11C-meta-hydroxyephedrine defects persist despite functional improvement in hibernating myocardium

Relevance of Chronic Total Occlusion for Outcome of Ventricular Tachycardia Ablation in Ischemic Cardiomyopathy

Background

Catheter ablation of ventricular tachycardia (VT) in patients with ischemic cardiomyopathy (ICM) is an effective tool to prevent VT recurrences. Chronic total occlusion (CTO) represents a clinically relevant entity in ICM patients and is an independent predictor of ventricular arrhythmia and mortality. The effects of CTO on the outcome of VT ablation are not well-studied.

Objective

This analysis aimed to identify the impact of CTO, revascularized, or not revascularized, on the outcome of VT ablation.

Methods and Results

Of 385 consecutive subjects with ICM-VT who underwent catheter VT ablation for monomorphic VT at Heart Center Leipzig between 2008 and 2017, 108 patients without CTO and 191 patients with CTO were included in the analysis. Within a median follow-up time of 557 days (IQR 149, 1095), VT recurred in 77 (40%) patients in the CTO and 40 (37.0%) in the non-CTO cohort (p = 0.62). In a multivariable model, a 10% stepwise change in LVEF as well as ICD on admission was associated with VT recurrence (HR_adj 1.82, 95% CI 1.04–3.18 and HR_adj 1.35, 95% CI 1.23–1.61, respectively). Of the CTO cohort before ablation, 45% had received revascularization, which was independently associated with a higher risk for VT recurrence (HR 2.12, 95% CI 1.35–3.34) as compared to nonrevascularized CTO.

Conclusion

In ICM patients with and without CTO, VT ablation was associated with equal effectiveness with regard to VT recurrence. However, in revascularized CTO patients, the risk of recurrence of VT after ablation was significantly increased.

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.

Cardiac Sympathetic Innervation Imaging with PET Radiotracers

PURPOSE OF REVIEW

The present article reviews the pathophysiology of cardiac sympathetic denervation, the principles of positron emission tomography (PET) imaging of the sympathetic innervation of the heart and its potential clinical role, based on current and expected future evidence.

RECENT FINDINGS

Imaging of cardiac sympathetic denervation can be performed with radiolabeled noradrenaline analogues, e.g., ¹¹C-hydroxyephedrine. A greater burden of sympathetic denervation carries prognostic significance, e.g., in patients with ischemic cardiomyopathy and a left ventricular ejection fraction ≤ 35%, who are more likely to experience sudden cardiac death. Abnormalities of sympathetic cardiac innervation have been demonstrated in hypertrophic, dilated, and arrhythmic right ventricular cardiomyopathies, and may be helpful in better phenotyping patients who will benefit from device therapy, e.g., cardiac resynchronization and implantable cardioverter-defibrillator implantation. The results of future trials, e.g., the Prediction of Arrhythmic Events with Positron Emission Tomography (PAREPET) II study, are awaited to inform on the role of PET cardiac sympathetic imaging in the selection of device therapy. PET cardiac sympathetic innervation imaging allows visualization and quantification of autonomic denervation secondary to various cardiac diseases, and has significant potential to influence clinical decision-making, e.g., the titration of pharmacotherapy and more directed selection of candidates for device implantation.

Recent Advances and Clinical Applications of PET Cardiac Autonomic Nervous System Imaging

PURPOSE OF REVIEW

The purpose of this review was to summarize current advances in positron emission tomography (PET) cardiac autonomic nervous system (ANS) imaging, with a specific focus on clinical applications of novel and established tracers.

