Atrial thrombus after total anomalous pulmonary venous connection repair

Background

Although left atrial (LA) morphology and volume reportedly change significantly following total anomalous pulmonary venous connection (TAPVC) repair, ¹ we are not aware of detailed analyses reported on the blood flow in the LA following TAPVC repair. Four-dimensional (4D) flow magnetic resonance imaging (MRI) is a promising tool for the comprehensive assessment of atrial hemodynamics.^2,3 Lee et al. ² used it to reveal substantial stasis in the LA appendage (LAA), and Gaeta et al. ⁴ used it to reveal the phases and functional components of normal LA inflow. Here, we used 4D flow MRI to analyze the blood flow in the LA following TAPVC repair.

Case presentation

A 6-year-old boy (18 kg) had undergone mixed-type TAPVC (supra + infra) repair using the sutureless technique 2 days after birth. Pulmonary venous (PV) stenosis release had been performed using a sutureless technique at 1 year of age. Thereafter, echocardiography revealed blood flow stasis in the LAA. The patient was prescribed anticoagulants and closely monitored. As he adopted a more active lifestyle, anticoagulants were discontinued and the blood flow stasis in the LA was re-evaluated. 4D flow MRI (CVI42; Circle Cardiovascular Imaging Inc., Calgary, AB, Canada) revealed blood inflow–outflow collision in the LA (Figure 1A) and low stasis velocity (0.04 m/s) in front of the LAA. Blood flow from the PVs to the LA was unidirectional during the early atrial diastolic phase; however, from the late stage onward, the blood flow returning from the LAA collided with the continuing blood flow from the PV (Figure 1B). T2-weighted MRI revealed blood stasis in the LAA (Figure 1C). Transesophageal echocardiography revealed a suspected thrombus in the LAA.

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Figure 1.

Blood flow before surgery. (A) Four-dimensional flow magnetic resonance imaging of early-diastolic phase in the ventricle. Green shows blood flow from the RPV, red shows blood flow from the LPV, and yellow shows blood flow from the LAA. (B) Blood flow velocity in the left atrium versus time (ms). The arrow shows the period during which LAA (yellow) blood flow collides with that from the RPV (green) and LPV (red). (C) T2-weighted magnetic resonance image. The arrow indicates the stasis in the LAA. LAA: left atrial appendage; LPV: left pulmonary vein; RPV: right pulmonary vein.

We performed LAA resection surgery owing to the risk associated with the patient using anticoagulants while maintaining an active lifestyle. Institutional review board approval was obtained (number: 50-8), and the patient's parents provided informed consent.

Median resternotomy was performed and cardiopulmonary bypass was commenced by reintroducing the venous blood from the bicaval cannulation into the ascending aorta. Antegrade cardioplegic arrest was attained. The LAA was externally resected and closed at its base. Although no thrombi were observed within the LAA (Figure 2A), a pathological diagnosis was requested owing to thickening of the trabecular structure. Eccentric intimal hyperplasia of the LAA was diagnosed by pathology; thrombus adhesions due to intimal thickening and blood flow stagnation had progressed slowly in some areas (Figure 2B and C). The patient was discharged without anticoagulants or incident on postoperative day 7. 4D flow MRI performed revealed no stasis and blood flow collision in the LAA 4 months postoperatively (Figure 3A and B).

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Figure 2.

Surgical specimen. (A) The opened left atrial appendage specimen shows thickening of the intima. (B) Low-power specimen stained with Elastica Masson shows normal elastic lamina and endocardium (yellow square) and thickened endocardium (blue square). (C) Enlarged specimen within the blue square of Figure 2B.

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Figure 3.

Blood flow 4 months postoperatively. (A) Four-dimensional flow magnetic resonance imaging of early-diastolic phase in the ventricle. (B) Blood flow velocity in the left atrium versus time (ms). Green shows blood flow from the RPV, red shows blood flow from the LPV. LPV: left pulmonary vein; RPV: right pulmonary vein.

Discussion and conclusions

The blood flow in the LA naturally forms vortices and two phases in one cardiac cycle owing to the inflow from the PV, without collision. ⁴ In our case, although the blood flow in the LA formed two gentle phases, the blood retained in the LAA collided with the inflow from the PV, and the blood flow velocity was 0.04 m/s, indicating stasis in the LAA. A distinctive feature of this case was that LAA stasis was caused by blood flow collision between the inflow from the PVs (below) and outflow from the LAA (above), from the late ventricular systolic phase almost to the diastolic phase. Such blood flow collisions typically appear following infra-cardiac TAPVC repair of vessel structures with an ‘antler appearance’, defined as the joining of upper and inferior PVs to form a common vein, which drains to form a confluence. The PV flow after such TAPVC repair is unidirectional from the lower area and collides with the blood flow in the LAA returning after stagnation due to a dead end. Blood flow stasis or collision may also occur after surgery for other congenital heart diseases. ⁵

In this case, no thrombus was detected during surgery, but its presence was pathologically suggested. In addition, T2-weighted MRI and 4D flow MRI clearly showed stasis in the LAA. The TAPVC with an antler appearance alerted us to the possibility of thrombus formation in the LAA.

Shi et al. ⁶ reported that the antler appearance is associated with PV stenosis after TAPVC repair, although the mechanism is unclear. Such blood flow collisions may lead not only to thrombus formation in the LAA but also to increases in anastomotic tension.

Infra-cardiac TAPVC with an antler appearance, resulting in abnormal blood flow in the LA from the PVs, may therefore be associated with thrombus development in the LAA and PVS after TAPVC repair, owing to blood flow collision in the LA.