Interventional Management of Acute Thrombosis of the Modified Blalock-taussig Shunt in a Case of Tricuspid Atresia

Shunt creation between the pulmonary and systemic circulations has been one of the biggest steps in the management of cyanotic congenital heart diseases (CCHD) [1]. The modified Blalock-Taussig shunt (mBTS) is a tubular conduit, made of polytetrafluoroethylene, interposed between the right subclavian artery/brachiocephalic trunk and the right pulmonary artery [2]. Initially used for the treatment of pulmonary stenosis/atresia associated with tetralogy of Fallot, implantation of a mBTS rapidly became one of the first palliative steps in the treatment of more complex CCHD, including univentricular physiology, such as tricuspid atresia [2]. In these conditions, the whole pulmonary circulation depends on the mBTS (Figure 1). As a result, shunt dysfunction may have catastrophic consequences in these patients, with a high mortality rate in the event of acute occlusion [3]. We are presenting a case of univentricular physiology, where the routine hemodynamic evaluation before bidirectional Glenn anastomosis was complicated by acute mBTS thrombosis.

Figure 1

An 11-month-old infant (weight: 7.5 kg) was admitted for routine cardiac catheterization before the Glenn procedure. The child was diagnosed intrauterine with cardiac malformation. Immediately after birth, echocardiography showed tricuspid atresia with normal relations of the great vessels, associated with right ventricular hypoplasia, unrestrictive ventricular septal defect, pulmonary valve atresia, and a hypoplastic main pulmonary artery. Cardiac dextroversion, a persistent left superior vena cava, and a patent ductus arteriosus were additionally described. Contrast enhanced computer tomographic (CT) examination revealed an atypical anatomy of the aortic arch and its main branches (Figure 2). As the pulmonary circulation was ductal dependent, prostaglandin-E1 infusion was started immediately, and at the age of two weeks, a palliative surgical intervention was performed: atrioseptectomy, ligation of the PDA and of the persistent left superior vena cava, completed with the implantation of a 3.5 mm diameter mBTS between the brachiocephalic trunk and the right pulmonary artery. The patient was readmitted at the age of 6 months, for the next surgical step of bidirectional cavopulmonary anastomosis, preceded by a routine invasive hemodynamic assessment. However, the cardiac catheterization and surgical intervention were postponed due to right atrial thrombosis at that time. As the mBTS was not clearly visible by echocardiography, repeated contrast enhanced CT examination demonstrated the patency of the shunt (Figure 3). Genetic assessment detected the following mutations associated with thrombophilia: methylenetetrahyd rofolatereductase (MTHFR) A1298C – homozygote, plasminogen activator inhibitor-1 (PAI-1) 4G/5G – heterozygote, and endothelial protein C receptor (EPCR) haplotype A3/A3. Anticoagulation was started for right atrial thrombosis and then continued long-term, prophylactically.

Figure 2

Figure 3

Cardiac catheterization was performed after 4 months due to repeated respiratory infections. Meanwhile, the right atrial thrombus disappeared. In general anesthesia, a mean pulmonary artery pressure of 10 mmHg was measured with pulmonary arterial resistances of 1.88 Wood units/m², and a peak-to-peak gradient of 18 mmHg was measured between the left ventricle and the ascending aorta. Angiography evidenced a bending associated with stenosis at the pulmonary anastomosis of the mBTS (Figure 4).

