Myocardial Viability in Ischemic Heart DZ: Assessment before Revascularization Intervention

1. Myocardial Viability in Ischemic Heart DZ:Assessment before Revascularization Intervention By: Ri黃彥霖

2. Outline • Introduction and definitions • Imaging Techniques • Conclusions

3. Introduction • Coronary heart dz. LV dysfunction heart failure death • Important determinant of prognosis: • LV function & LV myocardial viability • Outcome of medical tx remains poor • Revascularization intervention: • PCI or CABG • A promising treatment • Risk & perioperative mortality VS. Benefits

4. Introduction • In the last 2 decades, improvements in the use of imaging techniques to detect and assess myocardial viability, metabolism, perfusion, and function has made assessment before intervention possible

5. Definitions • Viable myocardium • Myocardial cells that are simply “alive” • No regard to functions, no clinical implications • Stunned myocardium • Temporary contractile dysfunction of viable myocardium caused by a brief period of ischemia followed by restoration of perfusion • Proposed hypothesis for temporary dysfunction • Oxyradical hypothesis & Calcium hypothesis • Lasts from an hour to days • Function ultimately returns to normal with normal perfusion

6. Definitions • Hibernating myocardium • Contractile dysfunction due to chronic reduced blood flow • Partially or completely recovery function after revascularization • Scarred/Infarcted myocardium • Nonviable myocardium with no remaining myocytes • Irreversible damage, will not recover even after reperfusion To attain the maximal benefits with minimal risk in patients with ischemic heart dz, determination of myocardial viability is important

7. Assessment Imaging Techniques

8. Angiography • Earliest imaging for assessment of ventricular function and coronary artery patency • Preoperative coronary angiography and contrast ventriculography • Important indicators of prognosis • Determine causal relationship between ventricular dysfunction and coronary anatomy • Determination between PCI or CABG • Noninvasive imaging techniques are now becoming more popular

9. Echocardiography • Function & Viability • Detect LV wall motion defects • Performed at rest and immediately after stress • Stress methods • Exercise: treadmill or bicycle • Bruce, Cornell, Naughton protocols • Pharmacological: dobutamine • Low dose 5~10μg/kg/min increase to higher dose every 3 minutes

10. Echocardiography • Increase in systolic contraction at low dose dobutamine  presence of viable myocardium • New regional wall motion defects, decline in EF, increase in end-systolic volume with stress  myocardial ischemia

11. SPECT • Perfusion & Viability • Evaluate myocardial regional radioisotope uptake and regional blood flow in response to stress • Stress: blood flow up to 5x • Exercise • Pharmacological: adenosine or dipyridamole

12. Thallium-201 SPECT • Potassium analogue, uptake by viable cells • The degree of uptake is related directly to the coronary blood flow • “Redistribution” • Region of ischemia initially appears as area of reduced uptake apparently normal over time • Region of infarction no redistribution on delayed image. • Redistribution protocols • Stress-4 hr redistribution protocol • Late-redistribution protocol (18 to 24 hrs) • Reinjection protocol • Rest-redistribution

13. Technetium-99m SPECT • Similar to Thallium-201, uptake by viable cells • Higher photon energy & shorter half-life, lower radiation, allowing larger dose of injection higher quality scan with fewer artifacts • Three Tc-labeled agents: sestamibi (most frequent) teboroxime tetrofosmin

14. PET • Myocardial perfusion Nitrogen-13 ammonia, oxygen-15 water, rubidium-82 • Myocardial Metabolism fluorine-18 deoxyglucose(FDG) (detection and quantification of exogenous glucose utilization) • Regarded as the gold standard for assessment of myocardial viability, but clinical application is limited due to the lack of cyclotron for production of radiopharmaceuticals

15. PET Metabolism Perfusion

16. MRI • Myocardial perfusion: • Inject contrast and continuously scanning the heart • Relative perfusion deficits in regions of low signal intensity • Myocardial viability: • Inject extracellular paramagnetic contrast agent: Gadolinium-DTPA • The proposed mechanism: contrast collection in interstitial edema associated with cell necrosis and capillary plugging • Imaging 10 to 20 min after contrast injection • Late enhancement regions of myocardial necrosis and irreversible injury • No late enhancementviable

17. MRI Gadolinium-DTPA

18. Radionuclide Angioventriculography • Assessment of ventricular function • Recording the movement of a bolus radionuclide (usually Tc-99m) during the first pass through the central circulation • Often used for the assessment of ventricular function before and after revascularization

19. Comparison of Imaging Techniques

20. Comparison of Imaging Techniques

21. Prognosis • How much hibernating myocardium must be present for an improvement in LVEF after revascularization to become evident?  Studies ranging from 8% to 53% with a mean of 22%.

22. Prognosis Most studies considered LVEF of 5% as significant

23. Prognosis Hib = hibernation Rev = revascularization Med = medical treatment

24. ClinicalAlgorithm

25. Thanks for Your Attention !

26. References • “Imaging Techniques for the Assessment of Myocardial Hibernation”, European Heart Journal, 2004 (25), 815-836 • “Noninvasive Imaging of Myocardial Viability: Current Techniques and Future Developments”, Circulation Research 2003 (93), 1146-1158 • “Role of Myocardial Perfusion Imaging for Risk Stratification in Suspected or Known Coronary Artery Disease”, Heart 2003 (89), 1291-1297 • Harrison’s Principle of Internal Medicine, Ch. 211 & Ch. 226