Multifocal (or multiform) atrial tachycardia (MAT) is an
abnormal heart rhythm,
specifically a type of
supraventricular tachycardia
Supraventricular tachycardia (SVT) is an umbrella term for fast heart rhythms arising from the upper part of the heart. This is in contrast to the other group of fast heart rhythms – ventricular tachycardia, which start within the lower cham ...
, that is particularly common in older people and is associated with exacerbations of
chronic obstructive pulmonary disease
Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease characterized by long-term respiratory symptoms and airflow limitation. The main symptoms include shortness of breath and a cough, which may or may not produce ...
(COPD). Normally, the heart rate is controlled by a cluster of cells called the
sinoatrial node (SA node). When a number of different clusters of cells outside the SA node take over control of the heart rate, and the rate exceeds 100 beats per minute, this is called multifocal atrial tachycardia (if the heart rate is ≤100, this is technically not a
tachycardia
Tachycardia, also called tachyarrhythmia, is a heart rate that exceeds the normal resting rate. In general, a resting heart rate over 100 beats per minute is accepted as tachycardia in adults. Heart rates above the resting rate may be normal (su ...
and it is then termed multifocal atrial rhythm).
"Multiform" refers to the observation of variable
P wave shapes, while "multifocal" refers to the underlying cause. Although these terms are used interchangeably, some sources prefer "multiform" since it does not presume any underlying mechanism.
Causes
MAT usually arises because of an underlying medical condition. Its prevalence has been estimated at 3 per 1000 in adult hospital inpatients and is much rarer in paediatric practice; it is more common in the elderly, and its management and prognosis are both those of the underlying diagnosis.
It is mostly common in patients with lung disorders, but it can occur after acute
myocardial infarction
A myocardial infarction (MI), commonly known as a heart attack, occurs when blood flow decreases or stops to the coronary artery of the heart, causing damage to the heart muscle. The most common symptom is chest pain or discomfort which may ...
and can also occur in the setting of
low blood potassium or
low blood magnesium
Magnesium deficiency is an electrolyte disturbance in which there is a low level of magnesium in the body. It can result in multiple symptoms. Symptoms include tremor, poor coordination, muscle spasms, loss of appetite, personality changes, and ...
.
It is sometimes associated with
digitalis toxicity in patients with heart disease.
It is most commonly associated with
hypoxia
Hypoxia means a lower than normal level of oxygen, and may refer to:
Reduced or insufficient oxygen
* Hypoxia (environmental), abnormally low oxygen content of the specific environment
* Hypoxia (medical), abnormally low level of oxygen in the tis ...
and
COPD. Additionally, it can be caused by
theophylline toxicity, a drug with a narrow therapeutic index commonly used to treat COPD. Theophylline can cause a number of different abnormal heart rhythms when in excess, and thus further predisposes COPD patients to MAT. Theophylline toxicity often occurs following acute or chronic overtreatment or factors lowering its clearance from the body.
Pathophysiology
The P-waves and P–R intervals are variable due to a phenomenon called wandering atrial pacemaker (WAP). The electrical impulse is generated at a different focus within the atria of the heart each time. WAP is positive once the heart generates at least three different P-wave formations from the same ECG lead. Then, if the heart rate exceeds 100 beats per minute, the phenomenon is called multifocal atrial tachycardia.
Diagnosis
Multifocal atrial tachycardia is characterized by an
electrocardiogram (ECG) strip with three or more discrete P wave morphologies in the same lead, not including that originating from the sinoatrial node, plus tachycardia, which is a heart rate exceeding 100 beats per minute (although some suggest using a threshold of 90 beats per minute). Furthermore, there should be irregular PP intervals, and the baseline should be isoelectric between P waves. Other findings that are commonly seen, but are not diagnostic include irregular PR and RR intervals. Variation in PR intervals has not been included in the diagnostic criteria because the PR interval varies with the length of the preceding RP interval.
[ ]
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Other diagnoses that may present with similar findings on electrocardiogram that should be included in the differential diagnosis include sinus tachycardia with frequent premature atrial contractions (this would have regular PP intervals), atrial flutter with variable AV node conduction (this would have regular PP intervals and flutter waves), atrial fibrillation (this would not have discrete P-wave morphologies), and wandering atrial pacemaker which would have a heart rate less than 100 beats per minute).
[
]
Additional workup
If arrhythmia persists despite the treatment of underlying medical conditions it may be worth checking a complete blood count and serum chemistry for signs of infection, anemia, or electrolyte abnormalities such as hypokalemia and hypomagnesemia.[
]
Treatment
Management of multifocal atrial tachycardia consists mainly of the treatment of the underlying cause.[ If treatment is indicated, therapy should begin with first correcting underlying electrolyte abnormalities with the repletion of potassium to maintain greater than 4 mEq/L and magnesium greater than 2 mEq/L. Studies have shown magnesium suppresses ectopic atrial activity and can be beneficial even if magnesium levels are within the normal range. Once electrolyte abnormalities have been corrected, possible treatment options include non-dihydropyridine calcium channel blockers, beta-blockers, and atrioventricular (AV) node ablation. Studies have found no role for antiarrhythmic agents, cardioversion, or anticoagulation. In the absence of underlying pulmonary disease, the first-line agent is beta-blockers. A beta-blockers act to suppress ]ectopic foci
An ectopic pacemaker, also known as ectopic focus or ectopic foci, is an excitable group of cells that causes a premature heart beat outside the normally functioning SA node of the heart. It is thus a cardiac pacemaker that is ectopia (medicine), ...
by reducing sympathetic stimulation and decreasing conduction through the atrioventricular node, thereby slowing the ventricular response. Studies have found an average decrease in heart rate of 51 beats per minute and 79% of patients reverted to sinus rhythm. Most patients did not need beta-blocker therapy long term as studies found long-term therapy was needed in only 25% of patients. Caution should be used in patients with an underlying pulmonary disease such as COPD and patients with decompensated heart failure due to the increased risk for bronchospasms and decreased cardiac output. Furthermore, beta-blockers should be avoided in patients with atrioventricular blocks unless a pacemaker has been implanted.[
In the presence of underlying pulmonary disease, the first-line agent is a non-dihydropyridine calcium channel blocker such as verapamil or diltiazem. These agents act to suppress atrial rate and decrease conduction through the atrioventricular node, thereby slowing the ventricular rate. Studies have found an average reduction in the ventricular rate of 31 beats per minute and 43% of patients reverted to sinus rhythm. Caution should be used in patients with preexisting heart failure or hypotension due to negative inotropic effects and peripheral vasodilation. Similarly, calcium channel blockers should also be avoided in patients with atrioventricular blocks unless a pacemaker has been implanted.][
In select cases of refractory multifocal atrial tachycardia, AV node ablation has been performed. Studies have found an average reduction in the ventricular rate of 56 beats per minute with adequate control of ventricular response in 84% of patients. However, AV node ablation creates a complete heart block and requires the placement of a permanent pacemaker.][
Administration of ]oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
may play a role in the treatment of some patients.
References
External links
{{Circulatory system pathology
Cardiac arrhythmia