Following the recent publication of five randomized trials (MR CLEAN, SWIFT PRIME, EXTEND-IA, ESCAPE, REVASCAT, THRACE) [8,20], mechanical thrombectomy, along with medical management, was established as the standard treatment for acute ischemic stroke caused by large vessel occlusion. Delays in performing mechanical thrombectomy for the purposes of awaiting results of intravenous alteplase for treatment of acute cerebral infarction are discouraged in the 2019 AHA/ASA guideline [8], as are recommendations to perform immediate mechanical thrombectomy on patients who visit the hospital within 6 h of the onset of symptoms and do not meet the exclusion criteria [8,20]. If the eligibility criteria for DAWN (within 6–16 h) or DEFUSE 3 (within 16–24 h) trials are met [1,17,20], mechanical thrombectomy is possible even in cases in which more than 6 h have passed since the onset of symptoms or the last normal time is unknown.

In the treatment of acute ischemic stroke, various mechanical thrombectomy strategies, such as stent retrieval technique and direct aspiration thrombectomy [20,27], are used in conjunction with novel devices such as balloon guide catheters (BGC) or large-bore distal-access catheters [3,10,16,31] for increased efficacy and efficiency [20]. The BGC, in particular, is known to lower the risk of distal embolization during the procedure and improve flow reversal effects by the deployment of a balloon, which causes the arrest of cerebral blood flow [7,21,28], Such an advantage has been reported in two recent clinical studies to increase recanalization rate and improve neurological outcome [6,16,27,28].

However, failure of the balloon to deflate during the BGC procedure can result in catastrophic complications, including aggravated hypoxic damage. This paper aims to share the resolution and methodological analysis of our experience with BGC balloon deflation failure, which was confirmed by a reproducible experiment under similar conditions.

A 104-year-old female patient presented to the emergency department with a chief complaint of altered consciousness and right hemiparesis. She was apparently normal 5 h prior to the presentation. No cerebral hemorrhage was detected on non-contrast brain computed tomography (CT). The patient had an Alberta Stroke Program Early CT Score (ASPECTS) of seven and a National Institutes of Health Stroke Scale (NIHSS) score of 15. An occlusion in the left proximal M1 segment was detected (Fig. 1A) on CT angiography of the brain, and mechanical thrombectomy was performed immediately (Fig. 2A).

Endovascular treatment has recently been established as an essential treatment for acute ischemic stroke [8,20]. BGC, in particular, has been widely used to improve the success rates of recanalization and shorten procedure time during stent retrieval thrombectomy [16,28].

Although there are various complications associated with endovascular procedures, there have been reports of coronary artery intervention for complications related to deflation failure [13,24,26]. The EuroPCR group has proposed a number of rescue therapeutic options in cases of non-deflatable coronary balloons (www.pcronline.com) [19].

Brinjikji et al. reported groin complications (groin or retroperitoneal hematoma, femoral artery bleeding, etc.) caused by large groin sheaths [6], whereas catheter instability, carotid artery dissection, and difficult aortic arch have been identified as potential complications [9]. However, there have been no reports of balloon deflation failures or discussions regarding potential solutions in the case of balloon deflation failure as observed in this case.

Balloon deflation failure is a very rare complication of BGC that occurred in this case, and the potential causes and solutions were analyzed. First, the composition ratio of the contrast solution used in the balloon may influence deflation failure. A 1:1 dilution of the contrast has been suggested as an optimal concentration considering visibility and balloon deflation time [11,14]. The contrast solution used in this case was also 1:1. Second, potential mechanical factors may also influence the deflation of the balloon. However, the possibility of mechanical error was excluded in this case, as the deflation failure occurred after several trials of successful ballooning and de-ballooning. The anatomical factors of the patient may also influence the deflation of the BGC. The patient in this case was an adult 104-year-old adult with a very steep vasculature entry angle and tortuous morphology (Fig. 1B). Her left ICA had a coiling morphology with a circular configuration, and her aorta had a vertical distance between the innominate artery and the top of the aortic arch that was more than twice the diameter of the left common carotid artery, which is considered unfavorable for an endovascular approach procedure (Fig. 1C, D) [2,15]. Even if the BGC was safely positioned at the proximal ICA before the circular segment, the position of the BGC may have shifted incidentally during the repetitive ballooning and de-ballooning process and stent retrieval. As a result, structural changes or damage to the inflation lumen of the BGC, such as torsion or kinking, could have occurred, leading to deflation failure.

Given the mechanism by which the balloon deflated after several attempts, it was surprising why the excision of the proximal portion of FlowGate^TM did not cause the balloon to deflate. The FlowGate^TM structure includes a lumen-shaped channel (inflation lumen) that is used to inflate the BGC balloon through an external injection of contrast solution (Fig. 3C). Because this lumen is embedded within the catheter wall, excision of the catheter should result in immediate drainage of the contrast solution and subsequent deflation of the balloon, though this did not happen in this study. Furthermore, given that deflation occurred immediately after the introduction and inflation of the cutting balloon, it is unclear whether the deflation was caused by the cutting balloon based on the profiles of the BGC and cutting balloon.

The cutting balloon was first invented by Dr. Peter Barath and was mainly used for the treatment of coronary artery diseases [4]. Unlike conventional balloon catheters, cutting balloons have three to four 0.005-inch atherotomes (razor blades) on the balloon surface (Fig. 3D) [4,5]. When the cutting balloon is inflated, the blades are designed to disrupt the fibroelastic continuity of the neointimal hyperplasia by making sharp transverse microincisions (Fig. 3E) [4,18,22]. Although deflation was attempted by inserting the cutting balloon into the BGC, it was impossible to deflate the balloon in the BGC with the 0.005-inch blade, due to the structure of the BGC wall, which requires a blade of at least 0.007 inches (Fig. 3C).

To simulate the situation, a FlowGate^TM was inserted into a rubber tube with the thickness of a blood vessel and ballooned with a 1:1 contrast solution. The cutting balloon was then inflated and monitored in real-time using fluoroscopy, but the balloon in the BGC did not deflate. The BGC balloon did not rupture despite several attempts with different positions of the cutting balloon and the application of sufficient pressure to cause the cutting balloon to rupture the BGC balloon (Fig. 4A, B).

The proximal portion of the BGC was then excised. Once a straight BGC was prepared and inflated in the aforementioned rubber tube, followed by excision of the proximal portion of the catheter, solution leakage occurred in the excised portion of the BGC, resulting in complete deflation within 30 s. The time was then recorded, while the BGC was used to create flexures ranging from 0 to 90°. It was discovered that at a 90° flexure, the balloon had only partially deflated even after 5 min, in contrast to the 30 s it took for the balloon to deflate at a 0° flexure (Fig. 4C, D).

In conclusion, the findings show that the cutting balloon does not cause damage to the BGC wall and that deflation is possible by excising a proximal portion of the BGC. However, it was demonstrated that in the presence of flexure in the BGC, the deflation time may be delayed, or only partial deflation may occur. Kinks in the catheter were found to be present in cases like this, where deflation failed to occur even after the proximal portion of the BGC was excised. As a result, inserting a stiff device into the interior of the BGC to straighten the collapsed catheter lumen caused by the kinking may be required as an additional procedure.

The BGC balloon deflation failure observed in this case is an extremely rare and unknown complication in the neurovascular field that can lead to fatal and catastrophic outcomes if not addressed immediately. Although rare, if the balloon fails to deflate during a BGC procedure, knowing how to restore luminal patency with a stiffer device and excising the BGC will help to successfully deal with this rare complication.