Impact of preoperative positron emission tomography in patients with severely impaired LV-function undergoing surgical revascularization

Prognostic value of global myocardial flow reserve in patients with history of coronary artery bypass grafting

AIMS

It is not well understood whether positron emission tomography (PET)-derived myocardial flow reserve (MFR) is prognostic among patients with prior coronary artery bypass grafting (CABG).

METHODS AND RESULTS

Consecutive patients with a clinical indication for PET were enrolled in the Houston Methodist DeBakey Heart and Vascular Center PET registry and followed prospectively for incident outcomes. The primary outcome was a composite of all-cause death, myocardial infarction (MI)/unplanned revascularization, and heart failure admissions. Cox proportional hazards models were used to study the association between MFR (<2 vs. ≥2) and incident events adjusting for clinical and myocardial perfusion imaging variables. The study population consisted of 836 patients with prior CABG; mean (SD) age 68 (10) years, 53% females, 79% Caucasian, 36% non-Hispanic, and 66% with MFR <2. Over a median (interquartile range [IQR]) follow-up time of 12 (4-24) months, there were 122 incident events (46 HF admissions, 28 all-cause deaths, 23 MI, 22 PCI/3 repeat CABG 90 days after imaging). In adjusted analyses, patients with impaired MFR had a higher risk of the primary outcome [hazard ratio (HR) 2.06; 95% CI 1.23-3.44]. Results were significant for admission for heart failure admissions (HR 2.92; 95% CI 1.11-7.67) but not for all-cause death (HR 2.01, 95% CI 0.85-4.79), or MI/UR (HR 1.93, 95% CI 0.92-4.05).

CONCLUSION

Among patients with a history of CABG, PET-derived global MFR <2 may identify those with a high risk of subsequent cardiovascular events, especially heart failure, independent of cardiovascular risk factors and perfusion data.

Prognosis of Patients With Reduced Left Ventricular Ejection Fraction and Chronic Total Occlusion According to Treatment Applied

BACKGROUND

Chronic total occlusion (CTO) is common among patients with coronary artery disease. Very few studies have focused on outcomes of patients with CTO and reduced left ventricular ejection fraction (LVEF), according to treatment applied. The aim of our study was to determine the potential influence of the selected treatment on the prognosis in patients with CTO associated with reduced LVEF.

METHODS

Between June 2010 and October 2013, all consecutive patients with at least one CTO and reduced LVEF (<40%) were enrolled. Major adverse cardiac events (MACE), defined as the composite of cardiac mortality or myocardial infarction (MI) and its individual components, were compared between three treatment groups: medical therapy (MT), percutaneous coronary intervention (PCI), and coronary bypass graft (CABG).

RESULTS

In 256 included patients, the follow-up was 1129 ± 556 days. The incidence of MACE was 40% in the MT group, compared with PCI (20.3%) and CABG (16.7%); p < 0.001. All-cause and cardiac mortality were also higher in the MT group (40.7% and 33.3%, respectively) versus the PCI (21.9% and 15.6%) and CABG (11.9% and 9.5%) groups (p < 0.001 for both endpoints); MI rate did not differ among groups. In the adjusted multivariate analysis, CABG had lower MACE risk, compared with MT (HR = 0.39, 0.17-0.91; p = 0.029); successful PCI also trended toward lower risk of MACE, compared with MT.

CONCLUSIONS

Patients with CTO and reduced LVEF treated with MT had a worse prognosis than those treated with revascularization (either CABG or PCI). Patients with an indication for CABG appeared to perform best during long-term follow-up.

Myocardial Viability Testing by Positron Emission Tomography: Basic Concepts, Mini-Review of the Literature and Experience From a Tertiary PET Center

Ischemic heart disease ranges in severity from slightly reduced myocardial perfusion with preserved contractile function to chronic occlusion of coronary arteries with myocardial cells replaced by acontractile scar tissue-ischemic heart failure (iHF). Progression towards scar tissue is thought to involve a period in which the myocardial cells are acontractile but still viable despite severely reduced perfusion. This state of reduced myocardial function that can be reversed by revascularization is termed "hibernation." The concept of hibernating myocardium in iHF has prompted an increasing amount of requests for preoperative patient workup, but while the concept of viability is widely agreed upon, no consensus on clinical testing of hibernation has been established. Therefore, a variety of imaging methods have been used to assess hibernation including morphology based (MRI and ultrasound), perfusion based (MRI, SPECT, or PET) and/or methods to assess myocardial metabolism (PET). Regrettably, the heterogeneous body of literature on the subject has resulted in few robust prospective clinical trials designed to assess the impact of preoperative viability testing prior to revascularization. However, the PARR-2 trial and sub-studies has indicated that >5% hibernating myocardium favors revascularization over optimized medical therapy. In this paper, we review the basic concepts and current evidence for using PET to assess myocardial hibernation and discuss the various methodologies used to process the perfusion/metabolism PET images. Finally, we present our experience in conducting PET viability testing in a tertiary referral center.

