Prediction of functional recovery after revascularization in patients with coronary artery disease and left ventricular dysfunction by gated FDG-PET

Construction of a Phantom for Image Quality Evaluation in PET/MRI System

Background: There is no phantom for image quality test in magnetic resonance imaging combined with positron emission tomography systems (PET/MRI systems). In MRI, radioactive water phantom containing 2-deoxy-2-[F-18] fluoro-D-glucose (¹⁸F-FDG) cannot be used due to the dielectric effect. Even for phantoms filled with MR-available solutions, the source current of the RF coil is strongly disturbed as the diameter of the phantom increases. Stable MR images require proper phantom size and solution selection. Previous reports have not provided these details. Other than that, few existing phantoms evaluate negative signals such as N-13 ammonia (¹³N-NH₃). We created a phantom for PET/MRI system for image quality test. Methods: The phantom for the PET/MRI system was assembled in two portions. One portion is a signal part containing ¹⁸F-FDG radioactive water. The other portion is filled with polyvinyl alcohol glue to construct MRI image to generate µ-map. The glue part is allowed to rewrite the table position overlaps with the first layer, and attenuation correction is performed. Signals are set as positive (4 times and twice higher than background radioactivity) and negative (no radioactivity) columns with different sizes (15 mm φ and 7 mm φ). The PET images with X-ray computed tomography-based attenuation correction (CT-AC) and MRI-AC were evaluated by %-contrasts, variation and uniformity. Results: The %-contrasts of the positive shallow signals with PET/magnetic resonance (MR) and PET/CT were 41.8% and 45.4%, respectively. And it of the positive deep signals with PET/MR and PET/CT were 40.7% and 44.9%. On the other hand, the %-contrasts of the negative shallow signals with PET/MR and PET/CT were 62.3% and 65.6%, respectively. And it of the negative deep signals with PET/MR and PET/CT were 60.7% and 63.7%. Moreover, the % Nj index of uniformity was 2.0% on PET/MRI images and 0.34% on PET/CT images. For negative signals that assume a decrease in myocardial blood flow, The image quality of MR-AC was almost the same as that of CT-AC. Consistency between the images after CT-AC and MR-AC correction were confirmed, and in particular, a stable MR-AC µ-map was obtained in the phantom study. Conclusion: The suggested prototype phantom for generating µ-map is reasonable and useful for evaluating PET/MRI image quality, based on the present standard.

Intravenous regular insulin is an efficient and safe procedure for obtaining high-quality cardiac 18F-FDG PET images: an open-label, single-center, randomized controlled prospective trial

BACKGROUND

An open-label, single-center, randomized controlled prospective trial was performed to assess the efficiency and safety of an insulin loading procedure to obtain high-quality cardiac 18F-FDG PET/CT images for patients with coronary artery disease (CAD).

METHODS

Between November 22, 2018 and August 15, 2019, 60 patients with CAD scheduled for cardiac 18F-FDG PET/CT imaging in our department were randomly allocated in a 1:1 ratio to receive an insulin or standardized glucose loading procedure for cardiac 18F-FDG imaging. The primary outcome was the ratio of interpretable images (high-quality images defined as myocardium-to-liver ratios ≥ 1). The secondary outcome was the patient preparation time (time interval between administration of insulin/glucose and 18F-FDG injection). Hypoglycemia events were recorded.

RESULTS

The ratio of interpretable cardiac PET images in the insulin loading group surpassed the glucose loading group (30/30 vs. 25/30, P = 0.026). Preparation time was 71±2 min shorter for the insulin loading group than for the glucose loading group (P < 0.01). Two and six hypoglycemia cases occurred in the insulin and glucose loading groups, respectively.

CONCLUSION

The insulin loading protocol was a quicker, more efficient, and safer preparation for gaining high-quality cardiac 18F-FDG images.

Myocardial viability with chronic total occlusion assessed by hybrid positron emission tomography/magnetic resonance imaging

BACKGROUND

The present study was performed to compare the relationship of 18F-fluorodeoxyglucose (FDG) uptake and late gadolinium enhancement (LGE) transmurality with the improvement of left ventricular function in patients with coronary chronic total occlusion (CTO) assessed by hybrid FDG positron emission tomography (PET)/magnetic resonance imaging (MRI).

METHODS

Thirty-eight consecutive patients with CTO underwent FDG PET/MRI. Twenty-three patients then underwent percutaneous coronary intervention (PCI), and the final study population comprised 15 patients who underwent both initial and follow-up MRI. The degree of wall motion abnormality in each of the 17 myocardial segments was evaluated based on the extent of wall thickening on cine MRI using a 5-point scale.

RESULTS

Among all 646 myocardial segments at baseline, FDG uptake significantly decreased as the transmurality of LGE is advanced. Of the 15 patients who underwent PCI, 152 segments showed wall motion abnormalities at baseline. The functional recovery of the wall motion abnormality of the PET-viable/MRI-viable segments was highest, and that of the PET-nonviable/MRI-nonviable segments was lowest. There were no differences in functional recovery between the PET-viable/MRI-nonviable and PET-nonviable/MRI-viable segments.

