Association of myocardial viability on nitrate-augmented technetium-99m hexakis-2-methoxylisobutyl isonitrile myocardial tomography and intermediate-term outcome in patients with prior myocardial infarction and left ventricular dysfunction

Phase analysis of gated myocardial perfusion single-photon emission computed tomography after coronary artery bypass graft surgery: reflection of late reverse remodeling in patients with patent grafts after coronary artery bypass graft surgery

OBJECTIVE

Phase analysis using gated myocardial perfusion single-photon emission computed tomography (GMPS) is a tool used to assess left ventricular (LV) dyssynchrony. We attempted to investigate the role of LV dyssynchrony assessed by GMPS using phase analysis for the late LV function after coronary artery bypass graft surgery (CABG) in patients with patent grafts.

METHODS

A total of 45 patients who received off-pump CABG with patent graft 1 year after CABG and preserved perfusion reserve were enrolled retrospectively. All patients underwent GMPS before and 3 months and 1 year after CABG. Using the Emory Cardiac Toolbox, both phase histogram bandwidth (PBW) and phase SD derived by phase analysis were used for the analysis, in addition to the conventional perfusion parameters. For the evaluation of LV function, transthoracic echocardiography was also performed.

RESULTS

All of the patients showed perfusion improvement (paired t-test, P<0.05) after CABG. Nonetheless, 30 of 45 patients showed LV dyssynchrony 3 months after CABG. One year after CABG, however, 25 out of 45 patients showed reverse remodeling. Among those patients with reverse remodeling, 19 patients had shown LV 3 months after CABG. Using stepwise logistic regression with forward selection, PBW 3 months after CABG could predict reverse remodeling 1 year after CABG (odds ratio 1.03, P<0.05). Using receiver operating characteristic analysis, PBW 3 months after CABG had the largest area under the curve to detect reverse remodeling 1 year after CABG with a cut-off value of 82 (sensitivity 0.95, specificity 0.56, P<0.001).

CONCLUSION

Postoperative LV dyssynchrony assessed by GMPS using phase analysis may reflect late reverse remodeling and potential of further functional improvement in patients with patent grafts and preserved perfusion reserve after CABG.

Long-term effects of percutaneous coronary intervention of the totally occluded infarct-related artery in the subacute phase after myocardial infarction

BACKGROUND

Despite observations suggesting a benefit for late opening of totally occluded infarct-related arteries after myocardial infarction, the Occluded Artery Trial (OAT) demonstrated no reduction in the composite of death, reinfarction, and class IV heart failure over a 2.9-year mean follow-up. Follow-up was extended to determine whether late trends would favor either treatment group.

METHODS AND RESULTS

OAT randomized 2201 stable patients with infarct-related artery total occlusion >24 hours (calendar days 3-28) after myocardial infarction. Patients with severe inducible ischemia, rest angina, class III-IV heart failure, and 3-vessel/left main disease were excluded. We conducted extended follow-up of enrolled patients for an additional 3 years for the primary end point and angina (6-year median survivor follow-up; longest, 9 years; 12 234 patient-years). Rates of the primary end point (hazard ratio, 1.06; 95% confidence interval, 0.88-1.28), fatal and nonfatal myocardial infarction (hazard ratio, 1.25; 95% confidence interval, 0.89-1.75), death, and class IV heart failure were similar for the percutaneous coronary intervention (PCI) and medical therapy alone groups. No interactions between baseline characteristics and treatment group on outcomes were observed. The vast majority of patients at each follow-up visit did not report angina. There was less angina in the PCI group through early in follow-up; by 3 years, the between group difference was consistently <4 patients per 100 treated and not significantly different, although there was a trend toward less angina in the PCI group at 3 and 5 years. The 7-year rate of PCI of the infarct-related artery during follow-up was 11.1% for the PCI group compared with 14.7% for the medical therapy alone group (hazard ratio, 0.79; 95% confidence interval, 0.61-1.01; P=0.06).

CONCLUSIONS

Extended follow-up of the OAT cohort provides robust evidence for no reduction of long-term rates of clinical events after routine PCI in stable patients with a totally occluded infarct-related artery and without severe inducible ischemia in the subacute phase after myocardial infarction.

Radionuclide Imaging of Viable Myocardium: Is it Underutilized?

Coronary artery disease is the major cause of heart failure in North America. Viability assessment is important as it aims to identify patients who stand to benefit from coronary revascularization. Radionuclide modalities currently used in the assessment of viability include (201)Tl SPECT, (99m)Tc-based SPECT imaging, and (18)F-fluorodexoyglucose ((18)F-FDG)-PET imaging. Different advances have been made in the last year to improve the sensitivity and specificity of these modalities. In addition, the optimum amount of viable (yet dysfunctional) myocardium is important to identify in patients, as a risk-benefit ratio must be considered. Patients with predominantly viable/hibernating myocardium can benefit from revascularization from a mortality and morbidity standpoint. However, in patients with minimal viability (predominantly scarred myocardium), revascularization risk may certainly be too high to justify revascularization without expected benefit. Understanding different radionuclide modalities and new developments in the assessment of viability in ischemic heart failure patients is the focus of this discussion.

