Complexities of junctional tachycardias

The atrioventricular junction is a compact area in which most of the known electrophysiologic substrates and mechanisms play a role in the genesis and maintenance of tachyarrhythmias. The purpose of this review is to summarize the data on normal atrioventricular junction anatomy and electrophysiologic function and correlate that information with surface electrocardiographic recordings, intracardiac electrophysiologic data, and interventional data from surgical and catheter techniques. Models of tachycardia mechanisms are proposed for typical and atypical atrioventricular nodal reentrant tachycardia, permanent junctional reciprocating tachycardia, and orthodromic supraventricular tachycardias utilizing "intermediate septal" accessory connections.

Computer-guided surgery for tachyarrhythmias in children: current results and expectations

OBJECTIVES

The purpose of this report is to summarize our entire surgical experience in the treatment of tachyarrhythmias in children. We emphasize our application of a newer computerized mapping system for use in both the electrophysiology laboratory and the operating room to localize points of activation of the tachyarrhythmias.

BACKGROUND

A retrospective review was undertaken to examine the results of operative procedures in 290 children undergoing surgical treatment for tachyarrhythmias from 1977 to the present.

METHODS

Operative procedures were performed in 290 children and consisted of the following: surgical ablation of accessory pathways of the Kent bundle type (210 children); surgery with cryoablation for atrial ectopic tachycardia (35 children); surgical excision or cryoablation, or both, for ventricular tachycardia (26 children); cryoablation for the permanent form of junctional reciprocating tachycardia (15 children) and atrioventricular (AV) node reentrant tachycardia (4 children).

RESULTS

The surgical cure rate for accessory pathway tachycardia in the era before computerized mapping was 80% (41 patients) in the period from 1977 to 1982 and 95% (86 patients) in the period from 1982 to 1988. This rate improved to 100% (83 patients) after the advent of the computerized mapping technique. These improved results are probably due to a combination of factors, including increasing experience in electrophysiologic mapping and surgery, and cannot be attributed to the computerized mapping system alone. Surgical cure or major improvement in symptoms was documented in 33 (94%) of 35 patients with atrial ectopic tachycardia. Surgical cure was accomplished in 25 (96%) of 26 patients with the complex form of ventricular tachycardia. In 19 patients with the permanent form of junctional reciprocating tachycardia and the more typical AV node reentrant tachycardia, the surgical cure rate was 100%.

CONCLUSIONS

In all forms of supraventricular reentrant tachycardia that occur in children, preoperative computerized mapping techniques combined with intraoperative computerized mapping and surgical ablation can eliminate tachycardia at a success rate of close to 100%. Computerized mapping techniques are less accurate in patients with atrial ectopic tachycardia because of multiple foci and a broader surface area to be mapped. This experience demonstrates that excellent results can be achieved in the surgical treatment of tachyarrhythmias in children.

Flecainide acetate for treatment of tachyarrhythmias in children: review of world literature on efficacy, safety, and dosing

A review of all published experience with flecainide in infants, children, and fetuses was performed to evaluate the appropriate place of the drug in pediatric practice and to determine dosing guidelines. A total of 704 case references was generated. Flecainide appeared to be safe (no deaths with usual oral dosing, < 1% serious proarrhythmia) and effective (73% to 100% control, depending on mechanism) in children with supraventricular tachycardia. The drug was very effective for treatment of fetal tachyarrhythmias. Flecainide may not be safe for children who have structurally abnormal hearts and atrial flutter or ventricular arrhythmias. The safety of flecainide for patients with ventricular arrhythmias and normal hearts requires further investigation. Pharmacokinetic data reveal an age-dependent change in elimination half-life. Patients younger than 1 year of age have a plasma elimination half-life that is similar to that in children older than 12 years (i.e., 11 to 12 hours). Children aged 1 to 12 years have a mean elimination half-life of 8 hours. The effective flecainide dose is 100 to 200 mg/m2/day or 1 to 8 mg/kg/day. Toxicity may occur with doses in excess of these ranges, especially when high doses are accompanied by low serum trough levels. Milk blocks flecainide absorption, and toxicity may become manifest when milk products are removed from the diet.

