Transient ischemic dilation in hypertrophic cardiomyopathy: A complex sign in a complex disease

Excerpt

Left ventricular (LV) cavity dilation, better known as transient ischemic dilation (TID), is an indirect marker of ischemia in myocardial perfusion imaging, already described in Thallium-201 scans several years ago. The proposed mechanisms for this abnormality are related to the presence of severe stress-induced ischemia.1 A first possible explanation is the occurrence of more pronounced ischemia in the subendocardial layer of the myocardium, with consequent apparent enlargement of the ventricular cavity.2 Alternatively, the systolic dysfunction due to ischemia could persist until the moment of image acquisition, according to the model of myocardial stunning, and the ensuing reduction in wall motion and thickening cause an apparent decrease in myocardial uptake due to the partial volume effect, which is mainly recognizable as an enlarged ventricular cavity.3 Experimental evidences have confirmed that a true increase in LV end diastolic dimensions is relatively rare, whilst a larger end systolic volume, with the additional consequence of a decrease in LV ejection fraction (EF) is a commonplace observation.3 Independently of the true mechanism, and most probably because they are often both involved, TID has been found to be a very important and reliable sign of severe ischemia.1,4 This has been confirmed within all different modalities of myocardial perfusion imaging, including all used tracers, stressors, and protocols, although various definitions and cutoff values have been proposed. Its sensitivity for the detection of multivessel coronary disease ranged from 38% to 80%, and its specificity was consistently higher than 90%.1,4 However, in the general population of patients studied for suspect or known epicardial coronary artery disease its incidence is quite low, probably less than 10%.5 …