MYOCARDIAL Viability assessment

1. ASSESSMENT OFVIABILITY: which
test for whom ?
PRESENTED BY – DR SIVANAND PATEL (DM
CARDIOLOGY – MAMC & GB PANT , NEW DELHI )

2. Mechanisms of acute and chronic adaptation to a temporary or
sustained reduction in coronary blood flow include
• Stunning
• Hibernation
• Ischemic preconditioning
Braunwald’s Heart Disease_ A Textbook of Cardiovascular Medicine (2018, Elsevier) 11th edition ch 16 page 291 -294

3. Stunned myocardium
• Observed after transient period of ischemia followed by reperfusion
(depressed function at rest but preserved perfusion)
• Regional myocardial function remains depressed for up to 6 hours after
resolution of ischemia following a 15-minute occlusion in the absence of
tissue necrosis
• Observed soon after coronary occlusion and reperfusion in the setting of
acute MI.
Braunwald’s Heart Disease_ A Textbook of Cardiovascular Medicine (2018, Elsevier) 11th edition ch 16 page 291 -294

4. Hibernating myocardium
• Adaptive response of myocardium to chronic or repetitive
episodes of ischemia resulting in reduced myocardial
function at rest (depressed function at rest and decreased
perfusion)
• Hibernation and stunning coexist
Braunwald’s heart disease_ a textbook of cardiovascular medicine (2018, elsevier) 11th edition ch 16 page 291 -294

5. Myocardial Viability
• Requirements for cellular viability include
(1) sufficient myocardial blood flow
(2) cell membrane integrity
(3) preserved metabolic activity
Braunwald’s Heart Disease_ A Textbook of Cardiovascular Medicine (2018, Elsevier) 11th edition ch 16 page 291 -294

6. Key non invasive methods to
identify viability
• 1.Echocardiography
• 2.Single Photon Emission Computed Tomography
• 3.Positron Emission Tomography
• 4.Magnetic Resonance

7. Echocardiography
Major techniques employed include:
• Dobutamine stress
• Myocardial contrast
• Adenosine speckle tracking stress echocardiography
Assessment of Myocardial Viability: A Review of Current Non Invasive Imaging Techniques Ahmed talib et al march 2014

8. Echocardiography
Resting echo: Diastolic wall thickness >= 6 mm supports viability
Stress Echo:
• Commonly used criterion to identify viable myocardium is by detection of
contractile reserve
• Stress achieved by using dobutamine, adenosine or dipyridamole
• An infusion of low-dose dobutamine (5–10 mg/ kg/min) results in increased
contractile function of viable segments whereas nonviable ones do not show such
response
• Myocardial viability can also be detected when using the biphasic response
(enhanced activity at low dose dobutamine suggesting viability and reduced
function at high dose dobutamine suggesting ischemia)
Assessment of Myocardial Viability: A Review of Current Non Invasive Imaging Techniques Ahmed talib et al march 2014

13. Abn

17. • Diagnostic accuracy of dobutamine echocardiography reduces with
increasing severity of regional and global LV dysfunction
• That is, the technique underestimates the extent of viability: 39% of all
recovering LV segments failed to exhibit inotropic contractile reserve
Pagano et al. Heart 1998;79:281-288
• Low-dose dobutamine failed to identify 45% of segments that ultimately
regained function 6 month post revascularisation (poor sensitivity)
• At the same time, specificity for identification of viability >90%
Wiggers et al. Am. Heart. J. 2000, 140, 928–
936.

