The diagnosis of left ventricular hypertrophy (LVH) in the presence of the left bundle branch block (LBBB) is difficult. In our study we compared commonly used ECG criteria with left ventricular mass index (LVMI) calculated during cardiac magnetic resonance imaging (CMRI) to verify their clinical value or the need to recalibrate. Methods: CMRI and ECG data of 36 patients were included in this study. Based on the ECG measures we used in our study selected ECG criteria for LVH detection in cases

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... ith LBBB: QRS duration, amplitude of S waves in V1, V2, V3; R waves in aVL, V5, V6 and combinations of amplitudes. LVH was defined as LVMI (CMRI) exceeding reference values. Results: LVH was diagnosed in 17 (47%) patients (6 women and 11 men). Following ECG parameters correlated the most prominently with LVMI -RV5: r = 0.5 (p = 0.002), RV6: r = 0.61 (p = 0.0001), SV1+RV5, 6: r = 0.64 (p = 0.001), RaVL+SV3: r = 0.5 (p = 0.002), SV2+RV5, 6: r = 0.71 (p = 0.0001), SV2, 3+RV5, 6: r = 0.75 (p = 0.0001). Based on the results of ROC analysis we proposed new cut points for LVH parameters. The highest diagnostic accuracy achieved S2+SV3 > 6 mV, SV2,V3+RV5,V6 > 4 mV, RaVL+SV3 > 3.5 mV (86-89%). Conclusions: In patients with LBBB the ECG parameters based on the amplitude of S wave in V2 or V3 and R wave in the leads aVL, V5, V6 have the highest clinical value in the prediction of the LVH determined by CMRI. It was necessary to recalibrate these parameters and it is needed to verify them in larger number of LBBB patients. (Cardiol J 2012; 19, 6: 591-596) Key words: ECG, left bundle branch block, left ventricular hypertrophy, cardiac magnetic resonance imaging 592 ECG criteria with left ventricular mass index (LVMI) calculated during CMRI to verify their clinical value or the need to update.