What Are the Parameters of a Cardiac Pacemaker?

Each pacemaker company has an out-of-box preset for many of the parameters that are used to decide how to modify the device from patient to patient. Pacemakers are not a one-size-fits-all device that you can just set and forget; they are delicate computers. Your cardiologist or electrophysiologist will decide which settings are best for your specific need and model.

Lower Rate Limit (LRL)

• The lower rate limit is the slowest the heart can beat before the pacemaker fires.

  The lower rate limit (LRL) is the parameter that affects how slow a heart rate can become before the pacemaker senses the need to pace. The LRL helps decrease symptoms of bradycardia that begin when the heart rate is too low. In patients with heart blocks, the LRL is important because the heart's natural rate may be almost nonexistent.

Upper Rate Limit (URL)

• The upper rate limit can sometimes be the same parameter as the lower rate limit.

  The upper rate limit (URL) is the parameter that dictates when the pacemaker will stop evaluating the heart rate. If the URL is set at 80 beats per minute (bpm), but the heart is firing faster on its own, the device will not sense it until the heart rate decreases below 80 bpm again. If the pacemaker is used for bradycardia or a heart block, the LRL and the URL are essentially the same.

Exercise Intolerance and Rate Response Considerations

• Rate response is one way devices adapt to meet the needs of patients who are exercise intolerant.

  With exercise intolerance, the heart rate does not rise and fall with the advent or cessation of activity. Once the patient begins to exercise, the pacemaker senses abnormalities in the heart rate and correlation concerning the vigor of activity. In some pacemaker models, rate response can be programmed on or off as needed.

Sensitivity Parameters

• Setting the pacemaker's sensitivity is based on understanding an inverse relationship.

  Device sensitivity can be called an "inverse relationship." If the sensitivity of the device is turned up, the device senses less of the waveforms it is measuring. This can cause the device to fire less than is actually needed. Conversely, if you turn the device's sensitivity down, the device senses more of the waveform and could cause the device to pace unnecessarily, which can deplete the battery prematurely.

Electrical Output

• The electrical output of the pacemaker is meant to mimic the heart's natural electrical forces.

  After implantation, the pacemaker energy output is much higher than necessary once the cardiac tissue acclimates to the pacing lead as it settles into the chamber in which the electrode was placed. Patients need to follow up with their cardiologist after the device is inserted. Electrical output must be tested soon after placement to make certain the internal leads have not migrated from the cardiac chamber wall, which can reduce the efficiency of the device.

Conserving Battery Power

• Adjusting the device's electrical output is crucial for the longevity of the pacemaker.

  Usually three to six months after the device is inserted, the patient will need to visit the cardiologist or clinic to have the overall energy output level turned down. The goal of this visit is to determine how the device can function properly while using the least amount of battery power.

Follow the Order of Only One Physician

• The pacemaker patient should be followed by only one doctor who will deal primarily with maintaining the device.

  If the patient sees a separate cardiologist for general heart health care and an electrophysiologist for pacemaker care, he needs to decide which physician will take the lead on the follow-up visits concerning the device. Maintaining one set of records by one pacemaker clinician is essential for the quality and continuity of the care of the patient's device.