Cardiac Pacemaker

Cardiac pacemakel-s are used to treat il hear1 that beats loo slowly. Sornelinles the natural pacemaker of the heart beats too diseased and does no1 kecp the heart beating regularly. The average hear1 rate is 60 to 100 beats per minute. The normal heart can occasionally beat as slowly as 40 times a minule while resting and as fast as 200 times a minule while exercising. However hence can be symptoms of weakness, dizziness and fainting when the heart beats Lo slowly.The heart may always be slow or the may be episodic pauses in the heartbeat that may lead to symptoms. Occasionally an EPS study may be necded to determine'the need for a pacemaker.

How do pacemakers work?

functions of pacemakers

Pacemakers consist of two inajor parts: the generalor, and thc leads.The generator is essentially a tiny, hermetically sealed computer - along with a Anti-Arrhythmic Drugs, Pacemakers, Defibrillators batteiy to run it - . housed in a titanium container. Most modern pacemaker generators are roughly the size of a 50 per cent piece, and approximately three times as thick. The battery life of most pacemaker generators today is 5-8 years.

The lead is a flexible insulated electrical wire. One end is attached to the generator and the other end is passed through a vein into the heart. Most pacemakers today use two leads - one placed in the right atiium, and the other in the right ventricle.

How it works: The pacemaker leads detect the heart's own electrical activity (in the right atiium and right ventricle), and transmit that information to the pacemaker generator. The generator - which, again, is a computer - analyzes the heart's electrical signals, and uses that information to decide whether, when, and where to pace. If the heart rate becomes too slow, the generator transmits a tiny electrical signal to the heart, thus stimulating the heart muscle to contract (This is called pacing).

Pacemakers that have two leads not only keep the heart rate from dropping too low, they can also maintain the optimal coordination between the atria and the ventricles (by pacing the atrium and the ventiicle in sequence).Thus, pacemakers do not take over the work of the heart - the heart still does its own beating - but instead, pacemakers merely help to regulate the timing of the heart beat.

Pacemaker Naming Code
The NASPEIBPEG generic (NPG) code is a pacemaker naming convention originally developed in 1974 that uses a 3-5 letter code to describe the main features of an artificial pacemaker. Each of the five positions signifies a particular aspects of pacemaker functionality. Using Lhis scheme, a designation of VAT00 would describe, for example, a pacemaker that sensed the atria and paced the ventricles in a triggered mode with no rate response or multisite pacing

Advancements in Pacemaker Function
When first invented, pi.icen~akers controlled only the rate at which the heart's two largest chambers, the ventricles, beat.Many advancements have been made to enhance the control of the pacemaker once implanted, Many of these enhancements have been made possible by the transition to microprocessor controlled pacemakers. Pacemakers that control not only the ventricles but the atria as well have become common. Pacemakers thatCommon  control both the atria and ventricles are called dual-chamber pacemalters. Timing the contractions of the atria to precede that of the ventricles improves the pumping efficiency of the heart and can be useful in congestive heart failure.

Implantation and Follow-up of Pacemakers
Pacemaker implantatioil today is minimally invasive surgery. It is done under local anesthesia, and generally takes less than 45 minutes.After the area under the patient's collarbone is numbed, a small incision is made (usually about three inches long,) and a "pocket" is fashioned in the tissue overlying the muscle. The leads are inserted through a vein near the site of the pocket, and advanced into the heart using fluoroscopy (X-rays) for guidance. The leads are then attached to the generator, the generator is placed in the pocket, and the incision is closed.

Once a paceinaker is implanted, it is important to program it. Pacemakers today are extremely flexible devices, and can vary their function according to the precise needs of the patient. But to do this, the doctor needs to program the devices.As noted, pacemaker generators are essentially tiny computers, and like any computer, before they can be optimally useful their software needs to be "tweaked" to suit the individual user. Pacemakers can be programmed non-invasively, with a handheld device that communicates with the pacemaker through the skin. The programming can be repeated as often as necessary if the patient's underlying heart rhythm problem changes.

What happens after the pacemaker is implanted?

Once the incision completely heals (which takes about 2-4 weeks,) the patient can largely return to a completely normal life. In fact, since pacemakers alleviate the symptoms of bradycardia, many patients find they are able to do even more after a pacemaker is implanted.Periodic pacemaker checks are necessary, to measure the function of the device and the amount of energy left in the battery. The "scheduled maintenance" for pacemakers generally consists of periodic telephone follow-up (every month or two,) and usually yearly visits to the doctor's office. The telephone follow-up is a simple procedure consisting of placing a special "trans-telephonic follow-up device" over the pacemaker, and transmitting data over the telephone.When the batteiy begins to get low, the doctor schedules an elective pacemaker replacement. This procedure is similar to the implantation procedure, except that usually the pacemaker leads do not need to be replaced. Under local anesthesia,the incision is opened, the generator is detached from the leads and thrown away,a new generator is attached, and the incision is then closed. (This is not merely a "battery change," though doctors sometimes call it that. No batteries are changed; instead, the entire old generator is discarded and a brand new one is placed).

