Invasive Pressure Measurements in Endovascular Procedures

When thinking about optimizing endovascular procedures in intracranial vessels, using techniques that have been developed in the cardiology field might be interesting to consider. In 1993, Pijls et al. proposed fractional flow reserve (FFR) as a lesion-specific index to determine the functional severity of a coronary artery stenosis. During coronary angiography it measures translesional pressure (Pd/Pa) to assess the severity of a blockage or narrowing in one of the coronary arteries [1]. FFR’s usefulness has been validated in several landmark randomized controlled trials, and a threshold FFR ≤ 0.80 has been established for intervention. FFR represents a risk of ischemia and major cardiovascular events, being performed under a pharmacologically induced hyperemic condition (i.e. when the coronary arteries are maximally dilated). Therefore, the resting full-cycle ratio (RFR), which is the ratio between the lowest post-stenotic and pre-stenotic pressure during the entire cardiac cycle, was subsequently used as a non-hyperemic index to overcome the limitations of FFR. Trans-lesion pressure can be measured with a microcatheter, connecting the microcatheter to a standard arterial pressure transducer, and a pressure wire (PW), which has its own computerized system. The pwFFR has been considered the gold standard for cardiovascular measurements due to its high accuracy, especially in cases of high-grade stenosis, where microcatheters could potentially constrict vessel lumens [2].

In recent years, PW measurements have proven valuable in guiding endovascular therapy for patients with middle cerebral artery stenosis and subclavian steal syndrome [3], and to assess intra-aneurysmal pressure changes after treatment with a flow diverter [4].

What about PW-derived indexes in venous sinus stenosis? A trans-lesion pressure gradient (Pd-Pa) > 8 mm Hg, usually located in the transverse-sigmoid junction, is one of the criteria for cerebral venous stenting in idiopathic intracranial hypertension (IIH) patients. Horev et al. [5] compared microcatheter gradients and PW gradients in 26 patients with venous sinus stenosis. Their findings demonstrated that the wire measurements aligned with the catheter measurements in identifying all cases indicated for a stent.

What about PW-derived indexes in intracranial arterial stenosis? Li et al. [6] recently investigated the RFR in intracranial atherosclerotic stenosis (ICAS), studying the relation between pwRFR and the relative cerebral blood flow ratio (rCBF) derived from arterial spin labeling (ASL) before and after intracranial stenting. Among twenty-five patients with ICAS (17 M1 and 8 intracranial ICA), 14 presented an increased rCBF after treatment (from rCBF < 0.9 to rCBF ≥ 0.9). Cut-off values of RFR=0.81 and a trans-lesion pressure gradient=8mm Hg were suggested to be associated with hemodynamic insufficiency. What about FFR in carotid artery stenosis (CAS)? Grading of carotid stenosis is routinely performed with non-invasive techniques, such as carotid ultrasound (CUS) and computerized tomography angiography (CTA), which have limitations in grading definition, generally related to the plaque characteristics. In a recently published study [7], we tested the correlation between RFR and CUS-CTA-DSA based on the degree of stenosis to define the suitability of RFR as a carotid stenosis index. In 15 patients, we performed CUS and PW measurements before and after stenting at four different sites (trans-lesion, distal cervical, petrous, and supraclinoid internal carotid artery [ICA] segments). We showed that pre-stent trans-lesion RFR was significantly higher than at other sites and decreased after intervention. These findings suggest that in cases involving intracranial arterial or venous stenosis, as well as carotid stenosis, the utilization of invasive pressure measurements has the potential to offer valuable hemodynamic data for guiding clinical decisions. This approach may effectively address the constraints associated with conventional imaging methods. Moreover, despite being separate fields, there exists an opportunity to merge the tools and expertise from cardiology into neurointervention for potential advancements in patient care.

---

References:

1. Pijls NH, van Son JA, Kirkeeide RL, et al. Experimental basis of determining maximum
   coronary, myocardial, and collateral blood flow by pressure measurements for
   assessing functional stenosis severity before and after percutaneous transluminal
   coronary angioplasty. Circulation 1993;87:1354–67.
   2. Pouillot C, Fournier S, Glasenapp J, Rambaud G, Bougrini K, Vi Fane R, Geyer C, Adjedj J. Pressure wire versus microcatheter for FFR measurement: a head-to-head comparison. EuroIntervention. 2018 Feb 2;13(15):e1850-e1856. doi: 10.4244/EIJ-D-17-00238. PMID: 28804057.
   3. Miao Z, Liebeskind DS, Lo W, et al. Fractional flow assessment for the evaluation of intracranial atherosclerosis: a feasibility study. Interv Neurol 2016; 5: 65–75. Crossref. PubMed. ISI.
   4. Tateshima S, Jones JG, Mayor Basto F, et al. Aneurysm pressure measurement before and after placement of a pipeline stent: feasibility study using a 0.014 inch pressure wire for coronary intervention. J Neurointerv Surg 2016; 8: 603–607. Crossref. PubMed.
   5. Horev A, Lorber D, Vardi-Dvash N, Zlotnik Y, Biederko R, Ifergane G, Shelef I, Zvenigorodsky V, Horev A. A Comparison Between Pressure Wire and Microcatheter Measurements for Evaluating the Cerebral Venous Pressure Gradient. Front Neurol. 2021 Oct 15;12:711870. doi: 10.3389/fneur.2021.711870. PMID: 34721256; PMCID: PMC8554017.
   6. Li L, Yang B, Dmytriw AA, Li Y, Gong H, Bai X, Zhang C, Chen J, Dong J, Wang Y, Gao P, Wang T, Luo J, Xu X, Feng Y, Zhang X, Yang R, Ma Y, Jiao L. Correlations between intravascular pressure gradients and cerebral blood flow in patients with symptomatic, medically refractory, anterior circulation artery stenosis: an exploratory study. J Neurointerv Surg. 2023 Jul 4:jnis-2023-020144. doi: 10.1136/jnis-2023-020144. Epub ahead of print. PMID: 37402573.
   7. Diana F, Peschillo S, Requena M, Romano DG, Frauenfelder G, de Dios Lascuevas M, Hernandez D, Ribó M, Tomasello A, Romoli M. Correlation between intravascular pressure gradients and ultrasound velocities in carotid artery stenosis: An exploratory study. Interv Neuroradiol. 2023 Dec 28:15910199231224007. doi: 10.1177/15910199231224007. Epub ahead of print. PMID: 38155483.