Clinical features and management of young patients with cardioinhibitory response during orthostatic testing

Neurocardiogenic syncope in children : current concepts in diagnosis and management

A wide variety of pharmacologic agents are currently used for the prevention of recurrent neurocardiogenic syncope in children and adolescents. Significant advances in the understanding of this syncopal disorder have occurred in the past decade, and the list of medications recommended has changed, reflecting the evolving understanding of the pathophysiology and development of agents with enhanced efficacy and fewer adverse effects. Clinicians have few randomized controlled trials available to guide their decisions about treating neurocardiogenic syncope, and even fewer when it comes to medications targeting the pediatric population. At the present time, beta-adrenergic receptor blockers, fludrocortisone, and also specific serotonin reuptake inhibitors and midodrine, appear to be favored treatment options. Ideally, specific therapy would be tailored to specific pathophysiologic mechanisms. Unfortunately, at present, specific treatments based on those abnormalities have not been identified.

Unexplained syncope: clinical management

The management of unexplained syncope begins with the patient's history and physical examination, which are oriented to help separate benign from serious causes. Malignant etiologies are more likely to occur with exertional syncope. Cardiac causes should be considered, particularly cardiomyopathy, postoperative congenital heart disease, right ventricular dysplasia, anomalous coronary artery, pulmonary artery hypertension, myocarditis, long QT syndrome, and Wolff-Parkinson-White syndrome. Neurological and metabolic disorders may underlie a syncope episode. After malignant causes of syncope have been excluded and the diagnosis of neurocardiac syncope has been established, treatment strategies include behavior modification, salt and increased fluids, and pharmacological agents. Efficacious agents include beta-blockers, dysopyramide, fludrocortisones, and alpha agents. Yet, behavior modification alone may be as effective as salt or pharmacological therapy. Because the natural history of neurocardiac syncope in children is spontaneous resolution, it is appropriate to try the simple measures before introducing drug therapy.

The medical therapy of cardioinhibitory syncope in pediatric patients

A small percentage of pediatric patients with neurally mediated syncope will have an asystolic response during upright tilt table testing. The purpose of this study is to evaluate the incidence of asystole during tilt table testing, and to assess the outcome of medical management of such patients. Of 398 patients undergoing evaluation for recurrent syncope between January 1989 and 1994, 18 (4.5%) experienced asystole lasting > or = 5 seconds during baseline tilt test. Patients had experienced a mean of four episodes of syncope, with a mean age at the time of tilt test of 11.1 +/- 4.0 years. The median duration of asystole was 10 seconds (range 5-40 s). Treatment was individualized to increased fluids and salt intake (3 patients), metoprolol (8 patients), pseudoephedrine (4 patients), disopyramide (1 patient), or combination therapy with fludrohydrocortisone (2 patients). During a median duration of follow-up of 31 months, no additional syncope was experienced by 78% of patients. Recurrent syncope in 4 patients was associated with either noncompliance or discontinuation of therapy in 3 patients; in 1 patient, increasing the dose of metoprolol was effective in preventing recurrences. We conclude that young patients with recurrent syncope and asystole during tilt test may be safely and effectively managed with pharmacological therapy, without resorting to pacemaker implantation.

Accelerometer systolic time intervals as fast-response sensors of upright posture in the young

BACKGROUND

Sensors of posture may improve rate-adaptive pacing in syndromes where syncope occurs in the upright posture, particularly in the young. No sensor of posture has been described to date. Previous studies suggest that two sensors currently under investigation (preejection period [PEP] and left ventricular ejection time [LVET] systolic time intervals [STIs] and accelerometers) may be affected by posture. A PEP-sensing pacemaker is available commercially in which heart rate (HR) decreases with an increase in PEP (delta(HR)/delta[PEP]< 0). In patients with upright syncope, it is not known how such algorithms respond to posture. Also, it is not known whether STIs correlate with posture independent of autonomic tone.

