Significance of ST depression during exercise treadmill stress and adenosine infusion myocardial perfusion imaging

Abstract

In most patients, the diagnosis of coronary artery disease cannot be detected from the history and rest electrocardiogram alone. Next to diagnostic coronary angiography a variety of non-invasive procedures have been developed to detect cardiac ischemia or confirm the suspicion of cardiac ischemia [1]. For a long time, exercise electrocardiographic stress testing has been an established procedure for the detection of coronary artery disease. A positive test is considered 1 mm or more of horizontal or downsloping ST depression in the presence of a normal rest ECG. This reflects changes in rest polarity of a myocardial segment based on ischemia-induced disturbances in the electrical state of the myocytes [2]. The sensitivity and specificity of this test is 60 and 77%with a wide variation due to patient selection and exercise methodology [3]. The sensitivity of SPECT perfusion imaging for the detection of coronary artery disease is higher, ranging from 85 to 90% with a specificity of 84–92% [4]. One could argue, that the electrocardiogram is useless and adds no additional information. Electrocardiographic monitoring would only be needed for the detection of arrhythmias or conduction dysturbances. Is that true? The paper of Yap [5] shows, that electrocardiographic changes occur in 5% of patients examined with myocardial perfusion imaging after adenosine infusion and 10% of patients after exercise stress testing. Although exercise induced ST segment changes correlated better with perfusion abnormalities than adenosine induced ECG abnormalities, in both stress modalities 2 mm ST depression was able to predict perfusion abnormalities with a positive predictive value of 63–71% and a negative predictive value of 68–86%. This means that electrocardiographic changes give additional information about the risk of coronary artery disease in those patients. Unfortunately, the study of Yap did not give us information about the coronary anatomy of those patients with a normal perfusion scan. Neither gives the paper information about the prognosis of those patients with a positive stress test and electrocardiographic abnormalities or those patients with a negative perfusion scan and electrocardiographic changes. One could speculate, that the first group could be a high risk population, whereas the second group would need further work-up to exclude coronary artery disease. Further research in this direction is needed to resolve this issue.