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Eliza Cinteza1,2

1„Carol Davila” University of Medicine and Pharmacy, Bucharest, Romania
2„Marie Curie” Emergency Children’s Hospital, Bucharest, Romania

Abstract: Pulmonary hypertension (PH) is a progressive disease with apparently implacable evolution. Among the thera-peutic methods in the advanced forms more and more various possibilities of interventional procedures are discussed. All of these usually are palliative methods, reserved either for refractory PH or as a bridge to lung transplantation. The older and the newer directions are discussed in turn, presenting the advantages, difficulties, complications and results obtained starting with the old one described and applied, balloon atrial septostomy, then the transcatheter Potts shunt creation and balloon pulmonary angioplasty in chronic thromboembolic pulmonary hypertension.

Keywords: pulmonary hypertension, balloon atrial septostomy, transcatheter Potts shunt creation, balloon pulmonary angioplasty, interventional treatment

INTRODUCTION

Pulmonary hypertension (PH) is a complex physio-pathological state, more frequently, a complication of different other disease, and rarely a primary disease. The diagnosis and classification of PH can be accura-tely established by right cardiac catheterization. PH means a value of the mean pulmonary arterial pressu-re (PAPm) which is higher or equal to 25 mmHg at rest. A simple classification of the PH consists in pre-capillary and postcapillary PH, depending on the mea-sured value of the pulmonary artery wedge pressure (PAWP ≤15 mmHg for precapillary PH associated with pulmonary vascular resistance index PVRi >3iWU)1,2. The precapillary may be encountered as pulmonary arterial hypertension (PAH) of idiopathic or heritable type, or induced by drugs or toxins, or associated to congenital heart disease (CHD), connective tissue di-sease, human immunodeficiency virus infection, portal hypertension or schistosomiasis. Other precapillary causes are related to lung diseases, chronic thrombo-embolic pulmonary hypertension (CTEPH) or other rare diseases. The postcapillary PH is mainly due to left heart disease (pulmonary veins stenosis, valvu-lopathies, left ventricle LV dysfunction – systolic or diastolic, cardiomyopathies)1. Sometimes, especially in chronic evolution of the heart disease, both types (pre- and postcapillary) of PH may be encountered in which case right and left cardiac catheterization is re-commended3.
The treatment of PH may vary depending on the severity and especially on the etiology. In PAH asso-ciated to CHD, which is found in 30% of the cases, the interventional treatment may be the treatment of choice for correctable systemic-to-pulmonary shunts (atrial septal defect-ASD, ventricular septal defect-VSD, patent ductus arteriosus-PDA). In such situati-ons, the cardiac defect is moderate to large, shunting left-to-right, with anatomical characteristics that ma-kes it suitable for interventional closure and the PVR is mildly to moderately increased4.
CHD associated with severe PAH is a complex situ-ation sometimes due to late presentation of the CHD. In such cases, some authors choose to close directly the defect. Such experience is showed by Sadiq on 45 patients with large PDA and severe PAH (mPAP 67 mmHg), of late presentation of a CHD (10 years of age). Depending on the oxygen saturation in room air (>97%) and the response to the pulmonary vasoreac-tivity test some of the defects were closed, safe and effective, with a success rate close to 90%5. But in 4 of 46 patients in the Sadiq study, although the PVR was reduced, the patients remained with severe PAH after the closure of the PDA. For such patients maybe, a better approach would be to fenestrate the device in-tended to close the defect with a short stent (4.5X20 mm), with the intension to reduce the flow but not to close it, like in the case published by Singh6. Also, the-re are custom-made fenestrated device reported for similar cases7. Implantation for ASD of an atrial flow regulator is another option8.
Recently, the interventional treatment in PH may be applied also in other cases then in those mentioned before, in which this may be a part of the paliative treatment or a bridge to transplantation. Creating a stable interatrial communication (with implantation of an atrial fl ow regulator) or by transcatheter creati-on of a pulmonary – aortic shunt (Potts shunt) both for decompressing the right heart and increasing the systemic cardiac index1. Practically, this interventions consist in transforming the a case of pulmonary arteri-al hypertension in a case with Eisenmenger physiology3 which was demonstrated to have a better RV perfor-mance and a more hypertrophied RV free wall, corre-lated with a better survival9. This methods developed in connection with the observations that the patients with patent foramen ovale and Eisenmenger syndrome live longer than those with similar mPAP, but without a comunication. Also, the cardiac index and the right ventricle (RV) performance are better in Eisenmenger syndrom10.
In CTEPH pulmonary artery angioplasty may be recommended in special cases in which the patients are either considered technically non-operable or the risk:benefit ratio for pulmonary endarterectomy is too high1.

