Prospective evaluation of a two-step therapeutic strategy in neurocardiogenic syncope: midodrine as second line treatment in patients refractory to beta-blockers

Twenty-four-hour urine NE level as a predictor of the therapeutic response to metoprolol in children with recurrent vasovagal syncope

BACKGROUND

Vasovagal syncope (VVS) is a heterogeneous disorder that creates challenges for treatment. Metoprolol is an important therapeutic option for children with VVS.

AIMS

The study examined the predictive value of 24-h urine norepinephrine (NE) levels in the assessment of the therapeutic efficacy of metoprolol for recurrent VVS in children.

METHODS

Thirty-eight children with recurrent VVS and 20 healthy children were enrolled in our study. Twenty-four-hour urine NE levels were measured by LC-MS-MS. VVS children were diagnosed by BHUTT and/or SNHUTT, and received metoprolol treatment for 3 months. Symptom scoring was utilized to evaluate the therapeutic effect. A ROC curve was used to investigate the predictive value of 24-h urine norepinephrine levels.

RESULTS

There exists significant correlation between 24-h urine NE levels and supine systolic and diastolic blood pressures. The 24-h urine NE levels of responders (40.75 ± 12.86 μg/24 h) were higher than those of nonresponders (21.48 ± 6.49 μg/24 h), and there was a significant difference between the two groups (P < 0.001). A ROC curve of the predictive value of 24 h urine NE levels revealed that the area under the curve was 0.926. A cutoff value for 24-h urine NE level of 34.84 μg/24 h produced both high sensitivity (70%) and specificity (100%) in predicting the efficacy of metoprolol therapy for VVS.

CONCLUSIONS

Patients with high 24-h urine NE levels have higher supine systolic and diastolic pressures and more effective responses to metoprolol. A 24-h urine norepinephrine level of > 34.84 μg/24 h was an indicator of the effectiveness of metoprolol therapy for VVS in children.

Plasma copeptin and therapeutic effectiveness of midodrine hydrochloride on postural tachycardia syndrome in children

OBJECTIVES

Midodrine hydrochloride is used clinically to treat children with postural tachycardia syndrome (POTS), but it is not effective in all patients. This study was designed to explore the changes in plasma copeptin and its predictive value in assessing the therapeutic efficacy of midodrine hydrochloride in children with POTS.

STUDY DESIGN

The study included 33 children with POTS and 26 healthy children. The group with POTS received midodrine hydrochloride treatment for 1.5-3 months. The plasma copeptin was measured using a sandwich immunoluminometric assay. A receiver operating characteristic curve was used to explore the predictive value of plasma copeptin.

RESULTS

The plasma copeptin in the group with POTS was significantly higher than that of the control group (10.827±2.459 pmol/L vs 8.845±1.471 pmol/L, P<.001). The plasma copeptin in responders to midodrine hydrochloride was significantly higher than that of nonresponders (12.082±1.998 pmol/L vs 9.646±2.301 pmol/L, P=.003). Receiver operating characteristic analysis on the predictive value of plasma copeptin showed that the area under the curve was 0.800 with a 95% CI of 0.640-0.959. Using a plasma copeptin level of 10.482 pmol/L as the cutoff point produced both favorite sensitivity (81.3%) and specificity (76.5%) in predicting the efficacy of midodrine hydrochloride therapy in children with POTS.

CONCLUSIONS

Plasma copeptin may be considered as a predictive biomarker for the likelihood of successful treatment of children with POTS with midodrine hydrochloride.

Recurrent postural vasovagal syncope: sympathetic nervous system phenotypes

BACKGROUND

The pathophysiology of vasovagal syncope is poorly understood, and the treatment usually ineffective. Our clinical experience is that patients with vasovagal syncope fall into 2 groups, based on their supine systolic blood pressure, which is either normal (>100 mm Hg) or low (70-100 mm Hg). We investigated neural circulatory control in these 2 phenotypes.

METHODS AND RESULTS

Sympathetic nervous testing was at 3 levels: electric, measuring sympathetic nerve firing (microneurography); neurochemical, quantifying norepinephrine spillover to plasma; and cellular, with Western blot analysis of sympathetic nerve proteins. Testing was done during head-up tilt (HUT), simulating the gravitational stress of standing, in 18 healthy control subjects and 36 patients with vasovagal syncope, 15 with the low blood pressure phenotype and 21 with normal blood pressure. Microneurography and norepinephrine spillover increased significantly during HUT in healthy subjects. The microneurography response during HUT was normal in normal blood pressure and accentuated in low blood pressure phenotype (P=0.05). Norepinephrine spillover response was paradoxically subnormal during HUT in both patient groups (P=0.001), who thus exhibited disjunction between nerve firing and neurotransmitter release; this lowered norepinephrine availability, impairing the neural circulatory response. Subnormal norepinephrine spillover in low blood pressure phenotype was linked to low tyrosine hydroxylase (43.7% normal, P=0.001), rate-limiting in norepinephrine synthesis, and in normal blood pressure to increased levels of the norepinephrine transporter (135% normal, P=0.019), augmenting transmitter reuptake.

CONCLUSIONS

Patients with recurrent vasovagal syncope, when phenotyped into 2 clinical groups based on their supine blood pressure, show unique sympathetic nervous system abnormalities. It is predicted that future therapy targeting the specific mechanisms identified in the present report should translate into more effective treatment.

