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 Heart Health - Detail

Cardiac Pacemakers

Dr. Raymond Dong, Cardiologist.

A cardiac pacemaker is a device that can be internally implanted to provide support for the heart’s electrical system. The heart normally operates by automatically sending an electrical signal from the upper right chamber to the rest of the heart. The natural timer speeds up or slows down according to the needs of the rest of the body, and the level of physical activity performed. The pumping muscles at the bottom of the heart are connected to this natural timer by a series of specialized cardiac muscle fibres that conduct the signal more rapidly than the rest of the muscle tissue.

On occasion, the electrical network starts to slow down because of the aging process, and the connecting fibres no longer allow electrical signals to pass from top to bottom. This is known as second- or third-degree heart block. Although the bottom of the heart can beat on its own, it does so with a very slow heart rate, often in the range of 30 to 35 beats per minute. This can lead to the person feeling lightheaded or faint, and can even cause blackouts. Less commonly the natural timer slows down so much that there can be a number of seconds that lapse between heartbeats. This is called sinus pausing or sinus arrest. There can be situations where the heartbeat can be very fast and then suddenly become very slow. Doctors may prescribe medication to control the fast heart beats, but the usual treatment for a heartbeat that is too slow and causing symptoms is to surgically implant a pacemaker.

Although the aging of the heart is what usually creates the need for a pacemaker, other conditions such as a heart attack, heart surgery, and even cardiac medications can create a need for a pacemaker. Some rare conditions in which abnormal proteins and other substances become stored in heart muscle tissue can also cause heart block.

The doctor may discover the need for a pacemaker when the patients presents with symptoms, and a diagnosis can be made with routine ECG recordings, or with 24 hour ECG monitors. However, if the symptoms are infrequent, it may take a number of recording before a diagnosis can be confirmed. Patients can also be seen in emergency rooms after a blackout, and are then found to have a very slow pulse. In an emergency, the doctor may decide to put in a temporary pacemaker through a vein in the neck or groin, which will stabilize the patient until a permanent pacemaker can be arranged.

Permanent pacemakers are implanted with local anesthetic and the usual site is under the skin, just below the collar bone. Pacemaker wires (or leads) are placed into the right upper and/or lower chambers of the right side of the heart, using an X-ray fluoroscope to guide the surgeon. The pacemaker generator contains both the battery and the computer chip in a completely sealed metal container. Once the leads are in the proper position, the pacemaker generator is connected to the leads, and the device is tested. If the device is functioning appropriately, it is implanted under the skin and the wound is closed.

After discharge, the pacemaker will receive its first checkup and adjustment approximately 6 weeks after implantation. The device is interrogated using a magnetic wand attached to a computerized programmer. Information about the pacemaker settings, the monitored cardiac events stored in the pacemaker computer chip, and the status of the battery can be obtained electronically. Similarly, the pacemaker can be adjusted with the same programming wand. Follow up visits are then scheduled according to the needs of the patient, the type of pacemaker, and the age of the battery.

There are several major categories of pacemakers. Some devices have a single lead that is either used to pace the top or bottom chamber of the right heart. Other devices have two leads that function in both chambers. The pacer lead is used by the computer chip to record signals naturally produced by the heart, in order that the pacemaker provides electrical support only when necessary. Some patients are 100% dependent on the pacemaker for their heartbeats, and others may rely on the pacemaker less than 10% of each day. Pacemaker batteries may last anywhere from 8 years to 12 or more years before they have to be replaced. At each follow up visit, the amount of battery life left is recorded and the doctor will make a decision as to when to replace the device. The pacemaker leads are not usually removed, and only the generator is replaced. Rarely, pacemaker leads are extracted (often with some difficulty) in circumstances where the lead is faulty, or infected.

There are specialized pacemakers now available that function not only to support a very slow heartbeat, but act to deliver an electric shock to a treat a dangerous, potentially lethal cardiac rhythm. These specialized devices are called AICDs (or defibrillators). AICDS are implanted in patients that have already experienced the need for an emergency electric shock, and in patients with very weak heart muscles. An even more specialized device is called a CRT, or resynchronization device. These computer chips use a third pacemaker lead placed in the left side of the heart to improve the timing of the contractions between the right and left heart pumps. CRTs can be helpful in some patients with poor cardiac pump function.

Many thousands of people in BC have pacemakers. These devices improve symptoms and can be life-saving if used in selected patients. Long term follow up is relatively easy and there is no maintenance needed as these devices function automatically and are fully programmable by the physician, who can tailor the device to the specific patient need. Most devices now feature a rate-responsive mode, which means that the heart rates available to the patient are variable and can automatically increase or decrease based on the patient’s level of activity and metabolic need.

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