PET myocardial perfusion imaging: Trends, challenges, and opportunities.

Various non-invasive images are used in clinical practice for the diagnosis and prognostication of chronic coronary syndromes. Notably, quantitative myocardial perfusion imaging (MPI) through positron emission tomography (PET) has seen significant technical advancements and a substantial increase in its use over the past two decades. This progress has generated an unprecedented wealth of clinical information, which, when properly applied, can diagnose and fine-tune the management of patients with different types of ischemic syndromes. This state-of-art review focuses on quantitative PET MPI, its integration into clinical practice, and how it holds up at the eyes of modern cardiac imaging and revascularization clinical trials, along with future perspectives.

Validation of resting full-cycle ratio and diastolic pressure ratio with [15O]H2O positron emission tomography myocardial perfusion.

Fractional flow reserve (FFR) and instantaneous wave-free ratio (iFR) are invasive techniques used to evaluate the hemodynamic significance of coronary artery stenosis. These methods have been validated through perfusion imaging and clinical trials. New invasive pressure ratios that do not require hyperemia have recently emerged, and it is essential to confirm their diagnostic efficacy. The aim of this study was to validate the resting full-cycle ratio (RFR) and the diastolic pressure ratio (dPR), against [15O]H2O positron emission tomography (PET) imaging. A total of 129 symptomatic patients with an intermediate risk of coronary artery disease (CAD) were included. All patients underwent cardiac [15O]H2O PET with quantitative assessment of resting and hyperemic myocardial perfusion. Within a 2 week period, coronary angiography was performed. Intracoronary pressure measurements were obtained in 320 vessels and RFR, dPR, and FFR were computed. PET derived regional hyperemic myocardial blood flow (hMBF) and myocardial perfusion reserve (MPR) served as reference standards. In coronary arteries with stenoses (43%, 136 of 320), the overall diagnostic accuracies of RFR, dPR, and FFR did not differ when PET hyperemic MBF < 2.3 ml min-1 (69.9%, 70.6%, and 77.1%, respectively) and PET MPR < 2.5 (70.6%, 71.3%, and 66.9%, respectively) were considered as the reference for myocardial ischemia. Non-significant differences between the areas under the receiver operating characteristic (ROC) curve were found between the different indices. Furthermore, the integration of FFR with RFR (or dPR) does not enhance the diagnostic information already achieved by FFR in the characterization of ischemia via PET perfusion. In conclusion, the novel non-hyperemic pressure ratios, RFR and dPR, have a diagnostic performance comparable to FFR in assessing regional myocardial ischemia. These findings suggest that RFR and dPR may be considered as an FFR alternative for invasively guiding revascularization treatment in symptomatic patients with CAD.

Left-ventricular volumes and ejection fraction from cardiac ECG-gated 15O-water positron emission tomography compared to cardiac magnetic resonance imaging using simultaneous hybrid PET/MR.

BACKGROUND: 15O-water PET is the gold standard for noninvasive quantification of myocardial blood flow. In addition to evaluation of ischemia, the assessment of cardiac function and remodeling is important in all cardiac diseases. However, since 15O-water is freely diffusible and standard uptake images show little contrast between the myocardium and blood pool, the assessment of left-ventricular (LV) volumes and ejection fraction (EF) is challenging. Therefore, the aim of the present study was to investigate the feasibility of calculating LV volumes and EF from first-pass analysis of 15O-water PET, by comparison with cardiac magnetic resonance imaging (CMR) using a hybrid PET/MR scanner. METHODS: Twenty-four patients with known or suspected CAD underwent a simultaneous ECG-gated cardiac PET/MR scan. The 15O-water first-pass images (0-50 seconds) were analyzed using the CarPET software and the CMR images were analyzed using the software Segment, for LV volumes and EF calculations. The LV volumes and EF were compared using correlation and Bland-Altman analysis. In addition, inter- and intra-observer variability of LV volumes and EF were assessed for both modalities. RESULTS: The correlation between PET and CMR was strong for volumes (r > 0.84) and moderate for EF (r = 0.52), where the moderate correlation for EF was partly due to the small range of EF values. Agreement was high for all parameters, with a slight overestimation of PET values for end-diastolic volume but with no significant mean bias for other parameters. Inter- and intra-observer agreement of volumes was high and comparable between PET and CMR. For EF, inter-observer agreement was higher for PET and intra-observer agreement was higher for CMR. CONCLUSION: LV volumes and EF can be calculated by first-pass analysis of a 15O-water PET scan with high accuracy and comparable precision as with CMR.

