A pacemaker is a small device designed to manage heart rhythm, but it does not completely prevent all forms of cardiac irregularity. The device is primarily intended to correct a heart rate that is too slow, a condition known as bradycardia. Because the pacemaker addresses only a specific electrical issue, other irregularities can still occur due to new or progressing heart conditions or technical issues with the device itself. Understanding the reasons behind this irregularity is the first step toward finding a solution.
Understanding Pacemaker Function
A pacemaker’s main purpose is to ensure the heart beats above a predetermined minimum rate by delivering timed electrical impulses. The device consists of a pulse generator, which contains the battery and computer circuitry, and thin wires called leads that connect to the heart muscle. The pacemaker constantly monitors the heart’s natural electrical activity through its leads.
Most modern pacemakers operate in a “demand” mode, only sending an electrical pulse when the heart’s natural rhythm drops below the programmed lower rate limit. If the heart beats normally, the pacemaker remains silent. The device is programmed to control the rate and timing of the electrical signals to ensure the lower chambers (ventricles) contract at a steady pace, but this function does not necessarily stop all problems related to the heart’s overall rhythm.
Causes of Irregular Heartbeats Despite a Pacemaker
Underlying Heart Conditions
An irregular heartbeat, or arrhythmia, can occur even with a fully functional pacemaker because the device does not cure the underlying heart disease. The most common reason for a new irregularity is the progression of the original condition or the emergence of a different type of arrhythmia. Atrial fibrillation (AFib), where the heart’s upper chambers quiver chaotically, is a frequent example that the pacemaker is not designed to suppress. Extensive pacing of the heart’s lower right chamber can sometimes be associated with an increased likelihood of developing new-onset AFib over time. The mechanical function of the heart is altered by the electrical impulse, which can lead to structural changes that promote irregularity. The pacemaker’s ability to treat AFib is limited to slowing down the ventricular rate if it becomes too fast, rather than restoring a normal rhythm.
Technical Malfunctions
Technical issues with the pacemaker system can also cause an irregular rhythm. One such issue is oversensing, where the device mistakenly interprets electrical noise, such as skeletal muscle activity or large T-waves, as a natural heartbeat. This can cause the pacemaker to inappropriately pause or inhibit pacing, leading to a slow or irregular beat. Conversely, undersensing occurs when the device fails to detect a genuine natural heartbeat, causing it to pace when it should not, a phenomenon known as asynchronous pacing.
Lead and Timing Issues
Lead displacement is another mechanical cause of irregularity. If a pacing lead shifts position, it can lose contact with the heart muscle, leading to a failure to capture. A displaced lead can also intermittently irritate the heart muscle, triggering premature ventricular contractions (PVCs) or other fast, irregular rhythms. Pacemaker Syndrome can occur, typically in patients with single-chamber pacemakers, where the timing between the upper and lower heart chambers is mismatched. This dyssynchrony reduces the heart’s efficiency and can cause symptoms that mimic an arrhythmia, such as dizziness and fatigue.
Recognizing Symptoms and Warning Signs
The sensation of an irregular heartbeat can manifest in several ways, often reflecting reduced blood flow or inefficient heart function. Patients may experience palpitations, described as a fluttering, pounding, or racing sensation in the chest. Other symptoms are linked to the heart’s inability to pump blood effectively due to the rhythm disturbance, including unexplained fatigue, weakness, light-headedness, or dizziness. Shortness of breath, particularly during light activity, can also be a sign of a rhythm issue.
Any sudden, severe symptoms require immediate medical attention, such as:
- Severe chest pain
- Prolonged loss of consciousness (syncope)
- Persistent shortness of breath
Next Steps: Diagnosis and Treatment Adjustments
When a patient reports symptoms of an irregular heartbeat, the first step is typically a non-invasive procedure called device interrogation. This allows the cardiologist to retrieve stored information from the implanted device, including the history of the heart’s rhythm, battery status, and lead integrity. If the irregularity is intermittent, a Holter monitor or external cardiac monitor may be used to capture the rhythm over several days or weeks.
Based on the findings, treatment adjustments often begin with reprogramming the pacemaker settings, such as adjusting timing intervals or sensor sensitivity to correct oversensing or undersensing. If a new arrhythmia like AFib is confirmed, treatment may involve adjusting or adding medications to control the heart rate or thin the blood. In cases of lead malfunction or Pacemaker Syndrome, a surgical procedure to reposition a lead or upgrade to a dual-chamber device may be necessary to restore optimal heart function.