Pathophysiological Significance of Velocity-Based Microvascular Resistance at Maximal Hyperemia in Peripheral Artery Disease

How much flow is enough: the use of fractional flow reserve in chronic limb-threatening ischemia in a series of patients with isolated occlusive tibial disease

The role of the fractional flow reserve to guide lower extremity peripheral vascular intervention, specifically in chronic limb-threatening ischemia, has remained unclear. This series presents a novel use of the fractional flow reserve in four patients to guide lower extremity endovascular interventions in patients with chronic limb-threatening ischemia.

A Systematic Review and Critical Appraisal of Peri-Procedural Tissue Perfusion Techniques and their Clinical Value in Patients with Peripheral Arterial Disease

OBJECTIVE

Many techniques have been introduced to enable quantification of tissue perfusion in patients with peripheral arterial disease (PAD). Currently, none of these techniques is widely used to analyse real time tissue perfusion changes during endovascular or surgical revascularisation procedures. The aim of this systematic review was to provide an up to date overview of the peri-procedural applicability of currently available techniques, diagnostic accuracy of assessing tissue perfusion and the relationship with clinical outcomes.

DATA SOURCES

MEDLINE, Embase, CINAHL, and the Cochrane Central Register of Controlled Trials.

REVIEW METHODS

This systematic review was conducted in accordance with the Preferred Reporting Items for Systematic review and Meta-Analysis (PRISMA) guidelines. Four electronic databases were searched up to 31 12 2020 for eligible articles: MEDLINE, Embase, CINAHL and the Cochrane Central Register of Controlled Trials. Eligible articles describing a perfusion measurement technique, used in a peri-procedural setting before and within 24 hours after the revascularisation procedure, with the aim of determining the effect of intervention in patients with PAD, were assessed for inclusion. The QUADAS-2 tool was used to assess the risk of bias and applicability of the studies.

RESULTS

An overview of 10 techniques found in 26 eligible articles focused on study protocols, research goals, and clinical outcomes is provided. Non-invasive techniques included laser speckle contrast imaging, micro-lightguide spectrophotometry, magnetic resonance imaging perfusion, near infrared spectroscopy, skin perfusion pressure, and plantar thermography. Invasive techniques included two dimensional perfusion angiography, contrast enhanced ultrasound, computed tomography perfusion imaging, and indocyanine green angiography. The results of the 26 eligible studies, which were mostly of poor quality according to QUADAS-2, were without exception, not sufficient to substantiate implementation in daily clinical practice.

CONCLUSION

This systematic review provides an overview of 10 tissue perfusion assessment techniques for patients with PAD. It seems too early to appoint one of them as a reference standard. The scope of future research in this domain should therefore focus on clinical accuracy, reliability, and validation of the techniques.

Angiographic flow velocity predicts lower limb outcomes after endovascular therapy: Application of the frame count method

INTRODUCTION

Several factors related to lesion characteristics and endovascular therapy (EVT) procedures have been reported to affect primary patency after EVT. However, it is unknown why these factors were associated with primary patency. We hypothesized patency failure was related to poor blood flow in affected arteries.

METHODS

This retrospective study included 131 consecutive patients who had received EVT with bare metal stents for peripheral artery disease caused by femoropopliteal artery lesions. Based on the tertile post-EVT flow velocity of the superficial femoral artery (SFA), patients were divided into high (n = 43), middle (n = 44), and low (n = 44) flow velocity groups. Flow velocity was measured using the frame count method. We measured incidence of major adverse limb events (MALE), composed of target lesion revascularization (TLR), non-TLR, and major amputation.

RESULTS

At a median follow-up period of 22.7 months, MALE had occurred in 7 (16.3%), 10 (22.7%), and 29 (65.9%) of patients from the high, middle, and low SFA flow velocity groups, respectively (p < 0.001). Kaplan-Meier analysis showed incidence of MALE was significantly higher in the patients of low SFA flow velocity (log-rank test χ² = 38.8, p < 0.001). Multivariate analysis found low SFA flow velocity to be an independent predictor for MALE (hazard ratio: 4.42; 95% CI: 2.27 to 8.60; p < 0.001) as was ankle-brachial index.

CONCLUSION

Post-EVT SFA flow velocity for femoropopliteal artery lesions treated with bare metal stents is an independent predictor of limb patency. The frame count method for assessing arterial flow velocity is convenient and has potential for wide applications in EVT.

