Influence of ejection fraction on the prognostic value of sympathetic innervation imaging with iodine-123 MIBG in heart failure

Impaired Cardiac Sympathetic Activity Is Associated With Myocardial Remodeling and Established Biomarkers of Heart Failure

BACKGROUND

123Iodine-meta-iodobenzylguanidine scintigraphy is useful for assessing cardiac autonomic dysfunction and predict outcomes in heart failure (HF). The relationship of cardiac sympathetic function with myocardial remodeling and diffuse fibrosis remains largely unknown. We aimed to evaluate the cardiac sympathetic function of patients with HF and its relation with myocardial remodeling and exercise capacity.

METHODS AND RESULTS

Prospectively enrolled patients with HF (New York Heart Association class II-III) were stratified into HF with preserved left ventricular ejection fraction [LVEF] ≥45%) and reduced LVEF. Ventricular morphology/function and myocardial extracellular volume (ECV) fraction were quantified by cardiovascular magnetic resonance, global longitudinal strain by echocardiography, cardiac sympathetic function by heart-to-mediastinum ratio from 123iodine-meta-iodobenzylguanidine scintigraphy. All participants underwent cardiopulmonary exercise testing. The cohort included 33 patients with HF with preserved LVEF (LVEF, 60±10%; NT-proBNP [N-terminal pro-B-type natriuretic peptide], 248 [interquartile range, 79-574] pg/dL), 28 with HF with reduced LVEF (LVEF, 30±9%; NT-proBNP, 743 [interquartile range, 250-2054] pg/dL) and 20 controls (LVEF, 65±5%; NT-proBNP, 40 [interquartile range, 19-50] pg/dL). Delayed (4 hours) 123iodine-meta-iodobenzylguanidine heart-to-mediastinum ratio was lower in HF with preserved LVEF (1.59±0.25) and HF with reduced LVEF (1.45±0.16) versus controls (1.92±0.24; P<0.001), and correlated negatively with diffuse fibrosis assessed by ECV (R=-0.34, P<0.01). ECV in segments without LGE was increased in HF with preserved ejection fraction (0.32±0.05%) and HF with reduced left ventricular ejection fraction (0.31±0.04%) versus controls (0.28±0.04, P<0.05) and was associated with the age- and sex-adjusted maximum oxygen consumption (peak oxygen consumption); (R=-0.41, P<0.01). Preliminary analysis indicates that cardiac sympathetic function might potentially act as a mediator in the association between ECV and NT-proBNP levels.

CONCLUSIONS

Abnormally low cardiac sympathetic function in patients with HF with reduced and preserved LVEF is associated with extracellular volume expansion and decreased cardiopulmonary functional capacity.

Prognostic Significance of Cardiac 123I-MIBG SPECT Imaging in Heart Failure Patients With Preserved Ejection Fraction

OBJECTIVES

The authors sought to elucidate the prognostic value of cardiac sympathetic nerve dysfunction as evaluated using iodine-123-labeled metaiodobenzylguanidine (¹²³I-MIBG) single-photon emission computed tomography (SPECT) imaging in patients with heart failure (HF) with preserved left ventricular ejection fraction (HFpEF).

BACKGROUND

Cardiac sympathetic nerve dysfunction assessed by ¹²³I-MIBG imaging is associated with poor outcomes in chronic HF patients with reduced left ventricular ejection fraction (HFrEF). However, no information is available on the prognostic vale of cardiac ¹²³I-MIBG SPECT imaging in patients with HFpEF.

METHODS

We studied 148 patients admitted for acute decompensated HF (ADHF) with nonischemic HFpEF and who underwent cardiac ¹²³I-MIBG imaging at discharge. The cardiac ¹²³I-MIBG heart-to-mediastinum ratio (H/M) was measured on the delayed planar image (late H/M). SPECT analysis of the delayed image was conducted, and the tracer uptake in all 17 regions on the polar map was scored on a 5-point scale by comparison with a sex-matched normal control database. The total defect score (TDS) was calculated by summing the score of each of the 17 segments. The primary endpoint was the association between TDS and cardiac events (the composite of emergent HF hospitalization and cardiac death).

RESULTS

During a mean follow-up period of 2.4 ± 1.6 years, 61 patients experienced cardiac events. TDS was significantly associated with cardiac events after multivariate Cox adjustment (P < 0.0001). Patients with high TDS levels had a significantly greater risk of cardiac events than those with middle or low TDS levels (63% vs 40% vs 20%, respectively; P < 0.0001; HR: 4.69; 95% CI: 2.29 to 9.61; and HR: 2.46; 95% CI: 1.14 to 5.29). C-statistic of TDS was 0.730 (95% CI: 0.651 to 0.799), which was significantly higher than that of late H/M (0.607; 95% CI: 0.524 to 0.686; P = 0.0228).

