Shock Wave Intravascular Lithotripsy: Shock the Rock

Origination of IVL

Shock wave lithotripsy was primarily used medically to treat urolithiasis in the 1980s.^[27] Before lithotripsy use the predominant method of stone extraction was surgery, and treatment carried a significant risk of surgery related complications. The introduction of a novel, non-invasive medical approach to treat renal stones revolutionized treatment, as extracorporeal shockwave lithotripsy allowed minimally invasive management of urinary tract stones. Evaluation the safety and effectiveness of extracorporeal shock wave liothotripsy have been favorable,^[28] but not complication free. Vascular rupture, actual kidney injury (secondary to tubular involvement), scarring and inflammation, with persistent impairment of kidney function are possible. These complications are reduced when utilizing a lower rate of shock-wave and stopping between each phase of the treatment.^[27] Further innovation has allowed for use of lithotripsy to treat stones in the gallbladder and bile duct, and within the coronary and peripheral vasculature.^[29] Using pulsatile sonic pressure waves to shatter and crack the calcium.

IVL: Device and procedure

Coronary IVL is currently performed using the Shockwave Medical device (Shockwave Medical, Inc, Santa Clara, CA). This is a single use disposable monorail catheter with an fluid filled 12 mm angioplasty balloon surrounding the shockwave emitters [Figure 1] connected to a portable energy generator. The balloon has a diameter ranging from 2.5 to 4.0 mm, with crossing profiles of 0.043” to 0.046” [Figure 1]. Catheter is inserted through a conventional coronary wire (0.014”) with a fast exchange platform. There are two lithotripsy emitters in the balloon shaft^[30] emanate IVL waves. These emitters produce acoustic pressure waves within the balloon. The electrical current from the emitters allows the fluid within the balloon to vaporize, creating sonic pressure waves as the gaseous bubble within the balloon rapidly expands and collapses. The shock waves travels through the vasculature soft tissue, selectively modifying calcification within the vessel wall, causing fractures evident with subsequent intravascular imaging.^[26,31] The both blood vessel layers (intima and medial layers) are affected. The calcium modification and fracture enhances vascular compliance, enabling controlled balloon dilation and better stent delivery and expansion.^[30] The balloon is filled with fluid to limit thermic damage to the vaculature, and several emitters across the shaft to permit shock waves to the extent of the lesion. The positive and negative peak pressures are monitored closely and lowered to minimize the tensile stress on the vessel wall, which can be compared to extracorporeal SWL.^[31]

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Figure 1:

Intravascular lithotripsy device.

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Balloon size is choosed depend on the diameter of the reference vessel (1:1 sizing). The indeflator device and balloon are developed by conventional procedure applying a solution of contrast dye and saline (50:50). Following a guidewire flush, saline is applied to the balloon and distal shaft to activate the hydrophilic coating. The cable connector is connected to one side of IVL and catheter on the another side [Figure 1]. The IVL balloon is positioned at the treatment site using proximal and distal markers, and then it is inflated to a pressure of no more than 4.0 atm. The balloon must be fully apposed to the vessel wall. When the connector button is switched on, ten pulses of IVL therapy are administered over 10 s. The balloon is expanded to 6.0 atm to a greater extent as per the balloon compliance and thereafter compressed, to admit blood flow to be restored. The process can be performed as many times as required to administer numerous cycles of IVL to the lesion with a maximal of 80 pulses per therapy segment. To ensure and maintain optimal distal perfusion, each cycle of 10 pulses must always be followed by an pause of at least 10 s. The balloon can be maneuvered across the lesion among rounds.^[32] Particular risks are linked with the coronary IVL procedure which includes vessel dissection, atrial or ventricular capture/extrasystole, device embolization, and allergic responses to any component of the device reported by the manufacturer.^[32] This is in contrast to the known risks of catheter-based therapies and general coronary interventional procedures. Coronary IVL is now approved for use in the balloon dilation of stenotic, severely calcified de novo coronary arteries preliminary to stenting. When performing IVL for lesions within 5 mm of prior stenting, advised with caution.^[32] off-label applications of the IVL method encompass in-stent restenosis (ISR), lesions post CABG, and stent under expansion [Figures 2 and 3].

