Determinants of the response of left ventricular ejection fraction to vasodilator stress in electrocardiographically gated 82rubidium myocardial perfusion PET

Dose-consistent dynamic SPECT

BACKGROUND

Coronary flow reserve (CFR) values measured by dynamic SPECT systems are typically consistent with other modalities (e.g., PET). However, large discrepancies are often observed for individual patients. Positioning of the region-of-interest (ROI), representing the arterial input function (AIF) could explain some of these discrepancies. We explored the possibility of positioning the ROI in a manner that evaluates its consistency with patient-based injected radiotracer doses.

METHODS

Dose-consistent dynamic SPECT methodology was introduced, and its application was demonstrated in a twenty-patient clinical study. The effect of various ROI positions was investigated and comparison to myocardial perfusion imaging was performed.

RESULTS

Mean AIF ratios were consistent with the injected dose ratios for all examined ROI positions. Good agreement (> 80%) between total perfusion deficit and CFR was found in the detection of obstructive CAD patients for all ROIs considered. However, for individual patients, significant dependence on ROI position was observed (altering CFR by typically 30%). The proposed methodology's uncertainty was evaluated (~ 7%) and found to be smaller than the variability due to choice of ROI position.

CONCLUSION

Dose-consistent dynamic SPECT may contribute to evaluating uncertainty of CFR measurements and may potentially decrease uncertainty by allowing improved ROI positioning for individual patients.

Prognostic value of early left ventricular ejection fraction reserve during regadenoson stress solid-state SPECT-MPI

BACKGROUND

We hypothesized early post-stress left ventricular ejection fraction reserve (EFR) on solid-state-SPECT is associated with major cardiac adverse events (MACE).

METHODS

151 patients (70 ± 12 years, male 50%) undergoing same-day rest/regadenoson stress 99mTc-sestamibi solid-state SPECT were followed for MACE. Rest imaging was performed in the upright and supine positions. Early stress imaging was started 2 minutes after the regadenoson injection in the supine position and followed by late stress acquisition in the upright position. Total perfusion deficit (TPD) and functional parameters were quantified automatically. EFR, ∆end-diastolic volume (EDV), and end-systolic volume (ESV) were calculated as the difference between stress and rest values in the same position. EFR < 0%, ∆EDV ≥ 5 ml, or ∆ESV ≥ 5 ml was defined as abnormal.

RESULTS

During the follow-up (mean 3.2 years), 28 MACE occurred (19%). In Kaplan-Meier analysis, there was a significantly decreased event-free survival in patients with early EFR < 0% (P = 0.004). Similarly, there was a decreased event-free survival in patients with ∆ESV ≥ 5 ml at early stress (P = 0.003). However, EFR, ∆EDV, and ∆ESV at late stress were not associated with MACE-free survival. Cox proportional hazards model adjusting for clinical information and stress TPD demonstrated that EFR, ∆EDV, and ∆ESV at early stress were significantly associated with MACE (P < 0.05 for all).

CONCLUSIONS

Reduced early post-stress EFR on vasodilator stress solid-state SPECT is associated with MACE.

Left ventricular ejection fraction, myocardial blood flow and hemodynamic variables in adenosine and regadenoson vasodilator 82-Rubidium PET

AIMS

In most Rubidium-(Rb)-positron emission tomography (PET) studies, dipyridamole was used as vasodilator. The aim was to evaluate vasodilator PET left ventricular ejection fraction (LVEF), myocardial blood flow (MBF), hemodynamics, and the influence of adenosine and regadenoson on these variables.

METHODS AND RESULTS

Consecutive patients (N = 2299) with prior coronary artery disease (CAD) or no prior CAD undergoing adenosine/regadenoson 82Rb-PET were studied and compared according to CAD status and normal/abnormal PET (summed stress score 0-3 vs. ≥4). Rest and stress LVEF differed significantly depending on CAD status and scan results. In patients with no prior CAD, rest/stress LVEF were 68% and 72%, in patients with prior CAD 60% and 63%. LVEF during stress increased 5 ± 6% in normal compared to 1 ± 8% in abnormal PET (P<0.001). Global rest myocardial blood flow(rMBF), stress MBF(sMBF) and myocardial flow reserve (sMBF/rMBF) were significantly higher in no prior CAD patients compared to prior CAD patients(1.3 ± 0.5, 3.3 ± 0.9, 2.6 ± 0.8 and 1.2 ± 0.4, 2.6 ± 0.8, 2.4 ± 0.8 ml/g/min, respectively, P<0.001) and in normal versus abnormal scans, irrespective of CAD status(no prior CAD: 1.4 ± 0.5, 3.5 ± 0.8, 2.8 ± 0.8 and 1.2 ± 0.8, 2.5 ± 0.8, 2.2 ± 0.7; prior CAD: 1.3 ± 0.4, 3.1 ± 0.8, 2.7 ± 0.8 and 1.1 ± 0.4, 2.3 ± 0.7, 2.2 ± 0.7 ml/g/min, respectively, P<0.001). LVEF and hemodynamic values were similar for adenosine and regadenoson stress. Stress LVEF ≥70% excluded relevant ischemia (≥10%) with a negative predictive value (NPV) of 94% (CI 92-95%).

