Shockwave Intravascular Lithotripsy for Calcified Coronary Lesions: First Real-World Experience

Abstract: Background. Calcified coronary lesions often cause suboptimal stent expansion, which is one of the greatest predictors of adverse outcomes such as stent thrombosis and restenosis. Shockwave intravascular lithotripsy (S-IVL; Shockwave Medical, Inc) is a recently approved technique used in the treatment of heavily calcified coronary lesions. We present our early real-world experience with the S-IVL device. Methods. All patients treated with S-IVL between October 2018 and January 2019 during their percutaneous coronary intervention (PCI) at our center were included. Results. During this period, a total of 26 patients undergoing PCI were treated with S-IVL prior to stent deployment (69% male; age, 72 ± 8 years). Indications for PCI were acute coronary syndromes (ACS) in 14 patients (54%), stable angina in 11 patients (42%), and PCI before transcatheter aortic valve implantation in 1 patient (4%). Seventy-one percent of the ACS cases undergoing PCI with S-IVL were to the perceived ACS culprit lesion during the index procedure, while 29% were staged PCIs to severe non-culprit lesions. Upfront S-IVL usage occurred in 58% of cases; the rest were bail-out procedures due to suboptimal initial balloon predilation. S-IVL was used most commonly in the left anterior descending coronary artery (50%), with 1.3 ± 0.5 stents implanted/target vessel. Angiographic success (<20% residual stenosis) occurred in all cases, with no procedural complications. Conclusion. S-IVL appears to be a useful modality in coronary calcium modification to optimize stent expansion. This device obviates the need for more complex lesion preparation strategies such as rotational atherectomy, except in severe undilatable cases where S-IVL is impossible. Further study is warranted to compare different calcium modification devices with conventional balloon angioplasty.  

J INVASIVE CARDIOL 2019;31(3):46-48. Epub 2019 February 15.

Key words: coronary calcium, lithotripsy

Calcified coronary lesions remain one of the challenges facing interventional cardiologists. Calcification is associated with suboptimal stent expansion, which is one of the biggest predictors of stent failure from mechanisms such as stent thrombosis and in-stent restenosis.¹ While aggressive balloon angioplasty can sometimes provide adequate predilation for stent deployment, the degree of luminal gain can often be limited. In particular, the luminal gain with balloon angioplasty in eccentric calcified lesions is achieved with stretching of the non-calcified wall, with minimal calcium modification. This is associated with increased risk of dissection at the edges, where the vessel is weakest.²

Shockwave intravascular lithotripsy (S-IVL; Shockwave Medical, Inc) is a recently approved device for the treatment of calcified coronary lesions. The Disrupt-CAD (Disrupt Coronary Artery Disease) optical coherence tomography substudy has shown that calcium modification is achieved through fracturing of the intimal and medial calcium layers when circumferential lithotripsy is used at low-pressure balloon expansion.³ S-IVL is safe, and can be performed without the conventional risks associated with rotational atherectomy, such as microembolization, slow-flow, perforation, and bradycardia in some cases. We present our real-world experience with S-IVL, including patients with acute coronary syndromes (ACS) and usage as a bail-out strategy when balloon angioplasty is unsuccessful.

Methods

All patients treated with S-IVL during percutaneous coronary intervention (PCI) at our center were sequentially included. Baseline demographics, indications for PCI, and procedural details were collected. PCI was performed in the conventional manner and 6 Fr transradial systems were used universally. All target lesions had at least moderate calcification angiographically. There were no angiographic exclusions, including length, tortuosity, bifurcation lesions, and prior stent placement. Angiographic success was defined as achieving <20% residual stenosis, no edge dissection, and Thrombolysis in Myocardial Infarction (TIMI) 3 flow. All procedure-related and in-hospital complications (death, myocardial infraction, target-vessel failure) were recorded. The primary procedural outcome was ability to deliver the S-IVL balloon and successful deployment of the desired stent. Successful clinical outcome was defined as stent delivery without procedural or in-hospital complications.

The S-IVL procedure. The S-IVL device is a monorail, balloon-based catheter with a central ultrasound core delivered over a 0.014˝ angioplasty wire. The device is compatible with ≥6 Fr guide catheters. Balloons are all 12 mm in length and range from 2.5-4.0 mm in diameter, and are chosen in a 1:1 ratio relative to the target-vessel reference diameter. Low-pressure inflation (4 atm) ensures balloon apposition prior to delivery of therapy. This low pressure is maintained through the therapy cycles. Lithotripsy is performed for a maximum of eight 10-second cycles per device. Each area of concern is recommended to undergo a minimum of two cycles of lithotripsy. Segments treated with lithotripsy can be overlapped.

Lithotripsy is delivered when emitters vaporize the fluid inside the S-IVL balloon, creating an expanding and collapsing bubble that generates sonic pressure waves. This acoustic energy wave travels through the vessel wall, selectively fracturing the intimal and medial calcium. This calcium modification ultimately increases vessel compliance and optimizes stent expansion.

During delivery of Shockwave cycles, electric signals that mimic pacing spikes may be seen on the electrocardiogram trace. There are two potential explanations for this. The first is an electric spark created by the fluid vaporization during delivery of S-IVL causing an artifact that is picked up by the electrocardiogram. Alternatively, it may be explained by the direct link between electrocardiogram signals and piezoelectricity.⁴ Piezoelectricity is the electric charge that accumulates in certain materials, including soft tissue, in response to mechanical stress (in this case, from sonic pressure waves).  

