The value of using Trimetazidine Technetium 99m sestamibi SPECT and Pulsed tissue Doppler mitral annulus velocity for assessment of myocardial viability in patients with coronary artery disease before revasularization

Abstract

Coronary heart disease is a main cause of mortality and morbidity in Western world, causing about two thirds of cases of left ventricular dysfunction. Not only are these patients at high risk for cardiac death, and recurrent hospitalizations for congestive heart failure, they also frequently have severe restrictions in their lifestyles and well-being. In many of these patients, the extent of remaining viable tissue is of clinical and prognostic significance. It can help to decide between revascularization and cardiac transplantation. Many subjects with heart failure and underlying coronary artery disease have an important amount of viable but dysfunctional myocardium, where akinetic or severely hypokinetic myocardium keeps the ability to contract if perfusion improves. The term “hibernation” implies an adaptive reduction of energy expenditure through reduced activity in a state of reduced energy supply. Since the early 1980s, it has been known that chronically dysfunctional myocardial segments demonstrate distinct morphological changes that can be verified by both the light and the electron microscope, in addition to metabolic alterations. The dysfunctional viable myocardium has unique characteristics (including integrated cell membrane, intact mitochondria, preserved glucose uptake and inotropic reserve) which form the basis for the different imaging modalities that are currently available for the assessment of myocardial viability. These modalities include different scintigraphic techniques, DSE, and recently MRI and CT modalities. Despite its advantages over thallium 201, the role of technetium sestamibi SPECT in detection of viability has been debatable and several protocols have been used to improve technetium sestamibi uptake by myocardial cells. One of these modalities is the addition of trimetazidine which has been shown to enhance technetium uptake and improve the results in viability detection. Dobutamine stress echocardiography is the most frequently used agent in this setting to assess jeopardized myocardium for viability. Viability is shown by noting improved contraction of a dysfunctional LV wall segment with low-dose dobutamine infusion, which provides adrenergic stimulation. In patients with jeopardized but viable myocardium, the LV ejection fraction will show improvement with low-dose DSE in direct proportion to the number of segments with contractile reserve. However, to overcome the subjective visual evaluation of regional wall motion, new technologies have been modified; one of these is to assess mitral annular velocity using tissue Doppler imaging.