Syncope: etiology, management, and when to refer

An abnormality of blood pressure control is by far the most likely cause of syncope in children; however, syncope in children may be due to primary cardiac dysrhythmias, particularly in the presence of structural heart disease. An appropriate work-up should include an ECG with a 60-second rhythm strip at first presentation. Tilt testing can usually wait until after a second occurrence on non-pharmacologic therapy. Patients who require more than a history and ECG by the algorithm in the Figure should probably be referred to a cardiologist familiar with the evaluation of syncope. The common form of neurally mediated syncope is also probably related to both breath-holding spells in toddlers, and to many of the cases of chronic fatigue syndrome.

Pediatric cardiac auscultation

Murmurs will be a frequent finding during the well child pediatric exam and perhaps more frequent during the evaluation of an acute illness, but most of these murmurs are innocent. Understanding the variety of causes of innocent murmurs should help identify them as such. However, referral to the pediatric cardiac specialist is appropriate in newborns and small infants, when the findings are not entirely consistent with an innocent murmur, or when there are other reasons to suspect heart disease.

Preventing sudden death after repair of tetralogy of Fallot: complex therapy for complex patients

Sudden arrhythmic death in patients with repaired tetralogy of Fallot or its variants has a variety of causes. Consequently, it can serve as a paradigm for management of potentially malignant arrhythmias in all pediatric patients, particularly with regard to the use of nonpharmacologic therapy for management. Five cases are presented as touchpoints for discussion and demonstrate a number of important issues concerning the assessment and reduction of sudden cardiac death risk in these patients. First, there are no clinical parameters that can be used to accurately assess risk. Second, pharmacologic agents alone rarely are adequate therapy. Third, catheter ablation and antitachycardia devices continue to play an ever increasing role in management of these patients, and, finally, additional data are necessary to establish clear management guidelines in patients with congenital heart disease at risk for arrhythmic death.

Value of programmed ventricular stimulation in patients with congenital heart disease

INTRODUCTION

The role of programmed ventricular stimulation (VSTIM) for risk stratification in congenital heart disease is unclear. We analyzed the results of VSTIM in selected congenital heart disease survivors at a single center to determine whether it improved the ability to predict a serious outcome.

METHODS AND RESULTS

Between July 1985 and September 1996, 140 primary VSTIM studies were performed on 130 patients (median age 18.1 years, range 0 to 51). Tetralogy of Fallot (33 %), d-transposition of the great arteries (25 %), and left ventricular outflow tract obstruction (12%) accounted for the majority of patients. Indications included spontaneous ventricular tachycardia (VT) of > or = 3 beats (72%) and/or symptoms (68%). Sustained VT was induced in 25% of the studies, and nonsustained VT in 12%. Atrial flutter or other supraventricular tachycardia was documented in 32% and bradyarrhythmias in 26%. By univariate analysis, mortality was increased in patients with positive VSTIM versus negative VSTIM (18% vs 7%, P = 0.04). Using multivariate analysis, positive VSTIM was associated with a sixfold increased risk of decreased survival and a threefold increased risk of serious arrhythmic events, allowing up to 87% sensitivity in predicting mortality. However, 7 (33%) of 21 patients with documented clinical VT had false-negative studies.

CONCLUSION

VSTIM in a large, selected group of congenital heart disease patients identified a subgroup with significantly increased mortality and sudden arrhythmic events. Failure to induce VT was a favorable prognostic sign, but the frequency of false-negative studies was high. Frequent supraventricular tachycardia further complicated risk stratification. Although VSTIM appears to be a reasonable tool for evaluation of this population, a larger, multicenter trial is recommended to clarify its utility.

The developmental character of cardiac autonomic responses to an acute noxious event in 4- and 8-month-old healthy infants

