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| [[Puzzle_2006_3_108 Answer|Answer]] | | [[Puzzle_2006_3_108 Answer|Answer]] |
| [[Image:Puzzle_2006_3_108_fig2.jpg|Figure 2|thumb]]
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| The ECG shows sinus rhythm (90 beats/min). The
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| electrical axis is shifted to the right. The PQ interval is
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| short (100 ms) and the QRS width is wide (120 ms).
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| There is initial slurring of the QRS complex, which is
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| positive in leads II, III, aVF, V2 to V5 and negative in
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| leads I and aVL. This indicates an initial electrical force
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| away from the left lateral free wall and can only be
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| based on activation via a Kent bundle, located in the
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| left lateral free wall. However, the terminal portion of
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| the QRS complex is slurring as well. It is negative in
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| the left lateral leads (I, aVL, V6) and positive in lead aVR
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| indicating a terminal force in the upward right direction,
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| which is obviously not explained by the intial ventricular
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| activation via the left lateral accessory pathway. This
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| configuration is compatible with right ventricular delay
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| (i.e. right bundle branch block). The lack of a terminal
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| R in lead V1 might be due to a slightly lower placement
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| of this lead. Hence, ventricular activation is the result of
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| pre-excitation via a left lateral Kent bundle and AV nodal
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| conduction with a pre-existent right bundle branch
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| block. Figure 2 shows the ECG (standard calibration)
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| after RF ablation of the bypass which indeed was located
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| in the left lateral wall. The PQ interval is longer and the
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| initial activation is now normal. As already anticipated
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| from the above analysis, the terminal right ventricular
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| activation and the QRS width are compatible with coexistent
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| right bundle branch block.
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