Shown below is an electrocardiogram depicting supraventricular tachycardia with group ventricular beating with clusters of regular rhythm at about 215 bpm. The regularity and group beating suggest that this is an organized rhythm and not atrial fibrillation. The interval between the 6th and 7th beats in lead II show atrial activity at about 215/min. This is a case where the diltiazem has slowed down the SVT which has allowed faster conduction down the AV node and hence increased ventricular rate.

Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/File:E2722.jpg

Shown below is an electrocardiogram of a supraventricular tachycardia. There appears to be a P wave on the last part of the last sinus T wave suggesting that this may be an ectopic atrial tachycardia or possibly an atypical form of A/V nodal reentry where one sees the retrograde P wave before the QRS.

Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/Main_Page