Ventricular size and function assessed by cardiac MRI predict major adverse clinical outcomes late after tetralogy of Fallot repair

BACKGROUND

Factors associated with impaired clinical status in a cross-sectional study of patients with repaired tetralogy of Fallot (TOF) have been reported previously.

OBJECTIVES

To determine independent predictors of major adverse clinical outcomes late after TOF repair in the same cohort during follow-up evaluated by cardiac magnetic resonance (CMR).

METHODS

Clinical status at latest follow-up was ascertained in 88 patients (median time from TOF repair to baseline evaluation 20.7 years; median follow-up from baseline evaluation to most recent follow-up 4.2 years). Major adverse outcomes included (a) death; (b) sustained ventricular tachycardia; and (c) increase in NYHA class to grade III or IV.

RESULTS

22 major adverse outcomes occurred in 18 patients (20.5%): death in 4, sustained ventricular tachycardia in 8, and increase in NYHA class in 10. Multivariate analysis identified right ventricular (RV) end-diastolic volume Z >or=7 (odds ratio (OR) = 4.55, 95% confidence interval (CI) 1.10 to 18.8, p = 0.037) and left ventricular (LV) ejection fraction <55% (OR = 8.05, 95% CI 2.14 to 30.2, p = 0.002) as independent predictors of outcome with an area under the receiver operator characteristic curve of 0.850. LV ejection fraction could be replaced by RV ejection fraction <45% in the multivariate model. QRS duration >or=180 ms also predicted major adverse events but correlated with RV size.

CONCLUSIONS

In this cohort, severe RV dilatation and either LV or RV dysfunction assessed by CMR predicted major adverse clinical events. This information may guide risk stratification and therapeutic interventions.

Spontaneously terminating apparent ventricular fibrillation during transesophageal electrophysiological testing in infants with Wolff-Parkinson-White syndrome

This article describes two infants with Wolff-Parkinson-White (WPW) syndrome in whom apparent VF occurred without antecedent AF or atrial flutter during routine transesophageal electrophysiological testing. Remarkably, this arrhythmia terminated spontaneously in both infants. The documentation of self-limited apparent VF, or polymorphic ventricular tachycardia close to VF, in transesophageal testing adds another dimension to the management of WPW.

Minimally invasive cardioverter defibrillator implantation for children: an animal model and pediatric case report

The smaller venous capacitance in infants and small children may hamper transvenous ICD lead implantation, and epicardial approaches require thoracotomy and have associated complications. The study evaluated the feasibility and performance of subcutaneous arrays and active can ICDs without transvenous shocking coils or epicardial patches. An immature and mature pig were anesthetized and ventilated. A pacing lead was inserted in the right ventricle for fibrillation induction and rate sensing. Subcutaneous arrays were positioned in the right and left chest walls. An ICD emulator was placed in abdominal and prepectoral pockets. Fluoroscopic images were acquired for each electrical vector configuration (array --> can, can --> array, array --> array, array + array --> can). Ventricular fibrillation was induced and DFT testing performed. Defibrillation was achieved in all ten trials in the immature piglet, with DFT < or = 9 J, regardless of vector configuration. Using a single subcutaneous array and active can, the shock impedance ranged from 28-36 ohms. With two arrays, shocking impedance fell to 15-22 ohms. In the adult pig, defibrillation was not accomplished with maximum energy of 40 J, using all vector configurations. Using data garnered from these experiments, this technique was then successfully performed in a 2-year-old child with VT and repaired congenital heart disease, needing an ICD. This study demonstrates the feasibility of leadless ICD implantation in an immature animal and successful implementation in a small child. A single subcutaneous array and active can resulted in excellent implant characteristics and DFTs with a minimally invasive approach. Defibrillation was not possible in a larger animal, possibly due to maximal available energy. This may be of value for small children requiring ICD implantation.

Postoperative ectopic atrial tachycardia in children with congenital heart disease

The causes and significance of postoperative ectopic atrial tachycardia (EAT) remain unknown. To identify factors associated with postoperative EAT in children after cardiac surgery, we retrospectively studied pre-, intra-, and postoperative variables. The median age for postoperative EAT cases was younger than the general population admitted for cardiac surgical procedures (6 vs 17 months old, p = 0.09). Trends for EAT cases included lower preoperative oxygen saturation (84% vs 99%, p = 0.001), more pre- and postoperative inotropic support, and atrial septostomy (24% vs 6%, p = 0.08). EAT cases had longer cardiopulmonary bypass times and clamp times (115 vs 88 minutes, p = 0.08; 63 vs 46 minutes, p = 0.03, respectively) and had a prolonged intensive care unit stay (10 vs 3 days, p <0.001). Deaths were recorded in 2 of 17 EAT cases versus 0 of 36 randomly selected controls (p = 0.10). EAT resolved before discharge in 10 of 16 surviving patients. The etiology of EAT appears to be multifactorial, and may include disruption of atrial septum, longer pump times, need for inotropic support, and potassium depletion. Thus, young, ill, cyanotic patients were most at risk for postoperative EAT. Although EAT was associated with prolonged intensive care, it resolved in most cases over time.

Supraventricular arrhythmias in children and young adults with implantable cardioverter defibrillators

INTRODUCTION

Rapidly conducted supraventricular tachycardias (SVTs) can lead to inappropriate device therapy in implantable cardioverter defibrillator (ICD) patients. We sought to determine the incidence of SVTs and the occurrence of inappropriate ICD therapy due to SVT in a pediatric and young adult population.

METHODS AND RESULTS

We undertook a retrospective review of clinical course, Holter monitoring, and ICD interrogations of patients receiving ICD follow-up at our institution between March 1992 and December 1999. Of 81 new ICD implantations, 54 eligible patients (median age 16.5 years, range 1 to 48) were identified. Implantation indications included syncope and/or spontaneous/inducible ventricular arrhythmia with congenital heart disease (30), long QT syndrome (9), structurally normal heart (ventricular tachycardia/ventricular fibrillation [VT/VF]) (7), and cardiomyopathies (7). Sixteen patients (30%) received a dual-chamber ICD. SVT was recognized in 16 patients, with 12 of 16 having inducible or spontaneous atrial tachycardias. Eighteen patients (33%) received > or =1 appropriate shock(s) for VT/VF; 8 patients (15%) received inappropriate therapy for SVT. Therapies were altered after an inappropriate shock by increasing the detection time or rate and/or increasing beta-blocker dosage. No single-chamber ICD was initially programmed with detection enhancements, such as sudden onset, rate stability, or QRS discriminators. Only one dual-chamber defibrillator was programmed with an atrial discrimination algorithm. Appropriate ICD therapy was not withheld due to detection parameters or SVT discrimination programming.

CONCLUSION

SVT in children and young adults with ICDs is common. Inappropriate shocks due to SVT can be curtailed even without dual-chamber devices or specific SVT discrimination algorithms.

Atrioventricular reciprocating tachycardia involving twin atrioventricular nodes in patients with complex congenital heart disease

INTRODUCTION

Histologic studies of autopsy specimens described the coexistence of two distinct AV nodes (so-called "Minckeberg sling" or "twin AV nodes") in specific congenital heart defects; however, the clinical electrophysiologic (EP) characteristics of twin AV nodes have not been characterized in detail.

