Vectorcardiographic criteria for the diagnosis of inferior myocardial infarction

Vectorcardiograms (VCG) from two patient groups were analyzed to develop and test quantitative criteria for the diagnosis of inferior myocardial infarction. The first group (219 patients) consisted of four subgroups and was used to develop the criteria. Patients were placed in the normal and infarct subgroups by clinical descriptors including history, course in the coronary care unit, and cardiac catheterization findings. The criteria which were found to give the fewest false positive results with acceptable sensitivity were as follows: In the frontal plane, generally clockwise early superior QRS forces must be present, i.e., forces which are initially either a) superior (rightward or leftward) or b) inferior and completely rightward for not more than 10 msec prior to becoming superior, and which subsequently cross the X axis to the left of the 0 point (or less commonly, the entire efferent limb remaining superior to the X axis). One of the following conditions must also be present: 1) Time from the 0 point to leftward X intercept of at least 25 msec and distance from the 0 point to leftward X intercept of at least 0.30 mV; 2) A maximal frontal plane QRS vector less than 15°; 3) A maximal superior deviation of at least 0.1 mV and a ratio of maximal superior deviation to maximal inferior deviation of at least 1:5. The performance of these proposed criteria were then tested prospectively using a second group (255 patients) which was similar to the criteria group. The proposed criteria were found to be statistically superior to both ECG Q wave criteria and to the VCG initial force criteria of Young and Williams. 2 The incidence of false positive diagnosis in the test group was less than 3%.