CONCLUSIONS

Rest/stress LVEF, LVEF reserve and MBF values are lower in abnormal compared to normal scans. Adenosine and regadenoson seem to have similar effect on stress LVEF, MBF and hemodynamics. A stress LVEF ≥70% has a high NPV to exclude relevant ischemia.

Gating Approaches in Cardiac PET Imaging

Cardiac PET provides high sensitivity and high negative predictive value in the diagnosis of coronary artery disease and cardiomyopathies. Cardiac, respiratory as well as bulk patient motion have detrimental effects on thoracic PET imaging, in particular on cardiovascular PET imaging where the motion can affect the PET images quantitatively as well as qualitatively. Gating can ameliorate the unfavorable impact of motion additionally enabling evaluation of left ventricular systolic function. In this article, the authors review the recent advances in gating approaches and highlight the advances in data-driven approaches, which hold promise in motion detection without the need for complex hardware setup.

Independent prognostic value of left ventricular contractile reserve and chronotropic response in patients with reduced left ventricular ejection fraction undergoing vasodilator stress myocardial perfusion imaging with Rb-82 positron emission tomography

Objectives

We evaluated the prognostic value of heart rate reserve (ΔHR) and left ventricular ejection fraction reserve (ΔLVEF) among patients with systolic dysfunction.

Background

Inadequate ΔHR (maximal stress HR - resting HR) and ΔLVEF (LVEF at stress - LVEF at rest) in response to stress are associated with adverse cardiac events. However, the significance of an abnormal ΔHR and ΔLVEF in patients with systolic dysfunction has not been described.

Methods and results

We performed a retrospective analysis of patients with rest LVEF < 45% who underwent dipyridamole stress-rest gated Rb-82 PET myocardial perfusion imaging (PET-MPI) at the Cleveland Clinic between 2006 and 2009. Stress LVEF and volumes were calculated using commercially available software (4DM). A Cox proportional hazards model (CPH) was used to examine the association between ΔLVEF, ΔHR, and all-cause death (ACD). Among 461 patients (mean age 65.7 ± 11.3 years, 82% men) 167 experienced ACD (median follow-up 1045 days). Survival was reduced among patients with ΔHR < 0 (1090 vs. 1300 days, P = 0.04) and ΔLVEF < 0 (1002 vs. 1057 days, P = 0.03). In a CPH after adjusting for confounding variables, ΔHR ≤ 0 and ΔLVEF ≤ 0 were associated with reduced survival (hazard ratio 0.93, P < 0.01 and 0.84, P = 0.01, respectively) with an interaction between age and ΔHR (χ2 = 8.1, P < 0.01). Our model predicts that the magnitude of ΔHR is associated with improved survival among younger patients. For any given ΔLVEF the magnitude of ΔHR has a greater positive effect on survival among younger patients.

Conclusion

Both ΔHR and ΔLVEF during pharmacologic stress PET-MPI provide incremental value in predicting ACD among patients with systolic dysfunction.

Myocardial blood flow and left ventricular functional reserve in hypertrophic cardiomyopathy: a 13NH3 gated PET study

INTRODUCTION

Ischemia in hypertrophic cardiomyopathy (HCM) is caused by coronary microvascular dysfunction (CMD), which is detected by measuring myocardial blood flow (MBF) with PET. Whether CMD may be associated with ischemic left ventricular (LV) dysfunction is unclear. We therefore assessed LV ejection fraction (EF) reserve in HCM patients undergoing dipyridamole (Dip) PET.

