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Nguyen, Thach

In the study of coronary artery disease (CAD), the mechanism of plaque formation and development was still the subject of continuing debate. The limitation of the current coronary angiogram (CAG) is that it can only show the static image of a narrowing on the arterial channel without identifying the mechanism of the disease or predicting its progression or regression. Therefore, the current recording of CAGs is reprogrammed by the present team of investigators. The new technique focuses on the identification of blood flow patterns and analysis of their normal or abnormal dynamics by adapting the same methodologies used by hydraulics engineers when moving fluid or gas through domestic or industrial pipes or pumps. This new technique of recording and interpretation of coronary angiography helps to identify different flow patterns in arteries and the application of the fluid dynamics principles to the coronary system. This new technique ushers in a new era of crucial insights and applications regarding the diagnosis, medical, surgical, and interventional management of atherosclerotic diseases.

Heart Failure (HF) is on the end stage of the disease spectrum with many confounders and thus no specific symptoms and signs. There is a need for a test that can effectively confirm the diagnosis of volume overload in HF at its earliest to guide the initial approach and subsequent management. This study aimed to evaluate the effectiveness of a new test noted as the Size and Expansion of Femoral Vein (SEFV) in the diagnosis and management of patients with HF. This test was used specifically on asymptomatic patients or those who presented with severe comorbidities. The patients who arrived at the emergency room with a diagnosis of HF or suspected HF were enrolled. Ten patients without HF formed the control group. All patients received a standard physical examination (PE). The patients with the obvious diagnosis of HF by PE formed the HF control group. All patients with tentative diagnoses formed the HF study group. All patients underwent the ultrasound test to measure the size of the common femoral vein (CFV) and artery (CFA). The study enlisted 167 patients with HF or suspected HF. The results showed that the SEFV test was more accurate (98%) than the PE (54%). The SEFV test accurately differentiated between severely sick patients with intravascular overload and moderately sick patients with extravascular overflow. The test was accurate in patients with severe comorbidities (93%) or hypotension (100%). The SEFV test was more accurate in confirming the presence of fluid overload in patients with severe comorbidities or hypotension.

Coronary artery disease (CAD) is one of the most common and severe medical conditions worldwide. The current research focused on investigating the mechanisms and prevention of the detrimental effects of CAD. Recently, the principles and practices of fluid mechanics were used to explain the formation of CAD with the help of a new angiographic recording and reviewing technique. This new method focused on identifying the types of blood flows and their effects on the intima. To automate the process, an Artificial Intelligence program was utilized to support the investigators in reviewing coronary flow. This paper analyzes AI methods that assisted physician investigators in the measurement of the arterial phase and in the identification of the types of coronary flows.

Background: Many patients with stable angina (SA) having moderate 50% lesions could deteriorate or stay stable for a long time. No present techniques nor test could accurately predict the progression to acute coronary syndrome (ACS) or stabilization of these moderate lesions. Based on the fluid dynamic methodology research, could turbulent flow further damage the plaque and rupture its cap? In contrast, could laminar flow delay the progression of the plaque and keep patients stable for a long period of time? Methods: Patients with stable angina (SA) were admitted to the intermediate care unit and underwent coronary angiography. Patients were selected if they had a single 50% coronary lesion. The baseline angiographic factors included the flow characteristics: laminar or turbulent, anterograde or retrograde direction, and duration of the turbulent flow across the lesion. The patients were followed up for 2 years. The main clinical endpoints included (A) the development of acute coronary syndrome (ACS), (B) the need for percutaneous coronary interventions (PCI), or (C) persistent stable angina without new clinical or interventional events. Results: 20 patients with moderate lesions were enrolled and followed up for 2 years. The majority of the lesions (18/20= 90%) were located at the mid-segment of the right coronary artery (RCA) or left anterior descending artery. There were six patients with turbulent flow seen at the lesion. 83% of these patients (5/6) developed ACS regardless of the blood pressure or low-density-lipoprotein (LDL) level. If the patients had laminar flow, with well-controlled HTN (SBP< 130mmHg) and LDL cholesterol (<75mg%), these patients had NO clinical ACS and event (= 93% 13/14 patients). Conclusions: The preliminary results of a pilot study with only 20 patients showed that patients with turbulent flow at the location of a moderate lesion progressed to ACS and PCI. The patients with laminar flow across the lesion remained stable without the need for PCI. Larger randomized studies are needed to confirm the above findings.

