Cardiac metaiodobenzylguanidine uptake in patients with moderate chronic heart failure: relationship with peak oxygen uptake and prognosis

Sex differences in 123I-mIBG scintigraphy imaging techniques in patients with heart failure

BACKGROUND

123I-mIBG-scintigraphy could be a useful stratifying tool for patients with heart failure (HF). The purpose of this retrospective study is to evaluate whether there are differences between men and women with HF in terms of the prediction of cardiac arrhythmic events (AE).

RESEARCH AND METHODS

A total of 306 patients, before implantable-cardioverter-defibrillator (ICD) implantation, were evaluated. They underwent 123I-mIBG-scintigraphy and an evaluation of the results was performed after 85 months of follow-up. Early and late planar and SPECT cardiac images were acquired. Heart-to-mediastinum ratio (HM) for planar images and the sum of the segmental scores (SS) for SPECT were calculated.

RESULTS

In the general population, age, early SS (ESS), late SS (LSS), and ejection fraction (EF) were statistically significant for the prediction of AE at Cox regression, while early and late HM (eHM,lHM) were not significative for the prediction of AE. Population was divided into females and males and univariate analysis was conducted separately for the two cohorts: no significant variables for prediction of AE were found in females. For males, ESS, LSS, EF, and late HM were statistically significant predictors of AE. The overall survival was similar in males and females, but the risk of AE is lower in males than in females.

CONCLUSIONS

123I-mIBG represents a more effective tool for the prediction of AE in male patients than in women.

Complementary Role of Combined Indirect and Direct Cardiac Sympathetic (Hyper)Activity Assessment in Patients with Heart Failure by Spectral Analysis of Heart Rate Variability and Nuclear Imaging: Possible Application in the Evaluation of Exercise Training Effects

In chronic heart failure (CHF), abnormalities in cardiac autonomic control, characterized by sympathetic overactivity, contribute to the progression of the disease and are associated with an unfavorable prognosis. Assessing cardiac autonomic status is clinically important in the management of patients with CHF. To this aim, heart rate variability (HRV) analysis has been extensively used as a non-invasive tool for assessing cardiac autonomic regulation, and has been shown to predict the clinical outcome in patients with CHF. Adrenergic nerve activity has also been estimated using iodine-123 (I-123) metaiodobenzylguanidine (MIBG), a noradrenaline analogue. MIBG is an analogue of norepinephrine sharing the same cellular mechanism of uptake, storage, and release in presynaptic sympathetic neurons. As an innervation tracer, 123I-MIBG allows for the evaluation of cardiac sympathetic neuronal function. Cardiac MIBG imaging has also been reported to predict a poor clinical outcome in CHF. MIBG provides direct information on the function of the presynaptic sympathetic nerve endings, whereas HRV, which depends on postsynaptic signal transduction, reflects the end-organ response of the sinus node. The aim of this brief review is to provide the reader with some basic concepts regarding the spectral analysis of HRV and MIBG, highlighting what is known about their respective roles in detecting cardiac sympathetic hyperactivity in CHF and, in perspective, their possible combined use in assessing non-pharmacological treatments in patients with CHF and reduced ejection fraction, with a particular focus on the effects of exercise training.

Cardiac 123I-mIBG Imaging in Heart Failure

Cardiac sympathetic upregulation is one of the neurohormonal compensation mechanisms that play an important role in the pathogenesis of chronic heart failure (CHF). In the past decades, cardiac ¹²³I-mIBG scintigraphy has been established as a feasible technique to evaluate the global and regional cardiac sympathetic innervation. Although cardiac ¹²³I-mIBG imaging has been studied in many cardiac and neurological diseases, it has extensively been studied in ischemic and non-ischemic CHF. Therefore, this review will focus on the role of ¹²³I-mIBG imaging in CHF. This non-invasive, widely available technique has been established to evaluate the prognosis in CHF. Standardization, especially among various combinations of gamma camera and collimator, is important for identifying appropriate thresholds for adequate risk stratification. Interestingly, in contrast to the linear relationship between ¹²³I-mIBG-derived parameters and overall prognosis, there seems to be a “bell-shape” curve for ¹²³I-mIBG-derived parameters in relation to ventricular arrhythmia or appropriate implantable cardioverter defibrillator (ICD) therapy in patients with ischemic CHF. In addition, there is a potential clinical role for cardiac ¹²³I-mIBG imaging in optimizing patient selection for implantation of expensive devices such as ICD and cardiac resynchronization therapy (CRT). Based on cardiac ¹²³I-mIBG data risk models and machine learning, models have been developed for appropriate risk assessment in CHF.

40 Years Anniversary of Cardiac 123I-mIBG Imaging: State of the Heart

Purpose of Review

This narrative review reflects on the body of evidence on cardiac 123I-mIBG imaging that has accumulated since the introduction in the late 1970s and focusses on to what extent cardiac 123I-mIBG imaging has fulfilled its potential in cardiology especially.

Recent Findings

In contrast to the linear relationship between 123I-mIBG-derived parameters and overall prognosis in heart failure, there seems a “bell-shape” curve for 123I-mIBG-derived parameters and arrhythmic events. In addition, there is a potential clinical role for cardiac 123I-mIBG in optimizing patient selection for expensive devices (i.e., ICD and CRT). This needs of course to be established in future trials.

Summary

Cardiac 123I-mIBG imaging is, despite the numerous of studies, sometimes mistakenly seen as a nice to have technique rather than a must have imaging modality. Although cardiac 123I-mIBG imaging has grown and matured over the years, its full clinical potential has still not been tested to the maximum.

The role of myocardial innervation imaging in different clinical scenarios: an expert document of the European Association of Cardiovascular Imaging and Cardiovascular Committee of the European Association of Nuclear Medicine

Cardiac sympathetic activity plays a key role in supporting cardiac function in both health and disease conditions, and nuclear cardiac imaging has always represented the only way for the non-invasive evaluation of the functional integrity of cardiac sympathetic terminals, mainly through the use of radiopharmaceuticals that are analogues of norepinephrine and, in particular, with the use of 123I-mIBG imaging. This technique demonstrates the presence of cardiac sympathetic dysfunction in different cardiac pathologies, linking the severity of sympathetic nervous system impairment to adverse patient's prognosis. This article will outline the state-of-the-art of cardiac 123I-mIBG imaging and define the value and clinical applications in the different fields of cardiovascular diseases.

Prognostic usefulness of planar 123I-MIBG scintigraphic images of myocardial sympathetic innervation in congestive heart failure: Follow-Up data from ADMIRE-HF

BACKGROUND

To evaluate whether planar 123I-MIBG myocardial scintigraphy predicts risk of death in heart failure (HF) patients up to 5 years after imaging.