Heart rate (HR) has been widely studied as a measure of an individual's response to painful stimuli. It remains unclear whether changes in mean HR or the variability of HR are specifically related to the noxious stimulus (i.e. pain). Neither is it well understood how such changes reflect underlying neurologic control mechanisms that produce these responses, or how these mechanisms change during the first year of life. To study the changes in cardiac autonomic modulation that occur with acute pain and with age during early infancy, the relationship between respiratory activity and short-term variations of HR (i.e. respiratory sinus arrhythmia) was quantified in a longitudinal study of term born healthy infants who underwent a finger lance blood collection at 4 months of age (n = 24) and again at 8 months of age (n = 20). Quantitative respiratory activity and HR were obtained during baseline, lance, and recovery periods. Time and frequency domain analyses from 2.2-min epochs of data yielded mean values, spectral measures of low (0.04-0.15 Hz) and high (0.15-0.80 Hz) frequency power (LF and HF), and the LF/HF ratio. To determine sympathetic and parasympathetic cardiac activity, the transfer relation between respiration and HR was used. At both 4 and 8 months, mean HR increased significantly with the noxious event (p > 0.01). There were age-related differences in the pattern of LF, HF, and LF/HF ratio changes. Although these parameters all decreased (p > 0.01) at 4 months, LF and LF/HF increased at 8 months and at 8 months HF remained stable in response to the noxious stimulus. Transfer gain changes with the lance demonstrated a change from predominant vagal baseline to a sympathetic condition at both ages. The primary finding of this study is that a response to an acute noxious stimulus appears to produce an increase in respiratory-related sympathetic HR control and a significant decrease in respiratory-related parasympathetic control at both 4 and 8 months. Furthermore, with increasing age, the sympathetic and parasympathetic changes appear to be less intense, but more sustained.

Catheter ablation of accessory pathways, atrioventricular nodal reentrant tachycardia, and the atrioventricular junction: final results of a prospective, multicenter clinical trial. The Atakr Multicenter Investigators Group

BACKGROUND

The purpose of this study was to evaluate the safety and efficacy of a temperature-controlled radiofrequency catheter ablation system.

METHODS AND RESULTS

The patient population included 1050 patients who had undergone ablation of atrioventricular nodal reentrant tachycardia (AVNRT), an accessory pathway (AP), or the atrioventricular junction (AVJ). Ablation was successful in 996 patients. The probability of success was highest among patients who had undergone ablation of the AVJ, lowest in patients who had undergone ablation of an AP, and in between for patients who had undergone ablation of AVNRT. A major complication occurred in 32 patients. Four variables predicted ablation success (AVJ, AVNRT, or left free wall AP ablation and an experienced center). Four factors predicted arrhythmia recurrence (right free wall, posteroseptal, septal, and multiple APs). Two variables predicted development of a complication (structural heart disease and the presence of multiple targets), and 3 variables predicted an increased risk of death (heart disease, lower ejection fraction, and AVJ ablation).

CONCLUSIONS

These findings may serve as a guide to clinicians considering therapeutic options in patients who are candidates for ablation.

Successful radiofrequency catheter ablation of congenital junctional ectopic tachycardia with preservation of atrioventricular conduction in a 9-month-old infant

An infant with congenital junctional ectopic tachyardia required frequent hospitalizations due to tachycardia acceleration despite multiple antiarrhythmic medications. At 9 months of age, he underwent successful radiofrequency catheter ablation of the tachycardia with preservation of AV conduction.

Respiration and blood pressure variability: mechanical and autonomic influences

The transfer function between broad-band respiratory activity and the heart rate (HR) response can be used to elucidate the frequency dependent phase and magnitude characteristics of the respiratory sinus arrhythmia (RSA). To understand the complex links between respiratory activity and arterial blood pressure (ABP), the transfer functions between instantaneous lung volume (ILV), parameters of arterial pressure, and central venous pressure (CVP) were determined in healthy human volunteers during 6-minute periods in which the respiratory rate was voluntarily controlled in a predetermined but erratic fashion, or CVP was perturbed with a similar pattern. Pharmacologic autonomic blockade was used to dissect the direct mechanical links between respiration and ABP from the effects of RSA on ABP. The results suggest that with HR fluctuations eliminated, respiration affects ABP in proportion to the rate of change of ILV; however, when neural control of HR remains intact, the RSA plays an important role in the genesis of ABP fluctuations.

Characteristics, management, and midterm outcome in infants with atrioventricular nodal reentry tachycardia

