Cardiac Sympathetic Imaging With mIBG in Heart Failure

Cardiac Uptake of the Adrenergic Imaging Agent meta-Iodobenzylguanidine (mIBG) Is Mediated by Organic Cation Transporter 3 (Oct3)

Heart failure (HF) is a chronic disease affecting 1%-2% of the global population.123I-labeled meta-iodobenzylguanidine (mIBG) is US Food and Drug Administration-approved for cardiac imaging and prognosis risk assessment in patients with HF. As a norepinephrine analog, mIBG is believed to be transported into adrenergic nerve terminals by the neuronal norepinephrine transporter (NET) and hence image sympathetic innervation of the myocardium. We previously showed that mIBG is an excellent substrate of organic cation transporter 3 (OCT3), an extraneuronal transporter expressed in cardiomyocytes. Here, we evaluated the in vivo impact of Oct3 on mIBG disposition and tissue distribution using Oct3 knockout mice. Oct3 +/+ and Oct3 -/- mice were administered with mIBG intravenously, and mIBG plasma pharmacokinetics and tissue exposures were determined. In Oct3 +/+ mice, mIBG exhibited extensive accumulation in multiple tissues (heart, salivary gland, liver, and adrenal gland). No difference was observed in overall plasma exposure between Oct3 +/+ and Oct3 -/- mice. Strikingly, cardiac mIBG was depleted in Oct3 -/- mice, resulting in 83% reduction in overall cardiac exposure (AUC0-24 h: 12.7 vs. 2.1 μg × h/g). mIBG tissue exposure (AUC0-24 h) was also reduced by 66%, 36%, and 31% in skeletal muscle, salivary gland, and lung, respectively, in Oct3 -/- mice. Our data demonstrated that Oct3 is the primary transporter responsible for cardiac mIBG uptake in vivo and suggested that cardiac mIBG imaging mainly measures OCT3 activity in cardiomyocytes but not NET-mediated uptake in adrenergic nerve endings. Our findings challenge the current paradigm in interpreting cardiac mIBG imaging results and suggest OCT3 as a potential genetic risk marker for HF prognosis. SIGNIFICANCE STATEMENT: 123I-labeled meta-iodobenzylguanidine is used for cardiac imaging and risk assessment in heart failure patients. Contrary to the current belief that meta-iodobenzylguanidine (mIBG) tracks cardiac sympathetic innervation due to its uptake by the neuronal norepinephrine transporter, the authors demonstrated that cardiac mIBG uptake is mediated by the extraneuronal transporter Oct3. Their findings warrant a re-evaluation of the scientific rationale behind cardiac mIBG scan and further suggest organic cation transporter 3 as a risk factor for disease progression in heart failure patients.

Chagas Cardiomyopathy and Myocardial Sympathetic Denervation

PURPOSE OF REVIEW

More than a century since its discovery, the pathogenesis of Chagas heart disease (CHD) remains incompletely understood. The role of derangements in the autonomic control of the heart in triggering malignant arrhythmia before the appearance of contractile ventricular impairment was reviewed.

RECENT FINDINGS

Although previous investigations had demonstrated the anatomical and functional consequences of parasympathetic dysautonomia upon the heart rate control, only recently, coronary microvascular disturbances and sympathetic denervation at the ventricular level have been reported in patients and experimental models of CHD, exploring with nuclear medicine methods their impact on the progression of myocardial dysfunction and cardiac arrhythmias. More important than parasympathetic impaired sinus node regulation, recent evidence indicates that myocardial sympathetic denervation associated with coronary microvascular derangements is causally related to myocardial injury and arrhythmia in CHD. Additionally, 123I-MIBG imaging is a promising tool for risk stratification of progression of ventricular dysfunction and sudden death.

Systemic Manifestations of COPD and the Impact of Dual Bronchodilation with Tiotropium/Olodaterol on Cardiac Function and Autonomic Integrity

Background: Chronic obstructive pulmonary disease (COPD) has significant systemic manifestations, including cardiovascular morbidity. The main aim of our study was to evaluate the effect of short-term COPD treatment with tiotropium/olodaterol (TIO/OLO) 5/5 μg on cardiac function and autonomic integrity. Methods: Twenty-nine patients with newly diagnosed moderate-to-severe COPD were enrolled. We performed pulmonary function tests, cardiac magnetic resonance, cardiac 123I-metaiodobenzylguanidine (123I-MIBG) imaging and analysis of blood biomarkers on our study subjects. The correlations between the tests' results were evaluated at baseline. The changes in pulmonary and cardiac parameters from baseline through 12 weeks were assessed. Results: Significant associations between pulmonary function tests' results and high-sensitivity C-reactive protein (hs-CRP), as well as interleukin-22 (IL-22), were observed at baseline. Treatment with TIO/OLO significantly improved lung function as measured by spirometry and body plethysmography. Moreover, we found that the cardiac index increased from 2.89 (interquartile range (IQR) 1.09) to 3.21 L/min/m2 (IQR 0.78) (p = 0.013; N = 18) and the late heart-to-mediastinum ratio improved from 1.88 (IQR 0.37) to 2 (IQR 0.41) (p = 0.026; N = 16) after 12 weeks of treatment. Conclusions: Treatment with TIO/OLO improves lung function and positively impacts cardiac function and autonomic integrity, suggesting that dual bronchodilation might have a potential in decreasing the risk for cardiac events in COPD. Hs-CRP and IL-22 might be beneficial in determining the intensity of systemic inflammation in COPD. Further research with a larger cohort is needed to enhance the initial results of this study.