Results

Between October 2018 and January 2019, a total of 26 patients undergoing PCI were treated with S-IVL prior to stent deployment. Sixty-nine percent of patients were male, with a mean age of 72 ± 8 years. Baseline demographics are shown in Table 1.

The indications for PCI were ACS in 14 patients (54%), stable angina in 11 patients (42%), and treatment before transcatheter aortic valve replacement in 1 patient (4%). Among the ACS cases, a total of 71% received S-IVL to the infarct-related artery during the index procedure, while 29% were staged PCIs to severe non-culprit lesions. Upfront S-IVL was used by the interventional cardiologist in 58% of cases, while the rest were used after inadequate predilation with balloon angioplasty. The usage rates of different-sized S-IVL balloons are shown in Table 2. Following S-IVL, a total of 46% of cases required further predilation with non-compliant balloons before stent deployment. The mean number of stents used was 1.3 ± 0.5.

Two patients required a 6 Fr GuideLiner (Teleflex) for S-IVL balloon delivery and 3 patients required a buddy-wire support technique. Both strategies could be achieved through a 6 Fr guide catheter. One patient had S-IVL therapy within an old under-expanded stent.

S-IVL was most commonly used in the left anterior descending coronary artery (50%), followed by the right coronary artery in 35% and left circumflex artery in 12%. A notable case included the S-IVL used in an unprotected left main stem ostium, which we believe is the first reported case in the literature.⁵ Another unique case was upfront S-IVL use in a patient with an inferior ST-elevation myocardial infarction. Multivessel use of S-IVL was done in the left anterior descending and right coronary artery in 1 patient. Procedural and clinical success was achieved in all cases, with no procedural or in-hospital complications.

Discussion

In our real-world experience, S-IVL has been shown safe and effective for the modification of various calcified coronary lesions to optimize stent expansion. We have included patients outside the Disrupt-CAD I study, including patients with ACS and unprotected left main stem intervention.⁶ In our experience, S-IVL has been useful both as an upfront calcium modification device and as a bail-out option when predilation with balloon angioplasty is inadequate. The utilization of S-IVL does not require specialized training for interventional cardiologists, as the S-IVL is compatible with all coronary guidewires, and the technique is comparable to balloon angioplasty.

S-IVL technology using the Shockwave C2 catheter was granted the European CE mark in May 2017 for coronary arteries, but the United States Food and Drug administration only approved it for calcified peripheral arteries in June 2017. The current iteration, while effective in plaque modification, remains a somewhat bulky device that requires some negotiation especially through tortuous vessels (crossing profile, 0.044 ± 0.002˝: 0.043˝ maximum for 2.5 mm, 0.044˝ maximum for 3.0-3.5 mm, and 0.046˝ maximum for 4.0 mm balloon options). It is small enough to be passed through ancillary guide-catheter extenders and can be used with buddy-wire support in a 6 Fr system. It is likely that future iterations may need to be developed with smaller crossing profiles.

The balloon has two radiopaque emitters 6 mm apart and two conventional marker bands 4 mm from the distal emitter and 2 mm from the proximal emitter, resulting in a working length of 12 mm. The S-IVL is available in 2.5-4 mm diameters in 0.5 mm increments. Its use is discouraged in recently deployed stents that have not endothelialized and the manufacturer does not recommend its use in aorto-ostial lesions.

The Disrupt-CAD study⁶ was a prospective, multicenter, single-arm study that treated 60 patients with severely calcified lesions with S-IVL. The primary endpoint was defined as a residual diameter stenosis <50% with no in-hospital major adverse cardiovascular events (MACE; death, myocardial infarction, target-vessel revascularization). There were no prespecified intravascular imaging endpoints. The primary safety endpoint was freedom from MACE through 30-day follow-up. The S-IVL balloon could be delivered in 59 patients and stent delivery was achieved in all patients with no major intraprocedural complications. Three patients (5%) had asymptomatic non-Q wave myocardial infarction. There were no reported MACE at 30 days.

The S-IVL technology appears to deliver immediate plaque modification facilitating stent delivery; the device is largely deliverable, and sometimes requires ancillary support. However, the impact on long-term healing and target-lesion failure is yet to be determined.

Study limitations. Our study did not have comparison groups utilizing other plaque-modifying techniques and included all patients where S-IVL was chosen at the operator’s discretion. This is our real-world experience with a new technology and included patients outside the existing evidence base. No intravascular imaging was systematically utilized. The follow-up was limited to hospital discharge and no long-term outcome data have been collected at this point. Lesion predilation to facilitate the use of S-IVL was allowed, as was postdilation after therapy to optimize stent expansion. These were variably applied in the cohort. As our experience increased, fewer lesions required balloon dilation post S-IVL therapy.

Conclusion

S-IVL is efficacious for calcium modification to optimize stent expansion in patients with calcified coronary lesions. A potential strategy for Shockwave use would be to optionally predilate with a 2.5 mm compliant or non-compliant balloon, deliver Shockwave therapy to facilitate full stent expansion through adequate plaque modification, then deliver the stent and postdilate with a non-compliant balloon. In our opinion, the only lesions requiring aggressive predilation are those where the Shockwave cannot be passed. Further study is warranted to compare S-IVL with balloon angioplasty and other calcium-modification approaches intraprocedurally and to assess its long-term outcomes.

References

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From the North Shore Hospital, Auckland, New Zealand.

Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. The authors report no conflicts of interest regarding the content herein.

Manuscript submitted February 11, 2019 and accepted February 12, 2019.

Address for correspondence: Bernard Wong, MBChB, North Shore Hospital, 124 Shakespeare Rd, Takapuna, Auckland 0620, New Zealand. Email: bernardwong@hotmail.co.nz