Increased expression of blood muscarinic receptors in patients with reflex syncope.

AIMS: Pathophysiology of reflex syncope is not fully understood but a vagal overactivity might be involved in this syncope. Previously, overexpression of muscarinic M2 receptors and acetylcholinesterase was found in particular in the heart and in lymphocytes of rabbits with vagal overactivity as well as in hearts of Sudden Infant Death Syndromes. The aim of this present study was to look at M2 receptor expression in blood of patients with reflex syncope. The second objective was to measure acetylcholinesterase expression in these patients. METHODS AND RESULTS: 136 subjects were enrolled. This monocenter study pooled 45 adults exhibiting recurrent reflex syncope compared with 32 healthy adult volunteers (18-50 years) and 38 children exhibiting reflex syncope requiring hospitalization compared with 21 controls (1-17 years). One blood sample was taken from each subject and blood mRNA expression of M2 receptors was assessed by qRT-PCR. Taking into account the non-symmetric distributions of values in both groups, statistical interferences were assessed using bayesian techniques. A M2 receptor overexpression was observed in adult and pediatric patients compared to controls. The medians [q1;q3] were 0.9 [0.3;1.9] in patients versus 0.2 [0.1;1.0] in controls; the probability that M2 receptor expression was higher in patients than in controls (Pr[patients>controls]) was estimated at 0.99. Acetylcholinesterase expression was also increased 0.7 [0.4;1.6] in patients versus 0.4 [0.2;1.1] in controls; the probability that acetylcholinesterase expression was higher in patients than in controls (Pr[patients>controls]) was estimated at 0.97. Both in adults and children, the expression ratio of M2 receptors over acetylcholinesterase was greater in the patient group compared with the control group. CONCLUSION: M2 receptor overexpression has been detected in the blood of both, adults and children, exhibiting reflex syncope. As in our experimental model, i.e. rabbits with vagal overactivity, acetylcholinesterase overexpression was associated with M2 receptor overexpression. For the first time, biological abnormalities are identified in vagal syncope in which only clinical signs are, so far, taken into account for differential diagnosis and therapeutic management. Further work will be needed to validate potential biomarkers of risk or severity associated with the cholinergic system.

Peculiar Clinical Presentation of Coxsackievirus B4 Infection: Neonatal Restrictive Cardiomyopathy.

Introduction Restrictive cardiomyopathy in fetuses and neonates is extremely rare and has a poor outcome. Its etiology in neonates is elusive: metabolic diseases (e.g., Gaucher, Hurler syndrome), neuromuscular disorders (e.g., muscular dystrophies, myofibrillar myopathies), or rare presentation of genetic syndromes (e.g., Coffin-Lowry syndrome) account for a minority of the cases, the majority remaining idiopathic. Case Study We report the case of a 17-day-old male infant presenting cardiogenic shock following a restrictive dysfunction of the left ventricle. Postmortem investigations revealed coxsackievirus B4 myocarditis with histological lesions limited to the left heart. However, polymerase chain reaction (PCR) for coxsackievirus B4 was positive in the left as well as in the right ventricular samples. Conclusion In conclusion, coxsackievirus myocarditis is a cause of restrictive cardiomyopathy, and its diagnosis should involve PCR screening as a more sensitive technique.

First model of spontaneous vagal hyperreactivity and its mode of genetic transmission.

BACKGROUND: The main purpose of our study was to define an animal model of vagal hyperreactivity and its genetic transmission. METHODS AND RESULTS: We first investigated the vagal reactivity with phenylephrine in conscious rabbits. Barosensitivity and the maximal bradycardic response were measured at the upper mean blood pressure plateau. Hyperreactive (H) animals were selected and crossbred with normal (N) ones. Results showed no significant difference between calculated barosensitivity values after the different doses of phenylephrine. In contrast, an increase of the values and a great dispersion appeared 1 to 5 beats after the end of the ramp. Marked pauses (6000 to 20 000 ms) were obtained with some rabbits, which were blocked by atropine. A significant excess of hyperreactive offspring was observed in HxH crossings compared with NxN ones (39.4% male and 42.3% female offspring versus 14.4% and 4.4%, respectively). Few female offspring were hyperreactive compared with males in NxH and NxN crossings (4.1% versus 23.4% and 4.4% versus 14.4%, respectively). CONCLUSIONS: This study describes the first model of spontaneous vagal pauses. The inheritance could be polygenic with a partial sex-limited character.

Cardiac muscarinic receptor overexpression in sudden infant death syndrome.

BACKGROUND: Sudden infant death syndrome (SIDS) remains the leading cause of death among infants less than 1 year of age. Disturbed expression of some neurotransmitters and their receptors has been shown in the central nervous system of SIDS victims but no biological abnormality of the peripheral vago-cardiac system has been demonstrated to date. The present study aimed to seek vago-cardiac abnormalities in SIDS victims. The cardiac level of expression of muscarinic receptors, as well as acetylcholinesterase enzyme activity were investigated. METHODOLOGY/PRINCIPAL FINDINGS: Left ventricular samples and blood samples were obtained from autopsies of SIDS and children deceased from non cardiac causes. Binding experiments performed with [(3)H]NMS, a selective muscarinic ligand, in cardiac membrane preparations showed that the density of cardiac muscarinic receptors was increased as shown by a more than doubled B(max) value in SIDS (n = 9 SIDS versus 8 controls). On average, the erythrocyte acetylcholinesterase enzyme activity was also significantly increased (n = 9 SIDS versus 11 controls). CONCLUSIONS: In the present study, it has been shown for the first time that cardiac muscarinic receptor overexpression is associated with SIDS. The increase of acetylcholinesterase enzyme activity appears as a possible regulatory mechanism.