CONCLUSIONS

Cardiac ¹²³I-MIBG SPECT imaging provided useful prognostic information in nonischemic ADHF patients with HFpEF. (Clinical Trial: Osaka Prefectural Acute Heart Failure Syndrome Registry (OPAR): UMIN 000015246).

Analysis of Differences in Assessment of Left Ventricular Function on Echocardiography and Nuclear Perfusion Imaging

Two widely used methods for left ventricular (LV) ejection fraction (EF) determination, echocardiography (echo) and gated single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI), often have wide limits of agreement. Factors influencing discrepancies between core laboratory echo and MPI LVEF determinations were examined in a large series of heart failure (HF) subjects and normal controls. 879 HF and 101 control subjects had core lab analyses of echo and MPI (mean time between procedures 7-8 days). LVEF differences were analyzed using one-way analysis of variance and Bland-Altman plots. Relationships between LVEF differences and patient characteristics and outcome endpoints (mortality and arrhythmias) were explored with logistic regression, Cox proportional hazards models, and Kaplan-Meier survival analyses. There was a systematic difference between the 2 modalities; echo LVEF was higher with more severe LV dysfunction, MPI LVEF higher when systolic function was normal. LVEF results were within ±5% in only 37% of HF and 23% of control subjects. Considering discordance around the LVEF threshold 35%, there was disagreement between the 2 methods in 305 HF subjects (35%). Male gender (odds ratio (OR) = 0.200), atrial fibrillation (OR = 2.314), higher body mass index (OR = 1.051) and lower LV end-diastolic volume (OR = 0.985) were the strongest predictors of methodologic discordance. Cardiac event rates were highest if both LVEF values were ≤35% and lowest when both LVEF values were >35%. In conclusion, substantial disagreements between LVEF results by echo and MPI are common. HF patients with LVEF ≤35% by both techniques have the highest 2-year event risk.

A simplified wall-based model for regional innervation/perfusion mismatch assessed by cardiac 123I-mIBG and rest 99mTc-tetrofosmin SPECT to predict arrhythmic events in ischaemic heart failure

AIMS

Cardiac 123iodine-meta-iodobenzylguanidine (123I-mIBG) single-photon emission computed tomography (SPECT) imaging provides information on regional myocardial innervation. However, the value of the commonly used 17-segment summed defect score (SDS) as a prognostic marker is uncertain. The present study examined whether a simpler regional scoring approach for evaluation of 123I-mIBG SPECT combined with rest 99mTc-tetrofosmin SPECT myocardial perfusion imaging could improve prediction of arrhythmic events (AEs) in patients with ischaemic heart failure (HF).

METHODS AND RESULTS

Five hundred and two ischaemic HF subjects of the ADMIRE-HF study with complete cardiac 123I-mIBG and rest 99mTc-tetrofosmin SPECT studies were included. Both SPECT image sets were read together by two experienced nuclear imagers and scored by consensus. In addition to standard 17-segment scoring, the readers classified walls (i.e. anterior, lateral, inferior, septum and apex) as normal, matched defect, mismatched (innervation defect > perfusion defect), or reverse mismatched (perfusion defect > innervation defect). Cox proportional hazards ratios (HRs) were used to determine if age, body mass index, functional class, left ventricular ejection fraction (LVEF), B-type natriuretic peptide (BNP), norepinephrine, 123I-mIBG SDS, 99mTc-tetrofosmin SDS, innervation/perfusion mismatch SDS, and our simplified visual innervation/perfusion wall classification were associated with occurrence of AEs (i.e. sudden cardiac death, sustained ventricular tachycardia, resuscitated cardiac arrest, appropriate implantable cardioverter-defibrillator therapy). At 2-year median follow-up, 52 subjects (10.4%) had AEs. Subjects with 1 or 2 mismatched walls were twice as likely to have AEs compared with subjects with either 0 or 3-5 mismatched walls (16.3% vs. 8.3%, P = 0.010). Cox regression analyses showed that patients with a visual mismatch in 1-2 walls had an almost two times higher risk of AEs [HR 2.084 (1.109-3.914), P = 0.001]. None of the other innervation, perfusion and mismatch scores using standard 17 segments were associated with AEs. BNP (ng/L) was the only non-imaging parameter associated with AEs.

