Introduction
Mechanical haemolysis is a rare but significant postsurgical complication. Several reports describe the occurrence based on mechanical causes such as abnormal flow patterns, Reference Xu, Kaliviotis, Munjiza, Avital, Ji and Williams1 residual defects, or exposure to foreign materials. Reference Chang, Hung, Huang and Wu2 In some cases, haemolysis disappeared after endothelialization. Reference Singh, Letsky and Stark3 In one case series, haemolysis could be prevented by a Dacron patch covered with autologous pericardium, after haemolysis had previously occurred following ventricular septal defect closure. Reference Singh, Letsky and Stark3
Case report
A 13-year-old boy was referred to our centre due to a complex, previously not corrected, congenital heart defect. His diagnosis included congenital corrected transposition of the great arteries with hypoplastic subpulmonary ventricle, double outlet right ventricle, a large inlet ventricular septal defect, and a severe subvalvular and valvular pulmonary stenosis in combination with dextrocardia and situs inversus totalis. Over time, he developed progressive pulmonary stenosis with exercise intolerance and declining oxygen saturation. Corrective surgery involved rerouting the pulmonary artery root via the inlet ventricular septal defect using a Dacron patch tunnel, partial resection of the subpulmonary stenosis (leaving a residual stenosis as a banding effect), and creation of a restrictive atrial septal defect. The surgery was completed without complications.
Postoperatively, the patient developed transient thrombocytopenia with multiple small bleeding sources requiring platelet transfusions. However, a persistent and severe decline in haemoglobin levels could not be fully explained by the bleeding (haemoglobin minimum 7.7 g/dL). Further investigation confirmed haemolysis, as evidenced by elevated lactate dehydrogenase, decreased haptoglobin, increased indirect bilirubin, and a compensatory reticulocytosis.
Since parameters such as flow acceleration before and after the operation did not differ and there were no signs of haemolysis before the procedure, we made a tentative diagnosis of mechanically induced foreign body-associated haemolysis.
Extensive differential diagnostics ruled out immunological and intrinsic red cell causes of haemolysis. Direct and indirect Coombs tests were negative. There were no signs of infection. Echocardiography revealed a narrow curved Dacron Patch tunnel connecting the subpulmonary ventricle to the pulmonary artery with turbulent flow and markedly increased flow velocities (>4 m/sec). Based on these findings, shear stress from the implanted material and altered flow dynamics were strongly suspected.
At discharge, haemolysis was compensated by good bone marrow function with no signs of organ dysfunction. The case was discussed interdisciplinary, and a wait-and-see approach with check-ups every two weeks was agreed upon, hoping that endothelialization of the Dacron patch would resolve the issue. Clinical improvement did not occur after 8 weeks. There was increasing pallor, icterus, and exercise limitation below the preoperative level. Echocardiography revealed a progressive stenosis with flow acceleration of >5 m/sec. Diagnostic cardiac catheterization was performed. Angiography revealed significant constriction in the subpulmonary outflow tract, with a supra-systemic left ventricular pressure of 125 mmHg in the context of transposition of the great arteries (see Figure 1). Several balloon angioplasties were performed (12×20 mm powerflex balloon [8 atm], 14×20 mm atlas balloon [16 atm]), leading to a substantial reduction in pressure below systemic levels. A stent (Andramed XL 16 × 30 mm) was implanted in the subpulmonary outflow tract, preserving the pulmonary valve, due to persistent distal narrowing and concern for restenosis. This led to a reduction of left ventricular pressure to 33 mmHg and improved outflow efficiency (see Figure 2). Echocardiography showed a post-interventional pressure gradient across the subpulmonary outflow tract of approximately 30 mmHg without insufficiency of the pulmonary valve.
Angiography showing subpulmonary stenosis in the anteroposterior and lateral views.
Angiography reveals improved outflow after stent placement.
Two weeks after the intervention, lab parameters normalized. There were no signs of haemolysis anymore. At 16-month follow-up, the patient was clinically well without recurrence of haemolysis, and the subpulmonary ventricle demonstrated good function with a 60 mmHg outflow tract gradient. No follow-up fluoroscopy or dynamic chest radiography was performed, as the patient remained asymptomatic with no clinical signs suggesting stent-related complications, including fracture.
Discussion
Mechanical haemolysis after prosthetic heart surgery is well described in the literature. The main reason for mechanical haemolysis is shear forces impacting the erythrocyte membrane. Reference Cannata, Cantoni, Sciortino, Bruschi and Russo4 In vitro analysis by Neavril et al. showed that shear stress of red blood cells greater than 3,000 dyn/cm2 can create haemolysis by deforming the cell membrane depending on time duration. Reference Nevaril, Lynch, Alfrey and Hellums5 Leverett et al. pointed out that a turbulent jet flow can create shear stress up to 40,000 dyn/cm2. Reference Leverett, Hellums, Alfrey and Lynch6 In vivo analysis suspected high acceleration, worsened by small diameters (<2 mm) and jet collision with solid structures, leading to mechanical haemolysis. Reference Garcia, Vandervoort and Stewart7 In our case, the estimated shear stress could be up to 33,325 dyn/cm Reference Chang, Hung, Huang and Wu2 (τ = D/4 * (ΔP/L), D = 0.4 cm, ΔP = 125 mmHg, L = 0.5 cm).
To find the source of haemolysis, a focused multidisciplinary diagnostic approach of echocardiography, laboratory tests, including transfusion-induced antibody-mediated haemolysis, as well as other hematological causes, should be considered. If the haemolysis is compensated by good bone marrow function and there are no signs of organ failure, a wait-and-see approach seems reasonable until endothelialization is complete. There is evidence that intracardiac grafts and grafts of the great arteries are endothelialized after 6–8 weeks. Reference Singh, Letsky and Stark3,Reference Shi, Wu and Onuki8 If haemolysis is severe, signs of organ failure are present, or haemolysis persists over the time of 6–8 weeks, expanded diagnostics such as interventional catheterization or even reoperation should be considered.
Conclusion
This case clearly demonstrates the damaging effect of high shear forces on blood cells, particularly in the presence of implanted prosthetic material.
Data availability statement
The datasets generated and/or analysed during the current study are available from the corresponding author upon reasonable request.
Financial support
This research received no specific grant from any funding agency, commercial, or not-for-profit sectors.
Competing interests
The authors declare none.
Statements and declaration
Permission was granted by the respective parents to publish the case report.
Ethical consideration
Consent was not required.
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