Multifocal Atrial Tachycardia (MAT) is a type of supraventricular tachycardia that originates in the atria (the heart’s two upper chambers). To understand MAT, it first helps to understand the heart’s normal electrical system.

A healthy heartbeat is controlled by the sinoatrial (SA) node, a small cluster of specialized cells in the right atrium. The SA node acts as the heart’s natural “chief pacemaker,” firing off regular electrical impulses that cause the heart to contract in a steady, coordinated rhythm, typically between 60 and 100 times per minute at rest.

In MAT, this orderly system collapses. Due to an underlying illness putting the body under immense stress, multiple different locations within the atria become highly irritable and start firing off their own rapid electrical impulses, all competing to be the pacemaker.

A helpful analogy is to think of the heart’s electrical system as an orchestra. The SA node is the conductor, standing at the front and setting a steady, regular beat for all the musicians to follow. In MAT, it is as if at least three different musicians in the atrial section have all decided they are the conductor. They start firing off their own signals at random, creating a chaotic, disorganized, and fast tempo. The heart’s lower chambers (the ventricles) try to keep up with this barrage of conflicting signals, resulting in a rapid and irregularly irregular heartbeat.

MAT is defined by three specific criteria on an electrocardiogram (ECG or EKG), the test that records the heart’s electrical activity:

1. Heart rate over 100 beats per minute.
2. An irregularly irregular rhythm.
3. The presence of at least three different forms (morphologies) of P-waves in the same ECG lead. (The P-wave is the part of the ECG that represents the electrical signal from the atria).

This third criterion is what confirms the “multifocal” nature of the arrhythmia, the different P-wave shapes prove that the signals are coming from multiple different locations within the atria. This helps doctors distinguish MAT from the more common irregular arrhythmia, atrial fibrillation (AFib), in which there are no discernible P-waves at all.

In my experience, MAT can sneak under the radar, often showing up as fast, irregular heartbeats in hospitalized or chronically ill patients, especially those with breathing issues.

MAT is caused by the electrical irritability of multiple sites within the atria. However, this irritability is not a primary problem with the heart’s electrical system itself. Instead, it is almost always triggered by a significant underlying physiological stressor that is affecting the entire body. The chaotic heart rhythm is a consequence of another severe medical condition. The stress from these conditions, particularly low oxygen levels (hypoxia) and high levels of adrenaline-like substances, is what makes the atrial cells unstable and prone to firing spontaneously.

Clinically, I’ve often seen MAT appear in hospitalized patients with low oxygen levels and multiple comorbidities, it’s more of a warning sign than a standalone diagnosis.

MAT develops as a complication of a severe acute or chronic illness. It is a condition most often seen in elderly patients who are already hospitalized with serious medical problems.

Severe Lung Disease: The Leading Cause

The single most common association, found in an estimated 60% of all MAT cases, is severe pulmonary (lung) disease. The arrhythmia is often triggered by an acute worsening of a chronic lung condition. These include:

• Chronic Obstructive Pulmonary Disease (COPD): An acute exacerbation of COPD is the most common MAT trigger.
• Pneumonia: A serious lung infection.
• Pulmonary Embolism: A blood clot in the lungs.
• Respiratory Failure: Any condition leading to very low oxygen and high carbon dioxide levels in the blood.

The strain that these conditions place on the right side of the heart, combined with low oxygen levels, is thought to be the primary driver of the atrial irritability that leads to MAT (American Heart Association, 2022).

Other Associated Conditions and Triggers

While lung disease is the most common cause, other conditions can also trigger MAT:

• Cardiac Conditions: Congestive heart failure and coronary artery disease can be associated with MAT. It can also occur in the period immediately following major heart surgery.
• Metabolic Disturbances: Severe imbalances in the body’s electrolytes can make the heart’s electrical system unstable. The most common disturbances linked to MAT are:
  • Hypokalemia (low potassium).
  • Hypomagnesemia (low magnesium).
• Medications: The overuse of certain medications, particularly bronchodilators like theophylline or high doses of inhaled beta-agonists used to treat asthma and COPD, can sometimes trigger the arrhythmia.
• Other Severe Illness: Any state of severe physiological stress, such as sepsis (a body-wide infection) or the period after a major non-cardiac surgery, can lead to MAT.

I remind my patients and their families that MAT is usually reversible, but it’s a red flag that the body is under significant stress.

MAT symptoms are often overshadowed by the severe symptoms of the underlying illness. For example, a patient with a severe COPD exacerbation will be primarily focused on their extreme shortness of breath and difficulty breathing, not necessarily their heart rhythm.

When the rapid and irregular heartbeat of MAT does cause symptoms, they can include:

• Palpitations: A common symptom, described as a feeling of a rapid, fluttering, chaotic, or pounding heartbeat.
• Dizziness or Lightheadedness.
• Shortness of Breath: This can be difficult to distinguish from the shortness of breath caused by the underlying lung disease.
• Chest Pain or Discomfort (Angina).
• Syncope (Fainting): This is less common but can occur if the heart rate is extremely fast, causing a significant drop in blood pressure.