Diagnostic and prognostic contribution of DPD scintigraphy in transthyretin V30M cardiac amyloidosis

BACKGROUND

Early diagnosis and prognostic stratification of cardiac transthyretin amyloidosis are crucial. Although 99mTc 3,3-diphosphono-1,2-propanedicarboxylic acid (DPD) scintigraphy is the preferred method for the non-invasive diagnosis, its accuracy appears to be limited in transthyretin amyloidosis protein (ATTR) V30M mutation. Furthermore, its prognostic value in this mutation is unknown. This study investigated the diagnostic value of DPD scintigraphy to detect ATTR cardiomyopathy in V30M mutation and explored its prognostic value regarding mortality.

METHODS

A total of 288 ATTR V30M mutation carriers (median age: 46 years; 49% males) without myocardial thickening (defined as septal thickness ≥13mm) attributable to other causes and who underwent DPD scintigraphy were enrolled. ATTR cardiomyopathy was defined by septal thickness ≥13mm and at least one of the criteria: late heart-to-mediastinum (H/M) 123I-metaiodobenzylguanidine (MIBG) uptake ratio <1.60; electrical heart disease or biopsy-documented amyloidosis.

RESULTS

ATTR cardiomyopathy was identified in 41 (14.2%) patients and cardiac DPD uptake in 34 (11.8%). During a mean follow-up of 33.6 ± 1.2 months, 16 patients died (5.6%). Mortality was 14 times higher in patients with ATTR cardiomyopathy, 13 times higher in those with DPD uptake and 10 times higher in those with late H/M MIBG <1.60. The combined assessment of septal thickness and cardiac DPD uptake improved risk stratification: patients without septal thickening and without DPD retention had an excellent prognosis while those who presented either or both of them had a significantly worse prognosis, with 5-year mortality rates ranging from 39.9 to 53.3%.

CONCLUSIONS

DPD scintigraphy is useful for prognostic stratification of ATTR V30M mutation carriers. Patients without septal thickening and no DPD uptake present the best prognosis compared to those with any signs of cardiac involvement.

Imaging of cardiac sympathetic dysfunction with 18F-FDOPA PET/CT in patients with heart failure: a pilot study

BACKGROUND

Routine use of cardiac sympathetic imaging in HF has been limited by the lower availability/sensitivity of radiotracers. This study was aimed to assess the feasibility of 18F-FDOPA (commonly available PET-radiotracer) in assessment of cardiac autonomic dysfunction.

METHODS

Twenty-four controls (46.5 ± 11.1 years, 16men) and 24 patients (43.5 ± 11.0 years, 18men) with diagnosed HF (Framingham-Criteria) underwent cardiac-PET/CT. Region(s) Of Interest were drawn over entire left ventricular myocardium (LV), individual walls, and mediastinum (M). Coefficient of Variation (CV) was calculated from individual wall counts.

RESULTS

HF patients had significantly lower myocardial 18F-FDOPA uptake (P < .001, independent t test) than controls [32.4% ± 9.5% global reduction; highest in apex (39.9% ± 7.0%)]. A cut-off of LV/M ≤ 1.68 could differentiate patients from controls with sensitivity and specificity of 100% and 95.8%, respectively. LV/M correlated positively with EF (Pearson coefficient = 0.460, P .031). During follow-up, 3 patients were lost to follow-up, 4 died (survival-20.5 ± 4 months), 2 worsened, and 15 remained stable/showed mild improvement. Patients who worsened/died during follow-up had higher CV than those with stable/improving symptoms [0.16 ± 0.05 vs 0.11 ± 0.05, P value .069 (independent t test); Cox regression P = .084].

CONCLUSION

Myocardial 18F-FDOPA uptake in patients with HF is significantly reduced. Higher reduction is seen in those with lower EF. CV, a maker of regional heterogeneity, is a potential prognostic marker.

123I-MIBG imaging in heart failure: impact of comorbidities on cardiac sympathetic innervation

PURPOSE

Heart failure (HF) is a primary cause of morbidity and mortality worldwide, with significant impact on life quality and extensive healthcare costs. Assessment of myocardial sympathetic innervation function plays a central role in prognosis assessment in HF patients. The aim of this review is to summarize the most recent evidence regarding the clinical applications of iodine-123 metaiodobenzylguanidine (¹²³I-MIBG) imaging in patients with HF and related comorbidities.

METHODS

A comprehensive literature search was conducted on PubMed and Web of Science databases. Articles describing the impact of ¹²³I-MIBG imaging on HF and related comorbidities were considered eligible for the review.

RESULTS

We collected several data reporting that ¹²³I-MIBG imaging is a safe and non-invasive tool to evaluate dysfunction of cardiac sympathetic neuronal function and to assess risk stratification in HF patients. HF is frequently associated with comorbidities that may affect cardiac adrenergic innervation. Furthermore, HF is frequently associated with comorbidities and chronic conditions, such as diabetes, obesity, kidney disease and others, that may affect cardiac adrenergic innervation.

CONCLUSION

Comorbidities and chronic conditions lead to more severe impairment of sympathetic nervous system in patients with HF, with a negative impact on disease progression and outcome. Cardiac imaging with ¹²³I-MIBG can be a useful tool to reduce morbidity and prevent adverse events in HF patients.

Simultaneous assessment of myocardial perfusion and adrenergic innervation in patients with heart failure by low-dose dual-isotope CZT SPECT imaging

BACKGROUND

In patients with heart failure (HF) sequential imaging studies have demonstrated a relationship between myocardial perfusion and adrenergic innervation. We evaluated the feasibility of a simultaneous low-dose dual-isotope 123I/99mTc-acquisition protocol using a cadmium-zinc-telluride (CZT) single-photon emission computed tomography (SPECT) camera.