METHODS

Resting and stress ¹³NH₃ dynamic as well as gated PET were performed in 34 HCM patients. Segmental MBF and transmural perfusion gradient (TPG = subendocardial / subepicardial MBF) were assessed. LVEF reserve was considered abnormal if Dip LVEF decreased more than 5 units as compared to rest.

RESULTS

Eighteen patients had preserved (group A) and 16 abnormal LVEF reserve (group B; range -7 to -32). Group B patients had greater wall thickness than group A, but resting volumes, LVEF, resting and Dip MBF, and myocardial flow reserve were similar. Group B had slightly higher summed stress score and summed difference score in visual analysis than group A, and a significantly higher summed stress wall motion score. In group B, resting TPG was slightly lower (1.31 ± 0.29 vs. 1.37 ± 0.34, p <0.05), and further decreased after Dip, whilst in group A it increased (B = 1.20 ± 0.39, p < 0.0001 vs. rest and vs. A = 1.40 ± 0.43). The number of segments per patient with TPG <1 was higher than in group A (p < 0.001) and was a significant predictor of impaired LVEF reserve (OR 1.86, p < 0.02), together with wall thickness (OR 1.3, p < 0.02).

CONCLUSION

Abnormal LVEF response is common in HCM patients following Dip, and is related to abnormal TPG, suggesting that subendocardial ischemia might occur under Dip and cause transient LV dysfunction. Although in vivo this effect may be hindered by the adrenergic drive associated with effort, these findings may have relevance in understanding exercise limitation and heart failure symptoms in HCM.

Benefit of ECG-gated rest and stress N-13 cardiac PET imaging for quantification of LVEF in ischemic patients

BACKGROUND

ECG-gated rest-stress cardiac PET can lead to simultaneous quantification of both left ventricular ejection fraction and flow impairment. In this study, our aim was to assess the benefit of rest and stress PET ejection fraction (EF) (EFp) in relation to single-photon emission computed tomography (SPECT) EF (EFs) and echocardiography EF (EFe). To this effect, the EFp was compared with EFs and EFe. Further, the relation between rest and stress EFp was also assessed.

METHODS

ECG-gated N-13 ammonia rest and stress PET imaging was performed in 26 patients. EFp values were obtained using gated reconstruction of the data in Flowquant. In 13 patients, EFs and EFe values were obtained through chart review. Correlation, analysis of variance, and Bland-Altman analyses were performed. P values less than 0.05 were used for statistical significance.

RESULTS

The rest and stress EFp values correlated significantly (r=0.80 and 0.71, respectively; P<0.05) with EFs values. There was moderate correlation with statistical significance (P<0.05) between the rest and stress EFp and EFe values (r=0.58 and 0.50, respectively). The mean rest and stress EFp values were not significantly different from mean EFs values. Also, the rest EFp and stress EFp values correlated well (r=0.81, P<0.05) and were not significantly different. Bland-Altman analysis showed no significant bias between the rest and stress EFp, and EFs, and EFe values.

CONCLUSION

Rest and stress EFp values obtained through an ECG-gated PET scan can be used for clinical diagnosis in place of conventional methods like SPECT and echocardiography.

Cardiac PET perfusion: prognosis, risk stratification, and clinical management

Myocardial perfusion imaging (MPI) with PET has expanded significantly over the past decade. With the wider availability of PET scanners and the routine use of quantitative blood flow imaging, the clinical use of PET MPI is expected to increase further. PET MPI is a powerful tool to identify risk, to quantify risk, and to guide therapy in patients with known or suspected coronary artery disease. A large body of evidence supports the prognostic value of PET MPI and ejection fraction in intermediate- to high-risk subjects, in women, in obese individuals, and in post-coronary artery bypass grafting individuals. A normal perfusion study indicates low risk (<1% annualized rate of cardiac events of cardiac death and non-fatal myocardial infarction), while an abnormal study indicates high risk. With accurate risk stratification, high-quality images, and quantitation, PET MPI may transform the management of patients with known or suspected coronary artery disease.

