Faculty Publications

Using Multiple Images Post-Stress To Enhance Diagnostic Accuracy Of Myocardial Perfusion Imaging: The Clinical Importance Of Determining Washin And Washout Indicates A Parabolic Function Between Coronary Perfusion (Blood Flow) And Cellular (“Uptake/Release”) Function

Document Type

Article

Keywords

Data validity, MPI, MPI accuracy, Multiple imaging, Myocardial infarction/injury (MII), Myocardial ischemia, Myocardial washin, Myocardial washout, Washout rate (WR)

Journal/Book/Conference Title

Heart Disease in Men

First Page

75

Last Page

100

Abstract

Background: Myocardial perfusion imaging (MPI) has evolved over the last several decades with improvements in equipment and isotopes. Despite these advances, sensitivity and specificity of the methodology remains 65-90%. Numerous investigators have recommended changes in protocols and quantification of data to increase the diagnostic accuracy of this non-invasive physiologic test. Initial investigations have demonstrated differences in initial and delayed results post stress which have increased the ability to detect cardiomyopathies and vasospastic coronary artery disease. This study explored MPI stress validity using early (5 minute) and delayed (60 minute) post stress imaging and findings noted on cardiac catheterization. Methods: Records of forty-one individuals undergoing cardiac evaluation were studied for pharmacologic and exercise stress approaches with either Sestamibi or Myoview using standardized protocols. Twenty-two (54%) were diagnostically studied following MPI in the cardiac catheterization laboratory. Findings from the post stress images were used to determine washing/washout rates (WR) for total, anterior and inferior regions of myocardium and compared with findings from coronary angiography. Results: Fifty-four percent (22 of 41) of the subjects studied underwent coronary angiography. Reading of MPI dynamic images at 60 minutes post stress resulted in 9 false (FNs) negatives (41%) and 2 false (FPs) positives (9%) in the anterior myocardium. Visual reading of inferior ischemia from dynamic images lead to 9 FNs (41%) and 3 FPs (14%). Evaluation of WR from multiple images obtained at 5 and 60 minutes post stress demonstrated a significant correlation between total heart WR and the average percent diameter (%DS) stenosis (r=0.45, p<0.05) and between inferior WR and inferior %DS (r=0.68, p<0.001). There was no correlation between anterior WR and anterior %DS for individuals with washout. However, when myocardial infarction/injury (MII) was taken into account there was an improved correlation (r=0.21) between anterior WR and anterior %DS. When washing occurred (total, anterior or inferior) a critical stenosis was noted at or near the ostium of a major epicardial vessel supplying a "large" region of viable myocardium at risk. This study also showed a significant increase in the incidence of MII in inferior regions of the heart when compared with anterior regions. The relationship between heart to lung (H:L) ratio was negatively (r=-0.38, p=NS) correlated with the presence of anterior MII. The relationship between left ventricular ejection fraction (EF) and anterior washout (W. Ant) was significant (r=0.46, p<0.002). Conclusions: Initial static (5 minute) and delayed dynamic (60 minutes) images demonstrate changes between initial and delayed imaging which cannot be accounted for on the basis of radioactive decay alone and which can be quantified as WR. Both washing and washout WR, clearly demonstrates that the uptake and release of Tc 99m compounds is an active process influenced by both myocardial ischemia and MII; although, primarily ischemia and as such can be used to not only more accurately detect ischemia compared with using the 60 minute image alone, but to also allow determination of %DS. An absence of WR is seen only with individuals who have no ischemia and no MII, viz. "normals" who were limited in this study, since the referral of such subjects did not occur in this setting. Total WR and Inferior WR were highly correlated with % DS seen on coronary angiography. These results confirm earlier findings that such information appeared to be diagnostically important in determining coronary intervention of viable myocardium supplied by severely stenotic arteries missed using only the single set of images obtained at 60 minutes post stress. Our findings confirm earlier work on WR and the degree of cardiomyopathy/CHF in individuals with reduced left ventricular ejection fractions (LVEF) resulting from anterior MII and ischemia. This study is the first to demonstrate that using multiple (static and dynamic) imaging post stress increases the diagnostic accuracy of detecting ischemia and resulted in important diagnostic decisions about patient care/treatment (e.g. Coronary artery stenting), which was not apparent using only the 60 minute image. On inquiry the American Heart Association could cite no prior information regarding the incidence of MII in different regions of the heart. This study demonstrated a significant difference in regional MII and the ability to confidently correlate %DS from the total and inferior WR, in addition to removing the effect of diaphragmatic attenuation noted with the 60 minute image only despite the use of Gadolinium for attenuation correction. Further work is needed to determine if WR obtained from multiple imaging at rest could increase the diagnostic information gleaned regarding the extent of myocardial damage (stunned, hibernating or infarcted) present and perhaps provide insight into why certain regions of the heart are more prone to MII. For example, does the architecture of the right coronary artery predispose it to flow limitations not seen in the other epicardial arteries, just as it makes it more difficult for the interventionalist to angioplasty or stent longer lesions without injury to the artery. Assessment of static images during intermediate times (between 5 and 60 minutes) and using multiple head static imaging may yield additional diagnostic information, the benefit of which can only be determined by looking at the results. Finally, these findings demonstrated a parabolic interactive model between coronary blood flow and cellular “uptake/release” of Technetium-99m tracers which more accurately detects coronary ischemia using a multiple post-stress imaging washing/washout model.

Original Publication Date

1-1-2009

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