METHODS AND RESULTS

Subjects from ADMIRE-HF were followed for approximately 5 years after imaging (964 subjects, median follow-up 62.7 months). Subjects were stratified according to the heart/mediastinum (H/M) ratio (< 1.60 vs ≥ 1.60) on planar 123I-MIBG scintigraphic images obtained at baseline in ADMIRE-HF. Cox proportional hazards models and Kaplan-Meier analyses were used to evaluate time to death, cardiac death, or arrhythmic events for subjects stratified by H/M ratio, baseline left ventricular ejection fraction (LVEF: < 25% and 25 to ≤ 35%), and by H/M strata within LVEF strata. All-cause mortality was 38.4% vs 20.9% and cardiac mortality was 16.8% vs 4.5%, in subjects with H/M < 1.60 vs ≥ 1.60, respectively (P < 0.05 for both comparisons). Subjects with preserved sympathetic innervation of the myocardium (H/M ≥ 1.60) were at significantly lower risk of all-cause and cardiac death, arrhythmic events, sudden cardiac death, or potentially life-threatening arrhythmias. Within LVEF strata, a trend toward a higher mortality for subjects with H/M < 1.60 was observed reaching significance for LVEF 25 to ≤ 35% only.

CONCLUSIONS

During a median follow-up of 62.7 months, patients with H/M ≥ 1.60 were at significantly lower risk of death and arrhythmic events independently of LVEF values.

Cardiac Imaging With 123I-meta-iodobenzylguanidine and Analogous PET Tracers: Current Status and Future Perspectives

Autonomic innervation plays an important role in proper functioning of the cardiovascular system. Altered cardiac sympathetic function is present in a variety of diseases, and can be assessed with radionuclide imaging using sympathetic neurotransmitter analogues. The most studied adrenergic radiotracer is cardiac ¹²³I-meta-iodobenzylguanidine (¹²³I-mIBG). Cardiac ¹²³I-mIBG uptake can be evaluated using both planar and tomographic imaging, thereby providing insight into global and regional sympathetic innervation. Standardly assessed imaging parameters are the heart-to-mediastinum ratio and washout rate, customarily derived from planar images. Focal tracer deficits on tomographic imaging also show prognostic utility, with some data suggesting that the best approach to tomographic image interpretation may differ from conventional methods. Cardiac ¹²³I-mIBG image findings strongly correlate with the severity and prognosis of many cardiovascular diseases, especially heart failure and ventricular arrhythmias. Cardiac ¹²³I-mIBG imaging in heart failure is FDA approved for prognostic purposes. With the robustly demonstrated ability to predict occurrence of potentially fatal arrhythmias, cardiac ¹²³I-mIBG imaging shows promise for better selecting patients who will benefit from an implantable cardioverter defibrillator, but clinical use has been hampered by lack of the randomized trial needed for incorporation into societal guidelines. In patients with ischemic heart disease, cardiac ¹²³I-mIBG imaging aids in assessing the extent of damage and in identifying arrhythmogenic regions. There have also been studies using cardiac ¹²³I-mIBG for other conditions, including patients following heart transplantation, diabetic related cardiac abnormalities and chemotherapy induced cardiotoxicity. Positron emission tomographic adrenergic radiotracers, that improve image quality, have been investigated, especially ¹¹C-meta-hydroxyephedrine, and most recently ¹⁸F-fluorbenguan. Cadmium-zinc-telluride cameras also improve image quality. With better spatial resolution and quantification, PET tracers and advanced camera technologies promise to expand the clinical utility of cardiac sympathetic imaging.

Prognostic effect and modulation of cardiac sympathetic function in heart failure patients treated with cardiac resynchronization therapy

BACKGROUND

Cardiac autonomic dysfunction as assessed by 123I-metaiodobenzylguanidine (123I-mIBG) scintigraphy is associated with poor prognosis in heart failure (HF) patients. Although cardiac resynchronization therapy (CRT) has emerged as an effective therapy in improving outcomes on HF patients, its effect on cardiac sympathetic nervous function is still not fully understood. We aimed to study the value of pre-implantation 123I-mIBG late heart-to-mediastinum ratio (HMR) as a predictor of response and outcomes after CRT and to correlate modification in this parameter with CRT response and functional improvement.

METHODS AND RESULTS

BETTER-HF (Benefit of exercise training therapy and cardiac resynchronization in HF patients) is a prospective randomized clinical trial including HF patients submitted CRT (mean LVEF 24 ± 8%, 74% NYHA class ≥ III) who underwent a clinical, echocardiographic, and scintigraphic assessment before and 6 months after CRT. One-hundred and twenty-one patients were included. Echocardiographic response was observed in 54% and composite outcome of cardiac mortality, cardiac transplant or heart failure hospitalization in 24% of patients. Baseline late HMR was an independent predictor of CRT response (regression coefficient 2.906, 95% CI 0.293-3.903, P .029) and outcomes (HR 0.066 95% CI 0.005-0.880, P .040). At follow-up, 123I-mIBG imaging showed positive changes in cardiac sympathetic nerve activity only in responders to CRT (1.36 ± 0.14 prior vs. 1.42 ± 0.16 after CRT, P .039). There was a significant correlation between improvement in late HMR and improvement in peak oxygen consumption (r 0.547, P < .001).

CONCLUSION

In our study, baseline cardiac denervation predicted response and clinical outcomes after CRT implantation. Cardiac sympathetic function was improved only in patients who responded to CRT and these positive changes were correlated with improvement in functional capacity.

Early therapeutic effects of adaptive servo-ventilation on cardiac sympathetic nervous function in patients with heart failure evaluated using a combination of 11C-HED PET and 123I-MIBG SPECT

RATIONALE

Adaptive servo-ventilation (ASV), a novel respiratory support therapy for sleep disorders, may improve cardiac function in heart failure (HF). However, the reasons that ASV improves cardiac function have not been fully studied especially in sympathetic nervous function (SNF). The purpose of the present study was to investigate the effects of ASV therapy on cardiac SNF in patients with HF.

METHODS

We evaluated ASV therapeutic effects before and 6 months after ASV therapy in 9 HF patients [57.3 ± 17.3 years old, left ventricular ejection fraction (LVEF) 36.1 ± 16.7%]. We performed echocardiography, polysomnography, biomarkers, 11C-hydroxyephedrine (HED) PET as a presynaptic function marker and planar 123I-metaiodobenzylguanidine (MIBG) to evaluate washout rate.

RESULTS

ASV therapy reduced apnea-hypopnea index (AHI) and improved plasma brain natriuretic peptide (BNP) concentration. In 123I-MIBG imaging, the early heart/mediastinum (H/M) ratio increased after ASV therapy (2.19 ± 0.58 to 2.40 ± 0.67; P = 0.045). Washout rate did not change (23.8 ± 7.3% to 23.8 ± 8.8%; P = 0.122). Global 11C-HED retention index (RI) improved from 0.068 ± 0.033/s to 0.075 ± 0.034/s (P = 0.029).

CONCLUSIONS

ASV reduced AHI and improved BNP. ASV might initially improve presynaptic cardiac sympathetic nervous function in HF patients after 6 months of treatment.

Pathophysiology, incidence, management, and consequences of cardiac arrhythmia in pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension

Arrhythmias are increasingly recognized as serious, end-stage complications of pre-capillary pulmonary hypertension, including pulmonary arterial hypertension (PAH) and chronic thromboembolic pulmonary hypertension (CTEPH). Although arrhythmias contribute to symptoms, morbidity, in-hospital mortality, and possibly sudden death in PAH/CTEPH, there remains a paucity of epidemiologic, pathophysiologic, and outcome data to guide management of these patients. This review summarizes the most current evidence on the topic: from the molecular mechanisms driving arrhythmia in the hypertrophied or failing right heart, to the clinical aspects of epidemiology, diagnosis, and management.

