Electrophysiological effects of ibutilide in patients with accessory pathways.

BACKGROUND: Atrial fibrillation (AF) may cause life-threatening ventricular arrhythmias in patients with Wolff-Parkinson-White syndrome. We prospectively evaluated the effects of ibutilide on the conduction system in patients with accessory pathways (AP). METHODS AND RESULTS: In part I, we gave ibutilide to 22 patients (18 men, 31+/-13 years of age) who had AF during electrophysiology study, including 6 pediatric patients

Reentrant tachycardia using two discrete atrioventricular nodes and a concealed atriofascicular pathway.

We describe a case of reentrant supraventricular tachycardia using two discrete atrioventricular (AV) nodes in the antegrade direction and a concealed atriofascicular pathway in the retrograde direction in a 21-year-old woman with superior-inferior ventricles and ventricular inversion. Using the Carto endocardial mapping system, two discrete AV nodes were identified as well as a separate decremental AV pathway located midway between the two nodes. Ablation of the separate pathway resulted in elimination of inducible tachycardia without loss of either AV node.

Intra-atrial reentry tachycardia in pediatric patients.

Intra-atrial reentry tachycardia (IART), also known as atrial flutter, is a major problem in pediatric cardiology and adult congenital cardiology. Patients have significant morbidity and even mortality associated with this arrhythmia. The use of antiarrhythmic medications has been disappointing in this population. Ablation techniques are being developed which offer some advantages over the use of medication. These techniques include: sophisticated mapping using entrainment, electro-anatomic and non-contact methods for assessment of the anatomy and the reentrant circuit; radiofrequency ablation methods which allow for the creation of linear and transmural lesions; and new methods for assessment of the effects of ablation which focus on the documentation of the creation of a new line of block. These new techniques provide hope for more effective ablation procedures and the possibility of definitive cure of atrial flutter in many patients in this population.

Endocardial stimulation of efferent parasympathetic nerves to the atrioventricular node in humans: optimal stimulation sites and the effects of digoxin.

UNLABELLED: The purposes of this study were to identify optimal sites of stimulation of efferent parasympathetic nerve fibers to the human atrioventricular node via an endocardial catheter and to investigate the interaction between digoxin and vagal activation at the end organ. METHODS: The ventricular rate was measured during atrial fibrillation, prior to and during parasympathetic nerve stimulation, in 8 patients taking digoxin and in 10 controls. High frequency electrical stimuli were delivered via an hexapolar or quadripolar electrode catheter, placed at the posteroseptal right atrium near the atrioventricular node (n=18 patients) or in the coronary sinus (n=12 of 18 patients). In 4 patients, stimulation was repeated after intravenous administration of 1 to 2 mg of atropine. RESULTS: Nerve stimulation prolonged the R-R interval in all patients. Stimulation close to the posteroseptal right atrium led to maximal atrioventricular nodal slowing. The mean R-R intervals at baseline and during parasympathetic nerve stimulation (60 mA) from the posteroseptal right atrium and the proximal coronary sinus were 581+/-79 ms, 2440+/-466, and 900+/-228 ms respectively (p=0.0001). The response to nerve stimulation was greater in patients taking digoxin than in patients not taking the drug (p=0.02). Junctional rhythm occurred during nerve stimulation in 8/8 patients taking digoxin and 0/10 not taking the drug (p=0.0001). The response to stimulation was eliminated after atropine (p=0.01). CONCLUSIONS: Parasympathetic nerves to the atrioventricular node were stimulated from the proximal coronary sinus as well as the posteroseptal right atrium. Stimulation at the posteroseptal right atrium resulted in the greatest response, and digoxin enhanced this response. The augmented response suggests that an interaction may exist between parasympathetic stimulation and digoxin at the end organ.

Congenital heart block: development of late-onset cardiomyopathy, a previously underappreciated sequela.

