Criteria of localisation of bundles of Kent.

The high success rate (> 90%) of radiofrequency ablation of accessory pathw ays is related to accurate mapping. This determines the site of the accessory pathway and the best target for a blation with the object of reducing the number of applications and the asso ciated morbidity. Analysis of the surface ECG is the first step of localisation of a Kent bun dle. Different algorithms may be used based on the correlation between the polar ity of the delta wave, of the QRS and the site of the accessory pathway con firmed at surgery or during radiofrequency ablation procedures. Some of the recent algorithms allow localisation of certain postero-septal or sub-epic ardial pathways, the ablation of which can only be accomplished via the cor onary sinus or one of its branches, or in an abnormally dilated coronary si nus, the so-called diverticulum. A relatively accurate localisation of the accessory pathway from the surfac e ECG reduces the duration of an ablation procedure and may economise the n eed for left-sided catheterisation. However, the endocavitary electrogrammes determine the precise target of ab lation whether this be the ventricular or atrial pole of the bundle of Kent . The association of the criteria obtained by bipolar and unipolar recordin gs in sinus rhythm, during pacing or reentrant tachycardia enables accurate localisation in the majority of cases. Ablation of some pathways may be more complex because of their site or the presence of associated congenital or acquired cardiac disease which alters the anatomical or electrical markers. In these cases, the electrical criter ia, especially those of the surface ECG may be erroneous and non invasive i nvestigations such as Doppler echocardiography, isotopic ventriculography w ith phase analysis are most valuable with a positive predictive value of ov er 90%.