What is Pacemaker Mediated Tachycardia?
Pacemaker mediated tachycardia (PMT) is a type of fast heartbeat condition, where the pacemaker plays a large part in causing it. There are multiple reasons why this type of fast heartbeat can develop. It could be because the pacemaker is tracking an abnormally fast heartbeat originating from the upper chambers of the heart (known as atrial tachycardia or sinus tachycardia), or because it’s tracking electrical disturbances from outside the body. However, traditionally, PMT, also known as endless loop tachycardia (ELT), refers to a type of fast heartbeat that happens in patients who have a two-chamber pacemaker. Here, the pacemaker forms the forward part of the looping electrical circuit responsible for heartbeats, while the AV node (or an alternate electrical pathway) forms the backward part of this loop.
What Causes Pacemaker Mediated Tachycardia?
Pacemaker mediated tachycardia, a type of fast heart rate issue, can be started and kept going due to several factors:
* The pacemaker must be set up in a way that it can detect the heartbeat in the upper chambers of the heart (atrium) and send signals to the lower chambers of the heart (ventricles) to beat (in modes known as DDD or VAT). This is why this fast heart rate issue can’t happen in pacemakers that only work in one chamber, or in other operating modes like VVI or AAI.
* There needs to be some sort of event that separates the P wave, which represents the electrical signal for the atria to contract, from the QRS complex, which represents the ventricles’ contraction, and starts the fast heart rate. Often, this event is a premature beat in the ventricles or atrium. However, it can also happen when the pacemaker occasionally fails to detect the atrial heartbeat or fails to make the atrium contract.
* There must be backwards electrical signal travel, either through the AV node (the heart’s electrical junction box connecting the atria and the ventricles) or through an extra, unnecessary path.
Moreover, the electrical signals from the bottom chambers of the heart going backwards to the top chambers (known as ventriculoatrial or VA conduction) needs to last long enough to be picked up by the lead in the atrium. By lasting long enough, it means that the signals persist beyond the time in which the atria are unable to respond to a new electrical signal (the “refractory period”).
Risk Factors and Frequency for Pacemaker Mediated Tachycardia
Pacemaker mediated tachycardia, a heart condition caused by a malfunction in the pacemaker, occurs in about 30-80% of individuals with pacemakers. It’s especially prevalent in people with specific conditions like sick sinus syndrome and AV block, both of which are common reasons for getting a pacemaker.
- Pacemakers tend to cause this type of tachycardia in 30-80% of patients.
- People with sick sinus syndrome and AV block are more likely to have pacemaker mediated tachycardia.
- About 20% of patients with VA conduction and 6% of all pacemaker users have experienced an episode of pacemaker mediated tachycardia, as per a study.
Signs and Symptoms of Pacemaker Mediated Tachycardia
Patients with PMT, or Paroxysmal supraventricular tachycardia, can experience a variety of symptoms. These symptoms are usually a result of the rapid heart rate caused by the condition or the impact it has on the body’s circulatory system.
Some symptoms that PMT patients may experience include:
- Heart palpitations
- Chest pain
- Dizziness
- Fainting (syncope)
- Increased heart failure symptoms
Interestingly, many patients do not experience any symptoms at all.
In a physical examination, the doctor might not find any issues other than a fast heart rate (tachycardia). However, if the abnormal heart rhythm persists for a long time, then signs of low blood pressure (hypotension) or heart failure may become noticeable.
Testing for Pacemaker Mediated Tachycardia
If you have a dual-chamber pacemaker and experience a fast heart rate, know as tachycardia, you may need to consider a condition called Pacemaker-Mediated Tachycardia (PMT). An electrocardiogram (EKG), a test that measures the electrical activity of your heart, may show that the lower chambers of your heart are being paced at or slightly below the maximum rate. This is usually accompanied with the upper chambers of your heart (the atria) being sensed and an A-V association, which is a normal sequence of electrical activity traveling from the atria to the ventricles.
