Genesis of high frequency notching of QRS complexes in an in vivo cardiac model.

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Abstract
High frequency notching of the QRS complex is associated with transmural infarction, cardiomyopathies, and ventricular hypertrophy from any cause. The mechanism producing notching is unknown; but the presence of a discrete anatomic lesion is not an essential feature. The hypothesis that notching was produced by activation across, rather than along, myocardial fibers was investigated by stimulation at 12 points around a clock electrode attached to the epicardium while mapping isoschronous lines in the area activated. All fibers at the subendocardial layer beneath the clock electrode were ligated by a pursestring suture. Propagation direction, as measured by isoschronous maps, produced more notched QRS compleses when the path was across, rather than paralled with, the myocardial fibers. Using grouped data and a 5 times 6 table, notches versus the angle formed between fiber direction and orientation of the direction of travel were shown to be related (P less than 0.001). The hypothesis that cross-fiber activation enhances notching was confirmed. retrograde activation did not increase notching nor did ligation of subendocardial fibers.