Heart block

A common disorder of the heartbeat caused by an interruption to the passage of impulses through the heart’s conducting system. There are several grades of heart block, from a slight delay between the contractions of the atria (see atrium) and ventricles (called a prolonged P-R interval) to complete heart block, in which the atria and ventricles beat independently. Heart block may be due to coronary artery disease, myocarditis, overdose of a digitalis drug, or rheumatic fever. A prolonged P-R interval causes no symptoms. In more severe heart block, the rate of ventricular contraction does not increase in response to exercise. This may cause breathlessness as a result of heart failure, or chest pains or fainting due to angina pectoris. If the ventricular beat becomes very slow, or if it stops altogether for a few seconds, loss of consciousness and seizure may occur due to insufficient blood reaching the brain. If the delay is prolonged, a stroke may result. Symptomless heart block may not need treatment. Heart block that is causing symptoms is usually treated by the fitting of an artificial pacemaker. Drugs, such as isoprenaline, that increase the heart-rate and the strength of the heart’s contractions, may be given as a temporary measure.


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