Echocardiographic assessment of right bundle branch injury after repair of tetralogy of Fallot

Nineteen patients, ages 3 1/2 -18 years, with electrocardiographic evidence of right bundle branch injury after intracardiac repair of tetralogy of Fallot, underwent invasive intracardiac electrophysiologic evaluation 1-13 years (mean 4.4 years) postoperatively. Categorization of the site of right bundle branch injury as proximal or distal was made by determining the V-RVA interval. In 11 of the patients, the V-RVA interval was prolonged (>35 msec), indicating proximal right bundle branch injury and in the other eight it was normal (<35 msec), indicating distal bundle branch injury. Within 24 hours of the study, all patients were studied by M-mode echocardiography. Measurements were made of the tricuspid valve closure, mitral valve closure and the difference between the two, or the delta value. All but one patient with distal bundle branch injury had delta values of less than 40 msec (range 8-38 msec), while 10 of 11 patients with proximal bundle branch injury had delta values greater than 40 msec (range 41-116 msec). There was a significant positive correlation (r = 0.74, p<0.001) between V-RVA and the delta value. We conclude that the delta value is an indicator of relative activation delay of the right ventricle, and therefore, in most cases, proximal vs distal bundle branch injury can be diagnosed noninvasively.