Pacemaker problems can rarely occur long after the implantation procedure.These "late" complications include generator failure (extremely rare), and lead failure (less rare). Lead failure can occur if the pacemaker is traumatized somehow, such as from the wear and tear of movement. (The most common cause of such trauma is the habit some people have of "twiddling" with their pacemaker). Manufacturers are required to report device failures to the FDA.Which will order companies to issue either "advisories" or recalls if a particular model seems prone te failure.

Following the suggested maintenance schedule usually ineans that pacemaker will be detected before they become serious.Anti-Arrhythmic Drugs, Pacemnk-However, it is important for patients to be aware of the symptoms of ers, Defibrillators bradycardia, symptoms that might indicate a pacemaker malfunction. Once again,these symptoms include weakness, easy fatigability, lightheadedness, dizziness,or loss of consciousness. Patients experiencing any of these symptoms should notify their doctor. A simple telephone check of the pacemaker is usually enough to lvle out a pacemaker problem.

What devices can interfere with pacemakers?
Home appliances do not inteifere with pacemakers, and should not cause any concern whatsoever. (This includes microwave ovens, despite the signs you still see posted in some restaurants).Arc welding equipment and other devices that generate powelful magnetic fields- medical devices and heavy duty industrial motors -can inhibit the function of pacen1akel.s.

Cellul;~ telephones, if held in close proximity to the pacemaker (which may happen if the phone is kept in a breast pocket) call potentially affect the function of a pacemaker. As long as the phone is kept six or more inches from the pacemaker there should not be a problem.MRI scanners can iiltenupt the pacing function of pacemakers, and under some circumstances may be dniigerous to the pacemaker and the patient. Many problems with MRI can be circumvented by taking special care during the procedure and limiting the MRI scan appl-opriately. Patients with pacemakers should discuss the risks and benefits of MRI scanning with their doctors.Radiation therapy for cancers can dainage the circuits of a pacemaker, and the pacemaker needs to be shielded .from the radiation field.Shock wave lithotripsy, used to break up kidney stones, can potentially damage pacemakers, espkcially if they are implanted in the abdomen instead of under the collarbone. Pacenlakers should be tested after lithotripsy to document that they are still functioning normally.

Methods of Pacing

External Pacing
Exteinal pacemakers can be used for initial stabilization of a patient, but implantation of a permanent internal pacemaker is usually required for most conditions. External cardiac pacing is typically performed by placing two pacing pads on the chest wall. Usually one pad is placed on the upper poi-tion of the sternum, while the other is placed along the left axilla, near the bottom of the rib cage. When an electlical impulse goes from one pad to the other, it will travel through the tissues between them and stimulate the muscles between them,including the cardiac muscle and the muscles of the chest wall. Electrically stimulating any muscle, including the heart muscle, will make it contract. The stimulation of the muscles of the chest wall will frequently make those muscles twitch at the same rate as the pacemaker is set.Pacing the heart via external pacing pads should not be relied upon for an extended period of time, If the person is conscious, he or she may feel discomfort due to the frequent stimulation of the rnuscles of the chest wall. Also,stimulation of the chest wall muscles does not necessarily mean that the heart is being stimulated as well.Common

Temporary Internal Pacing
An alternative to external pacing is the temporaly internal pacing wire. This is a wire that is placed under sterile conditions via a central line. The distal tip of the wire is placed into either the right atrium or right ventricle. The proximal tip of the wire is attached to the pacemaker generator, outside of the body. Temporary intei-nal pacing is often used as a bridge to permanent pacemaker placement.Under certain conditions, a person may require temporary pacing but would not require permanent pacing. In this case, a tempor~vy pacing wire may be the optimal treatment option.

Permanent Pacemaker Placement

Placement of a permanent pacemaker involves placement of one or more pacing wires within the chambers of the heart. One end of each wire is attached to the muscle of the heart. The other end is screwed into the pacemaker generator. The pacemaker generator is a hermetically sealed device containing a power source and the computer logic for the pacemaker.

Most commonIy, the generator is placed below the subcutaneous fat of the chest wall, above the muscles and bones of the chest. However, the placenlent may vary on a case by case basis.Another advancement in pacemaker technology is left ventricular pacing.' A pacemaker wire is placed on the outer susface of the"1eft ventricle, with the goal of more physiological pacing than what is available in standard pacemakers. This extra wire is implanted to improve symptoms in patients with severe heart failure.

Devices with Pacemaker Function
Sometimes devices resembling pacemakers, called ICDs (implantable cardioverter-defibrillators) are implanted. These devices' are often used in the treatment of patients at risk for sudden casdiac death. An ICD has the ability to treat many types of heart rhythm disturbances by means of pacing, cardioversion, or defibrillation.