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Diagnostic Tests – Multifocal Atrial Tachycardia (MAT)
Overview of MAT
Multifocal atrial tachycardia (MAT) is an arrhythmia in which the atria initiate electrical impulses from multiple different pacemaker sites rather than a single dominant focus. This leads to a rapid heart rhythm—typically over 100 beats per minute—with identifiable but variable P waves, each originating from a different atrial location. Unlike atrial fibrillation, where the baseline is chaotic and true P waves are absent, MAT shows distinct P-wave activity even though the atrial rhythm is disorganized. The impulses still travel through the AV node, producing normal, narrow QRS complexes that appear at irregular intervals.
EKG Characteristics
One of the key diagnostic features of MAT is its irregular timing between beats. Both P–P intervals and R–R intervals vary continuously, giving the rhythm an “irregularly irregular” appearance. What sets MAT apart from similar arrhythmias is the presence of at least three different P-wave morphologies, reflecting shifting atrial pacemaker sites. Because each focus conducts through the AV node differently, the PR intervals also change from beat to beat. When the heart rate is below 100 beats per minute but the same shifting pacemaker pattern is present, the rhythm is called a wandering atrial pacemaker, which represents a slower version of the same phenomenon.
Most Common Causes
The condition is most strongly linked to chronic lung disease, particularly during exacerbations of chronic obstructive pulmonary disease (COPD). Chronic hypoxia, hypercapnia, and increased sympathetic tone disrupt atrial electrical stability, causing multiple atrial sites to fire chaotically. Right atrial enlargement or stretch from long-standing pulmonary hypertension further destabilizes atrial conduction. Electrolyte abnormalities—especially low potassium or magnesium—often worsen atrial irritability. Medications such as theophylline, historically used for COPD, can also provoke MAT due to their stimulatory effects on the heart. Although conditions like pulmonary embolism and severe congestive heart failure can also produce similar arrhythmias, COPD remains the most common underlying cause.
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