CONCLUSION

A visual left ventricular wall-level based scoring method identified highest AE risk in ischaemic HF subjects with intermediate levels of innervation/perfusion mismatches. This simple technique for the evaluation of SPECT studies, which are often challenging in HF subjects, seems to be superior to the 17-segment scoring method.

Prognostic significance of cardiac I-123-metaiodobenzylguanidine imaging in patients with reduced, mid-range, and preserved left ventricular ejection fraction admitted for acute decompensated heart failure: a prospective study in Osaka Prefectural Acute Heart Failure Registry (OPAR)

AIMS

Cardiac 123I-metaiodobenzylguanidine (123I-MIBG) imaging provides prognostic information in patients with chronic heart failure (HF). However, there is little information available on the prognostic role of cardiac 123I-MIBG imaging in patients admitted for acute decompensated heart failure (ADHF), especially relating to reduced ejection fraction [HFrEF; left ventricular ejection fraction (LVEF) < 40%], mid-range ejection fraction (HFmrEF; 40% ≤ LVEF < 50%) and preserved ejection fraction (HFpEF; LVEF ≥ 50%).

METHODS AND RESULTS

We studied 349 patients admitted for ADHF and discharged with survival. Cardiac 123I-MIBG imaging, echocardiography, and venous blood sampling were performed just before discharge. The cardiac 123I-MIBG heart-to-mediastinum ratio (late H/M) was measured on the chest anterior view images obtained at 200 min after the isotope injection. The endpoint was cardiac events defined as unplanned HF hospitalization and cardiac death. During a follow-up period of 2.1 ± 1.4 years, 128 patients had cardiac events (45/127 in HFrEF, 28/78 in HFmrEF, and 55/144 in HFpEF). On multivariable Cox analysis, late H/M was significantly associated with cardiac events in overall cohort (P = 0.0038), and in subgroup analysis of each LVEF subgroup (P = 0.0235 in HFrEF, P = 0.0119 in HFmEF and P = 0.0311 in HFpEF). Kaplan-Meier analysis showed that patients with low late H/M (defined by median) had significantly greater risk of cardiac events in overall cohort (49% vs. 25% P < 0.0001) and in each LVEF subgroup (HFrEF: 48% vs. 23% P = 0.0061, HFmrEF: 51% vs. 21% P = 0.0068 and HFpEF: 50% vs. 26% P = 0.0026).

CONCLUSION

Cardiac sympathetic nerve dysfunction was associated with poor outcome in ADHF patients irrespective of HFrEF, HFmrEF, or HFpEF.

Changes in cardiac sympathetic nerve activity on 123 I-metaiodobenzylguanidine scintigraphy after MitraClip therapy

Aims

In patients with heart failure, over‐activation of the cardiac sympathetic nerve (CSN) function is associated with severity of heart failure and worse outcome. The effects of MitraClip therapy on the CSN activity in patients with mitral regurgitation (MR) remained unknown. In this study, we evaluated the impact of the MitraClip therapy on CSN activity assessed by ¹²³I‐metaiodobezylguanidine (MIBG) scintigraphy.

Methods and results

We enrolled consecutive patients with moderate‐to‐severe (3+) or severe (4+) MR who were scheduled to undergo MitraClip procedure in this prospective observational study. MIBG scintigraphy was performed at baseline and 6 months after the MitraClip procedure to evaluate the heart–mediastinum ratio and washout rate (WR). Changes in these MIBG parameters were analysed. Of the 13 consecutive patients, 10 were successfully treated with MitraClip procedure and completed follow‐up assessment. With regard to the MIBG parameters, changes in the early and delayed heart–mediastinum ratio from baseline to 6 months were not significant (2.16 ± 0.42 to 2.06 ± 0.34, P = 0.38 and 1.87 ± 0.39 to 1.83 ± 0.39, P = 0.43, respectively), whereas WR was significantly decreased (38.6 ± 3.9% to 32.6 ± 3.94%, P = 0.002).

Conclusions

The CSN activity of the WR on MIBG imaging was improved 6 months after MitraClip therapy in patients with 3+ or 4+ MR.

