Obstruction in Modified Blalock Shunts: A Quantitative Analysis With Clinical Correlation

Background Despite numerous reports describing the clinical course of patients undergoing a modified Blalock-Taussig shunt (MBTS), there is limited information on shunt obstruction. No studies have quantified MBTS stenosis histopathologically and correlated that with demographic and clinical risk factors. Methods From June 2001 to June 2003, 155 patients had MBTS takedown. The shunt operation (at median age 6 days; shunt size 3.5 mm in 56 [36%]; 4 mm in 84 [54%]; 5 mm in 15 [10%]) was performed on cardiopulmonary bypass (CPB) in 96 patients (62%). At elective takedown (at median 8.1 months), the shunt was excised and histopathologically analyzed for maximal narrowing. Demographics and clinical variables including age, weight, shunt size and duration, diagnosis, use of cardiopulmonary bypass, blood products, anastomosis sites, and concomitant antegrade flow were then tested for correlation with shunt stenosis. Results The mean value for maximal narrowing of the shunt lumen was 34% ± 22%, and 32 patients (21%) had greater than 50% stenosis. Myofibroblastic proliferation, often associated with organized thrombus, caused the obstruction. Smaller shunt size (<4 mm) was a statistically significant risk factor for stenosis greater than 50% (odds ratio [OR] = 2.51; p = 0.028). Other variables that showed a clinically important association with obstruction but did not reach statistical significance included age less than 14 days at shunt (OR = 2.08, confidence interval [CI] 0.8 to 5.2), shunt on bypass (OR = 2.07, CI 0.9 to 4.8), and platelet use at shunt operation (OR = 1.96, CI 0.9 to 4.4). Conclusions Most MBTS develop stenosis by the time of takedown, and 21% have greater than 50% obstruction. Shunt size less than 4 mm is a risk factor for high-grade stenosis. Younger age, CPB, and use of platelets are other clinically important factors. Better conduits and suppression of intimal proliferation could potentially improve outcomes.