Causes of abnormal heart rates. An abnormal heartbeat pattern is called an arrhythmia, and it happens because there is an issue with the path of the heart’s electrical impulses. An understanding of the underlying cause of such arrhythmia is imperative for making the choice to treat it with a pacemaker. Damage resulting from a previous heart attack, coronary artery disease, congenital heart defects, neurocardiogenic syncope, cardiomyopathies, the use of certain medications, and aging of the heart muscle are all potential causes of an irregular heartbeat from electrical impulse interruption. A pacemaker is not always the best solution to all of these underlying causes of arrhythmias. However, it can be the most effective treatment under certain circumstances.