METHODS AND RESULTS

Thirty-six patients with HF underwent simultaneous low-dose 123I-metaiodobenzylguanidine (MIBG)/99mTc-sestamibi gated CZT-SPECT cardiac imaging. Perfusion and innervation total defect sizes and perfusion/innervation mismatch size (defined by 123I-MIBG defect size minus 99mTc-sestamibi defect size) were expressed as percentages of the total left ventricular (LV) surface area. LV ejection fraction (EF) significantly correlated with perfusion defect size (P < .005), innervation defect size (P < .005), and early (P < .05) and late (P < .01) 123I-MIBG heart-to-mediastinum (H/M) ratio. In addition, late H/M ratio was independently associated with reduced LVEF (P < .05). Although there was a significant relationship (P < .001) between perfusion and innervation defect size, innervation defect size was larger than perfusion defect size (P < .001). At multivariable linear regression analysis, 123I-MIBG washout rate (WR) correlated with perfusion/innervation mismatch (P < .05).

CONCLUSIONS

In patients with HF, a simultaneous low-dose dual-isotope 123I/99mTc-acquisition protocol is feasible and could have important clinical implications.

F-18 meta-fluorobenzylguanidine PET imaging of myocardial sympathetic innervation

BACKGROUND

I-123 meta-iodobenzylguanidine (MIBG) imaging has long been employed to noninvasively assess the integrity of human norepinephrine transporter-1 and, hence, myocardial sympathetic innervation. Positron-emitting F-18 meta-fluorobenzylguanidine (MFBG) has recently been developed for potentially superior quantitative characterization. We assessed the feasibility of MFBG imaging of myocardial sympathetic innervation.

METHODS

16 patients were imaged with MFBG PET (30-minute dynamic imaging of chest, followed by 3 whole-body acquisitions between 30 minutes and 4-hour post-injection). Blood kinetics were assessed from multiple samples. Pharmacokinetic modeling with reversible 1- and 2-compartment models was performed. Kinetic rate constants were re-calculated from truncated datasets. All patients underwent concurrent MIBG SPECT.

RESULTS

MFBG myocardial uptake was rapid and sustained; the mean standardized uptake value (SUV (mean ± standard deviation)) was 5.1 ± 2.2 and 3.4 ± 1.9 at 1 hour and 3-4-hour post-injection, respectively. The mean K1 and distribution volume (VT) were 1.1 ± 0.6 mL/min/g and 34 ± 22 mL/cm3, respectively. Both were reproducible when re-calculated from truncated 1-hour datasets (Intraclass Correlation Coefficient of 0.99 and 0.91, respectively). Spearman's ϱ = 0.86 between MFBG SUV and VT and 0.80 between MFBG PET-derived VT and MIBG SPECT-derived heart-to-mediastinum activity concentration ratio.

CONCLUSION

MFBG is a promising PET radiotracer for the assessment of myocardial sympathetic innervation.

Serial changes in cardiac sympathetic nervous function after transcatheter aortic valve replacement: A prospective observational study using 123I-meta-iodobenzylguanidine imaging

BACKGROUND

Transcatheter aortic valve replacement (TAVR) can rapidly improve cardiac sympathetic nervous function (CSNF) within 2 weeks in patients with aortic stenosis (AS). However, whether such short-term improvements will be sustained thereafter remains unclear.

METHODS

Patients with severe AS who underwent TAVR between October 2017 and June 2019 were enrolled in this single-center, prospective, observational study. 123I-meta-iodobenzylguanidine imaging was performed at baseline, within 2 weeks after TAVR, and at 6 to 12 months post-TAVR to evaluate the heart-mediastinum ratio (H/M) and washout rate.

RESULTS

Of 183 consecutive patients, 75 (19 men; median age: 86 years) were evaluated. The late H/M significantly improved within 2 weeks after TAVR (P = .041) and further improved over 6 to 12 months after TAVR (P = .041). Multivariate analysis revealed that the baseline mean aortic valve pressure gradient (mPG) was an independent predictor of mid-term improvement in the late H/M (> 0.1) (P = .037). Patients with a high baseline mPG (≥ 58 mmHg) exhibited a significantly greater increase in the late H/M than those with a low baseline mPG (< 42 mmHg) (0.24 vs 0.01; P = .029).

CONCLUSION

CSNF demonstrated sustained improvement from within 2 weeks after TAVR until 6 to 12 months later. Such improvement was related to baseline hemodynamic AS severity.

The prognostic value of 123I-mIBG SPECT cardiac imaging in heart failure patients: a systematic review

This systematic review aimed to evaluate the prognostic value of Iodine123 Metaiodobenzylguanidine (123I-mIBG) SPECT myocardial imaging in patients with heart failure (HF) and to assess whether semi-quantitative SPECT scores can be useful for accurate risk stratification concerning arrhythmic event (AE) and sudden cardiac death (SCD) in this cohort. A systematic literature search of studies published until November 2020 regarding the application of 123I-mIBG SPECT in HF patients was performed, in Pubmed, Scopus, Medline, Central (Cochrane Library) and Web Of Science databases, including the words "MIBG", "metaiodobenzylguanidine", "heart", "spect", and "tomographic". The included studies had to correlate 123I-mIBG SPECT scores with endpoints such as overall survival and prevention of AE and SCD in HF patients. According to the sixteen studies included, the analysis showed that 123I-mIBG SPECT scores, such as summed defect score (SDS), regional wash-out (rWO), and regional myocardial tracer uptake, could have a reliable prognostic value in patients with HF. An increased SDS or rWO, as well as a reduced 123I-mIBG myocardial uptake, have proven to be effective in predicting AE- and SCD-specific risk in HF patients. Despite achieved results being promising, a more reproducible standardized method for semi-quantitative analysis and further studies with larger cohort are needed for 123I-mIBG SPECT myocardial imaging to be as reliable and, thus, accepted as the conventional 123I-mIBG planar myocardial imaging.

