography is available in only few research centres.
What treatment can be offered for complete heart block?
In heart attack, complete heart block may be reversible. Only a temporary artificial pacemaker to support the heart may be needed. If the block is permanent and irreversible, due to other causes, a permanent pacemaker is needed.