A 79-year-old woman was referred for aortic valve replacement. Baseline electrocardiogram showed sinus rhythm with normal intervals. After implantation of an aortic bioprosthesis, she presented an incessant and poorly tolerated wide-complex tachycardia. Brugada criteria for ventricular tachycardia were not met and the response to adenosine was an abrupt but transient termination of the arrhythmia, with noted PR prolongation and a left bundle branch block during sinus rhythm, similar as during tachycardia (fixed aberrancy). The diagnosis of an orthodromic atrioventricular re-entry tachycardia (AVRT) with left lateral accessory pathway (AP) was made during electrophysiological study, leading to a successful ablation of the AP.
This case shows us a concealed bypass tract which stayed clinically silent for almost 80 years. The induction of an orthodromic AVRT can be explained by the postoperative development of delay in the normal conduction system, sufficient to outlast the retrograde effective refractory period of the AP for that given cycle length (Figure). We believe that any aetiology of conduction delay, together with a properly timed premature impulse, can initiate re-entry by activation of a previously asymptomatic AP. Orthodromic AVRT may be poorly tolerated if induced in an acute setting (postoperative state, myocardial infarction), requiring ablation therapy of the AP.
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