The primary objective of this study is to evaluate the safety and efficacy of transcatheter Cutting Balloon therapy for branch pulmonary artery stenosis resistant to low pressure dilation.

The proposed study will be a prospective, multi-center, randomized, blinded trial comparing 2 treatments for pulmonary artery stenosis. Specifically, vessels that fail to respond to balloon inflation at 8 ATM will be individually randomized to 1 of 2 treatment pathways. In the first treatment pathway, the vessel is dilated using a CB, followed by additional low pressure balloon dilation (< 8ATM). In the second pathway,the vessel is dilated with high pressure balloon angioplasty, with balloon inflation pressures exceeding 15 ATM. Cross-over therapy will be permitted for failed high pressure treatment starting with enrollment of patient #15. The primary outcome assessment for efficacy will be a comparison of percent change in minimum lumen diameter before and after randomized therapy, as determined by a core laboratory blinded to pathway assignment. The primary outcome assessment for safety will be a comparison of the proportion of vessel dilations resulting in any serious adverse events, as determined by the Data and Safety Monitoring Board. Patient-level safety endpoints will also be tabulated. Patients can have multiple vessels enrolled; analytical techniques will adjust for potential intra-patient correlation.

Inclusion Criteria:

Patient Inclusion Criteria (Determined Prior to Cardiac Catheterization)

a. At least 1 branch pulmonary artery stenosis referred for planned catheterization for PA dilation b. At least one of the following: i.greater than one half systemic right ventricular pressure ii. regional decrease in pulmonary blood flow by lung scan iii. elevated pulmonary artery pressures (> 20 mmHg MPAP) iv. cyanosis at least in part due to PA stenosis c. Informed consent of patient and/or parent/guardian; assent of mature minors d. Agreement to participate in protocol, including follow-up testing

Vessel Inclusion Criteria (Determined During Cardiac Catheterization)

1. Native pulmonary artery or branch which fails balloon dilation up to 8 ATM; as defined by failure to eliminate a waist
2. Native pulmonary artery or branch with a balloon waist diameter less than 7.5 mm (i.e.,0.5 mm less than the largest available CB) with dilation at 8 ATM
3. All eligible vessels that are dilated during the catheterization must be enrolled as study vessels; "off-study" use of Cutting Balloons or high pressure dilations in eligible vessels is not allowed.

Exclusion Criteria:

3. Patient Exclusion Criteria (Determined Prior to Cardiac Catheterization)

1. Prior pulmonary artery angioplasty or surgery on the vessel within the previous 6 weeks
2. Pregnancy

Vessel Exclusion Criteria (Determined During Cardiac Catheterization)

1. Vessel with an aneurysm from a prior dilation or surgery, defined as a local enlargement of the vessel greater than 100% of the lumen diameter both proximally and distally to the aneurysm. The maximum aneurysm diameter and vessel lumen diameter proximal and distal to the aneurysm will be recorded. The location of the aneurysm relative to the angioplasty site will be determined and reported as proximal, distal, or in the region of waist formation.
2. Prior stent placement associated with the obstruction

i. balloon inflation for the purpose of expanding the diameter of the stent along its length with no residual waist proximal or distal to the stent edges ii. balloon inflation resulting in waist formation within the edges of a stent iii. dilation of a vessel through the cells of a stent c. Unifocalized nor non-unifocalized systemic to pulmonary artery collaterals. d. A vessel requiring therapy at a site not amenable to delivery or safe positioning of a Cutting Balloon device due to unfavorable anatomy as determined by the physician and based on as assessment of vessel angles, size, length, and proximity to other vessels.

Baseline data prior to vessel randomization

Patients were monitored for adverse events from the time of enrollment to follow-up assessment 2-4 months after the intervention.