When Is a Pacemaker Selected?

When your heart rate is unreliable or too slow due to a malfunction in your SA node, AV node or normal conduction pathway, your physician may recommend a pacemaker.

With advances in technology, artificial pacemakers today generally last eight to ten years (depending upon the type of heart condition) and, in most cases, allow a person to lead a normal life.

In addition, advances in pacemaker circuitry have reduced the interference risk from certain machinery, such as microwaves, which, in the past, may have altered or otherwise affected the pacemaker. Even so, certain precautions must be taken into consideration when a person has an artificial pacemaker.

A pacemaker is a small electronic device composed of three parts: a generator, one or more leads, and an electrode on each lead. A pacemaker signals the heart to beat when the heartbeat is too slow.

A generator is the "brain" of the pacemaker device. It is a small metal case that contains electronic circuitry and a battery sealed in a titanium case. The pulse generator is approximately the size of a silver dollar and usually placed beneath the skin on the right or left side of the upper chest.

The lead system is an insulated flexible wire, which is connected to the pulse generator and passed through a vein in the neck or shoulder into the right side of the heart. Depending on your particular needs, you may have one or two leads placed into your heart.

The lead carries signals from the heart muscle to the pulse generator when you have a normal heartbeat. When your heart misses a beat, the missed heartbeat is "sensed" by the pulse generator. This then initiates an electrical impulse from the pulse generator through the lead to your heart muscle. This electrical impulse will stimulate a heartbeat and keep your heart rate from becoming too slow.

When the heart is beating at a rate faster than the programmed limit, the pacemaker will monitor the heart rate, but will not pace. No electrical impulses will be sent to the heart unless the heart's natural rate falls below the pacemaker's low limit.

Pacemaker leads may be positioned in the atrium or ventricle or both, depending on the condition requiring the pacemaker to be inserted. An atrial dysrhythmia/arrhythmia (an abnormal heart rhythm caused by a dysfunction of the sinus node or the development of another atrial pacemaker within the heart tissue that takes over the function of the sinus node) may be treated with an atrial pacemaker.

A ventricular dysrhythmia/arrhythmia (an abnormal heart rhythm caused by a dysfunction of the sinus node, an interruption in the conduction pathways, or the development of another pacemaker within the heart tissue that takes over the function of the sinus node) may be treated with a ventricular pacemaker whose lead wire is located in the ventricle.

It is possible to have both atrial and ventricular dysrhythmias, and there are pacemakers that have lead wires positioned in both the atrium and the ventricle. There may be one lead wire for each chamber, or one lead wire may be capable of sensing and pacing both chambers.

There are a number of categories of patients with indications for pacemaker implantation.

  1. Symptoms documented to be related to slow heart rates
  2. Pauses of 3 seconds while awake
  3. Complete AV block
  4. Mobitz II AV block