Adaptation of baroreflex function to increased carotid artery stiffening in patients with transposition of great arteries

We have shown previously that TGA (transposition of great arteries) is associated with increased carotid artery stiffness. It has been established that stiffening of the barosensory vessel wall results in reduced baroreceptor activation and impaired BRS (baroreflex sensitivity). In the present study we tested the hypothesis that the increased carotid artery stiffness in TGA patients was associated with reduced cardiovagal BRS. We studied 32 TGA patients aged 9–19 years, 12±3 years after surgical repair and 32 age-matched healthy control subjects. Carotid artery diastolic diameter and pulsatile distension was determined by echo wall tracking; carotid blood pressure was measured by tonometry. BRS was measured using spontaneous techniques [BRS_seq and LF_gain (low-frequency transfer function gain)] and by the phenylephrine method (BRS_phe). Carotid artery distensibility was markedly reduced in patients as compared with controls (5.6±1.9×10⁻³ compared with 8.7±2.7×10⁻³/mmHg P<0.05, as determined using an unpaired Student's t test), but BRS was not different in patients and controls (20.3±14.7 compared with 21.7±12.7 for BRS_seq; 13.1±9.2 compared with 10.6±4.5 for LF_gain; and 19.1±8.6 compared with 24.8±7.2 for BRS_phe respectively). Carotid artery elastic function was markedly impaired in patients with TGA, but the increased stiffness of the barosensory vessel wall was not associated with reduced BRS. It appears that attenuation of baroreceptor stimulus due to arterial stiffening may be compensated by other, possibly neural, mechanisms when it exists as a congenital abnormality.