Distinguishing Features of Left Anterior Fascicular Block and Inferior Myocardial Infarction as Presented by Body Surface Potential Mapping

SUMMARY Total body surface maps obtained from 19 patients with previous inferior myocardial infarc-tion (IMI) were compared with maps obtained from 19 patients with left anterior fascicular block (LAFB) and six more patients in whom electrocardiographic changes were indistinguishable between IMI and LAFB. Three distinguishing features were detected: 1) abnormal high anterior positivity developed both in IMI and LAFB, but its onset was earlier in LAFB; 2) a broad rim of abnormal right lower negativity was seen in both groups, but in IMI it was within the first 40 msec, whereas in LAFB it was found in the middle and later parts of depolarization; 3) abnormal left lower negativity was seen in all the patients with LAFB, but was absent in IMI. Thus, despite similarities in the abnormalities detected, we found definite temporal and topographical differences that should aid in differentiating between IMI and LAFB in ambiguous cases. FREQUENTLY, it is difficult to distinguish elec-trocardiographic changes produced by left anterior fascicular block (LAFB) from those produced by remote inferior myocardial infarction (IMI).1 2 The reasons for this include the following: 1) The small ini-tial r wave in leads II, III and aVF characteristic of LAFB may be embryonic and difficult to visualize; 2) with the passage of time an initial r wave may reappear in leads II, III and aVF after IMI; and 3) coexistence of these two entities, in which one develops in the presence of the other, may produce a masking effect of either.' Some electrocardiographic and vectorcardiographic criteria that contribute singly or in combination to dis-tinguish one from the other have been reported.1-7 However, there appears to be no definitive means of distinction, based on the conventional means of re-cording the electrical activity of the heart. Previous work has shown the advantage of the surface map in more completely characterizing electrical forces in various forms of heart disease,8 "0 and in IMI in par-ticular.'-`3 In this study of 44 patients, we compared and con-trasted the changes produced in the body surface ma