First degree heart block
It may sound contradictory, but being very fit is one of the most common causes of first degree heart block. For example, the condition is widespread among elite long distance runners.
This is because vigorous and prolonged exercise can enlarge the heart muscles, which causes mild disruption to the electrical signals of the heart.
Other causes of first degree heart block include:
- myocarditis – inflammation of the heart muscle
- low levels of potassium in the blood (hypokalaemia)
- low levels of magnesium in the blood (hypomagnesemia)
Certain medications can also cause first degree heart block, including:
- medications for treating abnormal heart rhythms (antiarrhythmics), such as disopyramide
- medications that are used to treat high blood pressure, such as calcium channel blockers
- digoxin – a medication that is used to treat heart failure
Second degree heart block
As with first degree heart block, athletes can develop second degree heart block for the reasons discussed above.
Some children who are born with congenital heart disease (heart defects that are present at birth) can also develop second degree heart block.
Other causes of second degree heart block include:
- damage that develops during a heart attack
- lyme disease – a bacterial infection that is spread by tics
- certain medications, such as calcium-channel blockers (used to treat high blood pressure), amiodarone (used to treat abnormal heart rhythms) and pentamidine (used to treat some types of pneumonia)
Third degree heart block (congenital)
A large proportion of congenital third degree heart block cases develop in mothers who have an autoimmune condition, such as lupus (a long-term condition that causes inflammation in the body's tissues).
An autoimmune condition is where the immune system mistakenly attacks healthy cells and tissue. It is thought that the immune system mistakes the unborn baby for a foreign object (such as a virus) and sends antibodies to attack it. The antibodies damage the heart.
Some children with congenital heart disease are also born with third degree heart block.
Third degree heart block (acquired)
Many cases of third degree heart block are caused by damage to the muscles of the heart. The heart muscle can become damaged for a number of reasons, including:
- as a complication of heart surgery – this is thought to be one of the most common causes
- coronary heart disease – a condition where the heart does not receive enough blood
- as a complication of radiotherapy (a treatment for conditions such as cancer, thyroid disorders and some blood disorders)
- as a result of a serious infection, such as diphtheria (a bacterial infection that can cause inflammation of the heart) or rheumatic fever (a bacterial infection that damages the valves of the heart)
- poorly controlled high blood pressure (hypertension)
- cancer that spread from another part of the body into the heart
- a penetrating trauma to the chest, such as a stab wound or gunshot wound
A number of medications can also cause third degree heart block, including:
- digoxin
- calcium-channel blockers
- beta blockers – used to treat high blood pressure (hypertension)
- tricyclic antidepressants – an older type of antidepressant
- clonidine – used to treat a sudden, sharp rise in blood pressure (hypertensive crisis)