18. • Hence, while evidence of viability on DSE is a strong predictor
of likelihood of recovery post-revascularisation; absence of
viability especially in severe LV dysfunction patients may not
accurately predict those who will not benefit from
revascularisation

19. CONTRAST ECHOCARDIOGRAPHY
• Use intravenous micro-bubble contrast
• Demonstrate viability qualitatively
• Micro-bubbles are
 inert gases and stay in the vascular space
 behave like red blood cells
• Segments that have
 normal or patchy perfusion - viable
 no perfusion - non-viable
Assessment of Myocardial Viability: A Review of Current Non Invasive Imaging Techniques Ahmed talib et al march 2014

20. Wolfgang Lepper. Circulation. Myocardial Contrast Echocardiography,
Volume: 109, Issue: 25, Pages: 3132-3135, DOI:
(10.1161/01.CIR.0000132613.53542.E9)

21. ADENOSINE SPECKLE TRACKING
• With adenosine stress
Viable segments - increase their longitudinal strain
Non-viable – Unchanged
Ran H,et al. Clinic value of Two-Dimensional Speckle Tracking Combined with Adenosine
Stress Echocardiography for Assessment of Myocardial Viability.Echocardiography
2012;29:688-94.

22. Limitation and advantages
• Limitations of echocardiography ;
 • Operator dependence, both in data acquisition, and interpretation,
 • Adequate acoustic window acquisition - has greatly improved by using
contrast agents.
• Advantages of stress echocardiography
 • Good validity,
 • Wide availability,
 • Cost effectiveness,
 • Lack of ionizing radiation, and
 • Being friendly with implanted devices.
Assessment of Myocardial Viability: A Review of Current Non Invasive Imaging Techniques Ahmed talib et al march 2014

23. Prognostic value
• The VIAMI-trial (2012), Viability-Guided Angioplasty After Acute Myocardial Infarction RCT
• Investigating a viability-guided invasive approach in
• 261 patients recruited
• At least 48 hours after an acute MI who then underwent LDDE for the
• Detection of viability within 72 hours of MI
• Those with a viable myocardium randomized to invasive or conservative treatment
• The primary endpoint was the composite of death from any cause, recurrent MI and unstable
angina at 1-year follow-up.
• An invasive approach in patients with a high viability score had a substantial reduction in
ischemic events vis-à-vis conservative strategy
• Patients with low / no viable myocardium had low recurrent ischemia rates despite conservative
strategy
Assessment of Myocardial Viability: A Review of Current Non Invasive Imaging Techniques Ahmed talib et al march 2014

24. SPECT
• Administration of a radioactive tracer - thallium-201 or technetium Tc-99m (sestamibi
& tetrofosmin)
• Criterion for viable myocardium:
• Tracer activity of >50% and
• Redistribution of >10% in dysfunctional segments used as markers of
viability as a consequence of preserved membrane integrity (detected by thallium
SPECT)
• Tracer activity of >50% and improvement in tracer uptake after nitrates administration
is also taken as a markers of viability (as detected by technetium SPECT).
Assessment of Myocardial Viability: A Review of Current Non Invasive Imaging Techniques Ahmed talib et al march 2014

25. Standard SPECT imaging display.
A, The short-axis images
represent a portion of the
anterior, lateral, inferior, and
septal walls.
B, Vertical long-axis images
represent the anterior wall,
apex, and inferior wall.
C, Horizontal long-axis images
represent the septum, apex, and
lateral walls.

26. Imaging Protocols forAssessment of
Myocardial Viability
• Presence of 201Tl after redistribution implies preserved myocyte cellular viability
• After 201Tl reinjection, approximately 50% of regions with fixed defects on
stress-redistribution imaging show significant enhancement of 201Tl uptake ->
improvement in regional LV function .
• The presence of a severe 201Tl defect after reinjection -> very low probability of
improvement in function .
Assessment of Myocardial Viability: A Review of Current Non Invasive Imaging Techniques Ahmed talib et al march 2014

27. 201Tl rest redistribution
• Here we compare images between 3- to 4-hour versus 15- to 20-
minute images.
• Identification of a "reversible resting defect” reflects preserved
viability
• Less sensitive but specific sign of potential improvement in regional
function (good when shows viability)

28. 201Tl reinjection
• If severely hypoperfused, initial uptake very low & Redistribution
depends on the continued delivery of the tracer over the 3–4 hr period
• If blood concentration of tl- 201 decreases rapidly a fixed defect may
be seen due to insufficient delivery of the tracer (false negative for
viability)
• Second low dose rest injection of thallium with delayed imaging after
this repeat injection will give myocytes with reduced perfusion the
opportunity to sequester thallium and unmask severely hypoperfused
viable tissue.

