Physiologic evaluation of translesion pressure gradients in peripheral arteries: comparison of pressure wire and catheter-derived measurements

Utility and optimal dose of nicorandil for physiological assessment of the femoropopliteal artery

BACKGROUND

Nicorandil is widely used as a vasodilator for the physiological assessment of coronary arteries because of its usefulness and safety; however, there are no data on its use in peripheral arteries.

AIMS

To identify the utility of nicorandil and its appropriate dose for the physiological assessment on the femoropopliteal artery.

METHODS

We retrospectively enrolled patients from three institutes in which physiological assessment was carried out with various doses of nicorandil before treatment. Twenty-four femoropopliteal artery stenotic lesions from 22 patients were included. The nicorandil doses used were 2, 4, and 6 mg. Twenty-two lesions were also assessed using 30 mg of papaverine. The pressure gradient (PG) and peripheral fractional flow reserve (pFFR) were calculated based on the mean and systolic pressure levels. We examined the correlation of each parameter with the peak systolic velocity ratio (PSVR) based on the duplex ultrasound images using Spearman's rank correlation coefficient. Systemic blood pressure was assessed for safety.

RESULTS

The correlations were higher for mean pressure-based parameters than for systolic pressure-based parameters. As the nicorandil dose increased, the correlations among PG, pFFR, and PSVR also increased (mean pressure-based PG: 2 mg, r = 0.360; 4 mg, r = 0.498; 6 mg, r = 0.694, mean pressure-based pFFR: 2 mg, r = -0.479; 4 mg, r = -0.469; 6 mg, r = -0.641). The blood pressure after the administration of 6 mg of nicorandil was low, and the median systemic mean pressure was 65 mmHg.

CONCLUSION

A 4 mg dose of nicorandil is effective and safe for the mean pressure-based physiological assessment of lesions in the femoropopliteal artery.

Tibio-pedal arterial pressure assessment during endovascular intervention to improve quality-of-life in patients with intermittent claudication

Objective

The aim of this study is to compare the quality-of-life (QOL) outcomes and the tibio-pedal arterial pressure post-endovascular intervention.

Background

Physiological assessment of peripheral arterial lesions is infrequently performed during endovascular interventions.

Materials and methods

We retrospectively reviewed all 343 patients with intermittent claudication who underwent an endovascular intervention via tibio-pedal artery access from October 2018 to May 2021. The baseline and post-intervention tibio-pedal arterial pressures from the pedal sheaths were measured. QOL was assessed using a pre-validated Walking Impairment Questionnaire (WIQ) score before and at 30-day after intervention. We compared the baseline tibio-pedal arterial pressure, post-intervention tibio-pedal arterial pressure, delta pressure (post-intervention minus baseline), baseline WIQ scores, 30-day WIQ scores, and delta score (30-day minus baseline).

Results

All 343 patients had successful tibio-pedal accesses. The average tibio-pedal arterial pressure at baseline was 87.0 ± 1.8 mmHg vs. 135.5 ± 1.7 mmHg post-intervention (p < 0.001). Average baseline and 30-day WIQ scores were summation (99.8 ± 3.3 vs. 115.0 ± 3.1, p < 0.001), walking distance (35.7 ± 1.3 vs. 42.5 ± 1.3, p < 0.001), walking speed (21.1 ± 0.9 vs. 23.6 ± 0.8, p = 0.036), stair climbing (4.7 ± 1.4 vs. 24.2 ± 1.4, p = 0.019), and symptoms (18.8 ± 0.2 vs. 20.1 ± 0.2, p < 0.001), respectively. When comparing the increased post-intervention tibio-pedal arterial pressure <60 mmHg vs. ≥60 mmHg, the average delta WIQ scores were all significantly improved with summation (10.0 ± 3.9 to 25.8 ± 5.5, p = 0.01), walking distance (4.1 ± 1.7 to 9.8 ± 2.5, p = 0.02), walking speed (1.5 ± 1.1 to 4.3 ± 1.5, p = 0.02), stair climbing (2.3 ± 1.8 to 9.4 ± 2.5, p = 0.02), and symptoms (1.0 ± 0.3 to 1.8 ± 0.4, p = 0.04), respectively.

