It has been more than 25 years since the first reports of the use of echocardiographic imaging in conjunction with stress testing for the diagnosis of coronary artery disease. Since that time, both radionuclide and echocardiographic stress testing have become a routine part of the evaluation of patients with known or suspected coronary artery disease. Previous studies have indicated sensitivity and specificity of stress echocardiography in the range of 70% to 90%, compared with coronary angiography as a gold standard, for detecting hemodynamically significant obstructions. These differences have been explained by a variety of factors, including the extent of disease, reader experience, heart rate obtained during stress, concurrent medications, and other factors. Patients with abnormal results on stress exams (based on the development of new wall motion abnormalities), but with subsequent findings on coronary angiography indicating no significant coronary stenosis, are said to have had “false-positive” results. Echocardiography has been reported to have higher specificity and fewer “false-positive” results than other imaging modalities. Traditionally, these patients with “false-positive” examinations have been treated as if they had no significant coronary artery disease risk and are often dismissed from the care of cardiovascular specialists.
The study by From et al in this issue of JASE challenges the concept of “false-positive” stress echocardiographic results. The authors evaluated a consecutive group of 1477 patients with abnormal stress echocardiographic results who underwent coronary angiography. Of this group, approximately two thirds had significant coronary artery disease. The remaining patients had so-called false-positive results, because angiography demonstrated <50% stenosis. Despite this, during an average follow-up of 2.4 years, there was no significant difference in the overall death rate between those with and without 50% luminal narrowing on angiography. One might conclude that in light of the findings, patients with “false-positive” stress echocardiographic results should receive the same intensive risk factor modification and careful follow-up as patients with “true-positive” stress echocardiographic results (ie, confirmed by angiography). What are the possible explanations for these findings, and what are the potential implications?
Ischemia without Angiographic Stenosis
There are a variety of explanations for the development of ischemic wall motion abnormalities in the absence of traditional angiographically demonstrated occlusive plaque. These explanations include microvascular abnormalities, vasomotor changes, endothelial dysfunction, and small vessel coronary disease. Perfusion imaging by single photon-emission computed tomography and positron emission tomography has clearly shown defects in myocardial perfusion in the absence of angiographic stenosis. Furthermore, intravascular ultrasound studies have demonstrated significant plaque burden in the absence of 70% or even 50% compromise of the vessel lumen as demonstrated by angiography. Likewise, abnormal coronary flow reserve has been demonstrated in patients without significant lesions by traditional coronary angiography and abnormal single photon-emission computed tomographic perfusion.
Cabau et al performed intravascular ultrasound on a group of patients with abnormal radionuclide stress results and normal coronary circulation on angiography and demonstrated significantly increased plaque burden in that subset of patients. Similarly, Johnson et al demonstrated abnormal magnetic resonance spectroscopic results consistent with ischemia in a group of patients with normal coronary arteries on angiography.
It is clear that abnormal coronary flow, myocardial perfusion abnormalities, and occult atherosclerotic diagnosis can be seen in patients with <50% obstructive lesions on coronary angiography.
The Prognostic Power of the Stress Test
Several large studies have assessed the prognostic value of stress testing in groups of patients followed for cardiac events and death. Both echocardiographic and radionuclide stress tests have high prognostic power. Marwick et al reported in a group of >3000 patients that dobutamine stress echocardiography was an independent predictor of death, incremental to clinical and stress data. Ischemia and the extent of wall motion abnormalities were independent predictors of cardiac death. These data have been reproduced by a number of investigators. This prognostic power is similar when comparing radionuclide and echocardiographic imaging. Sicari et al reported that coronary angiography did not add to the prognostic power of stress echocardiography in >7000 patients. Magnetic resonance imaging has yielded similar independent prognostic information. Likewise, myocardial contrast echocardiography has shown similar prognostic value. Serious cardiac events are extremely uncommon following negative results on stress echocardiography.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
