Biomedical Engineering Reference
In-Depth Information
plaque cap adjacent to the lipid core. These results are consistent with previ-
ous studies that suggested that the larger lipid layers increase plaque cap stress
[53, 54].
12.3.4
Cardiac Mechanics
Assessment of regional heart wall motion (wall motion, thickening, strain, etc.)
can identify impairment of cardiac function due to hypertrophic or dilated car-
diomyopathies. It can provide quantitative estimates of the impairment of ven-
tricular wall function due to ischemic myocardial disease. The assessment of re-
gional heart motion is used in combination measures of perfusion and metabolic
uptake to diagnose and evaluate stunned/hibernating myocardium following
transient ischemic events. Stunned myocardium is characterized by decreased
or no contractile function but having normal perfusion and glucose utilization
[68-70]. Since stunned myocardium has normal perfusion and normal viability,
it can only be identified by localizing abnormal wall motion/contraction.
Hiber-
nating myocardium
is characterized by persistent ventricular myocardial dys-
function with preserved viability, decreased perfusion, and normal metabolic
uptake. Hibernating myocardium has been associated with a slower and in-
complete restoration of contractile function as compared with stunned my-
ocardium [71, 72]. Up to 50% of patients with ischemic heart disease and LV
dysfunction have significant areas of hibernating myocardium [73, 74] and
therefore would be predicted to benefit from identification and subsequent
revascularization.
The assessment of the size and location of infarction, in particular, the ex-
tent of viable tissue, and the mechanical function of the tissue can be extremely
valuable for predicting the utility and assessing the success of surgical inter-
ventions such as revascularization. Thus the measurement of local myocardial
deformation has potential to be an important diagnostic and prognostic tool for
the evaluation of a large number of patients.
The deformation of the human heart wall has been quantified via the at-
tachment of physical markers in a select number of human subjects [75]. This
approach provided valuable information but is far too invasive to be used in the
clinical setting. With the development of magnetic resonance imaging (MRI) tag-
ging techniques, noninvasive measurements of myocardial wall dynamics have
been possible [76].