In the continuing debate regarding the mechanism of atherosclerotic plaque formation in arteries, one question remains unanswered: While all arteries in a patient are exposed to the same systemic risk factors (hypertension, diabetes, aging, nicotine of cigarettes, etc.), why do plaques frequently present in the coronary arteries, and to a lesser extent in the arteries of the lower extremities, and still less in the carotid or renal arteries? Over the past five years, in order to find an answer to the above question, there has been a radical shift in our research strategy: The principles of fluid dynamics in industrial and domestic pipes/pipelines were employed to decipher changes in the cardiovascular system. The types of flow under investigation included laminar, entrance, turbulent, and helical flows in systole and diastole, as well as the interface between antegrade and retrograde flows resulting in water hammer shock and cavitation phenomena. We aim to highlight the similarities and differences among flow types in arteries and pipes and apply the same methodologies to study the formation, growth, and rupture of coronary plaques leading to inactive and active clinical syndromes and the beneficial mechanism of percutaneous coronary interventions (PCI). In this article, we list the questions and the answers based on the primary data of several completed studies and the preliminary results of ongoing projects from a fluid mechanics perspective. The angiographic coronary images of recirculation flow, vortex formation, collision, hammer water shock, and cavitation will be showcased in detail, and their videos in slow motion are uploaded in the addendum for further in-depth review.

Background. The differential diagnosis of chest pain in women is complex, ranging from atypical angina to chest pain in the absence of coronary artery disease (i.e., Syndrome X). The mechanism of these conditions remains unexplained. The purpose of this study was to examine coronary blood flow based on a new angiographic technique. Methods. Patients with chest pain were enrolled. In the new technique, as the contrast injection stopped, the blood in white color moved in and displaced the black contrast. Characteristics of blood flow could be observed and classified by type and time. The duration of the arterial phase was calculated and compared with the control. Results. Sixty patients were enrolled. Ten patients with normal coronary arteries and ventricular function; without chest pain served as controls. In the control group, the duration of the arterial phase in the RCA was 1.76 sec, while it was 3.76 sec for the syndrome X group (p<0.05). From the mMID segment to the distal segment, syndrome X patients had a much longer delay compared to control subjects (0.81 vs. 0.26 sec) (p<0.05). From the distal segment (bDIS) to the origin of the PDA, syndrome X patients had an average duration of 0.81 sec compared to 0.40 sec in controls (p<0.05). The largest difference was the period of time when the contrast left the PDA until flushed from the distal vasculature, which was 1.66 sec and 0.40 sec in syndrome X vs. control. Syndrome X patients with prolonged myocardial phase (1.89 sec) had dense and prolonged contrast retention at the myocardium. Conclusions. In patients with syndrome X, the prolonged arterial phase deprived the myocardium of highly oxygenated blood and triggered ischemia. This new imaging method allows for a better understanding of the mechanism of ischemia in Syndrome X patients.

Background: In the past 30 years, there has been a significant rise in coronary artery disease (CAD) and atherosclerosis, primarily attributed to dietary changes toward cholesterol-rich fast foods. Traditional research methodologies focusing on molecular biology have been insufficient in fully understanding the initiation mechanisms of these conditions. This paper reviews the literature and defines the knowledge gap for the need for a new dynamic coronary angiographic technique. Methods: Our approach involved a comprehensive review of fluid mechanics literature to identify gaps in current CAD research. This included analyzing major works from standard physiology textbooks, fluid mechanics reviews, and bioengineering journals. The study also introduced a new technique, "Dynamic Coronary Angiography," aimed at identifying and analyzing blood flow characteristics in coronary arteries using the principles and practices of fluid dynamics. Results: The literature review highlighted the pulsatile nature of coronary blood flow and the importance of wall shear stress (WSS) in the development of atherosclerosis. However, existing research showed limitations such as reduced applicability of animal model data to human pathophysiology and simplistic experimental designs. The new angiographic technique revealed various flow patterns in cardiac cycle phases, including laminar, turbulent, and retrograde flows, and their possible impacts on the arterial wall. Conclusions: Our findings suggest that turbulent flow may be critical in initiating atherosclerosis by damaging endothelial cells. This new perspective on the role of blood flow dynamics in CAD provides a promising avenue for understanding plaque formation and growth, potentially leading to significant advancements in cardiovascular medicine.

