II. PALPITATIONS, PREMATURE BEATS, AND IRREGULAR BEATS
Premature beats that arise from the atrium are called atrial premature beats (APBs). An atrial premature P-wave has a morphology different from that of the sinus P-wave and is usually followed a QRS complex similar to that of the normally conducted sinus beat (see Fig. 2). Atrial premature beats may trigger atrial tachycardia or atrial fibrillation.
2. Ventricular Premature Beats
Premature beats that arise in the ventricle are called ven¬tricular premature beats. These are bizarre looking beats with a wide QRS complex and an ST segment sloping off in a direction opposite to the abnormal QRS complex (see Fig. 3). There is no preceding P-wave and the extra beat is followed by a fully compensatory pause before the next normal sinus beat occurs. When this happens, the individual may feel that the heart has stopped for a second. A VPB following each normal beat (termed ventricular bigeminy) is a common occurrence in healthy individuals, but pairs (couplets) or runs of three beats (triplets, nonsustained ventricular) are not uncommon in those with heart disorders (see Figs. 3 and 4).