Hybrid solid-state SPECT/CT left atrial innervation imaging for identification of left atrial ganglionated plexi: Technique and validation in patients with atrial fibrillation

BACKGROUND

Ablating left atrial (LA) ganglionated plexi (GP), identified invasively by high-frequency stimulation (HFS) during pulmonary vein isolation (PVI), may reduce atrial fibrillation (AF) recurrence. 123I-metaiodobenzylguanidine (123I-mIBG) solid-state SPECT LA innervation imaging (LAII) has the spatial resolution to detect LAGP non-invasively but this has never been demonstrated in clinical practice.

METHODS

20 prospective patients with paroxysmal AF scheduled for PVI underwent 123I-mIBG LAII. High-resolution tomograms, reconstructed where possible using cardiorespiratory gating, were co-registered with pre-PVI cardiac CT. Location and reader confidence (1 [low] to 3 [high]) in discrete 123I-mIBG LA uptake areas (DUAs) were recorded and correlated with HFS.

RESULTS

A total of 73 DUAs were identified, of which 59 (81%) were HFS positive (HFS +). HFS + likelihood increased with reader confidence (92% [score 3]). 64% of HFS-negative DUAs occurred over the lateral and inferior LA. Cardiorespiratory gating reduced the number of DUAs per patient (4 vs 7, P = .001) but improved: HFS + predictive value (76% vs 49%); reader confidence (2 vs 1, P = .02); and inter-observer, intra-observer, and inter-study agreement (κ = 0.84 vs 0.68; 0.82 vs 0.74; 0.64 vs 0.53 respectively).

CONCLUSIONS

123I-mIBG SPECT/CT LAII accurately and reproducibly identifies GPs verified by HFS, particularly when reconstructed with cardiorespiratory gating.

Sympathetic nervous system activation and heart failure: Current state of evidence and the pathophysiology in the light of novel biomarkers

Heart failure (HF) is a complex clinical syndrome characterized by the activation of at least several neurohumoral pathways that have a common role in maintaining cardiac output and adequate perfusion pressure of target organs and tissues. The sympathetic nervous system (SNS) is upregulated in HF as evident in dysfunctional baroreceptor and chemoreceptor reflexes, circulating and neuronal catecholamine spillover, attenuated parasympathetic response, and augmented sympathetic outflow to the heart, kidneys and skeletal muscles. When these sympathoexcitatory effects on the cardiovascular system are sustained chronically they initiate the vicious circle of HF progression and become associated with cardiomyocyte apoptosis, maladaptive ventricular and vascular remodeling, arrhythmogenesis, and poor prognosis in patients with HF. These detrimental effects of SNS activity on outcomes in HF warrant adequate diagnostic and treatment modalities. Therefore, this review summarizes basic physiological concepts about the interaction of SNS with the cardiovascular system and highlights key pathophysiological mechanisms of SNS derangement in HF. Finally, special emphasis in this review is placed on the integrative and up-to-date overview of diagnostic modalities such as SNS imaging methods and novel laboratory biomarkers that could aid in the assessment of the degree of SNS activation and provide reliable prognostic information among patients with HF.

Knockout of MD1 contributes to sympathetic hyperactivity and exacerbates ventricular arrhythmias following heart failure with preserved ejection fraction via NLRP3 inflammasome activation

NEW FINDINGS

What is the central question of this study? In this study, we investigated whether MD1 interacted with the sympathetic nerves in ventricular arrhythmia (VA) during heart failure with preserved ejection fraction (HFpEF). What is the main finding and its importance? Mice with HFpEF showed increased susceptibility to VA, adverse electrical remodelling, impaired heart rate variability, enhanced sympathetic hyperactivity, activation of the NLRP3 inflammasome and increased interleukin-1β release. These changes induced by HFpEF were exacerbated by MD1 deficiency.

ABSTRACT

Sympathetic hyperactivity can promote malignant ventricular arrhythmia (VA), and myeloid differentiation 1 (MD1) has been reported to play an important role in obesity-induced VA. However, it is not known whether an interaction of MD1 with sympathetic hyperactivity contributes to the VA induced by heart failure with preserved ejection fraction (HFpEF). The aim of this study was to investigate the potential interaction between MD1 and sympathetic hyperactivity in HFpEF-induced VA and the underlying mechanism. Eight-week-old MD1-knockout (MD1-KO) and wild-type (WT) mice were subjected to a model of HFpEF induced by uninephrectomy, a continuous saline or d-aldosterone infusion and provision of drinking water containing 1.0% sodium chloride for 4 weeks. Echocardiography and haemodynamics were used to verify the model of HFpEF. An isolated electrophysiological study was performed to assess the susceptibility to VA. Four weeks later, the mice with HFpEF showed an increased heart weight to tibia length ratio, decreased left ventricular minimum rates of pressure rise (dP/dt_min ), increased τ, lung weight to tibia length ratio and preserved left ventricular ejection fraction compared with WT mice. The mice with HFpEF exhibited increased susceptibility to VA, as shown by the shortened effective refractory period, prolonged action potential duration (APD), increased APD alternans threshold and higher incidence of VA. Moreover, we also found that mice with HFpEF showed impaired heart rate variability, sympathetic hyperactivity, activation of the NLRP3 inflammasome and increased interleukin-1β release. These changes induced by HFpEF were exacerbated by MD1 deficiency. We conclude that MD1-KO contributes to sympathetic hyperactivity and facilitates VA in HFpEF via activation of the NLRP3 inflammasome. Treatment targeting MD1 and NLRP3 might decrease the risk of HFpEF-induced VA.