However, the most definitive way to diagnose PMT is by doing a device interrogation, an examination of the information recorded by your pacemaker, and looking at the recorded intracardiac electrograms, a chart demonstrating the electrical activity within the heart. In PMT, there is retrograde conduction – a reversed pattern, where the signals in the upper chambers of your heart follow signals from the lower chambers. Normally, signals from the upper chambers should come before the lower chambers. In layman’s terms, it’s like your heart beats in a reverse sequence because the pacemaker sends signals that disrupt the normal sequence of your heartbeat.
Treatment Options for Pacemaker Mediated Tachycardia
When you have a fast, irregular heartbeat due to your pacemaker (a condition known as PMT), there are several ways to manage it. One common way is to use a magnet. When a magnet is placed over the part of your body where the pacemaker is located, it can change the device into a set pacing mode. This means your pacemaker will keep a steady beat and won’t respond to extra heartbeats. By doing this, we can stop the fast, irregular heartbeat.
There are also other temporary measures which can help manage a fast heartbeat. For example, a gentle massage of the carotid artery in your neck or taking certain medications can help slow down the rapid heart rate. These medications work by blocking pathways in the heart that contribute to the irregular rhythm.
But to fully manage and prevent future episodes of PMT, we can adjust the settings of your pacemaker itself. One way we do this is to increase the period in which your pacemaker ignores signals from the heart. This adjustment makes it less likely that an irregular rhythm will be triggered. Another way is to fine-tune the pacemaker to only pick up on signals arising from your normal heart rhythm, while not picking up signals that can cause the irregular rhythm.
Modern pacemakers have special features that detect and stop PMT early on. These features might adjust the pacemaker settings in response to your heart rate, delay a beat if the heart rhythm is too fast, or skip a beat if the pacemaker has been working at its maximum capacity for a certain period.
What else can Pacemaker Mediated Tachycardia be?
If your heart has a rapid beat, like with atrial fibrillation or flutter, a heart device called an atrial lead can sense this and cause your heart’s ventricles to match this rapid pace. This behavior is different from what’s called PMT, or Pacemaker-Mediated Tachycardia, and doctors can tell the difference by looking at detailed heart wave patterns from inside your heart.
Other factors, such as electromagnetic interference or muscle signals from your chest wall, can also affect the function of your pacemaker, causing it to set your heart beating at its fastest possible speed.
Additionally, some pacemakers have a feature allowing them to react to different activity levels. If this feature is too sensitive or has an overly steep response curve, you may find your heartbeat speeding up even during low-level activities or normal bodily functions.
What to expect with Pacemaker Mediated Tachycardia
The long-term outlook is typically not affected by PMT, or premature ventricular contractions, and with the right treatment steps, it’s easy to treat, and reoccurrences can be prevented. However, it’s important to understand that long-lasting episodes could cause a worsening of heart failure due to the impact of rapid heartbeats in reducing the time for the heart to fill with blood.
Possible Complications When Diagnosed with Pacemaker Mediated Tachycardia
Periodic limb movements during sleep usually do not lead to lasting health issues. However, some people may feel dizzy or faint, which could lead to injuries such as a bump on the head.
Possible Symptoms:
- Dizziness
- Fainting (Syncope)
- Potential head injury as a result of fainting
Preventing Pacemaker Mediated Tachycardia
If you have a permanent pacemaker, it’s important to know that sometimes these devices can cause abnormal heart rhythms that may make your health worse. That’s why it’s crucial to regularly see your heart rhythm specialist to have routine checks on your device. During these check-ups, they can spot any unusual patterns and adjust the settings on your pacemaker if needed.
It’s also important to pay attention to how your heart feels. If you notice that your heart is beating faster than usual, or if you have symptoms like feeling faint or experiencing chest pain, it’s critical to take these signs seriously. When this happens, make sure to get medical help right away.
