Intraventricular conduction disturbances: A review of prevalence, etiology, and progression for ten years within a stable population of Israeli adult males

The ECG tracings of 5,204 working males aged 40 years and over, representing a random sample of Israeli civil service employees were reviewed, and 123 (2.36 per cent) displaying intraventricular conduction disturbances (IVCD) in the form of left anterior hemiblock (LAH), RBBB, RBBB + LAH and LBBB, were followed for a period of 10 years (1963 to 1973). While these patients were slightly older than the population they were derived from (53.5 versus 4938 years average age), there was no significant difference in ages between the various types of IVCD, but there was a marked increase in the frequency of all IVCD with age. Left anterior hemiblock constituted the most frequent IVCD (1.42 per cent), being twice as frequent as RBBB (0.65 per cent). The prevalence of RBBB + LAH was 0.17 per cent (7 per cent of all IVCD). To the best of our knowledge, this is the first time that the frequency of this condition has been assessed in an unselected male population. The vast majority of these ECG changes seem to be acquired. Ischemic heart disease (IHD) constituted the most frequent associated condition for all types of IVCD (28 per cent), its prevalence being similar (21 to 28 per cent) in LAH, RBBB and RBBB + LAH, but much higher in patients with LBBB (five of six patients). Hypertension (HT), not associated with IHD, was present in 24 patients and constituted the next most frequent factor (20 per cent). No definite etiology could be demonstrated in the remaining 64 patients (52 per cent), except for five (4 per cent of all IVCD and 0.1 per cent of the population studied) who displayed progressive IVCD and were considered to represent examples of a degenerative disease of the conduction system (DDCS). The latter confirms that monofascicular blocks (MFB) may represent an initial stage of DDCS. From the ECG point of view, 14 per cent of cases with MFB showed progression to bifascicular block (BFB) or complete heart block (CHB) within 10 years, regardless of etiology. This was more frequent in RBBB than in LAH (22.5 per cent versus 9.5 per cent). From the clinical point of view, the natural history of IVCD in patients with IHD parallels the natural history and prognosis of this disease. In contrast, the prognosis of IVCD in patients with isolated HT, or in asymptomatic subjects, was more benign even in patients reaching the stage of CHB. The natural history of DDCS began as RBBB or LAH in middle age or earlier and progressed to CHB through the stage of BFB. This process may last from a few years to a few decades; LBBB seems to be rarely if ever encountered in its course.