Impact of hibernating and viable myocardium on improvement in perfusion and left ventricular ejection fraction after coronary artery bypass graft

OBJECTIVES

The association between the extent and degree of perfusion-metabolism mismatch and improvement in perfusion and left ventricular ejection fraction (LVEF) after revascularization was assessed. The secondary aim was to identify the best precoronary artery bypass graft surgery (pre-CABG) PET parameter, if any, to predict the improvement in the perfusion and LVEF after CABG.

METHODS AND RESULTS

Overal, 31 patients (mean age: 58+8.3 years) with ischemic left ventricle dysfunction underwent NH3 and F-FDG PET for the assessment of myocardial viability. CABG was performed in these patients and after a mean interval of 3 months, NH3 PET was repeated. The percentages of viable myocardium (VM), hibernating myocardium, degree of mismatch, and LVEF in pre-CABG PET were calculated. These were compared, the median [INCREMENT]LVEF and percent increase in perfusion being 5 (interquartile range: 3-9) and 78.7 (interquartile range: 51.3-100), respectively. No significant association was observed between the severity or extent of perfusion defect/mismatch and improvement in perfusion or LVEF after CABG. Patients with at least 65% VM predicted a 5-unit increase in LVEF at 88.9% sensitivity (P=0.1).

CONCLUSION

There was no significant relation between the severity and extent of perfusion-metabolism mismatch with improvement in perfusion and LVEF after CABG. After CABG for ischemic left ventricle dysfunction, VM shows a tendency toward better improvement in LVEF.

PET/MRI early after myocardial infarction: evaluation of viability with late gadolinium enhancement transmurality vs. 18F-FDG uptake

AIMS

F-18 fluorodeoxyglucose (FDG) myocardial PET imaging is since more than two decades considered to delineate glucose utilization in dysfunctional but viable cardiomyocytes. Late gadolinium enhancement (LGE) MRI was introduced more than a decade ago and identifies increased extravascular space in areas of infarction and scar. Although the physiological foundation differs, both approaches are valuable in the prediction of functional outcome of the left ventricle, but synergistic effects are yet unknown. We aimed to compare the improvement of LV function after 6 months based on the regional FDG uptake and the transmurality of scar by LGE in patients early after acute myocardial infarction (AMI).

METHODS AND RESULTS

Twenty-eight patients with primary AMI underwent simultaneous PET/MRI for assessment of regional FDG uptake and degree of LGE transmurality 5-7 days after PCI. Follow-up by MRI was performed in 20 patients 6 months later. Myocardium was defined 'PET viable' based on the established threshold of ≥ 50% FDG uptake compared with remote myocardium or as 'MRI viable' when LGE transmurality of ≤ 50% was present. Regional wall motion was measured by MRI. Ninety-five dysfunctional segments were further analysed regarding regional wall motion recovery. There was a substantial intermethod agreement for segmental LGE transmurality and reduction of FDG uptake (κ = 0.65). 'PET viable' and 'MRI viable' segments showed a lower wall motion abnormality score (PET: initial: 1.4 ± 0.6 vs. 1.9 ± 0.8, P < 0.008; follow-up: 0.5 ± 0.7 vs. 1.5 ± 1.0, P < 0.0001; MRI: initial: 1.5 ± 0.6 vs. 2.0 ± 0.8, P < 0.002; follow-up: 0.7 ± 0.8 vs. 1.6 ± 1.0, P < 0.0001) and a better regional wall motion improvement (PET: -0.9 ± 0.7 vs. -0.4 ± 0.7, P < 0.0007; MRI: -0.8 ± 0.7 vs. -0.4 ± 0.7, P < 0.009) compared with 'PET non-viable' or 'MRI non-viable' segments, respectively. Eighteen per cent of the dysfunctional segments showed discrepant findings ('PET non-viable' but 'MRI viable'). At follow-up, the regional wall motion of these segments was inferior compared with 'PET viable/MRI viable' segments (1.1 ± 0.8 vs. 0.5 ± 0.7, P < 0.01), had an inferior functional recovery (-0.5 ± 0.6 vs. -0.9 ± 0.7, P < 0.03), but showed no difference compared with concordant 'PET non-viable/MRI non-viable' segments.