Conclusion

Increasing the post-intervention tibio-pedal arterial pressure by 60 mmHg can enhance QOL as suggested by improvement of WIQ scores.

Efficacy of pressure gradient measurement using peripheral fractional flow reserve in common femoral artery: a case report

Background

The severity of peripheral artery disease (PAD) is usually diagnosed by physiological assessments, such as the ankle brachial index (ABI) or peak systolic velocity (PSV) on ultrasonography. We examined peripheral fractional flow reserve (pFFR: distal mean pressure divided by proximal mean pressure) measured by a pressure wire and pressure gradient to diagnose PAD patients who do not have lowered ABI or high PSV on ultrasonography.

Case summary

An 84-year-old woman with intermittent claudication in her left leg had severe calcification in the left common femoral artery (CFA) on angiography. The exercise-stress ABI of pre-endovascular therapy (EVT) was 1.05/0.98. In addition, the PSV of the left CFA on ultrasonography was 230 cm/s. However, the pFFR using papaverine and alprostadil in the left CFA was 0.86, which was a significant score. In addition, the systolic pressure gradient between the distal and proximal regions was >20 mmHg. We performed EVT for the lesion, and the pFFR improved to 0.96. The systolic pressure gradient was only 1 mmHg at the lesion.

Discussion

Symptomatic PAD patients whose ABI or PSV on ultrasonography is insufficient for EVT could be diagnosed with ischaemia using a pressure gradient and pFFR.

CT perfusion in peripheral arterial disease-hemodynamic differences before and after revascularisation

Objectives

The purpose of this study was the assessment of volumetric CT perfusion (CTP) of the lower leg musculature in patients with symptomatic peripheral arterial disease (PAD) before and after interventional revascularisation.

Methods

Twenty-nine consecutive patients with symptomatic PAD of the lower extremities requiring interventional revascularisation were assessed prospectively. All patients underwent a CTP scan of the lower leg, and hemodynamic and angiographic assessment, before and after intervention. Ankle-brachial pressure index (ABI) was determined. CTP parameters were calculated with a perfusion software, acting on a no outflow assumption. A sequential two-compartment model was used. Differences in CTP parameters were assessed with non-parametric tests.

Results

The cohort consisted of 24 subjects with an occlusion, and five with a high-grade stenosis. The mean blood flow before/after (BFpre and BFpost, respectively) was 7.42 ± 2.66 and 10.95 ± 6.64 ml/100 ml*min⁻¹. The mean blood volume before/after (BVpre and BVpost, respectively) was 0.71 ± 0.35 and 1.25 ± 1.07 ml/100 ml. BFpost and BVpost were significantly higher than BFpre and BVpre in the treated limb (p = 0.003 and 0.02, respectively), but not in the untreated limb (p = 0.641 and 0.719, respectively).

Conclusions

CTP seems feasible for assessing hemodynamic differences in calf muscles before and after revascularisation in patients with symptomatic PAD. We could show that CTP parameters BF and BV are significantly increased after revascularisation of the symptomatic limb. In the future, this quantitative method might serve as a non-invasive method for surveillance and therapy control of patients with peripheral arterial disease.

Key Points

• CTP imaging of the lower limb in patients with symptomatic PAD seems feasible for assessing hemodynamic differences before and after revascularisation in PAD patients.

• This quantitative method might serve as a non-invasive method, for surveillance and therapy control of patients with PAD.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00330-021-07692-5.

Endovascular Pressure Measurements to Assess the Functional Severity of Mesenteric Arterial Stenoses

PURPOSE

To assess the ability of pressure measurements to discriminate clinically significant celiac artery (CA) or superior mesenteric artery (SMA) stenosis in patients with suspected chronic mesenteric ischemia (CMI).

MATERIALS AND METHODS

Single-center, retrospective cohort study of 41 intra-arterial pressure measurements during mesenteric angiography with intended revascularization, performed in 37 patients (mean age 67.7 ± 10.8 years, 62% female) between April 2015 and May 2017. Simultaneous prestenotic and poststenotic pressure measurements had been obtained before and after intra-arterial administration of nitroglycerin. Revascularization was performed in 38 of 41 procedures. Definitive diagnosis of CMI was defined as patient-reported symptom relief or improvement after successful revascularization.

