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Coronary artery disease is an inflammatory disease of the coronary arterial wall with a buildup of atherosclerotic plaques that compose of fats, cholesterol, calcium, platelets, fibrins and other materials from the blood stream (Diseases and disorders, 2008). The plaque composition varies in all CAD but can be mainly classified into stable plaque (SP) and unstable plaque (USP) (Glaudemans, 2010). SP have small, hard fatty core and thick fibrous cap, whereas the USP has large, soft fatty core with thin fibrous cap (Halpern, 2011). USP also known as vulnerable plaque is more susceptible to plaque rupture and acute coronary syndromes such as thrombotic occlusion than SP thus the larger the plaque, the greater is the probability of plaque rupture in USP. Autopsy studies from Virmani (2006) shown that the most common cause of cardiac death is due to ruptured of thin-cap fibroatheroma (TCFA), with superimposed thrombosis. Therefore, accurate detection of USP with the aim of preventing plaque rupture through early treatment/intervention thereby averting MI and sudden cardiac death lowers the mortality rate of CAD.
Secondly, progression of CAD usually does not present symptoms unless a >50% vessel stenosis or occlusion is present, resulting in significant haemodymically interference to the cardiac function. Hence, given this mechanism of CAD progression, high mortality rate is prevalent in CAD with 1 out of 6 deaths in United States accounting for 72 million of deaths/year and 12% of deaths worldwide due to late detection of CAD leading to subsequent clinical manifestations and consequentl reduced prognosis (Go et al, 2013). The most common symptoms due to clinical manifestation of CAD is the angina pectoris (Diseases & Disorders, 2008). Myocardial ischemia occurs when a reduction in vessel lumen diameter to >50% resulting in insufficient supply of oxygenated blood to the myocardium (Diseases & Disorders, 2008). Promptly diagnosis and treatment/intervention is needed to regain the blood supply to the myocardium before myocardial infarction (MI) occurs. Other than MI, other clinical manifestation includes impaired cardiac functions and sudden cardiac death (Fleg et al, 2012). Afterall, the clinical manifestations arises from the same pathophysiological process of CAD, resulting in a total prevalence of 6.4% in adults and noticeably higher prevalence in men than women with one in five male deaths and one in eight female deaths (Go et al, 2013). The incidence rate of CAD is the highest among developed countries due to higher social-economic status and occurs in approximately 200 out of 100,000 populations (Graz, 2012). Other risk factors of CAD identified by Gaze (2012) includes age >50 years old, smoking, hypertension, diabetes, sedentary lifestyles leading to high cholesterol and obesity, alcohol consumption and stress status. Due to the multiples risk factors of CAD, CAD remains as one of the leading cause of deaths (Gaze, 2012). An early & accurate detection of CAD is desire to improve patientââ‚¬â„¢s prognosis through earlier treatment & intervention methods. With that, the incidence of clinical manifestation of CAD can be managed promptly and subsequent reduce mortality rate and the morbidity associated with improved patient quality of life.
In current imaging practice, coronary angiography (CAG) is the gold standard to image CAD due to its high spatial resolution of 0.2mm and high temporal resolution of approximately 8ms (Oncel, 2008). The high accuracy of CAG is able to detect CAD with find the diagnostic value of CAG in detecting CAD. In addition, therapeutic interventions such as percutaneous coronary intervention (PCI), ballooning & stenting can be performed in the same session (Oncel, 2008). Therefore CAG is highly suggestive for symptomatic patients belonging to the high risk level so that time, money and resources can be saved by opting for a direct diagnosis and treatment modality. However, CAG has its limitations and risk associated due to administration of iodinated contrast medium, and invasiveness of the procedure with higher risk associated as compare to other imaging modality. The risk may be uncommon, but severe adverse effects do occur with a total complication rate of 1.8% and mortality rate of 0.1%. (Oncel, 2008). Serious complications of CAG constitute death 0.1-0.2%, non-fatal myocardial infarction 0.1% and cerebrovsacular accidents of 0.1%. Other minor complications include arrhythmias, vasovagal reactions, infections and allergic contrast reactions (Paech, 2011). Furthermore, about two-thirds of CAG performed were solely diagnostic with no haemodynamically significant lesions/significant CAD detected. Therefore developing a non-invasive imaging modality could serve as an alternative to image CAD with accurate assessment of coronary arterial system with high precision and reduced harm to patient yet achieving similar diagnostic results CAG provides. Such imaging modality would provide potential benefits in safer diagnosis of CAD without going through unnecessary CAG. Hospital stays can be minimise as a result of relatively safe non-invasive diagnostic imaging tests. Hence, cost effective will be able to achieve with a cheap non-invasive diagnostic modality together with reduce need for hospital stay leading to lesser cost for patients and higher preservation of hospital beds for patient who are more in need.
Computed tomography angiography (CTA) and magnetic resonance angiography (MRA) are chosen as the comparison imaging modality to image CAD. CTA and MRA were chosen due to their advancement in technology in terms of hardware and software.Hence, the context for the literature used will be within the 5 year limitation to achieve updated information. Secondly, many research studies proposed a comparison study between CTA & MRA due to their benefits in relations to diagnostic values as compare to other imaging modality. From my knowledge, there is no article which compares the advantages and disadvantages of CTA and MRA to image CAD within these five years .
Current research studies have recommended several imaging techniques such as intravascular ultrasound (IVUS) and CT calcium scoring (COROS) to image CAD. Although IVUS has excellent spatial and contrast resolution in detecting plaque (Nikolaou, Alkadhi, Bamberg, Leschka & Wintersperger, 2011). IVUS is a much more invasive test as a tranducer is introduced within the vessel lumen thus IVUS is excluded as a comparison modality due to its invasiveness. As for COROS, it has the benefit of non-invasive imaging, but it could only detect calcium to account for possible CAD. However, Glaudemans et al (2010) show that USP often lack calcium so COROS is not a comprehensive modality which can screen SP and USP. Furthermore, COROS provided a pooled result of the calcium present, localization of the calcium is not visible with COROS. Therefore, COROS is excluded as the comparison modality due to its limitation in localizing and plaque detection. Although most clinical practice are using Coros as a test for CAD, this study will examine the CTA due to its proven use by many clinical sites in imaging CAD without the invasiveness of IVUS and the ability to assess more than calcified plaque than COROS. As for MRA, the reason why MRA is chosen is firstly because MRI is the gold standard for myocardium viability imaging (Jankharia imaging, 2004). Grover, Srinivasan and Selvanayagam (2011) shows that CMRI can determine whether the myocardium is stunned to hibernating or both and determine whether the myocardium is viable for revascularization such that the myocardium will regain its function after the intervention as well as the prognosis of patient condition due to CAD. Secondly, if MRA could perform well in detecting CAD, MRI could function as a one stop diagnosis for CAD where the physician can know the degree of stenosis with good anatomical display and the viability of the myocardium so as to allow for treatment planning but this paper will only focus on the role for MRA in imaging CAD.
The aim of this study is to assist the physician in decision making for the modality of choice to detect CAD between CTA & MRA. Objective of the study involve a comparison between the advantages and disadvantages of CTA & MRA in detection of haemodynamically significant CAD accurately so as to determine which/whether a treatment/intervention or further test require such as myocardial viability test is require. Lastly, scope of study will involves a discussion of CTA & MRA using a patient & physician centered approach.