RECENT FINDINGS

[11C]-Meta-hydroxyephedrine (HED) has provided useful information in evaluation of normal and pathological cardiovascular function. Recently, [11C]-HED PET imaging was able to predict lethal arrhythmias, sudden cardiac death (SCD), and all-cause mortality in heart failure patients with reduced ejection fraction (HFrEF). In addition, initial [11C]-HED PET imaging studies have shown the potential of this agent in elucidating the relationship between impaired cardiac sympathetic nervous system (SNS) innervation and the severity of diastolic dysfunction in HF patients with preserved ejection fraction (HFpEF) and in predicting the response to cardiac resynchronization therapy (CRT) in HFrEF patients. Longer half-life 18F-labeled presynaptic SNS tracers (e.g., [18F]-LMI1195) have been developed to facilitate clinical imaging, although no PET radiotracers that target the ANS have gained wide clinical use in the cardiovascular system. Although the use of parasympathetic nervous system radiotracers in cardiac imaging is limited, the novel tracer, [11C]-donepezil, has shown potential utility in initial studies. Many ANS radioligands have been synthesized for PET cardiac imaging, but to date, the most clinically relevant PET tracer has been [11C]-HED. Recent studies have shown the utility of [11C]-HED in relevant clinical issues, such as in the elusive clinical syndrome of HFpEF. Conversely, tracers that target cardiac PNS innervation have been used less clinically, but novel tracers show potential utility for future work. The future application of [11C]-HED and newly designed 18F-labeled tracers for targeting the ANS hold promise for the evaluation and management of a wide range of cardiovascular diseases, including the prognostication of patients with HFpEF.

Prediction of all-cause death using (11)C-hydroxyephedrine positron emission tomography in Japanese patients with left ventricular dysfunction

OBJECTIVES

The aim of this study was to determine whether (11)C-hydroxyephedrine ((11)C-HED) can predict adverse events including all-cause death in Japanese patients with left ventricular (LV) dysfunction.

BACKGROUND

Although (11)C-HED PET has been used to assess cardiac sympathetic innervation in various disease conditions, data on their prognostic value are limited.

METHODS

Sixty patients (mean LVEF, 42 ± 14 %) with LV dysfunction (42 ischemic and 18 non-ischemic heart disease) underwent (11)C-HED PET. Myocardial retention was calculated for (11)C-HED PET as a measure of cardiac sympathetic neuronal integrity. Statistical analysis was performed using Cox proportional hazards regression and log-rank test.

RESULTS

Thirteen deaths (7 cardiac and 6 non-cardiac deaths) occurred during a mean follow-up period of 33 ± 23 months. The patients with death were associated with significantly lower (11)C-HED retention (7.1 ± 2.1 vs 9.0 ± 2.4, p = 0.015) than those without death. The hazard ratio for global (11)C-HED retention per unit (/min) was 0.762 (p = 0.039), which remained significant in multivariate analysis. When the patients were divided into the high (≥8.5) and low (<8.5) (11)C-HED retention groups, the low (11)C-HED retention group was associated with significantly poorer survival than the high (11)C-HED retention group (p = 0.004).

CONCLUSION

The low global (11)C-HED retention is a marker of poor overall survival in patients with LV dysfunction in this study.

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.

Sympathetic nerve damage and restoration after ischemia-reperfusion injury as assessed by (11)C-hydroxyephedrine

PURPOSE

An altered state of the cardiac sympathetic nerves is an important prognostic factor in patients with coronary artery disease. The aim of this study was to investigate regional sympathetic nerve damage and restoration utilizing a rat model of myocardial transient ischemia and a catecholamine analog PET tracer, (11)C-hydroxyephedrine ((11)C-HED).

METHODS

Transient myocardial ischemia was induced by coronary occlusion for 20 min and reperfusion in male Wistar rats. Dual-tracer autoradiography was performed subacutely (7 days) and chronically (2 months) after ischemia, and in control rats without ischemia using (11)C-HED as a marker of sympathetic innervation and (201)TI for perfusion. Additional serial in vivo cardiac (11)C-HED and (18)F-FDG PET scans were performed in the subacute and chronic phases after ischemia.

