Overview of the 2023 FDA Circulatory System Devices Advisory Panel meeting on the Recor Paradise Ultrasound-Based Renal Denervation System

Hypertension continues to be a prominent, avoidable factor contributing to major vascular issues on a global scale. Even with lifestyle adjustments and more aggressive medical treatments, maintaining optimal blood pressure levels remains challenging. This challenge has driven the emergence of device-oriented approaches to address hypertension. To assess the safety and efficacy of the Recor Paradise Ultrasound Renal Denervation System, the Circulatory System Devices Panel was convened by the US Food and Drug Administration (FDA). This manuscript provides a condensed overview of the information put forth by the sponsor and the FDA, along with an account of the considerations and conversations that took place during the meeting.

Detection of sympathetic denervation defects in Fabry disease by hybrid [11C]meta-hydroxyephedrine positron emission tomography and cardiac magnetic resonance

BACKGROUND

Myocardial glycosphingolipid accumulation in patients with Fabry disease (FD) causes biochemical and structural changes. This study aimed to investigate sympathetic innervation in FD using hybrid cardiac positron emission tomography (PET)/magnetic resonance imaging (MRI).

METHODS AND RESULTS

Patients with different stages of Fabry disease were prospectively enrolled to undergo routine CMR at 1.5T, followed by 3T hybrid cardiac PET/MRI with [11C]meta-hydroxyephedrine ([11C]mHED). Fourteen patients with either no evidence of cardiac involvement (n = 5), evidence of left ventricular hypertrophy (LVH) (n = 3), or evidence of LVH and fibrosis via late gadolinium enhancement (LGE) (n = 6) were analyzed. Compared to patients without LVH, patients with LVH or LVH and LGE had lower median T1 relaxation times (ms) at 1.5 T (1007 vs. 889 vs. 941 ms, p = 0.003) and 3T (1290 vs. 1172 vs. 1184 p = .014). Myocardial denervation ([11C]mHED retention < 7%·min) was prevalent only in patients with fibrosis, where a total of 16 denervated segments was found in two patients. The respective area of denervation exceeded the area of LGE in both patients (24% vs. 36% and 4% vs. 32%). However, sympathetic innervation defects ([11C]mHED retention ≤ 9%·min) occurred in all study groups. Furthermore, a reduced sympathetic innervation correlated with an increased left ventricular mass (p = .034, rs = - 0.57) and a reduced global longitudinal strain (GLS) (p = 0.023, rs = - 0.6).

CONCLUSION

Hybrid cardiac PET/MR with [11C]mHED revealed sympathetic innervation defects, accompanied by impaired GLS, in early stages of Fabry disease. However, denervation is only present in patients with advanced stages of FD showing fibrosis on CMR.

Pharmacological Ischemic Conditioning with Roxadustat Does Not Affect Pain-Like Behaviors but Mitigates Sudomotor Impairment in a Murine Model of Deep Hind Paw Incision

Purpose

The involvement of hypoxic response mechanisms in local functional impairments in surgical wounds is unclear. In the present study, we characterized tissue hypoxia in surgical wounds and investigated the role of pharmacological ischemic conditioning (PIC) using roxadustat, an oral prolyl hydroxylase domain enzyme inhibitor, in postoperative local functional impairments in a murine model of deep hind paw incision.

Methods

Male BALB/cAJcl mice aged 9-13 weeks were used in all experiments. Plantar skins of mice that underwent surgical incision were subjected to immunohistochemistry to localise tissue hypoxia. Pain-like behaviours and sudomotor function were compared between mice treated with 6-week perioperative PIC and control mice. The effects of PIC were examined in vitro by immunocytochemistry using sympathetically differentiated PC12 cells and in vivo by immunohistochemistry using plantar skins collected on postoperative day 21.

Results

Prominent tissue hypoxia was detected within axons in the nerve bundles underneath surgical wounds. Six-week perioperative PIC using roxadustat failed to ease spontaneous pain-like behaviors; however, it mitigated local sudomotor impairment postoperatively. Upregulation of sympathetic innervation to the eccrine glands was observed in the PIC-treated skins collected on postoperative day 21, in accordance with the in vitro study wherein roxadustat promoted neurite growth of sympathetically differentiated PC12 cells.

