Overview of Pacemakers

Overview of Pacemakers

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What is a permanent pacemaker?

A permanent pacemaker, a small device that is implanted under the skin (most often in the shoulder area just under the collarbone), sends electrical signals to start or regulate a slow heartbeat. A permanent pacemaker may be used to make the heartbeat if the heart’s natural pacemaker (the SA node) is not functioning properly and has developed an abnormal heart rate or rhythm, or if the electrical pathways are blocked.


What is an implantable converter defibrillator (ICD)?



The ICD has another type of treatment for certain fast rhythms called anti-tachycardia pacing (ATP). When ATP is used, a fast pacing impulse is sent to correct the rhythm. After the shock is delivered, a “back-up” pacing mode is used if needed for a short while.

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What is the reason for getting a pacemaker or an ICD?


Arrhythmias can cause problems with contractions of the heart chambers by:

  • not allowing a sufficient amount of blood to be pumped out to the body because the electrical signal is causing the heart to pump too slow or too irregularly.

The heart’s electrical system:

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The heart is, in the simplest terms, a pump made up of muscle tissue. Like all pumps, the heart requires a source of energy in order to function. The heart’s pumping energy comes from an intrinsic electrical conduction system.

How does the heart beat?

An electrical stimulus is generated by the sinus node (also called the sinoatrial node, or SA node), which is a small mass of specialized tissue located in the right atrium (right upper chamber) of the heart. The sinus node generates an electrical stimulus periodically (60-100 times per minute under normal conditions). This electrical stimulus travels down through the conduction pathways (similar to the way electricity flows through power lines from the power plant to your house) and causes the heart’s chambers to contract and pump out blood. The right and left atria (the two upper chambers of the heart) are stimulated first and contract a short period of time before the right and left ventricles (the two lower chambers of the heart). The electrical impulse travels from the sinus node to the atrioventricular (AV) node, where it stops for a very short period, then continues down the conduction pathways via the bundle of His into the ventricles. The bundle of His divides into right and left pathways to provide electrical stimulation to both ventricles.

Normally, as the electrical impulse moves through the heart, the heart contracts about 60 to 100 times a minute. Each contraction represents one heartbeat. The atria contract a fraction of a second before the ventricles so their blood empties into the ventricles before the ventricles contract.

Under some conditions, almost all heart tissue is capable of starting a heartbeat, or becoming the pacemaker. An arrhythmia occurs when:

  • the heart’s natural pacemaker develops an abnormal rate or rhythm
  • the normal conduction pathway is interrupted
  • another part of the heart takes over as pacemaker

In any of these situations, the body may not receive enough blood because the heart cannot pump out an adequate amount with each beat as a result of the arrhythmia’s effects on the heart rate. The effects on the body are often the same, however, whether the heartbeat is too fast, too slow, or too irregular. Some symptoms of arrhythmias include, but are not limited to:

  • weakness
  • fatigue
  • palpitations
  • low blood pressure
  • dizziness
  • fainting


What are the components of a permanent pacemaker/ICD?

A permanent pacemaker has three components:

  • electrodes on each lead

Older pacemakers sent out electrical signals at a constant rate, regardless of the heart’s own rate. Pacemaker technology is now much more advanced. Today, pacemakers can “sense” when the heart’s natural rate falls below the rate that has been programmed into the pacemaker’s circuitry.


A ventricular arrhythmia (an arrhythmia 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 arrhythmias, and there are pacemakers which 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.

An ICD has a lead wire that is positioned in the ventricle, as it is used primarily for fast ventricular arrhythmias.

Pacemakers that pace either the right atrium or the right ventricle are called “single-chamber” pacemakers. Pacemakers that pace both the right atrium and right ventricle of the heart and require two pacing leads are called “dual-chamber” pacemakers.

How is a pacemaker/ICD implanted?

X-ray of a single-chamber implanted pacemaker

Pacemaker/ICD insertion is usually an outpatient procedure, done in the cardiac catheterization laboratory, or the electrophysiology laboratory. The patient is awake during the procedure, although sedation may be given to help the patient relax during the procedure.


