Intracardiac covered stent for transcatheter completion of the total cavopulmonary connection: Anatomical, physiological and technical considerations

In the present review we discuss anatomical, physiological and technical aspects of the interventional transcatheter deployment of intracardiac covered stent for completion of the total cavopulmonary connection.

Optimal conduit size for extracardiac Fontan operation

BACKGROUND

Lack of conduit growth potential and thrombogenicity are the main drawbacks of the extracardiac Fontan operation (ECFO). Optimal size of the conduit according to the patients age and inferior vena cava diameter has not been established.

OBJECTIVES

We set out to ascertain whether the optimal dimensions of the conduit could be determined before an ECFO.

METHODS

Actual and expected age-related inferior vena cava diameters were compared with the extracardiac conduit diameter in 20 patients after ECFO. In 50 other pediatric and adult patients, the distance between intrapericardial part of the inferior vena cava and the undersurface of the right pulmonary artery (IVC-RPA) was measured. Cases of conduit thrombosis were analyzed.

RESULTS

The actual diameter of the inferior vena cava was variable and has a weak correlation with anthropometric data and expected diameter (R=0.07-0.23, P=0.32-0.76). The IVC-RPA distance correlated with height (R=0.87, P=0.0001), but was also variable. At the age of 2-4 years and body weight 12-15 kg IVC diameter and IVC-RPA distance are equal to 60-80% of adult values. Conduit thrombosis developed in two patients with unfavorable Fontan hemodynamics and oversized conduits.

CONCLUSIONS

Considering the inferior vena cava size, ECFO may be performed at the age of 2-3 years and at a body weight 12-15 kg, when a hemodynamically optimal almost adult sized conduit can be implanted. Optimization of the conduit is necessary on the basis of the actual inferior vena cava diameter and IVC-RPA distance. Anticoagulation postoperatively should be considered to prevent conduit thrombosis in patients with suboptimal Fontan circulation

Ultrastructural analysis of pseudo-intimal hyperplasia of polytetrafluoroethylene prostheses implanted into the venous and arterial systems

To evaluate and compare the pathogenesis of pseudo-intimal hyperplasia (PH) of venous and arterial prostheses, a segment of the inferior vena cava (n = 16) or abdominal aorta (n = 16) was substituted by a 3 mm internal diameter polytetrafluoroethylene tube graft (PTFE, 3 cm long, 30 microns in nodal distance) in albino rabbits. At designated time intervals (3-28 days) after the replacement, graft patency was examined and the dry weights of the intraluminal deposits measured as an indicator of the degree of PH. The harvested grafts were then subjected to an ultrastructural analysis by means of light microscopy (LM), and scanning electron and transmission electron microscopy (SEM, TEM). All the grafts remained patent during the entire observation period. The PH judged by the dry weight was significantly more extensive in the venous than in the arterial prostheses. The PH on day 28, observed by light microscopes was apparently most extensive in the mid-portion of venous prostheses but in the arteria prostheses it was mostly seen at the anastomotic sites. The lining of the intraluminal surface of the prostheses with endothelial-like cells observed by SEM was faster and more extensive in venous than in arterial prostheses. The process of PH in venous prostheses observed by TEM may be divided into the following steps: early thrombosis, phagocytosis of the thrombus, appearance of fibroblasts, growth of endothelial-like cells, appearance of smooth muscle cells, and pseudointimal thickening and proliferation of fibroblasts producing collagen fibrils. The process in arterial prostheses was essentially identical to that in venous prostheses but was much slower and less extensive. From these observations, it was concluded that the formation of PH occurs much faster in venous than in arterial prostheses, although the mechanism of PH is mostly identical in venous and arterial prostheses.

Blood compatibility of venous prosthesis made of textile or non-textile material

To study blood compatibility of venous prosthesis made of textile or non-textile material, the inferior vena cava of 37 rabbits was partly replaced by 3 mm internal diameter synthetic tube graft made of textile material (T: woven tetron) or non-textile material (P: polytetrafluoroethylene). At designated time intervals after the replacement (5 hours to 4 weeks), graft patency was examined and the dry weight of intraluminal deposits was measured. The harvested grafts were then subjected to light and scanning electron microscopy. All the T-grafts were occluded as early as 5 hours after grafting but when ticlopidine was administered prior to the grafting, all the grafts were patent. All the P-grafts were patent up to 4 weeks after grafting, though the amount of intraluminal deposits was increased in a time related manner, narrowing the lumen of the grafts. The luminal surface of the P-grafts harvested at 5 hours after grafting was covered by piles of fibrin networks entrapping erythrocytes without an association of platelet aggregates, which resembles the finding in the T-grafts harvested from the ticlopidine treated rabbits. In the P-grafts, both the proximal and distal luminal surfaces near the anastomosis were fully covered with endothelial cells by 2 weeks and the entire luminal surface was covered with these cells by 4 weeks. From these results, the following conclusions were obtained; (1) P-graft was superior to T-graft for venous prosthesis, which is mainly due to the inertness of P against platelet activation. (2) Though the luminal surface of the P-grafts was completely covered with endothelial cells by 4 weeks after grafting, the lumen was markedly narrowed by intimal hyperplasia.

Longevity of expanded polytetrafluoroethylene grafts for superior vena cava

We previously reported that the expanded polytetrafluoroethylene (ePTFE) graft for superior vena cava (SVC) substitution presents the problems of flexion and kinking when the graft is long. We therefore replaced the SVC of dogs with two types of prosthetic substitutes, ePTFE (Gore-Tex) and spiral-supported ePTFE (Im/praflex), and evaluated the long-term patency of the prosthetic substitutes. Total replacement of the SVC was performed in 9 adult mongrel dogs. The substitutes were ePTFE and spiral-supported ePTFE in 5 and 4 dogs, respectively. The animals were killed about 3 years after replacement of the SVC, and the harvested specimens were histologically examined by light microscopy and scanning electron microscopy. Evaluation of ePTFE revealed late occlusion in 1 of 5 dogs. The spiral-supported ePTFE showed patency in all dogs. In the group with ePTFE grafts, light microscopic examination revealed abnormalities of endothelial cells, granulation, and necrosis. There was no hyperplasia of the subendothelial connective tissue near the center. In the animals with spiral-supported ePTFE grafts, the subendothelial connective tissue showed favorable growth even in the center of the reconstructed site. There was no granulation in the spiral-supported ePTFE group. Scanning electron microscopic examination in the ePTFE group showed that endothelial cells were spindle-shaped and had an irregular surface. The spiral-supported ePTFE group showed an almost regular form of endothelial cells and no abnormalities except for the slightly spindled shape in the center. Therefore, we recommend that spiral-supported ePTFE should be used as an SVC substitute in clinical situations.