Background. Patients afflicted with aortic stenosis (AS) may present chest pain (CP), shortness of breath (SOB), syncope, and no lesion in the coronary arteries. So far, no clear mechanism could convincingly elucidate the pathophysiology of symptoms in such patients. We conducted a study to clarify the mechanism of CP, SOB, and syncope in AS patients without coronary artery stenosis based on coronary flow patterns or abnormalities. Methods. One hundred and thirty two (132) patients visiting the emergency room with CP, SOB, or syncope were screened for AS. Forty four (44) patients with a clinical diagnosis of AS underwent right and left heart catheterization and a novel dynamic coronary angiographic technique. Twenty AS patients without coronary artery disease (CAD) were enrolled. All patients were divided into either: group A for severe AS or group B for mild to moderate AS. The control group consisted of Five patients with normal left ventricular function without CAD or AS (group C). The flow data included the coronary transit time duration, the presence of retrograde flow at the proximal coronary segment, and the persistence of contrast spill-out from the coronary ostium. Results There was prolonged arterial phase and retrograde flow in the proximal coronary segment, including persistent spilling of contrast into the coronary sinus (p<0.01 when compared with groups B and C) in 20 patients with severe AS (group A). In 24 patients in the mild to moderate AS group (group C), there was only a moderately prolonged arterial phase without retrograde flow nor spilling of contrast from the ostium (p=0.99 when compared with control group C).  Conclusions In patients with AS, significantly prolonged arterial coronary transit time, reversed coronary flow, and retrograde ejection of contrast into the coronary sinus correlated statistically with the severity of AS. In patients with mild to moderate AS, with only moderate prolongation of the arterial phase without reversed coronary flow nor retrograde ejection of contrast into the coronary sinus.

Background: In the study of coronary artery disease, the mechanisms underlying atherosclerosis initiation and progression or regression remain incompletely understood. Our research conceptualized the cardiovascular system as an integrated network of pumps and pipes, advocating for a paradigm shift from static imaging of coronary stenosis to dynamic assessments of coronary flow. Further review of fluid mechanics highlighted the water hammer phenomenon as a compelling analog for processes in coronary arteries. Methods: In this review, the analytical methodology employed a comprehensive, multifaceted approach that incorporated a review of fluid mechanics principles, in vitro acoustic experimentation, frame-by-frame visual angiographic assessments of in vivo coronary flow, and an artificial intelligence (AI) protocol designed to analyze the water hammer phenomenon within an acoustic framework. In the analysis of coronary flow, the angiograms were selected from patients with unstable angina if they had previously undergone one or more coronary angiograms, allowing for a longitudinal comparison of dynamic flow and phenomena. Results: The acoustic investigations pinpointed pockets of contrast concentrations, which might correspond to compression and rarefaction zones. Compression antinodes were correlated to severe stenosis, due to rapid shifts from low-pressure diastolic flow to high-pressure systolic surges, resulting in intimal injury. Rarefaction antinodes were correlated with milder lesions, due to de-escalating transitions from high systolic pressure to lower diastolic pressure. The areas of nodes remained without lesions. Based on the locations of antinodes and nodes, a coronary acoustic action map was constructed, enabling the identification of existing lesions, forecasting the progression of current lesions, and predicting the development of future lesions. Conclusions: The results suggested that intimal injury was likely induced by acoustic retrograde pressure waves from the water hammer phenomenon and developed new lesions at specifically exact locations.

In the study of coronary artery disease (CAD), the mechanism of plaque formation and development is still an important subject for investigation. A limitation of current coronary angiography (CAG) is that it can only show static images of the narrowing of arterial channels without identifying the mechanism of the disease or predicting its progression or regression. To address this limitation, the CAG technique has been modified. The new approach emphasizes identifying and analyzing blood flow patterns, employing methodologies akin to those used by hydraulic engineers for fluid or gas movement through domestic or industrial pipes and pumps. With the new technique, various flow patterns and arterial phenomena—such as laminar, turbulent, antegrade, retrograde, and recirculating flow and potentially water hammer shock and vortex formation—are identified, recorded, and classified. These phenomena are then correlated with the presence of lesions at different locations within the coronary vasculature. The formation and growth of these lesions are explained from the perspective of fluid mechanics. As the pathophysiology of CAD and other cardiovascular conditions becomes clearer, new medical, surgical, and interventional treatments could be developed to reverse abnormal coronary flow dynamics and restore laminar flow, leading to improved clinical outcomes.