Reclassification of Heart Failure with Preserved Ejection Fraction Following Cardiac Sympathetic Nervous System Activation: A New Cutoff Value of 58

Heart failure (HF) with preserved left ventricular ejection fraction (LVEF) is a heterogeneous syndrome. An LVEF of 50% is widely used to categorize patients with HF; however, this is controversial. Previously, we have reported that patients with an LVEF of ≥ 58% have good prognoses. Further, cardiac sympathetic nervous system (SNS) activation is a feature of HF. In this retrospective, observational study, the cardiac SNS activity of HF patients (n = 63, age: 78.4 ± 9.6 years; male 49.2%) with LVEF ≥ 58% (n = 15) and LVEF < 58% (n = 48) were compared using 123I-metaiodobenzylguanidine scintigraphy. During the follow-up period (median, 3.0 years), 18 all-cause deaths occurred. The delayed heart/mediastinum (H/M) ratio was significantly higher in the LVEF ≥ 58% group than in the LVEF < 58% group (2.1 ± 0.3 vs. 1.7 ± 0.4, p = 0.004), and all-cause mortality was significantly lower in patients in the former than those in the latter group (log-rank, p = 0.04). However, when these patients were divided into LVEF ≥ 50% (n = 22) and LVEF < 50% (n = 41) groups, no significant differences were found in the delayed H/M ratio, and the all-cause mortality did not differ between the groups (log-rank, p = 0.09). In conclusion, an LVEF of 58% is suitable for reclassifying patients with HF according to cardiac SNS activity.

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.

PET Tracers for Imaging Cardiac Function in Cardio-oncology

PURPOSE OF REVIEW

Successful treatment of cancer can be hampered by the attendant risk of cardiotoxicity, manifesting as cardiomyopathy, left ventricle systolic dysfunction and, in some cases, heart failure. This risk can be mitigated if the injury to the heart is detected before the onset to irreversible cardiac impairment. The gold standard for cardiac imaging in cardio-oncology is echocardiography. Despite improvements in the application of this modality, it is not typically sensitive to sub-clinical or early-stage dysfunction. We identify in this review some emerging tracers for detecting incipient cardiotoxicity by positron emission tomography (PET).

RECENT FINDINGS

Vectors labeled with positron-emitting radionuclides (e.g., carbon-11, fluorine-18, gallium-68) are now available to study cardiac function, metabolism, and tissue repair in preclinical models. Many of these probes are highly sensitive to early damage, thereby potentially addressing the limitations of current imaging approaches, and show promise in preliminary clinical evaluations. The overlapping pathophysiology between cardiotoxicity and heart failure significantly expands the number of imaging tools available to cardio-oncology. This is highlighted by the emergence of radiolabeled probes targeting fibroblast activation protein (FAP) for sensitive detection of dysregulated healing process that underpins adverse cardiac remodeling. The growth of PET scanner technology also creates an opportunity for a renaissance in metabolic imaging in cardio-oncology research.

Myocardial innervation imaging: MIBG in clinical practice

123I-metaiodobenzylguanidine (MIBG) is a radiolabeled norepinephrine analog that can be used to investigate myocardial sympathetic innervation. 123I MIBG scintigraphy has been investigated with interest in many disease settings. In patients with systolic heart failure (HF), 123I MIBG scintigraphy can capture functional impairment and rarefaction of sympathetic terminals (which manifest as reduced early and late heart-to-mediastinum [H/M] ratio on planar scintigraphy), and increased sympathetic outflow (which can be visualized as high washout rate). These findings have been consistently associated with a worse outcome: most notably, a phase 3 trial found that patients with a late H/M 1.60 have a higher incidence of all-cause and cardiovascular mortality and life-threatening arrhythmias over a follow-up of less than 2 years. Despite these promising findings, 123I MIBG scintigraphy has not yet been recommended by major HF guidelines as a tool for additive risk stratification, and has then never entered the stage of widespread adoption into current clinical practice. 123I MIBG scintigraphy has been evaluated also in patients with myocardial infarction, genetic disorders characterized by an increased susceptibility to ventricular arrhythmias, and several other conditions characterized by impaired sympathetic myocardial innervation. In the present chapter we will summarize the state-of-the-art on cardiac 123I MIBG scintigraphy, the current unresolved issues, and the possible directions of future research.

Factors Influencing Cardiac Sympathetic Nervous Function in Patients With Severe Aortic Stenosis: Assessment by 123I-Metaiodobenzylguanidine Myocardial Scintigraphy

BACKGROUND

Numerous studies have shown that 123I-metaiodobenzylguanidine (MIBG) scintigraphy, an index of cardiac sympathetic nervous (CSN) activity, is useful for predicting prognosis in patients with heart failure. However, the factors influencing the CSN activity of patients with severe aortic stenosis (AS) remain unclear.

METHODS

We enrolled 91 patients with severe AS who underwent 123I-MIBG scintigraphy, coronary computed tomography (CCT), and transthoracic echocardiography. When CCT angiography (CCTA) showed an obstructive epicardial artery, invasive coronary angiography was performed within 1 week of CCTA.

RESULTS

There were 21 male and 70 female patients with a mean age of 84±5 years. Eighty-five (85) patients (93%) had hypertension and 13 patients (14%) had diabetes. Two (2) patients (2%) had previous myocardial infarction and eight (9%) had a previous coronary intervention. All patients had severe AS: aortic valve area was 0.63±0.18 cm² and the mean pressure gradient was 56±19 mmHg. Regarding 123I-MIBG parameters, early heart-to-mediastinum (H/M) ratio was 3.1±0.5, delayed H/M ratio was 2.8±0.6, and the washout rate (WR) was 35%±13%. Multivariable linear regression analysis showed that coronary artery disease (β=-0.30, p=0.002) was an independent predictor of delayed H/M ratio, and that aortic valve area (β=-0.20, p=0.048) was an independent predictor of WR.

CONCLUSIONS

Our findings suggest that coronary artery disease is an independent predictor of delayed H/M ratio, and aortic valve area is an independent predictor of WR in patients with severe AS.

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).

