The left hemiblocks: significance, prognosis and treatment.
This review article is concerned with the concept of left hemiblocks and analyses their significance, prognosis and treatment. It first stresses that the left bundle branch is not sensu stricto a bifascicular structure since it generally is either fanlike, or trifascicular. The anatomical situation, however, remains compatible with the physiological concept of the hemiblocks. The electrocardiographic features of left anterior and posterior hemiblocks are described. A histopathological investigation clearly demonstrates that both are signs of left bundle branch disease, often degenerative in nature and more widely spread than expected from the electrocardiographic terminology. The association of a left hemiblock with right bundle branch block is frequently considered as sign of poor prognosis. This is true in the setting of acute myocardial infarction where it accompanies large infarcts. In chronic cases, the prognosis is primarily influenced by the underlying pathology. Patients with partial bilateral bundle branch block should be investigated and, if needed, paced when they have symptoms, a PR interval which lengthens with the course of time, or signs of cardiomyopathy, or large anterior infarction. Asymptomatic individuals with apparent primary disease of the conducting system are neither studied, nor considered for prophylactic pacing.