29. Late redistribution images
• Third set of images at 24 hours
• Allow for redistribution of the tracer to very ischemic (yet viable) tissue
• It has been shown that 22% of fixed defects (at early redistribution
imaging) demonstrate normal tl-201 uptake at later redistribution
• This may indicate a poorly perfused, yet viable region (increased
sensitivity for viability prediction)
Wu KC, et al. Noninvasive Imaging of Myocardial Viability: Current Techniques and Future
Developments. Circulation Research. 2003;93(12):1146-58.

30. 99mTc-sestamibi and tetrofosmin
Performance 99mtc similar to 201tl.
• Do not share redistribution properties of 201tl
• Normal uptake -> preserved viability;
• Moderate reduction in uptake is -> admixture of viable and infarcted tissue; and
• Severe defect -> infarct.
• Administration of nitrates to improve blood flow at rest before injection of sestamibi
appears to improve ability of these tracers to detect myocardial viability
Assessment of Myocardial Viability: A Review of Current Non Invasive Imaging Techniques Ahmed talib et al march 2014

31. Limitation and advantages
The main limitations of SPECT include
• higher cost compared to echocardiography,
• limited spatial resolution,
• potential difficulty in interpreting results in patients with balanced myocardial
ischemia (3-vessel disease)
• risk of radiation.
The main advantages include
• extensive validation,
• increasing availability,
• good sensitivity and
• lower cost compared to PET
Assessment of Myocardial Viability: A Review of Current Non Invasive Imaging Techniques Ahmed talib et al march 2014

32. INFARCT STRESS INDUCED ISCHAEMIA

33. PET PERFUSION IMAGING
IMAGING OF GLUCOSE METABOLISM.
Principle :
-> glucose utilization may be preserved or increased relative to flow
in hypoperfused but viable (hibernating) myocardium, termed metabolism perfusion
mismatch.
-> Myocardial glucose use is absent in scarred or fibrotic tissue, represented by
metabolism-perfusion match

37. PET- Prognostic value
• A meta-analysis by Beanlands et al of 10 studies involving 1046 patients, found
that, the mortality rate was higher in those who did not undergo revascularization
despite a PET scan confirming significant myocardial viability.
• The annual death rate was 4% in those that had revascularization versus 17% in
those who did not undergo revascularization.
Beanlands RS, et al. Delay in revascularization is associated with increased mortality in patients with severe left
ventricular dysfunction and viable myocardium. Circulation 2010: 108: 1151-6

38. SPECT VS FDG PET
• Brunken et al published data from a comparison of tomographic
thallium images with PET images; 47% of the irreversible thallium
defects were identified as viable on PET images
Circulation. Nov 2002;96(5):1357-69.
• Tamaki et al subsequently confirmed these findings in 2 comparative
studies of SPECT and PET in which 38-42% of the irreversible thallium
defects had enhanced FDG uptake suggestive of viable myocardium.
Am J Cardiol. Oct 2009;104(14):860-5

39. The Combined Value of Perfusion/Metabolism PET
• Combination of perfusion PET and FDG PET - gold-standard for the identification
of hibernating myocardium;
• Region with low perfusion reserve by 13NH3 despite normal FDG uptake is highly
predictive of both functional recovery and survival post-revascularization.

40. Limitation and advantages
Main limitations of PET include
• high cost,
• limited availability
• the use of radio-active tracers
Main advantages include
• established validity
• excellent sensitivity
• Use in severe LV dysfunction as well as balanced ischemia
• Compared with SPECT, PET has better spatial and temporal
resolution, with better quality pictures and less radiation

41. MAGNETIC RESONANCE IMAGING
Gd-DTPA results in contrast enhancement by reducing the T1 of tissue in a
concentration dependent fashion
Healthy cells exclude Gd-DTPA and therefore this agent is restricted to the
extravascular and interstitial spaces
MRI modalities for viability assessment:
• Delayed enhancement (DE), known as late-gadolinium enhancement
(LGE)
• Dobutamine stress (DS-MRI) and
• End-diastolic wall thickness (EDWT)

