Orthodromic AVRT and functional left bundle branch block

Patient

54-year-old man with metabolic syndrome treated with flecainide and beta-blocker; palpitations; first tracing recorded during an episode of palpitations;

Trace

Narrow QRS tachycardia with probable 1:1 relationship between atria and ventricles; fixed RR intervals of 300 ms (200 bpm); atrial activity observable at the peak of the T wave; it appears negative in the inferior leads and in lead I; pattern compatible with an orthodromic tachycardia due to left lateral accessory pathway;

Trace

Tracing recorded a few minutes after the first tracing; 1:1 tachycardia between atria and ventricles with broad QRS (left bundle branch block pattern); RR cycle lenght slightly slower than on the previous tracing (330 ms);

Trace

Tracing recorded a few minutes after the first tracing; 1:1 tachycardia between the atria and ventricles with broad QRS (right bundle branch block pattern); RR cycle lenght identical to the first tracing (300 ms);

Trace

Recording of onset of a tachycardia due to an atrial extrasystole; left bundle branch block pattern;

Trace

Recording of a tachycardia pause; left bundle branch block pattern followed by acceleration of the rhythm occurring during the narrowing of the QRS, then termination;

Exergue

In a 1:1 tachycardia, the occurrence of a bundle branch block which slows the tachycardia cycle is suggestive of a tachycardia due to an accessory pathway on the side of the branch whose block is conduction-depressant (conduction-slowing left bundle branch block suggestive of a left accessory pathway).