Intravascular ultrasound in diagnosis of acute pulmonary embolism

Role of Intravascular Ultrasound in Pulmonary Embolism Patients Undergoing Mechanical Thrombectomy: A Systematic Review

BACKGROUND

Traditionally, mechanical thrombectomy performed for pulmonary embolism (PE) necessitates the utilization of iodinated contrast. Intravascular ultrasound (IVUS) has been used as a diagnostic and therapeutic modality in the management of acute high and intermediate-risk PE. Recently, with the shortage of contrast supplies and the considerable incidence of contrast-induced acute kidney injury (CI-AKI), other safer and more feasible IVUS methods have become desirable. The purpose of this systematic review was to evaluate the importance of IVUS in patients with PE undergoing thrombectomy.

METHODS

Medline/PubMed, Embase, Scopus, and Google Scholar were searched for review studies, case reports, and case series. Clinical characteristics, outcomes and the usage of IVUS-guided mechanical thrombectomy during the treatment of acute high and intermediate-risk PE were examined in a descriptive analysis.

RESULTS

In this systematic review, we included one prospective study, two case series, and two case reports from July 2019 to May 2023. A total of 39 patients were evaluated; most were female (53.8%). The main presenting symptoms were dyspnea and chest pain (79.5%); three patients (7.9%) presented with syncope, one with shock and one with cardiac arrest. Biomarkers (troponin and BNP) were elevated in 94.6% of patients. Most patients (87.2%) had intermediate-risk PE, and 12.8% had high-risk PE. All patients presented with right-heart strain (RV/LV ratio ≥ 0.9, n = 39). Most patients (56.4%) had bilateral PE. Mechanical thrombectomy was performed using IVUS without contrast utilization in 39.4% of the patients. After the initial learning curve, contrast usage decreased gradually over time. There was a significant decrease in the composite mean arterial pressure immediately following IVUS-guided thrombectomy from 35.1 ± 7.2 to 25.2 ± 8.3 mmHg (p < 0.001). Post-procedure, there was no reported (0%) CI-AKI, no all-cause mortality, no major bleeding, or other adverse events. There was a significant improvement in symptoms and RV function at the mean follow-up.

CONCLUSIONS

New evidence suggests that IVUS-guided mechanical thrombectomy is safe, with visualization of the thrombus for optimal intervention, and reduces contrast exposure.

Intravascular ultrasound guidance in percutaneous mechanical thrombectomy: A single-center experience from the FLASH registry

BACKGROUND

Traditionally, iodinated contrast is utilized during catheter-based mechanical thrombectomy for pulmonary embolism (PE). Recently, there have been disruptive contrast shortages. Furthermore, contrast can cause contrast-induced acute kidney injury especially in patients with pre-existing chronic kidney disease, necessitating an alternative imaging method. We present utilization and feasibility of an intravascular ultrasound (IVUS)-guided strategy for mechanical thrombectomy in PE from the FLASH registry.

METHODS

In this FLASH patient subset, IVUS was used to image the pulmonary arteries (PAs) before and after mechanical thrombectomy with the FlowTriever System at one study site comprising three hospitals. The Philips Visions PV 0.035" IVUS catheter was used for all the IVUS-guided cases in a standardized manner.

RESULTS

Between July 2019 and December 2021, 26 FLASH patients enrolled at this site underwent IVUS-guided thrombectomy. Most patients (96.2 %) had intermediate-risk PE and 3.8 % had high-risk PE. The mean baseline composite RV/LV ratio was 1.36 ± 0.27 and the mean simplified Pulmonary Embolism Severity Index (sPESI) score was 1.9 ± 1.2. A decreasing trend in contrast agent volume usage was observed over time and several later procedures were performed with IVUS guidance alone. Mean PA pressure significantly decreased immediately following thrombectomy from 34.8 ± 8.3 to 25.5 ± 7.3 mmHg (p < 0.0001). Systolic PA pressure also significantly decreased immediately from 55.4 ± 13.9 to 39.5 ± 12.5 mmHg (p < 0.0001). Significant improvements were seen in echocardiographic assessments of RV function at a mean 87-day follow-up compared with baseline.

CONCLUSIONS

In conclusion, the use of IVUS guidance with minimal or no angiographic contrast during mechanical thrombectomy for acute PE is technically feasible.