Endovascular renal sympathetic denervation to improve heart failure with reduced ejection fraction: the IMPROVE-HF-I study

Introduction

The aim of the present study was to assess the safety and efficacy of renal sympathetic denervation (RDN) in patients with heart failure with reduced ejection fraction (HFrEF).

Methods

We randomly assigned 50 patients with a left ventricular ejection fraction (LVEF) ≤ 35% and NYHA class ≥ II, in a 1:1 ratio, to either RDN and optimal medical therapy (OMT) or OMT alone. The primary safety endpoint was the occurrence of a combined endpoint of cardiovascular death, rehospitalisation for heart failure, and acute kidney injury at 6 months. The primary efficacy endpoint was the change in iodine-123 meta-iodobenzylguanidine (¹²³I‑MIBG) heart-to-mediastinum ratio (HMR) at 6 months.

Results

Mean age was 60 ± 9 years, 86% was male and mean LVEF was 33 ± 8%. At 6 months, the primary safety endpoint occurred in 8.3% vs 8.0% in the RDN and OMT groups, respectively (p = 0.97). At 6 months, the mean change in late HMR was −0.02 (95% CI: −0.08 to 0.12) in the RDN group, versus −0.02 (95% CI: −0.09 to 0.12) in the OMT group (p = 0.95) whereas the mean change in washout rate was 2.34 (95% CI: −6.35 to 1.67) in the RDN group versus −2.59 (95% CI: −1.61 to 6.79) in the OMT group (p-value 0.09).

Conclusion

RDN with the Vessix system in patients with HFrEF was safe, but did not result in significant changes in cardiac sympathetic nerve activity at 6 months as measured using ¹²³I‑MIBG.

Supplementary Information

The online version of this article (10.1007/s12471-021-01633-z) contains supplementary material, which is available to authorized users.

Cardiac Sympathetic Activity and Rhythm Control Following Pulmonary Vein Isolation in Patients with Paroxysmal Atrial Fibrillation-A Prospective 123I-mIBG-SPECT/CT Imaging Study

BACKGROUND

Pulmonary vein isolation (PVI) and antiarrhythmic drug therapy are established treatment strategies to preserve sinus rhythm in atrial fibrillation (AF). However, the efficacy of both interventional and pharmaceutical therapy is still limited. Solid evidence suggests an important role of the cardiac sympathetic nervous system in AF. In this blinded, prospective observational study, we studied left ventricular cardiac sympathetic activity in patients treated with PVI and with antiarrhythmic drugs. Prospectively, Iodine-123-benzyl-guanidine single photon emission computer tomography (¹²³I-mIBG-SPECT) was performed in a total of 23 patients with paroxysmal AF, who underwent PVI (n = 20) or received antiarrhythmic drug therapy only (n = 3), respectively. ¹²³I-mIBG planar and SPECT/CT scans were performed before and 4 to 8 weeks after PVI (or initiation of drug therapy, respectively). For semiquantitative SPECT image analysis, attenuation-corrected early/late images were analyzed. Quantitative SPECT analysis was performed using the AHA 17-segment model of the left ventricle.

RESULTS

PVI with point-by-point radiofrequency ablation led to a significantly (p < 0.05) higher visual sympathetic innervation defect score when comparing pre-and post PVI. Newly emerging innervation deficits post PVI were localized predominantly in the inferior lateral wall. These findings were corroborated by semiquantitative SPECT analysis identifying inferolateral segments with a reduced tracer uptake in comparison to SPECT before PVI. Following PVI, patients with an AF relapse showed a different sympathetic innervation pattern compared to patients with sufficient rhythm control.

CONCLUSIONS

PVI results in novel defects of cardiac sympathetic innervation. Differences in cardiac sympathetic innervation remodelling following PVI suggest an important role of the cardiac autonomous nervous system in the maintenance of sinus rhythm following PVI.

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.

Renal sympathetic denervation in patients with vasospastic angina

BACKGROUND

Sympathetic overactivity has been linked to vasospastic angina (VSA), although the exact pathophysiology of VSA is poorly understood. The purpose of this study is to assess if renal sympathetic denervation (RDN) reduces cardiac sympathetic nerve activity with a subsequent beneficial effect on angina relief in patients with refractory VSA.

METHODS AND RESULTS

Cardiac sympathetic nerve activity was assessed prior to procedure and at 6 months post-procedure using iodine-123 labeled meta-iodobenzylguanidine (123I-MIBG) imaging. The Seattle Angina questionnaire (SAQ) was used to assess the degree to which the disease impacts quality of life. No significant change was observed in early HMR (pre-RDN: 2.74 [2.10 to 3.21] vs 6 months post-RDN: 2.57 [2.20 to 3.00]; P = 0.76), and late HMR (pre-RDN: 2.56 [2.18 to 3.20] vs 6 months post-RDN: 2.36 [2.13 to 3.22]; P = 0.22). Additionally, no change was seen in WR (P = 0.22). SAQ results revealed significant improvements in perceived physical limitation, angina frequency, and quality of life at 6 months (P < 0.05 for all).

CONCLUSION

RDN resulted in improvements in angina class and quality of life at 6 months in patients with refractory VSA. RDN, however, did not result in significant changes in cardiac sympathetic nerve activity as measured using 123I-MIBG. The latter observation should be considered with caution given the small sample size of this study. Larger studies are needed to assess this further.

Nuclear cardiology in the context of multimodality imaging to detect cardiac toxicity from cancer therapeutics: Established and emerging methods

The complexity of cancer therapies has vastly expanded in the last decade, along with type and severity of cardiac toxicities associated with these treatments. Prevention of pre-clinical cardiotoxicity may improve cardiovascular outcomes and circumvent the decision to place life-sustaining chemotherapeutic agents on hold, making the early detection of cancer therapeutic related cardiac toxicity with non-invasive imaging essential to the care of these patients. There are several established methods of cardiac imaging in the areas of nuclear cardiology, echocardiography, computed tomography, and cardiac magnetic resonance imaging that are used to assess for cardiovascular toxicity of cancer treatments, with several methods under development. The following review will provide an overview of current and emerging imaging techniques in these areas.