CONCLUSION

Simultaneous assessment of FDG and LGE using a hybrid PET/MRI system can help to predict functional recovery after PCI in patients with CTO.

Value of 12-lead electrocardiogram to predict myocardial scar on FDG PET in heart failure patients

PURPOSE

A surface 12-lead electrocardiogram (ECG) is widely available, fast, inexpensive, and safe. However, its value to predict a true myocardial scar in patients with ischemic cardiomyopathy (ICM) has not been studied extensively yet. This study was conducted to assess whether Q waves on resting surface 12-lead ECG are predictive of non-viable myocardium in patients with ICM.

METHODS

We analyzed resting ECGs of 149 patients with ICM undergoing cardiac positron emission tomography (PET) with 13N-ammonia (NH3) and 18F-fluorodeoxyglucose (FDG) at our institution. Pathological Q waves and QS complexes were assigned to one of three coronary artery territories and compared to the PET findings. Myocardial scar was defined as 2 or more contiguous myocardial segments with an average (matched) reduction of NH3 and FDG uptake <50% of the maximum value.

RESULTS

Pathological Q waves had a sensitivity and specificity of 70% and 40%, respectively, and a PPV and NPV of 37% and 73%, respectively, to detect myocardial scar on FDG PET. For QS complexes, sensitivity and specificity were 46% and 59%, respectively, and PPV and NPV were 36% and 68%, respectively. Sensitivity was lower, but specificity was significantly higher in both the LCX and RCA compared to the LAD territory (p<0.001), particularly for QS complexes.

CONCLUSION

Pathological Q waves on resting 12-lead ECG have poor or at best moderate sensitivity and specificity to detect myocardial scar on FDG PET. These findings support the use of more advanced imaging techniques to assess myocardial viability in ICM.

Myocardial viability imaging using a novel non-breath-hold cardiac MRI protocol: a comparative assessment with 18F-FDG PET

Background

Delayed contrast enhancement on cardiac magnetic resonance imaging is a well-established MRI technique for the evaluation of myocardial tissue viability. A comprehensive cardiac MRI protocol for myocardial viability comprises of multiple breath hold sequences to provide information regarding chamber volumes, myocardial mass, and function in addition to viability. However, its routine use is limited mainly by lengthy acquisition time and patient’s inability to hold breath in multiple breath hold sequences. The important question to which the referring cardiologists/cardiac surgeons are seeking answer is that “What are the viable vascular territories that will benefit from revascularization?” In this study, we have analyzed the utility of non-breath-hold rapid delayed contrast-enhanced cardiac MR imaging protocol for myocardial viability assessment with 18-flourodeoxyglucose positron emission tomography (18F-FDG PET) as the reference standard.

Results

Forty patients of ischemic heart disease who met the inclusion criteria were included. All patients underwent both 18F-FDG PET and delayed contrast-enhanced cardiac magnetic resonance imaging as per the non-breath-hold protocol. In this free-breathing protocol, the breath hold cine sequences were omitted and, after localizers, post-contrast scans were obtained with a time gap of 15 min post-contrast administration. A total number of 680 myocardial segments and corresponding 120 vascular territories were assessed. MRI and 18F-FDG PET images were analyzed using a 17-segment model as proposed by AHA. Sensitivity, specificity, positive predictive value, and negative predictive value of non-breath-hold rapid delayed contrast-enhanced cardiac MR imaging protocol for assessing myocardial viability (on segment analysis) was 95.5%, 65.59%, 88.0%, and 84.72%, respectively, and of vascular territory analysis were 96.77%, 92.59%, 97.83%, and 89.29%, respectively, in relation to 18F-FDG PET used as the reference standard. Spearman’s rank correlation coefficient is 0.62.

Conclusion

This modified non-breath-hold delayed contrast-enhanced cardiac MR imaging protocol is a reliable tool to answer the clinically relevant question of myocardial viability with a significant reduction in acquisition time and overcomes the limiting need of breath hold.

Hybrid PET/MR imaging for the prediction of left ventricular recovery after percutaneous revascularisation of coronary chronic total occlusions

Purpose

To evaluate myocardial viability assessment with hybrid 2-deoxy-2-[¹⁸F]fluoro-d-glucose positron emission tomography/magnetic resonance imaging ([¹⁸F]FDG-PET/MR) in predicting left ventricular (LV) wall motion recovery after percutaneous revascularisation of coronary chronic total occlusion (CTO).

