Recent advances in coronary angioscopy

Hemodynamics of Saline Flushing in Endoscopic Imaging of Partially Occluded Coronary Arteries

PURPOSE

Intravascular endoscopy can aid in the diagnosis of coronary atherosclerosis by providing direct color images of coronary plaques. The procedure requires a blood-free optical path between the catheter and plaque, and achieving clearance safely remains an engineering challenge. In this study, we investigate the hemodynamics of saline flushing in partially occluded coronary arteries to advance the development of intravascular forward-imaging catheters that do not require balloon occlusion.

METHODS

In-vitro experiments and CFD simulations are used to quantify the influence of plaque size, catheter stand-off distance, saline injection flowrate, and injection orientation on the time required to achieve blood clearance.

RESULTS

Experiments and simulation of saline injection from a dual-lumen catheter demonstrated that flushing times increase both as injection flow rate (Reynolds number) decreases and as the catheter moves distally away from the plaque. CFD simulations demonstrated that successful flushing was achieved regardless of lumen axial orientation in a 95% occluded artery. Flushing time was also found to increase as plaque size decreases for a set injection flowrate, and a lower limit for injection flowrate was found to exist for each plaques size, below which clearance was not achieved. For the three occlusion sizes investigated (90, 95, 97% by area), successful occlusion was achieved in less than 1.2 s. Investigation of the pressure fields developed during injection, highlight that rapid clearance can be achieved while keeping the arterial overpressure to < 1 mmHg.

CONCLUSIONS

A dual lumen saline injection catheter was shown to produce clearance safely and effectively in models of partially occluded coronary arteries. Clearance was achieved across a range of engineering and clinical parameters without the use of a balloon occlusion, providing development guideposts for a fluid injection system in forward-imaging coronary endoscopes.

The CathCam: A Novel Angioscopic Solution for Endovascular Interventions

Peripheral arterial diseases are commonly managed with endovascular procedures, which often face limitations in device control and visualization under X-ray fluoroscopy guidance. In response, we developed the CathCam, an angioscope integrated into an expandable cable-driven parallel mechanism to enhance real-time visualization, precise device positioning and catheter support for successful plaque crossing. The primary objective of this study was to assess and compare the performance of the novel CathCam with respect to conventional catheters and the CathPilot (i.e., CathCam without the angioscope), for applications in crossing chronic total occlusions (CTO). We first assessed the system in 3D-printed phantom models, followed by an ex vivo evaluation with CTO samples from a patient's superficial femoral artery. We measured and compared success rates, crossing times, and fluoroscopy times in both experiments. The CathCam demonstrated a 100% success rate in phantom experiments and a 75% success rate in ex vivo experiments with CTO samples, compared to conventional catheters, with 35% and 25% success rates, respectively. The average crossing times for the CathCam and the conventional catheter were 31 s and 502 s for the phantom experiments and 210 s and 511 s for the actual CTO lesions. The Cathcam also showed to be a reliable endovascular imaging approach in an in vivo experiment. Compared to conventional catheters, the CathCam significantly increased the success rate and reduced crossing and fluoroscopy times in both phantom and ex vivo setups. CathCam can potentially improve clinical outcomes for minimally invasive endovascular interventions by offering high-resolution real-time imaging alongside accurate device control.

The role of intravascular ultrasound in percutaneous coronary intervention of complex coronary lesions

