[Left bifascicular block and percutaneous mitral valvuloplasty].

In some patients, the inflation of balloons through the mitral orifice during percutaneous mitral valvuloplasties may impair intraventricular conduction. In some cases, this appears to correspond to a block of the anterior and middle network within the left branch of the bundle of His. This left "biblock" is characterized by extreme left axial deviation of AQRS, of about -60 to -70 degrees, with a QS aspect on D2 and D3, RS on V1 and R on V6 with no major prolongation of ventricular activation time. If this hypothesis is correct, it would support the "trifascicular" concept of the left branch of the bundle of His.