Methods and results

Forty-nine patients with CTO and corresponding wall motion abnormality (WMA) underwent [¹⁸F]FDG-PET/MR imaging for viability assessment prior to percutaneous revascularisation. After 3–6 months, 23 patients underwent follow-up MR to evaluate wall motion recovery. In total, 124 segments were assigned to the CTO territories, while 80 segments displayed impaired wall motion. Of these, 68% (54) were concordantly viable in PET and MR; conversely, only 2 segments (2%) were assessed non-viable by both modalities. However, 30% showed a discordant viability pattern, either PET non-viable/MR viable (3 segments, 4%) or PET viable/MR non-viable (21 segments, 26%), and the latter revealed a significant wall motion improvement at follow-up (p = 0.033). Combined imaging by [¹⁸F]FDG-PET/MR showed a fair accuracy in predicting myocardial recovery after CTO revascularisation (PET/MR area under ROC curve (AUC) = 0.72, p = 0.002), which was superior to LGE-MR (AUC = 0.66) and [¹⁸F]FDG-PET (AUC = 0.58) alone.

Conclusion

Hybrid PET/MR imaging prior to CTO revascularisation predicts more accurately the recovery of dysfunctional myocardium than PET or MR alone. Its complementary information may identify regions of viable myocardium with increased potential for functional recovery.

Early risk stratification using Rubidium-82 positron emission tomography in STEMI patients

BACKGROUND

Assessment of infarct size after myocardial infarction is predictive of subsequent morphological changes and clinical outcome. This study aimed to assess subacute post-intervention Rubidium-82 (82Rb)-PET imaging in predicting left ventricle ejection fraction, regional wall motion, and final infarct size by CMR at 3-months after STEMI.

METHODS

STEMI patients undergoing percutaneous coronary intervention were included prospectively. Rest-only 82Rb-PET perfusion imaging was performed at median 36 hours [IQR: 22 to 50] after the treatment. The extent of hypoperfusion and absolute blood flow (mL·min·g) were estimated on a global and a 17-segment model with dedicated software. At 3-months follow-up patients completed the CMR functional and late gadolinium enhancement imaging.

RESULTS

42 patients were included, but only 35 had follow-up CMR and constituted the study population. Absolute blood flow was significantly lower in the infarct-related territory compared to remote myocardium, P < .005. Extent of hypoperfusion correlated with final infarct size, r = 0.58, P < .001, while blood flow correlated with ejection fraction, r = 0.41, P < .05. In linear mixed models, higher subacute absolute blood flow (β = 4.6, confidence interval [3.5; 5.2], P < .001, R2 = 0.67) was associated with greater wall motion. Segmental extent of subacute hypoperfusion (β = 0.43 [0.38; 0.49], P < .001, R2 = 0.58) was associated with the degree of late gadolinium enhancement at 3-months.

CONCLUSIONS

Subacute rest-only 82Rb-PET is feasible following STEMI and seems predictive of myocardial function and infarct size at 3-months.

Accuracy of myocardial viability imaging by cardiac MRI and PET depending on left ventricular function

AIM

To compare myocardial viability assessment accuracy of cardiac magnetic resonance imaging (CMR) compared to [¹⁸F]-fluorodeoxyglucose (FDG)- positron emission tomography (PET) depending on left ventricular (LV) function.

METHODS

One-hundred-five patients with known obstructive coronary artery disease (CAD) and anticipated coronary revascularization were included in the study and examined by CMR on a 1.5T scanner. The CMR protocol consisted of cine-sequences for function analysis and late gadolinium enhancement (LGE) imaging for viability assessment in 8 mm long and contiguous short axis slices. All patients underwent PET using [¹⁸F]-FDG. Myocardial scars were rated in both CMR and PET on a segmental basis by a 4-point-scale: Score 1 = no LGE, normal FDG-uptake; score 2 = LGE enhancement < 50% of wall thickness, reduced FDG-uptake ( ≥ 50% of maximum); score 3 = LGE ≥ 50%, reduced FDG-uptake (< 50% of maximum); score 4 = transmural LGE, no FDG-uptake. Segments with score 1 and 2 were categorized “viable”, scores 3 and 4 were categorized as “non-viable”. Patients were divided into three groups based on LV function as determined by CMR: Ejection fraction (EF), < 30%: n = 45; EF: 30%-50%: n = 44; EF > 50%: n = 16). On a segmental basis, the accuracy of CMR in detecting myocardial scar was compared to PET in the total collective and in the three different patient groups.

RESULTS

CMR and PET data of all 105 patients were sufficient for evaluation and 5508 segments were compared in total. In all patients, CMR detected significantly more scars (score 2-4) than PET: 45% vs 40% of all segments (P < 0.0001). In the different LV function groups, CMR found more scar segments than PET in subjects with EF< 30% (55% vs 46%; P < 0.0001) and EF 30%-50% (44% vs 40%; P < 0.005). However, CMR revealed less scars than PET in patients with EF > 50% (15% vs 23%; P < 0.0001). In terms of functional improvement estimation, i.e., expected improvement after revascularization, CMR identified “viable” segments (score 1 and 2) in 72% of segments across all groups, PET in 80% (P < 0.0001). Also in all LV function subgroups, CMR judged less segments viable than PET: EF < 30%, 66% vs 75%; EF = 30%-50%, 72% vs 80%; EF > 50%, 91% vs 94%.

