EXERCISE TOLERANCE TEST (ETT) OR MYOCARDIAL PERFUSION SCAN (MPS) � WHAT TO CHOOSE IN PATIENTS OF ISCHAEMIC HEART DISEASE (IHD)?

Myocardial Perfusion Scan

Abstract

Objective: To evaluate the validity of exercise tolerance test (ETT) with treadmill exercise in the diagnosis and follow-up of ischaemic heart disease (IHD), taking myocardial perfusion scan (MPS) as standard.
Study Design: Retrospective, validation study.
Place and Duration of Study: Nuclear Medical Centre (NMC) Armed Forces Institute of Pathology (AFIP), Rawalpindi, Pakistan, from 1 January to 31 December 2009.
Patients and Methods: One hundred and nineteen patients (88 males, 31 females), referred for MPS; were selected through non-probability, consecutive sampling. Patients of all ages and gender, fit to undertake treadmill exercise, were included. Patients with contraindications to ETT, like unstable angina, conduction abnormalities, etc., or those who had taken a beta blocker within the preceding 24 hours, were excluded. ETT through treadmill exercise was done, followed by MPS with single photon emission computed tomography (SPECT) technique, using Thallium-201 or Technetium-99 m 2-methoxy-isobutyl-isonitrile (MIBI). ETT was interpreted as positive or negative for ischaemia, with borderline changes considered positive. MPS was interpreted as positive or negative for ischaemia. Validity of ETT was evaluated in terms of sensitivity (Sn), specificity (Sp), and positive and negative predictive value (PPV and NPV), taking MPS as standard.
Results: Sensitivity of ETT was found to be 77.5% and specificity was 43.6%. PPV was 73.8% and NPV was 48.6%. Out of a total (n) of 119 patients, true positive (TP) cases were 62, true negative (TN) 17, false positive (FP) 22 and false negative (FN) 18.
Conclusions: ETT is an acceptably sensitive but non-specific test for evaluating myocardial ischaemia, with adequate PPV but low NPV, when validating it against MPS. Replacing the MPS with ETT, in the diagnosis and follow-up of IHD, is thus, not prudent. ETT can be useful as a screening test.