Calibrated scintigraphic imaging procedures improve quantitative assessment of the cardiac sympathetic nerve activity

Cardiac Sympathetic Nerve Function in Patients with Severe Aortic Stenosis Prior and After Transcatheter Aortic Valve Implantation: Evaluation by 5-Year Risk Model

Background: While the non-invasive assessment of cardiac sympathetic nerve dysfunction is readily accessible, its applicability in invasive intervention for structural heart disease has received limited investigation. Our study aimed to clarify the cardiac sympathetic nerve function in patients with severe Aortic stenosis (AS) and its postoperative changes after transcatheter aortic valve implantation (TAVI) using 123I-metaiodobenzylguanidine scintigraphy (MIBG) in combination with 5-year mortality prediction model. Methods: Consecutive 26 patients (83±5ys, male 4) with severe AS who underwent MIBG prior TAVI procedures were retrospectively enrolled. Of those, 15 patients underwent postoperative-follow up MIBG. The early and delayed heart-to-mediastinum ratio (e- and d-H/M), and washout rate (WR) were obtained from MIBG planner imaging. The MIBG 5-year mortality prediction model was employed to compare pre and after TAVI. Cardiac function and wall thickness were evaluated with transthoracic echocardiography. Results: Preoperative e-H/M, d-H/M, and WR were 2.4±0.5, 2.3±0.4, and 29±14% respectively, and WR showed significant correlation to left ventricular ejection fraction (LVEF) and brain natriuretic peptide (BNP) (r=-0.4 and 0.6; p=0.03, and 0.001 for LVEF and BNP, respectively). 102±28 days after TAVI, either H/M or WR did not show significant improvement among enrolled patients (2.5±0.3, 2.3±0.4, and 30±11% for e-, d-H/M, and WR for after TAVI), while the BNP level was significantly reduced (128±691 and 94±194 pg/dl, for pre vs. after, p=0.008). Five patients showed a significant recovery in WR (37.0±13.8 and 28.8±8.5% for pre and post, p=0.04), and left ventricular wall thickness was significantly thinner compared to those who did not recover (15.2±3.2 vs 11.2±2.4, p=0.02; 14.2±2.9 vs 10.8±1.8, p=0.02 for intraventricular septum and posterior wall, respectively). In 5-year prediction risk model, 7 patients showed a significant reduction in mortality risk, and the patients who did not show risk reduction had significantly reduced renal function (eGFR 57.5±18.8 vs. 38.2±11.3 ml/min/1.73m2, p=0.03 for recovered vs. not recovered). Conclusion: After a 3-month follow-up after TAVI, diverse response in cardiac MIBG parameters were observed among patients with severe AS, despite successful valve replacement. Cardiac MIBG serves as a non-invasive tool that can comprehensively evaluate and surrogate the severity of heart failure resulting from a multi-factorial condition.

Sympathetic 123I-metaiodobenzylguanidine index for Lewy body disease: probability-based diagnosis and identifying patients exempt from late imaging

OBJECTIVE

We aimed to establish a practical diagnostic index for Lewy body diseases (LBD), such as Parkinson's disease and dementia, with Lewy bodies in outpatient settings and criteria for exempting patients from late imaging.

METHODS

We acquired early and late 123I-metaiodobenzylguanidine (MIBG) images from 108 consecutive patients with suspected LBD and standardized heart-to-mediastinum (H/M) ratios for collimator conditions. Exclusions included young-onset Parkinson's disease (age < 50 years) and genetic transthyretin-type amyloidosis. We developed logistic models incorporating H/M ratios with or without age (n = 92). The sympathetic MIBG index for LBD (SMILe index), categorized LBD likelihood from 0 (lowest) to 1 (highest). Diagnostic accuracy was assessed as the area under the receiver operating characteristic (ROC) curve (AUC). The characteristics of the new index were compared with H/M ratios. The need for late imaging was explored using the SMILe index.