Late ventricular arrhythmia and sudden death following direct-current catheter ablation of the atrioventricular junction

Early reports of direct-current catheter ablation (DCCA) of the atrioventricular (AV) junction for resistant AV tachycardias documented efficacy of DCCA with little morbidity. Nine patients underwent DCCA at our institution 4 to 9 years ago: 3 patients had DCCA in the coronary sinus for permanent junctional reciprocating tachycardia, 2 patients had His ablation, 2 had coronary sinus and His ablation for permanent junctional reciprocating tachycardia, and 2 had DCCA for congenital tachycardia, and 2 had DCCA for congenital junctional ectopic tachycardia. Shocks (total 1 to 5) ranged from 12.5 to 400 J. Five patients had pacemaker implant at the time of DCCA. During follow-up, 3 patients developed clinical ventricular tachycardia: all 3 had DCCA of the His bundle. One asymptomatic patient with ventricular tachycardia, who had DCCA of the bundle of His, died suddenly 6 years later with ventricular fibrillation. Autopsy revealed 2 ventricular scars: 1 extending from the AV junction and 1 in the outflow tract. No patient with DCCA limited to the coronary sinus developed ventricular tachycardia. DCCA of the His bundle can result in late ventricular arrhythmias, possibly a result of extension of the DCCA lesion into the ventricle. These late findings should be considered in evaluating the safety and efficacy and follow-up for patients undergoing radiofrequency ablation.

Prolonged QT interval in neonates: Benign, transient, or prolonged risk of sudden death

To determine the factors relating to prognosis, the records of 15 neonates with persistent prolongation of the QT interval on the electrocardiogram after the fourth day of life were reviewed. Patients were admitted for symptoms (syncope, cardiac failure, or seizures), abnormal auscultation with an irregular heart rate or bradycardia, or because of a family history of a long QT syndrome. All infants had a long QTc, ranging from 0.46 to more than 0.70 second. Eight patients who had a QTc over 0.60 second developed severe ventricular arrhythmias (torsades de pointes, ventricular tachycardia) or second-degree AV block. Twelve of 15 were treated with beta-blocking agents, combined with ventricular pacing in five cases. Four infants died in the first month of life; they all had a very long QT interval and had experienced ventricular arrhythmias and AV block. Six children are still being treated with beta-blocking agents for the long QT syndrome and are doing well. In five infants, electrocardiographic abnormalities were transient and the QT interval returned to normal within 1 year. Therefore (1) prolongation of the QT interval in neonates may be transient or may represent an early form of the long QT syndrome and (2) the length of the QT interval may provide data on prognosis: those with a QTc less than 0.50 second returned to normal; those with a QTc greater than 0.60 second were associated with severe arrhythmias and four of eight infants died.

Electrocardiographic criteria for diagnosis of acute myocardial infarction in childhood

Myocardial infarction (MI), a common occurrence in adults, is generally considered to be rare in children. Electrocardiographic criteria for diagnosis of MI in adults are well known and accepted, but no general criteria exist for children. We report 37 autopsy-proved cases of transmural MI and electrocardiographic evidence of MI in 30 of these cases. A variety of conditions previously reported to produce "pseudo-infarction" are included in these cases of MI, including myocarditis, hypertrophic cardiomyopathy, and the cardiomyopathy of Duchenne's muscular dystrophy. Compilation of the electrocardiographic data in all patients allowed for the development of criteria for this diagnosis of MI in childhood, and include wide Q waves (greater than 35 ms) with or without Q-wave notching, ST-segment elevation (greater than 2 mm), and prolonged QT interval corrected for heart rate (QTc greater than 440 ms) with accompanying Q-wave abnormalities. With use of these electrocardiographic criteria, an additional 3 patients were subsequently diagnosed prospectively with MI and confirmed on autopsy. Pathologic evaluation confirmed the location of infarction predicted by the electrocardiograms in all 3 cases.

