michael s
(Michael S)
#1
18 What are hibernating and stunned
myocardium? What echocardiographic techniques
are useful for detecting them? How do these
methods compare with others available?
Petros Nihoyannopoulos
The physiologic abnormalities that are associated with resting
myocardial dysfunction and viable myocardium range from
reduced resting myocardial flow and preserved metabolic uptake
of^18 F-2-Deoxyglucose (FDG) (hhiibbeerrnnaattiinngg mmyyooccaarrddiiuumm) to
patients in whom resting myocardial flow is preserved (ssttuunnnneedd
mmyyooccaarrddiiuumm). Animal studies^1 suggest that stunning may
progress to hibernation as part of an adaptive response. As
coronary flow reserve decreases, fasting FDG uptake increases
while resting flow remains normal (chronic stunning). Later on,
during continuing ischaemia, flow is reduced while FDG uptake
continues, characteristic of hibernation.
Assessing myocardial viability is important in coronary artery
disease patients with ventricular dysfunction because its
presence improves left ventricular function and survival
following revascularisation.2,3 Diagnostic methods include
ppoossiittrroonn eemmiissssiioonn ttoommooggrraapphhyy ((PPEETT)), based on the detection of
metabolic activity,^220011 TTll ssiinnggllee--pphhoottoonn eemmiissssiioonn ccoommppuutteedd ttoommoogg--
rraapphhyy ((TTll--SSPPEECCTT)), to assess cell membrane integrity by
rest/redistribution and the assessment of contractile reserve by
ddoobbuuttaammiinnee ssttrreessss eecchhooccaarrddiiooggrraapphhyy. Echocardiography can
assess the presence of myocardial viability by looking at
contractile reserve following inotropic stimulation with
dobutamine (dobutamine stress echocardiography). This differ-
entiates viable myocardium (presence of contractile reserve) from
non-viable scarred myocardium (absence of contractile reserve)
in patients with ventricular dysfunction at rest. More recently,
mmyyooccaarrddiiaall ccoonnttrraasstt eecchhooccaarrddiiooggrraapphhyy ((MMCCEE))has been proposed
as a method to assess myocardial perfusion and viability.
Myocardial opacification produced by the presence of
microbubbles in the coronary microcirculation has been
considered synonymous with preserved microvascular integrity.
Using detailed histology from explanted hearts in patients
undergoing heart transplantation, Baumgartner et al. compared
PET, SPECT and echo to detect viable myocardium^4. While