METHODS AND RESULTS

We studied accelerometer-derived STIs in head-upright tilt-testing with beta-blockade and catecholamine stimulation in patients with syncope or presyncope using an ultra-low-frequency accelerometer placed on the chest. Thirty-two patients age 6 to 22 years with unexplained recurrent syncope or presyncope underwent tilt-testing involving two to four tilts (60 degrees) at baseline, during esmolol infusion (500 micrograms/kg load, 50 to 140 micrograms/kg per minute), after esmolol withdrawal, and during isoproterenol infusion if not contraindicated. PEP, LVET, and other indexes were quantified, and their relations to posture and to autonomic state were determined. With tilt, PEP increased from 98.9 +/- 2.2 to 109.1 +/- 2.8 msec (P < .0001), and LVET decreased (supine-to-upright) from 295.5 +/- 4.5 to 247.2 +/- 4.7 msec (P < .0001). PEP/LVET changed from 0.337 +/- 0.01 to 0.45 +/- 0.02 (P < .0001). Similar postural changes were observed during tilt with beta-blockade and esmolol withdrawal, and during isoproterenol infusion. STI changes occurred immediately on postural change and were stable. Postural change of PEP was greater than the beta-adrenergic effect by 6:1. Postural change of STIs was independent of vagal tone.

CONCLUSIONS

First, accelerometer-derived STIs detect postural changes. Because these changes are independent of autonomic tone and are rapid and stable, they may be useful as fast-response sensors of upright posture in rate-adaptive pacemakers. Second, with postural change, HR increases when PEP increases. However, PEP-sensing pacemakers presently under investigation assume the opposite (inverse) mathematical relationship. Therefore, current PEP-sensing pacemakers use an incorrect algorithm for physiological postural responses in syncope patients. These data predict a paradoxical tachycardic response to the supine posture in patients implanted with these devices.

Neurocardiogenic syncope in children with a normal heart

OBJECTIVES

The purpose of this study was to review the results of investigation and management of children with syncope and a structurally normal heart.

BACKGROUND

Syncope is a common clinical problem and has many etiologies. Autonomic testing and, in particular, the tilt/orthostatic test have helped to positively diagnose neurocardiogenic syncope in a high proportion of such patients.

METHODS

Patient case notes and autonomic test charts were reviewed in 162 children aged 1 to 20 years (mean age 12.8 years) with syncope. The autonomic test consisted of orthostatic maneuver, carotid sinus massage, diving reflex, Valsalva maneuver and dose response to intravenous boluses of isoproterenol and phenylephrine. Serum levels of epinephrine and norepinephrine were drawn during the orthostatic test. After confirmation of neurocardiogenic syncope, treatment was begun with fludrocortisone and salt, and beta-adrenergic blocking agents were used as a second line of therapy when indicated.

RESULTS

The orthostatic test was positive for neurocardiogenic syncope in 100 patients (62%) and negative in 62 (38%). Patients in the former group were older, were more often female and had a diminished response to carotid sinus massage, a higher Valsalva ratio and a higher supine epinephrine level. Both groups showed an increase in epinephrine and norepinephrine levels at 5 min of standing. In the orthostatic positive group at the time of syncope, norepinephrine levels decreased, whereas epinephrine levels increased. Patients in this group were also more sensitive to the vasodilating effect of isoproterenol but not to its chronotropic effects. Eleven patients had cardioinhibitory syncope (asystole > or = 3 s). Of these, three had pacemaker implantation. Fludrocortisone and salt used in 84 patients in the orthostatic positive group produced resolution of symptoms in 55 patients (65%) and improvement in 14 (17%). Ten patients received beta-blockers, with resolution in four and improvement in four.

CONCLUSIONS

Patients with orthostatic test-proved neurocardiogenic syncope show evidence of autonomic dysfunction. They also show beta-adrenergic hypersensitivity. Treatment initiated on the basis of the protocol was associated with amelioration of symptoms in the majority of patients.

Esmolol tilt testing with esmolol withdrawal for the evaluation of syncope in the young

BACKGROUND

Head-upright tilt (HUT) testing is valuable in evaluating syncope. Isoproterenol is used to increase sensitivity. However, isoproterenol is contraindicated or dangerous in undiagnosed heart disease and produces false-positives. We introduced esmolol withdrawal during esmolol HUT, hypothesizing that (1) acute withdrawal of the ultrashort-acting beta-blocker induces beta-adrenergic effects by unmasking endogenous catecholamines and may provoke syncope with fewer risks, and (2) response to esmolol/esmolol withdrawal may predict effective therapy.