Impact of an exercise training program on cardiac neuronal function in heart failure patients on optimal medical therapy : A randomized Iodine-123 metaiodobenzylguanidine scintigraphy study

BACKGROUND

The syndrome of heart failure (HF) is characterized by left ventricular dysfunction and a compensatory chronic over activation of the sympathetic nervous system. We wanted to investigate if the beneficial effects of exercise training (ET) in HF patients on optimal medical therapy (OMT) are associated with alterations in cardiac sympathetic activity.

METHODS

Cardiac sympathetic activity was evaluated at baseline and after 12 weeks using metaiodobenzylguanidine scintigraphy in 23 patients with stable HF participating in the SmartEx trial. Patients with HF in New York Heart Association class II or III and left ventricular ejection fraction <35 % were randomized to three different ET groups.

RESULTS

We found no statistically significant changes in cardiac sympathetic activity after 12 weeks of ET. Heart to mediastinum (H/M) ratio at 15 minutes (0.00174 ± 0.0841, P = 0.922), H/M ratio at 4 hours (-0.00565 ± 0.1163, P = 0.818) and washout ratio (WR) (-1.2666 ± 16.5412, P = 0.717). A further group-wise analysis of the three ET groups did not show any difference between the groups.

CONCLUSION

A 12-week ET program did not alter the abnormal cardiac sympathetic activity in stable HF patients on modern OMT.

Variability in Heart-to-Mediastinum Ratio from Planar 123I-MIBG Images of a Thorax Phantom for 6 Common γ-Camera Models

A heart-to-mediastinum (H/M) ratio of 1.6 or greater on planar ¹²³I-iobenguane (¹²³I-MIBG) images identifies heart failure patients at low risk of experiencing an adverse cardiac event. This phase-4 study used standardized phantoms to assess the intercamera, intracamera, and interhead variability in H/M ratio determinations from planar cardiac ¹²³I-MIBG imaging using commercially available, dual-head γ-cameras. Methods: A fillable thorax phantom was developed to simulate the typical uptake of ¹²³I-MIBG. The phantom had a nominal H/M ratio of 1.6 on the reference camera. Commercial cameras used in the study were dual-head and capable of 90° configuration for cardiac imaging. The target sample size was 8 units (examples) per camera model. Two imaging technologists independently analyzed planar images of simulated ¹²³I-MIBG uptake from the thorax phantom. H/M was the ratio of the average counts per pixel of the heart and mediastinum regions of interest. The primary endpoint, intercamera variability in H/M ratio from head 1, was determined for each camera model via comparison with the H/M ratio on the reference camera. Only cameras with at least 8 units tested (n ≥ 8) were included in the primary analysis. Intracamera and interhead variability in the H/M ratio were also evaluated. Results: Nine camera models were studied. The mean H/M ratio ranged from 1.342 to 1.677. The primary analysis (6 camera models) using a mixed-model, repeated-measures analysis showed no significant difference in H/M ratio between any camera model and the reference camera. Intracamera variability (head 1) in the H/M ratio among camera models with 8 units or more was high, with SDs ranging from 0.0455 to 0.1193. Interhead variability was low (SDs of the interhead difference, 0.017-0.074). Conclusion: Commonly used γ-cameras produced H/M ratios from simulated ¹²³I-MIBG phantom images that were not significantly different from those on the reference camera. This finding indicates that the results of previous clinical trials of ¹²³I-MIBG, involving many different clinical sites and camera models, are valid. The assessment of the performance of a given camera unit using an ¹²³I planar phantom before H/M results from ¹²³I-MIBG imaging are used for classifying risk in heart failure patients is encouraged.

Beta blocker dose and markers of sympathetic activation in heart failure patients: interrelationships and prognostic significance

Aims

Extent of cardiac sympathetic activation can be estimated from physiological parameters, blood biomarkers, and imaging findings. This study examined the prognostic value of three markers of sympathetic activity and their relationship to beta blocker dose in heart failure patients.

Methods and results

A post hoc analysis of 858 heart failure subjects in the ADMIRE‐HF trial was performed. Variables related to sympathetic activity were plasma norepinephrine, baseline heart rate, the heart to mediastinum (H/M) ratio of ¹²³I‐mIBG uptake, and beta blocker dose. Univariate and multivariate analyses for occurrence of mortality (all‐cause and cardiac) and arrhythmic events were performed. Beta blocker dose was significantly related to age, heart rate, b‐type natriuretic peptide (negatively), body mass index, body weight and plasma norepinephrine. Univariate predictors of all‐cause and cardiac mortality were baseline heart rate (χ² = 4.5, P = 0.029 and χ² = 5 .2, P = 0.022, respectively), plasma norepinephrine level (χ² = 8.9, P = 0.0006 and χ² = 8.6, P = 0.003, respectively), and H/M (χ = 22.4, P < 0.0001 and χ² = 17.8, P < 0.0001, respectively). In multivariate analyses, carvedilol‐equivalent dose (P = 0.017), plasma norepinephrine (P = 0.002), and H/M (P = 0.0001) were significant predictors of all‐cause mortality. In separate analyses using multiple measurements of heart rate, mean heart rate >67 b.p.m. was associated with significantly higher cardiac mortality.

Conclusions

Higher beta blocker dose was associated with lower mortality, but of the variables associated with sympathetic activity examined, cardiac ¹²³I‐mIBG uptake was the most powerful prognostic marker in heart failure patients. Elevated heart rate was associated with greater risk for cardiac death.

Effect of Nebivolol on MIBG Parameters and Exercise in Heart Failure with Normal Ejection Fraction

BACKGROUND

More than 50% of the patients with heart failure have normal ejection fraction (HFNEF). Iodine-123 metaiodobenzylguanidine (123I-MIBG) scintigraphy and cardiopulmonary exercise test (CPET) are prognostic markers in HFNEF. Nebivolol is a beta-blocker with vasodilating properties.

OBJECTIVES

To evaluate the impact of nebivolol therapy on CPET and123I-MIBG scintigraphic parameters in patients with HFNEF.

METHODS

Twenty-five patients underwent 123I-MIBG scintigraphy to determine the washout rate and early and late heart-to-mediastinum ratios. During the CPET, we analyzed the systolic blood pressure (SBP) response, heart rate (HR) during effort and recovery (HRR), and oxygen uptake (VO2). After the initial evaluation, we divided our cohort into control and intervention groups. We then started nebivolol and repeated the tests after 3 months.

RESULTS

After treatment, the intervention group showed improvement in rest SBP (149 mmHg [143.5-171 mmHg] versus 135 mmHg [125-151 mmHg, p = 0.016]), rest HR (78 bpm [65.5-84 bpm] versus 64.5 bpm [57.5-75.5 bpm, p = 0.028]), peak SBP (235 mmHg [216.5-249 mmHg] versus 198 mmHg [191-220.5 mmHg], p = 0.001), peak HR (124.5 bpm [115-142 bpm] versus 115 bpm [103.7-124 bpm], p= 0.043), HRR on the 1st minute (6.5 bpm [4.75-12.75 bpm] versus 14.5 bpm [6.7-22 bpm], p = 0.025) and HRR on the 2nd minute (15.5 bpm [13-21.75 bpm] versus 23.5 bpm [16-31.7 bpm], p = 0.005), but no change in peak VO2 and 123I-MIBG scintigraphic parameters.