Coronary flow reserve estimated by positron emission tomography to diagnose significant coronary artery disease and predict cardiac events

Coronary artery disease (CAD) is a major cause of death in Japan. Coronary angiography is useful to assess the atherosclerotic burden in CAD patients, but its ability to predict whether patients will respond favorably to optimal medical therapy and revascularization is limited. The measurement of the fractional flow reserve with angiography is a well-validated method for identifying ischemic vessels. However, neither an anatomical assessment nor a functional assessment can delineate microvasculature or estimate its function. The quantitative coronary flow reserve (CFR) estimated from sequential myocardial perfusion images obtained by positron emission tomography (PET) during stress provides an accurate index of hyperemic reactivity to vasodilatory agents in the myocardium. In fact, there is growing evidence that the CFR reflects disease activity in the entire coronary circulation, including epicardial coronary artery stenosis, diffuse atherosclerosis, and microvascular dilatory function. Importantly, reduced CFR is observed even in patients without flow-limiting coronary stenosis, and its evaluation can improve the risk stratification of patients at any stage of CAD. This review focuses on the application of CFR estimated by cardiac PET for the diagnosis and risk stratification of patients with CAD.

Consistency of myocardial mass computations as a quality control check on rest and stress left ventricular ejection fractions computed from (82)Rb PET data

PURPOSE

Changes in left ventricular (LV) ejection fraction (EF) seen in gated Rb data are of interest because the heart is in a genuinely different physiologic state during stress than at rest. A measure that validates internal consistency of LV EF data would be highly desirable. Left ventricular mass calculations are performed simultaneously with EF determinations, requiring similar operator choices, and although LV volumes may change from rest to stress, mass values should be constant. Constancy of LV mass calculations could provide a useful internal check on the consistency of LV EF computations.

PATIENTS AND METHODS

We retrospectively reviewed data for 205 patients referred for evaluation of known or suspected coronary disease who had rest and regadenoson stress gated Rb PET/CT myocardial perfusion imaging. Equilibrium gated myocardial perfusion PET data were analyzed to calculate LV volumes, EF, and simultaneously mass values.

RESULTS

Rest mass ranged from 62 to 284 g (median, 115 g), stress mass from 39 to 315 g (median, 120 g), and differences were -25 to +25 g (median, 1 g). Rest and stress mass values were statistically similar (121 ± 37 g vs 124 ± 49 g, P = 0.45) and correlated strongly with one another (r = 0.94, P < 0.0001).

CONCLUSIONS

Left ventricular mass calculations are constant from rest to stress over a wide range of ventricular volumes and ejection fractions. Consistency of LV mass values can serve as confirmation of the appropriateness of operator choices when LV EF calculations are performed.

The relationship between ischemia-induced left ventricular dysfunction, coronary flow reserve, and coronary steal on regadenoson stress-gated (82)Rb PET myocardial perfusion imaging

BACKGROUND

Gated rubidium-82 ((82)Rb) positron emission tomography (PET) imaging studies are acquired both at rest and during pharmacologic stress. Stress-induced ischemic left ventricular dysfunction (LVD) can produce a significant decrease in left ventricular ejection fraction (LVEF) from rest to stress. We determined the prevalence on PET of stress LVD with reduced ejection fraction (EF) and its association with absolute global and regional coronary flow reserve (CFR), and with relative perfusion defect summed difference score (SDS).

METHODS AND RESULTS

We studied 205 patients with known or suspected coronary disease (120 M, 75 F, age 69 ± 13 years) who had clinically indicated rest/regadenoson stress (82)Rb PET/CT studies. Data were acquired in dynamic gated list mode. Global and 17-segment regional CFR values were computed from first-pass flow data using a 2-compartment model and factor analysis applied to auto-generated time-activity curves. Rest and stress LVEF and SDS were quantified from gated equilibrium myocardial perfusion tomograms using Emory Cardiac Toolbox software. LVD was defined as a change in LVEF of ≤-5% from rest to stress. A subgroup of 109 patients also had coronary angiography. Stress LVD developed in 32 patients (16%), with mean EF change of -10 ± 5%, vs +6 ± 7% for patients without LVD (P < .0001). EF was similar at rest in patients with and without stress LVD (57 ± 18% vs 56 ± 16%, P = .63), but lower during stress for patients with LVD (47 ± 20% vs 61 ± 16%, P = .0001). CFR was significantly lower in patients with LVD (1.61 ± 0.67 vs 2.21 ± 1.03, Wilcoxon P = .002), and correlated significantly with change in EF (r = 0.35, P < .0001), but not with SDS (r = -0.13, P = .07). The single variable most strongly associated with high risk of CAD (i.e., left main stenosis ≥50%, LAD % stenosis ≥70%, and/or 3-vessel disease) was stress EF (χ(2) = 17.3, P < .0001). There was a higher prevalence of patients with territorial CFR values ≤1.0, consistent with coronary steal, in the LVD group than in the non-LVD group (39% vs 12%, P = .001).

