Atrial Tachycardia or Long RP Supraventricular Tachycardia!

The above electrocardiogram (ECG) was obtained in a patient with intermittent palpitations. The rhythm reveals regular narrow-QRS complex tachycardia at 133 beats per minute (BPM) as indicated by the green arrows in the rhythm strip. The atrial rhythm consists of negative P waves in the inferior leads, II, III and aVF, fusing with the T waves (red arrows) suggestive of a non-sinus origin. The initial impression, also suggested by the EKG machine automated reading, was atrial tachycardia. Closer scrutiny, however, of the P waves reveals that they are absent (blue stars) before the 8th and 14th QRS complexes. The absence of P waves despite the persistence of the QRS complexes makes atrial tachycardia highly unlikely, in which case a dropped atrial beat would be expected to result in a dropped QRS complex as well. Therefore, a more plausible explanation is that the rhythm is actually junctional or supraventricular tachycardia (SVT) with retrogradely conducted P waves and a long RP interval, with intermittent lack of VA conduction causing the dropped atrial beats.