CONCLUSION

Despite a better control in SBP, HR during rest and exercise, and improvement in HRR, nebivolol failed to show a positive effect on peak VO2 and 123I-MIBG scintigraphic parameters. The lack of effect on adrenergic activity may be the cause of the lack of effect on functional capacity.

Clinical Applications of Myocardial Innervation Imaging

Cardiac autonomic innervation plays an important role in regulating function. Adrenergic innervation imaging is possible with the norepinephrine analogue radiotracer iodine 123 meta-iodobenzylguanidine ((123)I-mIBG) and positron emitting tracers such carbon-11 hydroxyephedrine. (123)I-mIBG uptake is assessed globally via the heart to mediastinum ratio on planar images and regionally with tomographic imaging and has utility in various cardiac diseases. There is promise for guiding expensive invasive therapies such as implantable defibrillators, ventricular assist devices, and transplant. There are reports of utility in primary arrhythmic conditions, ischemic heart disease, and diabetes and after cardiac damaging chemotherapy.

Preoperative iodine-123 meta-iodobenzylguanidine imaging is a novel predictor of left ventricular reverse remodeling during treatment with a left ventricular assist device

Although left ventricular reverse remodeling (LVRR) is accompanied with an improved clinical course during LV assist device (LVAD) treatment, its preoperative prediction remains uncertain. Twenty-seven heart failure patients with dilated cardiomyopathy were enrolled in this study. Patients underwent (123)I-meta-iodobenzylguanidine (MIBG) scintigraphy before LVAD implantation, and were monitored at our institute from 2010 to 2014. This study investigated the prognostic value of preoperative (123)I-MIBG parameters for predicting postoperative LVRR. Of the preoperative variables studied, including (123)I-MIBG data, washout rate (WR) ≤ 39 % was the only significant, independent predictor of LVRR (defined as LV ejection fraction ≥35 % at 6 months post-LVAD implant using univariate and multivariate logistic regression analyses) (p = 0.036, odds ratio [OR]:14.45). Improved exercise capacity and more frequent opening of the native aortic valve, as well as lower B-type natriuretic peptide plasma levels, were observed in LVRR patients (p < 0.05 for all), although β-blocker doses were comparable with those of non-LVRR patients throughout the 6-month LVAD support period. In conclusion, preoperative (123)I-MIBG is a novel predictive tool of LVRR during LVAD support.

Radionuclide imaging of neurohormonal system of the heart

Heart failure is one of the growing causes of death especially in developed countries due to longer life expectancy. Although many pharmacological and instrumental therapeutic approaches have been introduced for prevention and treatment of heart failure, there are still limitations and challenges. Nuclear cardiology has experienced rapid growth in the last few decades, in particular the application of single photon emission computed tomography (SPECT) and positron emission tomography (PET), which allow non-invasive functional assessment of cardiac condition including neurohormonal systems involved in heart failure; its application has dramatically improved the capacity for fundamental research and clinical diagnosis. In this article, we review the current status of applying radionuclide technology in non-invasive imaging of neurohormonal system in the heart, especially focusing on the tracers that are currently available. A short discussion about disadvantages and perspectives is also included.

Transcatheter aortic valve implantation reduces sympathetic activity and normalizes arterial spontaneous baroreflex in patients with aortic stenosis

OBJECTIVES

This study sought to measure muscle sympathetic nerve activity (MSNA) in patients with aortic stenosis (AS) before and after transcatheter aortic valve implantation (TAVI) and to compare MSNA with that of control patients.

BACKGROUND

TAVI is an emerging therapeutic option in patients with severe AS at high risk of open heart surgery. Whether patients with AS have increased sympathetic activity remains to be established, and the effects of TAVI on the sympathetic nervous system are also unknown.

METHODS

We prospectively enrolled 14 patients with severe symptomatic AS treated by TAVI. Fourteen control patients matched for age, body mass index, and unscathed of AS were also included. All patients underwent MSNA and arterial baroreflex gain assessment at baseline and 1 week after TAVI for AS patients.

RESULTS

Patients with AS had lower blood pressure (BP) levels, a significant increase in MSNA (61.0 ± 1.7 burst/min vs. 55.4 ± 1.4 burst/min; p < 0.05), and a decrease in arterial baroreflex gain (2.13 ± 0.14% burst/mm Hg vs. 3.32 ± 0.19% burst/mm Hg; p < 0.01) compared with matched control patients. The TAVI procedures induced an increase in BP associated with a significant decrease in MSNA (from 61.0 ± 1.7 burst/min to 54.1 ± 1.0 burst/min; p < 0.01) and was associated with a significant increase in arterial baroreflex gain (from 2.13 ± 0.14% burst/mm Hg to 3.49 ± 0.33% burst/mm Hg; p < 0.01).

CONCLUSIONS

We report for the first time, through direct measurement of nerve activity, that patients with AS have increased sympathetic nervous system activity associated with a decrease in sympathetic baroreflex gain and that TAVI normalizes these parameters. This study provides evidence of a new beneficial effect of TAVI, namely, normalization of sympathetic nervous system hyperactivity.

The potential role of iodine-123 metaiodobenzylguanidine imaging for identifying sustained ventricular tachycardia in patients with cardiomyopathy

Implantable cardioverter-defibrillators (ICDs) significantly reduce mortality in patients with depressed left ventricular ejection fraction (LVEF) and heart failure (HF). However, shortcomings of LVEF to accurately identify those at greatest risk of ventricular tachyarrhythmias have led to the pursuit of alternative means to refine qualification criteria for ICD implantation. It is well established that imaging the cardiac nervous system with¹²³I meta-iodobenzylguanidine (¹²³I-mIBG) provides incremental prognostic value in patients with HF beyond LVEF. Whether ¹²³I-mIBG will also play an important role for identifying and/or predicting sustained ventricular tachyarrhythmias in patients with cardiomyopathy and determining those who may benefit from ICD implantation is currently under investigation. Novel imaging approaches that pinpoint the site of ventricular arrhythmias and guide ventricular tachycardia ablation are presented.

Influence of myocardial region of interest definition on quantitative analysis of planar 123I-mIBG images

PURPOSE

In planar (123)I-mIBG myocardial imaging, definition of the heart region of interest (ROI) is a critical step in quantifying uptake. The present study evaluated the impact of changes in heart ROI size on quantitative results in subjects with good and poor uptake.

METHODS

Reference irregular whole-heart and square upper mediastinum ROIs were defined visually on 531 planar (123)I-mIBG images. Based on the reference heart ROI, an automated program created two other ROIs: one larger (+1 pixel) and one smaller (-1 pixel), the stated numbers representing the spacing intervals between each epicardial boundary pixel. Two additional smaller ROIs (-2 and -3 pixels) were drawn for the 100 images (19 %) with a heart/mediastinum (H/M) ratio ≤1.30. The number of pixels, the counts per pixel, and the H/M ratio for each heart ROI were calculated and compared to that in the reference ROI. Washout rate and changes as a function of ROI size were also calculated for 110 subjects who had both early and late images.

