Transient ischemic dilation associated with poststress myocardial stunning of the left ventricle in vasodilator stress myocardial perfusion SPECT: True marker of severe ischemia?

In summary, the article of Hung et al1 supports information from prior studies regarding TID. It confirms that TID occurs with vasodilator stress and also provides further evidence that TID in this setting often reflects true ventricular dilation, particularly of end-systolic volume. If further studies provide angiographic confirmation, it may be that when TID is associated with poststress stunning, even in the absence of perfusion defects, the likelihood of severe and extensive CAD may be high enough to merit coronary angiography. The study also serves to remind us that it is likely that the earlier that SPECT acquisition is begun after stress, the higher the likelihood that poststress stunning and TID will be observed. With the wide availability of motion-correction algorithms that may correct for "upward creep of the heart" associated with very early starting of postexercise acquisition, it may be that imaging in conjunction with exercise stress should be begun as soon as possible after stress, with either Tl-201 or Tc-99m agent studies. With respect to vasodilator stress, if the patient cannot perform adjunctive walking, the ability to start imaging immediately after the Tl-201 stress injection and not immediately after the injection of a Tc-99m agent appears to provide an advantage to the use of Tl-201 for the stress agent in patients undergoing vasodilator MPS without walking.