Intravascular ultrasound-guided catheter-based aspiration thrombectomy in patients with acute submassive pulmonary embolism: A case series

Contrast pulmonary angiography by hand injection or power injection is widely used during catheter-based therapies for acute submassive and massive pulmonary embolism (PE). Particularly, in patients with pre-existing chronic kidney disease, this approach may present a prognostic challenge owing to a double-contrast load, initially during computed tomographic pulmonary angiography (CTPA), and during percutaneous treatment. Intravascular ultrasound (IVUS) has been used as an adjunctive imaging modality in the percutaneous treatment of chronic thromboembolic pulmonary hypertension, and in coronary and peripheral vascular interventions. We report a series of cases illustrating the use of IVUS in the management of acute PE. All five patients presented with an acute submassive PE with evidence of right ventricular (RV) strain (RV/LV ratio ≥ 0.90). Body mass index and B-type natriuretic peptide ranged from 18 to 47 kgm/m² and 56-932 pg/mL (ref. ≤ 78), respectively. Three of the five patients had renal impairment prior to the procedure (acute kidney injury, AKI, and chronic kidney injury, CKD). Post-catheter-directed pulmonary embolectomy there was a modest reduction in mean pulmonary artery pressure in all five patients (range: -4 mmHg to -9 mmHg). The first case serves as a proof of concept of IVUS use in acute PE. This case series demonstrates that an IVUS-only approach in the catheter-directed management of acute submassive PE is feasible and may be of particular importance in patients with pre-existing renal dysfunction.

[Progression and regression of atherosclerotic plaques. New results based on intracoronary ultrasound]

Intravascular ultrasound has been established as the gold standard for analyzing alterations in coronary artery atherosclerosis during monitoring investigations. Cross-sectional imaging can be used to visualize the area of the lumen and the vessel size and the plaque size as the difference between them. New technology allows the 3-D reconstruction of the volume for prespecified vessel segments using specific algorithms. Investigations on the natural course demonstrated predominantly progression. Even regression of coronary atherosclerosis can be visualized and quantified. Regression can only be expected when the level of low-density lipoprotein (LDL) cholesterol is below the critical level of 75 mg/dl. Prospective randomized studies with highly effective statins showed that regression occurred in up to two thirds of patients when LDL cholesterol was below a cut-off of 78 mg/dl and was, therefore, very close to the threshold, which was calculated based on investigations of the natural course. Although the absolute values for plaque volume are in the range of 1 % over 1-2 years, it must be taken into consideration that coronary artery diseases are chronic diseases and a 1 % change per year will correspond to an enormous effect on plaque growth of coronary vessels. The great success of statins in reducing cardiovascular events is due to the possibility for reduction of progression and induction of regression. New developments in medication will be measured against the effectiveness of statins.

Protein kinase C regulation of GABAA receptors

Pharmacological studies with drugs that activate or inhibit several protein kinase C (PKC) isozymes have identified the PKC family of serine-threonine kinases as important in the regulation of gamma-aminobutyric acid type A (GABA(A)) receptor function. PKC modulates GABA(A) receptor surface density, chloride conductance and receptor sensitivity to positive allosteric modulators such as neurosteroids, ethanol, benzodiazepines and barbiturates. Recent studies using PKC isozyme-selective reagents and gene-targeted mice have begun to identify critical roles for three isozymes, PKCbetaII, PKCvarepsilon and PKCgamma, in various aspects of GABA(A) receptor regulation. Progress in this field touches upon therapeutic areas that are of great clinical importance such as anxiety and addiction. Increased understanding of how PKC regulates GABA(A) receptors and which PKC isozymes are involved holds promise for development of new treatments for diverse neuropsychiatric disorders.

Intravascular ultrasound of the elastic pulmonary arteries: a new approach for the evaluation of primary pulmonary hypertension

OBJECTIVE

To assess the structural and functional characteristics of pulmonary arteries by intravascular ultrasound (IVUS) in the setting of primary pulmonary hypertension, and to correlate the ultrasound findings with haemodynamic variables and mortality at follow up.

DESIGN

Prospective observational study.

SETTING

University hospital (tertiary referral centre).

PATIENTS

20 consecutive patients with primary pulmonary hypertension (16 female; mean (SD) age, 39 (14) years).

METHODS

Cardiac catheterisation and simultaneous IVUS of pulmonary artery branches at baseline and after infusion of epoprostenol.

RESULTS

33 pulmonary arteries with a mean diameter of 3.91 (0.80) mm were imaged, and wall thickening was observed in all cases, 64% being eccentric. Mean wall thickness was 0.37 (0.13) mm, percentage wall area 31.0 (9.3)%, pulsatility 14.6 (4.8)%, and pulmonary/elastic strain index 449 (174) mm Hg. No correlation was observed between IVUS findings and haemodynamic variables. Epoprostenol infusion increased pulsatility by 53% and decreased the pulmonary/elastic strain index by 41% (p = 0.0001), irrespective of haemodynamic changes. At 18 (12) months follow up, nine patients had died. A reduced pulsatility and an increased pulmonary/elastic strain index were associated with increased mortality at follow up (12.0 (4.4)% v 16.4 (4.4)%, p = 0.03; 369 (67) v 546 (216) mm Hg, p = 0.02).