RESULTS

The mean changes in heart ROI size ranged from +19.0 % for the +1 pixel to -44.4 % for the -3 pixels ROI. For the +1 and -1 pixel ROIs, mean relative counts per pixel changes were -1.2 % and +0.7 %, respectively, with corresponding ranges of change in the H/M ratio of -0.12 to +0.05 and -0.05 to +0.11. For scans with H/M ratio ≤1.30, mean relative counts per pixel changes were 0, 0, -0.7 %, and -1.4 % for the four ROIs, with range of change in the H/M ratio from -0.13 to +0.05. Mean washout rates were almost identical for the reference ROIs (45.0 %) and the +1 pixel and -1 pixel heart ROIs (44.9 % and 45.1 %, respectively).

CONCLUSION

Significant changes in the size of the best visually defined heart ROI produce minimal, clinically inconsequential changes in the H/M ratio and washout rate, even in subjects with significantly reduced myocardial uptake of (123)I-mIBG.

Cardiac autonomic nervous system in heart failure: imaging technique and clinical implications

The autonomic nervous system interacts in the pathophysiology of heart failure. Dysfunction of the sympathetic nervous system has been identified as an important prognostic marker in patients with chronic heart failure. At present, cardiac sympathetic nerve imaging with 123-iodine metaiodobenzylguanidine [123-I MIBG] has been employed most frequently for the assessment of cardiac sympathetic innervation and activation pattern. The majority of studies have shown that cardiac sympathetic dysfunction as assessed with 123-I MIBG imaging is a powerful predictor for heart failure mortality and morbidity. Additionally, 123-I MIBG imaging can be used for prediction of potentially lethal ventricular tachyarrhythmias in heart failure patients. At present however, the lack of standardization of 123-I MIBG imaging procedures represents an evident issue. Standardized criteria on the use of 123-I MIBG imaging will further strengthen the clinical use of 123-I MIBG imaging in heart failure patients.

Quantitative I-123 mIBG SPECT in differentiating abnormal and normal mIBG myocardial uptake

BACKGROUND

The purpose of this study was to evaluate global quantitation of cardiac uptake on I-123 mIBG SPECT.

METHODS

The study included a pilot group of 67 subjects and a validation group of 1,051 subjects. SPECT images were reconstructed by filtered backprojection, ordered subsets expectation maximization, and deconvolution of septal penetration, respectively. SPECT heart-to-mediastinum ratio (H/M) was calculated by comparing the mean counts between heart and mediastinum volumes of interest drawn on transaxial images. Receiver operating characteristic (ROC) analysis was used to assess the capability of each SPECT method to differentiate the heart disease subjects from controls in comparison with that of the planar H/M.

RESULTS

In the validation group, the areas under the ROC curves were not significantly different between the SPECT and planar H/M. Order subsets expectation maximization had significantly larger area under the ROC curve than the other two SPECT methods.

CONCLUSION

H/M obtained from I-123 mIBG SPECT was equivalent to the planar H/M for differentiating between subjects with normal and abnormal mIBG uptake. Global quantification of cardiac I-123 mIBG SPECT may represent a viable alternative to the planar H/M.

Effect of left ventricular dyssynchrony on cardiac sympathetic activity in heart failure patients with wide QRS duration

BACKGROUND

Dyssynchrony has various detrimental effects on cardiac function, but its effect on cardiac sympathetic activity is not fully understood.

METHODS AND RESULTS

We studied 50 heart failure patients who underwent cardiac resynchronization therapy (CRT). Cardiac sympathetic activity was assessed by (123)I-metaiodobenzylguanidine ((123)I-MIBG) scintigraphy as the delayed heart-to-mediastinum ratio (H/M ratio). Echocardiography was performed before and 7 months after CRT, and response was defined as a ≥15% decrease in end-systolic volume. Dyssynchrony was determined by the time difference between the anteroseptal-to-posterior wall using speckle-tracking radial strain (≥130 ms predefined as significant). H/M ratio in patients with dyssynchrony was less than that in patients without dyssynchrony (1.62 ± 0.31 vs. 1.82 ± 0.36, P<0.05), even though ejection fraction was not significantly different (24 ± 6% vs. 25 ± 7%). Patients with dyssynchrony and H/M ratio ≥1.6 had a higher frequency of response to CRT (94%) and favorable long-term outcome over 3.0 years. In contrast, patients without dyssynchrony and H/M ratio <1.6 were more likely to show a lower frequency of response to CRT (0%) and unfavorable long-term outcome after CRT.

CONCLUSIONS

Dyssynchrony is associated with cardiac sympathetic activity, and (123)I-MIBG scintigraphy may be valuable for predicting the response to CRT.

Cardiac iodine-123 metaiodobenzylguanidine (123I-MIBG) scintigraphy parameter predicts cardiac and cerebrovascular events in type 2 diabetic patients without structural heart disease

BACKGROUND

Cardiac iodine-123 metaiodobenzylguanidine ((123)I-MIBG) scintigraphy is an established method of assessment of cardiovascular sympathetic function. The aim of the present study was to investigate the long-term cardiovascular predictive value of cardiac (123)I-MIBG scintigraphy parameters in Japanese type 2 diabetic patients without structural heart disease.

METHODS AND RESULTS

Cardiac (123)I-MIBG scintigraphy in 108 patients with type 2 diabetes who did not have structural heart disease, was evaluated. The washout rate (WR) was considered enhanced if it was ≥40%. Accurate follow-up information for 4.6 years was obtained in 54 enhanced WR patients (27 male; mean age, 61 ± 11 years) and in 54 sex- and age-matched preserved WR patients (27 male; mean age, 61 ± 10 years). Major adverse cardiac and cerebrovascular events (MACCE) were investigated. During follow-up, 10 enhanced WR patients developed MACCE including cardiac death, coronary revascularization, stroke, and congestive heart failure, while MACCE occurred in only 3 male patients. The Kaplan-Meier curves indicated that enhanced WR patients had higher incidence of MACCE than those with preserved WR (P<0.05). Cox proportional hazards regression analysis showed that age and enhanced WR were independently associated with the incidence of MACCE (hazard ratio, 4.06; 95% confidence interval: 1.194-18.76, P = 0.0237).

CONCLUSIONS

Abnormal WR of cardiac (123)I-MIBG scintigraphy at baseline has long-term cardiovascular predictive value in Japanese patients with type 2 diabetes without structural heart disease.

Evaluation of LMI1195, a novel 18F-labeled cardiac neuronal PET imaging agent, in cells and animal models

BACKGROUND

Heart failure has been associated with impaired cardiac sympathetic neuronal function. Cardiac imaging with radiolabeled agents that are substrates for the neuronal norepinephrine transporter (NET) has demonstrated the potential to identify individuals at risk of cardiac events. N-[3-Bromo-4-(3-[18F]fluoro-propoxy)-benzyl]-guanidine (LMI1195) is a newly developed 18F-labeled NET substrate designed to allow cardiac neuronal imaging with the high sensitivity, resolution, and quantification afforded by positron emission tomography (PET).