METHODS AND RESULTS

Since April 1993, a total of seven patients with complex congenital heart disease presented with AV reciprocating tachycardia suspected to be mediated by twin AV nodes. A common anatomic finding was AV discordance ([S,L,L] or [I,D,D]) with a malaligned complete AV canal defect in 5 of 7 patients. Intracardiac EP study was performed in five cases, and ablation was attempted in three patients with successful elimination of tachycardia inducibility by interruption or modification of 1 of the 2 AV nodes. Important EP characteristics included (1) the existence of two discrete nonpreexcited QRS morphologies, each with an associated His-bundle electrogram; (2) decremental as well as adenosine-sensitive anterograde and retrograde conduction; and (3) inducible AV reciprocating tachycardia with anterograde conduction over one AV nodal pathway and retrograde conduction over the alternate AV nodal pathway. The existence of two AV nodes was further supported in the group treated with radiofrequency ablation by the development of transient accelerated junctional rhythm during energy delivery with an identical QRS morphology to that generated by anterograde conduction over the targeted AV node.

CONCLUSION

Reciprocating tachycardia mediated by twin AV nodes can be a source of recurrent supraventricular tachycardia in patients with specific forms of complex congenital heart disease. Successful treatment with catheter ablation is possible.

Multi atrial maco-re-entry circuits in adults with repaired congenital heart disease: entrainment mapping combined with three-dimensional electroanatomic mapping

OBJECTIVES

We sought to characterize re-entry circuits causing intra-atrial re-entrant tachycardias (IARTs) late after the repair of congenital heart disease (CHD) and to define an approach for mapping and ablation, combining anatomy, activation sequence data and entrainment mapping.

BACKGROUND

The development of IARTs after repair of CHD is difficult to manage and ablate due to complex anatomy, variable re-entry circuit locations and the frequent co-existence of multiple circuits.

METHODS

Forty-seven re-entry circuits were mapped in 20 patients with recurrent IARTs refractory to medical therapy. In the first group (n = 7), ablation was guided by entrainment mapping. In the second group (n = 13), entrainment mapping was combined with a three-dimensional electroanatomic mapping system to precisely localize the scar-related boundaries of re-entry circuits and to reconstruct the activation pattern.

RESULTS

Three types of right atrial macro-re-entrant circuits were identified: those related to a lateral right atriotomy scar (19 IARTs), the Eustachian isthmus (18 IARTs) or an atrial septal patch (8 IARTs). Two IARTs originated in the left atrium. Radiofrequency (RF) lesions were applied to transect critical isthmuses in the right atrium. In three patients, the combined mapping approach identified a narrow isthmuses in the lateral atrium, where the first RF lesion interrupted the circuit; the remaining circuits were interrupted by a series of RF lesions across a broader path. Overall, 38 (81%) of 47 IARTs were successfully ablated. During follow-up ranging from 3 to 46 months, 16 (80%) of 20 patients remained free of recurrence. Success was similar in the first 7 (group 1) and last 13 patients (group 2), but fluoroscopy time decreased from 60 +/- 30 to 24 +/- 9 min/procedure, probably related to the increasing experience and ability to monitor catheter position non-fluoroscopically.

CONCLUSIONS

Entrainment mapping combined with three-dimensional electroanatomic mapping allows delineation of complex re-entry circuits and critical isthmuses as targets for ablation. Radiofrequency catheter ablation is a reasonable option for treatment of IARTs related to repair of CHD.

Electroanatomic mapping of entrained and exit zones in patients with repaired congenital heart disease and intra-atrial reentrant tachycardia

BACKGROUND

Characterization of reentrant circuits and targeting ablation sites remains difficult for intra-atrial reentrant tachycardias (IART) in congenital heart disease (CHD).

METHODS AND RESULTS

Electroanatomic mapping and entrainment pacing were performed before successful ablation of 18 IART circuits in 15 patients with CHD. Principal features of IART circuits were atrial septal defect (4 patients), atriotomy (3 patients), other atrial scar (3 patients), crista terminalis (3 patients), and right atrioventricular valve (5 patients). A median of 176 sites (range, 96 to 317 sites) was mapped for activation and 13 sites (range, 9 to 28 sites) for entrainment response. Postpacing intervals within 20 ms of tachycardia cycle length and stimulus-to-P-wave intervals of 0 to 90 ms (exit zones) were mapped to atrial surfaces generated by electroanatomic mapping. Criteria for entrainment were met over a median of 21 cm2 of atrial surface (range, 2 to 75 cm2), 19% (range, 1% to 81%) of total area tested. Using integrated data, relations between activation sequence and protected corridor of conduction could be inferred for 16 of 17 LARTs. Successful ablation was achieved at a site distant from the putative protected corridor in 9 of 18 (50%) circuits.

CONCLUSIONS

The right atrium in CHD supports a variety of IART mechanisms. Fusion of activation and entrainment data provided insight into specific IART mechanisms relevant to ablation.

Electroanatomic characterization of conduction barriers in sinus/atrially paced rhythm and association with intra-atrial reentrant tachycardia circuits following congenital heart disease surgery

INTRODUCTION

The electrophysiologic mechanism of intra-atrial reentrant tachycardia (IART) is generally thought to be a macroreentrant circuit revolving around a nonconductive or highly anisotropic barrier. However, the electrical and anatomic substrate that supports these circuits has been incompletely defined. Our objectives were to characterize the atria of patients with IART using electroanatomic mapping in sinus or atrially paced rhythm and to determine whether electrical barriers identified in sinus/atrially paced rhythm are associated with IART circuits.

METHODS AND RESULTS

Eighteen patients with IART and a remote history of repaired or palliated congenital heart disease were studied [8 biventricular repair, 8 single ventricle palliation (7 Fontan), and 2 Mustard repair]. Thirteen patients had a right AV valve. In sinus/atrially paced rhythm, electrical evidence of a crista terminalis was identified in 11 patients, an atriotomy in 12, and > or = 1 right atrial free-wall scar in 11. In 26 IART circuits characterized, 12 used the right AV valve as a central obstacle, 6 used a right atrial free-wall scar, 3 used an atriotomy, 3 used the crista terminalis, and 2 circuits used an atrial septal scar. All central obstacles used by IART circuits were identified in sinus/atrially paced rhythm.

CONCLUSION

The crista terminalis, atriotomy, and right atrial scars can be identified in patients with repaired congenital heart disease by electroanatomic mapping in sinus/atrially paced rhythm. These conduction barriers frequently function as the central obstacle for IART. Demonstration of such features may help focus investigational mapping without reliance on spontaneous initiation of the tachycardia.

Long-term results of the lateral tunnel Fontan operation

OBJECTIVES

Completion of a total cavopulmonary anastomosis with an intra-atrial lateral tunnel is known to yield good early and midterm results. In this study, we sought to determine the long-term outcome (10 years) after a lateral tunnel Fontan procedure.

METHODS

Between October 1987 and December 1991, 220 patients (aged 11 months to 32 years) with a wide range of underlying diagnoses underwent a fenestrated or nonfenestrated lateral tunnel Fontan procedure at our institution. Current follow-up information was available for 196 patients (94%, mean follow-up = 10.2 +/- 0.6 years). Risk factor analysis included patient-related and procedure-related variables, with death, failure, and bradyarrhythmia or tachyarrhythmia as outcome parameters.

RESULTS

There were 12 early deaths (<30 days or hospital death), 7 late deaths, 4 successful takedown operations, and 4 heart transplantations. Kaplan-Meier estimated survival was 93% at 5 years and 91% at 10 years, and freedom from failure was 90% at 5 years and 87% at 10 years. Freedom from new supraventricular tachyarrhythmia was 96% at 5 years and 91% at 10 years; freedom from new bradyarrhythmia was 88% at 5 years and 79% at 10 years. Three patients had evidence of protein-losing enteropathy. Multivariable risk factors for development of supraventricular tachyarrhythmia included heterotaxy syndrome, atrioventricular valve abnormalities, and preoperative bradyarrhythmia. Risk factors for bradyarrhythmia included systemic venous anomalies. The sole risk factor for late failure was a previous coarctation repair.

