Valeur et limitations de I’ECG 12-derivations pour le diagnostic différentiel des tachycardies régulières à complexes larges

The aim of this study was to assess the value of the 12-lead ECG for differentiating ventricular tachycardia (VT) from supraventricular tachycardia (SVT) with aberrant conduction in the presence of a regular wide QRS complex tachycardia. One hundred eighty-six wide complex tachycardia tracings were analyzed by 2 independant observers who had no knowledge of the mechanism of the tachycardia using the 4-steps algorithm proposed by Brugada: (1) presence of an R/S complex in any precordial lead? (2) R/S interval >100 ms? (3) atrio-ventricular dissociation? (4) morphologic criteria favouring VT in V1 and V6. In all cases, the exact mechanism of the tachycardia was proven by an electrophysiologic study (VT in 130/186; SVT with aberrant conduction in 56/186). A correct diagnosis of VT was made in 126/130 cases (97%) for the observer n° 1 and in 128/130 cases (98%) for the observer n° 2. The diagnosis was established during the first step of the algorithm in 22 cases, during the second step in 90 cases, during the third step in 12 cases, and during the fourth step in 2 cases. In 17 cases the algorithm incorrectly classified the tachycardia: 13 SVT with aberrant conduction were incorrectly classified as VT, essentially because of the presence of ventricular preexcitation (5/13), of class Ic antiarrhythmic drug therapy (1/13) and of atypical aberrant conduction (7/13). Four VTs were incorrectly classified as SVT with aberrant conduction (1 fascicular VT, 2 right ventricular outflow tract VT, 1 right ventricular dysplasia septal VT). In conclusion, in presence of a regular wide QRS complex tachycardia, a correct VT diagnosis can be made in 97 to 98% of the cases by simple analysis of the 12-lead ECG using the algorithm proposed by Brugada et al. Misdiagnosis is mainly related to ventricular preexcitation, class Ic drugs, atypical aberrancy or to the presence of rare (and usually benign) forms of VT.