Myocardial perfusion scintigraphy using Tc99m labelled compounds: correlations with coronary angiography

The increasing incidence of ischaemic heart disease with high mortality rate and the recent introduction of Tc99m labelled myocardial perfusion imaging agents, along with the advent of a Coronary Angiography programme in Trinidad and Tobago, prompted the comparison of the sensitivity and specificity of myocardial perfusion scintigraphy (MPS) with coronary angiography (CA). Using a standard one-day code-differential imaging protocol Single Photon Emission Computed Tomography (SPECT), images of the left ventricular myocardium of 30 patients were obtained at rest and following exercise: These images were analyzed for perfusion defects to assess each of the three main coronary arteries; the left anterior descending artery (LAD), the right coronary artery (RCA) and the left circumflex artery (LCx). The data were then correlated with the angiographic findings. MPS yielded an overall sensitivity of 97.5% and a specificity of 83.6% when compared to CA. Discordant data were obtained in the analysis of nine vascular territories with scintigraphy producing eight false positives and one false negative. The false positive cases were seen in two males and four females. Of the males, one was discovered to have intramyocardial tunnelling of the LAD artery and the other demonstrated differential perfusion between the LAD and LCx arteries. Of the females, one was classified as having Syndrome X and another demonstrated differential perfusion between the LAD and LCx arteries; the other two cases were attributed to breast attenuation. The one false negative was obtained in a patient who demonstrated good collateral circulation on angiography. MPS thus compares very well with CA in assessing the three main myocardial vascular territories.