Pulmonary artery banding and subaortic stenosis in patients with single ventricle: surgical alternatives and clinical outcome

Subaortic obstruction is a potential problem in patients with single ventricle and a subaortic outflow chamber. Previous reports have indicated an association between pulmonary artery banding and the development of subaortic obstruction. The purpose of this study was to determine the incidence of subaortic obstruction in our patients with this cardiac anomaly who have undergone pulmonary artery banding, and to determine the eventual outcome in those who did develop obstruction. By reviewing cardiac catheterizations performed between 1977 and 1985, we found 36 patients with single ventricle and a subaortic outflow chamber. Ten patients had been lost to follow-up or had died within 3 months of banding. Twelve of the remaining 26 patients developed a pressure gradient between the left ventricle and ascending aorta, although 7 of these 12 had minimal gradients. Eight of the 12 have undergone further surgery, with the best results in patients who underwent a combined modified Fontan and Damus-Kaye-Stansel procedure. We believe that although subaortic obstruction may develop in patients with single ventricle after pulmonary artery banding, the degree of obstruction is often minimal, and in more severe cases the obstruction can be alleviated with a Damus-Kaye-Stansel procedure. (Texas Heart Institute Journal 1992; 19:15-20)

Sudden cardiac death in the pediatric population

Sudden death in children as in adults is usually due to cardiac disease. Sudden death in the pediatric population may be divided into the sudden infant death syndrome, sudden death in previously apparently healthy children, and sudden death in patients with known cardiac disease. The sudden infant death syndrome is not proved to be due to a cardiac cause and may well be due to central nervous system and/or pulmonary causes. However, interest remains in the cardiac hypothesis. Recent work from our laboratory shows that screening for prolonged QT interval in normal infants is not likely to detect those prone to sudden infant death syndrome. In children with apparently normal hearts, symptoms of syncope or palpitation should be given close attention. Detailed electrocardiography and echocardiography will detect many, but not all, children with subtle forms of heart disease. Vigorous treatment may prevent sudden death in many of these children. Some sort of screening program should be devised for varsity athletes. Children with congenital heart defects are now, for the most part, corrected early in life, so that the congenital heart defect itself rarely causes sudden, unexpected death. The residua and sequelae of the heart defect and the surgery to repair it, however, may lead to sudden death. Improvements in surgical technique and earlier repair of congenital cardiac defects will ameliorate this problem. Prospective evaluation of postoperative patients and attention to dysrhythmias can prevent sudden deaths in those who are prone to them.

Surgery for ventricular and atrial tachyarrhythmias in children: state of the art, 1992

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The long QT syndrome. Prospective longitudinal study of 328 families

BACKGROUND

The Long QT Syndrome (LQTS) is an infrequently occurring familial disorder in which affected individuals have electrocardiographic QT interval prolongation and a propensity to ventricular tachyarrhythmic syncope and sudden death. We prospectively investigated the clinical characteristics and the long-term course of 3,343 individuals from 328 families in which one or more members were identified as affected with LQTS (QTc greater than 0.44 sec1/2).

METHODS AND RESULTS

The first member of a family to be identified with LQTS, the proband, was usually brought to medical attention because of a syncopal episode during childhood or teenage years. Probands (n = 328) were younger at first contact (age 21 +/- 15 years), more likely to be female (69%), and had a higher frequency of preenrollment syncope or cardiac arrest with resuscitation (80%), congenital deafness (7%), a resting heart rate less than 60 beats/min (31%), QTc greater than or equal to 0.50 sec1/2 (52%), and a history of ventricular tachyarrhythmia (47%) than other affected (n = 688) and unaffected (n = 1,004) family members. Arrhythmogenic syncope often occurred in association with acute physical, emotional, or auditory arousal. The syncopal episodes were frequently misinterpreted as a seizure disorder. By age 12 years, 50% of the probands had experienced at least one syncopal episode or death. The rates of postenrollment syncope (one or more episodes) and probable LQTS-related death (before age 50 years) for probands (n = 235; average follow-up 54 months per patient) were 5.0% per year and 0.9% per year, respectively; these event rates were considerably higher than those observed among affected and unaffected family members.

