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

Heart rate variability: reference values and role for clinical profile and mortality in individuals with heart failure

AIMS

To establish reference values and clinically relevant determinants for measures of heart rate variability (HRV) and to assess their relevance for clinical outcome prediction in individuals with heart failure.

METHODS

Data from the MyoVasc study (NCT04064450; N = 3289), a prospective cohort on chronic heart failure with a highly standardized, 5 h examination, and Holter ECG recording were investigated. HRV markers were selected using a systematic literature screen and a data-driven approach. Reference values were determined from a healthy subsample. Clinical determinants of HRV were investigated via multivariable linear regression analyses, while their relationship with mortality was investigated by multivariable Cox regression analyses.

RESULTS

Holter ECG recordings were available for analysis in 1001 study participants (mean age 64.5 ± 10.5 years; female sex 35.4%). While the most frequently reported HRV markers in literature were from time and frequency domains, the data-driven approach revealed predominantly non-linear HRV measures. Age, sex, dyslipidemia, family history of myocardial infarction or stroke, peripheral artery disease, and heart failure were strongly related to HRV in multivariable models. In a follow-up period of 6.5 years, acceleration capacity [HRperSD 1.53 (95% CI 1.21/1.93), p = 0.0004], deceleration capacity [HRperSD: 0.70 (95% CI 0.55/0.88), p = 0.002], and time lag [HRperSD 1.22 (95% CI 1.03/1.44), p = 0.018] were the strongest predictors of all-cause mortality in individuals with heart failure independently of cardiovascular risk factors, comorbidities, and medication.

CONCLUSION

HRV markers are associated with the cardiovascular clinical profile and are strong and independent predictors of survival in heart failure. This underscores clinical relevance and interventional potential for individuals with heart failure.

CLINICALTRIALS

GOV IDENTIFIER

NCT04064450.

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.

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.

Machine learning-based risk model using 123I-metaiodobenzylguanidine to differentially predict modes of cardiac death in heart failure

BACKGROUND

Cardiac sympathetic dysfunction is closely associated with cardiac mortality in patients with chronic heart failure (CHF). We analyzed the ability of machine learning incorporating 123I-metaiodobenzylguanidine (MIBG) to differentially predict risk of life-threatening arrhythmic events (ArE) and heart failure death (HFD).

METHODS AND RESULTS

A model was created based on patients with documented 2-year outcomes of CHF (n = 526; age, 66 ± 14 years). Classifiers were trained using 13 variables including age, gender, NYHA functional class, left ventricular ejection fraction and planar 123I-MIBG heart-to-mediastinum ratio (HMR). ArE comprised arrhythmic death and appropriate therapy with an implantable cardioverter defibrillator. The probability of ArE and HFD at 2 years was separately calculated based on appropriate classifiers. The probability of HFD significantly increased as HMR decreased when any variables were combined. However, the probability of arrhythmic events was maximal when HMR was intermediate (1.5-2.0 for patients with NYHA class III). Actual rates of ArE were 3% (10/379) and 18% (27/147) in patients at low- (≤ 11%) and high- (> 11%) risk of developing ArE (P < .0001), respectively, whereas those of HFD were 2% (6/328) and 49% (98/198) in patients at low-(≤ 15%) and high-(> 15%) risk of HFD (P < .0001).

CONCLUSION

A risk model based on machine learning using clinical variables and 123I-MIBG differentially predicted ArE and HFD as causes of cardiac death.

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.