RESULTS

Pressure gradients obtained after vasodilator administration were significantly higher in CAs and SMAs with ≥50% stenosis. Pressure ratios (pressure distal [Pd]/pressure aorta [Pa]) obtained after vasodilator administration were significantly higher in CAs with ≥50% stenosis. Subgroup analysis of 22 patients with a ≥50% stenosis of either CA or SMA showed significantly higher pressure gradients and Pd/Pa ratios after vasodilator administration in CMI patients (median pressure gradient: CMI [interquartile ratio] 36 [21-40] mm Hg versus no-CMI 20 [9-21] mm Hg, P = 0.041; Pd/Pa: CMI 0.703 [0.598-0.769] versus no-CMI 0.827 [0.818-0.906], P = .009). A ≤0.8 Pd/Pa cutoff value after administration of a vasodilator best identified a clinically relevant stenosis, with 86% sensitivity and 83% specificity. Complications related to the pressure measurements were not observed.

CONCLUSIONS

Intra-arterial pressure measurements are feasible and safe. Low Pd/Pa ratios were associated with clinically relevant CA or SMA stenosis.

A geometry-based model for non-invasive estimation of pressure gradients over iliac artery stenoses

The aim of this study was to develop and verify a model that provides an accurate estimation of the trans-lesion hyperemic pressure gradient in iliac artery stenoses in seconds by only using patient-specific geometric properties obtained from 3-dimensional rotational angiography (3DRA). Twenty-one patients with symptomatic peripheral arterial disease (PAD), iliac artery stenoses and an ultrasound based peak systolic velocity ratio between 2.5 and 5.0 underwent 3DRA and intra-arterial pressure measurements under hyperemic conditions. For each lesion, geometric properties were extracted from the 3DRA images using quantitative vascular analysis software. Hyperemic blood flow was estimated based on stenosis geometry using an empirical relation. The geometrical properties and hyperemic flow were used to estimate the pressure gradient by means of the geometry-based model. The predicted pressure gradients were compared with in vivo measured intra-arterial pressure measurements performed under hyperemic conditions. The developed geometry-based model showed good agreement with the measured hyperemic pressure gradients resulting in a concordance correlation coefficient of 0.86. The mean bias ± 2SD between the geometry-based model and in vivo measurements was comparable to results found by evaluating the actual computational fluid dynamics model (-1.0 ± 14.7 mmHg vs -0.9 ± 12.7 mmHg). The developed model estimates the trans-lesional pressure gradient in seconds without the need for an additional computational fluid dynamics software package. The results justify further study to assess the potential use of a geometry-based model approach to estimate pressure gradient on non-invasive CTA or MRA, thereby reducing the need for diagnostic angiography in patients suffering from PAD.

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.

Non-Invasive Assessment of Intravascular Pressure Gradients: A Review of Current and Proposed Novel Methods

Invasive catheterization is associated with a low risk of serious complications. However, although it is the gold standard for measuring pressure gradients, it induces changes to blood flow and requires significant resources. Therefore, non-invasive alternatives are urgently needed. Pressure gradients are routinely estimated non-invasively in clinical settings using ultrasound and calculated with the simplified Bernoulli equation, a method with several limitations. A PubMed literature search on validation of non-invasive techniques was conducted, and studies were included if non-invasively estimated pressure gradients were compared with invasively measured pressure gradients in vivo. Pressure gradients were mainly estimated from velocities obtained with Doppler ultrasound or magnetic resonance imaging. Most studies used the simplified Bernoulli equation, but more recent studies have employed the expanded Bernoulli and Navier⁻Stokes equations. Overall, the studies reported good correlation between non-invasive estimation of pressure gradients and catheterization. Despite having strong correlations, several studies reported the non-invasive techniques to either overestimate or underestimate the invasive measurements, thus questioning the accuracy of the non-invasive methods. In conclusion, more advanced imaging techniques may be needed to overcome the shortcomings of current methods.