Myocardial viability and survival in ischemic left ventricular dysfunction

BACKGROUND

The assessment of myocardial viability has been used to identify patients with coronary artery disease and left ventricular dysfunction in whom coronary-artery bypass grafting (CABG) will provide a survival benefit. However, the efficacy of this approach is uncertain.

METHODS

In a substudy of patients with coronary artery disease and left ventricular dysfunction who were enrolled in a randomized trial of medical therapy with or without CABG, we used single-photon-emission computed tomography (SPECT), dobutamine echocardiography, or both to assess myocardial viability on the basis of prespecified thresholds.

RESULTS

Among the 1212 patients enrolled in the randomized trial, 601 underwent assessment of myocardial viability. Of these patients, we randomly assigned 298 to receive medical therapy plus CABG and 303 to receive medical therapy alone. A total of 178 of 487 patients with viable myocardium (37%) and 58 of 114 patients without viable myocardium (51%) died (hazard ratio for death among patients with viable myocardium, 0.64; 95% confidence interval [CI], 0.48 to 0.86; P=0.003). However, after adjustment for other baseline variables, this association with mortality was not significant (P=0.21). There was no significant interaction between viability status and treatment assignment with respect to mortality (P=0.53).

CONCLUSIONS

The presence of viable myocardium was associated with a greater likelihood of survival in patients with coronary artery disease and left ventricular dysfunction, but this relationship was not significant after adjustment for other baseline variables. The assessment of myocardial viability did not identify patients with a differential survival benefit from CABG, as compared with medical therapy alone. (Funded by the National Heart, Lung, and Blood Institute; STICH ClinicalTrials.gov number, NCT00023595.).

Fractional flow reserve and myocardial viability as assessed by SPECT perfusion scintigraphy in patients with prior myocardial infarction

BACKGROUND

In patients with previous myocardial infarction (MI), assessment of myocardial viability and physiological significance of coronary artery stenoses are essential for appropriate guidance of revascularization. The aim of the study was to evaluate the relation between fractional flow reserve (FFR) and myocardial viability as assessed by gated SPECT MIBI perfusion scintigraphy in patients with previous MI undergoing elective PCI.

METHODS

The study population consisted of 26 patients (mean age 55 ± 7 years; 21 male) with a previous MI and a significant coronary stenosis in a single infarct-related coronary vessel for which PCI was being performed. In all patients, FFR was evaluated before and immediately after PCI. SPECT imaging was done before and 3 ± 1 months after PCI. A region representing the MI was considered viable if MIBI uptake was ≥55% of the normal region. Improvement in perfusion after revascularization was considered achieved if perfusion abnormalities decreased by 5% or more and there was a decrease in segmental score of ≥1 in three segments in PCI-related vascular territory.

RESULTS

Extent of perfusion abnormalities decreased from 32 ± 16% to 27 ± 19% after PCI (P < .001). In patients with myocardial viability in comparison to patients with no viability, there was significant difference in FFR before PCI (.57 ± .14 vs .76 ± .12, P = .002), despite almost the same values of diameter stenosis of infarct-related artery (63 ± 8% vs 64 ± 3%, respectively, P = .572). In addition, FFR prior to PCI was related to improvement in perfusion abnormalities after revascularization (P = .047), as well as with peak activity of creatine-kinase measured during previous MI (r = .56, P = .005).

CONCLUSION

Lower values of FFR before angioplasty are associated with myocardial viability and functional improvement as assessed by SPECT perfusion scintigraphy.

Quantity of viable myocardium required to improve survival with revascularization in patients with ischemic cardiomyopathy: A meta-analysis

BACKGROUND

This meta-analysis was conducted to determine optimal cutoff values for the assessment of viability using various imaging techniques for which revascularization would offer a survival benefit in patients with ischemic cardiomyopathy (ICM).

METHODS AND RESULTS

We searched five electronic databases to identify relevant studies through December 2008. Relative risks of cardiac death, both in patients with and without viability, were calculated in each study. In order to estimate the optimal threshold for the presence of viability, we assumed a linear relationship between the amount of viable myocardium and survival benefit of revascularization. Twenty-nine studies (4,167 patients) met the inclusion criteria. The optimal threshold for the presence of viability was estimated to be 25.8% (95% CI: 16.6-35.0%) by positron emission tomography using 18F-fluorodeoxyglucose-perfusion mismatch, 35.9% (95% CI: 31.6-40.3%) by stress echocardiography using contractile reserve or ischemic responses, and 38.7% (95% CI: 27.7-49.7%) by single photon emission computed tomography using thallium-201 or technetium-99m MIBI myocardial perfusion.

