Alterations in Carotid Arterial Velocity‐Time Profile Produced by the Blalock‐Taussig Shunt

Because the presence of a systemic artery-to-pulmonary artery communication can alter blood flow patterns in both the systemic circulation distal to the communication as well as the pulmonary circulation, the effect of a Blalock-Taussig anastomosis on carotid arterial flow was investigated using noninvasive, continuous-wave Doppler ultrasonography. Thirty-seven patients without a Blalock-Taussig shunt (group 1) and 17 patients with a Blalock-Taussig shunt (group 2) were studied using an 8-MHz continuous-wave Doppler velocitometer. All group 1 patients had quantitatively similar carotid arterial velocity-time profiles and continuous antegrade flow throughout the entire cardiac cycle in both carotid arteries. Eight patients in group 1 subsequently underwent creation of a Blalock-Taussig shunt with an increase of systemic arterial oxygen pressure greater than 20 mm Hg. Immediately after operation, all showed marked alterations in the ipsilateral carotid arterial velocity-time profile from the preoperative pattern. Six showed the flow velocity diminishing to zero by late diastole. Two showed continuous retrograde diastolic flow, and developed congestive heart failure. The velocity-time profile of the contralateral carotid artery remained normal. Of the remaining nine patients in group 2 studied 6 months to 8 years postoperatively, six showed diminution of the ipsilateral carotid arterial velocity to zero by later diastole and at catheterization were shown to have an adequate-sized Blalock-Taussig shunt. The other three patients showed continuous forward flow in the ipsilateral carotid artery and at catheterization had a markedly stenotic Blalock-Taussig shunt. All nine 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. Thus, 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.