METHODS AND RESULTS

Thirty-six patients with unexplained recurrent syncope/presyncope (7 to 35 years old, known heart disease or arrhythmia in 14) underwent 2 to 4 HUT tests (60 degrees, 49 minutes): (1) baseline, (2) esmolol (500 micrograms/kg plus 50 micrograms.kg-1.min-1), (3) esmolol withdrawal (HUT continued after esmolol stopped), and (4) isoproterenol if tests 1 through 3 were negative and isoproterenol was not contraindicated. A positive test reproduced symptoms with hypotension or bradycardia, requiring recumbency for recovery. Twenty-five had positive tests, and 11 had negative tests. In 5, only the baseline test was positive; in 15, esmolol/esmolol withdrawal tests were also positive, with 3 in whom esmolol withdrawal was positive although negative at baseline. Two isoproterenol tilts were positive. Esmolol withdrawal and isoproterenol tilts had the highest initial heart rate and similar maximal heart rate increment. Only isoproterenol caused hypertension. One isoproterenol test was false-positive, with hypertension-induced arterial baroreflex. Treatment was beta-blockers (8), Na/fludrocortisone (9), both (6), and DDD pacemakers (2). Esmolol/esmolol withdrawal accurately predicted therapeutic response in 15; isoproterenol predicted therapeutic response in none.

CONCLUSIONS

Esmolol withdrawal tilt testing is preferable to isoproterenol for provocative testing of syncope in the young, and it appears to be safer. Esmolol withdrawal testing has clinical utility before invasive testing as a first-line investigation for syncope in patients with or without heart disease.

Efficacy of alpha-adrenergic agonist therapy for prevention of pediatric neurocardiogenic syncope

OBJECTIVES

The purpose of our study was to determine whether alpha-adrenergic agonist therapy could prevent neurocardiogenic syncope in pediatric patients.

BACKGROUND

Recent reports from adult patients suggest that withdrawal of alpha-sympathetic stimulation contributes to neurocardiogenic syncope.

METHODS

Sixteen young patients (mean age 13.1 years, range 7 years 10 months to 17 years 10 months) with recurrent syncope and a positive baseline head-up tilt response were studied. After a positive baseline tilt response, phenylephrine was infused and repeat tilt was performed for 30 min or until the test result was positive. At discharge, patients were followed up on a regimen of oral pseudoephedrine to evaluate treatment effectiveness and side effects.

RESULTS

During baseline tilt, seven patients experienced vasodepressor syncope, seven had mixed vasodepressor-cardioinhibitory syncope and two had cardioinhibitory responses. All patients became symptomatic, reproducing their clinical symptoms. Baseline mean arterial pressure decreased slightly immediately on tilt testing and significantly at the end point (82 +/- 13 vs. 77 +/- 18 vs. 30 +/- 14 mm Hg, respectively, p < 0.0001). Although heart rate varied, the changes were not statistically significant (78 +/- 17 vs. 105 +/- 19 vs. 87 +/- 46 beats/min, respectively, p = NS). Phenylephrine was infused (mean 1.74, range 0.6 to 3.0 micrograms/kg per min) as patients underwent follow-up tilt testing. Fifteen patients remained asymptomatic without hemodynamic changes; the remaining patient manifested a blunted mixed response. During phenylephrine infusion, heart rate (64 +/- 12 vs. 81 +/- 17 vs. 76 +/- 16 beats/min, respectively, p = NS) and mean arterial pressure (96 +/- 15 vs. 83 +/- 19 vs. 80 +/- 18 mm Hg, respectively, p = NS) did not change. During outpatient oral pseudoephedrine treatment (mean 11.7, range 6 to 14) 15 of 16 patients reported that their clinical condition was controlled without side effects.

CONCLUSIONS

Alpha-adrenergic stimulation prevents pediatric neurocardiogenic syncope. Intravenous phenylephrine prevents neurocardiogenic syncope during head-up tilt, despite reflex vagal bradycardia. Oral pseudoephedrine alleviates symptoms in patients with neurocardiogenic syncope without causing significant side effects.