METHODS AND RESULTS

LMI1195 was evaluated in comparison with norepinephrine (NE) in vitro and 123I-meta-iodobenzylguanidine (MIBG) in vivo. The affinity (Ki) of LMI1195 for NET was 5.16 ± 2.83 μmol/L, similar to that of NE (3.36 ± 2.77 μmol/L) in a cell membrane-binding assay. Similarly, LMI1195 uptake kinetics examined in a human neuroblastoma cell line had Km and Vmax values of 1.44 ± 0.76 μmol/L and 6.05 ± 3.09 pmol/million cells per minute, comparable to NE (2.01 ± 0.85 μmol/L and 6.23 ± 1.52 pmol/million cells per minute). In rats, LMI1195 heart uptake at 15 and 60 minutes after intravenous administration was 2.36 ± 0.38% and 2.16 ± 0.38% injected dose per gram of tissue (%ID/g), similar to 123I-MIBG (2.14 ± 0.30 and 2.19 ± 0.27%ID/g). However, the heart to liver and lung uptake ratios were significantly higher for LMI1195 than for 123I-MIBG. In rabbits, desipramine (1 mg/kg), a selective NET inhibitor, blocked LMI1195 heart uptake by 82%, which was more effective than 123I-MIBG (53%), at 1 hour after dosing. Sympathetic denervation with 6-hydroxydopamine, a neurotoxin, resulted in a marked (79%) decrease in LMI1195 heart uptake. Cardiac PET imaging with LMI1195 in rats, rabbits, and nonhuman primates revealed clear myocardium with low radioactivity levels in the blood, lung, and liver. Imaging in rabbits pretreated with desipramine showed reduced heart radioactivity levels in a dose-dependent manner. Additionally, imaging in sympathetically denervated rabbits resulted in low cardiac image intensity with LMI1195 but normal perfusion images with flurpiridaz F 18, a PET myocardial perfusion imaging agent. In nonhuman primates pretreated with desipramine (0.5 mg/kg), imaging with LMI1195 showed a 66% decrease in myocardial uptake. In a rat model of heart failure, the LMI1195 cardiac uptake decreased as heart failure progressed.

CONCLUSIONS

LMI1195 is a novel (18)F imaging agent retained in the heart through the NET and allowing evaluation of the cardiac sympathetic neuronal function by PET imaging.

Diagnostic cutoff points for ¹²³I-MIBG myocardial scintigraphy in a Caucasian population with Parkinson's disease

PURPOSE

Molecular imaging with (123)I-metaiodobenzylguanidine (MIBG) has been used in Parkinson's disease (PD), but there is no consensual index to discriminate between normal and PD patients in the Caucasian population. The purpose of this study was to determine diagnostic cutoff points in the quantification of MIBG cardiac uptake in our population of PD patients. We have also calculated the reproducibility over a range of interpretation expertise.

METHODS

The study included 14 PD patients and 14 normal age- and sex-matched controls. Heart to mediastinum ratios (H/M) were calculated at 15 min (H/M15m) and 4 h (H/M4h) post-injection by three observers with different interpretation expertise, one of whom drew the regions of interest at three different times. The intraobserver and interobserver reliability was calculated (interclass correlation coefficient and coefficient of variability). Diagnosis was estimated by maximizing the Youden index for H/M and washout ratios. Discrimination ability was assessed by the area under the curve (AUC). Sensitivity and specificity were reported, using our thresholds.

RESULTS

The parameter with the best diagnostic accuracy was the H/M4h ratio, with a major AUC (0.976 area under the receiver-operating characteristic curve). The threshold was 1.43 with a 95% confidence interval of 1.37-1.50. Using this threshold, the sensitivity and specificity were 93 and 100%. The interobserver and intraobserver variabilities measuring this ratio were 3.2 and 3.1%, respectively.

CONCLUSION

The diagnostic cutoff point for (123)I-MIBG myocardial scintigraphy in a Caucasian population with PD was 1.43 for the H/M4h index, with a good sensitivity and specificity. The technique is easy to use, with a good reproducibility over a range of interpretation expertise.

Proposal for standardization of 123I-metaiodobenzylguanidine (MIBG) cardiac sympathetic imaging by the EANM Cardiovascular Committee and the European Council of Nuclear Cardiology

This proposal for standardization of (123)I-metaiodobenzylguanidine (iobenguane, MIBG) cardiac sympathetic imaging includes recommendations for patient information and preparation, radiopharmaceutical, injected activities and dosimetry, image acquisition, quality control, reconstruction methods, attenuation, scatter and collimator response compensation, data analysis and interpretation, reports, and image display. The recommendations are based on evidence coming from original or scientific studies whenever possible and as far as possible reflect the current state-of-the-art in cardiac MIBG imaging. The recommendations are designed to assist in the practice of performing, interpreting and reporting cardiac sympathetic imaging. The proposed standardization does not include clinical indications, benefits or drawbacks of cardiac sympathetic imaging, and does not address cost benefits or cost effectiveness; however, clinical settings of potential utility are mentioned. Standardization of MIBG cardiac sympathetic imaging should contribute to increasing its clinical applicability and integration into current nuclear cardiology practice.

Norepinephrine spillover during exercise as a novel parameter to evaluate the severity of heart failure

BACKGROUND

The washout rate (WR) of (123)I-metaiodobenzylguanidine (MIBG) is now widely used for assessing the severity of heart failure. Although the WR of MIBG is usually measured at rest, the assessment of WR of MIBG during exercise might have a different clinical relevance. In this study, we measured the WR rate of MIBG during low-grade exercise and studied the clinical importance of this novel index.

METHODS

Twenty-four patients with dilated cardiomyopathy (DCM) were enrolled in this study. Planar images were obtained 20 minutes after MIBG injection (first image) and after 270 minutes (second image); the third image was obtained after 15 minutes of low-grade (10 W) bicycle ergometer exercise (300 minutes after MIBG injection). The decay of the specific counts was calculated from the first two images. The estimated third counts were calculated from the resting decay and were compared with the actual third counts.

RESULTS

In the receiver operating characteristic (ROC) curve analysis, we set a 10% decrease from the estimated counts as a cut-off value for severe heart failure (New York Heart Association [NYHA] Class IIm or worse). In 15 patients, the actual third count value was within 10% of the estimated count (N-group). In nine patients, the WR during exercise was high, and the actual third count values showed more than a 10% decrease from the estimated count value (H-group). In the H-group, 78% of the patients were in NYHA class IIm or III. In contrast, in the N-group, no patient had NYHA class III, and only 20% of the patients were in class IIm. The brain natriuretic peptide (BNP) level was significantly higher in the H-group than in the N-group (525 ± 263 pg/mL vs 176 ± 144 pg/mL; P < .01). No significant differences were observed in heart/mediastinal (H/M) activity ratio, the regular WR, and left ventricular ejection fraction values between the two groups.

CONCLUSIONS

The WR of MIBG during exercise may be an independent prediction variable, with a clinical relevance different from that of the WR at rest. This measurement could be used as a new index for assessing the severity of heart failure.

Myocardial iodine-123 meta-iodobenzylguanidine imaging and cardiac events in heart failure. Results of the prospective ADMIRE-HF (AdreView Myocardial Imaging for Risk Evaluation in Heart Failure) study

OBJECTIVES

The ADMIRE-HF (AdreView Myocardial Imaging for Risk Evaluation in Heart Failure) study prospectively evaluated iodine-123 meta-iodobenzylguanidine ((123)I-mIBG) imaging for identifying symptomatic heart failure (HF) patients most likely to experience cardiac events.

BACKGROUND

Single-center studies have demonstrated the poorer prognosis of HF patients with reduced (123)I-mIBG myocardial uptake, but these observations have not been validated in large multicenter trials.