RESULTS

Early or late SMILe indexes using a single H/M ratio variable discriminated LBD from non-LBD. The AUC values for early and late SMILe indexes were 0.880 and 0.894 (p < 0.0001 for both), identical to those for early and late H/M ratios. The sensitivity and the specificity of early SMILe indexes with a 0.5 threshold were 76% and 90%, achieving accuracy of accuracy 86%. Similarly, the late SMILe index demonstrated a sensitivity of 76% and specificity of 87%, with an accuracy of 84%. Early SMILe indexes < 0.3 or > 0.7 (representing 84% patients) indicated a diagnosis without a late MIBG study.

CONCLUSION

The 123I-MIBG-derived SMILe indexes provide likelihood of LBD, and those with a 50% threshold demonstrated optimal diagnostic accuracy for LBD. The index values of either < 0.3 or > 0.7 accurately selected patients who do not need late imaging.

Sacubitril/Valsartan in the Treatment of Heart Failure With Reduced Ejection Fraction Focusing on the Impact on the Quality of Life: A Systematic Review and Meta-Analysis of Randomized Clinical Trials

There exists a paucity of research data reported by analyses performed on randomized clinical trials (RCTs) that encompass quality of life (QOL) and the aftermath for patients suffering from heart failure with reduced ejection fraction (HFrEF). This systematic review and meta-analysis of randomized clinical trials (RCTs) have been done to evaluate the drug sacubitril/valsartan in the treatment of heart failure (HF) with reduced ejection fraction (HFrEF) with a clear focus on the effect it bestows on measures of physical exercise tolerance and quality of life. A thorough systematic search was done in databases including Cochrane Central Register of Controlled Trials (CENTRAL), ClinicalTrials.gov, Embase, and PubMed from 1 January 2010 to 1 January 2023. The search only included published RCTs on adult patients aged 18 and above, with heart failure with reduced ejection fraction (HFrEF). Data analysis was performed by using the software RevMan 5.4 (Cochrane Collaboration, London, United Kingdom). The included studies' bias risk was assessed using the Cochrane Collaboration's Risk of Bias tool. The quality of evidence for the primary outcome was done using the Grading of Recommendations, Assessment, Development, and Evaluations (GRADE) framework. This systematic review and meta-analysis of RCTs yielded 458 studies, of which eight randomized clinical trials were included and analyzed. The meta-analysis of the included trials shows that the I2 value is 61% (i.e., I2 > 50%), demonstrating a substantial heterogeneity within the studies. The left ventricular ejection fraction (LVEF) expressed in percentage was reported in the five studies, and thereby, a subgroup analysis that yielded a confidence interval (CI) of 95% had the standard mean difference of 0.02 (-0.02, 0.07). The trials had disparity between the reporting of effect on peak oxygen consumption (VO2), measured through cardiopulmonary exercise testing (CPET) methods, six-minute walking test (6MWT), overall physical activity, and exercise capacity. Sacubitril/valsartan did not exponentially improve peak VO2 or 6MWT in these trials; however, the patient-reported data suggested that the quality of life was modestly influenced by the drug. A subgroup analysis was performed using the pooled effect value by the random effects model. The findings showed that the sacubitril/valsartan group significantly was better than the control group in improving HFrEF-associated health-related quality of life (HRQoL). This study is a systematic review and meta-analysis of randomized clinical trials that evaluated the drug sacubitril/valsartan in treating heart failure with reduced ejection fraction (HFrEF) and focused on its tangible effect on the measures of physical exercise tolerance and quality of life. It depicts that the statistical scrutiny due to the lack of significant data and parity across studies did not impart significant improvement of either LVEF, peak VO2, or 6MWT with the use of sacubitril/valsartan; however, the reported exercise tolerance, including daytime physical activity, had a modest impact with the said drug. The pooled values demonstrated that the sacubitril/valsartan group significantly outperformed the control group in improving HFrEF HRQoL.

