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Patient
79-year-old man with no known history or intimation of palpitations, hospitalized for multiple lipothymia episodes;
Trace
This first tracing performed on arrival in the emergency department shows a typical tracing of left lateral accessory pathway (short PR and delta wave) with a major pre-excitation pattern and a very broad QRS;
Trace
On this second tracing, there are blocked sinus P waves and P waves followed by a pre-excited ventricle identical to those of the previous tracing; this tracing suggests the presence of a complete block of the normal atrioventricular conduction pathways explaining the maximum pre-excitation pattern (exclusive conduction by the accessory pathway) and a second degree block in the bundle of Kent (alternation between conducted P waves and blocked P waves);
Exergue
A patient with an anterograde permeable accessory pathway exhibits a fully preexcited pattern (maximum pre-excitation) following the occurrence of a conduction block on the nodo-Hisian pathway. The accessory pathway typically has a protective effect in this setting.
In a patient with Wolff-Parkinson-White syndrome, sinus rhythm is usually conducted to the ventricles through two different pathways; the atrioventricular node and the bundle of Kent, the QRS reflects fusion of these two activations.