Prolonged asystole provoked by head-up tilt testing

We describe a patient with a history of neurocardiogenic syncopes who had a positive headup tilt test that resulted in an lasting asystole lasting 34 seconds. However, the previously carried out Schellong test with a 30-min phase of standing showed a normal result. The patient showed typical orthostatic symptoms while tilted at the angle of 75 degrees. Shortly before asystole occurred, heart rate variability showed high frequency bands, indicating vagal stimulation. The pathophysiology of neurocardiogenic syncope (NCS) in context with heart rate variability is discussed. This patient was successfully treated with propranolol. This case shows the utility of a provocative head-up tilt test in establishing the diagnosis of NCS. If the Schellong test is normal, still further examination by tilt-table test is indispensable.

Drug treatment of orthostatic hypotension because of autonomic failure or neurocardiogenic syncope

Orthostatic hypotension either because of autonomic failure or neurocardiogenic syncope can be very incapacitating and should be treated accordingly. Drug therapy is frequently needed to alleviate orthostatic symptoms. The physiopathological basis of neurocardiogenic syncope and of autonomic failure is completely different and their treatment should be distinct. In the past 5 years, many randomized, placebo-controlled trials have shed light on the efficacy of specific pressor drugs. In patients with orthostatic hypotension because of autonomic failure, alpha-adrenoceptor agonists, and midodrine in particular, have been shown to increase standing blood pressure and decrease orthostatic symptoms. Other drugs such as octreotide, indomethacin or ergotamine have also been shown to elevate standing blood pressure and/or orthostatic tolerance. Fludrocortisone is a well known and frequently used pressor drug but randomized controlled studies are needed to measure its efficacy. In patients with orthostatic hypotension associated with neurocardiogenic syncope, clinical trials have demonstrated that beta-blockers, especially beta(1)-selective agents without intrinsic sympathomimetic activity such as atenolol, midodrine and paroxetine can decrease recurrence of syncope. Treatment algorithms, such as those presented in this review, should always be interpreted in the light of individual patient characteristics. Many of the drugs used for orthostatic hypotension have multiple indications and contraindications that should influence therapeutic decisions. Little is known about the effectiveness and tolerability of specific combinations of pressor drugs. Consequently, sound clinical judgment and close follow-up of patients should always guide combination therapy.

Dysautonomia in chronic fatigue syndrome: facts, hypotheses, implications

The diagnosis of chronic fatigue syndrome (CFS) is based on patient history and treatment on cognitive behavior therapy and graded exercise. There is increasing evidence that dysautonomia occurs in CFS manifest primarily as disordered regulation of cardiovascular responses to stress. We impart our experience relating to diagnosis, monitoring, and treatment of CFS based on identification and management of dysautonomia. Recently proposed methods for assessment of the cardiovascular reactivity, the 'hemodynamic instability score' (HIS) and the 'Fractal and Recurrence Analysis-based Score' (FRAS), served for this purpose. On HUTT, a particular dysautonomia is revealed in CFS patients that differ from dysautonomia in several other disorders. This distinct abnormality in CFS can be identified by HIS >-0.98 (sensitivity 84.5% and specificity 85.1%) and FRAS > +0.22 (sensitivity 70% and specificity 88%). Therefore, the HIS and FRAS may be used, in the appropriate clinical context, to support the diagnosis of CFS, which until now, could only be subjectively inferred. A pilot study suggested that midodrine treatment, directed at the autonomic nervous system in CFS, results first in correction of dysautonomia followed by improvement of fatigue. This finding implies that dysautonomia is pivotal in the pathophysiology CFS, at least in a large part of the patients, and that manipulating the autonomic nervous system may be effective in the treatment of CFS.

Neurocardiogenic syncope: aetiology and management

Neurocardiogenic syncope is the most common cause of syncope presenting in the outpatient setting. It is usually encountered among individuals without an underlying heart disease, but not uncommonly participates in the syncope mechanism of patients with an obstructive or an arrhythmic cardiac cause for syncope as well. The vasovagal event is caused by a transient profound hypotensive reaction most commonly associated with inappropriate bradycardia resulting from activation of a complex autonomic reflex. The pathophysiology of neurocardiogenic syncope has been elucidated by tilt table testing, a noninvasive and well-tolerated method for reproducing the event in susceptible individuals. Although the majority of people with vasovagal fainting need no specific treatment, treatment is required for those presenting with problematic features such as frequent events accompanied by trauma or accidents, and occasionally by a severe cardioinhibitory pattern response. A number of different drugs have been proposed to favourably act on different aspects of the neurocardiogenic reflex but only a few randomised, placebo-controlled, drug-specific trials are currently available. Alternatively, cardiac pacing has also been introduced for patients who have symptoms that are drug-refractory or for those with a severe cardioinhibitory hypotensive response. The selection of the appropriate treatment plan should be individualised after consideration of patient history, clinical characteristics and preference, results of the baseline tilting study, and the existing evidence from the few randomised, controlled studies performed so far.

Evaluation and treatment of pediatric patients with neurocardiogenic syncope

Neurocardiogenic syncope is the most common form of syncope in children. The most widely accepted mechanism of its etiology is a vigorous contraction of the heart due to relative hypovolemia leading to stimulation of C-fibers and sympathetic withdrawal. Episodes usually occur with an upright position and are preceded by a typical prodrome. A classic history is paramount to the diagnosis. Tilt testing aids in the diagnosis in certain cases. The cornerstone of therapy is maintaining adequate hydration and avoiding situations that may lead to harm with syncopal events. Beta blockers, fludrocortisone, alpha adrenergic agents and disopyramide are commonly used to prevent syncope. Seratonin reuptake inhibitors, pacing with rate drop algorithms and tilt training are relatively new in the armamentarium of therapy.