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Figure 2:

Coronary angiography pre- and post-intravascular lithotripsy therapy.

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Figure 3:

(a) Pre-intravascular lithotripsy (IVL) OCT of calcification (b) post-IVL OCT of calcium fractures with increased lumen area.

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DISRUPT trial for CAD I

This trial,^[25] a small (n = 60) prospective multicenter study, evaluating the feasibility of IVL use in patients with severely calcified coronary lesions IVL. A clinical endpoint of MACE was used (defined in this trial as cardiac mortality, myocardial infarction, and target vessel revascularization), DISRUPT trial patients had MACE rates of 5.0% at 30 days and 8.6% at 6 months. The instrument success rate (defined as successful device delivery and IVL therapy at target lesion) and clinical success rate (defined as a residual stenosis of less than 50% and no in-hospital MACE) were both high (98.3% and 95.0%, respectively). According to OCT results, fracture was the main mechanism for calcium alteration, and it was independent of depth.^[25]

DISRUPT trial for CAD II

The DISRUPT II trial,^[33] followed on from DISRUPT I and was designed to evaluate safety and effectiveness of IVL, was a slightly larger (n = 120) prospective multicenter study, evaluating IVL use in patients with severely calcified coronary lesions IVL. The in-hospital MACE was an primary endpoint (MI, target vessel revascularization, and cardiac death). An OCT sub study was also conducted to evaluate the mechanism of calcium modification, and characteristics of the plaque fracture achieved. In hospital MACE was reported in 5.8% (due to 7 myocardial infarctions), no perforation or slow flow-no reflow, abrupt closure was noted in any of the DISRUPT II patients. There is 78.7% lesions having calcium fractures were showed in the te Post PCI OCT, with average of 2.6 fractures per lesion.^[33]

DISRUPT trial for CAD III

The DISRUPT III trial,^[30] followed on from DISRUPT II and was considered the pivotal study to confirm safety and effectiveness of coronary IVL, still a single arm prospective multicenter study it was performed in 4 countries and studied a larger (n = 431) cohort, evaluating IVL use in patients with severely calcified coronary lesions IVL. Freedom from MACE at 30 days was the major safety endpoint, while procedural success was the efficacy endpoint. While the procedural success rate was 92.4%, the overall primary safety endpoint reached was 92.2%. The procedure was well tolerated, and there were few periprocedural complications. The associated OCT sub study found 67.4% of the lesions had calcium fracture.^[30]

DISRUPT trial for CAD IV

This trial^[34] followed on from DISRUPT III and was designed to for regulatory approval of coronary IVL in Japan, still a single arm prospective multicenter study it studied only 64 patients, specifically evaluating IVL use in Japanese patients with severely calcified coronary lesions IVL. Again, freedom from MACE at 30 days was the primary endpoint, and operative success (residual stenosis <50%) was the major efficacy endpoint. Results from DISRUPT IV patients were also compared using propensity matching to previously published IVL control group from outside of Japan. The main outcomes were procedural success (cases 93.8% vs. control 91.6%, P = 0.007) and noninferiority for freedom from MACE at 30 d (cases 93.8% vs. control 91.2%, P = 0.008). During the procedure, no complications such as perforations, abrupt closure, or slow flow/no reflow were occurred.^[34]

