Song ZHANG, Dang-Hui SUN, Shuang LI, Yue LI,2,3,4,5,?

1.Department of Cardiology, the First Affiliated Hospital of Harbin Medical University, Harbin, China; 2.NHC Key Laboratory of Cell Translation, Harbin Medical University, Harbin, China; 3.Key Laboratory of Hepatosplenic Surgery, Harbin Medical University, Ministry of Education, Harbin, China; 4.Key Laboratory of Cardiac Diseases and Heart Failure, Harbin Medical University, Harbin, China; 5.Heilongjiang Key Laboratory for Metabolic Disorder & Cancer Related Cardiovascular Diseases, Harbin, China

? Correspondence to: ly99ly@hrbmu.edu.cn https://doi.org/10.26599/1671-5411.2023.04.003

ABSTRACT The main management principle for patients with coronary thrombus should be “more removal and less implantation”.Routine thrombus aspiration (TA) is ineffective for intracoronary thrombus or high residual thrombus burden after TA and may result in a refractory coronary thrombus.It is unwise to implant a stent in the vessel with high residual thrombus, which is associated with no-reflow, impaired microvascular perfusion, and consequently worse clinical outcomes.Therefore, increasing the efficiency of TA during percutaneous coronary intervention procedures, especially under some conditions of refractory coronary thrombus, is very important to restore myocardial reperfusion and improve microvascular dysfunction early.In the present work, we aimed to demonstrate the factors that may affect TA efficiency and introduce several highly effective approaches to treat refractory coronary thrombus.

Early trials, including TASTE (The Thrombus Aspiration in ST-Elevation Myocardial Infarction in Scandinavia) and TOTAL (The Trial of Routine Aspiration Thrombectomy with PCI versus PCI Alone in Patients with STEMI), have failed to demonstrate the beneficial effects of routine thrombus aspiration (TA) application.[1,2]In a subgroup analysis of the TOTAL trial, Bhindi,et al.[3]have found that the absolute pre-stent thrombus volume is not different between the TA group and the percutaneous coronary intervention (PCI) alone group.Some underlying factors may contribute to the invalid TA, including severe stenosis of the culprit lesion, poor aspiration ability of TA, and inappropriate strategy of thrombectomy.Another critical factor that affects the residual thrombus burden is whether different operators can correctly use manual aspiration catheters.[4]Therefore, enhancing the efficiency of TA during PCI, especially under conditions of refractory coronary thrombus, is crucial to restore myocardial reperfusion and improve microvascular dysfunction early.In the present work, we updated data that might affect the efficiency of TA and introduced a variety of approaches to treat refractory coronary thrombus.

SEVERAL HIGHLY EFFECTIVE MANAGEMENTS FOR REFRACTORY CORONARY THROMBUS

While there are various aspiration devices available,the clot burden can sometimes be so substantial that it becomes challenging to extract and restore blood flow.Furthermore, a larger residual thrombus burden after TA can result in worse microvascular dysfunction and more significant myocardial damage compared to a smaller residual thrombus burden.[5]

‘Mother-in-child’Thrombectomy Technique

Even with a smaller lumen area, catheters with a circle lumen tip shape, such as Export catheter (Medtronic,Minneapolis, MN, USA), perform better on aspiration efficiency than the crescent-shaped ones when aspirating human blood clots (Figure 1).[6]According to Poiseuille’s law of fluid dynamics, the velocity of a fluid through a narrow tube varies directly with the pressure and the fourth power of the radius of the tube, and inversely with the length of the tube and the viscosity of the fluid.Both the 5 Fr child catheter and the 6 Fr Export AP catheter have circle luman shapes that comply with the Poiseuille’s law, leading to the theoretical aspiration of the 5 Fr child catheter being about 3.5 times greater than the latter catheter (0.059 inchvs.0.043 inch in radius for the 6 Fr Export AP TA catheter).The original idea of the ‘Mother-in-child’technique was proposed by Takahashi,et al.[7]using a 5 Fr catheter in a 6 Fr guiding catheter (as mother and child catheters, respectively) to provide better support in chronic total occlusion lesions.In 2011, Li,et al.[8]used the ‘Mother-in-child’thrombectomy technique to treat the coronary thrombus using a 5 Fr ‘Heartrail II-ST01’catheter (Terumo Medical, Somerset, NJ, USA) within a 6 Fr guiding system(Figure 2).Since then, Li and their cardiac interventional team have used the ‘Mother-in-child’thrombectomy technique as routine TA treatment during primary PCI and for the management of some conditions with refractory thrombosis, such as subacute myocardial infarction patients with organized thrombus.[8,9]Moreover,the ‘Mother-in-child’thrombectomy technique not only resolves distal coronary thrombus but also avoids causing aortic ostial dissection, which is usually induced by the deeply inserted guiding catheter.[10]

