[Isolated left anterior hemiblock during attacks of angina pectoris]

The clinical significance and mechanism for changes in the axis of the QRS complex during attacks of angina pectoris (excluding cases of Prinzmetal's angina) are unknown. Previous work has suggested that left anterior hemiblock under these circumstances is a sign of unstable angina indicating a lesion in the anterior descending artery. Two cases with left anterior hemiblock associated with frequent attacks of angina have been the subject of careful study. In case one, atrial stimulation tests showed that the left axis deviation was not related to tachycardia. It only occurred when atrial stimulation was carried out for long enough to induce myocardial ischaemia as witnessed by precordial pain and disorders of repolarisation. In case two, the left anterior hemiblock came on at first at the same time as the attacks of angina, and then became permanent. Bypass graft of the anterior descending artery restored the QRS axis to normal, and corrected the repolarisation disorders which were of ischaemic origin. These findings argue in favour of an ischaemic origin of this conduction defect. Unlike ischaemia of the left anterosuperior subbranch, anterior left hemiblock is indicative of extensive ischaemia of the anterior wall of the left ventricle relative to an obstruction in the anterior descending artery or in the main trunk of the left coronary artery.