Conclusion

This study suggests that tissue hypoxia is involved in the pathogenesis of local sudomotor dysfunction associated with surgical trauma. Targeting the hypoxic response mechanisms with PIC may be of therapeutic potential in postsurgical local sympathetic impairments that can be present in complex regional pain syndrome.

Sympathetic Denervation and Pharmacological Stimulation of Parasympathetic Nervous System Prevent Pulmonary Vascular Bed Remodeling in Rat Model of Chronic Thromboembolic Pulmonary Hypertension

Chronic thromboembolic pulmonary hypertension (CTEPH) develops in 1.5-2.0% of patients experiencing pulmonary embolism (PE) and is characterized by stable pulmonary artery obstruction, heart failure, and poor prognosis. Little is known about involvement of autonomic nervous system (ANS) in the mechanisms of CTEPH. This study was aimed at evaluation of the effect of vagal and sympathetic denervation, as well as stimulation of the parasympathetic nervous system, on the outcomes of CTEPH in rats. CTEPH was induced by multiple intravenous injections of alginate microspheres. Sympathetic and vagal denervation was performed using unilateral surgical ablation of the stellate ganglion and vagotomy, respectively. Stimulation of the parasympathetic nervous system was carried out by administering pyridostigmine. The effect of neuromodulatory effects was assessed in terms of hemodynamics, histology, and gene expression. The results demonstrated the key role of ANS in the development of CTEPH. Sympathetic denervation as well as parasympathetic stimulation resulted in attenuated pulmonary vascular remodeling. These salutary changes were associated with altered MMP2 and TIMP1 expression in the lung and decreased FGFb level in the blood. Unilateral vagotomy had no effect on physiological and morphological outcomes of the study. The data obtained contribute to the identification of new therapeutic targets for CTEPH treatment.

Ventricular Arrhythmia Substrate Distribution and Its Relation to Sympathetic Innervation in Nonischemic Cardiomyopathy Patients

BACKGROUND

Nonischemic cardiomyopathy patients referred for catheter ablation of ventricular arrhythmias (VAs) typically have either inferolateral (ILS) or anteroseptal (ASS) VA substrate locations, with poorer outcomes for ASS. Sympathetic denervation is an important determinant of arrhythmogenicity. Its relation to nonischemic fibrosis in general and to the different VA substrates is unknown.

OBJECTIVES

This study sought to evaluate the association between VA substrates, myocardial fibrosis, and sympathetic denervation.

METHODS

Thirty-five patients from the Leiden Nonischemic Cardiomyopathy Study, who underwent electroanatomic voltage mapping and iodine-123 metaiodobenzylguanidine imaging between 2011 and 2018 were included. Late gadolinium-enhanced cardiac magnetic resonance data were collected when available. The relation between global cardiac sympathetic innervation and area-weighted unipolar voltage (UV) as a surrogate for diffuse fibrosis was evaluated. For regional analysis, patients were categorized as ASS or ILS. The distribution of low UV, sympathetic denervation, and late gadolinium enhancement (LGE) scar were compared using the 17-segment model.

RESULTS

Median area-weighted UV was 12.3 mV in patients with normal sympathetic innervation and 8.7 mV in patients with sympathetic denervation. Global sympathetic denervation correlated with diffuse myocardial fibrosis (R = 0.53; P = 0.02). ILS (n = 13) matched with low UV, sympathetic denervation, and LGE scar in all patients, whereas ASS (n = 11) matched with low UV in all patients, with LGE scar in 63% (P = 0.20), but with sympathetic denervation in only 27% of patients (P = 0.0002).

CONCLUSIONS

Global cardiac sympathetic denervation is related to fibrosis in nonischemic cardiomyopathy patients with VA. The mismatch between regional fibrosis and preserved innervation for ASS may contribute to a VA substrate difficult to control by catheter ablation.

