Background: Tetralogy of Fallot (TOF) and its surgical repair are associated with alterations in right ventricular systolic and diastolic functions. The cardiopulmonary baroreflex describes the peripheral vasoconstriction response to the volume-unloading deactivation of left and possibly right ventricular receptors. Alterations in cardiac geometry or distensibility and pulmonary vasculature of operated TOF may affect the mechanical stimulation of sensitive cardiopulmonary receptors leading to an impaired baroreflex function. There has to date been no report on the integrity of baroreflex function in postoperative TOF.
Objective: To characterize the combined cardiopulmonary and baroreflex response of patients successfully operated for TOF in early childhood to central volume unloading using graded lower body negative pressure (LBNP) application.
Methods: Fifteen patients operated on for TOF (mean+/-SEM) 15.7+/-1.4 years previously and 13 healthy age-matched control subjects were submitted to four consecutive 5 min LBNP applications at -10, -20, -30 and -40 mmHg. Forearm blood flow and vascular resistance, left ventricle end-diastolic diameter (LVEDD), arterial blood pressure and heart rate were obtained.
Results: TOF exhibited a lower LVEDD (42.7+/-1.5 mm) than control subjects (51.9+/-1.6). The forearm vascular resistance to LVEDD relationship was shifted left and upward in TOF compared with that of control subjects, but the slope of the relationship was not different between groups. LBNP -40 mmHg induced a lesser change in heart rate in TOF (+10.6+/-1.5%) than in control subjects (+14.7 +/-2.4%) and an increase (P<0.05) in diastolic blood pressure in TOF (-2.4+/-2.5%), which was not seen in control subjects (+4.3+/-2.9%).
Conclusions: Young adults successfully operated on for TOF in early childhood exhibit a resetting of the cardiopulmonary baroreflex to operate at smaller LVEDD and at a higher level of forearm vascular resistance. The blunted heart rate response to LBNP -40 mmHg is consistent with previous observations pointing to disturbances in the efferent arm of the baroreflex.