RESULTS

After transient ischemia, the (11)C-HED uptake defect areas in both the subacute and chronic phases were clearly larger than the perfusion defect areas in the midventricular wall. The subacute (11)C-HED uptake defect showed a transmural pattern, whereas uptake recovered in the subepicardial portion in the chronic phase. Tyrosine hydroxylase antibody nerve staining confirmed regional denervation corresponding to areas of decreased (11)C-HED uptake. Serial in vivo PET imaging visualized reductions in the area of the (11)C-HED uptake defects in the chronic phase consistent with autoradiography and histology.

CONCLUSION

Higher susceptibility of sympathetic neurons compared to myocytes was confirmed by a larger (11)C-HED defect with a corresponding histologically identified region of denervation. Furthermore, partial reinnervation was observed in the chronic phase as shown by recovery of subepicardial (11)C-HED uptake.

Quantification of [(11)C]-meta-hydroxyephedrine uptake in human myocardium

Background

The aims of this study were to determine the optimal tracer kinetic model for [¹¹C]-meta-hydroxyephedrine ([¹¹C]HED) and to evaluate the performance of several simplified methods.

Methods

Thirty patients underwent dynamic 60-min [¹¹C]HED scans with online arterial blood sampling. Single-tissue and both reversible and irreversible two-tissue models were fitted to the data using the metabolite-corrected arterial input function. For each model, reliable fits were defined as those yielding outcome parameters with a coefficient of variation (CoV) <25%. The optimal model was determined using Akaike and Schwarz criteria and the F-test, together with the number of reliable fits. Simulations were performed to study accuracy and precision of each model. Finally, quantitative results obtained using a population-averaged metabolite correction were evaluated, and simplified retention index (RI) and standardized uptake value (SUV) results were compared with quantitative volume of distribution (V_T) data.

Results

The reversible two-tissue model was preferred in 75.8% of all segments, based on the Akaike information criterion. However, V_T derived using the single-tissue model correlated highly with that of the two-tissue model (r² = 0.94, intraclass correlation coefficient (ICC) = 0.96) and showed higher precision (CoV of 24.6% and 89.2% for single- and two-tissue models, respectively, at 20% noise). In addition, the single-tissue model yielded reliable fits in 94.6% of all segments as compared with 77.1% for the reversible two-tissue model. A population-averaged metabolite correction could not be used in approximately 20% of the patients because of large biases in V_T. RI and SUV can provide misleading results because of non-linear relationships with V_T.

Conclusions

Although the reversible two-tissue model provided the best fits, the single-tissue model was more robust and results obtained were similar. Therefore, the single-tissue model was preferred. RI showed a non-linear correlation with V_T, and therefore, care has to be taken when using RI as a quantitative measure.

Electronic supplementary material

The online version of this article (doi:10.1186/s13550-014-0052-4) contains supplementary material, which is available to authorized users.

Assessment of cardiac autonomic neuronal function using PET imaging

The autonomic nervous system is the primary extrinsic control of cardiac performance, and altered autonomic activity has been recognized as an important factor in the progression of various cardiac pathologies. Molecular imaging techniques have been developed for global and regional interrogation of pre- and postsynaptic targets of the cardiac autonomic nervous system. Building on established work with the guanethidine analogue ¹²³I-metaiodobenzylguanidine (MIBG) for single-photon emission tomography (SPECT), development of radiotracers and protocols for positron emission tomography (PET) investigation of autonomic signaling has expanded. PET is limited in availability and requires specialized centers for radiosynthesis and interpretation, but the higher resolution allows for improved regional analysis and kinetic modeling provides more true quantification than is possible with SPECT. A wider array of radiolabeled catecholamines, analogues of catecholamines, and receptor ligands have been characterized and evaluated. Sympathetic neuronal PET tracers have shown promise in the identification of several cardiac pathologies. In particular, recent studies have elucidated a mechanistic role for heterogeneous sympathetic innervation in the development of lethal ventricular arrhythmias. Evaluation of cardiomyocyte adrenergic receptor expression and the parasympathetic nervous system has been slower to develop, with clinical studies beginning to emerge. This review summarizes the clinical and the experimental PET tracers currently available for autonomic imaging and discusses their application in health and cardiovascular disease, with particular emphasis on the major findings of the last decade.