Sympathetic Innervation Modulates Mucosal Immune Homeostasis and Epithelial Host Defense

Intestinal mucosal cells, such as resident macrophages and epithelial cells, express adrenergic receptors and are receptive to norepinephrine, the primary neurotransmitter of the sympathetic nervous system (SNS). It has been suggested that the SNS affects intestinal immune activity in conditions, such as inflammatory bowel disease; however, the underlying mechanisms remain ambiguous. Here, we investigated the effect of SNS on mucosal immune and epithelial cell functions. We employed 6-OHDA-induced sympathetic denervation (cSTX) to characterize muscularis-free mucosal transcriptomes by RNA-seq and qPCR, and quantified mucosal immune cells by flow cytometry. The role of norepinephrine and cytokines on epithelial functions was studied using small intestinal organoids. cSTX increased the presence of activated CD68⁺CD86⁺ macrophages and monocytes in the mucosa. In addition, through transcriptional profiling, the proinflammatory cytokines IL-1β, TNF-α, and IFN-γ were induced, while Arg-1 and CD163 expression was reduced. Further, cSTX increased intestinal permeability in vivo and induced genes involved in barrier integrity and antimicrobial defense. In intestinal organoids, similar alterations were observed after treatment with proinflammatory cytokines, but not norepinephrine. We conclude that a loss in sympathetic input induces a proinflammatory mucosal state, leading to reduced epithelial barrier functioning and enhanced antimicrobial defense. This implies that the SNS might be required to maintain intestinal immune functions during homeostasis.

Can early phase cardiac [123I]mIBG images be used to diagnose Lewy body disease?

PURPOSE

Some studies have suggested that cardiac [123I]metaiodobenzylguanidine images obtained 15-20 min after tracer administration are as accurate for dementia with Lewy bodies (DLB) diagnosis as standard images acquired after a delay of 3-4 h; some suggest delayed imaging is preferable. We compare early and delayed heart-to-mediastinum ratios (HMR) in a well-characterised research dataset and make recommendations for clinical practice.

METHODS

Images were acquired using a Siemens gamma camera with medium energy collimators. Early images were obtained at 20 min and delayed at 4 h (± 30) min. In total 167 pairs of images were reviewed: 30 controls, 39 people with dementia and 98 with mild cognitive impairment. HMR normal cutoff values derived from control data were ≥2.10 for early imaging and ≥1.85 for delayed.

RESULTS

HMR tended to drop between early and delayed for abnormal images, but increase for normal images. Histograms of early and delayed HMR showed a slightly better separation of results into two groups for delayed imaging. Accuracy results were slightly higher for delayed imaging than early imaging (73 vs. 77%), sensitivity 63 vs. 65% and specificity 82 vs. 88%. However, this was not statistically significant - in total only 8/167 (5%) of scans changed designation between early and delayed imaging.

CONCLUSION

We suggest that a delayed image could be acquired only if the early result is borderline. This removes the need for delayed imaging in about 70% of patients. Adopting this protocol in clinical practice would reduce the time most patients have to wait and could free up scanner time.

The Effect of Very Low Concentrations of Ethanol on Microvascular Artery and Vein Anastomosis: An Experimental Study

OBJECTIVES

This study investigated the effect of very low concentrations of ethanol on artery and vein anastomosis. Also, it was aimed to determine the appropriate ethanol concentration to be used in vasospasm.

METHODS

Rats were divided into five groups of eight rats, each group, as follows: Group i: saline; Group ii: 2.5% ethanol; Group iii: 5% ethanol; Group IV: 7.5% ethanol; and Group V: 10% ethanol. During the femoral artery and vein anastomosis, 1ml of the agent was used for irrigation in each group. Vessel diameters were measured before the anastomosis, at the fifth and 15th minutes, and the third week after the anastomosis. Histopathological samples were taken in the third week.

RESULTS

In Groups ii and iii, the mean vessel diameters were found to increase 15th minute. Also observed was an increase in mean vessel diameter that continued in the third week. Although acute vasodilation was detected in Groups IV and V, arterial and venous thrombosis was observed in the third week. Intima and media thickness decreased in Group ii, while it increased in Group iii. Perivascular inflammation and fibrosis increased as the ethanol concentration increased.

CONCLUSION

2.5% ethanol causes acute and prolonged vasodilation and does not cause endothelial cell damage, perivascular inflammation, and fibrosis. 2.5% ethanol will be a powerful alternative use in many situations that occur with vasospasm.

