Expanding the frequency response of the electrocardiogram and its derivative to 1,000 cps revealed notching in certain parts of the QRS complex which correlates with the presence of primary myocardial disease. Chi-square analysis of data from 169 patients with myocardial involvement indicated that notching on the downstroke of leads X, V4, and V6 separated abnormal from normal patients at the 1% level of significance, whereas fine and coarse slurring showed reverse correlation at the 1% level

more »

... significance. This suggests that notching and not slurring is the important evidence of disease. Neither notching nor slurring was significant at the peak of the R wave in any lead. Study of individual cases revealed that complete right and left bundlebranch blocks do not mask high-frequency components caused by myocardial disease nor do they produce high-frequency components. Conclusions regarding specific diagnostic criteria, however, should serve only as guidelines. ADD,ITIONAL INDEXING WORDS: Bundle-branch block Right ventricular hypertrophy