CONCLUSIONS

LVD developed in 16% of patients undergoing (82)Rb PET myocardial perfusion imaging, and was associated with multivessel coronary artery disease. There was a significant relationship between LVD and coronary blood flow during stress, with LVD corresponding to a low CFR. Territorial CFR ≤1.0 was more common in patients with LVD than those without, suggesting that coronary steal is an important pathophysiologic mechanism contributing to pharmacologic stress-induced LVD.

Detection of obstructive coronary artery disease using regadenoson stress and 82Rb PET/CT myocardial perfusion imaging

Our objective was to study the diagnostic performance of regadenoson (82)Rb myocardial perfusion PET imaging to detect obstructive coronary artery disease (CAD).

METHODS

We studied 134 patients (mean age, 63 ± 12 y; mean body mass index, 31 ± 9 kg/m(2)) without known CAD (96 with coronary angiography and 38 with low pretest likelihood of CAD). Stress left ventricular ejection fraction (LVEF) minus rest LVEF defined LVEF reserve. The Duke score was used to estimate the anatomic extent of jeopardized myocardium.

RESULTS

Regadenoson PET had a high sensitivity, 92% (95% confidence interval [CI], 83%-97%), in detecting obstructive CAD, with a normalcy rate of 97% (95% CI, 86%-99%), specificity of 77% (54/70 patients; 95% CI, 66%-86%), and area under the receiver-operator-characteristic curve of 0.847 (95% CI, 0.774-0.903; P < 0.001). Regadenoson PET demonstrated high sensitivity to detect CAD in patients with single-vessel CAD (89%; 95% CI, 70%-98%). The mean LVEF reserve was significantly higher in patients with normal myocardial perfusion imaging results (6.5% ± 5.4%) than in those with mild (4.3 ± 5.1, P = 0.03) and moderate to severe reversible defects (-0.2% ± 8.4%, P = 0.001). Also, mean LVEF reserve was significantly higher in patients with a low likelihood of CAD (7.2% ± 4.5%, P < 0.0001) and mild or moderate jeopardized myocardium than in those with significant jeopardized myocardium (score ≥ 6), -2.8% ± 8.3%.

CONCLUSION

Regadenoson (82)Rb myocardial perfusion imaging is accurate for the detection of obstructive CAD. LVEF reserve is high in patients without significant ischemia or significant angiographic jeopardized myocardium.

Left ventricular functional changes after adenosine vasodilator stress evaluated by gated single-photon emission computed tomography

OBJECTIVES

Gated single-photon emission computed tomography (SPECT) myocardial perfusion imaging is useful in assessing left ventricular (LV) myocardial perfusion and function. This study evaluated the LV functional changes after adenosine vasodilator stress, using gated SPECT.

METHODS

The study population consisted of 70 patients who underwent adenosine-mediated stress and rest SPECT. All patients underwent coronary angiography. Semi-quantitative assessment of perfusion was analyzed and produced the summed rest score (SRS), the summed stress score (SSS) and the summed difference score (SDS). The global LV function parameters [ejection fraction (EF), end-diastolic volume (EDV), end-systolic volume (ESV)] and regional LV function [the summed motion score (SMS) and the summed thickening score (STS)] were quantified by gated SPECT.

RESULTS

Patients were divided into 2 groups: group 1 comprised 16 patients with worsening of LVEF (LVEFrest-LVEFado ≥5%), and group 2 comprised the other 54 patients. Compared with group 2, patients in group 1 had a significantly higher SSS and SDS (9.1 ± 6.8 vs. 5.6 ± 4.5 and 6.6 ± 3.8 vs. 3.6 ± 4.0, respectively; p < 0.05) and the severity of coronary artery stenosis was more serious (p < 0.05).

CONCLUSION

Worsening of LVEF after adenosine-induced vasodilator stress, as shown by (99m)Tc-MIBI gated SPECT, is a valuable nonperfusion marker of significant CAD.

⁸²Rb PET myocardial perfusion imaging is superior to ⁹⁹mTc-labelled agent SPECT in patients with known or suspected coronary artery disease

PURPOSE

We compared the quality, interpretive confidence and interreader agreement between SPECT and PET myocardial perfusion imaging (MPI) in the same group of patients.