Sympathetic Denervation Alters the Inflammatory Response of Resident Muscularis Macrophages upon Surgical Trauma and Ameliorates Postoperative Ileus in Mice

Interactions between the peripheral nervous system and resident macrophages (MMs) modulate intestinal homeostatic functions. Activation of β2-adrenergic receptors on MMs has been shown to reduce bacterial challenges. These MMs are also crucial for the development of bowel inflammation in postoperative ileus (POI), an iatrogenic, noninfectious inflammation-based motility disorder. However, the role of the sympathetic nervous system (SNS) in the immune modulation of these MMs during POI or other noninfectious diseases is largely unknown. By employing 6-OHDA-induced denervation, we investigated the changes in the muscularis externa by RNA-seq, quantitative PCR, and flow cytometry. Further, we performed transcriptional phenotyping of sorted CX3CR1⁺ MMs and ex vivo LPS/M-CSF stimulation on these MMs. By combining denervation with a mouse POI model, we explored distinct changes on CX3CR1⁺ MMs as well as in the muscularis externa and their functional outcome during POI. Our results identify SNS as an important mediator in noninfectious postoperative inflammation. Upon denervation, MMs anti-inflammatory genes were reduced, and the muscularis externa profile is shaped toward a proinflammatory status. Further, denervation reduced MMs anti-inflammatory genes also in the early phase of POI. Finally, reduced leukocyte infiltration into the muscularis led to a quicker recovery of bowel motility in the late phase of POI.

The evolving role of interventional cardiology in the treatment of pulmonary hypertension

Pulmonary hypertension (PH) is a heterogeneous group of diseases defined by a mean pulmonary arterial pressure greater than 20 mmHg. Clinically, PH is classified into five groups and the group of PH generally defines the cause of PH and the therapeutic options. Currently, medical therapies that target the prostacyclin, endothelin, and nitric oxide pathways are used in pulmonary arterial hypertension and chronic thromboembolic PH (CTEPH) patients. Moreover, surgery can improve outcomes in PH as pulmonary thromboendarterectomy can be curative for CTEPH and lung transplantation is used for end-stage PH. Despite these diverse treatment options, PH patients continue to have high symptom burden and poor long-term outcomes. However, advances in percutaneous technology are opening new avenues for the management of PH. In this review, we discuss the available data supporting the use of four interventional procedures: balloon atrial septostomy, transcatheter Potts shunt, balloon pulmonary angioplasty, and pulmonary artery denervation for the treatment of PH. These procedures provide hemodynamic and functional improvements in PH patients, but they come with their own unique risk profiles. Hopefully, these procedures will continue to be refined and thereby provide a venue for interventional cardiology to safely and effectively improve outcomes for PH moving forward.

Effect of denervation on burn wound healing

The skin is a natural barrier between the interior milieu of the organism and its environment. This barrier has multiple physiological functions and may be affected by an array of pathologies including wounds and burns. The present study aims to determine the effect of the nervous system on wound healing. Specifically, this study tested the effect of denervation by chemical ablation on the burn wound healing process using guanethidine for denervation of the sympathetic postganglionic neurons and resiniferatoxin for denervation of the sensory capsaicin-sensitive fibres. Animals were divided into 8 different groups: (1) control group, (2) sensory denervated and burned, (3) sensory denervated non-burned, (4) sympathetic denervated and burned, (5) sympathetic denervated non-burned, (6) vehicle sensory burned, (7) vehicle sympathetic burned, (8) non-denervated burned. We measured different morphologic and biochemical parameters such as wound surface area, histological alterations and mast cells. In addition, NGF, IL-1β, IL-6 and IL-8 levels were determined using the ELISA technique. The gross observations, the histological data including mast cell modulation, as well as the molecular data, speak in favour of a significant delay in burn wound healing caused by sensory denervation. On the other hand, results support the positive role of sympathetic denervation in speeding up the healing process. The dual effect of the nervous system on burn wound healing is being documented in an animal model for the first time.

Influence of pseudo-resistance on the effect of renal denervation on 24-hour ambulatory blood pressure levels

BACKGROUND

Renal denervation (RDN) is a promising treatment option in addition to medical antihypertensive treatment in patients suffering from resistant hypertension. Despite the growing interest in RDN, the negative result of the Symplicity HTN-3 trial led to a debate on the efficacy of RDN.

METHODS

We systematically investigated the effects of RDN, evaluated by 24-hr ambulatory blood pressure measurements (ABPM), in a consecutive series of patients with resistant hypertension, which was defined by a mean office systolic blood pressure (SBP) >160 mm Hg (>150 mm Hg in patients with diabetes). Patients with a mean 24-hr SBP of less than 130 mm Hg at baseline were classified as pseudo-resistant, while all other patients were classified as true-resistant. After six months, we analyzed the response rates in true-resistant and in pseudo-resistant patients, respectively, by the means of 24-hr ABPM. Thereby, patients with a reduction of more than 5 mm Hg in 24-hr SBP were classified as responders.