CONCLUSION

The lateral tunnel Fontan procedure results in excellent long-term outcome even when used in patients with diverse anatomic diagnoses. The incidence of atrial tachyarrhythmia is low and mainly depends on the underlying cardiac morphology and preoperative arrhythmia. The good long-term outcome after an intracardiac lateral tunnel Fontan procedure should serve as a basis for comparison with other surgical alternatives.

Estimation of atrial response to entrainment pacing using electrograms recorded from remote sites

INTRODUCTION

Assessing the entrainment response by measuring postpacing intervals (PPIs) at the pacing site facilitates localization of reentrant circuits, but may be technically difficult.

METHODS AND RESULTS

There were 269 right atrial sites entrained in 21 circuits in congenital heart patients left atrial (LA) electrograms were recorded. Entrainment response was measured by two methods: (1) PPI-tachycardia cycle length, and (2) the difference in latencies between the stimulus artifact and the pacing site electrogram, referenced to the LA electrogram. PPI also was measured from the LA as an index of antidromic activation. Among 43 pacing sites with antidromic LA activation, half showed a discrepancy 225 msec between methods 1 and 2. At the other 226 sites, agreement between the two methods was high (mean discrepancy -3+/-8 msec, r = 0.975, 0 sites with discrepancy 225 msec). Correcting all sites by LA antidromicity reduced the mean discrepancy to +1+/-6 msec and improved correlation (r = 0.988).

CONCLUSION

LA electrograms can be used to estimate right atrial entrainment response, if antidromic activation of the LA is recognized and taken into account.

Recombinant rinderpest vaccines expressing membrane-anchored proteins as genetic markers: evidence of exclusion of marker protein from the virus envelope

Rinderpest virus (RPV) causes a severe disease of cattle resulting in serious economic losses in parts of the developing world. Effective control and elimination of this disease require a genetically marked rinderpest vaccine that allows serological differentiation between animals that have been vaccinated against rinderpest and those which have recovered from natural infection. We have constructed two modified cDNA clones of the vaccine strain RNA genome of the virus, with the coding sequence of either a receptor site mutant form of the influenza virus hemagglutinin (HA) gene or a membrane-anchored form of the green fluorescent protein (GFP) gene (ANC-GFP), inserted as a potential genetic marker. Infectious recombinant virus was rescued in cell culture from both constructs. The RPVINS-HA and RPVANC-GFP viruses were designed to express either the HA or ANC-GFP protein on the surface of virus-infected cells with the aim of stimulating a strong humoral antibody response to the marker protein. In vitro studies showed that the marker proteins were expressed on the surface of virus-infected cells, although to different extents, but neither was incorporated into the envelope of the virus particles. RPVINS-HA- or RPVANC-GFP-vaccinated cattle produced normal levels of humoral anti-RPV antibodies and significant levels of anti-HA or anti-GFP antibodies, respectively. Both viruses were effective in stimulating protective immunity against RPV and antibody responses to the marker protein in all animals when tested in a cattle vaccination trial.

Location of acutely successful radiofrequency catheter ablation of intraatrial reentrant tachycardia in patients with congenital heart disease

Intraatrial reentrant tachycardia (IART) is common after surgery for congenital heart disease (CHD). Radiofrequency (RF) catheter ablation of IART targets anatomic areas critical to the maintenance of the arrhythmia circuit, areas that have not been well defined in this patient population. The purpose of this study was to determine the anatomic areas critical to IART circuits, defined by activation mapping and confirmed by an acutely successful RF ablation at the site. A total of 110 RF ablation procedures in 88 patients (median age 23.4 years, range 0.1 to 62.7) with CHD were reviewed. Patients were grouped according to surgical intervention: Mustard/Senning (n = 15), other biventricular repaired CHD (n = 24), Fontan (n = 43), and palliated CHD (n = 6). In first-time ablation procedures, > or = 1 IART circuits were acutely terminated in 80% of Mustard/Senning, 71% of repaired CHD, and 72% of Fontan (p = NS). The palliated CHD group underwent 1 of 6 successful procedures (17%), and this patient was excluded. The locations of acutely successful RF applications in Mustard/Senning patients (n = 14 sites) were at the tricuspid valve isthmus (57%) and at the lateral right atrial wall (43%). In patients with repaired CHD (n = 18 sites), successful RF sites were at the isthmus (67%) and the lateral (22%) and anterior (11%) right atria. In the Fontan group (n = 40 sites), successful RF sites included the lateral right atrial wall (53%), the anterior right atrium (25%), the isthmus area (15%), and the atrial septum (7%). Location of success was statistically different for the Fontan group (p = .002). In conclusion, the tricuspid valve isthmus is a critical area for ablation of IART during the Mustard/ Senning procedure and in patients with repaired CHD. IART circuits in Fontan patients are anatomically distinct, with the lateral right atrial wall being the more common area for successful RF applications. This information may guide RF and/or surgical ablation procedures in patients with CHD and IART.

Cost-effectiveness and implications of newborn screening for prolongation of QT interval for the prevention of sudden infant death syndrome

OBJECTIVE

To determine the cost-effectiveness of universal and high-risk neonatal electrocardiographic (ECG) screening for QT prolongation as a predictor of sudden infant death syndrome (SIDS) risk in a theoretical group of neonates.

STUDY DESIGN

Incremental cost-effectiveness analysis with decision analytic modeling. A hypothetical cohort of healthy, term infants was modeled, comparing options of no screening, high-risk neonate screening, and universal screening. The high-risk strategy is speculative, because no currently accepted methodology is known for identifying infants at high risk for SIDS. Given the uncertain mechanisms of association between prolonged corrected QT interval (QTc) and SIDS, analyses were repeated under different assumptions. Sensitivity analyses were also performed on all input variables for both costs and effectiveness.

RESULTS

Under the assumption that neonatal electrocardiographic screening detects long QT syndrome responsive to conventional therapy, the cost-effectiveness of high-risk screening was $3403 per life year gained, whereas universal screening cost $18,465 per additional life year gained. However, if the effectiveness of SIDS therapy falls below 10%, the cost-effectiveness deteriorates to $28,376 per life year saved for the high-risk strategy and $118,900 for universal screening. The analyses were robust to a broad array of sensitivity analyses.

CONCLUSIONS

The acceptability of the cost-effectiveness of neonatal electrocardiographic screening is heavily dependent on the pathophysiologic mechanism of SIDS and on the efficacy of monitoring and antiarrhythmic treatment. The nature of this association must be elucidated before routine neonatal electrocardiographic screening is warranted.

Development of a genetically marked recombinant rinderpest vaccine expressing green fluorescent protein

In order to effectively control and eliminate rinderpest, a method is required to allow serological differentiation between animals that have been vaccinated and those which have recovered from natural infection. One way of doing this would be to engineer the normal vaccine to produce a genetically marked rinderpest virus (RPV) vaccine. We constructed two modified cDNA clones of the RPV RBOK vaccine strain with the coding sequence of the green fluorescent protein (GFP) gene inserted as a potential genetic marker. RPVINS-GFP virus was designed to produce independent and high level expression of GFP inside infected cells, whilst the GFP expressed by RPVSIG-GFP virus was designed to be efficiently secreted. Infectious recombinant virus was rescued in cell culture from both constructs. The effectiveness of these viruses in stimulating protective immunity and antibody responses to the marker protein was tested by vaccination of cattle and goats. All of the vaccinated animals were completely protected when challenged with virulent virus: RPV in cattle or peste-des-petits ruminants virus in the goats. ELISA showed that all of the animals produced good levels of anti-RPV antibodies. Three of the four cattle and the two goats vaccinated with RPVSIG-GFP produced detectable levels of anti-GFP antibodies. In contrast, no anti-GFP antibodies were produced in the four cattle and two goats vaccinated with RPVINS-GFP. Therefore, secretion of the GFP marker protein was absolutely required to elicit an effective humoral antibody response to the marker protein.