METHODS

The study group comprised 27 patients (age 55 ± 8.5 years, 12 men) with known or suspected coronary artery disease (CAD) who had undergone gated rest/stress MPI with (99m)Tc-labelled agent SPECT (with and without attenuation correction, AC), and subsequent clinical confirmation with (82)Rb PET. Three experienced readers blinded to the clinical information interpreted all MPI studies.

RESULTS

Interreader agreement was significantly superior for PET studies than for SPECT studies. Following consensus interpretation, the quality of 22 % of the non-AC SPECT studies, 33 % of the AC SPECT studies and 63 % of the PET studies was assessed as excellent or good (p = 0.016). Interpretations were definitely normal or abnormal in 7 % of non-AC SPECT studies, 30 % of AC SPECT studies and 85 % of PET studies (p = 0.046). In 13 patients who had received either invasive coronary angiography or CT angiography with no significant CAD, the true-positive rate for significant CAD was higher for PET, and the true-negative rate was equal for PET and AC SPECT, and lower for non-AC SPECT.

CONCLUSION

(82)Rb PET MPI, used as a confirmatory test after SPECT, offers improved image quality, interpretive confidence and interreader agreement.

Transient ischemic dilation ratio in 82Rb PET myocardial perfusion imaging: normal values and significance as a diagnostic and prognostic marker

In myocardial perfusion SPECT, transient ischemic dilation ratio (TID) is a well-established marker of severe ischemia and adverse outcome. However, its role in the setting of (82)Rb PET is less well defined.

METHODS

We analyzed 265 subjects who underwent clinical rest-dipyridamole (82)Rb PET/CT. Sixty-two subjects without a prior history of cardiac disease and with a normal myocardial perfusion study had either a low or a very low pretest likelihood of coronary artery disease or negative CT angiography. These subjects were used to establish a reference range of TID. In the remaining 203 patients with an intermediate or high pretest likelihood, subgroups with normal and abnormal TID were established and compared with respect to clinical variables, perfusion defect scores, left ventricular function, and absolute myocardial flow reserve. Follow-up was obtained for 969 ± 328 d to determine mortality by review of the social security death index.

RESULTS

In the reference group, TID ratio was 0.98 ± 0.06. Accordingly, a threshold for abnormal TID was set at greater than 1.13 (0.98 + 2.5 SDs). In the study group, 19 of 203 patients (9%) had an elevated TID ratio. Significant differences between subgroups with normal and abnormal TID ratio were observed for ejection fraction reserve (5.0 ± 6.4 vs. 1.8 ± 7.9; P < 0.05), difference between end-systolic volume (ESV) at rest and stress (ΔESV[stress-rest]; 1.8 ± 7.4 vs. 12.3 ± 13.0 mL; P < 0.0001), difference between end-diastolic volume (EDV) at rest and stress (ΔEDV[stress-rest]; 10.8 ± 11.5 vs. 23.8 ± 14.6 mL; P < 0.0001), summed rest score (1.8 ± 3.8 vs. 3.8 ± 7.6; P < 0.05), summed stress score (3.0 ± 5.4 vs. 7.5 ± 9.8; P < 0.002), summed difference score (1.3 ± 2.6 vs. 3.7 ± 5.3; P < 0.02), and global myocardial flow reserve (2.1 ± 0.8 vs. 1.7 ± 0.6; P < 0.02). Additionally, TID-positive patients had a significantly lower overall survival probability (P < 0.05). In a subgroup analysis of patients without regional perfusion abnormalities, TID-positive patients' overall survival probability was significantly smaller (P < 0.03), and TID was an independent predictor (exponentiation of the B coefficients [Exp(b)] = 6.22; P < 0.009) together with an ejection fraction below 45% (Exp[b] = 6.16; P < 0.002).

CONCLUSION

The present study suggests a reference range of TID for (82)Rb PET myocardial perfusion imaging that is in the range of previously established values for SPECT. Abnormal TID in (82)Rb PET is associated with more extensive left ventricular dysfunction, ischemic compromise, and reduced global flow reserve. Preliminary outcome analysis suggests that TID-positive subjects have a lower overall survival probability.