In Vivo Validation of Patient-Specific Pressure Gradient Calculations for Iliac Artery Stenosis Severity Assessment

Background

Currently, the decision to treat iliac artery stenoses is mainly based on visual inspection of digital subtraction angiographies. Intra‐arterial pressure measurements can provide clinicians with accurate hemodynamic information. However, pressure measurements are rarely performed because of their invasiveness and the time required. Therefore, the aim of the study was to test the feasibility of a computational model that can predict translesional pressure gradients across iliac artery stenoses on the basis of imaging data only.

Methods and Results

Patients (N=21) with symptomatic peripheral arterial disease and a peak systolic velocity ratio between 2.5 and 5.0 were included in the study. Patients underwent per‐procedural 3‐dimensional rotational angiography and hyperemic intra‐arterial translesional pressure measurements. Vascular anatomical features were reconstructed from the 3‐dimensional rotational angiography data into an axisymmetrical 2‐dimensional computational mesh, and flow was estimated on the basis of the stenosis geometry. Computational fluid dynamics were performed to predict the pressure gradient and were compared with the measured pressure gradients. A good agreement by overlapping error bars of the predicted and measured pressure gradients was found in 21 of 25 lesions. Stratification of the stenosis on the basis of the predicted pressure gradient into hemodynamic not significant (<10 mm Hg) and hemodynamic significant (≥10 mm Hg) resulted in sensitivity, specificity, and overall predictive values of 95%, 60%, and 88%, respectively.

Conclusions

The feasibility of the patient‐specific computational model to predict the hyperemic translesional pressure gradient over iliac artery stenosis was successfully tested. Presented results suggest that, with further optimization and corroboration, the model can become a valuable aid to the diagnosis of equivocal iliac artery stenosis.

Clinical Trial Registration

URL: http://www.trialregister.nl. Unique identifier: NTR5085.

Influence of Iliac Stenotic Lesions on Blood Flow Patterns Near a Covered Endovascular Reconstruction of the Aortic Bifurcation (CERAB) Stent Configuration

PURPOSE

To investigate the effect of distal stenotic lesions on flow patterns near a covered endovascular reconstruction of the aortic bifurcation (CERAB) configuration used in the treatment of aortoiliac occlusive disease.

METHOD

Laser particle image velocimetry measurements were performed using in vitro models of the aortic bifurcation with and without a CERAB configuration in place. A hemodynamically nonsignificant stenosis (ΔP: 9 mm Hg), a hemodynamically significant (ΔP: 26 mm Hg) stenosis, and a total occlusion were simulated in the left iliac arteries. Velocity fields and time-averaged wall shear stress (TAWSS) were calculated.

RESULTS

Hemodynamically significant distal lesions did not influence the inflow patterns or TAWSS (0.5-0.6 Pa) in either model. However, hemodynamically significant distal stenotic lesions caused a 2-fold decrease in peak outflow velocities (control: 106 vs 56 cm/s, CERAB: 96 vs 54 cm/s) and a 3-fold decrease in TAWSS (control: 1.34 vs 0.44 Pa, CERAB: 0.75 vs 0.21 Pa). There was a 2-fold decrease in wall shear stress in the CERAB outflow compared with the control, independent of lesion severity.

CONCLUSION

In the CERAB technique, adequate distal runoff is identified as an important parameter to ensure patency. This in vitro study showed that distal stenotic lesions influence aortic bifurcation outflow patterns and TAWSS more extensively in the CERAB configuration. Distal stenotic lesions could therefore increase the risk of disease progression and loss of stent patency. In vivo studies are necessary to confirm these observations.

Fractional flow reserve in below the knee arteries with critical limb ischemia and validation against gold-standard morphologic, functional measures and long term clinical outcomes

INTRODUCTION

The aim of this study was to assess the applicability of fractional flow reserve measurement (FFR) in below-the-knee (BTK) arteries and to evaluate its correlation with non-invasive functional parameters before and after angioplasty.

