A Narrow QRS Complex Tachycardia Sensitive to Isoptin

Author(s) A.A.M. Wilde, R.H. Bakker
NHJ edition: 2006,08:268
These Rhythm Puzzles have been published in the Netherlands Heart Journal and are reproduced here under the prevailing creative commons license with permission from the publisher, Bohn Stafleu Van Loghum.
The ECG can be enlarged twice by clicking on the image and it's first enlargement

A 54-year-old man presented with palpitations. He had no other symptoms. Physical examination revealed, with the exception of a fast regular heart rhythm (200 beats/min), no abnormalities. His ECG is shown in figure 1. Intravenous verapamil terminated the tachycardia and a second ECG (figure 2) was taken.

Figure 1
Figure 2

What is your diagnosis?