CONCLUSIONS

Among 232 probands and 1,264 family members with prospective follow-up, three factors made significant independent contributions to the risk of subsequent syncope or probable LQTS-related death before age 50 years, whichever occurred first (Cox hazard ratio; 95% confidence limits): 1) QTc (1.052; 1.017, 1.088), 2) history of cardiac event (3.1; 1.3, 7.2), and 3) heart rate (1.017; 1.004, 1.031). The findings from this prospective longitudinal study highlight the clinical features, risk factors, and course of LQTS.

Active fixation of endocardial pacing leads: the preferred method of pediatric pacing

Pacing system failure due to lead related problems may necessitate repositioning or explantation of the problem lead. Pediatric patients with permanent pacemakers have additional considerations that necessitate revision or explantation of pacing leads. Active fixation type leads appear to offer the physician advantages over passive fixation leads that may make them the lead of choice for use in children. We reviewed our experience with active fixation type leads to determine whether the ease with which these leads could be revised or explanted justified recommending their use in our patients. Eleven patients underwent 13 lead revisions. The time from implant to revision was a mean of 12.3 months. Six patients had previously undergone repair of a congenital heart defect. Modes of pacing were: DDD (seven); AAI (three); and VVI (one). Exposed, isodiametric leads accounted for 11/13 leads. Leads were successfully explanted in nine cases and repositioned in four cases. The only lead that could not be revised and resulted in retention was a nonisodiametric, retractable helix lead at the junction of the subclavian vein and clavicle. We conclude isodiametric active fixation leads can be safely repositioned or explanted in children and should be considered the preferred method for endocardial pacing in children.

Clinical course of idiopathic dilated cardiomyopathy in children

Previous studies in adults with dilated cardiomyopathy suggest that the presence of arrhythmia, especially ventricular tachycardia, correlates with increased mortality. We performed a retrospective analysis of 63 children with idiopathic dilated cardiomyopathy to determine the prognostic significance of arrhythmias and other findings with respect to mortality. The mean age at diagnosis of the cardiomyopathy was 4.96 +/- 5.3 years. The overall mortality rate was 16% over a 10 year follow-up period. Persistent congestive heart failure and ST-T wave changes correlated with increased mortality (p less than 0.05). No other variables affected outcome. Arrhythmias were found in 46% of the patients; of the arrhythmias, 48% were atrial arrhythmias. Ventricular tachycardia was present in six patients. Death occurred in 4 (14%) of 29 patients with known arrhythmia; 1 of the 5 died suddenly. The remaining 6 deaths in the series occurred in the 34 patients without a documented arrhythmia. It is concluded that 1) arrhythmias are frequently seen in children with dilated cardiomyopathy but are not predictive of outcome; 2) sudden death in children with this disease is rare; and 3) persistent congestive heart failure portends a poor prognosis.

Sudden death in the young

Sudden cardiovascular death in children and adolescents may occur without premonitory symptoms. Awareness of risk patterns can provide effective prevention in some cases. Antiarrhythmic therapy aimed at both atrial and ventricular tachyarrhythmias can reduce unexpected mortality. A major focus is curbing the risks faced by young athletes. Another is risk management after cardiac surgery.

The pulmonary artery lasso: epicardial pacing lead causing right ventricular outflow obstruction

Permanent pacing in small children may require placement of an epicardial pacing system. This report describes a young child who underwent pacemaker implantation with epicardial ventricular lead placement in infancy as an adjunct to antiarrhythmic therapy for congenital junctional ectopic tachycardia. At 5 years of age, a harsh systolic murmur was detected for the first time. Evaluation by catheterization and transluminal echocardiography showed right ventricular outflow obstruction (pressure gradient 40 mmHg) secondary to extrinsic compression by the epicardial lead. Surgical removal of the lead relieved the obstruction.

