Mechanisms of the Stable and Vulnerable Arterial Plaques and Their Associations with the Arterial Waveforms

Carotid plaque composition is a key factor of plaque stability and it carries a significant prognostic information. The carotid unstable plaques are characterized by thin fibrous cap ≤65μm with large lipid core (LC) while stable plaques have thicker fibrous cap and less LC. Identifying the percentage of plaque compositions is the clinical significant to predict the risk of cardiovascular events. This thesis aims to develop a non-invasive approach to distinguish stable and unstable plaques by defining the relationship between plaque composition and arterial waveform. An in vitro arterial system, composed with Harvard pulsatile flow pump and artificial circulation system, was used to investigate the effect of the plaque compositions on the pulsatile arterial waveforms. Artificial plaques, characterised as human carotid arterial plaques, were fabricated and implemented into the artificial blood vessels, representing the diseased artery. The pulsatile pressure, velocity and arterial wall movement were measured simultaneously at the site proximal to the plaque. Non-invasive wave intensity analysis (Non-WIA) was used to separate the waves into forward and backward components. The correlation between the plaque compositions and the forward and backward waveforms were quantitatively analysed. Five types of arterial plaques, composed of the LC, FC, Collagen (Col) and Calcium (Ca) with the percentage of compositions precisely same as the human carotid arterial plaques, were fabricated. The five typical artificial arterial plaques, classified by American Physiology Society, were implemented into the artificial carotid artery to represent the early stage of the diseased arterial system with 30% of blockage. Finally, two stable plaques (FC, FA), one unstable (PR) and one vulnerable plaque (TCFA) were tested with 75% blockage to investigate the effect of severe stenosis on arterial waveform and whether it is possible to characterise the vulnerable plaque or not at this stage. The experimental results for early stage of stenosis and from the advanced stage of diseased artery observed a significant backward wave intensity associated with stable plaques, whereas no considerable backward wave intensity was detected in unstable plaques. The strong correlation between the compositions of the plaques with the backward waveforms observed in this study demonstrated that the components of the arterial plaques could be distinguished by the arterial waveforms. Moreover, the difference between vulnerable and stable plaques can be detected by the backward wave intensity. This could open a door to identify the plaque ii vulnerability. These findings might lead to a potential novel non-invasive clinical tool to determine the compositions of the plaque and distinguish the stable and vulnerable arterial plaques at early and later stages.