METHODS

A total of 961 subjects with New York Heart Association (NYHA) functional class II/III HF and left ventricular ejection fraction (LVEF) < or =35% were studied. Subjects underwent (123)I-mIBG myocardial imaging (sympathetic neuronal integrity quantified as the heart/mediastinum uptake ratio [H/M] on 4-h delayed planar images) and myocardial perfusion imaging and were then followed up for up to 2 years. Time to first occurrence of NYHA functional class progression, potentially life-threatening arrhythmic event, or cardiac death was compared with H/M (either in relation to estimated lower limit of normal [1.60] or as a continuous variable) using Cox proportional hazards regression. Multivariable analyses using clinical, laboratory, and imaging data were also performed.

RESULTS

A total of 237 subjects (25%) experienced events (median follow-up 17 months). The hazard ratio for H/M > or =1.60 was 0.40 (p < 0.001); the hazard ratio for continuous H/M was 0.22 (p < 0.001). Two-year event rate was 15% for H/M > or =1.60 and 37% for H/M <1.60; hazard ratios for individual event categories were as follows: HF progression, 0.49 (p = 0.002); arrhythmic events, 0.37 (p = 0.02); and cardiac death, 0.14 (p = 0.006). Significant contributors to the multivariable model were H/M, LVEF, B-type natriuretic peptide, and NYHA functional class. (123)I-mIBG imaging also provided additional discrimination in analyses of interactions between B-type natriuretic peptide, LVEF, and H/M.

CONCLUSIONS

ADMIRE-HF provides prospective validation of the independent prognostic value of (123)I-mIBG scintigraphy in assessment of patients with HF. (Meta-Iodobenzylguanidine Scintigraphy Imaging in Patients With Heart Failure and Control Subjects Without Cardiovascular Disease, NCT00126425; Meta-Iodobenzylguanidine [123I-mIBG] Scintigraphy Imaging in Patients With Heart Failure and Control Subjects Without Cardiovascular Disease, NCT00126438).

Cardiac sympathetic activity is associated with inflammation and neurohumoral activation in patients with idiopathic dilated cardiomyopathy

BACKGROUND

Idiopathic dilated cardiomyopathy (IDC) is characterized by sympathetic nervous overactivity, inflammation and neurohumoral activation; however, their interrelationships are poorly understood.

METHODS AND RESULTS

We studied 99 patients with IDC (age 54 +/- 1 years, left ventricular ejection fraction (EF) 40 +/- 1%, maximum oxygen uptake (VO(2)max) 20 +/- 1 ml kg(-1) min(-2), mean +/- SEM) by using (123)I-metaiodobenzylguanidine (MIBG) imaging. MIBG washout and MIBG heart/mediastinum (H/M)-ratio at 4 h postinjection were calculated. In addition, the plasma levels of interleukin (IL)-6 and N-terminal B-type natriuretic peptide (NT-proBNP) were measured. MIBG washout and MIBG H/M ratio had a significant correlation with IL-6 (r = 0.42, P<0.001 and r = -0.31, P<0.01) and NT-proBNP (r = 0.48, P<0.001 and r = -0.40, P<0.001). During a median follow-up of 4.1 years, 20 patients (20%) had an adverse cardiac event (death, heart transplantation or application of biventricular pacemaker or implantable cardioverter-defibrillator). In these patients, MIBG washout was higher (53 +/- 4 versus 40 +/- 2%, P = 0.01) and H/M ratio lower (1.38 +/- 0.04 versus 1.51 +/- 0.02, P = 0.01) than in patients without an event.

CONCLUSIONS

In dilated cardiomyopathy, myocardial sympathetic innervation and activity are related to inflammation and neurohumoral activation. These relationships are at least partly independent of left ventricular function and exercise capacity.

Impact of mediastinal, liver and lung (123)I-metaiodobenzylguanidine ( (123)I-MIBG) washout on calculated (123)I-MIBG myocardial washout

PURPOSE

In planar (123)I-metaiodobenzylguanidine ((123)I-MIBG) myocardial imaging mediastinum (M) activity is often used as a background correction in calculating "washout" (WO). However, the most likely sources for counts that might produce errors in estimating myocardial (Myo) activity are lung (Lu) and liver (Li), which typically have higher counts/pixel (cpp) than M. The present study investigated the relationship between changes in Lu, Li and Myo activity between early and late planar (123)I-MIBG images, with comparison to M as the best estimator of non-specific background activity.

METHODS

Studies on 98 subjects with both early (e) and late (l) planar (123)I-MIBG images were analysed. There were 68 subjects with chronic heart failure (CHF), 14 with hypertension (HTN) but no known heart disease and 16 controls (C). For each image, regions of interest (ROIs) were drawn: an irregular whole Myo, Lu, upper M and Li. For each ROI, WO was calculated as [(cpp(e)-cpp(l:decay corrected))/cpp(e)]x100%.

RESULTS

Multivariable forward stepwise regression analysis showed that overall a significant proportion of the variation in Myo WO could be explained by a model containing M WO and Lu WO (37%, p < 0.001). Only in controls was M WO the sole variable explaining a significant proportion of the variation in Myo WO (27%, p = 0.023).

CONCLUSION

Although increased Myo WO in CHF subjects reflects disease severity, part of the count differences measured on planar (123)I-MIBG myocardial images likely reflects changes in the adjacent and surrounding Lu tissue. The results for the controls suggest that this is the only group where a mediastinum correction alone may be appropriate for cardiac WO calculations.

Radionuclide noninvasive evaluation of heart failure beyond left ventricular function assessment

The management of patients with heart failure (HF) is challenging and requires the integration of clinical skills and accurate ancillary tests for the correct diagnosis and estimation of individual prognosis. Although the basic characterization of patients with HF is supported primarily by echocardiographic assessment of the left ventricular function, other noninvasive imaging procedures are being developed, including those involved in the processes of myocardial perfusion, metabolism, cellular injury, intersticial dysregulation, and neurohormonal receptor function. Nuclear techniques for molecular imaging of the myocardium may provide valuable insights into the pathophysiology, severity, management (medical/mechanical/surgical), response to treatment, and prognosis of HF patients. This will permit individualized management decisions and hopefully facilitate better clinical outcomes for patients with HF.

Resting muscle sympathetic nerve activity, cardiac metaiodobenzylguanidine uptake, and exercise tolerance in patients with left ventricular dysfunction

BACKGROUND

Sympathetic nerve overactivity and reduced exercise tolerance are characteristic features of patients with heart failure. However, to what extent sympathetic nerve overactivity contributes to limiting exercise tolerance has not been clearly defined.

METHODS

Myocardial iodine 123-metaiodobenzylguanidine (MIBG) scintigraphy, muscle sympathetic nerve activity (MSNA), and cardiopulmonary exercise testing were performed within 3 days in 30 patients with left ventricular dysfunction (LVD). Cardiac sympathetic nerve activity was estimated using H/M ratio and washout rate (WR) of 123I-MIBG imaging. MSNA was recorded by microneurography.

RESULTS

The patients with peak VO(2) < 20 mL/minute/kg (group II, n = 15) had significantly higher MSNA and WR, and lower H/M ratio than those with peak VO(2) > or = 20 mL/minute/kg (group I, n = 15) (P < .05). Peak VO(2) had negative correlations with MSNA and WR (r = 0.58, 0.56), and positive correlations with early H/M ratio and delayed H/M ratio (r = 0.71, 0.75) in group II. Moreover, MSNA had negative correlations with early H/M ratio and delayed H/M ratio (r = 0.78, 0.66), and a positive correlation with WR (r = 0.79) in group II. However, similar relations were not found in group I.

