The double adenosine test: a simple and non-invasive tip to unmask unapparent pre-excitations: an example of Mahaim fibres

We report the case of a 16-year-old youth who was admitted for a wide QRS tachycardia caused by an atypical atriofascicular bypass tract (the so-called ‘Mahaim fibers’). These bypass tracts give rise to antidromic atrioventricular re-entrant tachycardias, in which the bypass tract serves as the anterograde limb of the circuit and the atrioventricular node as the retrograde limb of the re-entrant circuit. Unfortunately, in these patients, it is easy to make a misdiagnosis of supraventricular tachycardia with functional left bundle branch block or even of ventricular tachycardia. Indeed, due to the slow and decremental conduction properties of these bypass tracts, the baseline ECG is either normal or shows only subtle pre-excitation. Herein , we describe a simple tip, consisting of two successive administrations of adenosine [during ongoing tachycardia (upper panel) and during sinus rhythm (lower panel)], to make a non-invasive and definite diagnosis of this condition. Importantly, the use of this method to unmask an accessory pathway capable of anterograde conduction is not limited to the diagnosis of Mahaim fibres. Indeed, it can be used more generally in patients presenting with paroxysmal supraventricular tachycardia whenever the ECG following tachycardia termination does not definitely rule out the presence of an accessory p athway.
Source: Europace - Category: Cardiology Source Type: research