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| [[Puzzle_2007_1_33_Answer|Answer]] | | [[Puzzle_2007_1_33_Answer|Answer]] |
| [[Image:Puzzle_2007_1_33_fig2.png|Figure 2|thumb]] | | [[Image:Puzzle_2007_1_33_fig2.png|Figure 2|thumb]] |
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| The ECG shows sinus rhythm with a mean rate of 60
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| beats/min. There is some sinus arrhythmia present.
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| Conduction intervals are normal (PR 150 ms, QRS
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| 90 ms). Repolarisation abnormalities are present in the
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| right precordial leads V1 to V3 (terminal negative T
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| waves) and the ST-T segment in lead V4 is flat.
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| Two wide complexes are seen, the third and tenth
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| QRS complex. Both share a similar morphology with
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| a left bundle branch block and an almost vertical axis.
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| There is no discernible P wave prior to these wide QRS
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| complexes and the first is followed by a complete compensatory
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| pause in contrast to the second which does
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| not influence the underlying sinus rhythm. The
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| morphology of the wide complexes, the lack of P waves
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| and the presence of a complete compensatory pause all
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| point to a ventricular origin of this activity. Based on
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| the morphology, an origin in the right ventricular
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| outflow track (RVOT) is likely. In combination with
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| the ST-T segment abnormalities one should consider
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| arrhythmogenic right ventricular dysplasia (ARVD/C)
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| and additional imaging should be performed.
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| There are several electrocardiographic peculiarities
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| in this electrocardiogram. First, the second ventricular
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| extrasystole is not intervening with the sinus rhythm.
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| This is referred to as an interpolated ventricular extrasystole.
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| This is a relatively rare phenomenon usually
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| seen with a slow heart rate. In this case the heart rate
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| is not really slow.
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| Second, the conducting P wave of the P wave
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| following this extrasystole has a longer PR interval
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| (figure 2). This phenomenon is referred to as concealed
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| retrograde conduction; i.e. the ventricular extrasystole
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| conducts retrogradely in the AV node slowing the
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| anterograde conducting P wave. In the case of the first
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| extrasystole retrograde conduction actually blocks the
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| antegrade P wave completely.
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| In conclusion, this is a sinus rhythm with ventricular
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| extrasystoles originating in the RVOT (one of them
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| interpolated) with retrograde penetrance in the AV
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| node. The ST-T segment abnormalities in combination
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| with the extrasystole’s origin suggest the presence of
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| ARVC.
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