Percutaneous Therapies for Severe Pulmonary Hypertension
An alternative method of decompressing the right ventricle is by forming a direct anastomosis between the descending aorta (dAo) and the left pulmonary artery (LPA), a Pott's shunt. This offers several theoretical advantages over the creation of an AS. Blood is shunted directly into the dAo, which avoids exposing the brain and myocardium to desaturated blood. A Pott's shunt may offer more reliable shunting than would an atrial septal defect by addressing suprasystemic pulmonary artery surges. Furthermore, uncontrolled hypoxemia can be potentially avoided by the use of a pressure-restrictive shunt. The largest experience described in the literature is a series of 8 children, all of whom were in NYHA/World Health Organization functional class IV with symptoms of repeated syncope or signs of right heart failure. Six of 8 patients survived and remained well at a mean follow-up of 63 months, with improvements in RV dimensions on echocardiography, improved functional status, as well as lower BNP levels.
Transcatheter creation of an aortopulmonary shunt has been successfully performed in animals and more recently in humans. Ten piglets had a Pott's shunt created by radiofrequency perforation from the aorta to the pulmonary trunk, followed by stent implantation (bare-metal stents or polytetrafluoroethylene-covered coronary stents). Oxygen saturation improved from 63% (range 53% to 72%) in the right atrium to 84% (range 59% to 92%) in the pulmonary artery (p < 0.005). At follow-up, 4 of 6 stents were obstructed because of tissue ingrowth in the bare-metal stents and thrombus formation in the covered stents.
Percutaneous aortopulmonary shunt formation was also reported in a series of 4 adults in whom a modified Brockenbrough needle and the "stiff" end of a 0.014-inch wire were used to puncture the dAo and LPA. After balloon dilation, an iCAST 7 × 22-mm covered stents (Atrium Medical Corporation, Hudson, New Hampshire) spanning the LPA and dAo walls was implanted. Follow-up was limited to 4 to 10 months. This technique is very high risk, as any misjudgment in stent length to span the distance between the LPA and dAo can result in hemorrhage. One patient died 8 days post-procedure of pneumonia and multiorgan failure, and 1 died of catastrophic intrathoracic bleeding.
Another group described 3 patients with IPAH and severe PH who had a small patent ductus arteriosus or probe-patent patent ductus arteriosus. This allowed insertion of a stent to provide a communication between the dAo and LPA. The stent size used varied from 6 to 9 mm in diameter and was gradually dilated to equalize PAP and aortic pressure. After a mean follow-up of 14 ± 9 months, all 3 patients showed improved functional capacity and improved RV function. Importantly, there were no major complications or deaths.
Both of the series described were small but indicate a possible role for intervention as an additional therapy in an already difficult to-treat group of patients. After a stent anastomosis is created, there is the possibility that it could be further dilated to increase the degree of shunting. At present, these techniques are experimental and will require larger numbers of patients with longer follow-up periods to determine their full effects on survival. The optimal timing of the percutaneous Pott's shunt is yet to be determined. It currently appears to be high risk and should be reserved for patients in whom AS or lung transplantation is contraindicated.
Pott'S Shunt
An alternative method of decompressing the right ventricle is by forming a direct anastomosis between the descending aorta (dAo) and the left pulmonary artery (LPA), a Pott's shunt. This offers several theoretical advantages over the creation of an AS. Blood is shunted directly into the dAo, which avoids exposing the brain and myocardium to desaturated blood. A Pott's shunt may offer more reliable shunting than would an atrial septal defect by addressing suprasystemic pulmonary artery surges. Furthermore, uncontrolled hypoxemia can be potentially avoided by the use of a pressure-restrictive shunt. The largest experience described in the literature is a series of 8 children, all of whom were in NYHA/World Health Organization functional class IV with symptoms of repeated syncope or signs of right heart failure. Six of 8 patients survived and remained well at a mean follow-up of 63 months, with improvements in RV dimensions on echocardiography, improved functional status, as well as lower BNP levels.
Transcatheter creation of an aortopulmonary shunt has been successfully performed in animals and more recently in humans. Ten piglets had a Pott's shunt created by radiofrequency perforation from the aorta to the pulmonary trunk, followed by stent implantation (bare-metal stents or polytetrafluoroethylene-covered coronary stents). Oxygen saturation improved from 63% (range 53% to 72%) in the right atrium to 84% (range 59% to 92%) in the pulmonary artery (p < 0.005). At follow-up, 4 of 6 stents were obstructed because of tissue ingrowth in the bare-metal stents and thrombus formation in the covered stents.
Percutaneous aortopulmonary shunt formation was also reported in a series of 4 adults in whom a modified Brockenbrough needle and the "stiff" end of a 0.014-inch wire were used to puncture the dAo and LPA. After balloon dilation, an iCAST 7 × 22-mm covered stents (Atrium Medical Corporation, Hudson, New Hampshire) spanning the LPA and dAo walls was implanted. Follow-up was limited to 4 to 10 months. This technique is very high risk, as any misjudgment in stent length to span the distance between the LPA and dAo can result in hemorrhage. One patient died 8 days post-procedure of pneumonia and multiorgan failure, and 1 died of catastrophic intrathoracic bleeding.
Another group described 3 patients with IPAH and severe PH who had a small patent ductus arteriosus or probe-patent patent ductus arteriosus. This allowed insertion of a stent to provide a communication between the dAo and LPA. The stent size used varied from 6 to 9 mm in diameter and was gradually dilated to equalize PAP and aortic pressure. After a mean follow-up of 14 ± 9 months, all 3 patients showed improved functional capacity and improved RV function. Importantly, there were no major complications or deaths.
Both of the series described were small but indicate a possible role for intervention as an additional therapy in an already difficult to-treat group of patients. After a stent anastomosis is created, there is the possibility that it could be further dilated to increase the degree of shunting. At present, these techniques are experimental and will require larger numbers of patients with longer follow-up periods to determine their full effects on survival. The optimal timing of the percutaneous Pott's shunt is yet to be determined. It currently appears to be high risk and should be reserved for patients in whom AS or lung transplantation is contraindicated.
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