Balloon atrial septostomy and other possibilities
This is a method applied to decompress the right heart chambers by trans-atrial puncture and progres-sive balloon dilatation septostomy into the interatri-al septum. This has as objective both decompression of the right heart chambers and increment of the left ventricle stroke volume (by increasing the pre-load) and cardiac index1 with the adverse effect of systemic desaturation. Several methods were appli-ed: blade technic, graded balloon dilatation, stenting or, more recently, implantation of a fenestrated ASD device with the reason to secure the opening after initial transeptal puncture and atrial septostomy. The interatrial septum is perforated with a Brockenbrough needle, then the hole is progressively dilated with a Mullins’s dilator, under transesophageal or intracar-diac echocardiographic guidance11. Then non-compli-ant peripheral balloons of different sizes are used to complete the shunt dimension12. For perforation of the interatrial septum some authors recommend the radiofrequency use11. Sometimes, especially in the first mentioned techniques, the created hole is predispo-sed to spontaneous closure1,13,14 and this applies also for artisanal manufactured fenestrated devices10. For this reason, recent studies were published to emphasi-ze the importance to secure the standard hole with a fenestrated type device called atrial flow regulator (AFR) (from Occlutech), which would be implanted after the dilatation of the septum8. In the report of Rajeshkumar, at a follow-up media of 189 days, all 12 patients had a patent AFR8.
Indications for balloon atrial septostomy (BAS) are the patients usually on maximal medical therapy wai-ting for lung transplantation with limited response to the medical therapy, recurrent syncope, refractory ri-ght heart failure (WHO class III or IV). Mean right atri-al pressure >20 mmHg, oxygen saturation on room air <85%, severe right-heart failure manifested by low cardiac output and a LVEDP >18 mmHg are contrain-dications for the methods, the risks/benefit ratio and the procedural mortality in this situation being too high1,15. An increase of the LV volume, which is already elevated may lead to pulmonary oedema and respira-tory failure11.
Experiments on interatrial shunting in PH are more than 50 years old10. Initially, there were surgical inter-ventions. Although the first description of the balloon atrial septostomy was done by Raskind in 1966, only in 1983 this method was applied in PH patients. The first patient to whom the BAS was applied died in the first 24 hour. The stipulated cause may be a shunt of 9
mm that created pulmonary congestion or because of severe decrease in systemic oxygen saturation to 57% afterwards. In 1991, small series of patients were re-ported with progressive reduction in mortality rate10. Now, after each dilatation, evaluation of both syste-mic saturation and left ventricle end diastolic pressure (LVEDP) are done. The dilatation proces is stopped after obtaining a decrease of 10% in saturation com-paring with the initial saturation and for less than 18 mmHg LVEDP10 or if any complication appears (risk for pericardial tamponade is 1.2%)11. From all inter-ventional methods for PH, only BAS was approved in the palliative treatment of PH13. There are 372 pro-cedures reported on 324 patients in literature. The mortality rate is 14% (at 30 days). The rest of 86% of the patients had a 90% improvement in the functional capacity10. The mortality rate may vary according to the experience of the centres, between 5-50%15 and it is insisted that this intervention should be performed only in centres with a good experience in PH manage-ment and has BAS experience1,15.
Transcatheter Potts anastomosis creation Transcatheter Potts shunt (TPS) creation is more an experimental method for decompression of the pul-monary artery, which consists in creation of a direct communication between the left pulmonary artery and the descending aorta13,16. From physi-pathological point of view, this method is a better solution than the BAS, because the mixing of the blood (right-to-left shunt) is at the great vessels level, after the take-off of the coronary and carotid arteries, which means that the saturation in these territories is not decreased13.
This method was described by Potts, in 1946, as part of the surgical treatment in different congenital heart disease17. Recently, it was applied for the mana-gement of PAH, surgically (in 2004)18 and interventi-onally (in 2013, by Esch from Boston Children Hos-pital)19. Esch described a technique for transcatheter creation of a Potts shunt, using two femoral access (arterial and venous), a long sheath positioned into the descending aorta, through which a Brockenbrou-gh needle was advanced. With the help of a guiding positioned snare wire into the left pulmonary artery, the needle is advanced to perforate the aorta and the pulmonary artery, then the perforation is secured by balloons, used to progressively dilate the communica-tion, then a covered stent, called iCAST 7- × 22-mm, is placed between left pulmonary artery and descen-ding aorta and anchored to the vessel walls19. In this initial experience the success rate was 50% (from 4 patients attempted, one died during