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Using new low dose CT cardiac imaging techniques to help define pre-operative risk of silent MI in surgery

Why is this research needed?

Coronary heart disease is the UK’s single biggest killer. Nearly one in six men and more than one in ten women die from coronary artery disease (CAD) and around 2.3 million people live with a coronary heart disease in the UK. The cost of premature death, lost productivity, hospital treatment and prescriptions is estimated at £19 billion (1).

Patients undergoing surgery are at risk of major peri-operative cardiac events due to the increased stress on the heart. There is therefore a need to identify patients who are at high risk of cardiac events preoperatively so that effective informed consent, prognostication and risk modification can occur. Currently, preoperative assessments seek to identify “high risk” patients with consensus guidelines categorising patients into risk groups for cardiac complications using demographics, co morbidities, functional capacity and planned operation as discriminators. However, these methods discriminate only moderately well between patients at high versus low risk.

Background

Computed Tomography (CT), an imaging technique where an x-ray source is rotated around the patient (typically in a spiral fashion), cannot assess the coronary arteries as cardiac movement blurs them. Cardiac Computed Tomographic Angiography (CTCA), similar to standard CT, has been shown to be effective in demonstrating CAD in the pre-operative patient. However, it requires many more rotations around the patient which results in a higher radiation exposure, necessitating it being done as a separate scan.

Recent advances in CT technology have made it possible to perform cardiac CT using a new technique – prospective axial scanning. This scan only requires a small part of the cardiac cycle to obtain images and has been shown to be as accurate as a spiral CTCA in selected patients. This technique is more dose efficient and is typically less radiation then a standard CT scan.

However, such a technique has not been performed before and so there is no information on its accuracy. Two important pieces of information are required:

  1. Is it possible to obtain diagnostic images of the coronary arteries using this new technique in this patient population?
  2. Does performing CT of the chest with the new technique effect image quality (and therefore diagnostic accuracy) for the structures outside the heart? If it reduces image quality of these structures then clearly its applicability would be limited.

These key questions will form the basis of the project. Assessment of the potential role of the new technique requires the following stages:

  1. Systematic reviews of pre-operative risk assessment - to establish what is known.
  2. A feasibility study where patients receive both the conventional (spiral scan) and the new (axial scan) gated scan and subjective and objective comparison is made between the two to ensure non-inferiority for non-cardiac structures and accessibility of cardiac structures.
  3. The role of the new technique in pre-operative risk assessment and identification of high risk patients compared to conventional techniques will be developed during the PhD. Through Dr Mintos study we will see if CTCA can be used as a gate keeper for patients requiring cardiopulmonary stress testing (i.e. is a normal CTCA predictive of a normal exercise test?).

Aims and objectives

This study aims to improve the prediction of risk of cardiac events in patients about to undergo major operations and improve patient’s outcomes.

The key objectives of this project are:

  • To systematically review the best current methods of predicting cardiac risk.
  • To assess the feasibility of prospective axial cardiac CT scans.
  • To make a direct comparison between the spiral scans and the prospective axial scans objectively and subjectively for image quality.
  • To assess the number of coronary artery segments in each patient that can be seen and are assessable in this patient population.
  • To evaluate the addition in predictive risk likely to flow from use of prospective axial cardiac CT scans.

References

1. Coronary heart disease statistics A compendium of health statistics 2012 edition. Nick Townsend, Kremlin Wickramasinghe, British Heart Foundation Health Promotion Research Group. Department of Public Health, University of Oxford

2. Myocardial injury after noncardiac surgery: a large, international, prospective cohort study establishing diagnostic criteria, characteristics, predictors, and 30-day outcomes. Anesthesiology.2014 Mar;120(3):564-78

Further information

For more information, read the current project proposal. If you’d like to learn more, please contact Chun Lap Pang via Email

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