ECG marker of adverse electrical remodeling post-myocardial infarction predicts outcomes in MADIT II study

BACKGROUND

Post-myocardial infarction (MI) structural remodeling is characterized by left ventricular dilatation, fibrosis, and hypertrophy of the non-infarcted myocardium.

OBJECTIVE

The goal of our study was to quantify post-MI electrical remodeling by measuring the sum absolute QRST integral (SAI QRST). We hypothesized that adverse electrical remodeling predicts outcomes in MADIT II study participants.

METHODS

Baseline orthogonal ECGs of 750 MADIT II study participants (448 [59.7%] ICD arm) were analyzed. SAI QRST was measured as the arithmetic sum of absolute QRST integrals over all three orthogonal ECG leads. The primary endpoint was defined as sudden cardiac death (SCD) or sustained ventricular tachycardia (VT)/ventricular fibrillation (VF) with appropriate ICD therapies. All-cause mortality served as a secondary endpoint.

RESULTS

Adverse electrical remodeling in post-MI patients was characterized by wide QRS, increased magnitudes of spatial QRS and T vectors, J-point deviation, and QTc prolongation. In multivariable Cox regression analysis after adjustment for age, QRS duration, atrial fibrillation, New York Heart Association heart failure class and blood urea nitrogen, SAI QRST predicted SCD/VT/VF (HR 1.33 per 100 mV*ms (95%CI 1.11-1.59); P = 0.002), and all-cause death (HR 1.27 per 100 mV*ms (95%CI 1.03-1.55), P = 0.022) in both arms. No interaction with therapy arm and bundle branch block (BBB) status was found.

CONCLUSIONS

In MADIT II patients, increased SAI QRST is associated with increased risk of sustained VT/VF with appropriate ICD therapies and all-cause death in both ICD and in conventional medical therapy arms, and in patients with and without BBB. Further studies of SAI QRST are warranted.

Hibernating myocardium results in partial sympathetic denervation and nerve sprouting

Hibernating myocardium due to chronic repetitive ischemia is associated with regional sympathetic nerve dysfunction and spontaneous arrhythmic death in the absence of infarction. Although inhomogeneity in regional sympathetic innervation is an acknowledged substrate for sudden death, the mechanism(s) responsible for these abnormalities in viable, dysfunctional myocardium (i.e., neural stunning vs. sympathetic denervation) and their association with nerve sprouting are unknown. Accordingly, markers of sympathetic nerve function and nerve sprouting were assessed in subendocardial tissue collected from chronically instrumented pigs with hibernating myocardium (n = 18) as well as sham-instrumented controls (n = 7). Hibernating myocardium exhibited evidence of partial sympathetic denervation compared with the normally perfused region and sham controls, with corresponding regional reductions in tyrosine hydroxylase protein (-32%, P < 0.001), norepinephrine uptake transport protein (-25%, P = 0.01), and tissue norepinephrine content (-45%, P < 0.001). Partial denervation induced nerve sprouting with regional increases in nerve growth factor precursor protein (31%, P = 0.01) and growth associated protein-43 (38%, P < 0.05). All of the changes in sympathetic nerve markers were similar in animals that developed sudden death (n = 9) compared with electively terminated pigs with hibernating myocardium (n = 9). In conclusion, sympathetic nerve dysfunction in hibernating myocardium is most consistent with partial sympathetic denervation and is associated with regional nerve sprouting. The extent of sympathetic remodeling is similar in animals that develop sudden death compared with survivors; this suggests that sympathetic remodeling in hibernating myocardium is not an independent trigger for sudden death. Nevertheless, sympathetic remodeling likely contributes to electrical instability in combination with other factors.