Unresolved issues regarding myocardial viability

Dr. Muhammad Ayub, FCPSDiplomate Certification Board of Nuclear Cardiology

Diplomate Board of Cardiovascular Computed Tomography

Assistant Professor of Cardiology

Myocardial ViabilityKey questionsWhat is Viable Myocardium?Why to Detect?What can it predict?How to Detect?Which technique is better?

Viable MyocardiumNormal Reversible IschaemiaPartial Thickness InfarctionPartial Thickness Infarction + IschaemiaHibernatingStunning

Why to Detect?• Ischemic LV dysfunction is common cause of cardiac failure

resulting in bad prognosis.

• Patients with ischemic LV dysfunction and viable myocardium often improve after revascularization.

• Numerous studies have suggested that identification of viable myocardium also predicts improved survival following revascularization

What it can predict?Viability and PrognosisBased on 20 Studies (n=2362)

Viable Myocardium

Scarred Myocardium

1.0

0.8

0.6

0.4

0.2

0.0

Years from Randomization0 1 2 3 4 5 6

HR 95% CI P0.61 0.44,0.84 0.003

Card

iova

scul

ar M

orta

lity

Rate

Without viabilityWith viability

Without viability

With viability

Myocardial Viability and Cardiovascular Mortality

Univariate Multivariable

Chi-square p value Chi-square p value

8.81 0.003 0.91 0.339

114 99 85 80 63 36 16487 432 409 371 294 188 102

How to Detect viable Myocardium?Physiological Basis

Contractile ReservePreserved Cellular MetabolismCell Membrane Integrity

Contractile Reserve

Dobutamine Stress EchocardiographyGated Myocardial Perfusion SPECTDobutamine MRI

Dobutamine Echocardiography

Biphasic response to Dobutamine

Stress Echocardiography

Studies= 19 (n=448)Sensitivity: 84%

Specificity: 81%

Contractile Reserve with Gated SPECT for Myocardial Viability

·Both perfusion and wall motion detection.

·LV EF and ventricular volumes calculation.

·3-D display of endocardial, epicardial or of both.

·Regional quantitation by its polar map system.

GSPECT with Low Dose DobutamineBaseline GSPECT studyLow dose dobutamine SPECT study

Areas with contractile reserve – ViableAreas without contractile reserve -- Scar

Preserved Cell Metabolism

Glucose F-18 FDG

Free Fatty Acids I-123 BMIPP

C-11 Palmitate

C-11 Acetate

PET Perfusion and Metabolism

Perfusion

Metabolism

PET Perfusion /Metabolism Mismatch

Ghosh N et al. Eur Heart J 2010;eurheartj.ehq361

PET Perfusion /Metabolism Match

Ghosh N et al. Eur Heart J 2010

F-18 FDG PET

Studies= 11 (n=332)

Sensitivity: 88%Specificity: 73%

Cell Membrane Integrity

Imaging of choice, where PET is not available.

Thallium (Tl -201 ) or Tc-99m MIBI are commonly radioisotopes used for this purpose.

Cellular uptake of Tl-201 and Tc-99m Sestamibi is dependant on intact cell membrane.

Protocol of Tl-201 for HM

Stress, redistribution, and 24 hours delayed imaging.

Stress, redistribution, and reinjection imaging.

Stress, immediate reinjection, and redistribution imaging.

Rest and redistribution imaging.

Rest Redistribution Tl-201 SPECT

Rest Redistribution Tl-201 SPECTScar Myocardium

Tc-99m MIBI Second most commonly used perfusion agent. It enters passively through the cell membrane. Concentration in cytosol is 5:1, whereas it

increases up to 300:1 in mitochondria.Tc-99m Sestamibi does not redistribute after initial

uptakeAdministration of nitrates prior to Sestamibi

injection improves uptake in viable areas

Nitrates and Viability

Other Agents

Improvement with administration of nitrates as well as trimetazidine

TrimetazidineTricardin

Comparison of various techniques for the prediction of recovery of regional function after revascularization.

Ghosh N et al. Eur Heart J 2010

Cardiac MRI for myocardial viability

One of the non-invasive technique for viability.

High spatial and temporal resolutionSignificant concordance between Gated

MRI and post-revascularization findings.

time

N Myocardium

Gdinjection

infarct

1st pass Delayed enhancement

MR Assessment of Myocardial Viability

MDCT for Myocardial Viability

Final wordAll available techniques have good sensitivity

and specificity for detection of myocardial viability.

Techniques using contractile reserve are more specific but nuclear techniques are sensitive for assessment of myocardial viability.

Thank You for listening