CONCLUSION

CMR and PET reveal different diagnostic accuracy in myocardial viability assessment depending on LV function state. CMR, in general, is less optimistic in functional recovery prediction.

Imaging the myocardial ischemic cascade

Non-invasive imaging plays a growing role in the diagnosis and management of ischemic heart disease from its earliest manifestations of endothelial dysfunction to myocardial infarction along the myocardial ischemic cascade. Experts representing the North American Society for Cardiovascular Imaging and the European Society of Cardiac Radiology have worked together to organize the role of non-invasive imaging along the framework of the ischemic cascade. The current status of non-invasive imaging for ischemic heart disease is reviewed along with the role of imaging for guiding surgical planning. The issue of cost effectiveness is also considered. Preclinical disease is primarily assessed through the coronary artery calcium score and used for risk assessment. Once the patient becomes symptomatic, other imaging tests including echocardiography, CCTA, SPECT, PET and CMR may be useful. CCTA appears to be a cost-effective gatekeeper. Post infarction CMR and PET are the preferred modalities. Imaging is increasingly used for surgical planning of patients who may require coronary artery bypass.

Improvement of left ventricular ejection fraction in revascularized postmyocardial patients: indication for statistical fallacy

Background

Reduced left ventricular ejection fraction (LVEF) ≤30% is the most powerful prognostic indicator for sudden cardiac death (SCD) in patients after myocardial infarction (MI), but there are little data about long-term changes of LVEF after revascularization and the following implantation of a cardioverter defibrillator (ICD).

Methods

We performed a retrospective analysis of 277 patients with reduced LVEF at least 1 month after MI and complete revascularization. Patients (median time post-MI 23.4 months; 74.3% after PCI, 25.7% after CABG were assigned either to group 1 (LVEF <30%) or group 2 (LVEF 30–40%). Biplane echocardiography was redone after a mean follow-up of 441 ± 220 days.

Results

LVEF increased significantly in both two groups (group 1: 26.2 ± 4.8% to 32.4 ± 8.5%; p < 0.001; group 2: 38.2 ± 2.5% to 44.4 ± 9.6%; p < 0.001). However, statistical analysis of first and second LVEF measurement by means of a LOWESS regression and with an appropriate correction of the regression towards the mean effect revealed only a moderate increase of the mean LVEF from 35 to 37% (p < 0.001) with a large interindividual variation.

Conclusions

The impact of early revascularization on LVEF appears to be low in the majority of post-MI heart failure patients. Owing to the high variability, a single measurement may not be reliable enough to justify a decision on ICD indication.

Myocardial Viability: Survival Mechanisms and Molecular Imaging Targets in Acute and Chronic Ischemia

Myocardial responses to acute ischemia/reperfusion and to chronic ischemic conditions have been studied extensively at all levels of organization. These include subcellular (eg, mitochondria in vitro); intact, large animal models (eg, swine with chronic coronary stenosis); as well as human subjects. Investigations in humans have used positron emission tomographic metabolic and myocardial blood flow measurements, assessment of gene expression and anatomic description of myocardium obtained at the time of coronary artery revascularization, ventricular assist device placement, or heart transplantation. A multitude of genetic, molecular, and metabolic pathways have been identified, which may promote either myocyte survival or death or, most interestingly, both. Many of these potential mediators in both acute ischemia/reperfusion and adaptations to chronic ischemic conditions involve the mitochondria, which play a central role in cellular energy production and homeostasis. The present review is focused on operative survival mechanisms and potential myocardial viability molecular imaging targets in acute and chronic ischemia, especially those which impact mitochondrial function.

Role of PET-CT in the assessment of myocardial viability in patients with left ventricular dysfunction

AIM

Role of PET-CT in assessment of myocardial viability in patients with LV dysfunction.

METHODS

This prospective study included 120 patients with LV dysfunction who underwent 99mTechnetium-Sestamibi myocardial perfusion SPECT-CT and 18FFDG cardiac PET-CT. They also underwent serial echocardiography and coronary angiography along with myocardial perfusion and FDG PET study.

RESULTS

Thirty-three patients had single vessel disease, 48 had triple vessel disease, and rest had double vessel disease. Among 786 segments, matched defects were seen in 432 (55%) and mismatched defects in 354 (45%) segments. 78 patients were surgically managed, and 42 were medically managed. The change in LVEF after surgical management was statistically significant compared to medical management.

CONCLUSION

Viability assessment should be performed in patients who present after 12h of acute myocardial infarction or with LV dysfunction due to ischemic heart disease to decide upon appropriate surgical management.