Recently, the extension catheters, such as Guidezilla?(Boston Scientific, Natick, MA, USA) or GuideLiner?(Vascular Solutions Inc., Minneapolis, MN, USA), have been used as an alternative to child catheters for TA.These extension catheters are advanced into the distal intracoronary thrombus for aspiration, based on the basic guiding catheter.Kusumoto,et al.[11]have successfully retrieved heavy thrombus by using a 6 Fr guiding extension catheter (GuideLiner?) in combination with an original inserting filter device (Filtrap?, Nipro, Osaka, Japan) in the distal coronary region.

Figure 2 The ‘Mother-in-child catheter’technique is used to treat acute thrombosis in the LM artery.(A): On 22 April 2011, a male patient who presented with angina pectoris underwent coronary angiography, which showed bifurcation stenoses (Medina class 1.1.0).Diffusely severe stenosis along the LM and LAD was observed; (B): the LM to LAD was sequentially implanted with a 4.0 mm × 28 mm and a 4.0 mm × 23 mm drug eluting stents; (C):the angiography showed that a 4.0 mm × 10 mm non-compliant balloon was used to post-dilate the LM and LAD stent; (D): after postdilation, an acute thrombosis was seen in LM, the patient was accompanied by hemodynamic instability, and a temporary pacemaker was immediately placed into the right ventricular; (E): the remaining heavy thrombus was observed after the routine thrombus aspiration by an Export catheter.So, a 5Fr ‘Heartrail II-ST01’catheter(white arrow) was advanced into the original 6Fr BL3.0 guiding catheter to extract the thrombus; and (F): the angiography image showed the final satisfactory results with no residual thrombus.LAD:left anterior descending artery; LM: left main.

During the ‘Mother-in-child’thrombectomy technique, certain points require attention.Firstly, the indications should be selected with caution, and this technology is only suitable for proximal thrombus with relative larger lumen diameter and no severely tortuous vessels.Secondly, it is important not to forcefully push the child catheter if there is significant resistance.Instead,the catheter can be delivered across the culprit lesion with the assistance of a guidewire or even a balloon.Thirdly, in cases where severe stenosis is present at the proximal thrombus lesion, pre-dilation of the lesion with low pressure can facilitate delivery of the child catheter.Additionally, during the withdrawal of the child catheter, it is necessary to keep the guiding catheter within the ostial coronary artery to prevent the large thrombus from falling off and causing embolic complications.

Dedicated Stent Technique

Due to the time-dependent properties of thrombotic material, it is almost impossible to retrieve late intracoronary thrombi of high viscosity from patients with subacute myocardial infarction using routine TA catheters,particularly in large or ectatic coronary arteries.Interestingly, a ‘mesh-covered’stent is implanted during primary PCI to prevent distal embolization and no-reflow phenomenon.This stent was originally designed to capture and lock thrombus and plaque materials against the arterial wall.[12]However, due to the crushed pressure between the stent and the artery wall, the residual thrombus clot would extend along the longitudinal of the artery wall, rather than achieving complete thrombus retrieval.Furthermore, the mesh-covered stent has a higher rate of re-stenosis and in-stent thrombosis compared to contemporary drug eluting stents, and the absorption of residual thrombus can also lead to late-term stent malapposition.

