14th International Congress
THE "NEW FRONTIERS"
OF ARRHYTHMIAS 2000

Jan. 29 - Feb. 5, 2000
Marilleva, Trento, Italy

RT-141

How to predict and avoid complete AV block complicating radiofrequency ablation of AV nodal slow pathway

Pietro Delise, Aldo Bonso*, Leonardo Coro, Mauro Fantinel, Gianni Gasparini*, Antonio Raviele*.
Operative Units of Cardiology, Hospitals of Feltre and *Mestre, Italy

Abstract

Both fast and slow pathways can be selectively ablated to control common AV Node reentrant tachycardia (AVN RT). Slow pathway ablation is considered the better at preventing the risk of inadvertent AV block. However, also the slow pathway ablation has a low but significant risk of inadvertent complete AV block. In patients with normal or modestly impaired PR interval (<300 msec) the risk of block is about 0.5-2%. In patients with markedly prolonged PR interval (>300 msec) such risk may be significantly higher.

In patients with markedly prolonged PR interval, the block can be related to the lesion of the slow pathway in the absence of the anterograde conduction of the fast pathway. In cases with normal PR interval, the reason of block is unclear, if the the energy is delivered at the posterior aspect of the triangle of Koch, far from the usual site of the anterograde fast pathway and far from the compact AV node. A possible explanation in the latter case is an atypical location of the fast pathway, close to the slow pathway, or again the absence of its anterograde conduction. In such cases total AV block may be the consequence of the of the damage of both fast and slow pathway or of the damage of the only anterogradely conducting pathway.

In order to localize the anterogradely conducting fast pathway, we performed the pacemapping of the triangle of Koch in 60 patients who underwent the ablation of common AVN RT.In all cases, before ablation we calculated the St-H interval by stimulating the anteroseptal (AS), mid-septal (MS) and posteroseptal (PS) aspect of the triangle of Koch at a rate slightly faster than the sinus rate. In all patients common AVN RT was induced. In 53/60 patients (Gr. A, 88.3%) the shortest St-H interval was recorded on stimulating the AS region. In 5/60 patients (Gr. B, 8.3%) the shortest St-H interval was recorded on stimulating in the MS region. Finally, in 2/60 patients (Gr. C, 3.4%) the shortest St-H interval was recorded stimulating in the PS region. In Gr. C AH interval was significantly longer than in patients of Gr. A and B (200±99 msec vs 64±18 and 62±3 respectively, p <0.001). In Gr. A and B a posteroseptal slow pathway and in Gr. C an anteroseptal retrograde fast pathway were successfully ablated without AV block.

CONCLUSIONS. Pacemapping of the triangle of Koch can help to recognize patients in whom the anterograde conducting fast pathway is abnormally located far from the anteroseptal region or in whom the anterograde conduction of the fast pathway is absent. In these cases the risk of AV block can be reduced by performing the slow pathway ablation in a site sufficiently far from the site of the anterograde fast pathway or by ablating the retrogradely conducting fast pathway.

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