Intravascular ultrasound (IVUS) is a catheter-based coronary imaging technique. It utilises the emission & subsequent detection of reflected high frequency (30-60 MHz) sound waves to create high resolution, cross-sectional images of the coronary artery. IVUS has been the cornerstone of intracoronary imaging for more than two decades. When compared to the invasive coronary angiogram which studies only the silhouette of the contrast-filled artery lumen, IVUS also crucially images the vessel wall. Because of this capability, IVUS has greatly facilitated understanding of the coronary atherosclerosis process. Such insights from IVUS reveal how commonly and extensively plain angiography underestimates the true extent of coronary plaque, the characteristics of plaques prone to rupture and cause acute coronary syndromes (lipid rich, thin cap atheroma), and a realisation of the widespread occurrence of vessel remodelling in response to atherosclerosis. Similarly, IVUS has historically provided salutary mechanistic insights that have guided many of the incremental advances in the techniques of percutaneous coronary intervention (PCI). Examples include mechanisms of in-stent restenosis, and the importance of high-pressure post-dilatation of stents to ensure adequate stent apposition and thereby reduce the occurrence of stent thrombosis. IVUS also greatly facilitates the choice of correct diameter and length of stent to implant. Overall, a compelling body of evidence indicates that use of intravascular ultrasound in PCI helps to achieve optimal technical results and to mitigate the risk of adverse cardiac events. In this review, the role of intravascular ultrasound as an adjunct to PCI in complex coronary lesions is explored. The complex coronary situations discussed are the left main stem, ostial stenoses, bifurcation stenoses, thrombotic lesions, the chronically occluded coronary artery, and calcified coronary artery disease. By thorough review of the available evidence, we establish that the advantages of IVUS guidance are particularly evident in each of these complex CAD subsets. In particular, some consider the use of IVUS to be almost mandatory in left main PCI. A comparison with other intracoronary imaging techniques is also explored.

A new set of eyes: development of a novel microangioscope for neurointerventional surgery

BACKGROUND

Endovascular technological advances have revolutionized the field of neurovascular surgery and have become the mainstay of treatment for many cerebrovascular pathologies. Digital subtraction angiography (DSA) is the 'gold standard' for visualization of the vasculature and deployment of endovascular devices. Nonetheless, with recent technological advances in optics, angioscopy has emerged as a potentially important adjunct to DSA. Angioscopy can offer direct visualization of the intracranial vasculature, and direct observation and inspection of device deployment. However, previous iterations of this technology have not been sufficiently miniaturized or practical for modern neurointerventional practice.

OBJECTIVE

To describe the evolution, development, and design of a microangioscope that offers both high-quality direct visualization and the miniaturization necessary to navigate in the small intracranial vessels and provide examples of its potential applications in the diagnosis and treatment of cerebrovascular pathologies using an in vivo porcine model.

METHODS

In this proof-of-concept study we introduce a novel microangioscope, designed from coherent fiber bundle technology. The microangioscope is smaller than any previously described angioscope, at 1.7 F, while maintaining high-resolution images. A porcine model is used to demonstrate the resolution of the images in vivo.

RESULTS

Video recordings of the microangioscope show the versatility of the camera mounted on different microcatheters and its ability to navigate external carotid artery branches. The microangioscope is also shown to be able to resolve the subtle differences between red and white thrombi in a porcine model.

CONCLUSION

A new microangioscope, based on miniaturized fiber optic technology, offers a potentially revolutionary way to visualize the intracranial vascular space.

High-Resolution Scanning Fiber Angioscopy as an Adjuvant to Fluoroscopy During Endovascular Interventions

PURPOSE

To demonstrate the feasibility and potential utility of high-resolution angioscopy during common endovascular interventions.

METHODS

A 3.7-F scanning fiber angioscope was used in 6 Yorkshire pigs to image branch vessel selection, subintimal dissection, wire snaring, and stent placement. The angioscope was introduced in a coaxial fashion within a standard 6-F guide catheter. A clear field of view was provided using continuous heparinized saline flush through the outer guide catheter. The flush flow rate was manually adjusted to provide clear imaging depending on the diameter of the vessel and local blood flow conditions.

RESULTS

The scanning fiber angioscope was compatible with off-the-shelf catheters and devices commonly used in peripheral and aortic interventions. Video-rate, high-resolution images were obtained during all the interventions tested and provided information that was complementary to simultaneously acquired fluoroscopy. The scanning fiber angioscope was able to detect subintimal dissection and branch vessel stent coverage with higher resolution than fluoroscopy alone.

CONCLUSION

Endoluminal imaging with the scanning fiber angioscope is feasible with current endovascular devices and provides additional relevant information that cannot be assessed fluoroscopically. The scanning fiber angioscope represents a novel optical platform on which new endovascular techniques may be developed that will minimize radiation and contrast doses for patients.