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.

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.

A screen to identify Drosophila genes required for integrin-mediated adhesion

Drosophila integrins have essential adhesive roles during development, including adhesion between the two wing surfaces. Most position-specific integrin mutations cause lethality, and clones of homozygous mutant cells in the wing do not adhere to the apposing surface, causing blisters. We have used FLP-FRT induced mitotic recombination to generate clones of randomly induced mutations in the F1 generation and screened for mutations that cause wing blisters. This phenotype is highly selective, since only 14 lethal complementation groups were identified in screens of the five major chromosome arms. Of the loci identified, 3 are PS integrin genes, 2 are blistered and bloated, and the remaining 9 appear to be newly characterized loci. All 11 nonintegrin loci are required on both sides of the wing, in contrast to integrin alpha subunit genes. Mutations in 8 loci only disrupt adhesion in the wing, similar to integrin mutations, while mutations in the 3 other loci cause additional wing defects. Mutations in 4 loci, like the strongest integrin mutations, cause a "tail-up" embryonic lethal phenotype, and mutant alleles of 1 of these loci strongly enhance an integrin mutation. Thus several of these loci are good candidates for genes encoding cytoplasmic proteins required for integrin function.

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.

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.

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.

Left ventricular mechanics and geometry in patients with congenital complete atrioventricular block

BACKGROUND

Radiographic evidence of cardiomegaly is common in patients with congenital complete atrioventricular block (CCAVB). It has been speculated that left ventricular (LV) remodeling and increased stroke volume counteract the bradycardia, but the effects of slow heart rate and atrioventricular asynchrony on LV dimensions, geometry, wall stress, and function have not been examined in detail.

METHODS AND RESULTS

Thirty patients with CCAVB without associated congenital heart disease (mean age, 8.5+/-5.3 years; range, 0.2 to 20 years) were included in a cross-sectional two-institution study. Thirty-five echocardiograms were performed using standard techniques. ECG and 24-hour ECG recordings were reviewed. Seven patients did not receive a pacemaker, whereas 23 patients underwent pacemaker implantation after the echocardiogram. Compared with normal control subjects, LV volume (Z score=1.5+/-1.3) and LV mass (Z=1.2+/-1.5) were significantly increased, whereas LV mass-to-volume ratio (1.1+/-0.3) and geometry (short-axis diameter/length ratio=0.65+/-0.09) were normal. LV end-systolic stress (ESS) (a measure of afterload) was normal (Z score=0.2+/-2.3), whereas shortening fraction (Z=3+/-2.9) and velocity of circumferential fiber shortening (VCF) (Z=3+/-3.1) were increased. The relationship between VCF and ESS (a preload-insensitive and afterload-adjusted index of contractility) was increased (Z=2.2+/-2) with only small increase in preload (Z=1.02+/-1.1). Regression analyses showed no significant change over age in LV mass, volume, geometry, loading conditions, or systolic function. Patients who ultimately met criteria for pacemaker implantation did not differ from those who did not in terms of heart rate or LV function but did have increased LV volume (Z score=1.8+/-1.4 versus 0.4+/-0.9, P=.03) and LV mass (Z score=1.7+/-1.2 versus 0.2+/-1.7, P=.001) compared to the unpaced group.

CONCLUSIONS

In most patients with CCAVB, the LV was enlarged with normal geometry and enhanced systolic function during the first two decades of life. The degree of LV dilation and enhanced function did not significantly change with age. In patients who ultimately underwent pacemaker implantation LV function did not differ from those who remained unpaced, but evidence of a slightly increased load manifested as increased end-diastolic volume and mass.

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.

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.

Spontaneous accelerated junctional rhythm: an unusual but useful observation prior to radiofrequency catheter ablation for atrioventricular node reentrant tachycardia in young patients

Between May 1990 and March 1995, 5 of 29 young patients (ages 4.2-25 years; median 14.1 years) undergoing RF ablation for atrioventricular node reentrant tachycardia (AVNRT) presented with spontaneous accelerated junctional rhythm (AJR) (CL = 500-750 ms), compared to 0 of 58 age matched controls undergoing RF ablation for a concealed AV accessory pathway (P = 0.004). In 3 of the 5 patients with AVNRT and AJR, junctional beats served as a trigger for reentry. During attempted slow pathway modification in the five patients with AVNRT and AJR, AVNRT continued to be inducible until the AJR was entirely eliminated or dramatically slowed. These 5 patients are tachycardia-free in followup (median 15 months; range 6-31 months) with only 1 of the 5 patients continuing to experience episodic AJR at rates slower than observed preablation. Episodic spontaneous AJR is statistically associated with AVNRT in young patients and can serve as a trigger for reentry. Successful modification of slow pathway conduction may be predicted by the elimination of AJR or its modulation to slower rates, suggesting that the rhythm is secondary to enhanced automaticity arising near or within the slow pathway.

Syncope in the pediatric patient

Syncope in the pediatric patient is a common and usually benign event that frequently causes concern and anxiety. This article describes three general categories of syncope in children and adolescents: cardiac, noncardiac, and neurocardiogenic. The discussion includes specific pediatric issues and dissimilarities when compared to adult patients with syncope. In addition, a focused approach to the diagnostic evaluation of syncope in childhood is described.

Predictors of permanence of successful radiofrequency lesions created with controlled catheter tip temperature

Transient interruption of accessory pathway (AP) conduction is often encountered during creation of RF lesions, with return of conduction after seconds to weeks. Maximum catheter tip temperature (Tmax) has not been shown to be a good predictor of successful RF ablation. However, other indices related to catheter tip temperature (T) may predict permanent AP interruption. Ninety-one successful RF applications in 58 patients (mean age 11.9 +/- 5.5 years, 38 WPW syndrome, 18 concealed AP, 2 both) were reviewed retrospectively. Forty-two RF applications were transiently successful, with a median time of AP conduction recurrence of 120 seconds (sec; range, 1 sec to > 1 day). This group was compared with 49 permanently successful RF applications. T was measured and controlled using the Medtronic Atakr system (San Jose, CA, USA). RF lesion duration, power output, Tmax and time to Tmax (tmax) were not significantly different between the two groups. By univariate analysis, each of the following indices was able to discriminate between the transient and permanent lesions, and highly correlated with one another, T at the moment of AP interruption (Tsucc; transient 55.0 +/- 7.9 degrees C vs permanent 49.8 +/- 7.7 degrees C, P = 0.0025), time to success (tsucc; transient 4.0 +/- 3.0 sec vs permanent 1.8 +/- 1.3 sec, P = 0.0001), ratio of Tsucc/Tmax (transient 0.76 +/- 0.23 vs permanent 0.57 +/- 0.27, P = 0.0007) and ratio of tsucc/tmax (transient 0.91 +/- 0.69 vs permanent 0.41 +/- 0.41, P = 0.0001). By logistic regression analysis, no single variable or combination of variables was superior to tsucc for prediction of outcome, with a breakpoint of 2.3 seconds having a sensitivity of 74% and a specificity of 65%. During temperature controlled RF application, indices of time and temperature were well-correlated with permanent elimination of AP conduction. Time to interruption of AP conduction < 2.3 seconds after the onset of RF application was predictive of the permanence of successful RF applications. Known relations between RF lesion volume and catheter tip temperature suggest that early conduction block may be an indicator of anatomical proximity of the catheter tip and the AP. These data suggest that, in conjunction with electrogram criteria, selection criteria for optimal sites for RF, application may continue to be refined after the onset of RF application, and support the practice of terminating RF application if AP conduction is not rapidly interrupted.