Influence of patient motion on quantitative accuracy in cardiac 15O-water positron emission tomography.

BACKGROUND: Patient motion is a common problem during cardiac PET. The purpose of the present study was to investigate to what extent motions influence the quantitative accuracy of cardiac 15O-water PET/CT and to develop a method for automated motion detection. METHOD: Frequency and magnitude of motion was assessed visually using data from 50 clinical 15O-water PET/CT scans. Simulations of 4 types of motions with amplitude of 5 to 20 mm were performed based on data from 10 scans. An automated motion detection algorithm was evaluated on clinical and simulated motion data. MBF and PTF of all simulated scans were compared to the original scan used as reference. RESULTS: Patient motion was detected in 68% of clinical cases by visual inspection. All observed motions were small with amplitudes less than half the LV wall thickness. A clear pattern of motion influence was seen in the simulations with a decrease of myocardial blood flow (MBF) in the region of myocardium to where the motion was directed. The perfusable tissue fraction (PTF) trended in the opposite direction. Global absolute average deviation of MBF was 3.1% ± 1.8% and 7.3% ± 6.3% for motions with maximum amplitudes of 5 and 20 mm, respectively. Automated motion detection showed a sensitivity of 90% for simulated motions ≥ 10 mm but struggled with the smaller (≤ 5 mm) simulated (sensitivity 45%) and clinical motions (accuracy 48%). CONCLUSION: Patient motion can impair the quantitative accuracy of MBF. However, at typically occurring levels of patient motion, effects are similar to or only slightly larger than inter-observer variability, and downstream clinical effects are likely negligible.

Effect of PET-CT misalignment on the quantitative accuracy of cardiac 15O-water PET.

BACKGROUND: Quantification of myocardial blood flow (MBF) with PET requires accurate attenuation correction, which is performed using a separate CT. Misalignment between PET and CT scans has been reported to be a common problem. The purpose of the present study was to assess the effect of PET CT misalignment on the quantitative accuracy of cardiac 15O-water PET. METHODS: Ten clinical patients referred for evaluation of ischemia and assessment of MBF with 15O-water were included in the study. Eleven different misalignments between PET and CT were induced in 6 different directions with 10 and 20 mm amplitudes: caudal (+Z), cranial (- Z), lateral (±X), anterior (+Y), and anterior combined with cranial (+ Y and - Z). Blood flow was quantified from rates of washout (MBF) and uptake (transmural MBF, MBFt) for the whole left ventricle and the three coronary territories. The results from all misalignments were compared to the original scan without misalignment. RESULTS: MBF was only minorly affected by misalignments, but larger effects were seen in MBFt. On the global level, average absolute deviation across all misalignments for MBF was 1.7% ± 1.4% and for MBFt 5.4% ± 3.2 Largest deviation for MBF was - 4.8% ± 5.8% (LCX, X + 20) and for MBFt - 19.3% ± 9.6% (LCX, X + 20). In general, larger effects were seen in LAD and LCX compared to in RCA. CONCLUSION: The quantitative accuracy of MBF from 15O-water PET, based on the washout of the tracer, is only to a minor extent affected by misalignment between PET and CT.

Diagnosis of left ventricular hypertrophy using non-ECG-gated 15O-water PET.

AIM: To develop a method for diagnosing left ventricular (LV) hypertrophy from cardiac perfusion 15O-water positron emission tomography (PET). METHODS: We retrospectively pooled data from 139 subjects in four research cohorts. LV remodeling patterns ranged from normal to severe eccentric and concentric hypertrophy. 15O-water PET scans (n = 197) were performed with three different PET devices. A low-end scanner (66 scans) was used for method development, and remaining scans with newer devices for a blinded evaluation. Dynamic data were converted into parametric images of perfusable tissue fraction for semi-automatic delineation of the LV wall and calculation of LV mass (LVM) and septal wall thickness (WT). LVM and WT from PET were compared to cardiac magnetic resonance (CMR, n = 47) and WT to 2D-echocardiography (2DE, n = 36). PET accuracy was tested using linear regression, Bland-Altman plots, and ROC curves. Observer reproducibility were evaluated using intraclass correlation coefficients. RESULTS: High correlations were found in the blinded analyses (r ≥ 0.87, P < 0.0001 for all). AUC for detecting increased LVM and WT (> 12 mm and > 15 mm) was ≥ 0.95 (P < 0.0001 for all). Reproducibility was excellent (ICC ≥ 0.93, P < 0.0001). CONCLUSION: 15O-water PET might detect LV hypertrophy with high accuracy and precision.

