Original ArticleThe prevalence and predictive accuracy of quantitatively defined transient ischemic dilation of the left ventricle on otherwise normal SPECT myocardial perfusion imaging studies
Introduction
The appearance of post-stress LV cavity dilation on single photon emission computed tomography (SPECT) imaging is associated with increased risk and severity of CAD.1 It is most frequently observed in the presence of inducible ischemia and is commonly referred to as transient ischemic (cavity) dilation (TID). The usefulness of TID as a clinical tool for diagnosis and prognosis of CAD is the subject of many studies.2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12
Of particular interest, is the significance of an elevated TID ratio in a patient with otherwise normal myocardial perfusion and function, as this may provide a tool for identifying high risk patients with balanced ischemia or globally reduced myocardial flow reserve, which may not be demonstrated by focal perfusion defects.13,14 However, the most recent study of patients with TID and normal MPI shows a lack of correlation with either disease severity or outcome.15 Our study will suggest an explanation for the relatively poor and variable correlations of TID in patients with normal MPI, as we will show low and highly population-dependent predictive accuracy of TID in studies with otherwise normal MPI.
The measurement of TID is necessarily subject to error and this mandates that there will be some outlying measurements (false positive) beyond the normal range in patients with completely normal LV perfusion and function. There is no alternative gold standard measurement for the presence or absence of TID, and because of this, the sensitivity, specificity, and predictive accuracy of the finding of TID cannot be directly measured. We can, however, compare the statistically expected number of statistical outliers with the observed number of positives and thereby indirectly infer the predictive accuracy of TID in various patient populations. Because TID is inherently a “high risk” finding, it is essential to understand the probability of its being falsely positive.
Section snippets
Study Cohort
The study cohort consisted of 688 consecutive patients referred for 99mTc sestamibi gated SPECT study at the University of Virginia (UVA) Health System Nuclear Cardiology Laboratory between January 2010 and June 2010.
Stress Protocol
A total of 334 (48.6%) patients underwent treadmill exercise stress and 354 (51.4%) had pharmacological stress. Adenosine was used in 207/688 (30%), while regadenoson was used in 147/688 (21.4%). Exercise stress was treadmill-based and was performed according to a Bruce protocol.
TID in Otherwise Normal MPI
Of 688 patients referred for a clinically indicated SPECT study, 457 (66.4%) showed normal myocardial perfusion, normal LV function (global and regional), and normal LV volumes. (This group includes those with normal MPI but does not exclude patients with DM or any other predisposing factor or prior history of CAD.) Clinical and MPI characteristics of the study population are shown in Table 1. (In this referred population, 34% had abnormal SPECT. This corresponds reasonably with sequential
Discussion
If cardiac rhythm is stable so that the effect of post-stress arrhythmia is avoided, there remain two feasible causes of TID as a true pathological finding.
First, it is possible for the LV to actually dilate and remain dilated through the time of post-stress imaging. This would imply persistent changes in LV pressure loading with resultant change in volume. This would be a feasible explanation with dilated cardiomyopathy, such as illustrated in Capture 1, but unlikely to occur in a heart with
Conclusions
TID could be a significant finding for a patient with a high pretest likelihood of CAD. However, the clinical significance of TID in the setting of a normal perfusion scan, normal LVEF, and normal LV volume should be interpreted with caution. The prevalence of positive TIDr, and consequently, the predictive accuracy of positive TID in this population is low. Correction of the stress and rest LV volumes to body mass index, gender-specific, and stress-specific normal limits may improve predictive
Conflict of interest
The authors have indicated that they have no financial conflicts of interest.
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