Screening for asymptomatic coronary heart disease in the siblings of young myocardial infarction patients (SACHSMI)

© 2017 Dr. Nadim Mohammed ShahThe concept of screening entails detecting subclinical disease in the hope of altering the natural progression and thereby reducing long term mortality and morbidity. For a screening program to be effective it must be targeted at a disorder that is prevalent with accepted treatments and diagnostic tools. Coronary heart disease (CHD) is ideally positioned in this respect. There are multiple strategies available to diagnose asymptomatic CHD but the emerging field of coronary computer tomography angiography (CCTA) appears to have many of the required qualities. It is non-invasive, safe and has high sensitivity to diagnose CHD. The radiation dose has markedly decreased with evolving technology and the cost is comparable to current non-invasive cardiac investigation. An effective screening strategy for CHD maybe beneficial at all ages but applying it to the young may have a greater impact on society. The aim of this thesis was to highlight the burden of CHD in the young and to asses potential screening strategies to detect asymptomatic disease. In particular the potential role of CCTA as a screening tool has been investigated. Chapters 3 and 5 discusses the results of reviews looking at the literature focusing on myocardial infarction (MI) in the young and screening for asymptomatic CHD in the young respectively. Chapter 4 discusses the findings of a study that demonstrated the prevalence of MI in the young (defined as ≤55 years) in a low socioeconomic Australian urban setting was approximately 32%. The younger patients were more likely to be male, have a family history of premature CHD and be current smokers compared to the older cohort. In general this prevalence is higher than what is reported in the literature. Chapter 6 highlights the findings of a study that used CCTA to demonstrate the prevalence of asymptomatic CHD in the siblings of young MI patients. The participants of the study were aged 30-55 and 30-60 years if males and females respectively. Obstructive CHD (defined as ≥50% stenosis of at least one epicardial coronary artery) was demonstrated in 18% of participants. All of those with obstructive CHD were either current or ex-smokers. No statistically significant association was found between traditional cardiovascular risk scores and obstructive CHD by CCTA. A similar study conducted for this research project at another healthcare centre found the prevalence of asymptomatic CHD via screening CCTA in an all comer population was 18%. Males and those over the age of 55 years were more likely to have obstructive CHD. These results are discussed in chapter 7. Compared to the published literature the prevalence of obstructive CHD by CCTA demonstrated in these two studies is higher. Screening strategies have been demonstrated to alter modifiable risks in those who participate. Chapter 8 discusses the findings of a study that demonstrated 60% of the participants of a screening program for CHD using CCTA either stopped or reduced smoking one month after undergoing CCTA. This change was largely sustained at 12 months with 55% either stopping or reducing smoking. This rate appears to be high compared to more traditional methods such as nicotine replacement therapy. For CCTA to be accepted as an effective screening modality for CHD the risks of radiation exposure need to be as low as possible. Chapter 9 discusses the results of a study comparing the radiation doses associated with three new generation CT scanners when used to perform CCTA; the Siemens Somatom Definition Flash CT scanner, the GE Revolution CT scanner and the Toshiba Aquilion ONE ViSION CT scanner. The study found all three scanners exposed subjects to below a median dose of 5 mSv, fulfilling the Australian National Health and Medical Research Council guidelines of