METHODS

We enrolled 39 patients with severe BTK arterial lesions. Inclusion criteria were critical limb ischemia (Rutherford 4-6) and angiographically proven arterial stenosis of the distal lower limb (percent diameter stenosis ≥70%). Exclusion criteria were chronic total occlusion, diabetic foot syndrome and non-viable distal lower limb. The transstenotic distal/proximal pressure ratio was measured under resting (Pd/Pa) and hyperemic (FFR) conditions induced by 40mg intra-arterial Papaverin and was compared with quantitative angiography-, laser Doppler- and duplex ultrasound-derived measurements before and after percutaneous angioplasty (PTA).

RESULTS

Comparing measurements before and after PTA, we found significant improvements in the resting Pd/Pa values (0.79 [0.67-0.90] vs 0.90 [0.85-0.97]; p<0.001) and FFR values (0.60±0.19 vs 0.76±0.15; p<0.001), respectively. At baseline, Pd/Pa ratio and FFR were significantly albeit weakly correlated with % area stenosis (r:-0.31, p=0.05 and r:-0.31, p=0.05, respectively). After PTA, neither Pd/Pa nor FFR remained correlated with % area stenosis. Similarly, prior PTA, Pd/Pa ratio and FFR were significantly correlated with TcO2% and perfusion unit change (r:0.48, p<0.01 and r:0.34, p<0.05, respectively), but after intervention, these significant correlations vanished. Pd/Pa and FFR values did not show correlation with duplex ultrasound-derived measurements. At 1year, major adverse events (MAEs) and major adverse cardiovascular and cerebrovascular (MACCEs) were observed in 7 (17.9%) and in 9 (23.1%) patients, respectively.

CONCLUSION

CLI due to severe BTK arterial disease was associated with several impediments of baseline pressure measurements which were significantly improved after successful PTA and stenting. Significant relationships between pressure data and functional and imaging parameters existed prior intervention but vanished after. Further studies are required to determine the clinical value of pre- and post-PTA pressure measurements in BTK arterial disease.

How to define the hemodynamic significance of an equivocal iliofemoral artery stenosis: Review of literature and outcomes of an international questionnaire

Purpose

The goal of the study was to review current literature regarding the diagnosis of equivocal (50–70%) iliofemoral artery stenosis and compare these findings with the daily practice of an international panel of endovascular experts.

Methods

The Medline Database was searched for relevant publications, and an electronic survey was sent to experts in the field covering the following topics: definition of an equivocal iliofemoral artery stenosis, angiographic visualization and investigation protocols of an equivocal stenosis, intra-arterial pressure measurements, and definition of hemodynamic significance of an equivocal iliofemoral artery stenosis using a physiologic measure.

Results

Of the 37 invited endovascular experts, 21 (53.8%) agreed to participate in the survey. Analysis of existing literature shows that the level of evidence for diagnosing equivocal iliofemoral artery stenosis is mediocre and is not being implemented by experts in the field.

Conclusion

Studies have shown that a stenosis of between 50% and 70% iliofemoral lumen diameter reduction shows a wide range of trans-stenotic pressure gradients. Equivocal iliofemoral artery stenosis can best be identified using three-dimensional quantitative vascular analysis software. Although evidence for a clear hemodynamic cutoff point is weak, performing trans-lesion intra-arterial pressure measurements at rest and during maximal hyperemia is preferred. Diagnosing iliofemoral artery stenosis solely on lumen diameter reduction is inadequate.

Non-invasive pressure difference estimation from PC-MRI using the work-energy equation

Pressure difference is an accepted clinical biomarker for cardiovascular disease conditions such as aortic coarctation. Currently, measurements of pressure differences in the clinic rely on invasive techniques (catheterization), prompting development of non-invasive estimates based on blood flow. In this work, we propose a non-invasive estimation procedure deriving pressure difference from the work-energy equation for a Newtonian fluid. Spatial and temporal convergence is demonstrated on in silico Phase Contrast Magnetic Resonance Image (PC-MRI) phantoms with steady and transient flow fields. The method is also tested on an image dataset generated in silico from a 3D patient-specific Computational Fluid Dynamics (CFD) simulation and finally evaluated on a cohort of 9 subjects. The performance is compared to existing approaches based on steady and unsteady Bernoulli formulations as well as the pressure Poisson equation. The new technique shows good accuracy, robustness to noise, and robustness to the image segmentation process, illustrating the potential of this approach for non-invasive pressure difference estimation.

