医学精品资料：03&04.ARTIFICIALCARDIACPACEMAKERS.doc

1、ARTIFICIAL CARDIAC PACEMAKERS It has been well documented that artificial (electronic) cardiac pacing is one of the most important and reliable ways to manage various cardiac arrhythmias, particularly bradyarrhythmias. Until several years ago , the primary indication of permanent artificial pacing h

2、ad been for the treatment of complete atrioventricular (AV) block. However, the most common indication of permanent artificial pacemakers, at present, is in the treatment of sick sinus syndrome (SSS). In addition, artificial pacing with overdriving (faster than usual)pacing rate is often a life-savi

3、ng measure for refractory tachyarrhythmias . The term bradytachyarrhythmia syndrome (BTS) is used when the abnormal heart rhythms consist of a component of rapid rhythms as well as a slow rhythm. In this case, artificial cardiac pacing has a very important role because drug therapy alone is usually

4、ineffective. BTS is usually a late manifestation of SSS. The artificial (electronic) cardiac pacemaker functions in a manner very similar to the natural pacemaker in initiating the electrical impulses generated by small batteries . These impulses travel through small wires to the heart. The artifici

5、al pacemaker is timed to produce the impulses (usually about 70-72bpm) just like the cardiac impulses initiated by the natural pacemaker (the sinus node). In most cases, the heart is capable of pumping adequate amounts of blood under the control of an artificial pacemaker. Approximately 250,000 peop

6、le (500,000 according to some reports ) live with artificial cardiac pacemakers in the United States alone, and 25,000 to 40,000 (100,000 to 110,000 according to some medical reports) new patients will require an artificial pacemaker implantation annually. Although it is difficult to know exactly ho

7、w many people live with artificial pacemakers at the present time worldwide, it is estimated to be at least 500,000 people (750,000 to 1,000,000 people according to some reports). The total number of artificial pacemakers sold within the last 20 years is estimated to be approximately 1.5 to 2 millio

8、n and possibly more. It is clearly evident that artificial cardiac pacing can provide not only a prolongation of human lives, but also a significant improvement in the quality of human lives. Long-term administration of various drugs (e.g. isoproterenol, atropine, epinephrine) for bradyarrhythmias i

9、s no longer necessary because of a ready availability of artificial pacemakers in most civilized countries. The fundamental principles for the use of an artificial pacemaker were established as early as 1932 by Hyman, and later by Callaghan and Bigelow in 1951. External cardiac pacing was introduced

10、 into clinical medicine in 1952 by Zoll. In 1957, temporary direct myocardial stimulation in the treatment of complete AV block was introduced by Weirich et al , and a transistorized self-contained implantable pacemaker for long-term correction of chronic complete AV block was established in 1960 by

11、 Chardack et al . Until several years ago, mercury zinc cells had been used for the energy source, but today a lithium battery has replaced the mercury zinc battery lithium battery entirely for all types of artificial pacemaker. In general, a lithium battery may last 10 to 12 years in most clinical

12、circumstances. It is interesting to note that the earlier pacemakers lasted only 15 to 18 months, and therefore frequent replacement of the pulse generator was required at that time . The nuclear-powered pacemaker was introduced about 10 to 15 years ago in clinical medicine, but it is not commonly u

13、sed. There are many types of artificial pacemakers in the market, but the most commonly used model is a demand ventricular pacemaker. The demand pacemaker has a sensing device that cuts the pacemaker off if the natural heart rhythm is faster than the preset pacing rate. When the patients own heart r

14、hythm becomes slower than the preset pacing rate, the sensing device turns the artificial pacemaker on again. This is the reason the term demand or standby pacemaker issued. In other words, the demand artificial pacemaker works only when it is needed. In the past few years, multiprogrammable pacemak

15、ers have been introduced in clinical medicine. In this new type of artificial pacemaker, various functions of the pacemaker (e.g. pacing rate, energy output, and sensitivity) can easily be controlled and adjusted noninvasively (without surgery) after implantation in order to provide the best pacing

16、for a agiven patient. I predict that the multiprogrammble pacemakers will eventually replace all nonprogrammable pacemakers in the near future . The average cost of the artificial pacemaker itself ranges from 2000 to 3000 dollars. The total cost for the implantation of an artificial pacemaker, inclu

17、ding the surgeons fee, hospitalization, and various laboratory tests is about 6000 to 7000 dollars in most hospitals. Following implantation of an artificial pacemaker, every patient should have periodic medical checkups and should carry out necessary daily care because the artificial pace-maker nee

18、ds care like any other mechanical device, and complications or malfunctions may occasionally occur.Supplementary reading of artificial cardiac pacemaker The sick sinus syndrome refers to a combination of symptoms(dizziness, confusion, fatigue, syncope, and congestive heart failure) caused by sinus n

19、ode dysfunction and manifested by marked sinus bradycardia, sinoatrial block, or sinus arrest. Because these symptoms are nonspecific, and because ECG manifestations of sinus node dysfunction are not infrequently intermittent, it may be difficult to prove that such symptoms are actually caused by si

20、nus node dysfunction. Atrial tachyarrhythmias such as atrial fibrillation, atrial flutter , or atrial tachycardia may be accompanied by sinus node dysfunction. The bradycardia-tachycardia syndrome refers to paroxysmal atrial arrhythmia which upon termination is followed by prolonged sinus pauses or in which there are alternating periods of tachyarrhythmia and bradyarrhythmia. Syncope or presyncope may result from failure of the sinus node to recover function following suppression of automaticity by atrial tachyarrhythmia.