the procedure with uncontrolled haemothorax and another one died later on because of critical state and comorbidities). After this initial experience other centres performed it as well20-23. In 2015, five TPS cases were described by Baruteau, from the group of 24 interventional and surgical Potts shunt creation. The early postoperative complication rate was 25% and the early mortality rate 12.5% through low cardiac output for the hole group (both surgical and interventional cases). After a median of 2.1 years follow-up, all the rest of the patients were improved, clinically and functionally (20). Continuing the experience described by Baruteau, from the same centre, Boudjemline reported 6 cases of transcatheter Potts shunt creation21. Boudjemline reported 2 deaths, both in patients with severe pre-existing biventricular dysfunction in which the decre-ase of the LV preload, by shunt creation, contributed to low-output state followed by cardiac arrest. Also, he described a stent dislodgement and embolization, which was followed by implantation of the stent into the iliac artery and a second stent deployed success-fully21. Schranz described a Potts shunt creation in a patient suffering from Moya Moya syndrome associa-ted with PAH. The shunt creation was uneventful and the author used radiofrequency (RF) for perforating the aortic and pulmonary wall, which seems to be better in terms of controlled extravasation of blood (due to the fact that RF has the potential to coagulate the tissue and prevent extravasation). Also, the author emphasize the importance of magnetic resonance ima-ging (MRI) preoperatively, because it allows the mea-suring of the distance and evaluating the anatomy at the puncture places in the descending aorta and the left pulmonary artery, which should be preferably less than 4 mm (type I)22.
Also, a special form of Potts physiology was described by Latus. Latus created a “functional” Potts shunt, which was performed by inserting stents into the PDA of new-borns or small infants with supra-systemic pul-monary pressure24.
Balloon pulmonary angioplasty in chronic thromboembolic pulmonary hypertension Chronic thromboembolic pulmonary hypertension is a rare form of precapillary PH, with a prevalence and incidence of 3.2 cases per million and 0.9 cases per million per year 1, appeared as a complication in 0.5 to 2% of the acute pulmonary embolism many times associated with predisposing factors like thrombophi-lic disorders or splenectomy1.
Similar to the BAS as a palliative method, the balloon dilatation of the pulmonary arteries (BPA) in CTEPH is usually indicated in non-operable severe forms of CTEPH. The first description of this method was in 2001, by Feinstein on 18 patients and despite decrease of the PAPm, more than 50% developed reperfusion pulmonary oedema.
The purpose of the procedure is to ensure the pa-tency of the obstructed or stenotic vessel and consists of passage of a guidewire through a lesion then dilating the lesion by undersized balloon25. First, repeated angi-ographies are performed in different projections, using digital-substraction technique. Selective angiographies are performed to better delineate the anatomy: lo-cation and type26. They may appear as obstructions, narrowing, punching defects or webs25,26. Sometimes other imaging techniques may be necessary, optimal coherence tomography being more and more used, more than intravascular ultrasound, for its provided in-formation. Afterwards, a guiding catheter, 6-to-8 Fr, is fixed into the pulmonary branch, corresponding to the worst perfusion area on scintigraphy, usually the right lower lobe. Then the lesion is approached following the principle of stenosis dilatation, or vessel occlusion as for a chronic total occlusion type lesions25. Since 2001, the technique has been changed to the use of smaller balloons in several sessions (usually 4-5, up to 10), at more than one-week interval, with no more than 1-2 segmental inflations, sometimes assisted by intravascular imaging. Applying this technique, the risk for reperfusion pulmonary oedema decreased to 2% in individual centres1.
Complications of this procedure may appear. The most severe complications are reperfusion pulmonary oedema, haemoptysis, and death. Initially death was reported in 5.6% of the cases, but now decreased to 0.34%. Other more frequent complications are dissec-tion and rupture of the vessels, guidewire perforation and parenchymal or pleural bleeding. Indicators for success treatment are the duration of symptom onset, baseline diastolic PAP and diastolic pressure gradient25.
Hybrid therapy (surgical, interventional and medical treatment – riociguat) may be a good choice in the complex cases25,26.

CONCLUSION

All these methods may be applied to severe, refracto-ry cases or as a bridge to lung transplantation. BAS is the older method to decompress the right heart, but the mortality rate is still high. TPS creation is looked as an experimental method, only few cases being re-ported. The mortality rate is still very high, between 33-50%. Opposite to BAS, the BPA is more and more used, the main indication being represented by the non-operable CTEPH patients.

Conflict of interest: none declared.

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