The experiment shows that the dual latex balloon catheter can temporarily close a VSD in pigs for 2 weeks. The manipulation of the dual balloon catheter is simple, and there were no complications in the procedure. This balloon catheter may be a promising approach for bridge therapy.

The balloons were successfully advanced and located at the VSD, inflating and blocking the shunt in all pigs. The balloons are soft, size adjustable, and transformable with a crushing action. The balloons successfully blocked the shunt. This is similar to previous human cases in which successful blocking of acute post-infarction VSDs shunt with a Swan–Ganz catheter. [7, 8, 10]. They suggest that the latex balloon may temporarily close postinfarction VSDs.

Why Swan-Ganz catheter is not widely used to treat postinfarction VSDs. In the human patient, the Swan-Ganz catheter was advanced into the right ventricle via the VSD, which was then closed by inflating the balloon and reducing the shunt. However, the Swan-Ganz catheter is difficult to manipulate across VSD, and it is difficult to anchor onto the VSD. Furthermore, the balloon on Swan-Ganz is relatively tiny, and PIVSDs are usually big. Thus, we designed a dual latex balloon catheter with some improvements. We used an OTW design, allowing the dual catheter to easily advance over the 0.014-inch PTCA guidewire to cross the VSD. The dual balloon design allowed balloons inflation into a dumbbell-like shape that straddled the VSD and effectively closed the shunt in all the pigs for 2 weeks.

Although the shape of the postinfarction VSD is not regular in patients, the latex balloon can be reformed according to the pressure. Then, the balloon will change to a shape similar to that of the VSD and be able to block most of the shunt. When the VSDs are irregular and large, the balloon catheter may not completely close the irregular VSD in patients. However, the small residual VSD will not affect the midterm quality of life [11].

In animal experiments, we did observe mild tricuspid regurgitation in three pigs, but no tricuspid valve damage was found in postoperative autopsies. Therefore, we believe that as a transitional strategy, comparing the deterioration of hemodynamics in the acute phase, the hemodynamic changes caused by inflated balloons are acceptable. Meanwhile, the PIVSD may be larger than 3cm, the balloons should be designed to be bigger in the future, and the ideal shape of the inflated balloon may be disk-like to avoid the haemodynamic compromise.

Open surgery is the standard choice for postinfarction VSD [12], but very early surgery is accompanied by poor results. The operative mortality decreases when surgery is intentionally delayed [13]. Although this may result from selection bias, it also suggests that surgery for acute postinfarction VSD may have some limitations. First, the friable myocardium around the VSD cannot endure suturing, and the operation is complex. Second, surgery is highly invasive and requires support in the form of cardiopulmonary bypass; thus, AMI patients may have difficulty enduring the operation. Therefore, the guidelines recommend operating several weeks later if the patient is stable [14]. However, postinfarction VSDs are usually not stable and require early intervention to avoid multiorgan failure. Thus, a “divide and conquer” strategy may address this dilemma. This dual latex balloon catheter is designed for the acute phase treatment according to this strategy. It is soft and mini-invasive. This experiment suggests it may be effective in closing the VSD for 2 weeks. After further improvement and evaluations, it may be a bridge treatment to complement the open surgery.

Although the occluder device (usually a double-umbrella-shaped occluder) has been successfully used in some acute postinfarction VSD [15, 16], its usage in the acute phase is generally not satisfied in practice [17]. As devices are designed for congenital VSD, which has good tissue strength. Thus, these devices may be suited to chronic postinfarction VSD, not the acute phase. They have some shortcomings when used in acute phase [3]: 1) the occluder is too rigid to be anchored onto the friable myocardium, potentially resulting in device malpositioning and embolization; 2) its delivery sheath is rigid and may tear the borders of the VSD, 3) the device is small; frequently, they are not sufficient to close the VSD, which can be large and complex, especially when the size of the VSD increases during the healing of the infarction; 4) the device is difficult to retrieve after release, 5) the device cannot be used when the remnant rim of the VSD is excessively tiny. It may be a better choice than occluders for temporarily closing acute PIVSD. It also may complement the occluder. Recently, a novel occluder device, Occlutech PIVSD was produced. It has several innovative features that showed a good performance in the subacute PIVSD. [18] but its performance in the acute phase is not known. Compared with the available occluder devices, the dual latex balloon is softer, adjustable in size and can be more easily anchored. Besides, due to the flexible size of the balloon, it can adapt to the size of VSDs within a range during surgery, and the dual latex balloon can be chosen even when the remnant rim of the VSD is excessively small.

In this study, no thrombi or embolisms were found; in our pre-experiment, a thrombus was found between the two balloons in the VSD despite the pigs receiving rivaroxaban (10 mg qd) for anticoagulation. Thrombosis may be caused by the dead space formed among the two balloons and the ventricular septum. Thus, we designed a side hole between the two balloons to inject heparin to prevent thrombus formation in the dead space. This experiment suggests that anticoagulation via this side hole works well in preventing catheter-associated thrombus formation. During the experimental period, no obvious symptoms of embolism in other organs occurred.

This study has some limitations. First, limited to the methodology for creating the model, the locations of the VSD and AMI were not consistent. And the tissue strength is much better than that of postinfarct VSD, and the shapes of the VSD were regular and small. These obviously reduced the difficulty in closing the VSD in the pigs. Second, the sample size is small, and the follow-up time were short. Thirdly, even though the balloons remained intact under physiological cardiac pressure, more thorough study is needed on the reasonable volume and pressure ranges. It is essential to ensure the safety of the balloon catheter. Secondly, histology study on the myocardial tissue is needed to explore the balloon’s effects on the myocardium in future study. Lastly, evaluation of the embolism in downstream organs with angiongraphy or autopsy, is needed in future research

In conclusion, this dual latex balloon catheter is simple and effective. When used as part of a “divide and conquer” strategy, it may be a promising tool to temporarily close the acute postinfarction VSD, and further evaluation is needed.