Recently, the Solitaire? self-expanding retrievable stent from Medtronic in Minneapolis, USA, which is widely used for cerebral applications, has been used for mechanical thrombectomy of large intracoronary thrombi.[13]In a small cohort, the SolitaireTMstent successfully retrieves large residual thrombi during PCI, some of which have already been treated with the AngioJetTM(Possis Medical Inc., Minneapolis, MN, USA) thrombectomy system.[14]The device’s design allows for delivery within a small-profile microcatheter, minimizing distal embolization during manipulation and making it safe for use with no intraprocedural or post-procedural complications.

TA Catheter-assisted Twisting Wire Technique

Occasionally, refractory coronary thrombus embolism originating from the guiding catheter can occur during PCI,[15]and lead to disastrous consequences.The ‘twisted wire technique’was originally designed to solve the problem of guidewire fracture during PCI procedures.[16-18]In 2020, Li,et al.[19]have developed a novel ‘TA catheter-assisted twisting wire technique’in patients with a large thrombus burden undergoing PCI.This technique involves advancing an original aspiration catheter over the wire after the routine TA has failed.A 3Dshaped tip guidewire is then advanced through the central lumen of the aspiration catheter to the distal end of the thrombus (Figure 3).The guidewire is rotated continuously in one direction until it becomes difficult to rotate further under fluoroscopy, forming a double helix with the original wire.This captures and withdraws the distal refractory coronary embolism into the guiding catheter (Figure 4).Common workhorse wires, such as Sion (Asahi, Tokyo, Japan), are recommended as the second wire, and the tip of the second wire is reshaped using an inducer.After advancing the aspiration catheter to the distal end through a workhorse wire, the later 3D-shaped tip wire is advanced using an inducer.

In order to fully capture refractory thrombus, a second guidewire must be specially shaped to form a tight hinge, which is more effective than the conventional ‘twisting wire technique’in fixing the thrombus.The second guidewire’s unique form only allows for advancement through the over-the-wire chamber of an aspiration catheter or a double-lumen microcatheter.If severe stenosis is located at the proximal end of the thrombus, a low-profile single-lumen microcatheter can also be used to deliver the second wire.This technique enables capture the refractory thrombus in the distal coronary with a smaller diameter, making it a valuable tool in treating this condition.

Figure 3 Demonstration of the ‘3D-shaped’tip of the second guidewire.(A): The first U-shaped tip; and (B): different views of the second U-shaped curve at a location perpendicular to the first one to form a ‘3D-shaped’tip.

Figure 4 Description of the ‘thrombus aspiration catheter-assisted twisting wire technique’.(A): Advance the first guidewire (black) through the embolus; (B): advance the aspiration catheter over the wire and shape the head of the second guidewire (pink)into a ‘3D’pattern.Advance the second guidewire through the embolus as far as possible with the assistance of the thrombus aspiration catheter; (C): pull back the aspiration catheter into the guiding catheter; (D): rotate the second guidewire continuously in one direction; (E): withdraw the twisted guidewires with the retrieved embolus into the guiding catheter and pull the guiding catheter out;and (F): final results.

CONCLUSIONS

In conclusion, we concur with current guidelines that routine TA is not required for all ST-segment elevation myocardial infarction patients.However, we believe that manual TA is still a valuable tool for interventional cardiologists in certain situations, particularly when dealing with fresh thrombus and high thrombus burden.For proximal or ostial artery thrombus, we recommend using conventional TA catheters or ‘Mother-in-child’thrombectomy techniques (including extended catheters).In contrast, for distal coronary thrombus (especially in smaller diameter vessels) or iatrogenic refractory thrombus caused by the guide catheter, we recommend using the ‘TA catheter-assisted twisting wire’technique.

ACKNOWLEDGMENTS

All authors had no conflicts of interest to disclose.