[The electrocardiogram of high resolution during ventricular tachycardia]

To evaluate by the signal averaged-ECG (SAECG) the initial portion of the activation of the sustained ventricular tachycardia (SVT) and monomorphic repetitive ventricular tachycardia (MRVT), correlating the findings with those obtained during sinus rhythm (SR).

Ten patients was studied; five with SVT and five with MRVT. Patients with SVT presented a positive SAECG while patients with MRVT the test was negative, during SR. The findings of this two populations were compared with those obtained in a group of ten patients with advanced bundle branch block (ABBB: five RBBB and five LBBB). We analyzed in the vector-magnitude obtained during VT and ABBB, the root mean square of the initial 40 ms portion of the activation (RMS40) and the duration of the low amplitude signals < 40 microV from the beginning of the filtered QRS (LAS). To define the positiveness of the test in SR, we analyzed the final RMS40 (normal > 20 microV), the duration of the LAS < 40 microV at the end of the activation (normal < 38 ms) and the total QRS duration (QRSD-normal < 114 ms).

(mean)-SVT in SR: RMS40 = 11.2 +/- 6.2 microV; LAS = 47.4 +/- 5.8 ms; QRSD = 131.2 +/- 8.7 ms. SVT during VT: RMS40 = 6.9 +/- 4.5 microV; LAS = 54.5 +/- 9.1 ms. RMVT in SR: RMS40 = 59.7 +/- 49.0 microV; LAS = 28.3 +/- 8.5 ms; QRSD = 93.1 +/- 13.0 ms. MRVT during VT: RMS = 25.2 +/- 8.8 microV; LAS = 28.9 +/- 11.1 ms. RBBB: RMS = 53.3 +/- 34.2 microV; LAS = 22.6 +/- 9.8 ms. LBBB: RMS = 54.7 +/- 37.3 microV; LAS = 11.4 +/- 4.6 ms. The comparison between the data from SVT and MRVT/ABBB showed p < 0.01.

In the studied population, the SAECG was able to identify abnormal LAS initiating SVT, that were not present in MRVT and ABBB. This signals probably represents intra-myocardial slow conduction, as a portion of a re-entry circuit. There was an excellent correlation between the findings during SVT and MRVT with those obtained in SR.