A Novel Approach for Under-Expanded Stent: Excimer Laser in Contrast Medium

Abstract: The novel approach of using excimer laser in a contrast medium for treating an under-expanded stent in a calcified coronary artery is described. In this first reported case, the laser in a contrast medium was used to treat an under-expanded stent deployed 18 months prior in a calcified non-dilatable coronary artery lesion. The normal laser approach in saline medium flush during lasing to clear any contrast was not effective. The use of concurrent contrast during lasing was effective and successful to help expand the stent with a successful outcome.

J INVASIVE CARDIOL 2012;24(8):E161-E163

Key words: percutaneous coronary intervention, laser PCI, atherectomy, coronary artery disease, contrast media, high-speed rotational atherectomy, calcified coronary arteries, restenosis, debulking technique

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Increasingly, percutaneous coronary intervention (PCI) is performed in patients with complex coronary disease with heavy calcification.^1,2 Failure to cross and the inability to dilate calcified lesions with a balloon remain major limitations of PCI. The use of debulking techniques can help overcome these limitations,³ as postintervention luminal dimension predicts the likelihood of in-stent restenosis and is a factor responsible for stent thrombosis.^4,5 Heavily calcified lesions may limit success by restricting optimal stent dilatation.⁶ Antecedent placement of a stent prior to recognition that a lesion is nondilatable leaves limited therapeutic options and with the increased use of direct stent implantation, the propensity for incurring non-dilatable lesions has increased.

Debulking to facilitate dilation of calcified lesions prior to stent implantation can be achieved usually by using high-speed rotational atherectomy (HSRA), excimer laser, or cutting balloon-assisted PCI.^1-3,7-11

Excimer laser is usually used and activated in a saline medium with continuous saline flush, as the activation in the presence of a contrast medium will lead to the formation of large bubbles and may lead to vessel injury with dissection or perforation.

In this paper, a first report of the novel and successful experience of using excimer laser in a contrast medium for treating an under-expanded stent after failure to treat it with conventional non-compliant high-pressure balloon inflation and with excimer laser in saline medium, as recommended, is described.

Case Report

A 67-year-old male smoker with history of dyslipidemia and hypertension presented with troponin-positive acute coronary syndrome (ACS) with lateral T-wave inversion. He was treated medically and transferred to our center for intervention. Coronary angiography demonstrated a co-dominant system with evidence of coronary calcification and severe stenosis in the proximal left anterior descending (LAD) artery and total occlusion of the first obtuse marginal (OM1) with plaque disease in the right coronary artery. A consultant cardiologist colleague performed PCI to the LAD first with drug-eluting stent (DES) insertion; the OM1 was then wired and predilated with 2.0 balloon and stented with a 2.75 x 28 mm Xience DES (Abbott Vascular), which is a cobalt-chromium stent. It was evident that the stent in the OM1 was under-expanded proximally with a waist. Further postdilatation was performed with 3.0 and 3.5 non-compliant Quantum Maverick balloons (Boston Scientific) to a high pressure of 28 atm, but the stent could not be expanded fully and remained waisted (Figure 1). No further action was taken at the time and the patient was discharged home in a stable condition on dual anti-platelet therapy.

He was admitted 9 months later with troponin-negative acute coronary syndrome, which was treated medically. Subsequent myocardial perfusion scan showed a large area of reversible ischemia in the lateral wall corresponding to the OM1 territory. A repeat coronary angiography by his cardiologist was carried out at his district general hospital, and showed the LAD stent to be patent with severe in-stent restenosis in the OM1 stent at the previous area of under-expansion. He was referred for repeat PCI; after reviewing his coronary angiogram, I planned to admit him for PCI with excimer laser or to consider HSRA if laser was unsuccessful.

The repeat procedure was performed from the right radial artery using a 7 Fr sheath and a Q4 guiding catheter (Boston Scientific). He was preloaded with clopidogrel 600 mg and aspirin 300 mg and given heparin (100 U/Kg) at the start of the procedure. The lesion (Figure 2) was wired with a supportive Mailman wire (Boston Scientific) and a hydrophilic Pilot 50 wire (Abbott Vascular) and predilatation was attempted with a 2.75 mm non-compliant balloon without success (Figure 3). I proceeded with laser PCI using a 1.4 mm excimer laser catheter (Spectranetics Corporation) at a fluence of 40 mJ/mm2 and a frequency of 40 Hz/s then at 60/40. The laser pulses were delivered with continuous saline flush as recommended by the manufacturer. The laser catheter was advanced slowly at ~1 mm/min without success as it would not cross the lesion. At this stage, the next step would have been HSRA; however, the decision was made to attempt delivering the laser pulses in a contrast medium, given that the artery was protected and supported by a stent that was inserted 18 months earlier.