Comparison of Taiwanese and European Calibration Factors for Heart-to-Mediastinum Ratio in Multicenter 123I-mIBG Phantom Studies

Background: Cross-calibration of 123I-labeled meta-iodobenzylguanidine (mIBG) myocardial-derived indices is essential to extrapolate findings from several clinical centers. Here, we conducted a phantom study to generate conversion coefficients for the calibration of heart-to-mediastinum ratios and compare them between Taiwan and Europe. Methods: We used an acrylic phantom dedicated to 123I-mIBG planar imaging to calculate the conversion coefficients of 136 phantom images derived from 36 Taiwanese institutions. A European phantom image database including 191 images from 27 institutions was used. Conversion coefficients were categorized into five collimator types: low-energy (LE) high-resolution (LEHR), LE general-purpose (LEGP), extended LEGP (ELEGP), medium-energy (ME) GP (MEGP), and ME low-penetration (MELP) collimators. Results: The conversion coefficients were 0.53 ± 0.039, 0.59 ± 0.032, 0.79 ± 0.032, 0.96 ± 0.038, and 0.99 ± 0.050 for LEHR, LEGP, ELEGP, MEGP, and MELP collimators, respectively. The Taiwanese and European conversion coefficients for the LEHR, LEGP, and MELP collimators did not significantly differ. The coefficient of variation was slightly higher for the Taiwanese than the European conversion coefficients (3.7%-7.5% vs. 2.3%-5.6%). Conclusions: We calculated conversion coefficients for various types of collimators used in Taiwan using a 123I-mIBG phantom. In general, the Taiwanese and European conversion coefficients were comparable. These findings further corroborated and highlighted the need for 123I-mIBG standardization using the phantom-determined conversion coefficients.

Machine learning-based prediction of conversion coefficients for I-123 metaiodobenzylguanidine heart-to-mediastinum ratio

PURPOSE

We developed a method of standardizing the heart-to-mediastinal ratio in 123I-labeled meta-iodobenzylguanidine (MIBG) images using a conversion coefficient derived from a dedicated phantom. This study aimed to create a machine-learning (ML) model to estimate conversion coefficients without using a phantom.

METHODS

210 Monte Carlo (MC) simulations of 123I-MIBG images to obtain conversion coefficients using collimators that differed in terms of hole diameter, septal thickness, and length. Simulated conversion coefficients and collimator parameters were prepared as training datasets, then a gradient-boosting ML was trained to estimate conversion coefficients from collimator parameters. Conversion coefficients derived by ML were compared with those that were MC simulated and experimentally derived from 613 phantom images.

RESULTS

Conversion coefficients were superior when estimated by ML compared with the classical multiple linear regression model (root mean square deviations: 0.021 and 0.059, respectively). The experimental, MC simulated, and ML-estimated conversion coefficients agreed, being, respectively, 0.54, 0.55, and 0.55 for the low-; 0.74, 0.70, and 0.72 for the low-middle; and 0.88, 0.88, and 0.88 for the medium-energy collimators.

CONCLUSIONS

The ML model estimated conversion coefficients without the need for phantom experiments. This means that conversion coefficients were comparable when estimated based on collimator parameters and on experiments.

[The clinical value of 123I-metaiodobenzylguanidine myocardial imaging in the diagnosis of dementia with Lewy bodies]

Metaiodobenzylguanidine (MIBG) is an analog of norepinephrine that accumulates in sympathetic nerve endings soon after intravenous administration. The degree of accumulation reflects the uptake, storage and release of transmitters by noradrenergic neurons. Myocardial imaging with 123I labeled MIBG ( 123I-MIBG) can be used to estimate the extent of local myocardial sympathetic nerve damage, which has been widely used in the diagnosis and treatment of various heart diseases. In recent years, numerous studies have been carried out on the application of 123I-MIBG in the diagnosis of degenerative diseases of the nervous system (such as Parkinson's disease and dementia of Lewy body), and have made some achievements. The purpose of this review is to summarize the current clinical application of 123I-MIBG myocardial imaging in the diagnosis of dementia with Lewy bodies, the problems in imaging technology and the possible research directions in the future, so as to provide valuable reference information for clinicians to reasonably and accurately apply this technology in the early diagnosis and discrimination of dementia.