CONCLUSIONS

The calculated amount of viable myocardium determined to lead to improved survival was different among imaging techniques. Thus, separate cutoff values for imaging modalities may be helpful in determining which patients with ICM benefit from revascularization.

Nitrate-augmented myocardial perfusion imaging for assessment of myocardial viability: recent advances

Nitrate-augmented myocardial perfusion imaging has been demonstrated to improve the detection of myocardial viability and accurately predicts recovery of left ventricular (LV) function in patients with severe coronary artery disease and LV dysfunction. Recently, several studies showed the prognostic utility of nitrate imaging in evaluation of event-free survival in ischemic LV dysfunction. Furthermore, the diagnostic power of nitrate imaging compared with positron emission tomography or MRI, as well as the mechanism of nitrate-enhanced imaging, were also studied. We describe recent studies using nitrate-augmented myocardial perfusion imaging for the assessment of myocardial viability.

Incremental prognostic value of cardiac single-photon emission computed tomography after nitrate administration in patients with ischemic left ventricular dysfunction

BACKGROUND

We evaluated the incremental prognostic value of viability assessment by nitrate single-photon emission computed tomography (SPECT) in patients with ischemic left ventricular (LV) dysfunction.

METHODS AND RESULTS

One hundred and sixty-four patients with previous myocardial infarction and LV dysfunction (ejection fraction 29% +/- 15%) underwent two Tc-99m sestamibi SPECT studies, under control conditions and after sublingual nitrate administration, for evaluation of myocardial viability. In each patient, viability was defined as the presence of > or = 2 severely dysfunctional segments with preserved tracer uptake (> or = 55% of peak activity). Cardiac death, myocardial infarction, and late (> 2 months) revascularization were considered events. Follow-up was 98% complete at a mean period of 30 +/- 24 months. At baseline SPECT, 119 (73%) patients had evidence of viable myocardium, while 45 (27%) did not. Of these latter patients, 18 (40%) had evidence of viability after nitrate administration. Cardiac events occurred in 58 (35%) patients. Cumulative probability of event-free survival was similar in patients with and without viability at baseline SPECT (log rank 0.3, P = NS), while it was lower in patients with viability at nitrate SPECT compared to those without (log rank 6.3, P < .01). The addition of nitrate SPECT data significantly improved the prognostic power of the model including clinical, functional, angiographic, and baseline SPECT data (P < .01).

CONCLUSIONS

In patients with previous myocardial infarction and LV dysfunction, nitrate SPECT imaging provides incremental prognostic information over those obtained from clinical, functional, angiographic variables, and baseline SPECT data.

Comparison of the prognostic value of SPECT after nitrate administration and metabolic imaging by PET in patients with ischaemic left ventricular dysfunction

PURPOSE

We compared the prognostic value of 99mTc-tetrofosmin single-photon emission computed tomography (SPECT) after nitrate administration and positron emission tomography (PET) with 18F-fluorodeoxyglucose (FDG) in patients with ischaemic left ventricular (LV) dysfunction.

METHODS

Eighty-nine patients with previous myocardial infarction and LV dysfunction (LV ejection fraction 33 +/- 10%) underwent 99mTc-tetrofosmin SPECT under control conditions (baseline) and after sublingual administration of 10 mg of isosorbide dinitrate (nitrate). Within 1 week, all patients underwent PET imaging with 18F-FDG. Four patients were excluded because of inadequate FDG uptake caused by severe diabetes. Follow-up data were obtained by phone contact with patients and by review of hospital or physicians' records. Cardiac death, myocardial infarction and late revascularisation for unstable angina were considered as events. Follow-up data were not available in three patients. Follow-up was 96% complete at a mean period of 29 +/- 19 months.

RESULTS

At baseline SPECT, 59 (72%) patients had evidence of viable myocardium, while 23 did not. Of these latter patients, 12 (52%) demonstrated viable myocardium after nitrate and 13 (56%) had preserved metabolic activity. Cardiac events (cardiac death, myocardial infarction and late revascularisation for unstable angina) occurred in 24 (29%) patients. Event-free survival was similar in patients with and patients without viable myocardium at baseline SPECT (p = 0.8). In contrast, event-free survival was lower in patients with viable myocardium at nitrate SPECT and PET compared to those without viable myocardium (both p<0.05).

CONCLUSION

In patients with ischaemic LV dysfunction, the prognostic value of SPECT imaging after nitrate is comparable to that of PET metabolic imaging.