123I-MIBG for detection of subacute doxorubicin-induced cardiotoxicity in patients with malignant lymphoma

BACKGROUND

Doxorubicin is the mainstay of curative lymphoma treatment but is associated with a dose-dependent cardiotoxicity that is often recognized too late to avoid substantial irreversible cardiac injury. Iodine-123 metaiodobenzylguanidine (123I-MIBG) is a gamma-emitting tracer that mimics noradrenaline uptake, storage, and release mechanisms in adrenergic presynaptic neurons. 123I-MIBG scintigraphy can be used for assessment of doxorubicin-induced injury to myocardial adrenergic neurons during treatment and could be the tool for early detection of doxorubicin cardiotoxicity, which is currently lacking.

METHODS AND RESULTS

A total of 37 lymphoma patients scheduled for doxorubicin treatment were included in our study. 123I-MIBG imaging was performed prior to chemotherapy and after a median of 4 cycles of doxorubicin. Early and late heart-to-mediastinum ratios (H/Mearly and H/Mlate) and washout rate (WOR) were used for evaluation of cardiotoxicity. The prognostic value of 123I-MIBG results was assessed using left ventricular ejection fraction (LVEF) as measured by cardiac magnetic resonance at 1-year follow-up. We found a post-therapy increase in WOR (including nine patients with > 10% increase), which was not statistically significant (18.6 vs 23.4%, P = 0.09). The difference appeared to be driven by an increase in H/Mearly. LVEF decreased from baseline to 1-year follow-up (64 vs 58%, P = 0.03). LVEF change was not associated with changes in WOR (P = 0.5).

CONCLUSION

The present study does not provide evidence for 123I-MIBG imaging as a clinically applicable tool for early detection of doxorubicin-induced cardiotoxicity.

Molecular Imaging in Drug Discovery and Development

Noninvasive imaging has played an increasing role in the process of cardiovascular drug development. This review focuses specifically on the use of molecular imaging, which has been increasingly applied to improve and accelerate certain preclinical steps in drug development, including the identification of appropriate therapeutic targets, evaluation of on-target and off-target effects of candidate therapies, assessment of dose response, and the evaluation of drug or biological biodistribution and pharmacodynamics. Unlike the case in cancer medicine, in cardiovascular medicine, molecular imaging has not been used as a primary surrogate clinical end point for drug approval. However, molecular imaging has been applied in early clinical trials, particularly in phase 0 studies, to demonstrate proof-of-concept or to explain variation in treatment effect. Many of these applications where molecular imaging has been used in drug development have involved the retasking of technologies that were originally intended as clinical diagnostics. With greater experience and recognition of the rich information provided by in vivo molecular imaging, it is anticipated that it will increasingly be used to address the enormous time and costs associated with bringing a new drug to clinical launch.

Recent advances in cardiac SPECT instrumentation and imaging methods

Cardiac SPECT continues to play a critical role in detecting and managing cardiovascular disease, in particularly coronary artery disease (CAD) (Jaarsma et al 2012 J. Am. Coll. Cardiol. 59 1719-28), (Agostini et al 2016 Eur. J. Nucl. Med. Mol. Imaging 43 2423-32). While conventional dual-head SPECT scanners using parallel-hole collimators and scintillation crystals with photomultiplier tubes are still the workhorse of cardiac SPECT, they have the limitations of low photon sensitivity (~130 count s^-1 MBq^-1), poor image resolution (~15 mm) (Imbert et al 2012 J. Nucl. Med. 53 1897-903), relatively long acquisition time, inefficient use of the detector, high radiation dose, etc. Recently our field observed an exciting growth of new developments of dedicated cardiac scanners and collimators, as well as novel imaging algorithms for quantitative cardiac SPECT. These developments have opened doors to new applications with potential clinical impact, including ultra-low-dose imaging, absolute quantification of myocardial blood flow (MBF) and coronary flow reserve (CFR), multi-radionuclide imaging, and improved image quality as a result of attenuation, scatter, motion, and partial volume corrections (PVCs). In this article, we review the recent advances in cardiac SPECT instrumentation and imaging methods. This review mainly focuses on the most recent developments published since 2012 and points to the future of cardiac SPECT from an imaging physics perspective.

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.

Risk Stratification of Sudden Cardiac Death in Patients with Heart Failure: An update

Heart failure (HF) is a complex clinical syndrome in which structural/functional myocardial abnormalities result in symptoms and signs of hypoperfusion and/or pulmonary or systemic congestion at rest or during exercise. More than 80% of deaths in patients with HF recognize a cardiovascular cause, with most being either sudden cardiac death (SCD) or death caused by progressive pump failure. Risk stratification of SCD in patients with HF and preserved (HFpEF) or reduced ejection fraction (HFrEF) represents a clinical challenge. This review will give an update of current strategies for SCD risk stratification in both HFrEF and HFpEF.

First assessment of simultaneous dual isotope (123I/99mTc) cardiac SPECT on two different CZT cameras: A phantom study

BACKGROUND

We studied the impact of simultaneous dual-isotope acquisition on 123I/99mTc mismatch assessment using two CZT cameras (DNM 530c, GE Healthcare and DSPECT, Biosensors International).

METHODS

We used an anthropomorphic torso phantom (respectively filled with a solution of 123I alone, 99mTc alone, and a mixture of 123I and 99mTc) and its cardiac insert with two defects mimicking two matched and mismatched defects. Mismatch extent and reconstructed image contrast were evaluated.