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.

NUCLEAR IMAGING IN SUDDEN CARDIAC DEATH RISK ASSESSMENT

Sudden cardiac death is a cause of fatal outcomes in large proportion of cardiovascular patients. Left ventricle ejection fraction at the moment is the main criteria for sudden cardiac death risk stratification, however the parameter is not enough reliable. Nuclear imaging methods make it to visualize finer pathophysiological processes representing the probability of the life threatening ventricular arrhythmias development. The review is focused on recent data on nuclear imaging for cellular perfusion assessment, transient ischemia, vitality of myocardium and myocardial blood flow, metabolic disorders and sympathetic innervation.

Current Clinical Applications and Next Steps for Cardiac Innervation Imaging

PURPOSE OF REVIEW

Autonomic innervation is crucial for regulating cardiac function. Sympathetic innervation imaging with ¹²³I-mIBG and analogous PET tracers assesses disease in ways that differ from customary methods. This review describes practical use in various clinical scenarios, discusses recent guidelines, presents new data confirming risk stratification power, describes an ongoing prospective study, and looks forward to wider use in patient management.

RECENT FINDINGS

ASNC ¹²³I-mIBG guidelines are available, expanding on European guidelines. ADMIRE-HF patient follow-up increased to 2 years in ADMIRE HFX, demonstrating independent mortality risk reclassification. ADMIRE-HF findings were substantiated in a Japanese consortium study and in the PAREPET ¹¹C-HED PET study. Exciting potential uses of adrenergic imaging are management of LVADs and VT ablation. CZT cameras provide advantages, but derived parameters differ from Anger camera values. Independent risk stratification utility of adrenergic imaging with ¹²³I-mIBG and PET tracers is continuously being confirmed. An ongoing prospective randomized study promises to establish patient management utility. There is potential for wider use and improved images with newer cameras and PET.

Cardiac 123I-mIBG scintigraphy is associated with freedom of appropriate ICD therapy in stable chronic heart failure patients

AIM

Chronic heart failure (CHF) is a life-threatening clinical syndrome, partly due to sudden cardiac death (SCD). Implantable cardioverter defibrillators (ICD) for primary prevention of SCD have improved overall survival of CHF patients. However, a high percentage of patients never receives appropriate ICD therapy. This prospective multicentre study evaluated whether cardiac sympathetic activity assessed by ¹²³I-mIBG scintigraphy could be helpful in selecting patients for ICD implantation.

MATERIALS AND METHODS

135 stable CHF subjects (age 64.5±9.3years, 79% male, LVEF 25±6%) referred for prophylactic ICD implantation were enrolled in 13 institutions. All subjects underwent planar and SPECT ¹²³I-mIBG scintigraphy. Early and late heart-to-mediastinum (H/M) ratio, ¹²³I-mIBG washout (WO) and late summed scores were calculated. The primary endpoint was appropriate ICD therapy. The secondary endpoint was defined as the combined endpoint of all first cardiac events: appropriate ICD therapy, progression of heart failure (HF) and cardiac death.

RESULTS

During a median follow-up of 30months (6-68months), 24 subjects (17.8%) experienced a first cardiac event (appropriate ICD therapy [12], HF progression [6], cardiac death [6]). Late H/M ratio and defect size of ¹²³I-mIBG SPECT were not associated with appropriate ICD therapy. However, late H/M ratio was independently associated with the combined endpoint (HR 0.135 [0.035-0.517], p=0.001). Post-hoc analysis showed that the combination of late H/M ratio (HR 0.461 [0.281-0.757]) and LVEF (HR 1.052 [1.021-1.084]) was significantly associated with freedom of appropriate ICD therapy (p<0.001).