Coronary Microvascular Dysfunction, Left Ventricular Remodeling, and Clinical Outcomes in Patients With Chronic Kidney Impairment.

BACKGROUND: Cardiac dysfunction and cardiovascular events are prevalent among patients with chronic kidney disease without overt obstructive coronary artery disease, but the mechanisms remain poorly understood. Coronary microvascular dysfunction has been proposed as a link between abnormal renal function and impairment of cardiac function and cardiovascular events. We aimed to investigate the relations between chronic kidney disease, coronary microvascular dysfunction, cardiac dysfunction, and adverse cardiovascular outcomes. METHODS: Patients undergoing cardiac stress positron emission tomography, echocardiogram, and renal function ascertainment at Brigham and Women's Hospital were studied longitudinally. Patients free of overt coronary (summed stress score <3 and without a history of ischemic heart disease), valvular, and end-organ disease were followed up for the adverse composite outcome of death or hospitalization for myocardial infarction or heart failure. Coronary flow reserve (CFR) was determined from positron emission tomography. Echocardiograms were used to measure cardiac mechanics: diastolic (lateral and septal E/e') and systolic (global longitudinal, radial, and circumferential strain). Image analyses and event adjudication were blinded. The associations between estimated glomerular filtration rate (eGFR), CFR, diastolic and systolic indices, and adverse cardiovascular outcomes were assessed in adjusted models and mediation analyses. RESULTS: Of the 352 patients (median age, 65 years; 63% female; 22% black) studied, 35% had an eGFR <60 mL·min-1·1.73 m-2, a median left ventricular ejection fraction of 62%, and a median CFR of 1.8. eGFR and CFR were associated with diastolic and systolic indices, as well as future cardiovascular events (all P<0.05). In multivariable models, CFR, but not eGFR, was independently associated with cardiac mechanics and cardiovascular events. The associations between eGFR, cardiac mechanics, and cardiovascular events were partly mediated via CFR. CONCLUSIONS: Coronary microvascular dysfunction, but not eGFR, was independently associated with abnormal cardiac mechanics and an increased risk of cardiovascular events. Coronary microvascular dysfunction may mediate the effect of chronic kidney disease on abnormal cardiac function and cardiovascular events in those without overt coronary artery disease.

Quantitative [18F]florbetapir PET/CT may identify lung involvement in patients with systemic AL amyloidosis.

PURPOSE: The clinical diagnosis of pulmonary involvement in individuals with systemic AL amyloidosis remains challenging. [18F]florbetapir imaging has previously identified AL amyloid deposits in the heart and extra-cardiac organs. The aim of this study is to determine quantitative [18F]florbetapir pulmonary kinetics to identify pulmonary involvement in individuals with systemic AL amyloidosis. METHODS: We prospectively enrolled 58 subjects with biopsy-proven AL amyloidosis and 9 control subjects (5 without amyloidosis and 4 with ATTR cardiac amyloidosis). Pulmonary [18F]florbetapir uptake was evaluated visually and quantified as distribution volume of specific binding (Vs) derived from compartmental analysis and simpler semiquantitative metrics of maximum standardized uptake values (SUVmax), retention index (RI), and target-to-blood ratio (TBR). RESULTS: On visual analysis, pulmonary tracer uptake was absent in most AL subjects (40/58, 69%); 12% (7/58) of AL subjects demonstrated intense bilateral homogeneous tracer uptake. In this group, compared to the control group, Vs (median Vs 30-fold higher, 9.79 vs. 0.26, p < 0.001), TBR (median TBR 12.0 vs. 1.71, p < 0.001), and RI (median RI 0.310 vs. 0.033, p < 0.001) were substantially higher. Notably, the AL group without visually apparent pulmonary [18F]florbetapir uptake also demonstrated a > 3-fold higher Vs compared to the control group (median 0.99 vs. 0.26, p < 0.001). Vs was independently related to left ventricular SUVmax, a marker of cardiac AL deposition, but not to ejection fraction, a marker of cardiac dysfunction. Also, intense [18F]florbetapir lung uptake was not related to [11C]acetate lung uptake, suggesting that intense [18F]florbetapir lung uptake represents AL amyloidosis rather than heart failure. CONCLUSIONS: [18F]florbetapir PET/CT offers the potential to noninvasively identify pulmonary AL amyloidosis, and its clinical relevance warrants further study.