RESULTS

RDN was performed in 106 patients. By 24-hr ABPM, 20 patients (18.9%) were classified as pseudo-resistant patients. In this cohort, we only found two responders (response rate 10%) six months after RDN. By contrast, in true-resistant patients, the response rate was almost 60% and the mean BP reduction was -18.6/-9 mm Hg in 24-hr ABPM.

CONCLUSIONS

We found a significant BP reduction in almost 60% of patients with true-resistant hypertension, but only in 10% in patients with pseudo-resistant hypertension. According to our results, patient selection seems to be crucial for acceptable response rates after RDN.

Management of ventricular arrhythmias in structural heart disease

Ventricular arrhythmias (VA) are a source of significant morbidity and mortality in patients with structural heart disease (SHD). The advent of the implantable cardiac defibrillator (ICD) has had a positive effect on mortality, but the associated morbidity remains a significant problem. Modern treatment of VA has advanced far beyond medical therapy and includes strategies as simple as intelligent ICD programming and as complex as catheter ablation (CA). In these pages, the spectrum of management strategies will be discussed; from anti-arrhythmic drugs and ICD implantation and programming to CA and autonomic modulation. The focus of this review will be on strategies for secondary prevention of VA in patients with SHD, supported by clinical evidence for their utilization.

Are we on the path to solve the enigma of resistant hypertension: renal sympathetic denervation

Renal sympathetic denervation (RSD) opens new perspectives and possibilities not only in the treatment of resistant hypertension but also of other cardiometabolic diseases. In patients with hypertension, it has been demonstrated that activity of the sympathetic nervous system correlates with grade of hypertension. Decreasing sympathetic activity using RSD significantly reduces blood pressure in resistant hypertension. It is too early to say a definite opinion about appropriateness of this method in the treatment of resistant hypertension, because there are not great studies with huge number of the patients. After we get and evaluate these results through a longer span of time, only than we shall know what is the role of RSD in the treatment of resistant hypertension and other cardiometabolic conditions related to increased function of the sympathetic nervous system, such as heart failure, diabetes mellitus, obstructive sleep apnea, renal disease with microalbuminuria and macroalbuminuria.

Increase in visceral fat per se does not induce insulin resistance in the canine model

OBJECTIVES

To determine whether a selective increase of visceral adipose tissue content will result in insulin resistance.

METHODS

Sympathetic denervation of the omental fat was performed under general inhalant anesthesia by injecting 6-hydroxydopamine in the omental fat of lean mongrel dogs (n = 11). In the conscious animal, whole-body insulin sensitivity was assessed by the minimal model (SI ) and the euglycemic hyperinsulinemic clamp (SICLAMP ). Changes in abdominal fat were monitored by magnetic resonance. All assessments were determined before (Wk0) and 2 weeks (Wk2) after denervation. Data are medians (upper and lower interquartile).

RESULTS

Denervation of omental fat resulted in increased percentage (and content) of visceral fat [Wk0: 10.2% (8.5-11.4); Wk2: 12.4% (10.4-13.6); P < 0.01]. Abdominal subcutaneous fat remained unchanged. However, no changes were found in SI [Wk0: 4.7 (mU/l)(-1) min(-1) (3.1-8.8); Wk2: 5.3 (mU/l)(-1) min(-1) (4.5-7.2); P = 0.59] or SICLAMP [Wk0: 42.0 × 10(-4) dl kg(-1) min(-1) (mU/l)(-1) (41.0-51.0); Wk2: 40.0 × 10(-4) dl kg(-1) min(-1) (mU/l) (-1) (34.0-52.0); P = 0.67].

CONCLUSIONS

Despite a selective increase in visceral adiposity in dogs, insulin sensitivity in vivo did not change, which argues against the concept that accumulation of visceral adipose tissue contributes to insulin resistance.

