Myocardial perfusion scintigraphy: the evidence

Abstract

This review summarises the evidence for the role of myocardial perfusion scintigraphy (MPS) in patients with known or suspected coronary artery disease. It is the product of a consensus conference organised by the British Cardiac Society, the British Nuclear Cardiology Society and the British Nuclear Medicine Society and is endorsed by the Royal College of Physicians of London and the Royal College of Radiologists. It was used to inform the UK National Institute of Clinical Excellence in their appraisal of MPS in patients with chest pain and myocardial infarction. MPS is a well-established, non-invasive imaging technique with a large body of evidence to support its effectiveness in the diagnosis and management of angina and myocardial infarction. It is more accurate than the exercise ECG in detecting myocardial ischaemia and it is the single most powerful technique for predicting future coronary events. The high diagnostic accuracy of MPS allows reliable risk stratification and guides the selection of patients for further interventions, such as revascularisation. This in turn allows more appropriate utilisation of resources, with the potential for both improved clinical outcomes and greater cost-effectiveness. Evidence from modelling and observational studies supports the enhanced cost-effectiveness associated with MPS use. In patients presenting with stable or acute chest pain, strategies of investigation involving MPS are more cost-effective than those not using the technique. MPS also has particular advantages over alternative techniques in the management of a number of patient subgroups, including women, the elderly and those with diabetes, and its use will have a favourable impact on cost-effectiveness in these groups. MPS is already an integral part of many clinical guidelines for the investigation and management of angina and myocardial infarction. However, the technique is underutilised in the UK, as judged by the inappropriately long waiting times and by comparison with the numbers of revascularisations and coronary angiograms performed. Furthermore, MPS activity levels in this country fall far short of those in comparable European countries, with about half as many scans being undertaken per year. Currently, the number of MPS studies performed annually in the UK is 1,200/million population/year. We estimate the real need to be 4,000/million/year. The current average waiting time is 20 weeks and we recommend that clinically appropriate upper limits of waiting time are 6 weeks for routine studies and 1 week for urgent studies.

Fig. 1

The incremental value of resting MPS to predict cardiac events in emergency department patients with suspected ACS. Chi-square (y-axis) measures the strength of the association between individual factors added in incremental fashion (x-axis) and unfavourable cardiac events. RF, Risk factors; CP, chest pain. (Adapted from reference [232])

Fig. 2

The predictive value for death and infarction after initial stabilisation of unstable angina with medical therapy, according to whether the exercise ECG (Ex-ECG) is negative (light grey) or positive (dark grey) and whether MPS does not (light grey) or does (dark grey) show inducible ischaemia. Summary of three studies adapted from reference [238]

Fig. 3

Cox regression models displaying 1-year post-infarction risk of cardiac event according to LV ejection fraction and total LV ischaemia. Diagonal lines, Lines of equal risk. Risk increases as total LV ischaemia increases and LV ejection fraction decreases. LV ejection fraction and scintigraphic results for each of 92 patients who did (solid circles) or did not (open circles) have subsequent cardiac events over the entire follow-up period are plotted against calculated risk at 1 year. (From reference [246])

Fig. 4

Hard event rates over a mean of 15 months after myocardial infarction according to the number of segments with inducible ischaemia by MPS. Patients with more extensive ischaemia are at progressively higher risk (P=0.017). (From reference [248])

Fig. 5

Pre- and post-test likelihood of CHD calculated using Bayesian principles for the exercise ECG and MPS, using sensitivities of 68% and 92% respectively and specificities of 77% and 88% respectively. The curved lines from top to bottom represent MPS+, ECG+, ECG− and MPS−

Fig. 6

The 2-year costs of diagnosis (dark grey) and management (light grey) in patients without CHD but presenting with stable chest pain syndromes, according to strategy of investigation and type of hospital. The strategies of investigation are: 1, exECG-angio; 2, exECG-MPS-angio; 3, MPS-angio; 4, angio. MPS, Regular user of MPS; non-MPS, occasional user of MPS. [252]

Fig. 7

The 2.5-year costs of diagnosis (dark grey) and management (light grey) in 11,372 patients presenting with stable chest pain syndromes who underwent initial angiography or MPS with selective angiography, according to low, intermediate or high pre-test likelihood of CHD. [262]

Fig. 8

Growth of MPS in the UK from BNCS surveys

Fig. 9

Numbers of MPS studies in selected countries in 1994 (except where stated). (Adapted from references [280] and [290])

Fig. 10

Histogram of waiting times for MPS from the BNCS 2000 UK survey

Fig. 11

BCS recommended and actual numbers of procedures in 1994, adapted from reference [284]. Echo, Echocardiography; Ex ECG, exercise electrocardiography; Holter, 24-h ECG; Angio, coronary angiography; Revasc, myocardial revascularisation

Fig. 12

Numbers of procedures performed in USA in 1996 and UK in 2000. CAG, Coronary angiography; Revasc, myocardial revascularisation