Fractional flow reserve, instantaneous wave-free ratio, and resting Pd/Pa compared with [15O]H2O positron emission tomography myocardial perfusion imaging: a PACIFIC trial sub-study.

Aims: Guidelines recommend the use of fractional flow reserve (FFR) to guide percutaneous coronary intervention. For this purpose, physiological lesion assessment without adenosine may have a similar diagnostic accuracy as FFR. We aimed to investigate the performances of FFR, resting instantaneous wave-free ratio (iFR), and resting Pd/Pa compared with [15O]H2O positron emission tomography (PET) perfusion imaging. Methods and results: [15O]H2O PET and intracoronary pressure measurements were evaluated in 320 coronary arteries (of which 136 coronary stenoses) in 129 stable patients. The primary analysis consisting of the area-under-the-receiver-operating-characteristic curve for impaired PET hyperaemic myocardial blood flow (MBF) <2.3 mL⋅min-1⋅g-1 in coronary stenoses was 0.78 [95% confidence interval (CI): 0.70-0.85] for FFR, 0.74 (95% CI: 0.66-0.81) for iFR, and 0.75 (95% CI: 0.67-0.82) for Pd/Pa. No significant differences between area-under-the-receiver-operating-characteristic curve were observed for any two indices compared. In a secondary analysis, the diagnostic accuracy compared with impaired PET hyperaemic MBF in coronary stenoses was 72% (95% CI: 64-79%, κ: 0.44) for FFR ≤0.80, 72% (95% CI: 64-80%, κ: 0.44) for iFR ≤0.89, and 70% (95% CI: 62-78%, κ: 0.40) for Pd/Pa ≤0.92. Other secondary analyses included a comparison of physiological indices with PET hyperaemic MBF in all vessels and all of the aforementioned analyses using PET myocardial perfusion reserve as comparator. Statistical testing for the secondary analyses showed results that were consistent with the results of the primary analysis. Conclusion: Fractional flow reserve, iFR, and Pd/Pa showed a similar performance when compared with PET imaging. Our results support the validity of invasive physiological lesion assessment under resting conditions by iFR or Pd/Pa. Trial registration: Sub-study of the PACIFIC trial with clinicaltrials.gov identifier: NCT01521468.

Automatic calculation of myocardial external efficiency using a single 11C-acetate PET scan.

BACKGROUND: Myocardial external efficiency (MEE) is defined as the ratio of kinetic energy associated with cardiac work [forward cardiac output (FCO)*mean systemic pressure] and the chemical energy from oxygen consumed (MVO2) by the left ventricular mass (LVM). We developed a fully automated method for estimating MEE based on a single 11C-acetate PET scan without ECG-gating. METHODS AND RESULTS: Ten healthy controls, 34 patients with aortic valve stenosis (AVS), and 20 patients with mitral valve regurgitation (MVR) were recruited in a dual-center study. MVO2 was calculated using washout of 11C -acetate activity. FCO and LVM were calculated automatically using dynamic PET and parametric image formation. FCO and LVM were also obtained using cardiac magnetic resonance (CMR) in all subjects. The correlation between MEEPET-CMR and MEEPET was high (r = 0.85, P < 0.001) without significant bias. MEEPET was 23.6 ± 4.2% for controls and was lowered in AVS (17.2 ± 4.3%, P < 0.001) and in MVR (18.0 ± 5.2%, P = 0.004). MEEPET was strongly associated with both NYHA class (P < 0.001) and the magnitude of valvular dysfunction (mean aortic gradient: P < 0.001, regurgitant fraction: P = 0.009). CONCLUSION: A single 11C-acetate PET yields accurate and automated MEE results on different scanners. MEE might provide an unbiased measurement of the phenotypic response to valvular disease.

Whole-Body Biodistribution, Dosimetry, and Metabolite Correction of [11C]Palmitate: A PET Tracer for Imaging of Fatty Acid Metabolism.