Atrioventricular nodal reentry is a commonly recognized mechanism of supraventricular tachycardia (SVT) in adults, but is only rarely documented in the first year of life. The aim of this study was to elucidate characteristics, management, and outcome in infants with atrioventricular nodal reentrant tachycardia (AVNRT). Electrophysiologic studies performed between January 1988 and June 1996 were reviewed. Fifteen infants with AVNRT at 58 +/- 27 days (mean +/- SEM) were identified. Five had AVNRT detected following palliation of structural cardiac anomalies, including 4 with critical obstructions to left ventricular outflow. Typical AVNRT (ventriculoatrial interval 49 +/- 5 ms) was observed in 14 of 15 patients and atypical AVNRT (ventriculoatrial interval 191 +/- 22 ms) in 4 of 15. All patients received long-term therapy, beginning with digoxin in 13. Eight had symptomatic recurrences on digoxin and 6 of these were given beta blockers, with satisfactory control in 4. Three patients were controlled with class III agents, and 2 underwent slow pathway radiofrequency modification at ages 4.1 and 6.7 years, respectively. AVNRT was still inducible in 6 of 6 asymptomatic patients who underwent follow-up atrial stimulation studies after discontinuation of medical therapy. All 15 patients were alive with either absent or well-controlled AVNRT at age 45 +/- 7 months. We conclude that the course and outcome of AVNRT diagnosed in the first year of life are generally benign, but that a minority of patients have symptoms persisting beyond infancy. Digoxin is of questionable benefit in long-term control. AVNRT often remains inducible in asymptomatic patients, although the significance of this finding remains to be determined by long-term follow-up.

Duration of complete atrioventricular block after congenital heart disease surgery

Children with complete heart block following surgery for congenital heart diseases were prospectively followed to assess the timing for recovery of atrioventricular conduction, and to determine if there were clinical variables that reliably predict permanent heart block. Recovery of atrioventricular conduction occurred by postoperative day 9 in 97% of patients with transient heart block.

Predictors of fluoroscopy time and estimated radiation exposure during radiofrequency catheter ablation procedures

The objective of this study was to identify factors that predict fluoroscopy duration and radiation exposure during catheter ablation procedures. The patient population included 859 patients who participated in the Atakr Ablation System clinical trial at 1 of 9 centers (398 male and 461 female patients, aged 36 +/- 21 years). Each patient underwent catheter ablation of an accessory pathway, the atrioventricular junction, or atrioventricular nodal reentrant tachycardia using standard techniques. The duration of fluoroscopy was 53 +/- 50 minutes. Factors identified as independent predictors of fluoroscopy duration included patient age and sex, the success or failure of the ablation procedure, and the institution at which the ablation was performed. Catheter ablation in adults required longer fluoroscopy exposure than it did in children. Men required longer durations of fluoroscopy exposure than did women. The mean estimated "entrance" radiation dose was 1.3 +/- 1.3 Sv. The dose needed to cause radiation skin injury was exceeded during 22% of procedures. The overall mean effective absorbed dose from catheter ablation procedures was 0.025 Sv for female patients and 0.017 Sv for male patients. This degree of radiation exposure would result in an estimated 1,400 excess fatal malignancies in female patients and 2,600 excess fatal malignancies in male patients per 1 million patients.

Executive and motivational control of performance task behavior, and autonomic heart-rate regulation in children: physiologic validation of two-factor solution inhibitory control

Forty-two (42) children (mean age 10.6 years) from mainstream public (N = 22) and therapeutic schools (N = 20) completed performance tasks assessing executive and motivational influences on motor responses. In a separate protocol, children underwent physiologic challenges of paced breathing and supine to standing postural change, while heart rate was continuously monitored. Executive control was associated with vagal modulation of respiratory driven, high-frequency heart-rate variability (t = 2.20, p < .03), whereas motivational control was associated with sympathetic modulation of posturally driven, low-frequency heart-rate variability (t = -2.22, p < .03). These findings supported a two-factor solution of inhibitory control derived in a previous study.

Long-term performance of bipolar epicardial atrial pacing using an active fixation bipolar endocardial lead

Bipolar epicardial leads are not yet widely available for atrial use. Since September 1986, we have used a bipolar active fixation endocardial lead (Cardiac Pacemakers model number's 4266, 4268, and 4269) as a bipolar epicardial atrial lead by attaching the corkscrew tip to the atrial surface and imbricating atrial tissue around the more proximal electrode. A total of 77 bipolar epicardial atrial leads have been implanted using this approach in 72 patients with congenital heart disease (ages 3 months to 38.7 years; mean 8.9 +/- 8.8 years). Indications for atrial pacing included AV block (n = 46), sinus node dysfunction (n = 17), and antitachycardial pacing (n = 9). Indications for epicardial pacing included the presence of an intracardiac right to left shunt (n = 33), concomitant cardiac surgery (n = 26), surgeon preference (n = 7), and lack of transvenous access to the atrial endocardium (n = 6). Follow-up (median 23 months; mean 28.0 +/- 23.1 months; range 1-78 months) data beyond 1 month postimplantation were available for 44 leads. Atrial sensing was > or = 2.0 mV for 26 leads (59%) with sensing possible at > or = 0.75 mV for 42 leads (95%). Threshold data were available at 5 V for 37 leads and at 2.5 V for 36 leads with mean pulse width thresholds measuring 0.21 +/- 0.33 ms and 0.34 +/- 0.34 ms, respectively. Two leads failed (high capture thresholds at 5 days [n = 1], lead fracture at 42 months [n = 1]; one of which was replaced. Four additional leads were replaced electively (marginal thresholds [n = 1], intermittent phrenic nerve stimulation [n = 1], damaged during subsequent surgery [n = 1], clinically irrelevant insulation break [n = 1]) concomitant with additional cardiac surgery. Until a commercially available lead is developed and released, improvisation with a bipolar active fixation endocardial lead as a bipolar epicardial atrial lead is a reasonable approach to providing bipolar atrial sensing and pacing in patients for whom endocardial pacing is contraindicated.