Cardiac applications of PET

Routine use of cardiac positron emission tomography (PET) applications has been increasing but has not replaced cardiac single-photon emission computerized tomography (SPECT) studies yet. The majority of cardiac PET tracers, with the exception of fluorine-18 fluorodeoxyglucose (18F-FDG), are not widely available, as they require either an onsite cyclotron or a costly generator for their production. 18F-FDG PET imaging has high sensitivity for the detection of hibernating/viable myocardium and has replaced Tl-201 SPECT imaging in centers equipped with a PET/CT camera. PET myocardial perfusion imaging with various tracers such as Rb-82, N-13 ammonia, and O-15 H2O has higher sensitivity and specificity than myocardial perfusion SPECT for the detection of coronary artery disease (CAD). In particular, quantitative PET measurements of myocardial perfusion help identify subclinical coronary stenosis, better define the extent and severity of CAD, and detect ischemia when there is balanced reduction in myocardial perfusion due to three-vessel or main stem CAD. Fusion images of PET perfusion and CT coronary artery calcium scoring or CT coronary angiography provide additional complementary information and improve the detection of CAD. PET studies with novel 18F-labeled perfusion tracers such as 18F-flurpiridaz and 18F-FBnTP have yielded high sensitivity and specificity in the diagnosis of CAD. These tracers are still being tested in humans, and, if approved for clinical use, they will be commercially and widely available. In addition to viability studies, 18F-FDG PET can also be utilized to detect inflammation/infection in various conditions such as endocarditis, sarcoidosis, and atherosclerosis. Some recent series have obtained encouraging results for the detection of endocarditis in patients with intracardiac devices and prosthetic valves. PET tracers for cardiac neuronal imaging, such as C-11 HED, help assess the severity of heart failure and post-transplant cardiac reinnervation, and understand the pathogenesis of arrhytmias. The other uncommon applications of cardiac PET include NaF imaging to identify calcium deposition in atherosclerotic plaques and β-amyloid imaging to diagnose cardiac amyloid involvement. 18F-FDG imaging with a novel PET/MR camera has been reported to be very sensitive and specific for the differentiation between malignant and nonmalignant cardiac masses. The other potential applications of PET/MR are cardiac infectious/inflammatory conditions such as endocarditis.

Cardiovascular PET-CT imaging: a new frontier?

Cardiovascular positron-emission tomography combined with computed tomography (PET-CT) has recently emerged as an imaging technology with the potential to simultaneously describe both anatomical structures and physiological processes in vivo. The scope for clinical application of this technique is vast, but to date this promise has not been realised. Nonetheless, significant research activity is underway to explore these possibilities and it is likely that the knowledge gained will have important diagnostic and therapeutic implications in due course. This review provides a brief overview of the current state of cardiovascular PET-CT and the likely direction of future developments.

The role of PET quantification in cardiovascular imaging

Positron Emission Tomography (PET) has several clinical and research applications in cardiovascular imaging. Myocardial perfusion imaging with PET allows accurate global and regional measurements of myocardial perfusion, myocardial blood flow and function at stress and rest in one exam. Simultaneous assessment of function and perfusion by PET with quantitative software is currently the routine practice. Combination of ejection fraction reserve with perfusion information may improve the identification of severe disease. The myocardial viability can be estimated by quantitative comparison of fluorodeoxyglucose (¹⁸FDG) and rest perfusion imaging. The myocardial blood flow and coronary flow reserve measurements are becoming routinely included in the clinical assessment due to enhanced dynamic imaging capabilities of the latest PET/CT scanners. Absolute flow measurements allow evaluation of the coronary microvascular dysfunction and provide additional prognostic and diagnostic information for coronary disease. Standard quantitative approaches to compute myocardial blood flow from kinetic PET data in automated and rapid fashion have been developed for ¹³N-ammonia, ¹⁵O-water and ⁸²Rb radiotracers. The agreement between software methods available for such analysis is excellent. Relative quantification of ⁸²Rb PET myocardial perfusion, based on comparisons to normal databases, demonstrates high performance for the detection of obstructive coronary disease. New tracers, such as ¹⁸F-flurpiridaz may allow further improvements in the disease detection. Computerized analysis of perfusion at stress and rest reduces the variability of the assessment as compared to visual analysis. PET quantification can be enhanced by precise coregistration with CT angiography. In emerging clinical applications, the potential to identify vulnerable plaques by quantification of atherosclerotic plaque uptake of ¹⁸FDG and ¹⁸F-sodium fluoride tracers in carotids, aorta and coronary arteries has been demonstrated.

Myocardial scar identified by magnetic resonance imaging can predict left ventricular functional improvement after coronary artery bypass grafting

BACKGROUND

Previous studies have shown that viable myocardium predicts recovery of left ventricular (LV) dysfunction after revascularization. Our aim was to evaluate the prognostic value of myocardial scar assessed by late gadolinium-enhanced cardiovascular magnetic resonance imaging (LGE-CMR) on functional recovery in patients undergoing coronary artery bypass grafting (CABG).

METHODS

From November 2009 to September 2012, 63 patients with reduced left ventricular ejection fraction (LVEF) referred for first-time isolated CABG were prospectively enrolled, 52 were included in final analysis. LV functional parameters and scar tissue were assessed by LGE-CMR at baseline and 6 months after surgery. Patency of grafts was evaluated by computed tomography angiography (CTA) 6 months post-CABG. Predictors for global functional recovery were analyzed.

