Key words: Coronary Artery Disease, Coronary
Lithoplasty, Shockwave Lithotripsy
Calcified coronaries are always the nightmare of the
interventional cardiologist. They cannot be easily dilated by
balloon angioplasty and balloons might rupture while high
pressure inflation is attempted, leading to coronary
dissections and even perforations. Our Urology colleagues have
been using extracorporeal shockwaves to fragment renal stone
for over a quarter century. Some researchers have used a much
lower energy version these shockwaves to treat coronary artery
disease which is not amenable to percutaneous coronary
intervention or coronary artery bypass grafting with variable
success [1]. But these are extracorporeal shockwaves with the
shockwaves applied from outside the body using a water
cushion. Though they can target specific regions of the heart
using echocardiographic guidance, they cannot target specific
lesions within the coronaries. Coronary lithoplasty denotes
the use of shockwaves delivered within the coronary artery
using a specialised balloon catheter.
Basic principle of coronary lithoplasty
Unfocussed acoustic pulses are transmitted circumferentially
from transducers located inside a balloon catheter which is
positioned inside the calcific coronary lesion. Lithotripsy
waves travel outside the balloon and disrupt both superficial
and deep calcium within the vessel wall. The action of the
shockwaves is more on hard tissue than on soft tissue so that
damage to normal vessel wall tissue is minimal. Typically, the
balloon is inflated to a low pressure of about 4 atmospheres
while the shockwaves are delivered. This improves the
compliance of the vessel wall by producing fractures in the
calcium along the circumference of the vessel. Shockwave
delivery is followed by inflation of the balloon to nominal
pressures and later high-pressure inflation to prepare the
vessel for coronary stent implantation. The lithoplasty
balloon can be delivered over a conventional coronary
guidewire.
Clinical studies on coronary lithoplasty
DISRUPT CAD trial used Shockwave Coronary Rx Lithoplasty
System (Shockwave Medical, Fremont, California) to deliver
localised lithotripsy enhanced disruption of calcified
coronary lesions. A sub study using Optical Coherence
Tomography (OCT) evaluated 31 patients with severely calcified
coronary lesions [2]. Fracture of calcium within the plaque
was noted in 43% of cases, of which circumferential multiple
fractures were noted in more than 25%. More fractures occurred
in most severely calcified lesions. Mean gain of vessel lumen
after lithoplasty alone was 2.1 sq mm, which increased further
after stent implantation to achieve a minimal stent area of
5.94 ± 1.98 sq mm. Though deep dissections occurred in 13%
after initial balloon angioplasty, they were successfully
treated after stent implantation so that there was no acute
vessel closure, slow flow, no reflow or perforation. An
accompanying editorial by Patrick W.Serruys et al [3]
highlighted that final stent expansion was similar among all
tertiles of calcification, indicating more efficacy
lithoplasty with increasing severity of calcification. They
noted that this report is pertinent because it is the first
experience with a lithoplasty device to tackle the unmet need
in the management of severely calcific coronary lesions.
Stent under expansion due to heavily calcified plaque has been
successfully treated with coronary lithoplasty [4]. Shockwave
lithoplasty was used to disrupt the calcium surrounding the
stent, allowing correct stent expansion as documented by
angiography and intravascular ultrasound. Similar experience
as a novel treatment for stent under expansion has been
reported by Tovar Forero MN et al as well [5].
Though coronary lithoplasty was meant to improve on the
disadvantages of rotatational atherectomy, investigators have
combined the two together to treat severely calcified in-stent
neoatherosclerosis [6]. Rotational atherectomy tends to
produce more lesion clearance along the course of the
guidewire (guidewire bias) which can cause crater and tunnel
formation in tortuous or eccentric lesions leading to
perforation or stent malapposition. On the other hand,
lithoplasty produces circumferential clearance.
Non-coronary applications of lithoplasty
The Disrupt BTK study has shown that calcified stenoses in
infrapopliteal arteries can be safely treated with
intravascular lithotripsy [7]. Lithoplasty of iliac artery has
been used to facilitate transcatheter aortic valve
implantation (TAVI) by transfemoral route in patients with
poor vascular access due to calcific stenosis [8,9].
Conclusion
Shockwave lithoplasty is a promising new tool in the
armamentarium of the interventionalist to deal with heavily
calcific hitherto undilatable lesions. Only future large-scale
outocme trials will tells its real place in the cathlab.
References
1. Alunni G, Marra S, Meynet I, D'amico M, Elisa P, Fanelli A,
Molinaro S, Garrone P, Deberardinis A, Campana M, Lerman A.
The beneficial effect of extracorporeal shockwave myocardial
revascularization in patients with refractory angina.
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2. Ali ZA, Brinton TJ, Hill JM, Maehara A, Matsumura M, Karimi
Galougahi K, Illindala U, Götberg M, Whitbourn R, Van Mieghem
N, Meredith IT, Di Mario C, Fajadet J. Optical Coherence
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Lithoplasty. Cardiology. 2018 Nov 8;141(2):75-77.
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