Multifocal atrial tachycardia

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Heart, section through the middle

Multifocal atrial tachycardia

Definition:

Multifocal atrial tachycardia describes a rapid heart rate caused by inappropriate electrical impulses arriving at the lower heart chambers (ventricles) from multiple locations within the upper heart chambers (atria).

Causes, incidence, and risk factors:

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Normally, electrical impulses in the heart begin in the right atrium, in an area called the sinoatrial node (sinus node or SA node), which is the natural "pacemaker" of the heart. The node controls the heart's rhythm, which is essential to sustaining life.

The electrical impulses are conducted throughout the heart, and the heart responds to each impulse with a contraction. This usually occurs between 60 and 100 times per minute, so the normal heart rate in adults is 60 to 100 beats per minute. The normal rate is faster in children.

In multifocal atrial tachycardia (MAT), multiple locations within the atria "fire" and initiate an electrical impulse. Most of these impulses are conducted to the ventricles, leading to a rapid heart rate, anywhere from 100 to 250 beats per minute.

This very rapid rate greatly increases the heart's workload. Very rapid rates can also decrease the amount of time the heart has to fill with blood, which reduces the flow of blood to the brain and body.

MAT is most common in people aged 50 and over and it is often seen in patients admitted to the intensive care unit. These patients need critical care because MAT is usually associated with conditions that reduce the amount of oxygen in the blood: all types of respiratory failure, chronic pulmonary obstructive disease (COPD), bacterial pneumonia, congestive heart failure, lung cancer, and pulmonary embolism.

MAT is also associated with coronary heart disease, surgery within the last 6 weeks, overdose of theophylline, diabetes, and sepsis (widespread systemic infection).