The mechanism of angioplasty is to create dissection

Percutaneous transluminal angioplasty (PTA) increases the arterial lumen by pushing the plaque outward with enough force to cause the plaque to rupture or fracture (Figure 1). Because plaque accumulates and adheres to the innermost layer of the vessel wall, the intima is also torn during inflation. As more force is applied to the lesion, the dissection can expand in multiple directions: deeper into the vessel wall (media, adventitia) and/or along the length of the vessel (Figure 2).

Figure 1
Figure 1
Figure 2
Figure 2

Dissections are often underdiagnosed

Figure 3: Image courtesy of Christian Wissgott, MD
Figure 3: Image courtesy of Christian Wissgott, MD

Dissections appear on angiography when contrast collects between the fractured intima and the exposed media and/or adventitia (Figure 3). During endovascular procedures, physicians use a real-time visual estimate to identify and classify post-intervention dissections. Angiography, however, underestimates the presence and severity of post-intervention dissection, including medial and adventitial injury.1, 2 Challenges such as vessel overlap, foreshortening and non-concentric lesions can limit two-dimensional angiography. Like the plaque itself, dissections can be eccentric and misinterpreted or missed altogether if viewed from only one angle or if proper magnification isn’t used. Bone interference during angiography and small vessel caliber can also contribute to underdiagnosis of infrapopliteal dissections.

Figure 4: Image courtesy of Nicolas Shammas, MD

Intravascular ultrasound (IVUS) can be helpful in identifying post-intervention dissections that are missed using angiography (Figure 4). In the iDissection study, 4 to 6 times more dissections were identified with IVUS than with angiography alone.2

Dissections are often underestimated

While there is no established consensus on classifying peripheral arterial dissections, the National Heart, Blood and Lung Institute (NHLBI) classification for coronary arteries is often applied to the lower extremities. Six grades ranging from minor dissection (A) to total flow disruption (F) describe the severity of vessel damage.3

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Figure 5

During endovascular procedures, operators use real-time visual estimation to identify and classify post-intervention dissections. In the Tack Optimized Balloon Angioplasty (TOBA) study, investigator-reported dissection grades were compared with the findings of the angiographic core laboratory (Figure 5). Investigators graded dissection as ≥C in 25.8% of lesions, whereas the core laboratory determined that dissection ≥C was present in 74.0%. 4 Additionally, the iDissection study revealed that post-intervention dissections were significantly more severe than they appear with angiography.2

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Figure 6

In the TOBA II study dissection training improved the correlation between the physicians and the core laboratory (Figure 6). 5

This further underscores the fact that dissections are prevalent and often underestimated.

Which dissection grades matter?

While there is consensus that severe dissections result in poorer outcomes, an objective definition of “severe dissection” has yet to be made. NHLBI Type A and B dissections are generally excluded as severe dissections.  However, data demonstrates that these seemingly minor dissections still negatively impact long-term outcomes.

A retrospective by Fujihara et al6 investigated the incidence of post-PTA dissection. The overall dissection rate was 84%. Lesions with severe dissections (C-F) had a 34% TLR rate at six months. A 14% TLR rate was reported for the remaining lesions which included no dissection as well as grades A and B. Although the zero dissection group was included with grades A and B, the data reported that lesions with grade B dissections were nearly twice as likely to need revascularization than Grade A. In addition, the bail out stent implantation rate increased with dissection severity.

In the THUNDER study, Grade A-B dissections experienced similar rates of six-month TLR as did Grades C-E (33% and 44% respectively). At 24 months, TLR rates increased to 43% for Grades A-B and 78% for Grades C-E.7

For informational purposes only. You should always consult with your doctor when seeking medical advice or considering treatment.

References

  1. Korogi Y, Hirai T, Takahashi M. Intravascular ultrasound imaging of peripheral arteries as an adjunct to angioplasty and atherectomy. Cardiovasc Interv Radiol 1996;19:1-9.
  2. Shammas N, Torey J, Shammas W et al. Intravascular ultrasound assessment and correlation with angiographic findings demonstrating femoropopliteal arterial dissections post atherectomy: results from the iDissection study. J Invasive Cardiol. 2018;30(7):240-244
  3. National Heart, Blood and Lung Institute. Coronary artery angiographic changes after PTCA. In: Manual of operations: NHLBI PTCA registry. Bethesda, MD: NHLBI; 1985. p. 6-9.
  4. Bosiers M, Scheinert D, Hendriks JMH et al. Results from the Tack Optimized Balloon Angioplasty (TOBA) study demonstrate the benefits of minimal metal implants for dissection repair after angioplasty. J Vasc Surg 2016;64:109-16.
  5. Data on file, Intact Vascular, Inc.
  6. Fujihara M, Takahara M, Sasaki S et al. Angiographic dissection patterns and patency outcomes after balloon angioplasty for superficial femoral artery disease. J Endovasc Ther 2017;1-9.
  7. Tepe G, Zeller T, Schnorr B et al. High-grade, non-flow-limiting dissections do not negatively impact long-term outcome after paclitaxel-coated balloon angioplasty: an additional analysis from the THUNDER study. J Endovasc Ther 2013;20:792-800.