Heart Block

Heart block is either a blockage or delay in the electrical conduction system of the heart, as the electrical impulses originating in the sinoatrial node, travels down the atrioventricular node to the ventricles, via the bundle of his and its branches.

• Heart block may be asymptomatic or may cause symptoms such as bouts of fainting, dizzy feeling and general fatigue.
• Heart block can be diagnosed by electrocardiography.
• Artificial pacemaker is required in severe cases.

Heart block is more prevalent in the older age group. According to the severity of the block in the electrical conduction system, heart block is classified as first degree, second degree and third degree blocks.

• In first-degree heart block, which often does not show any symptoms, the electrical impulses starting in the sinus are all conducted to the ventricles but they are delayed a bit longer as it passes the atrioventricular node. Certain conditions such as an overactive vagus nerve which slows down the heart rate, structural defects of the heart, sarcoidosis and rheumatic diseases of the heart may cause a first-degree heart block. Even some drugs such as verapamil, amiodarone, digoxin, diltiazem and beta-blockers that slow down the electrical conduction may also induce it. Though common among youngsters, teenagers, and athletes who are well-trained, due to lack of symptoms, a first-degree heart block is usually diagnosed by an electrocardiography only.
• In second-degree heart block, only a few electrical impulses get transmitted to the ventricles due to which heart beat may become either slow or irregular or sometimes both.
• In third-degree heart block, the pumping capacity of the heart is greatly compromised, making it a very dangerous situation. The electrical impulses that originate in the sinus (sinoatrial node) in the atria fail to reach the ventricles. In the absence of stimulation from the atria, substitute pacemakers such as the atrioventricular node or the bundle of His or in certain cases the ventricles themselves take over but they are slower than the sinoatrial node. Moreover, they may be irregular and undependable. This causes the ventricles to contact irregularly as well as extremely slowly, sometimes at a rate as low as 30 – 40 beats per minute resulting in fainting bouts and dizziness. If the ventricular rate is above 40 beats a minute, the symptoms may not be severe and generally fatigue may be the only symptom. But since the output of the heart is greatly reduced, third-degree heart blocks require urgent medical attention.

Treatment of Heart Block

Treatment varies depending on the degree of heart block, the first-degree block not requiring any special treatment even if a heart disorder is causing it. While a second degree block may necessitate the installation of pacemaker in some cases, a third degree block invariably requires an artificial pacemaker in almost all cases. Heart block in people who suffered a heart attack may be temporary in nature, and may resolve on its own and heart rate may return to normal, but usually, artificial pacemakers are implanted for life.

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