The Use of Intravascular Ultrasound Imaging in Peripheral Arterial Endovascular Interventions

Author: Richard Allan

Allan, Richard, 2019 The Use of Intravascular Ultrasound Imaging in Peripheral Arterial Endovascular Interventions, Flinders University, College of Medicine and Public Health

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Endovascular intervention is the most common method of treating peripheral arterial disease but restenosis rates remain high. There is limited retrospective evidence suggesting that the use of intravascular ultrasound (IVUS) may improve outcomes of lower limb interventions. Calcium and dissection are important factors in endovascular intervention, but there is a lack of objective data to assess the available classification systems. Estimation of atheroma volume may have value in PAD, but it is unclear if IVUS is suitable for this purpose.

The aims of this research were: to investigate whether the use of IVUS in femoropopliteal artery interventions can lower the rate of binary restenosis; to investigate how well calcium scoring systems categorise calcium severity; to compare the performance of the two available dissection classifications at categorising dissection; and to investigate whether IVUS is technically adequate for atheroma volume estimation.

Patients undergoing endovascular interventions for occlusive femoropopliteal disease, at a single site, were recruited into a randomised clinical trial (RCT). Participants were randomised into a control group (treatment guided by angiography) and a treatment group (guidance by both angiography and IVUS). Target sample was 150 participants and interim results for 107 participants are presented. Participants were followed with regular duplex ultrasound surveillance to 12 months by providers blinded to the randomisation. The primary outcome was binary restenosis (duplex ultrasound PVR ≥ 2.4) within 12 months with survival analysis using Kaplan-Meier graphs and difference in survival tested with Log-rank test (interim analysis significance p=0.01).

IVUS from 60 consecutive cases from the RCT were analysed for evidence of calcium and dissection. Angiograms were assessed by two independent blinded raters and scored using multiple calcium and dissection classification systems. Angiographic grading of severity was assessed using the IVUS data and grading scores were tested for inter-rater reliability. IVUS from 38 consecutive cases were analysed for adequacy for use in volume analysis.

In the RCT, freedom from binary restenosis was 77.8% in the treatment group and 56.6% in the control group (p=0.007). Randomisation to the treatment group and the use of drug-coated balloons (DCB) were the only procedural parameters to be predictors of reduced rate of restenosis. There was a lower rate of restenosis for participants in the treatment group treated with DCB.

The hybrid Fanelli system was the only scoring system that was able to differentiate IVUS calcium measurements between mild and severe grades of calcification. Inter-rater reliability was fair/moderate for all scoring systems. Dissection classification systems had good agreement for grading severity but no differences in the IVUS measurements were found between severe and mild grades for either system. Most IVUS scans were not adequate for estimating atheroma volume.

In conclusion, the lower rate of restenosis in the participants with IVUS guidance suggests that the use of IVUS may be beneficial in femoropopliteal disease. Analysis using IVUS suggests that scoring systems incorporating CTA may be better at differentiating calcium severity. Dissection grading systems agree well but may not differentiate severity of dissections. Peripheral IVUS image quality is probably inadequate for estimating atheroma volume.

Keywords: Intravascular ultrasound, IVUS, peripheral arterial disease, endovascular interventions, vessel calcification, dissection, RCT

Subject: Cardiology thesis

Thesis type: Doctor of Philosophy
Completed: 2019
School: College of Medicine and Public Health
Supervisor: Prof Derek Chew