INTRODUCTION: Despite the decades long use of [11C]palmitate positron emission tomography (PET)/computed tomography in basic metabolism studies, only personal communications regarding dosimetry and biodistribution data have been published. METHODS: Dosimetry and biodistribution studies were performed in 2 pigs and 2 healthy volunteers by whole-body [11C]palmitate PET scans. Metabolite studies were performed in 40 participants (healthy and with type 2 diabetes) under basal and hyperinsulinemic conditions. Metabolites were estimated using 2 approaches and subsequently compared: Indirect [11C]CO2 release and parent [11C]palmitate measured by a solid-phase extraction (SPE) method. Finally, myocardial fatty acid uptake was calculated in a patient cohort using input functions derived from individual metabolite correction compared with population-based metabolite correction. RESULTS: In humans, mean effective dose was 3.23 (0.02) µSv/MBq, with the liver and myocardium receiving the highest absorbed doses. Metabolite correction using only [11C]CO2 estimates underestimated the fraction of metabolites in studies lasting more than 20 minutes. Population-based metabolite correction showed excellent correlation with individual metabolite correction in the cardiac PET validation cohort. CONCLUSION: First, mean effective dose of [11C]palmitate is 3.23 (0.02) µSv/MBq in humans allowing multiple scans using ∼300 MBq [11C]palmitate, and secondly, population-based metabolite correction compares well with individual correction.

Effects of exenatide on cardiac function, perfusion, and energetics in type 2 diabetic patients with cardiomyopathy: a randomized controlled trial against insulin glargine.

BACKGROUND: Multiple bloodglucose-lowering agents have been linked to cardiovascular events. Preliminary studies showed improvement in left ventricular (LV) function during glucagon-like peptide-1 receptor agonist administration. Underlying mechanisms, however, are unclear. The purpose of this study was to investigate myocardial perfusion and oxidative metabolism in type 2 diabetic (T2DM) patients with LV systolic dysfunction as compared to healthy controls. Furthermore, effects of 26-weeks of exenatide versus insulin glargine administration on cardiac function, perfusion and oxidative metabolism in T2DM patients with LV dysfunction were explored. METHODS AND RESULTS: Twenty-six T2DM patients with LV systolic dysfunction (cardiac magnetic resonance (CMR) derived LV ejection fraction (LVEF) of 47 ± 13%) and 10 controls (LVEF of 59 ± 4%, P < 0.01 as compared to patients) were analyzed. Both myocardial perfusion during adenosine-induced hyperemia (P < 0.01), and coronary flow reserve (P < 0.01), measured by [15O]H2O positron emission tomography (PET), were impaired in T2DM patients as compared to healthy controls. Myocardial oxygen consumption and myocardial efficiency, measured using [11C]acetate PET and CMR derived stroke volume, were not different between the groups. Eleven patients in the exenatide group and 12 patients in the insulin glargine group completed the trial. Systemic metabolic control was improved after both treatments, although, no changes in cardiac function, perfusion and metabolism were seen after exenatide or insulin glargine. CONCLUSIONS: T2DM patients with LV systolic dysfunction did not have altered myocardial efficiency as compared to healthy controls. Exenatide or insulin glargine had no effects on cardiac function, perfusion or oxidative metabolism. Trial registration NCT00766857.

Bisoprolol in idiopathic pulmonary arterial hypertension: an explorative study.

While beta-blockers are considered contraindicated in pulmonary arterial hypertension (PAH), the prognostic significance of sympathetic nervous system over-activity suggests a potential benefit of beta-blocker therapy. The aim of this randomised, placebo-controlled, crossover, single centre study was to determine the effects of bisoprolol on right ventricular ejection fraction (RVEF) in idiopathic PAH (iPAH) patients. Additional efficacy and safety parameters were explored.Patients with optimally treated, stable iPAH (New York Heart Association functional class II/III) were randomised to placebo or bisoprolol. Imaging and functional measurements were performed at baseline, crossover and end of study.18 iPAH patients were included, because inclusion faltered before enrolment of the targeted 25 patients. 17 patients completed 6 months of bisoprolol, 15 tolerated bisoprolol, one patient required intravenous diuretics. Bisoprolol was associated with a lower heart rate (17 beats per minute, p=0.0001) but RVEF remained unchanged. A drop in cardiac index (0.5 L·min(-1)·m(-2), p=0.015) was observed, along with a trend towards a decreased 6-min walking distance (6MWD).Although careful up-titration of bisoprolol was tolerated by most patients and resulted in a decreased heart rate, no benefit of bisoprolol in iPAH was demonstrated. Decreases in cardiac index and 6MWD suggest a deteriorated cardiac function. The results do not favour the use of bisoprolol in iPAH patients.

Myocardial denervation coincides with scar heterogeneity in ischemic cardiomyopathy: A PET and CMR study.

