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The intracardiac tracing presented in Fig. 1 shows that one atrial beat (A1) is followed by two QRS complexes (V1 and V2) and that the second atrial beat (A2) produces only one QRS complex (V3). This pattern is repetitive along the tracing. We were able to reproduce this rhythm by atrial pacing (AP) (Fig. 2a) and observed that each V was preceded by a His bundle potential (H), suggesting that the rhythm is supraventricular. Ventricular pacing (VP) at a cycle length of 500 ms repeatedly resulted in a VA Wenckebach: the atrial activation sequence changes (A4 and A5), the A–A interval decreases (A3–A4 and A4–A5), and the VA interval lengthens (VP4–A4, VP5–A5) (Fig. 2b). Notably, a narrow QRS complex [V(P)6] followed after A5. As the activation wavefront was conducted retrogradely from VP5 through the fast pathway to the atrium (A5), the fast pathway must be refractory. Therefore, the narrow QRS complex has to result from a second AV pathway, which is, in this case, a slow pathway (Fig. 2b; [1]). Thus, Fig. 1 shows a non-reentrant AV-nodal tachycardia (dual AV-nodal response) resulting from anterograde fast and slow pathway conduction [2]. The extremely prolonged slow pathway conduction (A1–V2) enables the His bundle to conduct the activation wavefront into a second QRS complex. Then, after A2, the slow pathway is refractory, and only the fast pathway conducts the activation wavefront (V3). In Fig. 2a, the same phenomenon occurred: AP1 initiates H1 and H2. We cannot conclude if H4 is a result of slow pathway conduction after AP2 or fast pathway conduction after AP3. The AP3–H4 time is shorter than the AP2–H3 time. Therefore, we assume that this beat also conducts through the slow pathway. However, the AP2–H3 time might be prolonged because of conduction in the relative refractory period. We successfully eliminated the non-reentrant AV-nodal tachycardia via slow pathway modification.
Fig. 1
Intracardiac tracing. For a detailed explanation, please see the text. Fast PW fast pathway, Slow PW slow pathway, A atrial activation, V ventricular activation
Fig. 2
Intracardiac tracing during atrial (a) and ventricular pacing (b). For a detailed explanation, please see the text. AP atrial pacing, H His bundle potential, V ventricular activation, A atrial activation, VP ventricular pacing, V(P) (pseudo) fusion, Fast PW fast pathway, Slow PW slow pathway, A→V conduction from the atrium to the ventricle, V→A conduction from the ventricle to the atrium. Coronary sinus diagnostic catheter (CS), ablation catheter (MAP) located on the His bundle (a) and in the right ventricle (b)
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Conflict of interest
D. Mol, E.A. Stel and I.E. Hof declare that they have no competing interests.
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Het Netherlands Heart Journal wordt uitgegeven in samenwerking met de Nederlandse Vereniging voor Cardiologie. Het tijdschrift is Engelstalig en wordt gratis beschikbaa ...
