The NICE guidelines on the assessment of chest pain
Authors: Khaled Alfakih, Sven Plein
Journal: Journal of the Royal Society of Medicine (2012)

The National Institute for Health and Clinical Excellence (NICE) published guidelines on the investigation of patients with chest pain of recent onset. The most prominent change to current protocols is that calcium scoring is proposed as the first-line investigation in patients with an estimated likelihood of coronary artery disease (CAD) of 10–29%, proceeding to multidetector computed tomography coronary angiography (CTCA) if the calcium score is above zero.1 For patients with 30–60% likelihood of CAD, functional testing is recommended with stress echocardiography, single photon emission computed tomography (SPECT) or cardiac magnetic resonance (CMR). For patients with 61–90% likelihood of CAD or calcium score greater than 400, X-ray invasive coronary angiography is recommended.

The rationale underpinning these recommendations is that cardiac CT is considered an accurate ‘rule out’ test in patients with low likelihood of CAD given the extensive data confirming excellent prognosis of a zero calcium score in asymptomatic populations, and the excellent negative predictive value of CTCA.2 Functional tests on the other hand have better diagnostic performance in patients with higher pretest likelihood of CAD than in patients with low likelihood (Bayes theorem).

It is hoped that the guidelines will reduce the high rate of normal coronary arteries at X-ray invasive coronary angiography, which was 39% in a recent ACC National Cardiovascular Data Registry, and is likely to be similar in most NHS Trusts.3 As exercise tolerance testing is no longer recommended; the guidelines will lead to an increase in referrals for imaging functional tests. The choice of imaging modality has been deliberately left open in the guidelines. Although this choice will often be driven by local availability, there are some differences in the evidence base and diagnostic yield and with the increasing awareness of the risks of ionizing radiation from medical exposure, the cumulative radiation burden of patients in their diagnostic journey, warrants particular consideration.

Until recently, the median radiation dose for CTCA has been as high as 22 mSv, which can equate to an estimated risk of future cancer of 1 in every 270 in 40-year-old women undergoing the test.4 However, it is now possible to significantly reduce the radiation dose from CTCA by reducing the scan length and the scanning field of view to cover just the heart, electrocardiographically controlled tube current modulation during the cardiac cycle and reduction of the output of computed tomography X-ray tube from 120 kVp to 100 kVp for non-obese patients. The most effective way to lower the radiation dose, suitable in patients with regular heart rates below 60 bpm, is prospective electrocardiogram-triggering, which limits the acquisition to 10% of the cardiac cycle reducing the dose to 2–4 mSv.5 This is lower than conventional X-ray invasive coronary angiography, but not the new dual axis rotational coronary angiography which reduces radiation dose and contrast load. Such low radiation doses will however not be achievable in many UK centres without some investment.