BACKGROUND: Mismatch between myocardial innervation and perfusion assessed with positron emission tomography (PET) is a potential risk marker for ventricular arrhythmias in patients with ischemic cardiomyopathy. This mismatch zone originates from residual viable myocardium that has sustained ischemic nerve injury. Heterogenic scar size assessed with late gadolinium-enhanced (LGE) cardiac magnetic resonance imaging (CMR) is also a risk marker of ventricular arrhythmias. These two imaging parameters may represent identical morphological tissue features. The current study explored the relation between innervation-perfusion mismatch and heterogenic scar size. METHODS: Twenty-eight patients (26 males, age 67 ± 8 years) with ischemic cardiomyopathy and a left ventricular ejection fraction below 35%, eligible for ICD implantation were included. All patients underwent both [11C]-hydroxyephedrine and [15O]-water PET studies to assess myocardial sympathetic innervation and perfusion. LGE CMR was conducted to assess total myocardial scar size, scar core size, and heterogenic scar size. RESULTS: Perfusion defect size was 16.6 ± 9.9% and innervation defect size was 33.7 ± 10.8%, which resulted in an innervation-perfusion mismatch of 17.6 ± 8.9%. Total scar size, scar core size, and heterogenic scar size were 21.2 ± 8.6%, 14.7 ± 6.6%, and 6.5 ± 2.9%, respectively. No relation between scar core size and perfusion deficit size was observed (r = 0.18, P = .36). Total scar size was correlated with the innervation defect size (r = 0.52, P = .004) and the heterogenic scar zone displayed a significant correlation with the innervation-perfusion mismatch area (r = 0.67, P < .001). CONCLUSIONS: Denerved residual viable myocardium in ischemic cardiomyopathy as observed with innervation-perfusion PET is related to the heterogenic scar zone as assessed with LGE CMR.

Clinical features, exercise hemodynamics, and determinants of left ventricular elevated filling pressure in heart-transplanted patients.

This study aimed to assess clinical, functional, and hemodynamic characteristics of heart-transplanted (HTX) patients during exercise. We performed comprehensive echocardiographic graft function assessment during invasive hemodynamic semi-supine exercise test in 57 HTX patients. According to hemodynamics findings, patients were divided into Group A: normal left ventricular (LV) filling pressure (FP): pulmonary capillary wedge pressure (PCWP) <15 mmHg at rest and <25 mmHg at peak exercise, and Group B: elevated LV-FP: PCWP ≥15 mmHg at rest or ≥25 mmHg at peak exercise. Thirty-one patients (54%) had normal LV-FP and 26 patients (46%) had elevated LV-FP. The latter had higher cumulative rejection burden (P < 0.01) and were more symptomatic (NYHA class >1) (P < 0.05), and cardiac allograft vasculopathy (CAV) was more prevalent (P < 0.05). With exercise, the changes in both left- and right-sided filling pressures were significantly increased, whereas LV longitudinal myocardial deformation was lower (P < 0.05) in patients with elevated LV-FP than in patients with normal LV-FP. No between-group difference was observed for cardiac index or LV ejection fraction (LVEF) during exercise. In conclusion, elevated LV-FP can be demonstrated in approximately 50% of HTX patients. Patients with elevated LV-FP have impaired myocardial deformation capacity, higher prevalence of CAV, and higher rejection burden, and were more symptomatic. Exercise test with the assessment of longitudinal myocardial deformation should be considered in routine surveillance of HTX patients as a marker of restrictive filling (ClinicalTrials.gov Identifier: NCT02077764).

Impact of anatomical and functional severity of coronary atherosclerotic plaques on the transmural perfusion gradient: a [15O]H2O PET study.

