The Quest for Optimal Peripheral Angioplasty: Controlling Dissections

The Quest for Optimal Peripheral Angioplasty: Controlling Dissections

From the Midwest Cardiovascular Research Foundation, Davenport, IA, USA

Key words: angioplasty, dissection, restenosis, dissection repair, stent, procedural success, patency

Address all correspondence to:

Nicolas W Shammas, MD, MS, FACC, FSCAI
Midwest Cardiovascular Research Foundation
1622 E Lombard Street,
Davenport, IA 52803
shammas@mchsi.com

Relevant Conflict of Interest: Dr Shammas receives educational and research grants from VentureMed Group, Intact Vascular, Boston Scientific, Bard and Phillips.

There are several imaging predictors of restenosis following percutaneous transluminal balloon angioplasty (PTA) of infrainguinal interventions. These include dissections involving the media and external elastic lamina, small vessel diameter, longer lesions, high residual narrowing post intervention, and inadequate stent expansion or asymmetry.1-3

Dissections are an inevitable consequence of PTA. When treating de-novo disease with PTA, the gain in minimal luminal area (MLA) is driven by several mechanisms, including plaque compression or fracture, direct arterial stretching, and dissections.4 Dissections are an important mechanism preventing recoil and allowing better vessel stretching. However, dissections have negative consequences. Depending on their magnitude, they have been shown to predict acute vessel closure or loss of patency.5,6 NHLBI types C-F showed a significantly lower patency rate (p<.001) and higher clinically driven TLR (p<.001) compared to types A and B dissections. Although drug-coated balloons seem to mitigate some of the negative consequences of dissections seen on angiography, stenting remains necessary in over 30% of complex femoropopliteal disease. Furthermore, paclitaxel-coated technologies (DCB or DES) in peripheral arterial interventions have been recently associated with a questionable increase in mortality, leading to a significant drop in their use.7 The interest in alternative non-paclitaxel therapies seems renewed. 

The NHLBI classification for coronary dissections has been applied to infrainguinal peripheral arterial interventions. An incremental increase in the dissection grade using this classification was shown to correlate with higher restenosis and need for target lesion.5,6 However, the NHLBI classification of dissections is very limited in scope. It only considers the single worst dissection, regardless of the number of dissections, and does not consider the length, depth, and extent of dissections. Recent data indicate that deeper vessel wall injury involving the media and adventitia leads to a higher rate of restenosis.1 These deeper injuries may not be visible or may appear low grade on angiogram. Larger flaps are also more likely to cause acute or subacute lumen compromise, particularly if they fall near the center of the lumen. These dissection flaps may be completely missed on an angiogram. Therefore, angiographic evaluation of dissections is suboptimal. In addition, angiography underestimates calcium severity, intraluminal thrombus, vessel diameter, and residual narrowing post intervention (particularly stenting), in addition to being unable to evaluate plaque morphology.3 

Precise imaging

Precise imaging within the vessel wall is critical to evaluate the degree and extent of dissections. The iDissection grading system uses intravascular ultrasound (IVUS) to classify dissections in infrainguinal interventions. The depth of dissection is graded as A (intima), B (media), and C (adventitia). The arc of dissection is graded as 1 (less than 180 degrees) or 2 (more or equal 180 degrees). This 6-grade classification (A1, B1, C1, A2, B2, C2) is reliable and can quickly be performed during the procedure.8 The more our ability to precisely identify the number, length, depth, and arc of dissections by IVUS, the more likely this will allow us to develop devices and refine techniques to control their severity. 

The iDissection grading system was used for the first time in a small study evaluating the number, depth, and extent of dissections following atherectomy.9 In this study, Jetstream atherectomy (n=13) and B-laser (n=2) were used. De-novo and non-stent restenotic lesions were included. Angiography and IVUS (Eagle Eye Platinum, Phillips) were performed at baseline, post atherectomy, and post adjunctive balloon angioplasty. Core angiographic (Midwest Cardiovascular Research Foundation, Davenport, IA) and intravascular ultrasound (Midwest Cardiovascular Research Foundation, Davenport, IA, and St. John Hospital, Detroit, MI) laboratories evaluated all images. In this study, critical limb ischemia was present in 26.7% of patients, and 60% of lesions had grade 3 and 4 PACCS grade calcification. Adjunctive balloon angioplasty was performed in all patients (Shockwave 33.3%, drug-coated balloons 100%). Mean balloon pressures and inflation times were 10.3 atmospheres and 310 seconds. Procedural success (<30% residual narrowing at end of procedure) was accomplished in all patients, and residual narrowing post angioplasty was 19.7%. Dissections were identified 4 to 6 times more on IVUS when compared to angiography (post atherectomy and adjunctive angioplasty IVUS to angiographic dissection ratios were 5.75 to 1 and 3.55 to 1, respectively) (Figure 1). Wider dissections > 180 degrees were also noted on IVUS in 13% and 31% post atherectomy and adjunctive PTA, respectively. Furthermore, deeper dissections involving the media and adventitia occurred in 39.1% and 33.3% post atherectomy and adjunctive PTA, respectively. Finally, IVUS identified intramural hematoma in 13.3% of vessels post atherectomy. These results may offer an explanation as to why atherectomy of de-novo or non-stent restenotic lesions in the femoropopliteal arteries does not improve long-term outcomes and has similar target lesion revascularization to PTA, despite higher successful acute angiographic procedural results (defined as less dissections and bailout stenting) than PTA.

