The flexibility of manually performed MVP-based PFRs, which allow tailored fenestrations, makes them attractive for individualized applications. These devices hold significant potential for novel percutaneous transcatheter treatments of complex heart diseases.

Regardless of the technique used—scalpel, punch, laser, cautery, or other methods—effective endovascular PA-bands are crucial. Optimal PFR placement depends on adequate device selection, delivery process and implantation technique. It is desirable to confirm angiographically optimal PFR positioning, including the relationship between device and vessel dimensions, as well as the quality of distal pulmonary artery perfusion, especially the upper lobe branches, before releasing the device. This ensures tangential alignment of the PFRs during high blood flow in the pulmonary artery, reducing the risk of distal device migration. In newborns with an extremely small ascending aorta (AAO), placing a right-sided PFR distally—even with an unprotected right upper lobe—can be an accepted strategy to avoid potential AAO compression by an oversized PFR in the right pulmonary artery branch.

On the other hand, as noted earlier, inadvertent device migration can be managed by placing the tapered bare metal portion at the entry of the upper lobe branch [25]. Due to the current lack of larger MVP-based devices, we have used this technique in older infants with DCM (Fig. 7a). Furthermore, for older infants with DCM who are not candidates for surgical PAB, double device placement, in the upper and lower pulmonary arteries on one side may be considered.

The efficiency of bilateral PFRs is reflected in body weight gain, reduced cardio-vascular workload, particularly in neonates and infants with single ventricle pathophysiology. Pulmonary to systemic blood flow (Qp/Qs) should be balanced, the ratio of oxygen supply and consumption should be stabilized, and the growth of the pulmonary vascular bed should not be inhibited. Sufficient transpulmonary blood flow is essential for final Fontan circulation as well as in neonates with biventricular physiology and borderline left heart structures to achieve adequate oxygenation with adequate left ventricular preload for further ventricular growth. Thus, the placement of bilateral PFRs should be part of a holistic treatment plan that includes pathophysiological considerations as well as maternal bonding, stress reduction (e.g. oral feeding), and prophylactic treatment with ß1-specific beta-blockers [29].

The extent of vascular obstruction achieved by PFRs after percutaneous S1P is demonstrable by the systolic-diastolic Doppler flow profile, regardless of whether the fenestrations was achieved by resection of an entire or half of the PTFE-covered end-cell diamonds of the MVP device. This may also be due to an asymmetrical positioning at the proximal conical end and the partial lack of contact with the vessel wall. The diameter of the non-contacted fenestration is likely to be minimally affected unless the device is excessively oversized. Several factors influence the requirements for fenestration, including body weight, single or biventricular (patho-) physiology, and the presence, diameter, and function of a right-left shunting arterial duct. A well-planned periprocedural treatment strategy is essential.

For patient safety, the elective implantation of bilateral PFRs as part of percutaneous S1P under routine general anesthesia with intubation and ventilation should be reconsidered. General anesthesia-based transcatheter S1P might significantly impact vulnerable hemodynamics and ultimately PFR properties. Scenarios such as pulmonary overcirculation prior to PFR placement or seemingly reduced PFR efficiency afterward, could lead to minimized fenestrations, affecting pulmonary vascular development and causing disproportionate single ventricle hypertrophy. Additionally, the effects of excessive blood flow and pressure on the thin PTFE membrane need to be considered. Focusing on a MVP fenestration as small as possible is neither necessary nor desirable. When structural reasons or reasons or mechanical improvements are not indicated, appropriate drug therapy (e.g. prophylactic ß1-specific beta-blocker) can compensate for Qp/Qs imbalances and prevent myocardial dysfunction.

Two decades ago, bilateral surgical pulmonary PA-branch banding was performed using complicated pressure gradient measurements. The method by Galantowicz, using 3 or 3.5 mm PTFE-tubes, superseded these pressure measurements and simplified the entire surgical component of the Hybrid approach [7]. In the 1990s, institutions like Giessen listed newborns with HLHS primarily for HTX. These patients received ductal stents instead of continuous prostaglandin E1 infusion, but without bilateral PA-banding, while waiting for a donor heart, even at home. The main difference between the survivors who received transplants after waiting for 4 to 6 months and those who are now being bilaterally banded was the loss of body weight gain. Today, following percutaneous S1P, infants achieving age-appropriate weight can proceed comprehensive stage 2 surgery determined at an age of [3] to 4 months. Therefore, even an unprotected left or right upper pulmonary lobe branch—due to a too distally positioned or migrated PFR—does not preclude a successful three-stage procedure. Adequate pulmonary vascular development without right ventricular dysfunction even facilitates Fontan completion at ages two and three years. All HLHS patients who underwent complete percutaneous S1P [15] have since undergone an uneventful Fontan operation. It appears more advantageous to ensure the largest possible, but still effective, fenestration with a preserved systolic-diastolic Doppler profile.

In general, catheter procedures in patients with mixed shunt lesions, particularly those with single ventricle physiology and a right-to-left shunting duct, should be kept as short and simple as possible. Potential risks of right-left embolization of air, blood clots, or microparticles are associated with intravenous administration of medications, exchange of guidewires, or flushing of catheters.

Measures such as stent implantation in the arterial duct [32] or careful PFR positioning is adequate. Re-transversing MVP-based PTFE fenestration should be avoided to prevent inadvertent injury to the PTFE membrane. The thin and fragile membrane offers advantages when the PFR function is no longer required; restrictive PFR function can be even gradually relieved by balloon dilatation or stent placement, similar to transcatheter de-banding of surgically placed PABs.

From a user and applicability perspective, MVP-based PFRs have nearly ideal characteristics, although there is still room for improvement, particularly in device sizes for all age groups. The flow characteristics through MVP-based PFR are intriguing, with harmoniously contrasting angiographic images of wide-open pulmonary branches and minimal angiographic jet flow characteristics. Further investigation is needed to determine if these flow characteristics minimize thrombus formation compared to a device with centered jets, and whether the inside-out properties of the endoPAB reduce vascular damage to a single endothelial lesion, potentially making them superior to surgical bPAB used in the Hybrid approach. While current experience with the fate of the pulmonary branch arteries after removal of endo-banding by MVP-based PFRs is limited, the results are cautiously optimistic.