RESULTS

The baseline LVEF was 32.7 ± 9.2%, which improved to 41.6 ± 11.0% 6 months later and 32/52 patients improved LVEF by ≥ 5%. Multivariate logistic regression analysis showed that the most significant negative predictor for global functional recovery was the number of scar segments (Odds ratio 2.864, 95% Confidence Interval 1.172-6.996, p = 0.021). Receiver-Operator-Characteristic (ROC) analysis demonstrated that ≤ 4 scar segments predicted global functional recovery with a sensitivity and specificity of 85.0% and 87.5%, respectively (AUC = 0.91, p<0.001). Comparison of ROC curves also indicated that scar tissue was superior to viable myocardium in predicting cardiac functional recovery (p<0.001).

CONCLUSIONS

Our findings indicated that scar tissue on LGE-CMR is an independent negative predictor of cardiac functional recovery in patients with impaired LV function undergoing CABG. These observations may be helpful for clinicians and cardiovascular surgeons to determine which patients are most likely to benefit from surgical revascularization.

Cardioprotective effects of adenosine within the border and remote areas of myocardial infarction

Background

Adenosine may have beneficial effects on left ventricular function after myocardial infarction (MI), but the magnitude of this effect on remote and MI areas is controversial. We assessed the long-term effects of adenosine after MI using electrocardiogram-triggered ¹⁸ F-fluorodeoxyglucose positron emission tomography.

Methods

Wistar rats were subjected to coronary ligation and randomized into three groups treated daily for 2 months by NaCl (control; n = 7), 2-chloroadenosine (CADO; n = 8) or CADO with 8-sulfophenyltheophilline, an antagonist of adenosine receptors (8-SPT; n = 8).

Results

After 2 months, control rats exhibited left ventricular remodelling, with increased end-diastolic volume and decreased ejection fraction. Left ventricular remodelling was not significantly inhibited by CADO. Segmental contractility, as assessed by the change in myocardial thickening after 2 months, was improved in CADO rats compared to control rats (+1.6% ± 0.8% vs. −2.3% ± 0.8%, p < 0.001). This improvement was significant in border (+5.6% ± 0.8% vs. +1.5% ± 0.8%, p < 0.001) and remote (−4.0% ± 1.0% vs. −10.4% ± 1.3%, p < 0.001) segments, but absent in MI segments. Histological analyses revealed that CADO reduced fibrosis, cardiomyocyte hypertrophy and apoptosis. Protective effects of CADO were blunted by 8-SPT.

Conclusion

Long-term administration of adenosine protects the left ventricle from contractile dysfunction following MI.

Hypodense regions in unenhanced CT identify nonviable myocardium: validation versus 18F-FDG PET

PURPOSE

The aim of the present study was to evaluate the accuracy of hypodense regions in non-contrast-enhanced cardiac computed tomography (unenhanced CT) to identify nonviable myocardial scar tissue.

METHODS

Hypodense areas were visually identified in unenhanced CT of 80 patients in the left ventricular anterior, apical, septal, lateral and inferior myocardium and CT density was measured in Hounsfield units (HU). Findings were compared to (18)F-fluorodeoxyglucose uptake by positron emission tomography (FDG PET), which served as the standard of reference to distinguish scar (<50 % FDG uptake) from viable tissue (≥50 % uptake).

RESULTS

Visually detected hypodense regions demonstrated a sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of 74, 97, 84 and 94 %, respectively. A receiver-operating characteristic (ROC) curve analysis revealed a cutoff value of mean HU at <28.8 for predicting scar tissue with an area under the curve of 0.93 yielding a sensitivity, specificity, PPV and NPV of 94, 90, 67 and 99 %, respectively.

CONCLUSION

Hypodense regions in unenhanced cardiac CT scans allow accurate identification of nonviable myocardial scar tissue.

Use of gated 13N-NH3 micro-PET to examine left ventricular function in rats

INTRODUCTION

Myocardial perfusion gating techniques offer the possibility of measurement of left ventricular end-systolic (ESV) and end-diastolic volume (EDV) and left ventricular ejection fraction (LVEF) in clinical and preclinical trials. The aim of this study was to evaluate left ventricular volumes (LVV) and LVEF with 13N-NH3 in comparison with the reference 18F-FDG in different rat models.

METHODS

In this study, 18 male Wistar rats, 12 control rats and 6 rats with myocardial infarction (MI) were imaged with micro-PET. The ratswere scanned with gated 13N-NH3 and 18F-FDG sequentially for the assessment of LVV and LVEF. A validated three-dimensional segmentation algorithm was used to calculate LVV and LVEF.