Randomized comparison of renal denervation versus intensified pharmacotherapy including spironolactone in true-resistant hypertension: six-month results from the Prague-15 study

This prospective, randomized, open-label multicenter trial evaluated the efficacy of catheter-based renal denervation (Symplicity, Medtronic) versus intensified pharmacological treatment including spironolactone (if tolerated) in patients with true-resistant hypertension. This was confirmed by 24-hour ambulatory blood pressure monitoring after excluding secondary hypertension and confirmation of adherence to therapy by measurement of plasma antihypertensive drug levels before enrollment. One-hundred six patients were randomized to renal denervation (n=52), or intensified pharmacological treatment (n=54) with baseline systolic blood pressure of 159±17 and 155±17 mm Hg and average number of drugs 5.1 and 5.4, respectively. A significant reduction in 24-hour average systolic blood pressure after 6 months (-8.6 [95% cofidence interval: -11.8, -5.3] mm Hg; P<0.001 in renal denervation versus -8.1 [95% cofidence interval: -12.7, -3.4] mm Hg; P=0.001 in pharmacological group) was observed, which was comparable in both groups. Similarly, a significant reduction in systolic office blood pressure (-12.4 [95% cofidence interval: -17.0, -7.8] mm Hg; P<0.001 in renal denervation versus -14.3 [95% cofidence interval: -19.7, -8.9] mm Hg; P<0.001 in pharmacological group) was present. Between-group differences in change were not significant. The average number of antihypertensive drugs used after 6 months was significantly higher in the pharmacological group (+0.3 drugs; P<0.001). A significant increase in serum creatinine and a parallel decrease of creatinine clearance were observed in the pharmacological group; between-group difference were borderline significant. The 6-month results of this study confirmed the safety of renal denervation. In conclusion, renal denervation achieved reduction of blood pressure comparable with intensified pharmacotherapy.

Expression of nerve growth factor in the prostate of male rats in response to chronic stress and sympathetic denervation

Nerve growth factor (NGF) has been found in the normal prostate of the Wistar rat and is regarded as an important prostatic mitogen. We have previously shown that chronic stress induced epithelial hyperplasia while sympathetic denervation caused atrophy in the male Wistar rat prostate. NGF may have been a contributing mechanism to the hyperplasia and atrophy response that was observed. The aim of the present study was to investigate the expression of NGF in the prostate of the male rat in response to chronic stress and denervation. Two weeks of restraint water-immersion stress were used to induce a chronic stress model in Wistar rats. Denervation of the peripheral sympathetic nerve was induced by 6-hydroxydopamine. The expression levels of NGF in the dissected prostate lobes were examined by immunohistochemistry. After 14 days of stress, proliferation of the epithelium in the ventral lobes was observed, whereas the dorsolateral lobes were almost unaffected. NGF immunoreactive protein was localized to the columnar secretory epithelium lines of the prostate tissue. Stress and denervation led to an increase in NGF expression in the ventral lobes. In conclusion, NGF was involved in the hyperplasia and atrophy in the prostate of the male rat in response to chronic stress and sympathetic denervation, and thus may be a contributing factor in the pathophysiology of the prostate.

The influence of epidural anesthesia on the electrical activity of heart atria

Introduction

High thoracic epidural anesthesia (TEA) causes blockade of sympathetic fibers involved in innervation of the heart (segments T1-T4), which results in changes of cardiac electrophysiology. The anti-arrhythmic effects of TEA on supraventricular arrhythmias, mainly atrial fibrillation, are controversial.

The aim of the study

The aim of the study was to assess the influence of epidural anesthesia on the electrical function of heart atria, including proven markers of increased risk of perioperative atrial fibrillation, such as P wave dispersion and P wave maximum duration.

Material and methods

The study involved 50 male patients, without a history of previous heart diseases, scheduled for elective surgical procedures. Patients received thoracic epidural anesthesia (group T, n = 25) or lumbar epidural anesthesia (group L, n = 25). The measurements were obtained from a continuous recording of ECG before epidural anesthesia and after the detection of blockade (T1 or T8 segment sensory block in groups T and L, respectively).

Results

The statistical analysis of electrocardiographic parameters, including the maximum, minimum and mean P wave duration; P wave dispersion; the maximum, minimum and mean PR interval duration; and PR interval dispersion, did not show any inter- or intragroup differences at selected time points.

Conclusions

Regardless of its location, epidural anesthesia and sympathetic blockade associated with this procedure do not significantly affect the electrical functions of the cardiac atria reflected in superficial ECG, including the electrocardiographic parameters that are considered to be markers of increased risk of perioperative atrial fibrillation, such as P wave dispersion and its maximum duration.