Evaluation of a staged treatment protocol for rapid automatic junctional tachycardia after operation for congenital heart disease

OBJECTIVES

This study sought to 1) develop an efficient treatment protocol for postoperative automatic junctional tachycardia (JT) using conventional drugs and techniques, and 2) identify clinical features associated with this disorder by analyzing a large study group.

BACKGROUND

Postoperative JT is a transient arrhythmia that may be fatal after operation for congenital cardiac defects. Its precise cause is unknown. A variety of palliative treatments have evolved, but because of a low incidence of JT, large studies of the most efficient therapeutic sequence are lacking.

METHODS

A protocol for rapid JT (>170 beats/min) was adopted in 1986, and was tested in 71 children between 1986 and 1994. Staged therapy involved 1) a reduction of catecholamines; 2) correction of fever; 3) atrial pacing to restore synchrony; 4) digoxin; 5) phenytoin or propranolol or verapamil; 6) procainamide or hypothermia; and 7) combined procainamide and hypothermia. Effective therapy was defined as a sustained reduction of JT rate <170 beats/min within 2 h. Clinical profiles of the study group were contrasted with all patients without JT from this same era to identify features associated with JT.

RESULTS

Of the multiple treatment stages, only correction of fever and combined procainamide and hypothermia appeared to be efficacious. By refining the protocol to eliminate nonproductive stages, the time to JT control was significantly shortened for the last 30 patients. Treatment was ultimately successful in 70 of 71 children. Postoperative JT was strongly associated with young age, transient atrioventricular block and operations involving ventricular septal defect closure.

CONCLUSIONS

A staged approach to therapy, with emphasis on combined hypothermia and procainamide in difficult cases, appears to be an effective management strategy for postoperative JT. These results may also serve as comparison data for evaluation of newer and promising JT options, such as intravenous amiodarone. Trauma to conduction tissue may play a central role in the etiology of this disorder.

Intra-atrial reentrant tachycardia after palliation of congenital heart disease: characterization of multiple macroreentrant circuits using fluoroscopically based three-dimensional endocardial mapping

INTRODUCTION

The anatomic substrate of intra-atrial reentrant tachycardia (IART) following congenital heart surgery is poorly understood, but is presumed to be different than common atrial flutter.

METHODS AND RESULTS

To study the mechanisms of IART, we used a new technique for high-density endocardial mapping using recordings from a multipolar basket recording catheter (25 bipolar pairs). For each recording, biplane fluorographic reference points were digitized to obtain the spatial locations of electrode pairs, and activation times were calculated using temporal reference points from the surface ECG. Using custom software, data were combined to create three-dimensional atrial activation sequence maps, which were displayed as animated sequences. Using this technique, recordings were made in induced and/or spontaneous IART in 8 patients following congenital heart surgery (5 Fontan, 2 tetralogy of Fallot repair, 1 ventricular septal defect repair), and in 3 patients with normal intracardiac anatomy (1 with type I atrial flutter). Ten discrete IART activation sequences were recorded; 2 patients had 2 sequences each. IART maps were constructed using a median of 108 electrode positions (range 27 to 197) from a median of 6 recordings/sequence (range 3 to 11). Sinus or paced atrial rhythms were also recorded, and maps were created in a similar fashion. Visual analysis of activation sequences of sinus and paced rhythm were anatomically concordant with known mechanisms of atrial activation. IART sequences revealed diverse mechanisms; only 1 IART circuit was similar to that associated with common atrial flutter. Activation wavefront emergence from presumed zones of slow conduction, lines of conduction block, and apparent bystander activation were observed.

CONCLUSIONS

High-density atrial activation sequence maps demonstrate that IART following congenital heart surgery utilizes diverse circuits and is distinct from common atrial flutter. The technique used to create these three-dimensional activation sequences may improve understanding of these complex atrial arrhythmias and assist in the development of ablative therapies.

Factors that influence the development of atrial flutter after the Fontan operation

OBJECTIVES

Atrial flutter is a frequent, potentially fatal complication of the Fontan operation, but risk factors for its development are ill defined. We evaluated clinical features that might predict the development of atrial flutter in patients who had a Fontan operation.

METHODS

We evaluated 334 early survivors of a Fontan operation done between April 1973 and July 1991 (mean follow-up, 5.0 +/- 3.8 years). Evaluation included electrocardiography, Holter monitor recordings, and chart review. Modifications of the Fontan operation included an extracardiac conduit (n = 43), an atriopulmonary anastomosis (n = 117), or a total cavopulmonary anastomosis (n = 174). Patient, time, and procedure-related variables were analyzed with respect to the development of atrial flutter.

RESULTS

Atrial flutter was identified in 54 (16%) patients at a mean of 5.3 +/- 4.7 years (range 0 to 19.7 years) after Fontan operation. Atrial flutter developed sooner and was more likely to occur in patients who were older at the time of Fontan operation (12.4 +/- 7.6 vs 6.3 +/- 5.2 years; p < 0.001), had a longer follow-up interval (8.7 +/- 3.9 vs 4.4 +/- 3.4 years; p < 0.001), had a prior atrial septectomy or pulmonary artery reconstruction (p < 0.01), and had worse New York Heart Association class symptoms (p < 0.02). The presence of sinus node dysfunction was associated with a higher incidence of atrial flutter (p < 0.001). Although there was a lower prevalence of atrial flutter in those patients with a total cavopulmonary anastomosis, the follow-up for this group was shorter. Anatomic diagnoses, perioperative hemodynamics, and other previous palliative operations were not associated with an increased incidence of atrial flutter. Multivariate analysis identified age at operation, duration of follow-up, extensive atrial baffling, and type of repair as factors associated with the development of atrial flutter after Fontan operation.

CONCLUSION

Atrial flutter continues to develop with time after the Fontan operation. Further follow-up is necessary to determine whether a total cavopulmonary anastomosis reduces the incidence of atrial flutter.