Below-the-Ankle Arrival Time as a Novel Limb Tissue Perfusion Index: Two-dimensional Perfusion Angiography Evaluation

Purpose: To identify lower limb 2-dimensional (2D) perfusion angiographic parameters that are related to skin perfusion pressure (SPP), a predictor of wound healing in patients with chronic limb-threatening ischemia (CLTI) undergoing below-the-knee (BTK) endovascular treatment (EVT). Materials and Methods: Thirty-three consecutive patients (mean age 74.5 years; 18 men) with 47 isolated BTK lesions in 33 limbs (Rutherford category 3–5) underwent EVT. Dorsal and plantar SPPs were measured before EVT and the day after. The indexed blood flow below the ankle was measured using 2D perfusion angiography before and after EVT to determine changes in perfusion parameters [arrival time (AT), time to peak, wash-in rate, mean transit time, and width and area under the time-density curve] at rest vs during hyperemia induced with a 20-mg intra-arterial papaverine infusion. Correlations between the 2D perfusion parameters and SPPs were assessed using the Pearson coefficient. The cutoff points to predict mean SPPs >40 mm Hg were analyzed using a receiver operating characteristic curve; outcomes are reported as the area under the curve (AUC) with 95% confidence interval (CI). Results: After EVT at rest and during hyperemia, only AT was significantly changed, although hyperemia produced significant changes in all the pre-/post-EVT 2D perfusion parameters except the wash-in rate. Dorsal and plantar SPPs after EVT were significantly increased and correlated with hyperemic AT and the AT ratio (hyperemia/at rest values) below the ankle. Hyperemic ATs <6.3 seconds and AT ratios <0.78 were predictive factors for a mean SPP >40 mm Hg, with AUCs of 0.83 (95% CI 0.67 to 0.99) and 0.78 (95% CI 0.61 to 0.95), respectively. Conclusion: Hyperemic ATs <6.3 seconds or AT ratios <0.78 below the ankle may be essential to obtain sufficient SPPs for limb salvage in BTK lesions. Thus, the use of 2D perfusion angiography enabled the monitoring of lower limb tissue perfusion throughout EVT and may thereby optimize treatment of CLTI.

Pressure- and Velocity-Based Physiological Assessment of Stenotic Lesions at Hyperemia in Superficial Femoral Artery Disease: Importance of Hyperemic Stenosis Resistance

Background: In superficial femoral artery (SFA) stenosis, stenosis resistance may increase, but the relationship between stenosis resistance and stenotic severity remains to be seen. This study aimed to investigate the physiological response, through a hyperemic condition, and the pathophysiological significance of Doppler flow and stenosis resistance in SFA. Methods: Twenty-four limbs with focal stenosis of the SFA were analyzed. We assessed the fractional flow reserve (FFR), hyperemic stenosis resistance (h-SR), and vascular flow reserve (VFR) of the SFA with a pressure/Doppler flow sensor-tipped combination guidewire before and after endovascular therapy (EVT). Results: FFR, h-SR, and VFR changed significantly after EVT. h-SR was more strongly correlated with % area stenosis, measured by intravascular ultrasound than FFR (FFR: r=-0.716, h-SR: r=0.741, p<0.0001, respectively). However, VFR was not associated with % area stenosis. A receiver operating characteristic curve showed cut-offs h-SR >0.36 mmHg·sec/cm, and FFR <0.88 predicted >75% area stenosis with area under curves of 0.883 and 0.828, respectively. Conclusion: h-SR can indicate stenotic severity in an SFA focal lesion more prominently than FFR and may be a new physiological index to determine indication for EVT. VFR was not feasible for assessment in SFA focal stenosis.

The Use of Fractional Flow Reserve for Physiological Assessment of Indeterminate Lesions in Peripheral Artery Disease

Peripheral artery disease (PAD) is a prevalent disorder in the United States, associated with significant morbidity and mortality. Fractional Flow Reserve (FFR) is a physiological test used to assess the hemodynamic significance of intermediate lesions on conventional angiography. It is well studied in coronary artery disease and is as an important tool to guide decisions regarding revascularization in a significant percentage of patients with intermediate lesions. As compared to coronary FFR, the use of FFR in peripheral artery disease (PFFR) is much less prevalent. Overall data regarding the use of the PFFR is sparse. There are limited studies that have shown the correlation of PFFR with non-invasive testing including ankle-brachial index (ABI) and Doppler Imaging. Unlike coronary FFR, the optimal pharmaceutical agents and doses to induce maximal hyperemia in the peripheral vascular bed are also not well established. Moreover, there are no established standardized procedural protocols for measuring PFFR. Various studies have employed varying techniques, hyperemic agents and doses. The aim of this literature review is to summarize the current evidence on PFFR, the correlation with noninvasive studies used in PAD and to increase awareness of the potential role of the PFFR in peripheral interventions.