Regional myocardial sympathetic denervation predicts the risk of sudden cardiac arrest in ischemic cardiomyopathy. J Am Coll Cardiol. 2014;63:141-149. [PMID: 24076296 DOI: 10.1016/j.jacc.2013.07.096]

OBJECTIVES

The PAREPET (Prediction of ARrhythmic Events with Positron Emission Tomography) study sought to test the hypothesis that quantifying inhomogeneity in myocardial sympathetic innervation could identify patients at highest risk for sudden cardiac arrest (SCA).

BACKGROUND

Left ventricular ejection fraction (LVEF) is the only parameter identifying patients at risk of SCA who benefit from an implantable cardiac defibrillator (ICD).

METHODS

We prospectively enrolled 204 subjects with ischemic cardiomyopathy (LVEF ≤35%) eligible for primary prevention ICDs. Positron emission tomography (PET) was used to quantify myocardial sympathetic denervation ((11)C-meta-hydroxyephedrine [(11)C-HED]), perfusion ((13)N-ammonia) and viability (insulin-stimulated (18)F-2-deoxyglucose). The primary endpoint was SCA defined as arrhythmic death or ICD discharge for ventricular fibrillation or ventricular tachycardia >240 beats/min.

RESULTS

After 4.1 years follow-up, cause-specific SCA was 16.2%. Infarct volume (22 ± 7% vs. 19 ± 9% of left ventricle [LV]) and LVEF (24 ± 8% vs. 28 ± 9%) were not predictors of SCA. In contrast, patients developing SCA had greater amounts of sympathetic denervation (33 ± 10% vs. 26 ± 11% of LV; p = 0.001) reflecting viable, denervated myocardium. The lower tertiles of sympathetic denervation had SCA rates of 1.2%/year and 2.2%/year, whereas the highest tertile had a rate of 6.7%/year. Multivariate predictors of SCA were PET sympathetic denervation, left ventricular end-diastolic volume index, creatinine, and no angiotensin inhibition. With optimized cut-points, the absence of all 4 risk factors identified low risk (44% of cohort; SCA <1%/year); whereas ≥2 factors identified high risk (20% of cohort; SCA ∼12%/year).

CONCLUSIONS

In ischemic cardiomyopathy, sympathetic denervation assessed using (11)C-HED PET predicts cause-specific mortality from SCA independently of LVEF and infarct volume. This may provide an improved approach for the identification of patients most likely to benefit from an ICD. (Prediction of ARrhythmic Events With Positron Emission Tomography [PAREPET]; NCT01400334).

Regulation of NGF and NT-3 protein expression in peripheral targets by sympathetic input

Nerve growth factor (NGF) and neurotrophin-3 (NT-3) are target-derived proteins that regulate innervating sympathetic neurons. Here, we used western blot analysis to investigate changes in NGF and NT-3 protein in several peripheral tissues following loss of sympathetic input. Following removal of the superior cervical ganglion (SCG), large molecular weight (MW) NGF species, including proNGF-A, were increased in distal intracranial SCG targets, such as pineal gland and extracerebral blood vessels (bv). Mature NGF was a minor species in these tissues and unchanged following sympathectomy. Large MW NGF species also were increased when sympathectomy was followed by in vivo NGF administration. Mature NT-3, which was abundant in controls, was significantly decreased in these targets following sympathetic denervation. The decrease in mature NT-3 was enhanced following NGF administration. The trigeminal ganglion, which provides sensory input to these targets, showed increased NGF, but decreased NT-3, in these treatments, demonstrating that decreased NT-3 at the targets did not result from enhanced NT-3 uptake. Unlike pineal gland and extracerebral bv, the external carotid artery, an extracranial proximal SCG target, showed no change in NGF following denervation, and mature NT-3 was significantly increased. Following NGF administration, NT-3 was significantly decreased. We provide evidence for sympathetic regulation of NGF and NT-3 in peripheral targets and that elevated NGF can depress NT-3. The differential response in distal and proximal adult targets is consistent with the idea that neurons innervating proximal and distal targets may serve different roles in regulating neurotrophin protein. In addition, we conclude that previous ELISA results showing increased NGF protein following sympathetic denervation may have resulted from increases in large MW species, rather than an increase in mature NGF.