Multimodal laser-based angioscopy for structural, chemical and biological imaging of atherosclerosis

The complex nature of atherosclerosis demands high-resolution approaches to identify subtle thrombogenic lesions and define the risk of plaque rupture. Here, we report the proof-of-concept use of a multimodal scanning fiber endoscope (SFE) consisting of a single optical fiber scanned by a piezoelectric drive that illuminates tissue with red, blue, and green laser beams, and digitally reconstructs images at 30 Hz with high resolution and large fields-of-view. By combining laser-induced reflectance and fluorescence emission of intrinsic fluorescent constituents in arterial tissues, the SFE allowed us to co-generate endoscopic videos with a label-free biochemical map to derive a morphological and spectral classifier capable of discriminating early, intermediate, advanced, and complicated atherosclerotic plaques. We demonstrate the capability of scanning fiber angioscopy for the molecular imaging of vulnerable atherosclerosis by targeting proteolytic activity with a fluorescent probe activated by matrix metalloproteinases. We also show that the SFE generates high-quality spectral images in vivo in an animal model with medium-sized arteries. Multimodal laser-based angioscopy could become a platform for the diagnosis, prognosis, and image-guided therapy of atherosclerosis.

Multimodal laser-based angioscopy for structural, chemical and biological imaging of atherosclerosis

The complex nature of atherosclerosis demands high-resolution approaches to identify subtle thrombogenic lesions and define the risk of plaque rupture. Here, we report the proof-of-concept use of a multimodal scanning fiber endoscope (SFE) consisting of a single optical fiber scanned by a piezoelectric drive that illuminates tissue with red, blue, and green laser beams, and digitally reconstructs images at 30 Hz with high resolution and large fields-of-view. By combining laser-induced reflectance and fluorescence emission of intrinsic fluorescent constituents in arterial tissues, the SFE allowed us to co-generate endoscopic videos with a label-free biochemical map to derive a morphological and spectral classifier capable of discriminating early, intermediate, advanced, and complicated atherosclerotic plaques. We demonstrate the capability of scanning fiber angioscopy for the molecular imaging of vulnerable atherosclerosis by targeting proteolytic activity with a fluorescent probe activated by matrix metalloproteinases. We also show that the SFE generates high-quality spectral images in vivo in an animal model with medium-sized arteries. Multimodal laser-based angioscopy could become a platform for the diagnosis, prognosis, and image-guided therapy of atherosclerosis.

Diagnostic and Interventional Optical Angioscopy in Ex Vivo Carotid Arteries

BACKGROUND: Angioscopy – or endovascular endoscopy – is a catheter-based technique employing a flexible fiberoptic angioscope to directly visualize arterial lumen. Poor resolution and excessive stiffness of pre-existent angioscopes limited their use clinically. Recent advances resulted in novel fused optical fiber bundle angioscopes with improved flexibility and imaging resolution. Use of these devices in endovascular neurosurgery is still largely unexplored.

OBJECTIVE: To evaluate image quality and feasibility of optical angioscopes for diagnostic and interventional neuro-angioscopy in carotid arteries of human cadavers.

METHODS: A 5-F optical angioscope was used in human cadaveric carotid arteries to inspect integrity of arterial walls, identify atherosclerotic plaques and associated lesions prone to thrombogenicity, place intravascular occlusion coils, and deploy endovascular stents with real-time visualization.

RESULTS: Angioscopy provided key information about endoluminal anatomy such as presence and characteristics of atherosclerotic plaques and thrombogenic lesions not detected by conventional diagnostic methods. Direct real-time visualization of vascular lumen during endovascular interventions provided information on spatial distribution of coils, coil loop herniation, and apposition of stent cells against carotid artery wall complementary to angiography.

CONCLUSIONS: Fused optical fiber bundle angioscopes provide good-quality endoluminal images in human carotid arteries. Their use can feasibly assist in navigation of extracranial carotid arteries to inspect integrity of the arterial wall and identify atherosclerotic plaques and associated lesions vulnerable to thrombogenicity, allow placement of intravascular occlusion coils, and assess apposition of stents to vessel wall. Further in Vivo validation needs to be conducted along with additional research to improve image quality, flexibility, and size of angioscopes.

Practical application of coronary imaging devices in cardiovascular intervention

The significant morbidity and mortality associated with coronary artery disease has spurred the development of intravascular imaging devices to optimize the detection and assessment of coronary lesions and percutaneous coronary interventions. Intravascular ultrasound (IVUS) uses reflected ultrasound waves to quantitatively and qualitatively assess lesions; integrated backscatter and virtual histology IVUS more precisely characterizes plaque composition; angioscopy directly visualize thrombus and plaque; optical coherence tomography using near-infrared (NIR) light with very high spatial resolution provides more accurate images; and the recently introduced NIR spectroscopy identifies chemical components in coronary artery plaques based on differential light absorption in the NIR spectrum. This article reviews usefulness of these devices and hybrids thereof.