Multipolar endocardial mapping of the right heart using a basket catheter: acute and chronic animal studies

The development of catheter-based ablative techniques for primary atrial and ventricular arrhythmias is likely to be assisted by improved techniques for systematic endocardial activation sequence mapping. RA mapping using a multielectrode basket catheter has been shown to be feasible with minimal acute toxicity in a prior study. The objectives of the current study are to investigate: (1) the utility of the basket catheter for mapping RV activation; and (2) the evolution of acute endocardial lesions produced by basket catheter use in both the RA and RV over 4-8 weeks time. A flexible, 5-spoke basket catheter bearing 25 electrode pairs was placed in the RA (n = 9) or the RV (n = 13) in 22 juvenile sheep (22-56 kg). The catheter was deployed for 0.1-4.1 hr (RA) and 0.3-3.9 hr (RV). In 20 of these 22 animals, 32 recordings were made of filtered (30-250 Hz) bipolar electrograms and surface ECG. Electrograms were timed and used to construct activation sequences based on a schematic of catheter geometry. Hearts were examined either acutely (4 RA and 9 RV studies) or 4-8 weeks after the procedure (5 RA and 4 RV studies). One animal undergoing RA placement had an air embolism resulting in cardiac arrest immediately prior to basket placement; all other animals were stable during placement. RA electrograms of sufficient quality to determine activation time were recorded from 82% of pairs in RA maps, and RV electrograms from 89% of pairs in RV maps. Mean activation sequence duration in RV was 16 ms versus 47 ms in RA (P < 0.0001), making construction of RV maps more difficult. Acute postmortem studies of RV placement revealed a silent apical RV puncture in one animal. Superficial abrasion or ecchymosis of RV endocardium and/or tricuspid valve were noted in six animals. Postmortem exams in both RA and RV chronic studies showed healed endocardial lesions, with only superficial scarring. Rapid RV activation mapping using a basket catheter is feasible, but requires precision recording techniques. Endocardial abrasions produced in lambs both by RA and RV placement of the catheter are healed in < 4-8 weeks, with trivial residua. The multielectrode basket catheter may be applicable to the mapping of tachycardias originating in or involving the right ventricle.

Novel missense mutation in the cyclic nucleotide-binding domain of HERG causes long QT syndrome

Autosomal-dominant long QT syndrome (LQT) is an inherited disorder, predisposing affected individuals to sudden death from tachyarrhythmias. To identify the gene(s) responsible for LQT, we identified and characterized an LQT family consisting of 48 individuals. DNA was screened with 150 microsatellite polymorphic markers encompassing approximately 70% of the genome. We found evidence for linkage of the LQT phenotype to chromosome 7(q35-36). Marker D7S636 yielded a maximum lod score of 6.93 at a recombination fraction (theta) of 0.00. Haplotype analysis further localized the LQT gene within a 6.2-cM interval. HERG encodes a potassium channel which has been mapped to this region. Single-strand conformational polymorphism analyses demonstrated aberrant bands that were unique to all affected individuals. DNA sequencing of the aberrant bands demonstrated a G to A substitution in all affected patients; this point mutation results in the substitution of a highly conserved valine residue with a methionine (V822M) in the cyclic nucleotide-binding domain of this potassium channel. The cosegregation of this distinct mutation with LQT demonstrates that HERG is the LQT gene in this pedigree. Furthermore, the location and character of this mutation suggests that the cyclic nucleotide-binding domain of the potassium channel encoded by HERG plays an important role in normal cardiac repolarization and may decrease susceptibility to ventricular tachyarrhythmias.

Low-temperature mapping predicts site of successful ablation while minimizing myocardial damage

BACKGROUND

Temperatures near 50 degrees C can cause reversible loss of excitability in myocardial cells.

METHODS AND RESULTS

Low-temperature, short-duration applications of radiofrequency energy were used to determine the adequacy of electrophysiological mapping of accessory pathway (AP) locations in 15 patients at 27 target sites using a closed-loop, temperature-controlled generator set to 50 degrees C. Energy was delivered until evidence of conduction block, or for a maximum of 10 seconds. If AP block occurred, a full 70 degrees C set point radiofrequency application was delivered to the same site. In the absence of AP block, tests with higher temperature settings (60 degrees C and 70 degrees C) were delivered to determine if inadequate temperature or catheter position led to failure of the initial 50 degrees C test. At 15 successful target sites where permanent AP block was achieved, the 50 degrees C test resulted in AP block in 14 (93%). Conduction returned in 13 of 14 APs after radiofrequency power was turned off. The time to block for the 70 degrees C applications was significantly shorter than for the 50 degrees C tests, and the peak temperature achieved was significantly higher. At unsuccessful sites where permanent AP block was not achieved, no block was induced with 11 of 12 tests at 50 degrees C, 6 of 6 tests at 60 degrees C, and 1 of 2 tests at 70 degrees C, suggesting that failure was due to incorrect catheter position. The sensitivity and positive predictive values of a 50 degrees C test identifying a successful site were > 90%.

CONCLUSIONS

Low-temperature radiofrequency applications that cause transient AP block predict permanent success when a higher-temperature application is delivered at the same site. The time to achieve conduction block is a function of the temperature set point, and low-temperature tests produce reversible conduction block, suggesting minimal permanent injury.

Conversion of modified Fontan procedure to lateral atrial tunnel cavopulmonary anastomosis

After modified Fontan procedures with atriopulmonary anastomoses or right atrium-right ventricle conduits, some patients have progressive exercise intolerance, effusions, arrhythmias, or protein-losing enteropathy. Theoretic advantages of a lateral atrial tunnel cavopulmonary anastomosis and published clinical results suggest that conversion of other Fontan procedures to the lateral atrial tunnel may afford clinical improvement for some patients. Eight patients (8 to 25 years old) with tricuspid atresia (n =4), double-inlet left ventricle (n = 3), and double-outlet right ventricle (n=1) underwent conversion to a lateral tunnel procedure between December 1990 and November 1994. An arbitrary clinical score was assigned before the lateral tunnel procedure and at follow-up. Before conversion, patients had decreased exercise tolerance (n = 8), arrhythmias (n = 6), effusions (n = 4), and protein-losing enteropathy (n = 8). At catheterization, all had a low cardiac index (1.9 +/- 0.7 L x min(-1) x M(-2), five had elevated pulmonary vascular resistance (>3 Wood units), and three had right pulmonary venous return obstruction by compression of an enlarged right atrium. Fenestrated lateral tunnel construction was undertaken 7.3 +/- 3.6 years after atriopulmonary anastomosis, with one early death related to low cardiac output. After the lateral tunnel procedure, two patients had no clinical improvement (no change in clinical score) but five patients had either marked or partial improvement. The right pulmonary vein compression present in three patients was resolved after conversion. The mean clinical scores improved from 4.5 +/- 1 to 3.0 +/- 2 (p < 0.04). In conclusion, conversion to a lateral tunnel procedure led to clinical improvement in five of eight patients at short-term follow-up and may be particularly indicated for patients with giant right atria or pulmonary vein compression who have symptoms. Pulmonary vein compression should be looked for in patients after modified Fontan procedures and can be relieved by conversion to the lateral tunnel procedure.

Missense mutation in the pore region of HERG causes familial long QT syndrome

BACKGROUND

Long QT syndrome (LQT) is an inherited cardiac disorder that results in syncope, seizures, and sudden death. In a family with LQT, we identified a novel mutation in human ether-a-go-go-related gene (HERG), a voltage-gated potassium channel.

METHODS AND RESULTS

We used DNA sequence analysis, restriction enzyme digestion analysis, and allele-specific oligonucleotide hybridization to identify the HERG mutation. A single nucleotide substitution of thymidine to guanine (T1961G) changed the coding sense of HERG from isoleucine to arginine (Ile593Arg) in the channel pore region. The mutation was present in all affected family members; the mutation was not present in unaffected family members or in 100 normal, unrelated individuals.

CONCLUSIONS

We conclude that the Ile593Arg missense mutation in HERG is the cause of LQT in this family because it segregates with disease, its presence was confirmed in three ways, and it is not found in normal individuals. The Ile593Arg mutation may result in a change in potassium selectivity and permeability leading to a loss of HERG function, thereby resulting in LQT.

Long-term outcome in patients with pacemakers following the Fontan operation

Patients with pacemakers after Fontan surgery compared favorably with nonpaced patients with respect to survival. In patients with atrioventricular block, dual chamber pacing was superior to VVI pacing.

