Cardiac pacemakers
Cardiac pacemakersCardiac Pacemakers
The heart is bestowed with a specialized system that automatically generates rhythmic control via the sinus node, located in the superior lateral wall of the right atrium near the opening of the superior vena cava. The specialized pacemaker cells dictate control of the rest of the heart through regular electrical impulses that propagate from the right atria to the lower ventricles. The rapid conduction of these impulses cause the muscle cells of the atria to contract and squeeze blood into the ventricles, which contract and force blood into the aorta and pulmonary arteries. Abnormalities of the heart rhythm, called arrhythmias, can disrupt this normal cardiac control making it necessary to use some artificial means to regulate the rhythm of the heart. Today, some half a million men and women, most of them over the age of sixty, carry implanted cardiac pacemakers that take over the duties of the natural conduction system. Tens of thousands of these devices are implanted each year in this country alone. Over the past thirty years cardiac pacemakers have evolved from simple devices only capable of fixed-rate stimulation of a single chamber of the heart to more sophisticated "implanted computers" that medical personnel can interrogate and reprogram from outside the patient's body. These refinements have allowed for more physiologic pacing with maintenance of atrioventricular synchrony and cardiac output. There are various types of cardiac pacemakers available today that can be surgically implanted to treat specific arryhythmic disorders in the heart.
Abnormal rhythms in the heart are one of the most frequent causes of heart malfunction, and in most cases necessitate some type of cardiac pacing unit. Cardiac arrhythmias are common in the elderly, in whom age-related physiologic changes often alter the conduction system of the heart. Such changes may remain asymptomatic, or they may progress to syncope, or possibly sudden death. In the event of acute myocardial infarction, arrhythmias are no more frequent in the elderly than in younger subjects; in fact, ventricular premature beats are seen less commonly in patients aged seventy years and older. Age is also not a factor in determining the success of resuscitation from cardiac arrest, although it may be a predictor of six-month survival. In general, there is nothing unique about arrhythmias in the elderly. All of the commonly encountered arrhythmias may be seen in older patients. Arrhythmias may occur in otherwise normal hearts, but with increasing age, associated cardiac disease becomes more likely. A possible exception is atrial flutter; in younger patients, its presence almost always indicates a serious cardiac disorder. There are two indications for antiarrhythmic therapy: relief of symptoms and prevention of more malignant arrhythmias. In elderly patients, pacemakers are the preferred treatment for bradyarrhythmias.
Most arrhythmias occur in response to the aging heart. In the sinoatrial node, the number of pacemaker cells decreases, until often less than 10%...
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