Cardiac PET/CT for the evaluation of known or suspected coronary artery disease

Positron emission tomography (PET) is increasingly being applied in the evaluation of myocardial perfusion. Cardiac PET can be performed with an increasing variety of cyclotron- and generator-produced radiotracers. Compared with single photon emission computed tomography, PET offers lower radiation exposure, fewer artifacts, improved spatial resolution, and, most important, improved diagnostic performance. With its capacity to quantify rest-peak stress left ventricular systolic function as well as coronary flow reserve, PET is superior to other methods for the detection of multivessel coronary artery disease and, potentially, for risk stratification. Coronary artery calcium scoring may be included for further risk stratification in patients with normal perfusion imaging findings. Furthermore, PET allows quantification of absolute myocardial perfusion, which also carries substantial prognostic value. Hybrid PET-computed tomography scanners allow functional evaluation of myocardial perfusion combined with anatomic characterization of the epicardial coronary arteries, thereby offering great potential for both diagnosis and management. Additional studies to further validate the prognostic value and cost effectiveness of PET are warranted.

Prognostic implications of post-stress ejection fraction decrease detected by gated SPECT in the absence of stress-induced perfusion abnormalities

PURPOSE

The prognostic meaning of a post-stress ejection fraction (EF) decrease detected by perfusion gated SPECT is still unclear.We therefore followed up patients with post-stress EF decrease in the absence of stress-induced perfusion abnormalities.

METHODS

We prospectively enrolled 57 consecutive patients with post-stress EF drop ≥ 5 EF units and summed difference score (SDS) ≤ 1. They were followed up for more than 1 year and their outcome was compared with a group of sex- and age-matched controls with the same SDS but without EF decrease.

RESULTS

During follow-up there were 13 events (1 cardiac death, 1 non-fatal myocardial infarction, 1 congestive heart failure and 10 late revascularizations). In the control group we registered six events. There was a significant difference (p<0.0001) between the event-free survival curves of the two groups.

CONCLUSION

The event rate of patients with post-stress EF decrease ≥ 5 EF units is relatively high and is significantly worse than that of a control group of patients with similarly normal SDS but without EF changes. Therefore, a post-stress EF decrease without stress-induced perfusion abnormalities should be cautiously interpreted.

Clinical Role of Hybrid Imaging

Recent technological advances have fueled the growth in hybrid radionuclide and CT imaging of the heart. Noninvasive imaging studies are reliable means to diagnose coronary artery disease (CAD), stratify risk, and guide clinical management. Myocardial perfusion scintigraphy is a robust, widely available noninvasive modality for the evaluation of ischemia from known or suspected CAD. Cardiac CT (coronary artery calcium score and coronary CT angiography) has emerged as a clinically robust noninvasive anatomic imaging test, capable of rapidly diagnosing or excluding obstructive CAD. Both anatomic and functional modalities have strengths and weaknesses, and can complement each other by offering integrated structural and physiologic information. As we discuss below, in selected patients, hybrid imaging may facilitate more accurate diagnosis, risk stratification, and management in a "one-stop shop" setting.

Reference ranges for LVEF and LV volumes from electrocardiographically gated 82Rb cardiac PET/CT using commercially available software

Electrocardiographic gating is increasingly used for (82)Rb cardiac PET/CT, but reference ranges for global functional parameters are not well defined. We sought to establish reference values for left ventricular ejection fraction (LVEF), end systolic volume (ESV), and end diastolic volume (EDV) using 4 different commercial software packages. Additionally, we compared 2 different approaches for the definition of a healthy individual.

METHODS

Sixty-two subjects (mean age +/- SD, 49 +/- 9 y; 85% women; mean body mass index +/- SD, 34 +/- 10 kg/m(2)) who underwent (82)Rb-gated myocardial perfusion PET/CT were evaluated. All subjects had normal myocardial perfusion and no history of coronary artery disease (CAD) or cardiomyopathy. Subgroup 1 consisted of 34 individuals with low pretest probability of CAD (<10%), and subgroup 2 comprised 28 subjects who had no atherosclerosis on a coronary CT angiogram obtained concurrently during the PET/CT session. LVEF, ESV, and EDV were calculated at rest and during dipyridamole-induced stress, using CardIQ Physio (a dedicated PET software) and the 3 major SPECT software packages (Emory Cardiac Toolbox, Quantitative Gated SPECT, and 4DM-SPECT).

RESULTS

Mean LVEF was significantly different among all 4 software packages. LVEF was most comparable between CardIQ Physio (62% +/- 6% and 54% +/- 7% at stress and rest, respectively) and 4DM-SPECT (64% +/- 7% and 56% +/- 8%, respectively), whereas Emory Cardiac Toolbox yielded higher values (71% +/- 6% and 65% +/- 6%, respectively, P < 0.001) and Quantitated Gated SPECT lower values (56% +/- 8% and 50% +/- 8%, respectively, P < 0.001). Subgroup 1 (low likelihood) demonstrated higher LVEF values than did subgroup 2 (normal CT angiography findings), using all software packages (P < 0.05). However, mean ESV and EDV at stress and rest were comparable between both subgroups (p = NS). Intra- and interobserver agreement were excellent for all methods.

