Are there any useful investigations that predict which patients with bifascicular block will develop third degree atrioventricular block?

摘要

Syncope is a common symptom, particularly in the elderly. In patients with cardiovascular disease, it is associated with a high mortality within the first year.1 Therefore, patients with syncope that might be of cardiac origin need thorough investigation, and, if possible, should be offered a reliable treatment. One such treatment for bradyarrhyth-mias is pacing. The mortality in patients with documented heart block without pacing is about 50% during the first year.2 Second degree heart block has a similar prognosis.3 Heart block arises most often in patients with conduction tissue fibrosis, and less often in those with coronary or other heart disease. A less serious form of conduction disease is intraventricular conduction delay in the bundle branches and their various fascicles. None the less, in some cases this form of "minor" conduction disease progresses to complete heart block, often accompanied by syncope or attacks of the type described by Adams-Stokes-Morgagni. Furthermore, the association of newly acquired bifascicular block and some acute myocardial infarction is related to complete heart block (when a long HV interval is present) and to increased cardiovascular death. There are many problems associated with bifascicular block. First, because the electrocardiogram often shows normal atrioventricular conduction after syncope we can only be certain that the syncope was caused by heart block. Nor can we predict which patients with bundle branch block (left bundle branch block or right bundle branch block with left hemiblock) will progress to complete heart block. Electrophysiological measurements are often abnormal, but seldom to the extent (in the case of the HV interval prolonged to 80-100 ms) that is associated with a high incidence of progression. Finally, even in patients with severe distal conduction disease, syncope may be caused by other, coexistent abnormalities.