Right-branch bundle block in circumpolar Inuit.

The prevalence of right-branch bundle block (RBBB) has been examined in the Inuit residents of Igloolik (69 degrees 40'N, Canadian N.W.T.) over a twenty-year period. Original reports of a very high prevalence of RBBB probably reflected a selective testing of patients with chronic respiratory disease by visiting physicians. Cases of RBBB are certainly seen somewhat more frequently than in a southern community, but the majority of subjects show no more than a slight notching of the R wave of the electrocardiogram, with no appreciable broadening of the QRS complex. While a few of the more marked cases of RBBB may be attributable to chronic respiratory disease, the majority are associated with high normal values for both lung function and predicted maximal oxygen intake. The probable cause is thus a ventricular hypertrophy due to the vigorous physical activity demanded by life in a northern community rather than chronic respiratory disease. The physical demands of life in Igloolik have diminished over the past two decades, and an apparent increase in the prevalence of RBBB over this period is probably due mainly to a great awareness+ of the condition by those reading the electrocardiograms.