Left bundle branch block: prevalence, incidence, follow-up and outcome

In a randomly selected population screening study of 8450 menand 9039 women 33 to 71 years of age conducted in Iceland in1967–1977, 27 men and 17 women were found to have leftbundle branch bock (LBBB). The prevalence of LBBB at that timewas 0.43% for men and 0.28% for women. The incidence of LBBBwas 3.2 per 10 000 per year for men and 3.7 per 10 000 per yearfor women.All except one of 37 alive patients with LBBB wereexamined in 1984 including chest X-ray, echocardiography andexercise testing (Bruce protocol). Eight men had had myocardialinfarction (P<0.05), 12 had angina pectoris, 15 had hypertension,7 had cardiomyopathy, 13 had primary conduction disease, and3 had pacemakers. Five men and two women had died in comparisonwith 18 men and 1 woman in an age-matched control group of 176people (P ns). Three of 5 decreased LBBB men had cardiomyopathyat autopsy. Three men died suddenly. The two women died of noncardiaccauses. Only one patient in the control group had cardiomyopathy(P< 0.01). There was no significant difference in other cardiacdiagnoses between the groups. Eleven LBBB women out of thirteenhad a normal exercise duration (6 min) and 11/17 men exercisednormally (7 min). In comparison with the control group, theLBBB patients had an increased LV diameter 2.85±0.38vs 2.58±0.38 cm m^-2 body surface area (P<0.01). Therewas no difference between the groups in left atrial diameteror LV wall thickness.In conclusion, the prevalence of LBBB was0.43% for men and 0.28% for women of middle age. The incidencewas 3.2 per 10 000 per year for men and 3.7 per 10 000 per yearfor women. The prognosis of LBBB is relatively benign apartfrom its association with dilated cardiomyopathy. Few patientsrequire pacemakers. The mean LV diameter is increased in randomlyselected patients with LBBB, but only those with an underlyingdisorder.