RESULTS

Mean LVEF measured with 13N-NH3 was 45.6±8.9 and 75.3±9.4%, mean ESV was 0.40±0.12 and 0.14±0.11 ml, and mean EDVwas 0.53±16 and 0.75±0.18 ml for MI and control rats, respectively. Moderate to good correlations were observed between values of 13N-NH3 and 18F-FDG for calculation of ESV [r=0.80, P<.0001, standard error of estimate (SEE)=0.10], EDV (r=0.63, P=.005, SEE=0.14) and LVEF (r=0.84, P<.0001, SEE=9.5). LVEF measured with 13N-NH3 was significantly lower in MI rats in comparison to measurement with 18F-FDG (45.6±8.9 vs 54.9±9.3 %; P=.04).

CONCLUSION

Correlations were moderate to good for the assessment of ESV, EDV and LVEF between gated 13N-NH3 and 18F-FDG. LVEF was underestimated with gated 13N-NH3 in rats with myocardial infarction. In healthy rats, LV volumes and LVEF can be measured reproducibly with either approach.

Ischemic heart disease: comprehensive evaluation by cardiovascular magnetic resonance

Considerable technical advances over the past decade have increased the clinical application of cardiovascular magnetic resonance (CMR) imaging. A comprehensive CMR examination can accurately measure left and right ventricular size and function, identify the presence and extent of reversible versus irreversible myocardial injury, and detect inducible ischemia. Streamlined protocols allow such a CMR examination to be a time-efficient diagnostic tool in patients with coronary artery disease. Moreover, edema imaging with T2-weighted CMR allows the detection of acute coronary syndromes. In this review, we present the relevant CMR methods and discuss practical uses of CMR in acute and chronic ischemic heart disease.

Prediction of global left ventricular functional recovery in patients with heart failure undergoing surgical revascularisation, based on late gadolinium enhancement cardiovascular magnetic resonance

BACKGROUND

The new gold standard for myocardial viability assessment is late gadolinium enhancement-cardiovascular magnetic resonance (LGE-CMR); this technique has demonstrated that the transmural extent of scar predicts segmental functional recovery. We now asked how the number of viable and number of viable+normal, segments predicted recovery of global left ventricular (LV) function in patients undergoing CABG. Finally, we examined which segmental transmural threshold of scarring best predicted global LV recovery.

METHODS AND RESULTS

Fifty patients with reduced LV ejection fraction (EF) referred for CABG were recruited, and 33 included in this analysis. Patients underwent CMR to assess LV function and viability pre-operatively at 6 days and 6 months. Mean LVEF 38% ± 11, which improved to 43% ± 12 after surgery. 21/33 patients improved EF by ≥3% (EF before 38% ± 13, after 47% ± 13), 12/33 did not (EF before 39% ± 6, after 37% ± 8). The only independent predictor for global functional recovery after revascularisation was the number of viable+normal segments: Based on a segmental transmural viability cutoff of <50%, ROC analysis demonstrated ≥10 viable+normal segments predicted ≥3% improvement in LVEF with a sensitivity of 95% and specificity of 75% (AUC = 0.9, p < 0.001). Transmural viability cutoffs of <25 and <75% and a cutoff of ≥4 viable segments were less useful predictors of global LV recovery.

CONCLUSIONS

Based on a 50% transmural viability cutoff, patients with ≥10 viable+normal segments improve global LV function post revascularisation, while patients with fewer such segments do not. LGE-CMR is a simple and powerful tool for identifying which patients with impaired LV function will benefit from CABG.

TRIAL REGISTRATION

Research Ethics Committee Unique Identifier: NRES:05/Q1603/42. The study is listed on the Current Controlled Trials Registry: ISRCTN41388968.URL: http://www.controlled-trials.com.

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

In patients with ischemic cardiomyopathy, coronary artery bypass grafting (CABG) offers an important therapeutic option but is still associated with high perioperative mortality. Although previous studies suggest a benefit from revascularization for patients with defined viability by a non-invasive technique, the role of viability assessment to determine suitability for revascularization in patients with ischemic cardiomyopathy has not yet been defined. This study evaluates the hypothesis that the use of PET imaging in the decision-making process for CABG will improve postoperative patient survival. We reviewed 476 patients with ischemic cardiomyopathy (LV ejection fraction ≤0.35) who were considered candidates for CABG between 1994 and 2004 on the basis of clinical presentation and angiographic data. In a Standard Care Group, 298 patients underwent CABG. In a second PET-assisted management group of 178 patients, 152 patients underwent CABG (PET-CABG) and 26 patients were excluded from CABG because of lack of viability (PET-Alternatives). Primary endpoint was postoperative survival. There were two in hospital deaths in the PET-CABG (1.3%) and 30 (10.1%) in the Standard Care Group (P = 0.018). The survival rate after 1, 5 and 9.3 years was 92.0, 73.3 and 54.2% in the PET-CABG and 88.9, 62.2 and 35.5% in the Standard Care Group, respectively (P = 0.005). Cox-regression analysis revealed a significant influence on long-term survival of patient selection by viability assessment via PET (P = 0.008), of LV-function (P = 0.017), and age >70 (P = 0.016). Preoperative assessment of myocardial viability via PET identifies patients, who will benefit most from CABG.