OBJECTIVE: We report 16 infants with complete congenital heart block (CHB) who developed late-onset dilated cardiomyopathy despite early institution of cardiac pacing. BACKGROUND: Isolated CHB has an excellent prognosis following pacemaker implantation. Most early deaths result from delayed initiation of pacing therapy or hemodynamic abnormalities associated with congenital heart defects. METHODS: A multi-institutional study was performed to identify common clinical features and possible risk factors associated with late-onset dilated cardiomyopathy in patients born with congenital CHB. RESULTS: Congenital heart block was diagnosed in utero in 12 patients and at birth in four patients. Ten of 16 patients had serologic findings consistent with neonatal lupus syndrome (NLS). A pericardial effusion was evident on fetal ultrasound in six patients. In utero determination of left ventricular (LV) function was normal in all. Following birth, one infant exhibited a rash consistent with NLS and two had elevated hepatic transaminases and transient thrombocytopenia. In the early postnatal period, LV function was normal in 15 patients (shortening fraction [SF] = 34 +/- 7%) and was decreased in one (SF = 20%). A cardiac pacemaker was implanted during the first two weeks of life in 15 patients and at seven months in one patient. Left ventricular function significantly decreased during follow-up (14 days to 9.3 years, SF = 9% +/- 5%). Twelve of 16 patients developed congestive heart failure before age 24 months. Myocardial biopsy revealed hypertrophy in 11 patients, interstitial fibrosis in 11 patients, and myocyte degeneration in two patients. Clinical status during follow-up was guarded: four patients died from congestive heart failure; seven required cardiac transplantation; one was awaiting cardiac transplantation; and four exhibited recovery of SF (31 +/- 2%). CONCLUSIONS: Despite early institution of cardiac pacing, some infants with CHB develop LV cardiomyopathy. Patients with CHB require close follow-up not only of their cardiac rate and rhythm, but also ventricular function.

Radiofrequency catheter ablation: indications and complications.

Radiofrequency catheter ablation was first described in pediatric patients in the early 1990s. Since then, multiple advances in the technology and understanding of radiofrequency ablation have allowed this technique to blossom into one of the most powerful therapeutic tools available to the pediatric electrophysiologist. This treatment has, in the majority of cases, replaced arrhythmia surgery as the definitive cure for most arrhythmias. Ablation therapy is commonly implemented as an elective procedure to treat paroxysmal reentrant supraventricular tachycardia. There are several advantages to this therapy when used in the common indications: no exercise restrictions, no need for chronic drug therapy, and the avoidance of hospital visits for breakthrough episodes. This review will discuss the indications for radiofrequency ablation in the current era. In order to fully discuss this issue, this review will include the prior treatment of arrhythmias, current success rates, complications, and potential long-term issues.

Importance of atrial flutter isthmus in postoperative intra-atrial reentrant tachycardia.

BACKGROUND: In survivors of congenital heart surgery, intra-atrial reentrant tachycardia (IART) often develops. Previous reports have emphasized the atriotomy scar as the central barrier around which a reentrant circuit may rotate but have not systematically evaluated the atrial flutter isthmus in such patients. We sought to determine the role of the atrial flutter isthmus in supporting IART in a group of postoperative patients with congenital heart disease. METHODS AND RESULTS: Nineteen postoperative patients with IART underwent electrophysiological studies with entrainment mapping of the atrial flutter isthmus for determining postpacing intervals. Radiofrequency ablation was performed at the identified isthmus in an effort to create a complete line of block. Twenty-one IARTs were identified in 19 patients, with a mean tachycardia cycle length of 293+/-73 ms. The atrial flutter isthmus was part of the circuit in 15 of 21 (71. 4%). In the remaining 6 of 21, the ablation target zone was at sites near atrial incisions or suture lines. Ablation was successful in 19 of 21 (90.4%) IARTs and in 14 of 15 (93.3%) cases at the atrial flutter isthmus. CONCLUSIONS: In most of our postoperative patients, the atrial flutter isthmus was part of the reentrant circuit. The fact that the atrial flutter isthmus is vulnerable to ablation suggests that whenever IART occurs late after repair of a congenital heart defect, the atrial flutter isthmus should be evaluated. These data support the theory that some form of conduction block between the vena cava is essential for the establishment of a stable substrate for the atrial flutter reentrant circuit.