CONCLUSION

¹²³I-mIBG scintigraphy seems to be helpful in selecting CHF subjects who might not benefit from ICD implantation.

Assessment of 123I-mIBG and 99mTc-tetrofosmin single-photon emission computed tomographic images for the prediction of arrhythmic events in patients with ischemic heart failure: Intermediate severity innervation defects are associated with higher arrhythmic risk

RATIONALE

123I-mIBG planar image heart-to-mediastinum ratios effectively risk-stratify heart failure (HF) patients. The value of single-photon emission computed tomographic (SPECT) imaging for identifying increased risk of ventricular arrhythmias is less clear. This study sought to determine if findings from simultaneous interpretation of 123I-mIBG and 99mTc-tetrofosmin SPECT are predictive of arrhythmic events (ArEs).

METHODS

123I-mIBG SPECT images from 622 patients with ischemic HF were presented in standard displays alongside 99mTc-tetrofosmin images. Consensus interpretations using a 17-segment model produced summed scores. Cox proportional hazards analyses related findings to adjudicated ArEs over 2 years.

RESULTS

471 patients had images adequate for total 17-segment scoring. There were 48 ArEs (10.2%). Neither 123I-mIBG nor 99mTc-tetrofosmin SPECT summed scores were univariate predictors. On multivariate proportional hazards analysis, the 123I-mIBG SPECT score was independently predictive of ArEs (HR: 0.975, 95% CI 0.951-0.999, P = 0.042), but HR<1 indicated that risk decreased with increasing score. This occurred because patients with intermediately abnormal SPECT studies had a higher likelihood of ArEs compared to patients with extensive abnormalities.

CONCLUSIONS

The presumption of a monotonic increase in ArE risk with increasing summed 123I-mIBG SPECT score may not be correct as ischemic HF patients with abnormalities of intermediate extent appear at highest risk.

Life-Threatening Ventricular Arrhythmias: Current Role of Imaging in Diagnosis and Risk Assessment

Sudden cardiac arrest continues to be a major cause of death from cardiovascular disease but our ability to predict patients at the highest risk of developing lethal ventricular arrhythmias remains limited. Left ventricular ejection fraction is inversely related to the risk of sudden death but has a low sensitivity and specificity for the population at risk. Nevertheless, it continues to be the main variable considered in identifying patients most likely to benefit from implantable defibrillators to prevent sudden death. Imaging myocardial sympathetic innervation with PET and SPECT as well as imaging characteristics of myocardial infarcts using gadolinium-enhanced cardiac magnetic resonance are emerging as imaging modalities that may further refine patient selection beyond ejection fraction. This review will primarily focus on employing advanced imaging approaches to identify patients with left ventricular dysfunction that are most likely to develop lethal arrhythmias and benefit from inserting a primary prevention implantable cardiac defibrillator. While not yet tested in prospective studies, we will review risk prediction models incorporating quantitative imaging and biomarkers that have been developed that appear promising to identify those at highest risk of sudden death.

The role of nuclear cardiac imaging in risk stratification of sudden cardiac death

Sudden cardiac death (SCD) represents a significant portion of all cardiac deaths. Current guidelines focus mainly on left ventricular ejection fraction (LVEF) as the main criterion for SCD risk stratification and management. However, LVEF alone lacks both sensitivity and specificity in stratifying patients. Recent research has provided interesting data which supports a greater role for advanced cardiac imaging in risk stratification and patient management. In this article, we will focus on nuclear cardiac imaging, including left ventricular function assessment, myocardial perfusion imaging, myocardial blood flow quantification, metabolic imaging, and neurohormonal imaging. We will discuss how these can be used to better understand SCD and better stratify patient with both ischemic and non-ischemic cardiomyopathy.

Prognostic Significance of Imaging Myocardial Sympathetic Innervation

There has been a longstanding interest in understanding whether the presence of inhomogeneity in myocardial sympathetic innervation can predict patients at risk of sudden cardiac arrest from lethal ventricular arrhythmias. The advent of radiolabeled norepinephrine analogs has allowed this to be imaged in patients with ischemic and non-ischemic cardiomyopathy using single, photon emission computed tomography (SPECT) and positron emission tomography (PET). Several observational studies have demonstrated that globally elevated myocardial sympathetic tone (as reflected by reduced myocardial norepinephrine analog uptake) can predict composite cardiac end-points including total cardiovascular mortality. More recent studies have indicated that quantifying the extent of regional denervation can predict the risk of lethal ventricular arrhythmias and sudden cardiac death. This review will summarize our current understanding of the prognostic significance of altered myocardial sympathetic innervation.