42. Cardiovascular Magnetic Resonance Imaging
• From early CMR studies:
• End-diastolic wall thickness of 5.5 mm or more and Dobutamine-induced systolic
wall thickening of 2 mm or more have excellent sensitivity and specificity in the
prediction of segmental contractile recovery after revascularization
• Transmural extent of myocardial scar depicts a progressive stepwise decrease in
functional recovery despite successful coronary revascularization, especially in
myocardial regions of akinesia or dyskinesia.

43. DE/LGE techniques -> myocardial perfusion and tissue enhancement by i.v.
administration of gadolinium chelated contrast
• After 5min of contrast agent images are acquired which show regions of myocardial
infarction exhibiting high signal intensity i.e. high contrast enhancement.
• This hyperenhancment is larger in scar tissue/non viable myocardium, than in normal
viable myocardium and correlates inversely with functional recovery of the
myocardium following revascularization.

46. AKINETIC SEGMENT
SCAR ON MRI
NON VIABLE
SCAR AND
AKINESIS WAS
PERSISTENT POST
REVASCULARISATION
IRREVERSIBLE
DYSFUNCTION

47. Limitation and advantages
• The main limitations of CMR include;
• high cost,
• long study time,
• requirement for breath-holding sequences and restrictions in patients with implant
devices and impaired renal function.
• However, advances in MRI technology are holding promises to reduce imaging
time, increase spatial resolution and adapt to scan implanted devices.
• The main advantages of CMR include
• excellent anatomical details using steady state free precision (SSFP) cine
sequences in EDWT,
• good sensitivity/specificity with good interobserver/intraobserver agreement
in DE imaging, and
• excellent sensitivity offered with DS.

48. Prognostic value
• Gerber et al studied 144 patients with ischemic lv dysfunction who had undergone
DE imaging , then either received revascularization with PCI or CABG or were
managed conservatively
• It demonstrated good prediction of survival, which was significantly lower in
patients who did not undergo revascularization.
Gerber BL, et al. Prognostic value of myocardial viability by delayed enhanced magnetic resonance in patients with coronary
artery disease and low ejection fraction: impact of revascularization therapy. JACC. 2012;59(9):825-35.

49. Meta-analysisdemonstratingoutcomeofpatientswithischemicleft
ventriculardysfunctionafterviabilitytesting
Gerber BL, et al. Prognostic value of myocardial viability by delayed enhanced
magnetic resonance in patients with coronary artery disease and low ejection fraction: impact of revascularization therapy. JACC. 2012;59(9):825-35.

50. Comparison of Imaging Techniques for
ViabilityAssessment
• Dobutamine echocardiography is more specific and PET / CMR
techniques have better accuracy
• For patients with more severe LV dysfunction, in whom thinner
myocardial walls are often present, an advantage of PET and CMR is
their better spatial resolution for imaging thinner objects.

51. Ahmed talib et al march 2014

53. Conclusion
• The recommended approach to assess myocardial viability begins with either
dobutamine echocardiography or radionuclide myocardial perfusion imaging, depending
upon availability .
• With severe LV dysfunction and triple vessel disease, PET / CMR more suitable even as
initial strategy
• Before labelling a not-obviously scarred myocardial segment (echo diastolic thickness >=
6mm) as non-viable based on stress echo alone, testing with more sensitive modalities
warranted
• Hence, viable on DSE ----- Revascularise
• Not viable on DSE (and not obviously scarred) ----- Assess further

54. Markers of Viable Myocardium

55. Thankyou….

56. ACC/AHA/ASNC Guidelines for the Clinical Use of Cardiac Radionuclide Imaging—Executive Summary A Report of the American
College of Cardiology/American Heart Association Task Force on Practice Guidelines (ACC/AHA/ASNC Committee to Revise the
1995 Guidelines for the Clinical Use of Cardiac Radionuclide Imaging) ( Circulation. 2003;108:1404–1418.)