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Purpose: The NICE guidance has placed non-invasive ischaemia testing as the primary role for assessing patients with moderate pre test probability for obstructive coronary artery disease. Functional tests like MPI, have led to a reduced role for invasive coronary angiography (ICA) in initial patient assessment. Aim of our audit was to assess the specificity of our nuclear service compared with ICA retrospectively. The standard was set at a false positive rate of no more than 73%.
Methods: A search was conducted (between Aug2012-Feb2013). MPIs were reported by a radiologist and a cardiologist. A standard 17-segment model was used for MPI interpretation. Coronary angiograms were interpreted for the absence/presence of epicardial luminal narrowing >50% by referencing the clinical report on the patient electronic record. The cases which were positive enough to warrant recommendation for ICA the true positive and false positive rate was determined.
Results: This cross –sectional study included 51 cases.33 had a stenosis in a major coronary artery of>50% giving a true positive rate of 65%. There were18 false positive studies (35%). 5 cases were regarded as having evidence of transient ischaemic dilatation (TID), all of which had a subsequent negative angiogram.3 studies had notable artefact due to patient body habitus, or inability to position the patient optimally. The percentage of myocardium defects was determined for each case at stress. The average percentage in the true positive studies was 17%, in the false positive studies it was7%, excluding those regarding as having TID.
Conclusions: MPI studies deemed sufficiently abnormal to justify a coronary angiogram have a moderate likelihood of predicting a significant stenosis being present on ICA. False positive scans are frequent when only TID and significant artefacts are present. It is likely that CT calcium scoring with MPI will increase the specifity of this imaging. It will also allow CT coronary angiography to be used in cases where artefact is present and the calcified atheroma burden is low.
The audit standard was not met. Suggested changes in practice. 1. Greater caution in recommending ICA for cases where the only evidence for ischaemia is transient ischaemic cardiomyopathy. 2. Increased use of CT to determine cases where significant reversible ischaemia is present in the context of none or low burden of coronary calcification.
Clinical Relevance/Application: MPI assesses myocardial perfusion by using radiotracers injected under stress/rest conditions. |