RESULTS

The acquisition mode (single vs dual) significantly impacted (i) 99mTc (but not 123I) reconstructed segmental activities using both camera (P < .001), and (ii) image contrast (using 123I and DNM 530c, P < .0001; and using both 123I and 99mTc with DSPECT, P < .0001). However, the defect and mismatch size were not impacted by the type of acquisition. With both DNM 530c and DSPECT, Lin's concordance correlation coefficient and Bland-Altman analysis demonstrated an almost perfect concordance and agreement between single- and simultaneous dual-isotope segmental activity (123I and 99mTc).

CONCLUSIONS

This study found no impact of the acquisition mode (single vs dual) or the type of camera (DSPECT vs DNM 530c) on 123I and 99mTc defect size and mismatch, providing a new step toward simultaneous dual-isotope acquisition for combined innervation and perfusion assessment.

Sympathetic Dysautonomia in Heart Failure by 123I-MIBG: comparison between Chagasic, non-Chagasic and heart transplant patients

Background

Heart failure (HF) is a severe public health problem because of its high morbidity and mortality and elevated costs, thus requiring better understanding of its course. In its complex and multifactorial pathogenesis, sympathetic hyperactivity plays a relevant role. Considering that sympathetic dysfunction is already present in the initial phases of chronic Chagas cardiomyopathy (CCC) and frequently associated with a worse prognosis, we assumed it could be more severe in CCC than in cardiomyopathies of other etiologies (non-CCC).

Objectives

To assess the cardiac sympathetic dysfunction ¹²³I-MIBG) of HF, comparing individuals with CCC to those with non-CCC, using heart transplant (HT) patients as denervated heart parameters.

Methods

We assessed 76 patients with functional class II-VI HF, being 25 CCC (17 men), 25 non-CCC (14 men) and 26 HT (20 men), by use of cardiac ¹²³I-metaiodobenzylguanidine ¹²³I-MIBG) scintigraphy, estimating the early and late heart-to-mediastinum ratio (HMR) of ¹²³I-MIBG uptake and cardiac washout (WO%). The 5% significance level was adopted in the statistical analysis.

Results

The early and late HMR values were 1.73 ± 0.24 and 1.58 ± 0.27, respectively, in CCC, and 1.62 ± 0.21 and 1.44 ± 0.16 in non-CCC (p = NS), being, however, higher in HT patients (p < 0.001). The WO% values were 41.65 ± 21.4 (CCC), 47.37 ± 14.19% (non-CCC) and 43.29 ± 23.02 (HT), p = 0.057. The late HMR values showed a positive weak correlation with left ventricular ejection fraction (LVEF) in CCC and non-CCC (r = 0.42 and p = 0.045; and r = 0.49 and p = 0.015, respectively).

Conclusion

Sympathetic hyperactivity ¹²³I-MIBG) was evidenced in patients with class II-IV HF, LVEF < 45%, independently of the HF etiology, as compared to HT patients.

Relationships between left ventricular sympathetic innervation and diastolic dysfunction: the role of myocardial innervation/perfusion mismatch

BACKGROUND

A possible relationship between cardiac sympathetic denervation and left ventricular (LV) diastolic dysfunction has been suggested. However, an evaluation of the interactions between myocardial adrenergic tone and LV perfusion and diastolic function is lacking.

METHODS AND RESULTS

Seventy-two patients underwent 99mTc-tetrofosmin/123I-metaiodobenzylguanidine (123I-MIBG) cardiac Cadmium-Zinc-Telluride (CZT) imaging. The summed rest score (SRS) and summed 123I-MIBG score (SS-MIBG) were computed as measures of regional perfusion and innervation heterogeneities. LV segments showing an impaired innervation, despite a relatively preserved perfusion (99mTc-tetrofosmin-123I-MIBG tracers' uptake ≥25%), were individuated (innervation/perfusion mismatch). The peak filling rate (PFR) was computed as a measure of LV diastolic function. Nineteen of the 72 (26%) patients presented a normal LV diastolic function, while 29 (40%) and 24 (34%) had a mild and overt diastolic dysfunction. Subjects with diastolic dysfunction showed more abnormal SRS and SS-MIBG values (P < 0.001). In the global population, 502/1224 (41%) LV segments showed an innervation/perfusion mismatch. A modest correlation between the extent of cardiac innervation/perfusion mismatch and PFR values was evident (R = -0.27, P = 0.029). On multivariate analysis, the extent of regional innervation/perfusion mismatch remained an independent predictor of overt LV diastolic abnormalities (P = 0.017).

CONCLUSIONS

The burden of LV regions showing an innervation/perfusion mismatch associates with the occurrence of overt diastolic dysfunction.

Regional Cardiac Sympathetic Nervous System Evaluation Using 123I-mIBG SPECT in Patients with Heart Failure

BACKGROUND

Heart failure (HF) involves both mechanical and autonomic nervous system dysfunction that can lead to sudden cardiac death. In the failing human heart, there is increased release of norepinephrine from neurons and reduced uptake. Iodine-123-labeled metaiodobenzylguanidine (123I-mIBG) demonstrates reduced global uptake and increased washout associated with increased mortality in HF. This research examined the potential benefits of single-photon emission computed tomography (SPECT) regional quantitation in risk stratification of HF patients and its role in prediction of cardiac morbidity and mortality.

METHODS

Twenty-two clinically diagnosed HF patients were recruited into this study. The subjects underwent myocardial perfusion SPECT and cardiac sympathetic imaging with 123I-mIBG. Early (at 15 min after injection) and delayed (four hours after injection) planar and SPECT were performed. Visual and semiquantitative analysis was conducted, and global (from planar imaging) and regional (from SPECT imaging) uptake and washout indices determined. The patients were clinically followed for up to two years, and the cardiac events (CEs) in these patients were recorded and correlated with the various parameters.

