Multifocal atrial tachycardia
Synonyms and keywords: MAT, Chaotic atrial tachycardia, Supraventricular tachycardia

# Overview
Multifocal atrial tachycardia (MAT) is a cardiac arrhythmia which is specifically a type of supraventricular tachycardia with an irregular, rapid atrial rhythm arising from multiple ectopic foci within the atria with a heart rate exceeding 100 beats per minute. It is characterized by an organized atrial activity yielding three or more different non-sinus P wave morphologies in the same lead with variable or irregular PP, PR and RR intervals. There's an isoelectric baseline between P waves with the most P waves being conducted to the ventricles and some R waves being aberrantly conducted. This variability pattern makes MAT look irregular on the surface ECG, thus oftenly leading to misinterpretion as atrial fibrillation. It is typically seen in elderly patients with a variety of underlying comorbidities, the most common being chronic obstructive pulmonary disease (COPD) and congestive heart failure (CHF) and eventually it develops into atrial fibrillation. A rhythm with similar ECG characteristics but at a slow rate is referred to as multifocal atrial rhythm (MAR). The pathogenesis of MAT is not well understood and the patients are generally asymptomatic with mostly being hemodynamically stable. Typically, no treatment is required beyond treatment of underlying conditions in the majority of the MAT patients. However, it is very important to evaluate such patients as this arrhythmia is a poor prognostic sign in the setting of an acute illness.

# Historical Perspective
- In the late 1960s, the term ''MAT'' became a commonplace terminology.
- In 2001, Bradley et al reported the clinical course of MAT in infants and children.

# Pathophysiology
- The exact pathology behind production of MAT is not well understood, however, the multiple discrete p wave morphologies along with variable PR intervals suggest an atrial pacemaker activity most likely originating from multiple ectopic foci within the atria. Hence, each unique P wave corresponds to a different site of atrial origin.
- The possible underlying mechanism for MAT includes:
Right atrial enlargement
Hypoxia
Hypercapnia
Adrenergic stimulation in pulmonary disease
- Right atrial enlargement
- Hypoxia
- Hypercapnia
- Adrenergic stimulation in pulmonary disease
- MAT has been reported in >20% of the pediatric patients and up to 60% of the adult patients with coexisting pulmonary disease.
- The following factors are considered to be responsible for the infant-predominant age distribution of MAT and its favorable outcome in idiopathic infant cases:
The immaturity of both the lungs and the heart in infants.
The growth and development of bronchopulmonary system and pulmonary vessels in infants continues for at least 2 years (unlike that in adults).
Immature and vulnerable atrium in utero is considered as an important contributor for fetal MAT detected in utero.
- The immaturity of both the lungs and the heart in infants.
- The growth and development of bronchopulmonary system and pulmonary vessels in infants continues for at least 2 years (unlike that in adults).
- Immature and vulnerable atrium in utero is considered as an important contributor for fetal MAT detected in utero.
- The following table shows the proposed theories explaining the underlying mechanism of MAT but none of these theories has yet been demonstrated conclusively.

# Causes
Following is a list of potential causes of multifocal atrial tachycardia:

## Life Threatening Causes
Life-threatening causes include conditions which may result in death or permanent disability within 24 hours if left untreated and include the following:
- Aminophylline toxicity
- Theophylline toxicity
- Isoproterenol toxicity
- Congestive heart failure
- Hypokalemia
- Hypoxia
- Myocardial infarction
- Pulmonary embolism
- Sepsis
- Pneumomediastinum (is a complication of surgical emphysema, the MAT gets reverted to sinus rhythm after aspiration of air from mediastinum).

## Common Causes
- Chronic obstructive pulmonary disease is the most common cause, as MAT is associated with:
60% cases of significant lung disease
20% patients of acute respiratory failure
17% patients hospitalized with COPD
- 60% cases of significant lung disease
- 20% patients of acute respiratory failure
- 17% patients hospitalized with COPD
- Chronic renal failure
- Congestive heart failure
- Coronary artery disease
- Diabetes mellitus
- Major surgery
- Hypokalemia
- Hypoxia
- Myocardial infarction
- Valvular heart disease
- Pneumonia
- Pulmonary embolism
- Sepsis

## Causes by Organ System

## Causes in Alphabetical Order
- Aminophylline
- Chronic obstructive pulmonary disease
- Chronic renal failure
- Congestive heart failure
- Diabetes mellitus
- Hypercapnia
- Hypokalemia
- Hypomagnesemia
- Hypoxia
- Isoproterenol
- Lung cancer
- Myocardial infarction
- Pneumonia
- Postoperative complication
- Pulmonary embolism
- Sepsis
- Valvular heart disease

# Epidemiology and Demographics
- Multifocal atrial tachycardia is a relatively uncommon arrhythmia with low incidence.
- It is seen only in 0.05% to 0.32% of electrocardiograms in general hospital admissions.
- The average age of patients affected by MAT is approximately 70 years.
- Prevalence of pulmonary disease in MAT has been well established in adult MAT patients with up to 60% of the adult patients having a coexisting pulmonary disease, particularly those with chronic obstructive pulmonary disease.
- MAT is a relatively rare condition with clinical features not well established in pediatric ages.
- It accounts for less than 1% of supraventricular tachycardia in infants and children and is reported to affect >20% of the pediatric patients.
- Multifocal atrial tachycardia though rare in neonates, can be diagnosed prenatally by cardiotocography.
- MAT is difficult to treat in infancy but it resolves frequently and spontaneously within the first year of life.