Dye-Staining Angioscopy for Coronary Artery Disease

Novel imaging techniques using biomarkers have clarified the mechanisms of hitherto unanswered or misunderstood phenomena of coronary artery disease and enabled evaluation of myocardial blood and tissue fluid flows in vivo. Dye-staining coronary angioscopy using Evans blue (EB) as the biomarker can visualize fibrin and damaged endothelial cells, revealing that the so-called platelet thrombus is frequently a fibrin-rich thrombus; occlusive transparent fibrin thrombus, but not platelet thrombus, is not infrequently a cause of acute coronary syndrome; "fluffy" coronary luminal surface is caused by fibrin threads arising from damaged endothelial cells and is a residue of an occlusive thrombus after autolysis in patients with acute coronary syndrome without angiographically demonstrable coronary stenosis; and web or membrane-like fibrin thrombus is a cause of stent edge restenosis. Fluorescent angioscopy using visual or near-infrared light wavelengths is now used clinically for molecular imaging of the substances such as lipoproteins and cholesterol that constitute coronary plaques. Dye-staining cardioscopy using EB or fluorescein enables direct and real-time visualization of subendocardial microcirculation.

High-resolution angioscopic imaging during endovascular neurosurgery

BACKGROUND

Endoluminal optical imaging, or angioscopy, has not seen widespread application during neurointerventional procedures, largely as a result of the poor imaging resolution of existing angioscopes. Scanning fiber endoscopes (SFEs) are a novel endoscopic platform that allows high-resolution video imaging in an ultraminiature form factor that is compatible with currently used distal access endoluminal catheters.

OBJECTIVE

To test the feasibility and potential utility of high-resolution angioscopy with an SFE during common endovascular neurosurgical procedures.

METHODS

A 3.7-French SFE was used in a porcine model system to image endothelial disruption, ischemic stroke and mechanical thrombectomy, aneurysm coiling, and flow-diverting stent placement.

RESULTS

High-resolution, video-rate imaging was shown to be possible during all of the common procedures tested and provided information that was complementary to standard fluoroscopic imaging. SFE angioscopy was able to assess novel factors such as aneurysm base coverage fraction and side branch patency, which have previously not been possible to determine with conventional angiography.

CONCLUSION

Endovascular imaging with an SFE provides important information on factors that cannot be assessed fluoroscopically and is a novel platform on which future neurointerventional techniques may be based because it allows for periprocedural inspection of the integrity of the vascular system and the deployed devices. In addition, it may be of diagnostic use for inspecting the vascular wall and postprocedure device evaluation.

After the triumph of cardiovascular medicine over acute myocardial infarction at the end of the 20th Century. -Can we predict the onset of acute coronary syndrome? (Con)-

Predicting acute cardiovascular ischemic events is a crucial and urgent issue in the current cardiovascular field. An enormous effort to develop methodologies to achieve this purpose is being undertaken in cardiovascular institutes worldwide. However, currently, there is no established method of determining acute cardiovascular ischemic events in advance. This article reviews the latest progress on understanding how these events occur and how they can be detected. This goal represents a great dream that has realistic expectations.

Intravascular imaging tools in the cardiac catheterization laboratory: comprehensive assessment of anatomy and physiology

Intravascular imaging modalities have an imperative role in contemporary cardiovascular research. Currently, there are several invasive imaging modalities available in the cardiac catheterization laboratory and new technologies are under development. In the current review, we aimed to provide an update on the research applications of contemporary intravascular imaging tools in the cardiac catheterization laboratory. For the purpose of this review, we separately discuss imaging tools for assessment of epicardial disease (fractional flow reserve and hyperemic stenosis resistance), microvascular function (coronary flow reserve, hyperemic microvascular resistance, and index of microcirculatory resistance), endothelial function, atherosclerotic plaque and vascular remodeling (intravascular ultrasound, optical coherence tomography, angioscopy, and near-infrared spectroscopy), and finally the emerging modalities (palpography and wall shear stress profiling).