Bundle of His Recordings in Congenital Complete Heart Block

Abstract

Six children, aged between 3 and 19 years, with congenital complete heart block without associated cardiac disease were studied by His bundle electrography. All were symptomatic with resting ventricular rates over 40 beats/min, and electrocardiograms that showed a normal axis and QRS complex. His bundle to ventricular activation was within the normal range in all and the block was proximal to the bundle of His. Ventricular and atrial pacing did not result in retrograde or antegrade conduction. All the patients were thought to have a lesion proximal to the site where the bundle of His potential was recorded and, therefore, were unlikely to develop symptoms or require treatment. Additional Indexing Words: QRS frontal vectorVentricular conduction Long-term survival CONGENITAL complete heart block is a rare but important form of atrioventricular (A-V) block.' Although most children with it are asymptomatic and the lesion is compatible with longevity,24 Stokes-Adams attacks and death do occur.5' 6 A clinical study is in progress to determine the natural history of this entity,7 but the mortality in infancy and childhood is estimated at not less than 5%8 Most reports1 6, 7do not separate heart block with associated cardiac disease from From the

Complete congenital heart block. Report of 35 cases.

“…His bundle studies may help to localise the site of the block. '0 11 In congenital heart block with no accompanying cardiac lesion this is situated most frequently proximal to the bundle of His. 12 We did not carry out any His bundle recordings in any of our patients.…”

Electrophysiological characteristics of junctional pacemakers in congenital A‐V block and following his bundle cryoablation

“…reported a correlation between the corrected recovery time of the subsidiary pacemaker and symptoms in congenital heart block and the corrected recovery time and the site of block in surgically induced heart block in children. However most previous reports on the characteristics of the escape rhythms in congenital (Kelly et al .• 1972;Nasrallah et al .• 1975;Rosen et al .• 1971) and surgically induced complete heart block (Gonzalez et al .• 1981;Klein et al .• 1981;Rosen et al .• 1971) have concentrated on the basic escape rate and its response to either atropine or isoproterenol. This study has evaluated the response of the effect of overdrive suppression in both groups of patients and the effects of both atropine and isoproterenol.…”

“…Although the site of block in congenital heart block has generally been considered to be situated within the A-V node. or at least proximal to the His bundle deflection (Kelly et al .• 1972;Rosen et al .• 1971). several reports have suggested that intra-Hisian block may also infrequently occur (Guimond and Puech.…”

“…Both groups showed similar, significant responses to isoproterenol. Isoproterenol is known to improve automaticity of subsidiary pacemakers regardless of their site of origin (Kelly et al .• 1972;Klein et al, 1980;Rosen et al, 1971;Thilenius et al .• 1972) and is therefore of limited clinical use in localization of the site of block or as an index of prognosis.…”

Heart block in children

“…A review of the types of dysrhythmia observed (ie, tachycardia, asystole, or a combination) during Stokes-Adams attacks leaves little cause to doubt this conclusion [10,17] . [7,12,211, sympathetic stimulation [4,11,12], and exercise [9,19,24] ; and location of site of block with His bundle electrocardiography [5,11,12,21,23] . In general, results have shown that almost all patients with heart block have an increase in ventricular rate in response to sympathetic stimu- lation and exercise regardless of the site of block or the presence or absence of symptoms and that symptoms may occur in patients with block above the His bundle recording site whether or not they have an increase in ventricular rate following parasympathetic block .…”