CONCLUSION

The reference range of LVEF and LV volumes from gated (82)Rb PET/CT varies significantly among available software programs and therefore cannot be used interchangeably. LVEF results were higher when healthy subjects were defined by a low pretest probability of CAD than by normal CT angiography results.

Perspectives of nuclear diagnostic imaging in diabetic cardiomyopathy

Diabetic cardiomyopathy is a ventricular dysfunction in the absence of coronary artery disease, valvular or hypertensive heart disease. The mechanisms underlying diabetic cardiomyopathy may involve metabolic disturbances, myocardial fibrosis, small vessel disease, microcirculation abnormalities, cardiac autonomic neuropathy and insulin resistance. Diagnostic problems emerge because no specific disease pattern characterizes the disease and because there may be coexistence in diabetes of coronary artery disease and hypertension as independent but compounding causes of biochemical, anatomical and functional alterations impairing cardiac function. In this paper we will review the role of nuclear imaging today, concentrating on the diagnostic capabilities of radionuclide ventriculography, to study the effect of insulin resistance and, more extensively, gated-single photon emission computed tomography with Tc-99m labelled agents. A broad analysis will be dedicated to: 1) positron emission tomography using perfusion agents, with the potential to quantify resting and stress blood flow and coronary flow reserve; 2) radionuclide procedures evaluating aerobic and anaerobic cardiac metabolism; and 3) cardiac neurotransmission imaging, studying the autonomic neuropathy.

Incremental prognostic value of gated Rb-82 positron emission tomography myocardial perfusion imaging over clinical variables and rest LVEF

OBJECTIVES

This investigation sought to study the incremental value of gated rubidium (Rb)-82 positron emission tomography (PET) myocardial perfusion imaging (MPI) over clinical variables for predicting survival and future cardiac events.

BACKGROUND

The prognostic value of Rb-82 PET-MPI and left ventricular ejection fraction (LVEF) reserve (stress minus rest LVEF) is not well defined.

METHODS

1,432 consecutive patients undergoing gated rest/vasodilator stress rubidium-82 PET were followed up for at least 1 year. Of these, rest and peak stress LVEF and LVEF reserve were available in 985 patients. Cardiac events (CE) including cardiac death or nonfatal myocardial infarction and all-cause death were assessed.

RESULTS

Over a mean follow-up of 1.7 +/- 0.7 years, 83 (5.8%) CE and 140 (9.7%) all-cause death were observed. There was an increase in risk for both end points with an increasing percentage of abnormal and ischemic myocardium. With normal, mild, moderate, or severely ischemic scans, the observed annualized rates of CE were 0.7%, 5.5%, 5%, and 11% and of all-cause death were 3.3%, 7.2%, 6.9%, and 12.5%, respectively. In 985 patients with peak stress gated data, the observed annualized rates of CE (2.1% vs. 5.3%, p < 0.001) and all-cause death (4.3% vs. 9.2%, p < 0.001) were higher in patients with an LVEF reserve <0% compared with those with an LVEF reserve >or=0%. On Cox proportional hazards analysis, after consideration of clinical, historical, and rest LVEF information, stress PET results and LVEF reserve yielded incremental prognostic value with respect to both CE and all-cause death.

CONCLUSIONS

Vasodilator stress Rb-82 PET-MPI provides incremental prognostic value to historical/clinical variables and rest LVEF to predict survival free of CE and all-cause death. An increasing percentage of ischemia on PET-MPI is associated with an increase in the risk of CE and all-cause death. Left ventricular ejection fraction reserve provides significant independent and incremental value to Rb-82 MPI for predicting the risk of future adverse events.

Cardiac positron emission tomography: current clinical practice

In the last two decades, the field of nuclear cardiology has experienced significant progress. The introduction of positron emission tomography (PET) imaging represented a major breakthrough that has significantly contributed to a better understanding of physiology and pathophysiology of several heart diseases. Currently, PET imaging is recognized as a well-established method to assess cardiac perfusion, function, metabolism, and viability. This article summarizes the main clinical applications of state-of-the art cardiac PET technology.