Advances in the treatment of cardiac rhythm disturbances.

Many advances in the care of children with cardiac rhythm disturbances have been made in the past year. From the fetus with supraventricular tachycardia to the adolescent with vasovagal syncope, new and effective therapies have evolved. Molecular genetics has led to monumental leaps in the understanding of long QT syndrome, and a new pharmacologic alternative to cardioversion has been introduced. There have also been new and noteworthy developments in the more established area of radiofrequency ablation. These concern safety and also touch on one of today's most controversial areas, cost effectiveness. This article discusses each of these advances in the realm of pediatric cardiac electrophysiology.

Characterization of sinoatrial parasympathetic innervation in humans.

INTRODUCTION: The response to sinoatrial parasympathetic nerve stimulation (shortened atrial refractoriness) was used to determine the atrial distribution of these nerve fibers in humans. We hypothesized that, in humans, parasympathetic nerves that innervate the sinoatrial node also innervate the right atrium and that the greatest density of innervation is near the sinoatrial nodal fat pad. METHODS AND RESULTS: Temporary epicardial wire electrodes were sutured in pairs in the sinoatrial nodal fat pad, high right atrium, and right ventricle by direct visualization during coronary artery bypass surgery in nine patients. Appropriate electrode placement was confirmed by electrically stimulating the fat pad in the operating room to prolong sinus cycle length by 50%. Experiments were performed in the electrophysiology laboratory 1 to 5 days after surgery. Programmed atrial stimulation was performed via an endocardial electrode catheter advanced to the right atrium. The catheter tip electrode was moved in 1-cm concentric zones around the epicardial wires by fluoroscopic guidance. Atrial refractoriness was determined in the presence and absence of sinoatrial parasympathetic nerve stimulation at each catheter site. In 8 of 9 patients, parasympathetic nerve stimulation reproducibly prolonged sinus cycle length by 50%. There was no effect on AV nodal conduction (no prolongation of PR interval) and no change in AV nodal refractoriness. Atrial effective refractory periods reproducibly shortened in response to parasympathetic nerve stimulation in 1-cm zones up to 3 cm surrounding the fat pad, by a mean (+/- SEM) of 26.6+/-4.3 msec (zone 1), 11.4+/-1.8 msec (zone 2), and 10.0+/-2.5 msec (zone 3), respectively (P = 0.0001). At distances > 3 cm from the fat pad, the effective refractory period did not shorten. CONCLUSION: Stimulation of parasympathetic nerves that innervate the sinoatrial node shortened atrial refractoriness in humans.

Preexcitation secondary to fasciculoventricular pathways in children: a report of three cases.

INTRODUCTION: Fasciculoventricular connections are the rarest form of accessory pathways leading to preexcitation. Electrophysiologic characteristics of these pathways include ventricular preexcitation with normal PR and AH intervals and short HV intervals during sinus rhythm. In addition, atrial overdrive pacing prolongs the PR interval without affecting the HV interval or the degree of preexcitation. METHODS AND RESULTS: From March 1994 through February 1997, 3 of 59 pediatric patients referred for electrophysiologic study for preexcitation on surface ECGs were found to have fasciculoventricular pathways. Two patients had no inducible supraventricular tachycardia. One patient had successful ablation of both a left lateral pathway and a concealed anterolateral pathway that had facilitated antidromic and orthodromic supraventricular tachycardias, respectively. CONCLUSION: Children often manifest minimal preexcitation via accessory AV pathways due to rapid AV conduction and/or left lateral pathway location. Fasciculoventricular pathways may masquerade as Wolff-Parkinson-White syndrome. Separation of the two diagnoses depends on the demonstration of specific electrophysiologic criteria.

Severe cyanosis in a newborn after transvenous pacing wire placement.

Inadvertent disruption of tricuspid valve apposition by a pacing catheter in a neonate is described. Severe cyanosis due to atrial level shunting resulted, similar to the pathophysiologic state seen in Ebstein's anomaly.

Electrical-anatomic correlations between typical atrial flutter and intra-atrial re-entry following atrial surgery.

