CORONARY CT ANGIOGRAM: CURRENT APPLICATIONS & FUTURE PROSPECTS

The current decade has seen MDCT as a valuable imaging tool for effective evaluation and monitoring of Coronary Artery Disease (CAD).MDCT has shown its ability to examine various structural and functional aspects of a heart with a level of details that were not previously possible. Future prospects of MDCT in identifying & evaluating useful cardio-vascular risk markers are in offing. 

 Coronary CTA is a non-invasive, widely available & safe procedure. A Single data set provides multiple information (Coronary Calcium score, Evaluation of Myocardium, Vascular morphology, Plaque characterization, Triple rule out in the emergency situation, Myocardial perfusion & CT-FFR estimation ) for effective evaluation & treatment planning in CAD. It also helps in identifying/evaluating Epicardial Adipose Tissue (EAT) and Endothelial Shear Stress (ESS) as useful cardio-vascular risk markers.

Coronary CTA provides unmatched image morphology with excellent luminal assessment & plaque characterization including Coronary calcium score non-invasively and is considered as the gold standard.

Coronary CTA is gaining ground as a fast noninvasive chest pain screening tool in hospital emergency rooms (NPV of 99-100%) for quick screening of CAD, Aortic Dissection & Pulmonary Embolism (triple rule out).CT screening of chest pain patients is faster, more accurate and less costly than employing SPECT- MPI protocol in the evaluation of acute low-risk chest pain patients in the emergency department.

Whether stenotic vessel merits treatment or not, has been left to nuclear perfusion imaging/MR Perfusion to asses myocardial viability or invasive catheter angiogram based- FFR measurement. Recent studies on CT- Myocardial Perfusion and   Non-invasive CT-FFR (CT-fractional flow reserve with Heart-Flow's CT-FLOW software) have established their grounds in assessing myocardial perfusion and CT-FFR non-invasively for effective treatment planning in CAD. Coronary CTA angiography and CT-myocardial perfusion imaging (CT-P)/ CT-FFR have robust diagnostic accuracy for identifying patients with flow-limiting coronary artery disease in need of myocardial revascularization.

Recent studies have shown that MDCT helps in assessing cardiovascular risk markers associated with atherogenesis which include Epicardial adipose tissue (EAT)-A potential quantifiable risk marker & Endothelial Shear Stress (ESS) - A biomechanical risk factor.

EAT is visceral fat and positioned between the visceral & parietal pericardium. It is a biologically active organ and associated with a higher incidence of Cardio-Vascular events in the individual having increased Epicardial adipose tissue.EAT is a quantifiable risk marker and measured as Epicardial  /Pericoronary fat thickness and Epicardial fat volume.

Association of ESS with atherogenesis is well established. Low ESS predisposes development of atherogenic plaque and their subsequent progression. Shear stress is difficult to measure directly in-vivo. Currently, ESS measurement is depended on invasive procedures (Catheter Angiogram & IVUS) followed by vascular mapping using computational fluid dynamics (CFD). It provides an accurate assessment of local ESS and helps in identifying the site for early plaque formation. However, the invasive nature of the test limits its widespread use.

Non-invasive measurement of ESS can be done by using computational fluid dynamics (CFD) if an accurate description of the vessel geometry is available (3-D model of vessels). Advanced MDCT technology with volumetric data set provides excellent 3-D images of coronary arteries. Several studies have shown that MDCT provides an accurate 3-D model of coronary arteries which can be used for CFD calculations & measurement of ESS.

Coronary CTA  is a novel imaging technique in cardiac imaging which provides a  number of vital information needed in day-to-day  Cardiological practice starting from diagnosis to therapeutic decision making and risk stratification for future prevention of Coronary artery diseases.

 

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