Constitutive overexpression of muscarinic receptors leads to vagal hyperreactivity.

BACKGROUND: Alterations in muscarinic receptor expression and acetylcholinesterase (AchE) activity have been observed in tissues from Sudden Infant Death Syndrome (SIDS). Vagal overactivity has been proposed as a possible cause of SIDS as well as of vasovagal syncopes. The aim of the present study was to seek whether muscarinic receptor overexpression may be the underlying mechanism of vagal hyperreactivity. Rabbits with marked vagal pauses following injection of phenylephrine were selected and crossed to obtain a vagal hyperreactive strain. The density of cardiac muscarinic receptors and acetylcholinesterase (AchE) gene expression were assessed. Blood markers of the observed cardiac abnormalities were also sought. METHODOLOGY/PRINCIPAL FINDINGS: Cardiac muscarinic M(2) and M(3) receptors were overexpressed in hyperreactive rabbits compared to control animals (2.3-fold and 2.5-fold, respectively) and the severity of the phenylephrine-induced bradycardia was correlated with their densities. A similar overexpression of M(2) receptors was observed in peripheral mononuclear white blood cells, suggesting that cardiac M(2) receptor expression can be inferred with high confidence from measurements in blood cells. Sequencing of the coding fragment of the M(2) receptor gene revealed a single nucleotide mutation in 83% of hyperreactive animals, possibly contributing for the transcript overexpression. Significant increases in AchE expression and activity were also assessed (AchE mRNA amplification ratio of 3.6 versus normal rabbits). This phenomenon might represent a compensatory consequence of muscarinic receptors overexpression. Alterations in M(2) receptor and AchE expression occurred between the 5th and the 7th week of age, a critical period also characterized by a higher mortality rate of hyperreactive rabbits (52% in H rabbits versus 13% in normal rabbits) and preceeded the appearance of functional disorders. CONCLUSIONS/SIGNIFICANCE: The results suggest that cardiac muscarinic receptor overexpression plays a critical role in the development of vagal hyperreactivity, whereas AchE hyperactivity appears as a compensatory consequence of it. Since similar vagal disorders were observed recently by us in SIDS, muscarinic receptor overexpression could become a marker of risk of vasovagal syncopes and SIDS.

Daily on-line haemodiafiltration: a pilot trial in children.

BACKGROUND: Despite major improvements in paediatric dialysis over the last two decades, cardiovascular outcome is often poor. As France gives priority to kidney transplantation over dialysis, children in chronic haemodialysis are generally pre-adolescents or adolescents with long medical histories and low compliance. In them, the usual weekly schedule of dialysis is often unsuitable. We conducted a study of conversion to daily dialysis, which allowed an enhanced dialysis dose, a gentle ultrafiltration rate and achievement of dry body weight. METHODS: In this single-centre, observational, prospective, non-randomized study, five oligoanuric dialysis patients (mean age: 13.8 +/- 3.2 years) were converted from standard on-line haemodiafiltration (S-OL-HDF) (4 h, three times/week) to daily on-line haemodiafiltration (D-OL-HDF) (3 h, six times/week). Patient selection was based on both the presence of uraemic cardiomyopathy (left ventricular hypertrophy and reduced fractional shortening) and their reduced therapeutic compliance. The D-OL-HDF parameters were the same as for the S-OL-HDF. RESULTS: Increasing the number of sessions from three to six weekly positively impacted the weekly dialysis dose. On D-OL-HDF, mean arterial blood pressure decreased significantly (from 95 +/- 15 to 82 +/- 13 and 87 +/- 9 mmHg at 6 and 12 months, respectively). Left ventricular hypertrophy decreased and its fractional shortening improved markedly (from 26.6 +/- 17% to 31 +/- 14% and 46.6 +/- 15% at 6 and 12 months, respectively). Pre-dialytic plasma phosphorus also decreased markedly (from 1.87 +/- 0.23 to 1.43 +/- 0.22 and 1.28 +/- 0.29 mmol/l at 6 and 12 months, respectively), as did the calcium-phosphorus product. The post-dialytic recovery time disappeared and so did perception of fatigue. Fasting the day before dialysis to avoid excess weight gain (necessitating longer dialysis) disappeared. Combined with an improved appetite, these changes resulted in higher caloric and protein intake (nPCR), from 1.28 +/- 0.23 to 1.43 +/- 0.24 g/kg at 6 months, and school attendance became regular. The only pre-pubertal child included showed catch-up growth. CONCLUSIONS: Increasing dialysis frequency to daily sessions without shortening the durations of sessions excessively allowed us to overcome the "free diet" imposed on these paediatric, very uncompliant patients. This strategy led to a reduction in blood pressure and an improvement of left ventricular size and function, normalization of pre-dialytic plasma phosphorus and improvements in general well-being and dialysis acceptance. Long-term, however, this protocol is only acceptable for the children if associated with the potential of clinical recovery allowing inscription on the kidney transplantation waiting list.