Prominent anterior QRS force as a manifestation of left septal fascicular block

Summary In the examination of 1,000 consecutive VCG records, prominent anterior QRS force (PAF) was frequently observed in ischemic heart disease, diabetes mellitus and hypertrophic cardiomyopathy not combined with high posterior infarction or right ventricular hypetrophy. PAF was observed especially in higher incidence in angina pectoris, papillary muscle dysfunction and hypertrophic cardiomyopathy. In a case of papillary muscle dysfunction who died suddenly, the septal fascicle of the left bundle was found to be markedly fibrotic by serial histological examination of the intraventricular conduction system. A case of angina pectoris with PAF later developed anteroseptal myocardial infarction. Ischemia of the anterior wall of the left ventricle might cause prominence or absence of the anterior QRS force in VCG. The prominence may be explained by left septal fascicular block, and the absence may be caused by the loss of the electromotive forces of the heart due to myocardial necrosis. Intermittent PAF was also observed, which was an important finding to support the existence of this new type of fascicular block. Left septal fascicular block should be considered as a type of conduction disturbance of the division of the left bundle in addition to the well-known left anterior or posterior hemiblock.