The classification of pacemakers into different types is based on the mode of application of the stimulating pulses to the heart. EXTERNAL PACEMAKERS:
These are used when the heart block presents itself as an emergency and when it is expected to be present for a short time i.e during critical post operative periods and in patients during cardiac surgery, involving the valves or septum. * The pacemaker is placed outside the body. It may be in the form of wrist watch or in the pocket, from that one wire will go into the heart through the vein. * The electrodes are called endocardiac electrodes and are applied to the heart by means of an electrode catheter with electrode’s tip situated in the apex of the right ventricle. These are in contact with the inner surface of the heart chamber. * It does not necessitate the open chest surgery.
* The battery can be easily replaced and any defect or adjustment in the circuit can be easily attended without getting any help from a medical doctor. During placement , swelling and pain do not arise due to minimum foreign body reaction. * Mostly these are used for temporary heart irregularities. INTERNAL PACEMAKERS:
These are used in causes requiring long term pacing because of permanent damage that prevents normal self triggering of the heart. Here the pacemaker itself may be implanted in the body below the right or left clavicle (collar bone). The patient is able to move about freely. Internal leads connect to electrodes that are directly in contact with the inside of the right ventricle or the surface of the myocardium. * The pacemaker is miniaturized and is surgically implanted beneath the skin near the chest or abdomen with its output leads directly connected to heart muscle. * The electrodes are called myocardiac electrodes and are in contact with the outer wall of the myocardium (heart muscle). * It requires an open chest minor surgery to place the circuit. * The battery can be replaced only by the minor surgery. Further any defect or adjustment in the circuit cannot be easily attended. Doctor’s help is necessary to rectify the defect in the circuit. During placement swelling and pain arise due to foreign body reaction. * Mostly these are used for permanent heart damages.
The internal pacemakers are further classified into:
* FIXED RATE UNITS OR ASYNCHRONOUS PACEMAKERS:
These are used for patients having permanent block. The rate can be varied externally from 70 to 95 beats per minute by magnetically actuating built in relay. * THE R – WAVE CONTROLLED PACEMAKERS:
These are used I heart block with occasional sinus rhythm. The pacemaker detects the R-wave of ECG and stimulates the ventricles after a very short delay of few milliseconds. * ATRIAL TRIGGERED PACEMAKERS:
In fixed pacemakers, atrio ventricular coordination is not maintained. This lessens the contribution of atrium to the cardiac output. This is compensated by a pacemaker which allows ventricular contraction to take place after a sufficient interval to permit atrial filling. The advantage of this pacemaker is its ability to augment the cardiac output changes to meet the physiological requirements. * THE BI-FOCAL DEMAND PACEMAKER:
This pacemaker stimulates both atria and ventricles in sequence. Thus the pacemaker functions automatically according to patient needs.
There are three basic types of permanent pacemakers, classified according to the number of chambers involved and their basic operating mechanism:
* Single chamber pacemaker
* Dual chamber pacemaker
* Rate-responsive pacemaker
SINGLE CHAMBER PACEMAKER:
A single-chamber pacemaker uses one lead, placed either in the right atrium or the right ventricle of your heart. (Most single-chamber pacemakers have a lead attached to the right ventricle.) When Attached in the Atrium-
Leads attached in the right atrium are designed to correct abnormalities in the heart's sino atrial (SA)...