Figure 4

At the end of the catheterization procedure, pulse oximetry indicated a sudden drop of systemic oxygen saturation. Arterial blood gas analysis evidenced an oxygen saturation of 40%, despite increasing the fraction of inspired oxygen (FiO₂) from 30% to 100%. The severe systemic desaturation was accompanied by bradycardia (70 beats/minute). The suspicion of acute mBTS thrombosis was confirmed by selective contrast media injection into the shunt (Figure 5). Although the mBTS was not completely occluded, persistent contrast staining was observed at the site of the distal bend and stenosis. A 0.014” balance middleweight (BMW, Abbott, USA) coronary guidewire was advanced through the mBTS into the right pulmonary artery, and a 3x12 mm semi-compliant balloon (Solarice, Medtronic, USA) was inflated three times to the nominal pressure of 8 atmospheres at the site of thrombosis. Although the angiographic appearance improved for a time, the clinical status remained unchanged, and selective catheter-directed thrombolysis was started using a 4F Judkins right diagnostic catheter positioned in the proximal part of the mBTS. A dose of 0.1 mg/kg tissue plasminogen activator was infused directly into the shunt during a period of 10 minutes. However, the clinical status of the patient did not improve, and repeated angiography evidenced worsening thrombosis at the pulmonary anastomosis (Figure 6). As a bailout procedure, a 3.5x15 mm pre-mounted drug-eluting coronary stent (Resolute Onyx, Medtronic, USA) was implanted at the nominal pressure of 12 atmospheres in the distal part of the mBTS using radiographic anatomical landmarks. A good angiographic result was obtained (Figure 7), with an immediate raise in oxygen saturation to 80%. No other periprocedural complications occurred; the arterial and venous sheaths were removed at 6 hours after the administration of tissue plasminogen activator and manual compression was performed until definitive hemostasis. The Glenn procedure and shunt removal were performed in stable conditions after one week of uneventful evolution. The patient was discharged in good clinical condition, on chronic acenocumarol and aspirin therapy, three weeks after surgery.

Figure 5

Figure 6

Figure 7

To the best of our knowledge, this is the first report of a patient with acute thrombosis of a mBTS managed by catheter intervention in Romania.

According to Virchow, the triad of blood stasis (in our case, caused by the bending and stenosis at the anastomotic site), endothelial injury (in our case, caused by the catheter tip advanced to the pulmonary artery for hemodynamic assessment), and hypercoagulability (in our case, previously documented thrombophilia) are responsible for intravascular thrombosis. Additional risk factors of mBTS thrombosis include small shunt diameter, arrhythmias, infection, dehydration, hypotension, and perioperative shunt clamping [4,5]. Thrombus formation in a small, 3.5mm PTFE shunt could thus easily complicate the hemodynamic assessment before the Glenn procedure in our patient or any other case of univentricular physiology with shunt-dependent pulmonary circulation.

Catheter-based management of acute mBTS thrombosis is a high-risk procedure, authors reporting a major complication rate up to of 9.1% [6] and a failure rate between 10-21.2% [6-8]. However, the procedure is frequently lifesaving in critically ill patients and the alternative of surgical revision is also not a compelling one due to high operative mortality [3].

There are three options for catheter-based treatment of mBTS thrombosis. Selective thrombolysis could be effective even if a low-dose of 0.1 mg/kg tissue plasminogen activator is administered selectively into the thrombosed conduit, especially if completed with balloon angioplasty [4]. Balloon angioplasty at the site of conduit stenosis/occlusion is also frequently successful [8]. However, neither of these strategies was effective in our case, and the third option of stent implantation was performed as a bailout procedure. Because femoral artery occlusion could be a potential major complication [8], we considered it too dangerous to use a 6F guiding catheter (the smallest available in our catheterization laboratory). Accordingly, to prevent acute ilio-femoral occlusion, the stent was implanted through the 4F arterial sheath without a guiding catheter, only using radiographic anatomical landmarks.

Even a routine hemodynamic evaluation can be complicated by a potentially fatal event (such as acute mBTS thrombosis), especially if predisposing factors are present (see Virchow triad above). Therefore, one must be prepared to quickly diagnose the condition and to have efficient bailout strategies for its successful management. In our case, the catheter-based treatment allowed the subsequent surgical step – the bidirectional cavopulmonary anastomosis – to be performed in a clinically stable condition.

The presented catheter-based bridge-to-surgery strategy with stent implantation seems to be safe and effective for the management of acute mBTS thrombosis.

Apprehending the predisposing factors for complications in advance, and having the entire cathlab team aware of them, can make the difference between a successful hemodynamic investigation and a catastrophic one, especially in univentricular hearts.