Premature Atrial Beats and Complexes
Premature Atrial Beats and Complexes
Supraventricular premature beats and complexes are electrical signals that originate within the atria or the AV node instead of the SA node.
Premature atrial beats (PABs) and premature atrial complexes (PACs) are triggered from within the atrial myocardium and can occur in different clinical situations. They can be triggered by anxiety, the use of sympathomimetic or beta-agonist drugs, digoxin toxicity, excess caffeine intake, hypokalemia, hypomagnesemia, and myocardial ischemia. They occur more frequently than premature supraventricular beats that arise from the AV junction.
PABs and PACs appear before the next normally expected sinus P wave and present with a deformed P wave. The change in P wave morphology indicates that the origin of signal conduction is located away from the SA node but in the right atrium. The PR interval may be shorter or longer than normal, depending on the site of origin of the PAB.
Patients who present with a heart rate faster than baseline have a PAB with an abnormal P wave hidden within the preceding T wave. The effect produces a peaked or camel hump appearance of the T wave, which also makes the PAB harder to identify.
When the origin of the electrical signal is a focus near the coronary sinus (i.e., a location in the inferior aspect of the right atrium), the ECG shows negative P waves in the inferior leads II, III, and aVF. If the site of the electrical signal is a focus in either the right or left atrium, the negative P wave appears in leads I, aVL, V5, and V6. If the precordial lead V1 shows a positive p wave, then only the left atrium is involved.