Staged operation to Fontan increases the incidence of sinoatrial node dysfunction

Morbidity and mortality of total cavopulmonary connection (modified Fontan procedure) may be decreased in many patients with single ventricle in whom the risk of surgery is high by performing the operations in a staged fashion. Each operative intervention, however, exposes the sinoatrial node region to risk of injury, and a multistaged approach may increase the risk of altered sinoatrial node function in these patients. The purpose of this study was to compare the prevalence of perioperative arrhythmias in patients undergoing either a primary or staged approach to the Fontan operation. Records were retrospectively reviewed for all patients having a Fontan procedure between January 1988 and December 1992. Of 324 patients undergoing a Fontan operation, 227 had a Fontan operation without a prior cavopulmonary shunt (group 1) and 97 had a cavopulmonary shunt before a Fontan operation (group 2). Arrhythmias were classified as altered sinoatrial node function, supraventricular tachycardia, or atrioventricular block. The prevalence of both transient (resolving before hospital discharge) and fixed (persisting until hospital discharge) altered sinoatrial node function was similar for the two groups after cavopulmonary shunt or primary Fontan despite a heterogeneous patient population (group 1: 10.6%/4.4%; group 2: 10.3%/3.1%; p=0.28). Conversion from cavopulmonary shunt to Fontan in group 2 resulted in a higher prevalence of altered sinoatrial node function in the early postoperative period (transient: 23.7%; fixed: 23.7%; p < 0.001) and on follow-up (group 1: 7.7%; group 2: 16.7%; p < 0.02). In group 2, 40 of 82 patients without arrhythmia after first intervention (cavopulmonary shunt) had an arrhythmia after the second intervention (Fontan) (49%); of 14 with an arrhythmia after the first operation, 10 (71%) had one at the second intervention (p < 0.01). In conclusion, a multistaged operative pathway to Fontan reconstruction is associated with a higher early risk of altered sinoatrial node function. The occurrence of altered sinoatrial node function after cavopulmonary shunt is itself a risk factor for arrhythmia after the Fontan operation. Longer follow-up is needed to assess the full impact of this finding.

Embolic complications associated with radiofrequency catheter ablation. Atakr Investigator Group

Both early and late thromboembolic events are known complications of radiofrequency catheter ablation. This review of 758 patients undergoing 830 radiofrequency ablation procedures finds that embolic complications after radiofrequency ablation in patients without other risk factors for thromboembolism are rare (<0.2%).

Efficacy and risks of medical therapy for supraventricular tachycardia in neonates and infants

To assess the efficacy and safety of current pharmacologic therapy for supraventricular tachycardia (SVT) in infants, we reviewed 112 infants treated between July 1985 and March 1993. The SVT mechanism was determined by esophageal electrophysiologic study and involved an accessory pathway in 86, atrioventricular (AV) node reentry in 10, atrial muscle reentry in 11, and an ectopic atrial tachycardia in 5 patients. Of six infants not treated, none had clinical recurrences of SVT. Of the 106 patients treated, 70% remained free of tachycardia while receiving digoxin, propranolol, or both. Class I antiarrhythmic agents were necessary for 13 patients, and class III agents were required for another 13 infants. Verapamil was used in one infant with AV node reentry tachycardia. Nine infants with complex clinical presentations were believed to have failed medical management and underwent radiofrequency ablation. Five patients died, four of complications related to structural heart disease and one shortly after radiofrequency ablation was performed. No deaths appeared to be related to antiarrhythmic medications. No drug-related side effects requiring medication change occurred, and no proarrhythmia was observed. Thus medical therapy appears to be effective and safe in infants with SVT. Radiofrequency ablation should be reserved for rare infants who fail aggressive medical regimens or when the situation is complicated by ventricular dysfunction, severe symptoms, or complex congenital heart disease.

High-density endocardial activation mapping of the right atrium in three dimensions by composition of multielectrode catheter recordings

The use of radiofrequency ablation for treatment of complex arrhythmia substrates has prompted interest in transcatheter endocardial activation mapping. Technical constraints on catheter fabrication and the intention to use such maps to guide ablation both demand innovative approaches to mapping. A fluoroscopically based endocardial mapping technique is proposed to improve the ability of electrophysiologists to interpret large amounts of data acquired using multielectrode catheter arrays, improving their ability to visualize the data and act on its content. This technique addresses previous limitations imposed by the number of electrodes that can be deployed and by the difficulty in determining their relative spatial locations. It is based on the composition of multiple activation sequence mappings made in a single rhythm, with the spatial locations of recording electrode pairs determined in orthogonal fluoroscopic views referenced to stable intrathoracic markers. Rather than imposing a geometry determined primarily by the measurement apparatus, the spatial locations of only those electrodes in proximity to the endocardial surface, as determined by their ability to record bipolar electrograms, are measured. In this manner, the geometry of the endocardium may be approximated by measurements made of electrode position. Using this approach, the number of endocardial sites that can be sampled in a stable rhythm is theoretically unlimited, resulting in the realization of high-resolution activation maps. Spatiotemporal data may be used to create three-dimensional activation sequence maps, displayed as animated sequences. This technique was used in anatomically normal and diseased human right atria to create activation maps of sinus and paced rhythms, classic atrial flutter, and postoperative intraatrial reentrant tachycardia, using a median of 108 electrode positions (range, 27-197) in 25 maps. The activation sequences represented by these maps were diverse, but qualitatively concordant with known mechanisms of atrial activation. High-density catheter-based activation mapping of the right atrium is feasible and may improve understanding of complex arrhythmias and assist in the development of ablative techniques. Further research is needed on the spatial correlation between cardiac anatomy and fluorography, suppression of spatial artifact, and optimal mapping densities.

Myocardial mechanics before and after ablation of chronic tachycardia

Chronic tachycardia has been shown to cause a congestive cardiomyopathy; however, previous methods of evaluating ventricular function are highly dependent on cardiac loading conditions. Mean velocity of fiber shortening and its relation to end-systolic wall stress (ESS) is a preload independent index of contractility that incorporates afterload. We reviewed 33 patients (aged 5 months to 20 years; mean 9.7 years) with ectopic atrial tachycardia (EAT) (n = 19), permanent junctional reciprocating tachycardia (PJRT) (n = 12), or ventricular tachycardia (n = 2), who underwent nonpharmacological elimination of tachycardia ; 28 by radiofrequency ablation and 5 surgically. Ventricular function was evaluated by echocardiographic measurements of shortening fraction, mean velocity shortening corrected for heart rate (VcFc), and afterload as ESS. Contractility, expressed as the stress-velocity index, was determined by comparing the Ess/VcFc relation to the predicted normal VcFc for the measured ESS. Myocardial dysfunction was seen in 21 patients: 13 with EAT; 7 with PJRT; and 1 with ventricular tachycardia. In patients with EAT, the mean heart rate in tachycardia was significantly faster in those with dysfunction than in those without dysfunction (176.8 +/- 23.2 vs 136.7 +/- 28.2; P < 0.02). Of the 21 patients with dysfunction, full recovery was seen in 17 of 18 patients restudied after intervention (mean 17.5 +/- 17.6 weeks), and the remaining patient improved markedly, but did not normalize entirely. Dysfunction, seen in 64% of young patients with chronic tachycardia, was due to depressed myocardial contractility, and is generally reversible within 3 months of definitive therapy.

