Statistical comparison of triage tool with exercise MPS data in a cohort of Maltese patients

Ischaemic heart disease (IHD), caused primarily by coronary artery stenosis, continues to be the most significant cause of premature mortality and a major cause of disability worldwide. In fact, approximately 38% of all deaths in Malta are related to diseases of the circulatory system, with IHD claiming more lives than cancer within the local scenario. Coronary artery stenosis of 50% or more is reliably identified with a myocardial perfusion scintigraphy (MPS) stress examination, a nuclear medicine scan performed under maximal myocardial stress.

An MPS stress examination consists of an ECG stress test during which the patient is injected with a radioactive tracer, followed by an MPS scan. The patient can be stressed either by undergoing exercise or a pharmacological stress test. Physicians prefer the use of treadmill exercise stress testing, since it provides additional information on the patent’s functional ability. However, for the exercise stress test to be conclusive, the radioactive tracer needs to be injected when the patient reaches 85% of the target heart rate. Failure to reach this end point may result in an incomplete exercise stress test and therefore a submaximal MPS stress scan.

Myocardial perfusion SPECT scan of the heart showing normal (A) and abnormal (B) vertical long axis images, labelled with technetium 99m-sestamibi (Tc 99m-MIBI).

Within the clinical setting it is difficult to identify patients who will reach 85% of the target heart rate. A triage tool would provide a prompt way to assess the functional status of a patient prior to the exercise stress test. Our research was conducted as part of a PhD study, using a mixed-methods, multiphase approach involving four phases. Several data collection methods were used, for which ethical permission was obtained, including an international online survey; retrospective analysis of 252 patient medical files; six qualitative interviews with physicians; and a triage tool completed by 300 patients.

The results of the online survey in phase 1, confirmed the need for a patient triage tool. In 17 NM centres (n = 43) the respondents were unsure of the presence of stress testing protocols. Phase 2 identified a set of population-based IHD risk factors, including diabetes (p = 0.012), smoking (p = 0.003) and previous myocardial infarction (p < 0.001), statistically related to the results of the MPS stress scan. In phase 3, the interviews indicated the lack of local common referral criteria for MPS stress examinations. The final phase integrated the literature findings and the Maltese population-based IHD risk factors, with the results of the interviews, in order to develop a triage tool. Phase 4 also confirmed that the triage tool was statistically related to the patients’ ability to complete the exercise stress test, providing an effective method that could be used within the local clinical setting, and integrated into international NM practices once confirmed as appropriate to population-specific IHD risk factors.

Myocardial perfusion SPECT scan of the heart showing normal (A) and abnormal (B) short axis images, labelled with technetium 99m-sestamibi (Tc 99m-MIBI).

Karen Borg Grima is an assistant lecturer at the University of Malta, Faculty of Health Sciences, Radiography Department.

Research Presentation Session
RPS 1714 Medical imaging challenges: nuclear medicine and radiography

A statistical comparison of a triage tool with exercise myocardial perfusion scan (MPS) data in a cohort of Maltese patients
K. Borg Grima1, P. Bezzina2, L.A. Rainford3; 1Naxxar/MT, 2Malta/MT, 3Dublin/IE

Read the full abstract in the ECR 2020 Book of Abstracts
Borg Grima K, et al. (2020) A statistical comparison of a triage tool with exercise myocardial perfusion scan (MPS) data in a cohort of Maltese patients. Abstract RPS 1714-4 in: ECR 2020 Book of Abstracts. Insights Imaging 11, 34 (2020). DOI 10.1186/s13244-020-00851-0