It is well known that in typical (or type I) atrial flutter, conduction proceeds counterclockwise, up the interatrial septum and down the right atrial wall anterior to the crista terminalis (CT). Recent careful mapping studies using entrainment pacing have clearly shown the importance of the CT and the eustachian valve ridge (EVR), which act as fixed barriers to intra-atrial conduction and interact with other barriers, including the tricuspid valve, inferior vena cava (IVC), and coronary sinus os, to create a long macroreentrant circuit. Ablative lesions are directed at the isthmus between the tricuspid valve and the IVC or between the tricuspid valve and the EVR. Patients who have had cardiac surgery may have typical atrial flutter, either counterclockwise or clockwise, and prior surgery may act to stabilize the circuit. Such patients may also have atypical flutter, which does not utilize this circuit. Surgical closure of septal defects requires a long anterior oblique atriotomy. Commonly, reentrant circuits are identified that use this barrier, as well as the tricuspid valve and CT, and are confined to the anterior atrial wall and do not involve the typical flutter isthmus. These may be ablated at the lower or the upper end of the atriotomy, extending the block to the tricuspid valve, IVC, or superior vena cava. After the Senning or Mustard procedure, typical flutter is common, and the baffle bisects the isthmus at the site of the EVR, perhaps enforcing block. Anterior atriotomy-mediated reentry also is seen, and both circuits need to be approached in a retrograde manner. After the Fontan atriopulmonary connection, atriotomies and atrial dilation may interact to make reentry more likely. After the "lateral tunnel" Fontan (cavopulmonary connection) suture lines are similar to those of the Senning procedure, but nearly all right atrial anatomy is in the pulmonary venous atrium. Such circuits may need to be approached via an atrial fenestration.

Atrial flutter: an uncommon pediatric manifestation of hyperthyroidism.

OBJECTIVE: Atrial flutter is an uncommon arrhythmia in the pediatric population except for the immediate newborn period or following atrial repair of congenital heart disease. In children the diagnosis of atrial flutter may be difficult, attributable to rapid atrioventricular conduction and superimposition of flutter waves on QRS and T waves. Atrial flutter secondary to hyperthyroidism has been rarely reported in older adults, but there are no reports of children presenting with atrial flutter as the initial manifestation of hyperthyroidism. CASE REPORT: We report an interesting case of hyperthyroidism in a 3-year-old presenting with congestive heart failure and atrial flutter with 1:1 atrioventricular conduction. The responses to adenosine administration and to cardioversion were unusual and ultimately helpful in suggesting the diagnosis of hyperthyroidism. CONCLUSION: When atrial flutter is encountered in a pediatric patient in whom there is 1:1 atrioventricular conduction, a lack of a response to adenosine, and persistent sinus tachycardia after cardioversion, the clinician should be alert to the possibility of thyrotoxicosis.

Radiofrequency ablation of accessory pathways associated with congenital heart disease.

The coexistence of significant congenital cardiac disease with accessory pathways is not uncommon, and presents a number of issues for clinical management. These issues include the propensity of such patients to have poorly tolerated tachycardia; the difficulties in choosing appropriate medical management given potential problems with preexisting sinus node disease, poor contractility, and the possibility of proarrhythmia; the need to seriously consider ablation prior to, or at the time of, intracardiac repair of congenital cardiac defects; and finally, the difficulties that complex anatomy may pose to the interventional electrophysiologist. Definitive management requires expertise both in electrophysiology and in pediatric cardiology. Success can usually be achieved with a careful, anatomically precise approach, combined with imagination and persistence. Because of the difficulties with medical management, catheter ablation may be the most attractive modality for control of accessory pathway tachycardia in this patient population.

Indications for radiofrequency ablation in the pediatric population.

Pediatric radiofrequency ablation procedures have become commonplace since their introduction to clinical practice 6 years ago. Excellent success rates coupled with low complication rates have allowed these procedures to be offered as first-line therapy to many children. This review focuses on the current indications for radiofrequency ablation in children. These indications are not the same as for adults. They are based on the natural history of various forms of arrhythmias, the risks of the procedure, and the current success rates of the procedures, all of which are dependent upon the age of the patient.