RESULTS

The occurrence of a CE in HF was independent of the patients' demographics or the cause of HF. Genetic biomarkers were unable to reliably predict CEs. Global or regional uptake had limited ability to predict a CE, whereas regional washout from the inferior wall (P = .005) was a statistically significant predictor of CEs. Similarly, a high washout of 40% or more from the peri-infarcted and noninfarcted segments on myocardial perfusion scintigraphy was also a significant predictor of CEs (P = .035).

CONCLUSION

HF is a complex, multifactorial, progressive disease that appears to begin regionally. 123I-mIBG provides a valuable tool in imaging the global and regional sympathetic nervous system innervation of the heart. This may allow early identification and stratification of patients at risk of sudden cardiac death.

Feasibility of myocardial PET imaging using a benzylguanidine analog: meta-(3-[18F]fluoropropyl)benzylguanidine ([18F]mFPBG)

INTRODUCTION

Global and regional sympathetic activity in the heart can be evaluated using [¹²³I]meta-iodobenzylguanidine ([¹²³I]mIBG) imaging. However, [¹²³I]mIBG is associated with low image spatial resolution and sensitivity in cardiac imaging. We investigated the capability of an F-18-labeled mIBG derivative, meta-(3-[¹⁸F]fluoropropyl)benzylguanidine ([¹⁸F]mFPBG), for identifying ischemic and viable myocardium in a rat model of myocardial infarction.

MATERIALS AND METHODS

The ex vivo biodistribution and in vivo metabolic stability of [¹⁸F]mFPBG were investigated in Sprague-Dawley rats. Selective cardiac adrenergic activation was confirmed via a blocking experiment involving pretreatment with desipramine (2 mg kg^-1), followed by the administration of [¹⁸F]mFPBG. Imaging properties of [¹⁸F]mFPBG were compared with those of traditional cardiac imaging radiotracers ([¹²³I]mIBG and [^99mTc]MIBI) in a rat model of myocardial infarction. Non-invasive image-based measurements of infarct sizes were then compared with histological findings by using Bland-Altman analysis.

RESULTS

The differences in infarct sizes determined using histological analysis and [¹⁸F]mFPBG PET were -2.55 ± 4.99% (range: -12.33 to 7.22), -2.35 ± 3.32% (range: -8.87 to 4.16), and -3.15 ± 6.16% (range: -15.24 to 8.93) at 5, 20, and 40 min, respectively. Furthermore, [¹⁸F]mFPBG PET was superior to traditional imaging methods in assessing the degree of ischemia in areas of myocardial infarction, as well as the actual infarct size.

CONCLUSION

Compared to [¹²³I]mIBG, [¹⁸F]mFPBG showed improved spatial resolution and sensitivity in a rat model of myocardial infarction. This result suggested that [¹⁸F]mFPBG is a promising cardiac PET imaging agent for potential diagnostic application in PET cardiology.

Catecholamines influence myocardial 123I MIBG uptake in neuroblastoma patients

Aim: Cardiac 123I metaiodobenzylguanidine (MIBG) imaging can be influenced by several factors. We evaluated the relationship between catecholamine measurements and cardiac 123I MIBG uptake in neuroblastoma patients. Patients, methods: 30 neuroblastoma patients were retrospectively assessed on cardiac 123I MIBG uptake and urinary catecholamine dopamine and metabolites, homovanillic acid (HVA) and vanillylmandelic acid (VMA). Cardiac 123I MIBG uptake was quantified by heart-to-mediastinum (H/M) ratios, which were calculated into standard deviation scores (SDS) using age-specific reference values. Results: In 17 (57%) and 12 patients (40%) H/M ratio measurements were below –1.0 and –2.0 SDS at diagnosis. A significant inverse correlation between the average of urine metabolites HVA and VMA, and H/M ratio SDS was observed (r -.39, p = 0.04). Furthermore, there was a significant correlation between the urinary catecholamine metabolite HVA and H/M ratio SDS (r -.40, p = 0.04). Conclusion: Routine calculation of H/M ratios in 123I MIBG scintigrams of neuroblastoma patients is not helpful because it will not identify cardiac ventricular dysfunction in this patient category. A low H/M ratio on 123I MIBG scintigraphy is explained by increased cathecholamine levels secreted by neuroblastoma tumours.

Responses of PKCε to cardiac overloads on myocardial sympathetic innervation and NET expression

Protein kinase C (PKC) is a key mediator of many diverse physiological and pathological responses. PKC activation play an important regulatory role of cardiac function. The present study was performed to investigate whether there were differential activations of the PKCε and how the activation coupled with norepinephrine transporter (NET) surface expression, sympathetic innervation pattern and extracellular matrix remodeling in different cardiac hemodynamic overloads induced by abdominal aortic constriction or aortocaval fistula. At 8weeks after the operations, heart failure were induced, accompanied with myocardial hypertrophy, which was more pronounced in pressure overload (POL) than that of volume overload (VOL) rats, left ventricular dysfunction and increased plasma norepinephrine (NE). In POL rats there was an increase in myocardial collagen deposition, in contrast, the amount decreased in VOL as compared with the sham rats. POL remarkably upregulated PKCε membrane-cytosol ratio and downregulated NET membrane fraction, whereas, in VOL induced opposite changes. Accompanied with the PKCε activation, nerve sprouting, evidenced by myocardial GAP43 protein increased, and different nerve phenotypes were found, in POL tyrosine hydroxylase (TH) positive nerve density increased with NET and choline acetyltransferase (ChAT) immunoreactivity density decreased, in contrast, in VOL NET and ChAT increased, TH did not change. The overloads did not induce alteration of NET mRNA expression, but resulted in different myocardial β₁-AR mRNA expression, in POL β₁-AR mRNAwas significantly downregulated, while in VOL rats unaltered. Conclusion, the present results suggested that the different cardiac hemodynamic overload could differentially activate a common signaling, PKCε intermediate and thereby generate biological diversity.