The commonest cause of arrhythmias is an acute myocardial infarction. The arrhythmias usually occur in the first few hours after the onset of symptoms and settle rapidly. Arrhythmias may also occur in chronic ischaemia.
Conduction disturbances are also a common sequelae to MIs. Anterior MIs are associated with development of AV blocks that result in right or left bundle branch blocks. The intraventricular conduction disturbance often persists after the AV block has resolved. AV blocks that occur in the context of inferior MIs tend to have a benign course.
Other causes of arrhythmias and conduction disturbances include: drugs, myocarditis, thyroid disease, electrolyte imbalance, cardiomyopathy, cardiac dilatation, specific heart muscle disease.
Re-entrant supraventricular tachycardias and pre-excitation syndromes are the result of congenital aberrant conduction pathways.
Note that right bundle branch block may be a normal finding in young people. Left bundle branch block is almost always of pathological significance.
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