Nuclear Cardiology in Viability Assessment

1. Nuclear CardiologyinViability Assessment V. R. Dabbagh , M.D. Associate Professor DSNMC NMRC; MUMS www.DSNMC.ir No:1/4; Mollasadra 11; Mollasadra Blvd; Mashhad; IRAN Tel:+98(51) 38411524; +98(51)38472927

2. Nuclear Cardiology & Hibernating Medical vs. Revascularization management Nuclear Medicine Procedures Some differences with other modalities

3. Hibernating myocardium Persistently impaired function at rest (wall motion and thickening ) & Reduced coronary blood flow.

4. Hibernating myocardium • Moderate to severe LV dysfunction: • Morbidity and mortality : • Revascularization??? • The important clinical issue • Viable myocardium identified • and revascularized: • Improvement in • LV function and survival

5. Meta-Analysis 3088 Pts

6. Viability Assessment • Dobutamine echocardiography; • Contractile reserve • Myocardial Perfusion SPECT • Gated Myocardial Perfusion SPECT • PET

7. Nuclear Medicine Techniques • Gated myocardial perfusion SPECT • Tl201 Imaging: • Stress---3-h re-distribution • Stress--------24h re-distribution • Stress----- Re-injection: The best Protocol: assessment of both stress-induced ischemia and viability • Rest------- re-distribution: Only assessment of Viability • Tc99m-Sestamibi Imaging • PET • 18F-FDG-PET (FDG-blood flow mismatch)

8. Myocardial Perfusion SPECT & Viability • Viable: • Membrane integrity • Electromechanical gradients across sarcolemma In theory imaging agents that reflect regional myocardial BF and membrane integrity should provide good information regarding tissue viability.

9. Modifications in 201Tl Imaging protocols • Late Tl-201 Redistribution Imaging • Redistribution is a continual process • 22%-54% of irreversible defects at 3-4-hr after stress show reversibility at 24-hr • Tl-201 Re-injection Imaging • Greater accuracy for detection of viability

10. Evaluate for ischemia Stress induced Ischemia and hinbernation

11. Modifications in 201Tl Imaging protocols • Rest-Redistribution Tl-201 imaging • Only for assessment of viability of the regions with systolic dysfunction • Accurate viability data: • NPV>90% • Defect • Reversibility: better predictor • Level of Tl-201 activity: Mild persistent defect • No assessment of stress-induced ischemia

12. Tl-201: Rest Redistribution

13. Tl-201 vs FDG PET • Bonow and coworkers: Tl 201 reinjection imaging has an 88% concordance with 18FDG PET imaging.

14. Tc99m-Sestamibi Imaging • No redistribution after its initial uptake • Underestimates of viability in chronic CAD and LV dysfunction • Excellent as a perfusion agent for assessment of inducible ischemia • Useful for viability: quantitative analysis of Tc99m-MIBI uptake at rest

15. Enhance the Use ofTc-99m Sestamibi as a Viability Agent 1- Nitrates: improve collateral blood flow to hypoperfused areas • Meta-analysis: nitrate-enhanced sestamibi imaging : a sensitivity of 86% and a specificity of 83% in predicting myocardial viability. 2- ECG-Gated SPECT: Concomitant assessment of ventricular function 3- A novel approach: acquiring ECG-gated SPECT images at • baseline and • during low dose dobutamine infusion • looking not only at tracer uptake, but also at changes in wall motion to assess contractile reserve.

16. Gated SPECTViability assessment Levin et al. showed Gated SPECT Increase sensitivity and overall accuracy of viability detection compared to the SPECT

17. Perfusion agent FDG 18F-FDG Imaging • In viable myocardium: • Metabolic substrate: greater glucose use rather than use of fatty acids or lactate • FDG-PET ----- Blood Flow Imaging • Mismatched defect • Accurate marker

18. Medial Basal Apical Medial Basal Apical Metabolism – Hibernation Perfusion (99mTc-MIBI-SPECT) Glucose Metabolismus (18F-FDG-PET)

20. Perfusion-Metabolism-Mismatch Di Carli et al., Am J Cardiol 1993

21. PET Metabolic Imaging: Assessment of viability • Extent and magnitude of the FDG-blood flow mismatch • predict the magnitude of recovery in global LV function after revascularization

22. Perfusion agent FDG Normal myocardium

23. Perfusion agent FDG Hibernating Myocardium Defect

24. Perfusion agent FDG Infarcted Myocardium Defect Defect

25. Viability assessment • Heart transplant centers: often use PET to determine those patients in whom coronary artery bypass grafting can be performed rather than transplantation. • 30 to 50% of patients referred for transplantation have hibernating myocardium based on PET. • These patients do well when revascularized.

26. Viability assessment • Haas and coworkers: • Patients sent to surgery with no viability assessment: significantly worsened postoperative course, including a lower 12-month survival rate, 79% versus 97%

27. Hibernating myocardium Nuclear Techniques • CAD: • Nuclear imaging appears to require fewer viable cells for detection • Higher sensitivity but a lower specificity than stress echocardiography for predicting post-revascularization improvement of ventricular function. • Because the gold standard in the papers was improvement of LV function after revascularization • . LV functional improvement may not always be necessary for clinical improvement

28. Stress Echo • There may be a critical mass of myocardium: detect viability in: • Stress echocardiography • Functional improvement after revascularization. • More histologically viable cells : for a segment to exhibit viability as compared to the NM techniques. • Segments with 25% viable myocytes showed evidence of viability with: • Stress echo in only 19% of cases, • FDG PET or Tl-201 SPECT in more than 33%of cases • Radionuclide imaging techniques: • Require fewer viable cells to show viability, which in many cases may be insufficient to, at least initially, show functional improvement after revascularization.

29. Viability assessment • The principal goal of myocardial viability assessment: • Identify patients whose symptoms and natural history may improve after revascularization.

30. Prognostic Implications of FDG PET Myocardial Imaging • Up to 50% with perfusion-metabolic mismatch defects: a cardiac event in 12 months in the absence of intervention • The greater the number of mismatched segments, the greater the risk for subsequent cardiac event • Predictive after Revascularization: • For improvement in heart failure symptoms • Significant improvement in survival

31. Nuclear Medcine Techniques • Preservation of the small areas viability detected by perfusion imaging techniques may improve clinical outcome by • Stabilizing the electrical milieu & preventing lethal arrhythmias • Preventing a subsequent MI • Improving symptoms and functional capacity through prevention of deleterious myocardial dilation and remodeling.

32. ???????? • The extent of viability needed for a patient to benefit from revascularization is unclear and may vary in different clinical circumstances. • It is not clear that improvement of ventricular function, regional or global, is necessary :for patient benefit.