# Natural history, Complications and Prognosis
- Multifocal atrial tachycardia is considered to be a relatively benign arrhythmia with likely good outcome in the absence of a severe underlying illness.
- MAT can be well controlled if treated with appropriate drugs along with a suggested long follow-up period.
- In the case of a required pharmacologic intervention, amiodarone is suggested as an excellent choice.
- Baek et al reported in a study that:
Usually, MAT affects infants with a favorable prognosis especially the idiopathic infant group.
But in the presence of other comorbidities with MAT, it may have a variable clinical course.
- Usually, MAT affects infants with a favorable prognosis especially the idiopathic infant group.
- But in the presence of other comorbidities with MAT, it may have a variable clinical course.
- Although most patients with multifocal atrial tachycardia are hemodynamically stable, still MAT is a poor prognostic sign in the setting of an acute illness.
- MAT is associated with a 60% in-hospital mortality rate.
- The mean survival of patients with MAT is just over one year.

# Diagnosis
The diagnosis of MAT is usually not clinical rather the following electrocardiographic diagnostic criteria is used:

## Electrocardiography
ECG of MAT has following characteristics:
- Atrial rate of greater than 100 beats per minute (although some also suggest a threshold of 90 beats per minute for MAT diagnosis)
- Irregularly irregular rhythm
- There are P waves of varying morphology from at least three different foci.
- There is an absence of one dominant atrial pacemaker.
- Variable or irregular PP intervals, RR intervals, and PR intervals (however, variation in PR intervals is not yet included in the diagnostic criteria because of the variation of PR interval depends on the length of the preceding RP interval).
- Can be mistaken for atrial fibrillation if the p waves are of low amplitude.

## Other diagnostic workup
- As multifocal atrial tachycardia is mostly associated with the underlying medical conditions such as cardiac and pulmonary disease, so its diagnosis does not typically warrant any additional workup, other than the workup required for the suspected underlying conditions.
- If the arrhythmia persists despite of treating the underlying medical conditions, following tests should be done to check for any signs of infection, anemia, or electrolyte abnormalities such as hypokalemia and hypomagnesemia:
Complete blood count
Serum chemistry panel
- Complete blood count
- Serum chemistry panel

## Challenges in MAT pediatric patients
- Pediatric practitioners usually face the following four challenges regarding MAT in children:

## History and Symptoms
- Mostly patients with multifocal atrial tachycardia are asymptomatic.
- MAT is often incidentally found during the routine electrocardiogram.
- Once the diagnosis of MAT is made, a thorough history should be obtained with main focus on commonly associated conditions such as cardiac and pulmonary diseases particularly congestive heart failure and chronic obstructive pulmonary disease respectively.
- The clinical manifestations of MAT differ from those of other tachyarrhythmias in that symptoms predominantly relate to the underlying precipitating illness rather than the arrhythmia itself.
- Patients usually present with:
Irregular heart rate greater than 100 beats per minute (mostly identified only during the physical examination by the health care provider)
Palpitations (rare)
Presyncope (rare)
Syncope (rare)
- Irregular heart rate greater than 100 beats per minute (mostly identified only during the physical examination by the health care provider)
- Palpitations (rare)
- Presyncope (rare)
- Syncope (rare)
- Picture of a typical MAT patient is as follows:
Elderly patient
Decompensated pulmonary disease
Decompensated heart failure
Postoperative
Usually hemodynamically stable (no severe hemodynamic compromise associated with MAT)
- Elderly patient
- Decompensated pulmonary disease
- Decompensated heart failure
- Postoperative
- Usually hemodynamically stable (no severe hemodynamic compromise associated with MAT)
- High mortality ECG features in MAT patients include:
P waves with 3 forms
Atrial rate usually 100 to 200 bpm
Irregular atrial rate
Variable PR interval
Isoelectric baseline between P waves
May progress to atrial fibrillation
- P waves with 3 forms
- Atrial rate usually 100 to 200 bpm
- Irregular atrial rate
- Variable PR interval
- Isoelectric baseline between P waves
- May progress to atrial fibrillation

## Physical Examination
- Physical examination findings of patients with multifocal atrial tachycardia include:
Elevated heart rate usually greater than 100 bpm
Irregularly irregular rhythm
Hemodynamically stable (mostly)
- Elevated heart rate usually greater than 100 bpm
- Irregularly irregular rhythm
- Hemodynamically stable (mostly)
- As MAT is associated with underlying medical conditions, hence, it is suggested to carry out a general assessment for the signs of cardiopulmonary disease, especially because MAT can trigger  the decompensation of underlying cardiac and pulmonary disease.

# Treatment

# Prevention

## Primary Prevention
- Patients with chronic obstructive pulmonary disease and congestive heart failure, both conditions associated with magnesium deficiency and MAT, should be treated with magnesium-sparing diuretics in order to prevent magnesium deficiency leading to MAT.

# Differentiating Multifocal Atrial Tachycardia from other Diseases
Multifocal atrial tachycardia must be differentiated from the following:
- Atrial fibrillation (has discrete P wave morphologies)
- Atrial flutter with variable AV node conduction (has regular PP intervals and flutter waves)
- Atrioventricular nodal reentry tachycardia (AVNRT)
- Paroxysmal supraventricular tachycardia
- Premature atrial contractions (PAC)
- Wolff-Parkinson-White syndrome (WPW)
- Ventricular fibrillation (VF)
- Ventricular tachycardia (VT) with frequent premature atrial contractions (has regular PP intervals)
- Wandering atrial pacemaker (has heart rate less than 100 beats per minute)