PROLONGATION OF ISOVOLUMIC CONTRACTION TIME IN LEFT BUNDLE BRANCH BLOCK

Phonocardiograms were recorded in 25 patients with chronic complete left bundle branch block (LBBB) and were compared with findings in 29 normal subjects of comparable age. Two additional patients with intermittent left bundle branch block served as their own controls. In left bundle branch block: 1. 1. The common auscultatory impression of diminished intensity of the first heart sound was demonstrated in patients with intermittent LBBB. 2. 2. The average Q-M1 interval was significantly prolonged in chronic LBBB but was unchanged in intermittent LBBB. 3. 3. The average Q-A2 interval was significantly prolonged, resulting in paradoxical splitting of the second heart sound in 84 per cent of patients. 4. 4. Isovolumic contraction time of the left ventricle was significantly prolonged and was mainly responsible for delayed aortic valve closure. 5. 5. Left ventricular ejection time was significantly shortened which may reflect a decreased stroke volume. Prolonged isovolumic contraction of the left ventricle is the most important alteration in the time relationships of ventricular contraction in patients with LBBB. It may be associated with asynchronous contraction which results in diminished force and velocity of contraction of an already compromised left ventricle in many patients. © 1969.