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Introduction: Hypertension (HTN) is a strong risk factor of coronary artery disease. Hypothesis: Based on the damages induced by flow abnormalities in pipes, our research is built on the hypothesis that flow disturbances start the atherosclerotic process. Our strategy is to use today’s practice of fluid mechanics to unlock the mechanism of HTN on coronary plaques. Methods: All patients with uncontrolled HTN and unstable angina underwent coronary angiography and were selected if they had 1 or 2 moderate lesions. At first. contrast was injected until the index artery was completely opacified. As the injection stopped, the blood moved in and displaced the contrast. The movements and interactions of the blood flow in white color above a black background could be clearly analyzed. At the same time, Artificial Intelligence (Machine Learning (ML algorithms) program had 2 models built on Python. Model 1 was based on U-net and Densenet-121 for vessel segmentation. Model 2 was used for classification and movement of flow. Model 2 was trained based on the convolutional neural network. The main measurements were the types, durations and directions of flows. Results: 20 patients were enrolled. 80% of lesions happened at the mid right coronary artery, near the bifurcation of the left anterior descending artery and diagonal, and of the circumflex artery and obtuse marginal. At the locations of lesions, 100% patients had turbulence caused by collision of the antegrade against the retrograde flow (water hammer shock). If there was excessive diastolic HTN >100mmHg, the duration of retrograde flow was short ( 0.30 sec) and 80% turbulence happened PROXIMAL to the collision/bifurcation site due to higher gradient from distal to proximal. Conclusions: Uncontrolled diastolic HTN exaggerated the strength of antegrade flow and turbulence DISTAL to the collision/bifurcation site while uncontrolled systolic HTN intensified the retrograde flow and turbulence PROXIMAL to the collision/bifurcation site. Both inflicted damage on the intima and started the atheroslerotic process.

Introduction: Acute coronary syndrome (ACS) is caused by rupture of coronary plaques. What triggers these ruptures? Hypothesis: In the field of hydraulics, in a setting of a tank and draining pipe, if the valve at the distal end of the pipe is open, the fluid flows normally. If the valve closes abruptly, the flow next to the valve stops. However the fluid from the tank continues to flow forward and can collide with the distal stationary fluid. This is called water hammer shock. Could the same event happen in coronary arteries? The contraction of the left ventricle (LV) is similar to the abrupt closure of a valve, stopping the myocardial capillary flow. Could the systolic LV contraction trigger water hammer shock? Methods: Angiograms with culprit lesions of ACS (recorded at 15 images/second or 0.06 second per image) were reviewed. The first image was of the artery completely filled with contrast. The subsequent images showed the blood in white color blood moving in over a background of black contrast. The normal flow was laminar. When there was retrograde on top of turbulent flow, this was evidence of a collision between antegrade and retrograde flow (or water hammer shock). The measurements by visual angiographic evaluation and by Machine Learning (ML) included (1) the duration and (2) size of coronary segment with turbulence. The ML program had 2 models (build on Python). Model 1 was built based on U-net and Densenet-121 for vessel segmentation. Model 2 was used for classification of flow. The model 2 was trained based on the convolutional neural network. Results: Angiograms of 20 ACS patients showed laminar flow (90%) in diastole. The flow became turbulent during systole with retrograde flow. The area of collision or water hammer shock showed diffuse coarse mixing of black (contrast) and white (blood). The presence of turbulence matched the location of 85% of ruptured plaques. The duration of turbulence lasted 80% of systole. Special protocols were used successfully to train AI to recognize the lesions, retrograde and turbulent flow. Conclusions: With the new angiographic technique, detailed images of water hammer shock matched the location of ruptured plaques in ACS patients. These results may help to understand the genesis and offer precise prevention and treatment for ACS