Mechanisms and therapy of complex arrhythmias in pediatric patients

In recent years, the distinction between the diagnostic and therapeutic techniques used in the assessment and management of pediatric and adult patients with arrhythmias has gradually blurred. Nonetheless, arrhythmias in the pediatric patient are still often different from the adult patient in one of two important ways. First, a variety of arrhythmia mechanisms remain relatively unique to the pediatric population, some because of developmental issues and others because of early presentation of an incessant tachycardia. Second, the presentation and management of certain arrhythmias is sometimes markedly affected by patient age or the presence of structural congenital heart disease. A sampling from each of the above categories is reviewed and discussed.

Sotalol for refractory arrhythmias in pediatric and young adult patients: initial efficacy and long-term outcome

Sotalol is an antiarrhythmic medication that has properties of both a beta-blocker and a class III agent and has been used safely and effectively to treat arrhythmias of multiple mechanisms in pediatric patients. The purpose of this study was to review our institutional experience with sotalol in 45 patients with refractory arrhythmias and determine their long-term outcome. Patients responded to sotalol with 80% efficacy and a 22% incidence of adverse side effects. The mean sotalol dose was 116 mg/m2/day, and the average duration of therapy was 15.2 months. In spite of 80% efficacy, only 22% of patients remained on sotalol long-term. Sotalol was discontinued most commonly for either spontaneous resolution of disease or definitive cure by radiofrequency ablation. Other reasons for discontinuation of effective therapy included adverse side effects and arrhythmia control with either an antitachycardia pacemaker or another medication. One patient died while taking sotalol, but this case was considered a failure of treatment rather than an adverse side effect. Of the patients who still receive therapy, several have complex structural heart disease and require a combination of therapies, including sotalol, for adequate rhythm control.

Conversion of atrial flutter in pediatric patients by transesophageal atrial pacing: a safe, effective, minimally invasive procedure

Atrial reentry tachycardia, often termed atrial flutter, is an arrhythmia that is uncommon in the general pediatric population but is seen frequently in patients with congenital heart disease. One goal in treating the arrhythmia is to terminate it, returning the atrium to its underlying rhythm. This report describes the use of transesophageal atrial pacing to attempt termination of atrial reentry in 102 pediatric patients (158 episodes). The patients ranged in age from 1 hour to 41.5 years. Conversion was successful for 112 (71%) of 158 episodes. Six of the 112 episodes required an infusion of procainamide after initial attempts at pacing led to atrial fibrillation. There were no significant differences between the ages of patients or the duration of the tachycardia in comparing successful versus unsuccessful conversions. In contrast, the atrial cycle lengths for the successfully converted tachycardias were significantly greater than for unsuccessful attempts. Transesophageal atrial pacing is a safe and effective means of terminating atrial flutter in the pediatric population. It is minimally invasive, it can often be performed in an outpatient setting, and the technique may occasionally be facilitated by infusion of intravenous procainamide.

Use of adenosine-sensitive nondecremental accessory pathways in assessing the results of radiofrequency catheter ablation

Adenosine can cause conduction block in about 20% of nondecremental accessory pathways. Along with atrial activation mapping, adenosine may help differentiate retrograde AV node conduction versus residual accessory pathway conduction after radiofrequency catheter ablation; however, it is important to test the accessory pathway response to adenosine before ablation, particularly with a concealed accessory pathway.

Factors influencing impedance during radiofrequency ablation in humans

Impedance during radiofrequency (RF) catheter ablation procedures is dependent on a variety of parameters related to the catheter, cabling, reference patch, body size, and temperature. To examine the influence of body size, impedance was measured during clinical ablation procedures in 93 patients (Group I) with a wide range of body sizes. In 14 other patients (Group II), impedance was measured during variations in catheter tip size (5, 6 and 7 Fr), reference patch size (120 and 60 cm2), patch location (chest vs. thigh), and catheter tip tissue contact. The average impedance was also compared to average tip temperature in Group II patients. Impedance decreased with increasing catheter tip size, reference patch size and proximity of the patch to the heart. However, the effects of body geometry were complex. For example, using a chest patch, impedance increased with body surface area, but using a thigh patch it decreased, suggesting that lung volume may increase impedance, but body width may actually decrease it. An increase in tip tissue contact, relative to blood contact, increased the impedance, suggesting that impedance may be a useful measure of tip tissue contact. Finally impedance decreased with increasing tip temperature, suggesting that impedance may be useful as a real time measure of tissue and blood heating. The results are interpreted in terms of an electrical analog which suggests further that despite the lower total power when the same voltage is applied to a higher impedance, less voltage should be applied to achieve the same tissue effect when the measured impedance is higher.

Benefits and potential risks of atrial antitachycardia pacing after repair of congenital heart disease

Atrial reentry tachycardia is common after surgical repair of congenital heart disease. The arrhythmia is often difficult to treat and is occasionally life-threatening. This study reports experience with atrial antitachycardia (AAIT mode) pacing for the management of atrial reentry tachycardia, with emphasis on the risks and benefits of automatic pacing therapy. Eighteen patients (2-32 years of age) with a variety of congenital heart lesions underwent atrial antitachycardia pacemaker placement for recurrent atrial tachycardia that was amenable to pace termination prior to the implantation procedure. An appropriate antitachycardia program was determined by repeated induction and termination of atrial tachycardia using the noninvasive programmed stimulation mode of the pacemaker. Over 4-30 months of follow-up, 6 patients had 189 episodes of tachycardia successfully converted with AAI-T pacing, 4 patients had 8 episodes of tachycardia detected but not successfully converted, and 8 patients had no episodes of tachycardia with antibradycardia pacing alone. The number of patients receiving pharmacological therapy other than digoxin or beta blockade fell from 12 to 6. Two subjects died suddenly, 1 while wearing a Holter monitor. In both, tachycardia was detected and pace cardioversion attempted.

CONCLUSIONS

Atrial antitachycardia pacing is a useful tool in the management of patients with congenital heart disease and atrial arrhythmias; however, in selected cases, it may not prevent and may even exacerbate the lethal complications of the tachycardia. Antitachycardia function evaluation is recommended under varying levels of autonomic stress prior to institution of automatic therapy.

Effects of propofol or isoflurane anesthesia on cardiac conduction in children undergoing radiofrequency catheter ablation for tachydysrhythmias

BACKGROUND

To determine suitability for ablation procedures in children, two commonly used anesthetic agents were studied: propofol and isoflurane.

METHODS

Twenty patients presenting for a radiofrequency catheter ablation procedure were included and randomly assigned to two groups. A baseline electrophysiology study was performed during anesthesia with thiopental, alfentanil, nitrous oxide, and pancuronium in all patients. At the completion of the baseline electrophysiology study (EPS), 0.8-1.2% isoflurane was administered to patients in group 1 and 2 mg/kg propofol bolus plus an infusion of 150 micrograms.kg-1.min-1 was administered to patients in group 2. Nitrous oxide and pancuronium were used throughout the procedure. After 30 min of equilibration, both groups underwent a repeat EPS. The following parameters were measured during the EPS: cycle length, atrial-His interval, His-ventricle interval, corrected sinus node recovery time, AV node effective refractory period, and atrial effective refractory period. Using paired t tests, the electrophysiologic parameters described above measured during propofol or isoflurane anesthesia were compared to those measured during baseline anesthesia. Statistical significance was accepted as P < 0.05.

RESULTS

There was no statistically significant difference in the results obtained during baseline anesthesia when compared with those measured during propofol or isoflurane anesthesia.

CONCLUSIONS

Neither propofol nor isoflurane anesthesia alter sinoatrial or atrioventricular node function in pediatric patients undergoing radiofrequency catheter ablation, compared to values obtained during baseline anesthesia with alfentanil and midazolam.