ABC | Volume 110, Nº3, March 2018

Review Article Ket et al Practical Implications of Myocardial Viability Studies Arq Bras Cardiol. 2018; 110(3):278-288 Table 1 – Comparison between myocardial viability assessment methods Radiation dose Contrast/tracer redistribution Protocol duration Contrast phases * Sensitivity Specificity Dobutamine echocardiography n/a n/a 30 min n/a 77-89% 68-93% 99m Tc-Sestamibi SPECT Moderate Absent 90 a 120 min Two injections 81% 69% 201 Tálio SPECT High Present 3h with additional 24h imaging if necessary One injection 87% 54% 18 F-FDG PET Moderate Absent 1h One injection 92% 63% Delayed enhancement / coronary computed tomography angiography Moderate Absent 25 minutes Two injections n/a n/a Cardiac magnetic resonance n/a Absent 35 minutes Two injections 92-95% 51-89% n/a: non-applicable; DS: dobutamine-induced stress; Gad: gadolinium delayed enhancement. *Contrast phases are correlated with better evaluation when the contrast is injected in the stress phase only or in both phases, stress and rest phases. SPECT: single-photon emission computed tomography; 18 F-FDG: fluorodeoxyglucose F18; PET: positron-emission tomography Comparison between the techniques: For practical purposes, the most appropriate methods for viability assessment are those in which the clinician or the institution have the highest experience. Echocardiography with dobutamine has, in general, high positive predictive value, and thus, is relatively more specific whereas nuclear medicine techniques are more sensitive to diagnosis, with a significative negative predictive value, as can be seen in the study by Panza et al., 54 who compared the echocardiography and 201 Tálio myocardial scintigraphy methods. Hakimeh et al. 55 evaluated viable kinetic segments by resting 99m Tc‑Sestamibi, and observed that the number of these segments was significantly greater than those showing a contractile response to dobutamine. Hence, due to its greater accessibility, echocardiography may be the method of choice in the screening for the presence of viability, and in a second line of investigation, a nuclear method could be used. 56 99m Tc-Sestamibi has been used as an alternative to 201 Tálio for its higher quality combined with lower exposure to radiation. In cases when 99m Tc-Sestamibi imaging are not conclusive, or when greater viability is still clinically possible, the use of 201 Tálio is indicated for its higher detection rate, especially in severe hypoperfusion areas. 25 An excellent method for assessment of hibernating myocardium is 18 F-FDG PET, for its higher sensitivity in detecting dysfunctional, but viable, myocardium. Although a sensitivity of 93% was shown for this technique in a metanalysis, 35 other authors reported a lower specificity (58%). 57-59 With respect to MR and nuclear medicine techniques, comparison of contrast MR imaging, with dobutamine echocardiography and 201 Tálio rest-redistribution showed an agreement of 83% and 75%, respectively. 60 Klein et al. 51 showed a good agreement between contrast MR and 18 F-FDG PET; in patients with CAD and severely reduced LVEF, MR imaging can identify fibrotic areas with results similar to those obtained by PET measurements, provided by comparison of flow and glucose metabolism. MR also provides other parameters of tissue viability, such as wall thickness, contractile reserve and delayed enhancement. 59-62 In addition, in comparison with CT, MR has higher contrast resolution for soft tissues, without requiring radiation exposure. CT and PET 41 may be an alternative test to MR for patients with pacemakers, implantable cardioverter defibrillator or mechanical cardiac valve. Table 1 summarizes the comparison between these methods of assessment of myocardial viability. Prognosis: Observational studies have suggested that the presence of viable myocardium is directly associated with favorable progress of left ventricular function and good prognosis after revascularization. Patients who seem to benefit more fromsurgical revascularization are those with ischemic symptoms and severe left ventricular dysfunction. A significant perioperative risk should be considered in relation to long-term benefits on mortality. 62-66 Comparison of randomized studies of miocardial viability Today, there is little evidence of randomized studies on this theme, with conflicting results. Stich trial Randomized, multicenter study involving 1,212 patients, 601 assessed for myocardial viability by dobutamine echocardiography (130 patients), SPECT (321 patients) or both (150 patients). 67 In the myocardial viability study, 298 patients were randomly allocated to receive conservative treatment plus surgical revascularization, and 303 patients to receive pharmacological therapy alone. Median follow-up period was 56 months (12 months – 100 months). 67 No statistically significant benefit of surgical intervention on mortality, or of assessment of myocardial viability on surgical intervention, suggesting that investigation of a viable myocardium do not differentiate patients who would benefit from revascularization from those who would benefit from medical therapy alone. 67 284