BACKGROUND: Myocardial ischaemia occurs principally in the subendocardial layer, whereas conventional myocardial perfusion imaging provides no information on the transmural myocardial blood flow (MBF) distribution. Subendocardial perfusion measurements and quantification of the transmural perfusion gradient (TPG) could be more sensitive and specific for the detection of coronary artery disease (CAD). The current study aimed to determine the impact of lesion severity as assessed by the fractional flow reserve (FFR) on subendocardial perfusion and the TPG using [(15)O]H2O positron emission tomography (PET) imaging in patients evaluated for CAD. METHODS AND RESULTS: Sixty-six patients with anginal chest pain were prospectively enrolled and underwent [(15)O]H2O myocardial perfusion PET imaging. Subsequently, invasive coronary angiography was performed and FFR obtained in all coronary arteries irrespective of the PET imaging results. Thirty (45%) patients were diagnosed with significant CAD (i.e. FFR ≤0.80), whereas on a per vessel analysis (n = 198), 53 (27%) displayed a positive FFR. Transmural hyperaemic MBF decreased significantly from 3.09 ± 1.16 to 1.67 ± 0.57 mL min(-1) g(-1) (P < 0.001) in non-ischaemic and ischaemic myocardium, respectively. The TPG decreased during hyperaemia when compared with baseline (1.20 ± 0.14 vs. 0.94 ± 0.17, P < 0.001), and was lower in arteries with a positive FFR (0.97 ± 0.16 vs. 0.88 ± 0.18, P < 0.01). A TPG threshold of 0.94 yielded an accuracy to detect CAD of 59%, which was inferior to transmural MBF with an optimal cutoff of 2.20 mL min(-1) g(-1) and an accuracy of 85% (P < 0.001). Diagnostic accuracy of subendocardial perfusion measurements was comparable with transmural MBF (83 vs. 85%, respectively, P = NS). CONCLUSION: Cardiac [(15)O]H2O PET imaging is able to distinguish subendocardial from subepicardial perfusion in the myocardium of normal dimensions. Hyperaemic TPG is significantly lower in ischaemic myocardium. This technique can potentially be employed to study subendocardial perfusion impairment in more detail. However, the diagnostic accuracy of subendocardial hyperaemic perfusion and TPG appears to be limited compared with quantitative transmural MBF, warranting further study.

Outcome prediction by myocardial external efficiency from 11 C-acetate positron emission tomography in cardiac amyloidosis.

AIMS: This study aimed to study the prognostic value of myocardial oxygen consumption (MVO2 ) and myocardial external efficiency (MEE) from 11 C-acetate positron emission tomography (PET) in cardiac amyloidosis (CA) patients. METHODS AND RESULTS: Forty-eight CA patients, both transthyretin (ATTR) and immunoglobulin light chain (AL) amyloidosis, and 20 controls were included. All subjects were examined with 11 C-acetate PET and echocardiography. MVO2 , forward stroke volume (FSV), and left ventricular mass (LVM) were derived from 11 C-acetate PET and used to calculate MEE. CA patients were followed for survival and the prognostic impact of clinical, echocardiographic, and 11 C-acetate PET parameters was analysed. MVO2 and MEE were reduced in CA compared with controls, but without significant difference between deceased and surviving CA patients. The ratio of 11 C-acetate PET-derived FSV and LVM was also reduced in CA and significantly lowered in deceased patients compared with survivors. In univariate analysis, New York Heart Association class, N-terminal pro-brain natriuretic peptide, and the 11 C-acetate PET parameters FSV/LVM and MEE were the strongest prognostic factors. Of the 11 C-acetate PET parameters, FSV/LVM was the strongest survival predictor with hazard ratio of 0.56 per 0.1 mL/g (95% confidence interval 0.39-0.81, P = 0.002) and independently prognostic in a multivariate model. MEE significantly separated deceased from surviving CA patients with the cut-off of 15.7% (P = 0.032). Survival was significantly shorter with FSV/LVM below 0.27 mL/g (P < 0.001), also when separating AL- and ATTR-CA. CONCLUSIONS: Reduced MEE was associated with shorter survival in CA patients, but FSV/LVM was the strongest survival predictor and the only independently prognostic 11 C-acetate PET parameter in multivariate analysis.

Quantitation of mitral regurgitation using positron emission tomography.

BACKGROUND: Cardiac positron emission tomography (PET) offers non-invasive assessment of perfusion and left ventricular (LV) function from a single dynamic scan. However, no prior assessment of mitral regurgitation severity by PET has been presented. Application of indicator dilution techniques and gated image analyses to PET data enables calculation of forward stroke volume and total LV stroke volume. We aimed to evaluate a combination of these methods for measurement of regurgitant volume (RegVol) and fraction (RegF) using dynamic 15O-water and 11C-acetate PET in comparison to cardiovascular magnetic resonance (CMR). RESULTS: Twenty-one patients with severe primary mitral valve regurgitation underwent same-day dynamic PET examinations (15O-water and 11C-acetate) and CMR. PET data were reconstructed into dynamic series with short time frames during the first pass, gated 15O-water blood pool images, and gated 11C-acetate myocardial uptake images. PET-based RegVol and RegF correlated strongly with CMR (RegVol: 15O-water r = 0.94, 11C-acetate r = 0.91 and RegF: 15O-water r = 0.88, 11C-acetate r = 0.84, p < 0.001). A systematic underestimation (bias) was found for PET (RegVol: 15O-water - 11 ± 13 mL, p = 0.002, 11C-acetate - 28 ± 16 mL, p < 0.001 and RegF: 15O-water - 4 ± 6%, p = 0.01, 11C-acetate - 10 ± 7%, p < 0.001). PET measurements in patients were compared to healthy volunteers (n = 18). Mean RegVol and RegF was significantly lower in healthy volunteers compared to patients for both tracers. The accuracy of diagnosing moderately elevated regurgitant volume (> 30mL) was 95% for 15O-water and 92% for 11C-acetate. CONCLUSIONS: LV regurgitation severity quantified using cardiac PET correlated with CMR and showed high accuracy for discriminating patients from healthy volunteers.

