Pacemakers are small electronic devices surgically implanted to help manage irregular heart rhythms. While pacemakers generally improve quality of life, certain situations can lead to unintended rapid heart rates. This article explores pacemaker-mediated tachycardia, explaining its mechanism and addressing concerns about its potential impact.
Understanding Pacemaker-Mediated Tachycardia
Pacemaker-mediated tachycardia (PMT), sometimes called endless loop tachycardia, is a rapid heart rhythm that can occur in individuals with dual-chamber pacemakers. These pacemakers have leads in both the atrium and ventricle to maintain synchronized beating.
PMT occurs when the pacemaker inadvertently creates a rapid heart rhythm, forming an electrical “endless loop.” This process typically begins with a premature ventricular contraction (PVC) or another event that disrupts the normal heart cycle.
Following a ventricular beat, an electrical signal can sometimes conduct backward from the ventricle to the atrium, known as retrograde VA conduction. If this retrograde atrial signal occurs after a specific protective interval, called the Post-Ventricular Atrial Refractory Period (PVARP), the pacemaker’s atrial lead senses it as a natural atrial beat. The pacemaker, programmed to maintain synchrony, then responds by pacing the ventricle. This ventricular pacing can again lead to retrograde conduction to the atrium, restarting the cycle.
Recognizing the Signs
Individuals experiencing pacemaker-mediated tachycardia often notice a sudden onset of symptoms related to the rapid heart rate. Common signs include palpitations, lightheadedness, or dizziness, as the heart’s efficiency may be reduced. Other symptoms can include fatigue, shortness of breath, or a general feeling of unease. In some instances, chest pain or fainting (syncope) may occur, especially if the rapid heart rate significantly impacts blood flow. Any new or unusual feelings related to the pacemaker warrant medical attention.
Assessing the Danger and Risks
While pacemaker-mediated tachycardia can be uncomfortable, it is typically not immediately life-threatening. However, it requires prompt medical evaluation to prevent complications. The primary concern is when the rapid heart rate reduces the heart’s pumping effectiveness.
Persistent PMT can lead to decreased cardiac output, causing profound dizziness, presyncope, or fainting. Prolonged episodes can also exacerbate underlying heart conditions, such as congestive heart failure, by increasing the workload on a weakened heart and reducing filling time.
In rare cases, especially with existing coronary artery disease, increased heart rate from PMT can lead to myocardial ischemia, where the heart muscle does not receive enough blood flow. The persistent symptoms and anxiety associated with recurrent PMT can also affect a person’s overall quality of life.
Diagnosis and Management
Diagnosing pacemaker-mediated tachycardia typically involves clinical assessment and device evaluation. Doctors confirm PMT through an electrocardiogram (ECG) during an episode, showing characteristic patterns of ventricular pacing.
Further confirmation comes from interrogating the pacemaker device, where a special programmer connects to the implanted device. This allows review of stored data and intracardiac electrograms, definitively showing the “endless loop” pattern and confirming retrograde conduction triggering pacing.
Once PMT is diagnosed, immediate termination can often be achieved by placing a magnet over the pacemaker, which temporarily switches the device to an asynchronous pacing mode, breaking the reentrant circuit.
The primary long-term solution for PMT involves reprogramming the pacemaker settings. A key adjustment is lengthening the Post-Ventricular Atrial Refractory Period (PVARP), which ensures that any retrograde atrial signals are ignored. This prevents the endless loop.
Modern pacemakers also feature algorithms designed to detect and automatically prevent PMT. In rare and complex situations, if reprogramming alone is insufficient, other interventions might be considered, such as certain medications or lead revision. Consulting a cardiologist or electrophysiologist is crucial for proper diagnosis and tailored management.