Cardiac sympathetic activity and relationship to cardiac events and left ventricular reverse remodeling in patients with non-ischemic dilated cardiomyopathy

BACKGROUND

Delayed heart-to-mediastinum ratio (HMR) has been associated with catecholamine levels and contractile reserve in dilated cardiomyopathy (DCM); however, there is scant evidence regarding the association between cardiac sympathetic activity and left ventricular reverse remodeling (LV-RR). We calculated the ¹²³I-metaiodobenzylguanidine (¹²³I-mIBG) HMR and washout rate (WR) in patients with DCM and investigated their associations with LV-RR.

METHODS

From April 2003 to January 2020, in 120 patients with DCM who underwent ¹²³I-mIBG scintigraphy. 66 patients undergoing follow-up echo and taking a beta-blocker from baseline were examined the relationship between ¹²³I-mIBG and LV-RR. After that, this prognostic value for composite cardiac events was evaluated in the entire 120 patients.

RESULTS

In LV-RR analysis, patients were 50.4 ± 12.2 years, with a mean left ventricular ejection fraction of 28.6%. Of 66 patients, 28 (42.4%) achieved LV-RR. Multiple logistic regression analysis of LV-RR revealed that not delayed HMR but the WR (cutoff value: 13.5%) was an independent predictor of LV-RR (odds ratio 6.514, p = 0.002). In the analysis for composite cardiac events, even though WR itself does not have the prognostic capacity, Kaplan-Meier survival curves divided by the cutoff value (delayed HMR = 2.0, WR = 13.5) showed that delayed HMR and WR values enabled the stratification of high-risk patients (log-rank p < 0.001).

CONCLUSIONS

The ¹²³I-mIBG WR was associated with the prevalence of LV-RR in patients taking 100% of beta-blockers and 98.5% of renin-angiotensin system inhibitors. Reflecting the contractile reserve, the combined assessment of the delayed HMR and WR could be used to further precisely stratify the patients with DCM.

Influence of brain atrophy using semiquantitative analysis in [123I]FP-CIT single-photon emission computed tomography by a Monte Carlo simulation study

The specific binding ratio (SBR) is an objective indicator of N-ω-fluoropropyl-2β-carbomethoxy-3β-(4-[123I] iodophenyl) nortropane ([¹²³I]FP-CIT) single-photon emission computed tomography (SPECT) that could be used for the diagnosis of Parkinson’s disease and Lewy body dementia. One of the issues of the SBR analysis is that the setting position of the volume of interest (VOI) may contain cerebral ventricles and cerebral grooves. These areas may become prominent during the brain atrophy analysis; however, this phenomenon has not been evaluated enough. This study thus used Monte Carlo simulations to examine the effect of brain atrophy on the SBR analysis. The brain atrophy model (BAM) used to simulate the three stages of brain atrophy was made using a morphological operation. Brain atrophy levels were defined in the descending order from 1 to 3, with Level 3 indicating to the most severe damage. Projection data were created based on BAM, and the SPECT reconstruction was performed. The ratio of the striatal to background region accumulation was set to a rate of 8:1, 6:1, and 4:1. The striatal and the reference VOI mean value were decreased as brain atrophy progressed. Additionally, the Bolt’s analysis methods revealed that the reference VOI value was more affected by brain atrophy than the striatal VOI value. Finally, the calculated SBR value was overestimated as brain atrophy progressed, and a similar trend was observed when the ratios of the striatal to background region accumulation were changed. This study thus suggests that the SBR can be overestimated in cases of advanced brain atrophy.

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

Purpose of Review

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

Recent Findings

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

Summary

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