Alterations in carotid arterial velocity-time profile produced by the Blalock-Taussig shunt.

Abstract

Because the presence of a systemic artery-to-pulmonary artery communication can alter blood flow patterns in the systemic circulation distal to the communication and the pulmonary circulation, the effect of a Blalock-Taussig anastomosis on carotid arterial flow was investigated using noninvasive continuous-wave Doppler ultrasonography. Patients (37) without a Blalock-Taussig shunt (group 1) and 17 with a Blalock-Taussig shunt (group 2) were studied using an 8 MHz continuous-wave Doppler velocitometer. Group 1 patients had quantitatively similar carotid arterial velocity-time profiles and continuous antegrade flow throughout the entire cardiac cycle in both carotid arteries. In group 1, 8 patients subsequently underwent creation of a Blalock-Taussig shunt with an increase of systemic arterial O2 pressure > 20 mm Hg. Immediately after operation, all showed marked alterations in the ipsilateral carotid arterial velocity-time profile from the preoperative pattern; 6 showed the flow velocity diminishing to zero by late diastole; 2 showed continuous retrograde diastolic flow and developed congestive heart failure. The velocity-time profile of the contralateral carotid artery remained normal. Of the remaining 9 patients in group 2 studied 6 mo. to 8 yr postoperatively, 6 showed diminution of the ipsilateral carotid arterial velocity to zero by later diastole and at catheterization showed an adequate-sized Blalock-Taussig shunt. The other 3 patients showed continuous forward flow in the ipsilateral carotid artery and at catheterization had a markedly stenotic Blalock-Taussig shunt. All 9 patients showed continuous antegrade flow in the contralateral carotid artery. Features of the carotid arterial velocity profiles that separated groups 1 and 2 were unaffected by age or heart rate. A nonstenotic Blalock-Taussig shunt alters the ipsilateral carotid arterial velocity-time profile and induces characteristic changes that confirm the patency of the shunt. A shunt large enough to produce congestive heart failure produces additional distinctive alterations in the carotid arterial velocity-time profiles, e.g., diastolic retrograde flow.