Figure 1. Dissection on IVUS and Angio

Many technologies were developed to control dissections as seen on angiography. These include cutting (Boston Scientific Corp) and scoring balloons (AngioSculpt® scoring balloon (Phillips); ULTRASCORE Focal Force (BD/Bard)); the FLEX VP atherotome (VentureMed Group); the Serranator (Cagent Vascular), the lithotripsy shockwave balloon (Shockwave Medical); and atherectomy.

Cutting balloons (CB) continue to show angiographic dissections post treatment of femoropopliteal lesions, and more than half of these dissections are NHLBI type C or higher (54.8%). High-grade angiographic dissections have been shown to correlate with loss of patency on follow-up. CB was shown by IVUS to be more effective than scoring balloons10,11 in modifying calcified plaque with a higher acute luminal gain and better stent symmetry. In calcified lesions, the larger luminal gain occurs in lesions with evidence of dissections and without significant change in vessel expansion (external elastic lumen surface area remains unchanged) or plaque-media cross-sectional area. On the other hand, CB in non-calcified lesions yields larger lumen area mostly by larger plaque reduction and less vessel expansion compared to PTA.12 The depth and extent of dissections seen by IVUS following CB has not been well defined. CB as a sole intervention has not been shown to yield better outcomes than PTA in treating restenotic or femoropopliteal disease.  

The AngioSculpt scoring balloon (Phillips) has three nitinol spiral elements mounted on the surface of a semi-compliant balloon. This allows a homogenous transmission of pressure over the plaque, theoretically reducing dissections regardless of calcification. AngioSculpt, when assessed by IVUS, increased minimal luminal area post stenting13 and had a low rate of angiographic dissections and stenting.14-16 It also had no impact on target lesion revascularization. The ULTRASCORE Focused Force PTA balloon (Bard/BD) has two longitudinal wires intended to concentrate the force against the plaque for a controlled fracture at low pressure. IVUS based patterns of dissections with this balloon are lacking. 

The FLEX Vessel Prep System (VentureMed Group) is a one-size-fits-all device with 3 atherotomes mounted on a self-expanding treating element, designed to create multiple longitudinal, controlled-depth, continuous micro-incisions across the entire lesion length. Early data from 255 patients (mean age 71.8±9.1 years) treated with the FLEX VP System at 38 centers (average lesion length 133±88 mm, 44.3% with a chronic total occlusion) suggest that this device reduces flow-limiting dissection with no vessel perforation or embolization.17 Minor angiographic dissections occurred in 5.9% of patients (type A or B). Provisional stenting was performed in 49 (19.2%) patients. Predictors of stenting were dissections, longer lesions, and conventional balloon dilation. These results were encouraging. IVUS based analysis post FLEX VP was recently published and confirmed less deep dissections (media and adventitia) than seen with historical data from some atherectomy devices.18 In 15 patients treated with the FLEX VP followed by adjunctive balloon angioplasty (Shockwave 33.3%, PTA 26.7%, Drug-coated balloon 40%) for de-novo or non-stent restenotic femoropopliteal disease, procedural success was 86.7% (<30% residual narrowing at end of procedure). Minimal luminal area increased from a median of 5.2 mm2 to 15.0 mm2 (p<.001) with no change in reference lumen diameter or plaque burden area (p=.32). Of all new dissections (n=37) post FLEX VP and PTA, 18.9% were more than 180 degrees in circumference and 21.6% involved the media and adventitia. These numbers appear favorable compared to rotational and aspiration atherectomy, but head-to-head comparison data are not available. The low number of large flaps and deeper dissections may offer an explanation to the low provisional stenting seen with this device. The impact of these encouraging acute results on long-term outcomes is not yet known. 

Lithotripsy using the Shockwave balloon utilizes sound waves to disrupt calcium in the vessel wall. Optical coherence tomography (OCT) has shown that lithoplasty modifies calcium, with fracture as the predominant mechanism, leading to significant favorable luminal area gain and stent expansion.19 Applications of lithoplasty to calcified stenotic common femoral artery also showed excellent acute success with no dissections needing stenting. There were only 5 NHLBI type B non-flow-limiting dissections (out of 21 patients treated), and no perforation, distal embolization, or abrupt closure.20 Patterns of dissections using IVUS with Shockwave lithoplasty have not been defined. 

Dissection repair

Dissection repair has been recently introduced as a strategy to improve outcomes of infrainguinal interventions. Repair of dissections in the TOBA BKA study showed a freedom from CD-TLR of 93.5% and patency of 78.4% at 1 year, significantly better than historic control .21 In the TOBA II study, 213 patients with 100% dissected vessels following plain old balloon angioplasty or drug-coated balloons underwent repair of their dissections using the Endovascular Tack system. Of all dissections identified, 92.1% were repaired. Freedom from TLR and patency at 1 year were 86.5% and 79.3%, respectively. Bail-out stent rate was 0.5%.22

In conclusion, high-grade dissections predict a higher TLR rate and reduced patency. By using IVUS, the number, depth, and width of dissections can be more accurately classified. Several devices, including the FLEX VP, are now available to reduce dissections, but more data are needed to determine their impact on long-term outcomes. Dissection repair is emerging as an important strategy to reduce TLR rates and restenosis following balloon angioplasty.

References
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Figure 1. Dissections as seen on angiogram and intravascular ultrasound (IVUS)following atherectomy. Angiography showed no dissections. IVUS identified several dissections in the same treated blood vessel.