Myocardial External Efficiency in Asymptomatic Severe Primary Mitral Regurgitation Using 11C-Acetate PET.

Subjects with asymptomatic moderate-to-severe or severe primary mitral regurgitation are closely observed for signs of progression or symptoms requiring surgical intervention. The role of myocardial metabolic function in progression of mitral regurgitation is poorly understood. We used 11C-acetate PET to noninvasively measure myocardial mechanical external efficiency (MEE), which is the energetic ratio of external cardiac work and left ventricular (LV) oxygen consumption. Methods: Forty-seven patients in surveillance with mitral regurgitation and no or minimal symptoms prospectively underwent PET, echocardiography, and cardiac MRI on the same day. PET was used to simultaneously measure cardiac output, LV mass, and oxygen consumption to establish MEE. PET findings were compared between patients and healthy volunteers (n = 9). MEE and standard imaging indicators of regurgitation severity, LV volumes, and function were studied as predictors of time to surgical intervention. Patients were followed a median of 3.0 y (interquartile range, 2.0-3.8 y), and the endpoint was reached in 22 subjects (47%). Results: MEE in patients reaching the endpoint (23.8% ± 5.0%) was lower than in censored patients (28.5% ± 4.5%, P = 0.002) or healthy volunteers (30.1% ± 4.9%, P = 0.001). MEE with a cutoff lower than 25.7% was significantly associated with the outcome (hazard ratio, 7.5; 95% CI, 2.7-20.6; P < 0.0001) and retained independent significance when compared with standard imaging parameters. Conclusion: MEE independently predicted time to progression requiring valve surgery in patients with asymptomatic moderate-to-severe or severe primary mitral regurgitation. The study suggests that inefficient myocardial oxidative metabolism precedes clinically observed progression in mitral regurgitation.

Association of Right Ventricular Myocardial Blood Flow With Pulmonary Pressures and Outcome in Cardiac Amyloidosis.

BACKGROUND: Cardiac amyloidosis (CA) is a restrictive and infiltrative cardiomyopathy, characterized by increased biventricular filling pressures and low output. Symptoms are predominantly of right heart origin. The role of right ventricular (RV) myocardial blood flow (MBF) in CA has not been studied. OBJECTIVES: This study aimed to first associate RV MBF measured by using positron emission tomography (PET) with reference standards of RV pressures and then to explore its prognostic value in CA. METHODS: Cardiac PET was performed at rest in 52 patients with CA and 9 healthy control subjects. MBF was quantified from the right and left ventricles by using 11C-acetate, 15O-water, or both (n = 25). RV pressure was measured invasively or by echocardiography. Associations between biventricular MBF toward symptoms, RV function, and outcome (death or acute heart failure) were studied in patients with CA. RESULTS: MBF of the right ventricle (MBFRV) and the ratio of MBFRV and MBF of the left ventricle (MBFRV/LV) for the 2 tracers were significantly correlated (r > 0.92). MBFRV was directly correlated with RV systolic pressures with both tracers (P ≤ 0.005). MBFLV was inversely correlated with wall thickness (P < 0.0001). MBFRV/LV was significantly associated with N-terminal pro-B-type natriuretic peptide levels, NYHA functional class, RV pressures, and RV systolic function (all; P < 0.001). Twenty-six cardiac events (25 deaths) occurred during follow-up (median 44 months). MBFRV/LV higher than 56% was associated with a diagnosis of pulmonary hypertension (AUC: 0.96 [95% CI: 0.91-1.00]; P < 0.0001); and predicted outcome with HR: 9.0 (95% CI: 4.2-14.5), P < 0.0001). CONCLUSIONS: Measurements of MBFRV using PET are feasible, as confirmed with 2 different tracers. Imbalance between RV and LV myocardial perfusion is associated with increased RV load and adverse events in cardiac amyloidosis.