CONCLUSIONS

IVUS demonstrated pulmonary artery wall abnormalities in all patients with primary pulmonary hypertension, mostly eccentric. The severity of the changes did not correlate with haemodynamic variables, and epoprostenol improved pulmonary vessel stiffness. There was an association between impaired pulmonary artery functional state as determined by IVUS and mortality at follow up.

Comparison of normal and diseased pulmonary artery morphology by intravascular ultrasound and histological examination

The study was performed to determine the morphological characteristics of normal and diseased pulmonary arteries by ultrasound (intravascular ultrasound, IVUS) and histology. Forty-nine cadaver segments of pulmonary arteries from 16 postmortem patients were imaged in vitro by IVUS and compared to matched histological sections. The pulmonary vasculature of 11 patients with pulmonary hypertension was investigated in vivo by IVUS. In the in vitro study, 34 of a total of 143 histological sections of the segmental pulmonary arteries showed fibrotic wall components; the remaining 109 sections had regular components. Imaged by IVUS, the wall of the regular and fibrotic arteries revealed a single layer histologically, representing the intima, media, adventitia and connective tissue. Adjacent lung tissue could be detected by IVUS and was confirmed by the histological section. In three patients with a history of chronic embolic pulmonary hypertension, IVUS revealed thrombi or a double vessel wall layer. Histologically, the material extracted after pulmonary thromboendarterectomy in two patients showed wall-adherent thrombus features of early organization. In all other patients only a single wall layer was seen. The vessel walls (intima, media, adventitia and connective tissue) of regular and slightly fibrosed pulmonary arteries show only a single layer. Wall-adherent organized thrombi in chronic embolic pulmonary hypertension can be detected by IVUS as a second inner vessel layer. Thus IVUS may represent an additional tool for detecting chronic embolic pulmonary hypertension when the results of pulmonary angiography or computed tomography are not definite.

Intravascular ultrasound in patients with acute pulmonary embolism after treatment with intravenous urokinase and high-dose heparin

OBJECTIVE

To compare the diagnostic value of intravascular ultrasound (IVUS) with angiography in patients with pulmonary embolism.

DESIGN

Open, prospective clinical study.

SETTING

Two university hospitals.

PATIENTS

Angiography and IVUS were used in 11 patients (5 men) (mean (SD) age 50 (18) years) with acute pulmonary embolism.

INTERVENTIONS

At a mean (SD) of 6 (4) hours after thrombolytic therapy with urokinase and full-dose heparin, all patients underwent pulmonary artery angiography. Then 3.5 F mechanical, 20 or 30 MHz IVUS catheters were advanced into the pulmonary circulation.

MAIN OUTCOME MEASURES

The pulmonary circulation was studied by both methods to detect the presence of thrombus, and a modified Miller score (assessing perfusion defects only and not velocity of flow) was used to quantify the angiographic images.

RESULTS

The modified Miller score was mean (SD) 7.4 (2.3) points. 168 pulmonary artery segments (diameter range 2-14 mm) were studied by angiography and IVUS. On angiography, seven segments showed complete obstruction and 49 partial obstruction; 112 were normal. Two distinct types of thrombus formation were found by IVUS. Type A thrombus only partly adhered to the wall but otherwise was mobile and type B predominantly adhered to the wall. IVUS confirmed all seven angiographically complete obstructions but missed three (6%) of the 49 partial occlusions. Forty (87%) of the remaining 46 segments had type A thrombus and six (13%) type B. IVUS indicated a thrombus in 38 (34%) of the 112 angiographically normal segments; 20 (53%) showed a type A pattern and 18 (47%) a type B pattern (P < 0.001).

CONCLUSION

IVUS was more sensitive than angiography in detecting thrombus but the clinical impact of this finding is not clear as yet.

Intravascular and intracardiac ultrasound: a tool of the future

Intravascular ultrasonography has the capability to visualize the vessel wall and perivascular structures, to identify the spatial distribution and composition of atherosclerotic plaque, and to measure accurately vessel and wall dimensions. This article discusses relevant principles of instrumentation, issues pertaining to the validation and interpretation of intravascular ultrasound images, and the current and potential applications of intravascular (and intracardiac) imaging. Emphasis is placed on uses that are likely to be of interest to the critical care physician.

Intravascular ultrasound to assess anastomotic patency after lung transplantation

Pulmonary arterial anastomotic stenosis is an unusual complication after single-lung transplantation. Intravascular ultrasound, performed at the bedside with an introducer sheath and guidewire, is a new technique that provides high-resolution tomographic images of the anastomotic site. This modality was used early in the postoperative course of a 58-year-old man to exclude significant pulmonary arterial anastomotic narrowing after right single-lung transplantation for primary pulmonary hypertension.