The 1.4 mm laser catheter was used again at 40/40 with concomitant contrast injection while lasing, and this resulted in the catheter passing (Figure 4). Subsequent dilatation was performed with a 3.5 mm non-compliant balloon, which expanded the old under-expanded stent (Figure 5). Subsequently, two DESs (Xience 3.0 x 18 mm and 4.0 x 18 mm) were inserted and postdilated with a 4.0 non-compliant balloon with excellent final results (Figure 6). The patient tolerated the procedure well with no complications and he was monitored on the ward and allowed home in a stable condition on secondary prevention measures and dual antiplatelet therapy.

Discussion

Laser PCI in a contrast medium offers an innovative approach to dealing with difficult cases of undilatable and under-expanded stents with successful outcome.

PCI is increasingly performed in elderly patients with complex disease and heavily calcified lesions. These calcified lesions can be resistant and difficult to treat, with resultant under-deployed stents that have a higher rate of future complications such as restenosis or thrombosis.

Angiography is less sensitive than intravascular ultrasound (IVUS) in detecting coronary calcification.¹² In this case, IVUS was not used up front to assess the degree of calcification before stent deployment on the first occasion, as there was no difficulty in delivering the predilatation balloon and the stent. Deployment of a stent without recognition of the calcification in a lesion will lead to under-expansion and leaves limited therapeutic options, one of which is non-compliant high-pressure balloon inflation. However, as in this case, this may fail to fully expand the stent and lead to future restenosis, thrombosis, and continuous symptoms. Inadequately expanded stent in a non-dilatable calcified lesion can be a barrier to conventional debulking technique, such as HSRA. The stent can act as a barrier between the burr and the calcific plaque. Furthermore, there is a potential for damaging the exposed stent struts.¹³ Likewise, cutting balloons offer similar constraints to success, although, in the author’s experience, both HSRA and cutting balloons have been used on occasion with successful outcome. It is unlikely that a stainless-steel stent that has more radial force would have any difference in comparison to the cobalt-chromium stent that was used. This is due to the fact that the under-expansion is all related to the heavily calcified and non-compliant arterial wall.

Excimer laser contains a mixture of xenon and chloride gases.¹⁴ The absorption of the laser energy by blood and contrast leads to fast vapor bubble expansion and implosion intraluminally, causing explosive dilation and invagination of adjacent arterial wall after each excimer laser pulse.¹⁵ The use of saline infusion at the time of activation and laser pulse delivery has been shown to reduce vessel wall injury due to acoustic damage.^16,17 This is the current recommendation and training for cardiologists using excimer laser PCI.

In this case, the conventional method of using laser with saline infusion did not succeed in crossing the under-expanded stent and the heavy calcium in the arterial wall. A different strategy had to be used and it was felt that the arterial wall was supported and protected by the stent which, at 18 months post implantation, would also have a reasonable degree of endothelium and be part of the arterial wall. Based on that, the decision was made to use the contrast medium during laser activation to help create larger-sized bubbles and help in debulking and softening the calcium behind the stent to further expand it fully. This strategy proved effective and successful without any complications.

There have been previous reports of using excimer laser in cases of under-deployed stents in both calcified and non-calcified but undilatable lesions.^13,18 The author regularly uses laser for under-expanded stents with success.

To the author’s knowledge, this is the first report of successfully utilizing the excimer laser catheter in a contrast medium to treat a non-dilatable, under-deployed, and under-expanded stent within a calcified coronary lesion. The stent was sub-optimally expanded despite high-pressure inflation of non-compliant balloons and conventional laser activation in saline medium, which failed to facilitate the full expansion of the stent.

The use of contrast media with laser activation helped in the development of cavitary implosion and shock wave trauma to cause the modification of the calcified plaque behind the stent. The presence of the previously deployed stent provided sufficient protection to avoid any potential complications.

The use of the excimer laser should continue to be done as recommended in a medium of saline flush to minimize any possible complications. However, in circumstances similar to this case and in the presence of a previously deployed stent, the use of contrast medium with excimer laser by experienced operators may offer a way of overcoming resistant, undilatable, and under-expanded stents.

References

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From the Cardiac Department, Freeman Hospital, Newcastle upon Tyne, United Kingdom.
Disclosure: The author has completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. He discloses that he is a proctor and trainer for Spectranetics.
Manuscript submitted October 28, 2011, provisional acceptance given November 22, 2011, final version accepted December 1, 2011.
Address for correspondence: Mohaned Egred, BSc (Hons), MB ChB, MD, FRCP, FESC, Consultant Interventional Cardiologist & Honorary Senior Lecturer, Freeman Hospital, Newcastle University, Newcastle upon Tyne, NE7 7DN United Kingdom. Email: m.egred@nuth.nhs.uk