Palpitations Again, Have a Closer Look: Difference between revisions

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[[Puzzle_2006_11_393_Answer|Answer]]
[[Puzzle_2006_11_393_Answer|Answer]]
[[Image:Puzzle_2006_11_393_fig2.jpg|Figure 3. Detail from the aVR, aVL and aVF leads during the tachycardia. The arrows point to the (retrograde) P top.|thumb]]
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.
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