A 72 year old woman with history of hypertension and type 2 diabetes reports worsening dyspnea on exertion. She presents for exercise stress with myocardial perfusion imaging:
Myocardial perfusion images do not demonstrate a regional perfusion defect (note the similar appearance of stress and rest perfusion on polar map displays).
However, notice that the left ventricular cavity appears larger on post-stress images compared to rest images. The calculated cavity volume at stress is 1.5 times the volume at rest. This is a pattern known as transient ischemic dilation (TID).
This patient had reproduction of presenting symptoms during exercise with 1-2 mm horizontal ST depression in the lateral chest leads. A subsequent cardiac catheterization demonstrated >90% stenosis in the proximal LAD artery.
Transient ischemic dilation (TID) is an imaging pattern of increased left ventricular volume on post-stress images. This appearance is associated with multivessel coronary disease, or left main/proximal LAD stenosis, and denotes a higher risk of cardiac events. Abidov A, et al. J Am Coll Cardiol 2003;42:1818-25. The TID ratio refers to the left ventricular volume after stress divided by the volume at rest. A ratio >1.2 with myocardial SPECT imaging has been show to be a marker of coronary disease, while >1.1 may be a more appropriate threshold for PET imaging. Xu, et al. J Nucl Cardiol 2012;19:465-73. Rischpler C. et al. J Nucl Med 2012;53:723-30.
TID is so described because of the appearance of dilation on imaging studies. Although true dilation of the left ventricle is possible with stress-induced stunning, the more likely mechanism for this appearance is subendocardial ischemia. Emmett L, et al. J Nucl Cardiol 2012;19:735-42.
Take a look at the dynamic perfusion images from this cardiac stress MRI in a different patient (resting images on left, stress images on the right):
This patient, who had multivessel 70-80% stenoses on subsequent catheterization, has multiple areas of stress-induced subendocardial ischemia (seen as hypoenhancement around the ventricular cavity and in the papillary muscles).
These hypoenhancing areas would also likely have decreased or absent radiotracer uptake on a nuclear stress test, so it’s easy to imaging the ventricular cavity appearing larger on stress images.