Tricyclic antidepressants and cardiac autonomic control in children and adolescents

OBJECTIVE

To elucidate the effects of tricyclic antidepressants on sympathetic and vagal modulation of heart rate variability.

METHOD

Seventy-five children and adolescents (mean age 10.5 years, SD 2.0) from therapeutic and regular schools underwent challenges of paced breathing and orthostatic postural change, while heart rate was continuously recorded. Teachers completed dimensional ratings of behavior to quantity anxiety and conduct disorder. Spectral analysis of heart rate variability was utilized to decompose the postural (sympathetic) and respiratory (vagal) contributions to beat-to-beat variations in heart rate.

RESULTS

Under conditions in which cardiac vagal effects were expected to predominate, subjects medicated with tricyclic antidepressants (n = 13) showed significantly reduced vagal modulation of heart rate variability (F[5,69] = 5.23, p < .003), higher heart rates (F[5,69] = 5.54, p < .002), and higher relative sympathovagal balance (F[5,69] = 5.51, p < .002) than nonmedicated (n = 42) and medicated comparison groups (n = 20), even after controlling for the effects of age and psychopathology.

CONCLUSIONS

The relative loss of cardiac vagal control in young subjects medicated with tricyclic antidepressants, considered in the context of factors known to be associated with the development of tachyarrhythmias, presents as yet another risk, especially when coupled with factors such as maturational effects and psychopathology.

Five-year experience with radiofrequency catheter ablation: implications for management of arrhythmias in pediatric and young adult patients

OBJECTIVE

A review of the results of the first 5 years of radiofrequency catheter ablation procedures performed at Children's Hospital, Boston, a large tertiary referral center for patients with congenital heart disease and arrhythmias common to the infant, child, and young adult.

STUDY DESIGN

A retrospective review of 410 consecutive procedures in 346 patients who underwent at least one application of radiofrequency energy for the treatment of recurrent supraventricular or ventricular tachycardia.

RESULTS

The overall final success rate for all diagnoses was 90%, with a higher success rate in patients with an accessory pathway (96%). During the 5-year study period, the success rate improved while the rates of failures and late recurrences declined. The incidence of serious complications was 1.2% (1 late death, 1 ventricular dysfunction, 1 complete heart block, 1 cardiac perforation, and 1 cerebrovascular accident).

CONCLUSIONS

This report of a large series of radiofrequency catheter ablation procedures performed at an institution committed to treating congenital heart disease and pediatric arrhythmias confirms the safety and efficacy of this procedure. The pediatric cardiologist/electrophysiologist treating such patients must be aware of specific technical, anatomic, and electrophysiologic variations in the pediatric patient that are critical to the success of this therapy.

Interpreting open- and closed-loop transfer relations between cardiorespiratory parameters: lessons learned from a computer model of beat-to-beat cardiovascular regulation

A computer model of cardiovascular control has been developed based on the response characteristics of cardiovascular control components derived from experiments in animals and humans. Results from the model were compared to those obtained experimentally in humans, and the similarities and differences were used to identify both the strengths and inadequacies of the concepts used to form the model. Findings were confirmatory of some concepts but contrary to some which are firmly held in the literature, indicating that understanding the complexity of cardiovascular control probably requires a combination of experiments and computer models which integrate multiple systems and allow for determination of sufficiency and necessity.

