Right ventricular infundibular β-adrenoceptor complex in tetralogy of Fallot patients

Abstract

Patients with tetralogy of Fallot may have episodes of paroxysmal hypoxic spells ('tet spells') or could be asymptomatic. In patients who have these episodes, treatment with a β-adrenoceptor (βAR) blocking agent can often ameliorate or attenuate the severity of the symptoms. Additionally, excitement, crying, and situations associated with increased sympathetic activity could provoke the occurrence of these hypoxic spells. We hypothesized that altered myocardial βAR function may contribute to the development of paroxysmal hypoxic spells in the symptomatic tetralogy patient. Surgically excised right ventricular infundibular myocardial specimens from symptomatic (patients with spells) and asymptomatic patients were used to determine total β1 and β2 βAR density and βAR adenylyl cyclase activity. Symptomatic patients had a significantly greater number of total βAR. The relative proportion of β1 and β2 receptors was comparable in both patient groups. βAR-stimulated adenylyl cyclase activity was found to be more enhanced in the symptomatic patient group. Our results indicate that infundibular βARs may play a role in the development of paroxysmal hypoxic spells.