[Left bundle branch block. Electrocardiographic and prognostic aspects].
The concept of left bundle branch block (LBBB) was recognised at the beginning of the 20th century but confusion, due to the extrapolation data from animal experimentation, persisted for many years between the electrocardiographic appearances of LBBB and right bundle branch block (RBBB). The typical appearances of LBBB are now well known and consist of: 1) increased duration of the QRS complex > 0.12 seconds; 2) a wide, exclusive R wave with a plateau or notched summit in the left precordial leads and usually in D1 and aVL; 3) an important delay in the intrinsecoid deflection in the left precordial leads (0.08 to 0.12 seconds after the onset of QRS); 4) an axis of repolarisation opposite that of the QRS complex with so-called "secondary" abnormalities. The authors emphasise that some electrocardiographic variants carry a poor prognosis, in particular those with major QRS axis deviation to the left or, much less commonly, to the right. The diagnosis of left ventricular hypertrophy is possible in cases of LBBB by using the criteria of QRS amplitude in the left precordial leads. On the other hand, the diagnosis of myocardial infarction is more difficult, the criteria being very specific but having a sensitivity < 50%. The deleterious effects of LBBB on the haemodynamics are well known but their study has become a new firld of research since the introduction of bi-ventricular pacing for the treatment of cardiac failure. In dilated cardiomyopathy, LBBB increases the duration of functional mitral regurgitation and decreases left ventricular filling times. The prognostic implications of LBBB have been the object of many studies: the reports in the literature indicate a large increase in mortality when LBBB develops in patients over 44 years of age. The progression to complete atrioventricular block is common only when the HV interval exceeds 100 ms. In other cases, the prophylactic implantation of a cardiac pacemaker does not improve the prognosis which depends on the severity of the underlying cardiac disease.
Deharo
J C
JC
Service de cardiologie, hôpital Sainte-Marguerite, Marseille.
D002037:Bundle-Branch Block / Q000175:diagnosis / Q000503:physiopathology*; D004562:Electrocardiography / Q000379:methods*; D006801:Humans; D009203:Myocardial Infarction / Q000175:diagnosis; D011379:Prognosis