[Value of continous electrocardiography (Holter monitoring) in mitral valve prolapse].

Twenty three patients with mitral valve prolapse underwent ambulatory 20 to 24 hour electrocardiography to study the incidence and severity of ventricular arrhythmias. These arrhythmias were found in 20 cases (87 p. 100).

["Habitual" left branch block alternating with 2 "disguised" bracnch block].

Two cases of alternating left bundle branch block and "masquerading block" (with left bundle branch morphology in the stnadard leads and right bundle branch block morphology in the precordial leads) were studied by serial tracings and his bundle electrocardiography. In case 1 "the masquerading" block was associated with a first degree AV block related to a prolongation of HV interval. This case is to our knowledge the first cas of alternating bundle branch block in which his bundle activity was recorded in man.