Novel Imaging Approaches for Predicting Arrhythmic Risk

Determination of ventricular arrhythmic risk is crucial for guiding management of cardiac disease. Although for patients at increased risk an implantable cardioverter-defibrillator is recommended, it is widely acknowledged that current criteria for device use based predominantly on left ventricular ejection fraction are deficient. Genesis of ventricular arrhythmias involves a complex interaction of myocardial substrate abnormalities, precipitating triggers, and modulating factors. There are much data showing that by more directly assessing these factors, noninvasive imaging using echocardiography, radionuclide imaging, and cardiac magnetic resonance enhances arrhythmic risk stratification beyond ejection fraction and commonly used electrocardiographic and serum biomarkers. It is anticipated that further technological advancements studied in well-designed clinical trials will provide both more precise determination of risk and guide therapies to enhanced survival and patient well-being.

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.

Prognostic Significance of Neuroadrenergic Dysfunction for Cardiovascular Events in Patients With Acute Myocardial Infarction

BACKGROUND

The dysregulation of systemic blood pressure (BP) variation or cardiac neuroadrenergic dysfunction is associated with adverse cardiovascular events. We aimed to clarify the prognostic significance of neuroadrenergic dysfunction for cardiovascular events in patients with acute myocardial infarction (AMI).

METHODS AND RESULTS

We enrolled 63 AMI patients (mean age, 67±12 years) underwent ambulatory BP monitoring (ABPM) and cardiac iodine-(123)metaiodobenzylguanidine (MIBG) imaging within 4 weeks after AMI onset. We analyzed the circadian BP pattern and heart-to-mediastinum (H/M) MIBG uptake ratio. All the patients were followed for 2 years. The study endpoint was a composite of major adverse cardiovascular events, including all-cause death, MI, coronary revascularization except for the MI culprit lesion, and stroke. Patients with a non-dipper pattern (n=29) or an H/M ratio <1.96 (n=28) had a worse prognosis than those with either a dipper pattern (n=34) or an H/M ratio ≥1.96 (n=35; log-rank, P=0.013 and 0.010, respectively). Patients with both a non-dipper pattern and an H/M ratio <1.96 (n=12) had a significantly worse prognosis than did the other patients (P=0.0020).

CONCLUSIONS

Dysregulation of BP variation and cardiac MIBG uptake were associated with cardiovascular events following AMI. Examining ABPM with MIBG imaging may potentially improve risk stratification in these patients.

Alterations of left ventricular deformation and cardiac sympathetic derangement in patients with systolic heart failure: a 3D speckle tracking echocardiography and cardiac ¹²³I-MIBG study

PURPOSE

Myocardial contractile function is under the control of cardiac sympathetic activity. Three-dimensional speckle tracking echocardiography (3D-STE) and cardiac imaging with (123)I-metaiodobenzylguanidine ((123)I-MIBG) are two sophisticated techniques for the assessment of left ventricular (LV) deformation and sympathetic innervation, respectively, which offer important prognostic information in patients with heart failure (HF). The purpose of this investigation was to explore, in patients with systolic HF, the relationship between LV deformation assessed by 3D-STE and cardiac sympathetic derangement evaluated by (123)I-MIBG imaging.

METHODS

We prospectively studied 75 patients with systolic HF. All patients underwent a 3D-STE study (longitudinal, circumferential, area and radial) and (123)I-MIBG planar and SPECT cardiac imaging.

RESULTS

3D-STE longitudinal, circumferential and area strain values were correlated with (123)I-MIBG late heart to mediastinum (H/M) ratio and late SPECT total defect score. After stratification of the patients according to ischaemic or nonischaemic HF aetiology, we observed a good correlation of all 3D-STE measurements with late H/M ratio and SPECT data in the ischaemic group, but in patients with HF of nonischaemic aetiology, no correlation was found between LV deformation and cardiac sympathetic activity. At the regional level, the strongest correlation between LV deformation and adrenergic innervation was found for the left anterior descending coronary artery distribution territory for all four 3D-STE values. In multivariate linear regression analyses, including age, gender, LV ejection fraction, NYHA class, body mass index, heart rate and HF aetiology, only 3D-STE area and radial strain values significantly predicted cardiac sympathetic derangement on (123)I-MIBG late SPECT.