Validation of pressure gradient and peripheral fractional flow reserve measured by a pressure wire for diagnosis of iliofemoral artery disease with intermediate stenosis

Objective

To examine the pressure gradient and peripheral fractional flow reserve (pFFR) measured by a pressure wire as indicators of hemodynamic significance in iliofemoral angiographic intermediate stenosis.

Background

The utility of pressure measurements using a pressure wire with vasodilators is unclear in cases with intermediate iliofemoral stenosis.

Methods

The mean pressure gradient (MPG) and mean pressure ratio (MPR) were measured at baseline and after injection of isosorbide dinitrate in 23 lesions with angiographically intermediate iliofemoral stenosis. Patients with complex lesions, infrapopliteal artery lesions, chronic total occlusion, and surgical bypass grafts were excluded. Hyperemic MPR was considered equivalent to pFFR. Changes in parameters in response to vasodilators were assessed and correlations of peak systolic velocity ratio (PSVR) with hyperemic MPG and pFFR were examined using duplex ultrasound.

Results

After injection of isosorbide dinitrate, hyperemic MPG increased significantly (from 9.0±5.7 to 16.3±6.2 mmHg; P<0.05) and hyperemic MPR (pFFR) decreased significantly (from 0.92±0.06 to 0.81±0.07; P<0.05). PSVR was significantly correlated with hyperemic MPG (R=0.52; P<0.05) and pFFR (R=−0.50; P<0.05). The optimal cut-off value of pFFR as an indicator of significant hemodynamic stenosis (PSVR >2.5) was 0.85 (area under the curve 0.72; sensitivity 94%; specificity 50%, P<0.05).

Conclusion

pFFR measured using a pressure wire is reliable for prediction of hemodynamic significance in iliofemoral intermediate stenosis.

Diagnostic value of peripheral fractional flow reserve in isolated iliac artery stenosis: a comparison with the post-exercise ankle-brachial index

PURPOSE

To examine in claudicant patients with aortoiliac lesions the relationship between the post-exercise ankle-brachial index (ABI) and the peripheral fractional flow reserve (p-FFR), a physiological test that has heretofore been used to assess coronary and renal artery stenosis.

METHODS

Sixteen male patients (mean age 68.1±7.5 years) with isolated iliac artery lesions detected by ultrasound in 17 limbs were enrolled in this study. Resting ABI was measured and a treadmill test was administered to measure the post-exercise ABI. During angiography, the p-FFR was measured using a pressure guidewire after administration of papaverine to induce hyperemia. Changes in the ABI during exercise and p-FFR at hyperemia were calculated.

RESULTS

The mean resting ABI and post-exercise ABI were 0.87±0.12 and 0.65±0.24, respectively. There was no complication during the measurement of p-FFR. The mean p-FFR at hyperemia was 0.71±0.14. A significant linear correlation was observed between post-exercise ABI and p-FFR at hyperemia (r=0.857, p<0.001), which was stronger than the correlation between post-exercise ABI and peak-to-peak pressure gradient at hyperemia (r= -0.626, p=0.013).

CONCLUSIONS

Measuring p-FFR appears to be a feasible and safe procedure, and there is a significant linear correlation between post-exercise ABI and p-FFR in aortoiliac lesions. The p-FFR was more accurate than a peak-to-peak pressure gradient in assessing the physiological significance of a stenosis. Though larger studies are required, p-FFR might be used to physiologically assess stenosis in PAD patients with isolated aortoiliac lesions.