In many cases, MAT is an asymptomatic finding discovered on an ECG performed during the evaluation of a patient’s primary illness.

I’ve seen patients with COPD who report worsening breathlessness and are surprised to learn their irregular heartbeat was contributing to their symptoms.

MAT is diagnosed by a 12-lead electrocardiogram (ECG or EKG). A doctor or technician will place electrodes on the patient’s chest, arms, and legs to get a detailed recording of the heart’s electrical activity.

As mentioned previously, a cardiologist or other trained physician will look for the three specific diagnostic criteria on the ECG trace:

1. Tachycardia: A heart rate over 100 beats per minute.
2. Irregularly Irregular Rhythm: The distance between the heartbeats (the R-R interval) is variable and has no predictable pattern.
3. Variable P-wave Morphology: There must be at least three different shapes of P-waves visible in the same lead, confirming that the electrical signals are originating from multiple different points in the atria.

The Diagnostic Workup

Once MAT is identified on the ECG, the healthcare team’s focus immediately shifts to diagnosing and treating the underlying cause. The arrhythmia itself is a red flag signaling a deeper problem. The workup will typically include:

• A thorough physical examination, focusing on the lungs and cardiovascular system.
• Blood Tests: To check for signs of infection, to measure levels of electrolytes like potassium and magnesium, and to check arterial blood gases to assess oxygen and carbon dioxide levels.
• Chest X-ray: To look for evidence of pneumonia, heart failure, or other lung abnormalities.
• Other tests as needed, like a CT scan to look for a pulmonary embolism.

In practice, MAT should prompt a thorough search for systemic triggers, treating the rhythm without correcting the cause rarely helps long term.

The main goal is treating the underlying cause of MAT. It is a consequence of another illness, and the arrhythmia will not resolve until the condition that is triggering it is brought under control. The primary treatment for MAT is to treat lung disease, infection, or metabolic problem.

1. Treating the Underlying Trigger

• Aggressively treat a COPD or asthma exacerbation with bronchodilators, oxygen, and systemic steroids.
• Administer intravenous antibiotics for pneumonia or sepsis.
• Provide supplemental oxygen to correct hypoxia.
• Vigorously replenish electrolytes, especially magnesium and potassium.
• Discontinue any potentially offending medications.

In many cases, as the patient’s underlying condition improves and their physiological stress lessens, the MAT will resolve on its own without any direct cardiac intervention.

2. Managing the Heart Rate

If the heart rate from MAT remains very rapid (e.g., over 130-140 beats per minute) and is causing symptoms like low blood pressure or worsening heart failure after treatment for the underlying cause has begun, then medications may be used to slow the heart rate.

• Caution is Key: The choice of medication is very delicate because the drugs typically used to slow the heart rate can have negative effects on patients with severe lung disease.
• Calcium Channel Blockers (like verapamil or diltiazem) or Beta-Blockers (like metoprolol) are often used, but they must be administered with extreme caution as they can potentially worsen bronchospasm in patients with severe COPD or asthma.
• It is important to note that electrical cardioversion (an electric shock to the heart) is not effective for treating MAT because there are too many chaotic sites in the atria for a single shock to reset the rhythm.

Prognosis

The prognosis, or outlook, for a patient with MAT is not determined by the arrhythmia itself. The arrhythmia is generally not life-threatening. The prognosis is determined entirely by the severity of the patient’s underlying disease (Merck Manual, 2023). MAT is a marker of severe illness, and as such, it is associated with a high mortality rate. But this mortality is from the underlying condition, not the heart rhythm.

I always stress to colleagues: MAT is more of a clinical signal than a cardiac emergency, it tells us the patient’s underlying condition needs urgent attention.

Multifocal Atrial Tachycardia is a rapid, irregular heart rhythm that serves as a critical diagnostic clue for physicians. It is not a primary cardiac arrhythmia but rather a manifestation of severe physiological stress on the body, most often from an exacerbation of a chronic lung disease like COPD. Its presence on an ECG is a red flag that directs the medical team to aggressively search for and treat the root cause of the patient’s illness. While the chaotic heartbeat can be concerning, the most effective treatment for Multifocal Atrial Tachycardia is, in fact, the successful treatment of the underlying lung, metabolic, or infectious disease that has put the heart under such extreme stress.

American Heart Association. (2022). Other Tachycardia. Retrieved from https://www.heart.org/en/health-topics/arrhythmia/about-arrhythmia/other-tachycardia

Merck Manual Professional Version. (2023). Multifocal Atrial Tachycardia. Retrieved from https://www.merckmanuals.com/professional/cardiovascular-disorders/arrhythmias-and-conduction-disorders/multifocal-atrial-tachycardia