Heart rate variability: origins, methods, and interpretive caveats

Components of heart rate variability have attracted considerable attention in psychology and medicine and have become important dependent measures in psychophysiology and behavioral medicine. Quantification and interpretation of heart rate variability, however, remain complex issues and are fraught with pitfalls. The present report (a) examines the physiological origins and mechanisms of heart rate variability, (b) considers quantitative approaches to measurement, and (c) highlights important caveats in the interpretation of heart rate variability. Summary guidelines for research in this area are outlined, and suggestions and prospects for future developments are considered.

Efficacy of radiofrequency ablation for control of intraatrial reentrant tachycardia in patients with congenital heart disease

BACKGROUND

Intraatrial reentrant tachycardia (IART) is a common problem in patients with congenital heart disease (CHD). The progression of clinical symptoms of IART and their response to radiofrequency (RF) ablation are not yet well described.

OBJECTIVES

The objective of the study was to determine the early and midterm success rates of RF ablation in effecting a reduction of clinical arrhythmic events in patients with IART and CHD.

METHODS

Clinical records of patients undergoing early, successful RF ablation were analyzed retrospectively to document the occurrence and frequency of documented IART, cardioversion and arrhythmia-related hospital visits before and after ablation.

RESULTS

Fifty-five catheterizations for intended RF ablation of IART were performed in 45 patients (mean [+/-SD] age 24.5 +/- 10.5 years, 40 after surgical palliation of CHD). Early success was achieved for one or more IART circuits in 33 patients (73%). Mean clinical follow-up of those patients with successful ablation is 17.4 +/- 11.3 months (total 574 patient-months). Documented IART recurrence was noted after 21 (53%) of 40 early, successful catheterizations in 17 (52%) of 33 patients, with a mean time to recurrence of 4.1 months, often with electrocardiographically novel configurations. A more prolonged and frequent history of IART was a univariate risk factor for recurrence. Seven patients underwent repeat RF ablations, and eight patients were restarted on antiarrhythmic medications after ablation. Two patients who had severe ventricular dysfunction before RF ablation died 1.5 and 11 months after RF ablation without known arrhythmia recurrence. Clinical events related to IART increased steadily in frequency for 24 months before RF ablation. Radiofrequency ablation resulted in a reduction of event frequency to levels significantly lower than those in the 12-month period before RF ablation and not significantly different from those levels observed at baseline 3 to 4 years before RF ablation.

CONCLUSIONS

In patients with successful RF ablation, the frequency of subsequent events was reduced compared with the 2 preceding years. However, recurrence of IART in patients who showed clinical improvement was frequent, and often revealed the presence of new IART configurations.

Radiofrequency ablation of intraatrial reentrant tachycardia after surgery for congenital heart disease

Intraatrial reentry tachycardia is a common cause of both morbidity and mortality after surgery for a variety of congenital heart defects. Despite an armamentarium of arrhythmia management tools, including drug therapy, antibradycardia, and antitachycardia pacing, and catheter ablation, management of these arrhythmias remains a challenge. This report briefly reviews the problem, assesses the current successes and failures of radiofrequency catheter ablation for treating it, and discusses a number of ongoing developments that may improve both early and late outcome.

High-rate atrial pacing as an innovative bridging therapy in a neonate with congenital long QT syndrome

INTRODUCTION

The neonatal presentation of the long QT syndrome is rare, although it is frequently accompanied by life-threatening arrhythmias. Infants may not survive childhood despite traditional management with beta-adrenergic blockade and pacing.

METHODS AND RESULTS

This case describes a newborn with a long QT interval, T wave alternans, intermittent 2:1 AV block, ventricular arrhythmias, and a family history of sudden death. After failing medical therapy, conventional VVI and DDD pacing were unsuccessful due to prolonged ventricular refractoriness and proarrhythmia. At 2 months of life, the child was treated with high-rate (180 ppm) atrial pacing to produce intentional 2:1 AV block. Following an episode of possible syncope at 16 months of age, an automatic implantable cardioverter defibrillator (ICD) was added. Finally, as recently reported, acutely induced hyperkalemia led to both a marked decrease in QTc and functional improvement in repolarization (consistent 1:1 AV conduction at rates to 180 beats/min). Spironolactone and dietary potassium were added and have produced the same effects chronically.

CONCLUSIONS

High-rate atrial pacing with 2:1 AV block is presented as a novel and "bridging" therapy for neonatal long QT syndrome and 2:1 AV block with ventricular arrhythmias. Definitive therapy with ICD implantation was then possible when patient size was substantially increased. The electrophysiologic response to intentional elevation of the serum potassium suggests a genetic defect in an inward potassium channel and demonstrates a possible therapy of long QT syndrome in some future patients.