Pooled evidence disrupt I-IV

Data from all 4 DISRUPT trials have been pooled and recently published^[31] discussing outcomes of all 628 patients in these single arm IVL trials from Japan, Northern American, Australia, and Europe. Major reported findings were that coronary IVL had a high rate of procedural success and facilitated safe successful stent implantation in severely calcified coronary lesions. The average length of calcified stenosis treated over all 4 studies was found to be 41.5 ± 20.0 mm. Safety and efficiency endpoint were met in ≥92% of patients. Reported rates of target lesion failure were 7.2%, cardiac death 0.5%, and stent thrombosis 0.8%. Rates of post-IVL complications were 2.1% and rates of serious angiographic complications were 0.3%, no IVL-associated perforations, abrupt closure, or episodes of no reflow in the entire pooled cohort. Editorial comment was primarily positive but also noted the need for future control group comparison where PCI was used without lithotripsy, and the issue of lesion choice where calcium may not be circumferential, and therefore less favorable for IVL, concluding more data, particularly RCT data were required^[23] [Table 3].

Acute coronary syndrome (ACS)

Data describing IVL in the setting of ACS have also been described in a small number of patients.^[37-41]

Wong et al. reported real world data in patients treated with IVL (n = 44). In this registry 57% of patients had ACS at presentation. Wong reported that angiographic success in all 44 cases of angiographic success were documented. There were no adverse outcomes or in-hospital complications were observed. At 1-year follow up 1 cardiovascular death due to hemorrhagic stroke, 3 NSTEMIs, (and 3 non-cardiac deaths were reported) three NSTEMIs occurred at 1 year. More IVL treated ACS cases are reported by Aziz et al. in their registry (n = 190) of ACS data collected from 6 centers in the United kingdom and Italy.^[39] In this cohort 47.8% were ACS. Procedural success was achieved in every patients except one. The complications rate was 3%. Six coronary perforations were reported. There was one in-hospital death. At final follow up (median 222 days) a MACE rate of 2.6% was reported. There were three cases of TVR, two cardiac mortality, and one MI.

A lower rate of IVL use in ACS was reported by El Jattari et al., evaluating German registry data (n = 134).^[40] El Jattari et al. reported 29.9% of the patients selected for IVL treatment presented with ISR, and 70.1% had de novo lesions. In this registry 88.1% of cases had successful procedural outcomes. MACE at 1 month was 3%, with 2 cardiovascular deaths, and 2 of non-cardiac deaths, 1 case of stent thrombosis occurred, and 1 dissection that requiring further stenting, 13 IVL balloon ruptures occurred (9.7%) (with no adverse sequelae), and 1 coronary artery perforation causing death was reported.

Rola et al. evaluated polish registry data (n = 52), including patients with lesion described as previously “un-dilatable” 82.7% of whom had ACS.^[41] In this case series, clinical success with IVL was attained in 98.1% of cases. One patient experienced ventricular arrhythmia due to ongoing ischemia rather than IVL therapy. One balloon ruptured, and one patient had a residual stenosis more than 50% (despite 100 IVL pulses). Two significant bleeding events were reported, and one in-hospital stroke.

Under expansion of stents

IVL has also been used successfully for stent under expansion. Data from the multicenter SMILE registry, (n = 34) found a success rate of 87.1% with IVL.^[42] Authors reported 30 days outcomes in this cohort of no, stent thrombosis, artery perforation, TLR, and cardiac mortality. At median of 13 months this registry reported, 1 non-fatal peri-procedural MI post rupture of IVL balloon.

Combined therapy “Rotatripsy”

Calcium modification with a combination of both IVL and rotablation has also been described. Aziz et al. reported cause of ombined therapy with both IVL and rotablation in 34/190 (18%) of patients treated with IVL, but did not report subgroup outcomes for those treated with “rotatripsy.”^[39] Buono et al.,^[43] report outcomes of a retrospective analysis of thirty-four “Rotatripsy” cases. In all cases rotablation preceded IVL, either during the index procedure (79%) or staged procedure during the same hospital admission. The procedures success was reported in 100% of cases. Adverse outcomes at 1 year were reported and included t2 target vessel MIs, and the all cause at a rate of 9%. Three coronary perforations occurred; they were successful treated without further deterioration.