The child with recurrent syncope: autonomic function testing and beta-adrenergic hypersensitivity

Recurrent syncope in the child with a normal heart poses both diagnostic and therapeutic problems. To assess autonomic contributions to syncope, formal autonomic function testing was performed in 22 children (aged 7 to 18 years) with recurrent syncope and a normal heart. Autonomic testing consisted of eight to nine separate tests; 14 of the 22 patients had reproduction of syncope or symptoms during testing. Patients with a positive test had a lower norepinephrine level while supine (334 +/- 86 versus 547 +/- 169 pg/ml, p less than 0.01) and lower norepinephrine level in the upright position (628 +/- 219 versus 891 +/- 270 pg/ml, p less than 0.05) than did patients with a negative test. The slope of heart rate response versus log isoproterenol dose was greater in patients with a positive test than in those with a negative test (1.70 +/- 0.70 versus 0.89 +/- 0.19, p less than 0.01). All five patients with a positive test who were given intravenous propranolol had elimination of syncope with repeat testing. Eight of 10 patients with a positive test were successfully treated with atenolol, including 2 patients without prior resolution of symptoms after pacemaker implantation for symptoms attributed to bradycardia. Beta-adrenergic hypersensitivity may cause recurrent syncope in young patients. Inappropriate heart rate response to standing may elicit the Bezold-Jarisch reflex, resulting in bradycardia or hypotension, or both, in some patients. Beta-adrenergic blockade is of benefit in many of these patients.

Bradycardia and syncope in children not controlled by pacing: beta-adrenergic hypersensitivity

Cardiac pacing is frequently employed in the therapy of children with syncope and documented bradycardia. This report describes two children, ages 7 and 9 years, who underwent placement of demand ventricular pacing systems for documented bradycardia and syncope. Cardiac catheterization and intracardiac electrophysiological studies failed to show evidence of structural abnormalities, sinus node or conduction system disease, inducible arrhythmias, or VA conduction in each patient. Both patients had persistent symptoms after pacemaker implantation. Autonomic function testing with continuous heart rate and blood pressure monitoring revealed exaggerated beta-adrenergic responses to simple standing and small doses of isoproterenol. Symptoms were completely eliminated with atenolol. In these two children, cardiac pacing alone was not adequate for relief of symptoms. Autonomic mechanisms of bradycardia and hypotension should be considered prior to implantation of permanent pacing systems in children.

Electrophysiologic evaluation of sinus node dysfunction in postoperative children and young adults utilizing combined autonomic blockade

Sinus node dysfunction is a recognized problem following surgery for congenital heart disease. Seven postoperative patients with sinus node dysfunction (5 Mustard, 1 tetralogy of Fallot, 1 Fontan) underwent electrophysiology study of sinus node function during combined autonomic blockade (CAB) utilizing propranolol 0.2 mg/kg i.v. and atropine 0.04 mg/kg i.v. to evaluate intrinsic sinus node function isolated from autonomic control. During CAB, intrinsic heart rate, intrinsic corrected sinus node recovery time, and intrinsic sinoatrial recovery time were measured. These results were compared with age-matched normal intrinsic data from our lab [normal (n = 7, mean age 9 years) IHR 128 +/- 24, intrinsic corrected sinus node recovery time 135 +/- 40 ms, intrinsic sinoatrial conduction time 86 +/- 19 ms]. Among postoperative Mustard patients (n = 5, mean age 13 years, mean years postoperative 11) 2 of 5 had clearly abnormal intrinsic sinus node function with nonsinus rhythm during CAB; 3 of 5 had sinus rhythm during CAB with normal or mildly abnormal intrinsic sinus node function. The postoperative case of tetralogy of Fallot (age 20 years, postoperative 14 years) had mildly abnormal intrinsic sinus node electrophysiology study. The postoperative case of Fontan (age 16 years, postoperative 1.5 years) had sinus rhythm at rest but left atrial rhythm during CAB. Different aspects of sinus node dysfunction may be expressed during resting electrophysiology study vs. electrophysiology study utilizing CAB. The pathophysiology of sinus node dysfunction among postoperative pediatric patients is not homogeneous with regard to the contribution of intrinsic sinus node dysfunction. In those patients with normal or mildly abnormal intrinsic sinus node function, an important pathophysiologic influence of the autonomic nervous system is implicated.