Left bundle branch block (LBBB) is a conduction abnormality in the heart that can be seen on an electrocardiogram (ECG).

In the lateral leads (I, aVL, V5-V6) the QRS complexes are usually predominantly positive with a slow upstroke last >60ms to the R-wave peak.

The ST segments typically slur into the T-wave and often appear elevated in leads with negative QRS complexes.

Second, the presence of an appreciable (≥1 mm or 0.1 mV) discordant ST deviation in low‐voltage QRS complexes was considered as a positive criterion for AMI.

Under these criteria, an ECG is positive for an AMI in the presence of LBBB if any of the following criteria are present: The BARCELONA algorithm attained the highest sensitivity (95%), significantly higher (P<0.01) than Sgarbossa and Modified Sgarbossa rules, as well as the highest negative predictive value (97%), while maintaining 89% specificity.

The global performance of the BARCELONA algorithm was significantly better than previous algorithms: It achieved the highest efficiency (91%) and the highest area under the ROC curve (0.92), which was significantly higher (P<0.01) than the ones obtained by the Sgarbossa and Modified Sgarbossa rules.