Catheter-induced errors in pressure measurements in vessels: an in-vitro and numerical study

Accurate measurement of blood pressure is important because it is a biomarker for cardiovascular disease. Diagnostic catheterization is routinely used for pressure acquisition in vessels despite being subject to significant measurement errors. To investigate these errors, this study compares pressure measurement using two different techniques in vitro and numerical simulations. Pressure was acquired in a pulsatile flow phantom using a 6F fluid-filled catheter and a 0.014” pressure wire, which is considered the current gold standard. Numerical simulations of the experimental set-up with and without a catheter were also performed. Despite the low catheter-to-vessel radius ratio, the catheter traces showed a 24% peak systolic pressure overestimation compared to the wire. The numerical models replicated this difference and indicated the cause for overestimation was the increased flow resistance due to the presence of the catheter. Further, the higher frequency pressure oscillations observed in the wire and numerical data were absent in the catheter, resulting in an overestimation of the pulse wave velocity with the latter modality. These results show that catheter geometry produces significant measurement bias in both the peak pressure and the waveform shape even with radius ratios considered acceptable in clinical practice. The wire allows for more accurate pressure quantification, in agreement with the numerical model without a catheter.

Noninvasive assessment of transstenotic pressure gradients in porcine renal artery stenoses by using vastly undersampled phase-contrast MR angiography

PURPOSE

To compare noninvasive transstenotic pressure gradient (TSPG) measurements derived from high-spatial- and temporal-resolution four-dimensional magnetic resonance (MR) flow measurements with invasive measurements obtained from endovascular pressure wires with digital subtraction angiographic guidance.

MATERIALS AND METHODS

After Animal Care and Use Committee approval, bilateral renal artery stenosis (RAS) was created surgically in 12 swine. Respiratory-gated phase-contrast vastly undersampled isotropic projection (VIPR) MR angiography of the renal arteries was performed with a 1.5-T clinical MR system (repetition time, 11.4 msec; echo time [first echo], 3.7 msec; 18,000 projection angles; imaging volume, 260 × 260 × 200 mm; acquired isotropic spatial resolution, 1.0 × 1.0 × 1.0 mm; velocity encoding, 150 cm/sec). Velocities measured with phase-contrast VIPR were used to calculate TSPGs by using Navier-Stokes equations. These were compared with endovascular pressure measurements (mean and peak) performed by using fluoroscopic guidance with regression analysis.

RESULTS

In 19 renal arteries with an average stenosis of 62% (range, 0%-87%), there was excellent correlation between the noninvasive TSPG measurement with phase-contrast VIPR and invasive TSPG measurement for mean TSPG (R² = 95.4%) and strong correlation between noninvasive TSPG and invasive TSPG for the peak TSPG measures (R² = 82.6%). The phase-contrast VIPR-derived TSPG measures were slightly lower than the endovascular measurements. In four arteries with severe stenoses and one occlusion (mean, 86%; range, 75%-100%), the residual lumen within the stenosis was too small to determine TSPG with phase-contrast VIPR.

CONCLUSION

The unenhanced MR angiographic technique with phase-contrast VIPR allows for accurate noninvasive assessment of hemodynamic significance in a porcine model of RAS with highly accurate TSPG measurements.

Limitations of angiography for the assessment of renal artery stenosis and treatment implications

Renovascular hypertension due to atherosclerotic renal artery stenosis is the most common cause of secondary hypertension. Percutaneous catheter-based renal artery revascularization has been increasingly utilized for the treatment of renal artery stenosis. Renal artery stenting has a high technical success rate, but the rate of improvement in hypertension is somewhat less than expected with this technique. Misinterpretation of angiographic images may play a role in these unfavorable clinical results. We present a case in which the diagnosis of severe renal artery stenosis was not apparent by angiography. Intravascular ultrasound and translesional pressure gradient measurements during arteriography can help to determine the precise severity of stenosis and may augment the clinical results of percutaneous renal artery stent placement.

Recent advances in hemodynamics: noncoronary applications of a pressure sensor angioplasty guidewire

The use of the pressure sensor coronary guidewire is expanding into the peripheral circulation as well as into the realm of valvular heart disease. Small mechanistic studies and case reports have described the use of pressure wire technology in the renal and femoral arteries as well as in mechanical aortic valves. The use of this technology to measure hemodynamically significant stenoses in noncoronary locations will be discussed and a review of basic and more advanced hemodynamics in relation to problems encountered in clinical practice will be provided.