CONCLUSIONS

A link between cardiac and peripheral sympathetic nerve activities contributed to limiting exercise tolerance in patients with LVD patients and reduced exercise tolerance.

Evaluating presynaptic and postsynaptic innervation in heart failure

Congestive heart failure increasingly contributes to the overall morbidity and mortality associated with cardiovascular disease. Although significant advances in therapies allow patients to feel better and have improved functional status and survival, not all patients respond equally to these therapies. Moreover, for any given level of left ventricular systolic dysfunction, it is difficult to predict who will have progressive heart failure leading to death or transplantation or who will die suddenly. It has long been recognized that the sympathetic nervous system plays a major role in the morbidity and mortality associated with congestive heart failure from systolic left ventricular dysfunction. Although some of the sympathetic effect occurs at the systemic level, malfunction at the ventricular myocyte-sympathetic nerve terminal interface is likely a major contributor to sudden death and progressive heart failure. Imaging the cardiac sympathetic nervous system can be used to evaluate this myoneural interface and to predict outcome.

123I-mIBG scintigraphy to predict risk for adverse cardiac outcomes in heart failure patients: design of two prospective multicenter international trials

BACKGROUND

ADMIRE-HF (AdreView Myocardial Imaging for Risk Evaluation in Heart Failure) consists of two identical prospective open-label, multicenter, phase 3 studies (MBG311 and MBG312) evaluating the prognostic usefulness of (123)I-mIBG scintigraphy for identifying subjects with heart failure who will experience a major adverse cardiac event.

METHODS

Subjects with NYHA class II and III heart failure and left ventricular ejection fraction < or = 35% were eligible for the trials. Subjects underwent planar and SPECT (123)I-mIBG myocardial imaging, as well as echocardiography and gated SPECT (99m)Tc-tetrofosmin myocardial perfusion imaging. Subjects are then monitored on a regular basis for 2 years. Time to first occurrence of one of the following--NYHA class progression; potentially life-threatening arrhythmic event (including ICD discharge); or cardiac death, as verified by an independent adjudication panel---will be analyzed in comparison to quantitative parameters derived from (123)I-mIBG imaging. The primary efficacy analysis will employ the heart/mediastinum ratio on 4-hour delayed planar imaging, while secondary efficacy analyses will examine quantitative results from both planar and SPECT (123)I-mIBG images, as well as from (99m)Tc-tetrofosmin SPECT and echocardiography.

CONCLUSION

The results of the ADMIRE-HF trials will provide prospective validation of the potential role of (123)I-mIBG scintigraphy in assessing prognosis and developing management strategies for patients with heart failure.

Diagnostic and prognostic imaging of the cardiac sympathetic nervous system

Individuals with systolic dysfunction congestive heart failure may have decreased neuronal density, decreased neuronal function (reuptake or retention of norepinephrine), or a combination of these, plus reduction in postsynaptic beta-receptor density. Cardiac neuronal distribution and function can be imaged with standard gamma cameras and PET using radiolabeled analogs of norepinephrine. Postsynaptic beta-adrenergic receptor distribution and density can be determined using PET. Multiple imaging studies of the presynaptic component have reported that those individuals with the lowest retention or fastest washout of the radiolabeled analogs have a much greater annual mortality than do those with greater retention or slower washout rate. The results of some studies have suggested that the image abnormalities are better predictors of death than are more common predictors of outcome such as ejection fraction, heart rate variability, and microvolt T-wave alternans. The variability between these studies makes it unclear which measure of presynaptic dysfunction is the most predictive. beta-Receptor imaging has not been evaluated as extensively as a prognostic tool as has presynaptic imaging. Preliminary data suggest that regional mismatch between beta-receptors and presynaptic norepinephrine transporter function may serve as a marker for adverse outcome.

Risk stratification assessed by combined lung and heart iodine-123 metaiodobenzylguanidine uptake in patients with idiopathic dilated cardiomyopathy

Iodine-123 metaiodobenzylguanidine (123I-MIBG) has been used to assess myocardial sympathetic nervous activity and severity of heart failure. (123)I-MIBG is also used as a potential marker of pulmonary endothelial cell function and may be related to pulmonary hypertension. Thus, we hypothesized that combined assessment of lung and heart 123I-MIBG kinetics predicts future clinical outcome more accurately than myocardial evaluation alone in patients with chronic heart failure. To test this hypothesis, we examined 123I-MIBG scintigrams in 62 consecutive patients with idiopathic dilated cardiomyopathy. Anterior planar images were obtained 15 minutes and 3 hours after 123I-MIBG injection. Cardiac and pulmonary 123I-MIBG activities were quantified as heart-to-mediastinum activity ratio and lung-to-mediastinum activity ratio. We introduced lung-to-heart activity ratio as the new 123I-MIBG parameter including myocardial sympathetic nerve activity and pulmonary endothelial cell function. Delayed lung-to-heart ratio was correlated with pulmonary vascular resistance (r = 0.48, p <0.0001), disease duration (r = 0.49, p <0.0001), and number of heart failure episodes (r = 0.55, p <0.0001). During a mean follow-up of 25 months, 15 patients had a cardiac event. Area under receiver operating characteristic curves for prediction of the event was greatest in delayed lung-to-heart ratio (lung to heart 0.92, heart to mediastinum 0.83, lung to mediastinum 0.80). In multivariate analysis, the lung-to-heart ratio (hazard ratio 2.76/0.1 increase, p = 0.002) was selected as an independent predictor for a future cardiac event. In conclusion, the combined assessment of lung and heart 123I-MIBG uptake may help to predict future clinical outcome for patients with idiopathic dilated cardiomyopathy more accurately than myocardial evaluation alone.

Prognostic value of myocardial 123I-metaiodobenzylguanidine (MIBG) parameters in patients with heart failure: a systematic review

AIMS

To derive a more precise estimate of the prognostic significance of myocardial 123I-metaiodobenzylguanidine (MIBG) parameters [early heart mediastinal ratio (H/M), late H/M, and myocardial washout] in heart failure (HF).

METHODS AND RESULTS

Eighteen studies with a total of 1755 patients, stratifying survival, and cardiac events in patients with HF by MIBG, were eligible for analysis. The pooled hazard ratio (HR) estimates for cardiac death and cardiac events associated with washout showed no significant heterogeneity and were 1.72 [95%CI (confidence interval), 1.72-2.52; P = 0.006] and 1.08 (95%CI: 1.03-1.12; P < 0.001), respectively. The pooled HR estimates for cardiac death and cardiac events associated with early H/M and late H/M showed significant heterogeneity (I2 > or = 75%). Limiting the pooling to the qualitative best three studies rendered I2 insignificant (I2 = 0) and resulted in a pooled HR of late H/M for cardiac death of 1.82 (95%CI: 0.80-4.12; P = 0.15) and for cardiac events of 1.98 (95%CI: 1.57-2.50; P < 0.001).

CONCLUSION

Our results indicate that patients with HF and decreased late H/M or increased myocardial MIBG washout have a worse prognosis compared with those with normal semi-quantitative myocardial MIBG parameters.