A pacemaker is a small, battery-powered device implanted under the skin, typically near the collarbone, designed to manage the heart’s rhythm. While highly effective, its function is often limited to addressing specific types of heart rhythm problems. It is possible to have an irregular heartbeat, also known as an arrhythmia, even with a functioning pacemaker. This can happen due to the type of arrhythmia, the progression of underlying heart disease, or technical issues with the device itself.
The Pacemaker’s Primary Function in Rhythm Control
A pacemaker’s main role is to act as a reliable backup for the heart’s natural electrical system. The device has two fundamental functions: sensing and pacing. Sensing involves continuously monitoring the heart’s natural electrical activity, checking to see if a beat occurs on time.
The primary indication for a pacemaker is often to treat bradycardia (a heart rate that is too slow) or to manage heart block where electrical signal transmission is impaired. If the device senses a missed beat or the heart rate drops below a pre-set lower limit, it sends a small electrical impulse. This impulse stimulates the heart muscle to contract, ensuring a consistent heart rate.
Pacemakers use thin, flexible wires called leads, which carry the electrical impulse from the generator to the heart muscle. Devices may be single-chamber (pacing one chamber) or dual-chamber (pacing both the atrium and ventricle) to synchronize the heart’s action. Pacing maintains the lower-limit heart rate, preventing symptoms associated with a slow heart rate, such as fainting or fatigue.
Underlying Reasons for Persistent or New Arrhythmias
Despite preventing a slow heart rate, the pacemaker is not a cure for all cardiac rhythm disorders. The device primarily defends against bradycardia but cannot stop or prevent other irregular rhythms that develop independently. This limitation is the most common reason a patient with a pacemaker may still experience an irregular heartbeat, particularly rapid rhythms.
Rapid heart rhythms, known as tachyarrhythmias (such as Atrial Fibrillation or Ventricular Tachycardia), often originate from different electrical pathways than the bradycardia the pacemaker was implanted to correct. When a fast rhythm takes over, the pacemaker’s slower, programmed rate is overridden by the faster, abnormal electrical signal. While advanced devices like an Implantable Cardioverter-Defibrillator (ICD) can treat these rapid rhythms, a standard pacemaker generally cannot.
The original heart condition that led to implantation can progress over time, or new cardiac issues may emerge. Underlying heart disease may worsen, creating new areas of electrical instability that the existing lead placement cannot address. The device itself can sometimes induce an irregular rhythm, such as pacemaker-mediated tachycardia, though this can often be prevented or terminated with specific programming.
Technical issues with the pacing system can also lead to irregular heart activity. The insulated wires, or leads, can sometimes move from their original position on the heart wall, a phenomenon called lead displacement. If a lead shifts, the device may fail to properly deliver the electrical impulse or incorrectly sense the heart’s natural beat, leading to intermittent pacing failure. Battery depletion is another concern, as the pulse generator’s power gradually decreases, potentially leading to a loss of consistent pacing function.
Recognizing Symptoms of Irregular Heart Activity
When the pacemaker is not adequately controlling the rhythm, or a new arrhythmia is present, patients often experience noticeable physical symptoms. The most commonly reported symptom is palpitations, described as a fluttering, pounding, or racing sensation in the chest. These feelings indicate the heart is beating too fast or irregularly.
Other symptoms relate to the heart’s reduced ability to pump blood effectively during the irregular rhythm. Patients may feel lightheadedness or dizziness, which can progress to syncope (fainting). Shortness of breath, fatigue, and chest discomfort are frequent complaints, particularly when the irregular rhythm is sustained. If any of these symptoms occur, especially new or worsening ones, contact a healthcare provider promptly to investigate the cause.
Diagnostic Steps and Adjustments to Treatment
Once a persistent irregularity is suspected, the initial step involves pacemaker interrogation. This non-invasive procedure uses a specialized computer programmer placed over the chest to wirelessly communicate with the implanted device. Interrogation allows the clinician to review the device’s stored data, including the patient’s heart rhythm history, the percentage of time the device has paced, and any recorded episodes of irregular heartbeats.
The stored data often reveals the exact nature of the arrhythmia and whether the device is functioning as intended. If the rhythm issue is intermittent or not captured by the device, external monitoring tools, such as a Holter monitor, may be used to record the heart’s electrical activity over a longer period. These diagnostic steps guide the subsequent treatment plan, which may involve device reprogramming.
Reprogramming the pacemaker can change parameters such as the lower rate limit, the sensitivity of the sensing function, or the timing between the atrial and ventricular beats. For rapid rhythms the pacemaker cannot stop, treatment may be adjusted to include anti-arrhythmic medications to suppress the abnormal rhythm. If a technical problem like lead displacement is identified, a surgical procedure (lead revision or device replacement) may be necessary.