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'''What is your diagnosis?''' | '''What is your diagnosis?''' | ||
[[Puzzle_2006_11_393_Answer|Answer]] | |||
Figure 1 shows a narrow-complex tachycardia with an | |||
RR interval of 390 msec (rate 155 beats/min). In the | |||
latter part the arrhythmia is slightly slower (RR interval | |||
410). In the differential diagnosis of any narrowcomplex | |||
tachycardia, the position of the P wave (and | |||
its number) is critical for the correct diagnosis. | |||
A close look for the P waves reveals a P wave in | |||
every other T wave in the left part of the ECG. After | |||
the 15th QRS complex, the P wave is present in every | |||
T wave (see rhythm strip lead II at the bottom of the | |||
ECG and figure 3, arrows). Comparison of the T waves | |||
with and without superimposed P waves reveals a | |||
negative morphology of the P wave in lead II. In lead | |||
aVR the morphology is clearly positive. The timing of | |||
the P wave is between 40 and 80 ms after the QRS | |||
complex. | |||
The number of P waves indicates a dissociation | |||
between the atrial and ventricular rate and the morphology | |||
indicates retrograde (VA) conduction. The | |||
presence of VA dissociation is only compatible with | |||
AV-nodal reentrant tachycardia and it excludes AVreentry | |||
tachycardia (orthodromic circus movement | |||
tachycardia), atrial tachycardia and atrial flutter, the | |||
most important differential diagnostic entities for a | |||
narrow-complex tachycardia with the present rate. A | |||
rare alternative diagnosis would be a His-bundle tachycardia | |||
with 2:1 VA conduction. Actually the position | |||
of the P wave would be in favour of this diagnosis. | |||
An invasive electrophysiological study revealed the | |||
presence of dual nodal characteristics and, under | |||
isoprenaline, the induction of an AV-nodal reentrant | |||
tachycardia. Slow pathway ablation successfully | |||
modified the arrhythmogenic substrate. |