CONCLUSION

This study indicated that 3D-STE measurements are correlated with (123)I-MIBG planar and SPECT data. Furthermore, 3D-STE area and radial strain values, but not LVEF, predict cardiac sympathetic derangement in human postischaemic HF.

The effect of bone marrow mononuclear stem cell therapy on left ventricular function and myocardial perfusion

BACKGROUND

Bone marrow stem cell (BMC) transfer is an emerging therapy with potential to salvage cardiomyocytes during acute myocardial infarction and promote regeneration and endogenous repair of damaged myocardium in patients with left ventricular (LV) dysfunction. We performed a meta-analysis to examine the association between administration of BMC and LV functional recovery as assessed by imaging.

METHODS AND RESULTS

Our meta-analysis included data from 32 trials comprising information on 1,300 patients in the treatment arm and 1,006 patients in the control arm. Overall, BMC therapy was associated with a significant increase in LV ejection fraction by 4.6% ± 0.7% (P < .001) (control-adjusted increase of 2.8% ± 0.9%, P = .001), and a significant decrease in perfusion defect size by 9.5% ± 1.4% (P < .001) (control-adjusted decrease of 3.8% ± 1.2%, P = .002). The effect of BMC therapy was similar whether the cells were administered via intra-coronary or intra-myocardial routes and was not influenced by baseline ejection fraction or perfusion defect size.

CONCLUSIONS

BMC transfer appears to have a positive impact on LV recovery in patients with acute coronary syndrome and those with stable coronary disease with or without heart failure. Most studies were small and a minority used a core laboratory for image analysis.

Role of nuclear cardiology for guiding device therapy in patients with heart failure

Heart failure is a dynamic condition with high morbidity and mortality and its prognosis should be reassessed frequently, particularly in patients for whom critical treatment decisions may depend on the results of prognostication. In patients with heart failure, nuclear cardiology techniques are useful to establish the etiology and the severity of the disease, while fewer studies have explored the potential capability of nuclear cardiology to guide cardiac resynchronization therapy (CRT) and to select patients for implantable cardioverter defibrillators (ICD). Left ventricular synchrony may be assessed by radionuclide angiography or gated single-photon emission computed tomography myocardial perfusion scintigraphy. These modalities have shown promise as predictors of CRT outcome using phase analysis. Combined assessment of myocardial viability and left ventricular dyssynchrony is feasible using positron emission tomography and could improve conventional response prediction criteria for CRT. Preliminary data also exists on integrated positron emission tomography/computed tomography approach for assessing myocardial viability, identifying the location of biventricular pacemaker leads, and obtaining left ventricular functional data, including contractile phase analysis. Finally, cardiac imaging with autonomic radiotracers may be useful in predicting CRT response and for identifying patients at risk for sudden cardiac death, therefore potentially offering a way to select patients for both CRT and ICD therapy. Prospective trials where imaging is combined with image-test driven therapy are needed to better define the role of nuclear cardiology for guiding device therapy in patients with heart failure.

Outcome prediction in heart failure with atrial fibrillation: relative role of left ventricular ejection fraction and neurohormonal measures

BACKGROUND

Since atrial fibrillation (AF) impacts the measurement and interpretation of left ventricular ejection fraction (LVEF), we hypothesized that the outcome in heart failure (HF) with AF and LVEF ≤ 35% would be more strongly associated with neurohormonal measures than LVEF.

METHODS AND RESULTS

Cardiac adverse events [CAE; HF progression (HFP), life-threatening arrhythmia (ARR), and cardiac death (CD)] and all-cause mortality (ACM) were recorded prospectively in 954 patients with HF and LVEF ≤ 35%: 852 in sinus rhythm (SR) and 102 in AF. Cox proportional hazard models found that the univariate hazard ratios (HR) for LVEF and the first CAE (primary outcome), HFP, ARR, CD, and ACM were significant in SR (0.933, P < .001, 0.933, P < .001, 0.929, P < .001, 0.916, P < .001, 0.945, P = .001, respectively), but not in AF (1.002, P = .95, 1.060, P = .24, 0.922, P = .15, 0.885, P = .09, 0.932, P = .25). HRs for CAEs and ACM and one or more neurohormonal measures (iodine 123 m-iodobenzylguanidine cardiac parameters, B-type natriuretic peptide, and plasma norepinephrine) were significant in SR and AF. The multivariate models for the first CAE and HFP included neurohormonal measures and LVEF in SR and neurohormonal measures in AF.

CONCLUSIONS

In HF with LVEF ≤ 35% with AF, neurohormonal measures, but not LVEF, were related to outcomes.