Ischemic cardiomyopathy: a clinical nuclear cardiology perspective

Ischemic cardiomyopathy results from severe extensive coronary artery disease, which is associated with left ventricular dysfunction and also, in many cases, with significant left ventricular dilatation. Mortality is high, especially in patients who satisfy myocardial viability criteria but who have not undergone revascularization. Although age, exercise capacity and comorbidity influence survival, the most important prognostic factors are the extent of the ischemia, myocardial viability and left ventricular remodeling, all of which can be successfully evaluated by gated myocardial perfusion single-photon emission computed tomography (SPECT).

Metabolic imaging using PET

INTRODUCTION

There is growing evidence that myocardial metabolism plays a key role not only in ischaemic heart disease but also in a variety of diseases which involve myocardium globally, such as heart failure and diabetes mellitus. Understanding myocardial metabolism in such diseases helps to elucidate the pathophysiology and assists in making therapeutic decisions.

MEASUREMENT

As well as providing information on regional changes, PET can deliver quantitative information about both regional and global changes in metabolism. This capability of quantitative measurement is one of the major advantages of PET along with physiological positron tracers, especially relevant in evaluating diseases which involve the whole myocardium.

DISCUSSION

This review discusses major PET tracers for metabolic imaging and their clinical applications and contributions to research regarding ischaemic heart disease and other diseases such as heart failure and diabetic heart disease. Future applications of positron metabolic tracers for the detection of vulnerable plaque are also highlighted briefly.

Myocardial viability by contrast-enhanced cardiovascular magnetic resonance in patients with coronary artery disease: comparison with gated single-photon emission tomography and FDG position emission tomography

BACKGROUND

The aim of this study was to assess the value of contrast-enhanced cardiovascular magnetic resonance (CMR) in viability for patients with coronary artery disease and left ventricular (LV) dysfunction (ejection fraction [EF] </=50%), comparing to gated thallium-201 ((201)Tl) single photon emission computed tomography (SPECT) and (18)F-fluorodeoxyglucose (FDG) positron emission tomography (PET).

METHODS AND RESULTS

One hundred sixteen patients (EF 37.8 +/- 16.2%) underwent stress-reinjection or rest-redistribution gated-SPECT and CMR (46 FDG-PET) within 1 month. All images were analyzed in a 17-segment and 0-4 scales system. Of 1972 segments, delayed enhancement (DE) on CMR correlated well with (201)Tl reduction (r = 0.90, p < 0.0001). The agreement of SPECT (>/=50% maximal (201)Tl activity) and CMR (</=50% DE) was 96.8% (kappa = 0.62). CMR detected more subendocardial scars in 18 subjects (60 segments). Reduced (201)Tl activity but none DE were observed in 19 subjects (76 segments; more inferior) who had lower EF and larger end-systolic volume (p < 0.05). Of 411 dysfunctional segments from 46 patients, FDG-PET (>/=50% of maximal FDG uptake) detected more viability (9%).

CONCLUSION

The extent of DE correlated (201)Tl activity well. CMR could detect more small infarcts, while FDG-PET could detect more viability. CMR could distinguish between artifacts or infarction on SPECT, especially in poor LV function.

FDG PET as a predictor of response to resynchronisation therapy in patients with ischaemic cardiomyopathy

PURPOSE

Although resynchronisation therapy (CRT) is a promising addition to heart failure therapy, a substantial number of patients do not respond to CRT. As FDG PET has routinely been used for prediction of improvement after revascularisation in ischaemic cardiomyopathy, it was hypothesised that there is also a relationship between the extent of viable tissue and improvement as a result of CRT.

METHODS

Thirty-nine patients with ischaemic cardiomyopathy (ejection fraction 27 +/- 9%) and a wide QRS complex underwent temporary pacing to determine the optimal pacing combination, i.e. that with the highest increase in cardiac index (CI) compared with baseline (measured by Doppler echocardiography). All patients also underwent FDG PET imaging. In 19 patients, CI measurements were repeated 10-12 weeks after permanent biventricular pacemaker implantation.

RESULTS

Echocardiography (13-segment model) showed a mean of 9.8 +/- 1.6 dyssynergic segments, with preserved FDG uptake in 4.1 +/- 2.4 segments. CI improvement at the optimal pacing site was 20 +/- 9%. There was a linear relationship between the extent of viable tissue and CI improvement during pacing (p < 0.001). Using a cut-off value of more than three viable segments (ROC analysis), FDG PET had a sensitivity of 72% and a specificity of 71% for detection of the presence of haemodynamic improvement (i.e. a CI improvement >15%). The relation between CI improvement and viable tissue was similar at follow-up.

CONCLUSION

A correlation was found between the extent of viable tissue and the haemodynamic response to CRT in patients with ischaemic cardiomyopathy, suggesting that FDG PET imaging may be useful to discriminate between responders and non-responders to CRT.