A Particular Bigeminy During Atrial Tachycardia

The ECG shows clearly visible P waves only in lead V1 (Fig. 1). Regular PP intervals and an isoelectric baseline are present between the P waves, so the diagnosis is atrial tachycardia [1]. During the ECG recording, lead V1 shows 12 P waves but some of these are not visible because they are concealed by the QRS complex (Fig. 2). In lead V1, the beats following the long RR intervals are conducted by the first and the seventh P wave and the premature QRS complexes are conducted by the third and the ninth P wave because the fourth and the tenth P wave are too close to the following QRS complex to conduct the impulse. Consequently, the atrial tachycardia presents an alternating 2:1 and 4:1 conduction. However, the long RR interval is less than twice the short RR interval and the PR intervals of