CONCLUSION

The simultaneous assessment of LGE and FDG uptake using a hybrid PET/MRI system is feasible. The established PET and MRI 'viability' parameter prior to revascularization therapy also predicts accurately the regional outcome of wall motion after AMI. In a small proportion of segments with discrepant FDG PET and LGE MRI findings, FDG uptake was a better predictor for functional recovery.

Decision making and results of coronary artery bypass grafting for patients with poor left ventricular function

BACKGROUND

The aim of this study is to determine the results of coronary artery bypass surgery in patients with a low ejection fraction. Between January 2007 and January 2011, 3556 consecutive patients who underwent coronary artery bypass grafting at the Cardiovascular Surgery Clinic at Sifa University Hospital, Izmir, Turkey, were analyzed retrospectively.

METHODS

The patients were divided into 2 groups. Patients undergoing isolated first-time elective coronary bypass surgery were classified according to their preoperative ejection fraction; Patients in Group I had an ejection fraction between 20% and 35% with poor left ventricular function (n = 1246; 695 men and 551 women; mean age, 62.25 ± 5.72 years, range, 47-78 years). Control patients in Group II underwent elective coronary artery bypass grafting at the same time and had left ventricular ejection fraction between 36% and 49% (n = 2310; 1211 men and 1099 women; mean age, 61.83 ± 8.12 years, range, 41-81 years). The mean follow-up time for all patients was 24 ± 9.4 months (range, 12-48 months). Patients were followed postoperatively at the end of the first month and every 6 months. The left ventricular ejection fraction was assessed by transthoracic echocardiography.

RESULTS

The mean number of distal anastomoses, myocardial infarction, and mean age was not significantly different between the 2 groups; however, cross-clamp time was longer in Group I. Patient recovery time was significantly longer in Group I. Morbidity (14.5% in Group I versus 7.4% in Group II, P < .005) and mortality (1.76% versus 0.30%, P < .005) were higher in Group I. During late follow-up, the 2-year survival rate (85.1% versus 94.5%) and 2-year event-free rate (77.6% versus 86.9%) were significantly lower in Group I when compared to Group II. Postoperative left ventricular ejection fraction values were significantly superior in Group I compared to Group II.

CONCLUSION

Coronary artery bypass grafting can be safely performed in patients with low ejection fraction with minimal postoperative morbidity and mortality. The viable myocardium could be reliably determined by positron emission tomography. Low ejection fraction patients could greatly benefit from coronary bypass surgery regarding postoperative ejection fraction, increased long-term survival, improvement in New York Heart Association classification, and higher quality of life.

Evaluating the prognostic value of positron-emission tomography myocardial perfusion imaging using automated software to calculate perfusion defect size

BACKGROUND

Myocardial perfusion imaging by positron-emission tomography (PET MPI) is regarded as a valid technique for the diagnosis of coronary artery disease (CAD), but the incremental prognostic value of PET MPI among individuals with known or suspected CAD is not firmly established.

HYPOTHESIS

Myocardial perfusion defect sizes as measured by PET MPI using automated software will provide incremental prognostic value for cardiac and all-cause mortality.

METHODS

This study included 3739 individuals who underwent rest-stress rubidium-82 PET MPI for the evaluation of known or suspected CAD. Rest, stress, and stress-induced myocardial perfusion defect sizes were determined objectively by automated computer software. Study participants were followed for a mean of 5.2 years for cardiac and all-cause mortality. Cox proportional hazards models were developed to evaluate the incremental prognostic value of PET MPI.

RESULTS

A strong correlation was observed between perfusion defect sizes assessed visually and by automated software (r = 0.76). After adjusting for cardiac risk factors, known CAD, noncoronary vascular disease, and use of cardioprotective medications, stress perfusion defect size was strongly associated with cardiac death (P < 0.001). Rest perfusion defects demonstrated a stronger association with cardiac death (P < 0.001) than stress-induced perfusion defects (P = 0.01), yet both were highly significant. Similar patterns held for all-cause death.

CONCLUSIONS

The current study is the largest to date demonstrating PET MPI provides incremental prognostic value among individuals with known or suspected CAD. Automated calculation of perfusion defect sizes may provide valuable supplementary information to visual assessment.