Dr. Erika Berman Rosenzweig

Despite medical advances in the treatment of idiopathic pulmonary arterial hypertension, it remains a severe and progressive disease, usually leading to right heart failure, significant morbidity, and early mortality. However, adolescents and young adults with end-stage pulmonary arterial hypertension who have failed medical therapies are finding renewed hope at NewYork-Presbyterian/Columbia University Irving Medical Center, where a novel unidirectional-valved shunt approach is providing an enduring bridge to lung transplant.

“A little over a decade ago, the Potts shunt was revitalized as a reversed Potts shunt in Europe to provide a pop-off from the left pulmonary artery to descending aorta to treat end-stage pulmonary arterial hypertension,” says Erika Berman Rosenzweig, MD, Director of the Pulmonary Hypertension Comprehensive Care Center at NewYork-Presbyterian/Columbia. “While the reversed Potts shunt approach has the potential to delay the need for lung transplantation and offers a treatment for those who are transplant ineligible, it may lead to bidirectional shunting.”

A Novel Shunt Design: One Direction is Better than Two

To address the challenges of bidirectional shunting, Dr. Berman Rosenzweig, Matthew D. Bacchetta, MD, an adjunct professor at Columbia’s Department of Biomedical Engineering and a thoracic surgeon with Columbia at the time, and their colleagues designed a novel unidirectional-valved shunt (UVS) as a pressure release valve to permit flow from the main pulmonary artery to the descending aorta only during periods of suprasystemic pulmonary arterial pressure. Unlike the classic reversed Potts shunt, the UVS provides the physiologic benefit of unloading the right ventricle while preventing “reversed” flow from the aorta to the pulmonary circulation when systemic blood pressure exceeds pulmonary arterial pressure.

“When the pulmonary artery or lung circulation is under high pressure the UVS enables the right heart to decom­press, allows the right ventricle to function under less strain, and maintains fully oxygenated blood flow to the upper body, thereby improving exercise tolerance and reducing the risk of syncope and cardiovascular collapse,” explains Dr. Berman Rosenzweig. “The UVS is incorporates a Contegra pulmonary valved conduit wrapped in a GORE-TEX graft so that it doesn’t expand under pressure. What we did that was novel was put in a one-way valve within this shunt so that the blood only goes from right to left and doesn’t back flow into the lungs from left to right. The addition of a unidirectional pop-off valve has the benefit of allowing right-to-left shunting during suprasystemic pulmonary hypertensive crises, while preventing left-to-right shunting into the pulmonary artery when pulmonary artery pressure falls below systemic pressure.”

“The one-way valve allows the blood to flow only from the pulmonary artery to the descending aorta. It doesn’t ‘back flow’ when the heart relaxes, so it avoids any additional trauma to lung circulation, which is already relatively fragile in these patients.” — Dr. Erika Berman Rosenzweig

In November 2016, a Columbia medical and surgical team was the first to perform the palliative unidirectional-valved shunt in a young adult with severe idiopathic pulmonary arterial hypertension. The team has since performed the UVS procedure on another four patients with IPAH. Their retrospective review of the five cases – four males and one female, ages 12 to 22 – was published in the November 14 online issue of The Journal of Thoracic and Cardiovascular Surgery. The procedures took place between November 2016 and May 2019, with follow-up through August 2019.

UVS design shows the site of surgical insertion of the valved conduit from the superior aspect of the main pulmonary artery to the descending aorta distal to left subclavian artery.
(Credit: Journal of Thoracic and Cardiovascular Surgery)

Patient Considerations

“We specifically selected patients with very high lung pressure – the sickest of the sick,” notes Dr. Berman Rosenzweig. “All patients had suprasystemic pulmonary arterial pressure, poor right ventricular function, and World Health Organization functional class IV symptoms at baseline. These patients typically have severe restlessness with exertion, can barely walk a city block or two, and are very limited in their activities. Some have chest pain with exertion or they’re fainting. UVS is only considered for patients who’ve been treated with the maximal medical therapy – including fusions with prostacyclines and continuous IV infusions – without success. They are at the end of their treatment options except for atrial septostomy or transplant.”

Surgical Features

Dr. Emile A. Bacha

“The unidirectional-valved design captures the physiologic benefit of right ventricle-pulmonary arterial unloading while preserving upper body oxygenation and preventing the negative impact of reversed left to right shunting on a vulnerable pulmonary arterial system,” explains Emile A. Bacha, MD, Chief of the Division of Cardiac, Thoracic, and Vascular Surgery at NewYork-Presbyterian/Columbia. “The surgery is performed through a midline sternotomy in case these patients eventually go on to lung transplant, which our surgeons generally perform though a clamshell incision. We try very hard to stay out of the pleural spaces to allow for easier lung transplant in the future. Patients are on cardiopulmonary bypass, and it is critical to have an experienced anesthesia team for safe induction of these patients, as well as quick access to ECMO or bypass in the event of a pulmonary hypertension crisis during induction. We also have a very low threshold to transition to veno-venous percutaneous ECMO post-op and even extubate patients while on VV-ECMO to allow for a slow ECMO wean.”

“All five patients are alive and transplant free at the latest follow-up, and three who were listed have been taken off the active lung transplant list. This is very exciting as it opens up a whole new arena for some of these patients who have deadly disease.” — Dr. Emile A. Bacha

The surgery involves positioning the proximal graft slightly off center from the anterior main pulmonary artery in a direction that allows for natural passage to the aortic anastomosis. The distal anastomosis is established beyond the takeoff of the left carotid artery. “Given this was our early experience, we took a cautious approach by leaving a small atrial communication, 3 to 6 mm, to ensure adequate decompression of the right atrium in the early postoperative period and to ensure there was a safety shunt in the event of UVS failure,” notes Dr. Bacha. “The atrial communication can be closed percutaneously if the need arises.”

Takeaways

“We believe the UVS provides a better bridge for patients than atrial septostomy and delays the need for lung transplant,” adds Dr. Berman Rosenzweig. “This is particularly true for a teenager who may typically have only a 50 or 60 percent five-year survival following lung transplantation. We want to treat our patients as long as we can before they need that transplant. The UVS procedure is potentially a way to alleviate the right heart strain, which gives the patients more time, but also improves their symptoms.”

Transthoracic 2-dimensional echocardiogram of unidirectional-valved shunt (parasternal short axis view) showing the main pulmonary artery, unidirectional valved shunt, and descending aorta without (left) and with color Doppler (right).
(Credit: Journal of Thoracic and Cardiovascular Surgery)

“All five patients are alive and transplant free at the latest follow-up, and three who were listed have been taken off the active lung transplant list,” says Dr. Bacha. “This is very exciting as it opens up a whole new arena for some of these patients who have deadly disease.”

The authors conclude that the UVS and classic reversed Potts shunts are evolving into durable palliative approaches for the management of medication-refractory idiopathic pulmonary arterial hypertension and will both be treatment options for end-stage group 1 PAH in in older children and young adults with suprasystemic pulmonary arterial pressure.

Dr. Berman Rosenzweig sees a possible application of the UVS for patients with Eisenmenger syndrome. “Perhaps we could use the same concept and provide them with a much better quality of life if they have fully oxygenated blood going to their heads and hearts,” she says. “We’re working on other potential applications that could be completely game-changing and would help many more people worldwide.”