New ECG Criteria for Acute Myocardial Infarction in Patients With Left Bundle Branch Block

ensitive and specific criteria for the detection of acute myocardial infarction (AMI) in patients with left bundle branch block (LBBB) have eluded electrocardiographers for many years.The article by Di Marco et al in this issue of the Journal of the American Heart Association (JAHA) 1 suggests that enhanced criteria are a possibility.In 1996, Sgarbossa et al introduced new criteria for the diagnosis of AMI in LBBB purely on the basis of ST changes, with a sensitivity of 36%, a specificity of 96%, and a positive predictive value of 88%. 2 At the time, they represented a new approach, but they were enhanced later by Smith et al, whose modified Sgarbossa criteria 3 had a sensitivity of 91% and a specificity of 90%, although the study group was somewhat small.3 A follow-up case-control study that assessed the same criteria produced results of 80% sensitivity and 99% specificity in 45 patients with an acute coronary occlusion and 249 controls.4 The modification of Smith et al 3 was to replace one Sgarbossa criterion (STj ≥0.5 mV discordant with QRS) with a new criterion, namely |STj/Samp| ≥0.25 with STj ≥0.1 mV in the same lead. See Article by Di Marco et al.In the article by Di Marco et al, the sensitivity and specificity in the test group of 107 patients were 93% and 94%, respectively.1 This compares with 33% and 99% for the original Sgarbossa 2 criteria and 68% and 94% for the modified Sgarbossa criteria, 3,4 all based on the same test population of patients.Thus, the new approach represents a remarkable improvement in sensitivity, in particular compared with earlier approaches. DEFINITION OF LBBBThe authors chose a relatively conventional definition of LBBB with the QRS duration >0.12 seconds, QS or rS complex in V1, and an R wave peak time >60 ms in lead I, V5, or V6 along with the absence of a Q wave in these leads. 1 There was no requirement for notching or slurring of the R wave in I, V5, and V6 as in the long-standing World Health Organization definition of LBBB. 5 In 2009, an American Heart Association/American College of Cardiology Foundation/Heart Rhythm Society recommendations article 6 produced a broader definition of LBBB, which stated that ST-T waves are usually oppositely directed to the QRS complex, and positive T waves in the presence of an upright QRS complex may be normal.Subsequently, Strauss et al introduced a definition of strict LBBB with a QRS duration ≥130 ms in women and ≥140 ms in men.7 A QS or rS complex in V1 and V2, as well as notching or QRS slurring in mid-QRS in ≥2 contiguous leads, completed their definition.They argued that many ECGs reported as showing LBBB had a wide QRS because of a combination of left ventricular hypertrophy and left anterior fascicular block and not LBBB.Their research was aimed at assessing the likelihood of success of cardiac resynchronization