Noninvasive evaluation of Blalock-Taussig shunts: Determination of patency and differentiation from patent ductus arteriosus by Doppler echocardiography

Abstract

Pulsed Doppler echocardiography has been used to detect continuous turbulent flow in the right pulmonary artery after Blalock-Taussig shunts. Since continuous turbulent flow could also arise from patent ductus arteriosus (frequently present in the neonate), continuous turbulent flow in the right pulmonary artery is not specific for Blalock-Taussig shunt function. We evaluated 35 Blalock-Taussig shunts from suprasternal or high parasternal approach for flow in the right pulmonary artery, and in the Blalock-Taussig shunts themselves. From precordial approach, Doppler evaluations of the main pulmonary artery were also made in search of flow characteristic of patent ductus arteriosus. Doppler detection of flow within the Blalock-Taussig shunts indicated shunt patency, and indicated that continuous turbulent flow in the right pulmonary artery was not due to only patent ductus arteriosus. Shunts were proven patent in 31 patients, occluded in four. Twelve patients also had patent ductus arteriosus. By Doppler, the right pulmonary artery had continuous turbulent flow in 30 of 31 patients in whom the right pulmonary artery was found. From the suprasternal or high parasternal approach, the right Blalock-Taussig shunts were detected by marked continuous turbulent flow directed away from the transducer, between the aortic and superior vena caval flow signals. Left Blalock-Taussig shunts had similar directional continuous turbulent flow. Prosthetic shunts were identified by the dense shunt material. Twenty-four of 31 functional shunts were identified, and all contained continuous turbulent flow. Three left-sided shunts were missed. All four occluded shunts were identified by Doppler, and had no lumen flow within. Blalock-Taussig shunts were not confused with parent ductus in any patient. Doppler provided correct diagnosis (detection plus patency or occlusion) in 80% of all Blalock-Taussig shunts, and in 91% of prosthetic shunts. Pulsed Doppler echocardiography has good accuracy in evaluation of Blalock-Taussig shunts per se, and in differentiation from patent ductus. Doppler is also very useful when no murmur is heard, or when a murmur could be attributed to shunt, patent ductus, or to both.