A rapid heart rate caused by inappropriate electrical impulses arriving at the ventricles (the lower chambers of the heart) from multiple locations within the atria (the upper chambers of the heart).
Causes, incidence, and risk factors
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. This controls its 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 (M.A.T.), 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.
M.A.T.is most common in people 50 years old and over and it is often seen in patients admitted to the intensive care unit. These patients need critical care because M.A.T. 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 . M.A.T. can also occur in coronary heart disease , can be caused by surgery within the last 6 weeks, overdose of theophylline or digitalis, diabetes mellitus , and sepsis (widespread systemic infection).
Signs and tests
An examination shows a heart rate of 100 to 180 beats per minute. Blood pressure is normal or low. There may be signs of poor circulation.
Tests that reveal M.A.T. include:
ECG Continuous ambulatory monitoring (24-hour Holter monitor ). For hospitalized patients, the heart rhythm is monitored 24 hours a day with telemetry.
Long-term loop recorders: outpatients who may have M.A.T. not detected during a Holter monitoring session can receive these portable systems, which allow the person to trigger the recording if symptoms appear. Electrophysiologic study (EP study). If doubts persist about the the diagnosis, or if there are additional arrhythmias which can complicate diagnosis, your doctor may recommend an EPS. During an EPS, wires are inserted through your veins up to your heart to study the cardiac conduction system.
Treatment
Any underlying conditions that can precipitate M.A.T should be treated first. Improving oxygenation, administering intravenous magnesium, and discontinuing certain medications -- such as theophylline -- may be enough to terminate the M.A.T. Anti-arrhythmic agents such as calcium channel blockers (verapamil, diltiazem) or selective beta-blockers may be needed to control the disorder in some patients.
Expectations (prognosis)
M.A.T. is controllable if the underlying condition can be controlled.
Calling your health care provider
Call your health care provider if:
Rapid or irregular heartbeat is associated with other M.A.T. symptoms.
Symptoms worsen, do not improve with treatment, or new symptoms develop.
Prevention
To reduce the risk of developing M.A.T., promptly treat the disorders that cause it.