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.

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.

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.

Induction of atrial tachycardia and fibrillation in the mouse heart.

BACKGROUND: Atrial tachycardia and fibrillation in humans may be partly consequent to vagal stimulation. Induction of fibrillation in the small heart is considered to be impossible due to lack of a critical mass of > 100-200 mm2. Even with the recent progression of the technology of in vivo and in vitro mouse electrophysiological studies, few reports describe atrial tachycardia or fibrillation in mice. The purpose of this study was to attempt provocation of atrial tachyarrhythmia in mice using transvenous pacing following cholinergic stimulation. METHODS AND RESULTS: In vivo electrophysiology studies were performed in 14 normal mice. A six-lead ECG was recorded from surface limb leads, and an octapolar electrode catheter was inserted via jugular vein cutdown approach for simultaneous atrial and ventricular endocardial recording and pacing. Atrial tachycardia and fibrillation were inducible in one mouse at baseline electrophysiology study and eleven of fourteen mice after carbamyl choline injection. The mean duration of atrial tachycardia was 126 +/- 384 s. The longest episode lasted 35 min and only terminated after atropine injection. Reinduction of atrial tachycardia after administration of atropine was not possible. CONCLUSION: Despite the small mass of the normal mouse atria, sustained atrial tachycardia and fibrillation can be easily and reproducibly inducible with endocardial pacing after cholinergic agonist administration. This finding may contribute to our understanding of the classical theories of arrhythmogenesis and critical substrates necessary for sustaining microreentrant circuits. The techniques of transcatheter parasympathetic agonist-mediated atrial tachycardia induction may be valuable in further murine electrophysiological studies, especially mutant models with potential atrial arrhythmia phenotypes.

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.

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.

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.

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.

Phenotypic screening for heart rate variability in the mouse.

We developed a technology for heart rate (HR) variability (HRV) analysis in the mouse for characterization of HR dynamics, modulated by vagal and sympathetic activity. The mouse is the principal animal model for studying biological processes. Mouse strains are now available harboring gene mutations providing fundamental insights into molecular mechanisms underlying cardiac electrical diseases. Future progress depends on enhanced understanding of these fundamental mechanisms and the implementation of methods for the functional analysis of mouse cardiovascular physiology. By telemetric techniques, standard time and frequency-domain measures of HRV were computed with and without autonomic blockade, and baroreflex sensitivity testing was performed. HR modulation in the high-frequency component is predominantly mediated by the parasympathetic nervous system, whereas the low-frequency component is under the influence of both the parasympathetic and sympathetic systems. The presented technology and protocol allow for assessment of autonomic regulation of the murine HR. Phenotypic screening for HR regulation in mice will further enhance the value of the mouse as a model of heritable electrophysiological human disease.

Focal ablation of chaotic atrial rhythm in an infant with cardiomyopathy.

Chaotic atrial rhythm in infants has been defined similar to multifocal atrial tachycardia in adults, implying a multifocal etiology. However, its ECG appearance resembles atrial fibrillation, which sometimes has a unifocal ectopic mechanism amenable to catheter ablation. Curative focal radiofrequency ablation was performed in a 4-month-old infant with chaotic atrial rhythm and dilated cardiomyopathy. Left ventricular function subsequently returned to normal. Reversibility of associated cardiomyopathy supports aggressive rhythm management of chaotic atrial rhythm. In this patient, the unifocal origin allows insight into the pathophysiology of the rhythm and demonstrates the potential utility of catheter ablation for refractory cases.

Sudden death in patients after transcatheter device implantation for congenital heart disease.

To explore whether transcatheter intracardiac devices increase risk for sudden death, we analyzed patient and device-related variables with a case-control design. Sudden death was defined as unexpected death with abrupt onset and rapid deterioration. Cases included all patients known to have died suddenly after device closure at our institution, using 3 large databases. Controls (2:1), matched on year of procedure, were chosen randomly from the same databases. Data were obtained from medical record review. Of 777 patients who received implants between February 1989 and February 1999, 9 were known to have died suddenly (1.2%). In 27 cases and controls, diverse defects were occluded: atrial (n = 16), ventricular (n = 4), Fontan fenestration (n = 4), or other (n = 3). Cases were more likely to have had a history of serious arrhythmias (p = 0.008), severe valve regurgitation (p = 0.03), > or =1 cardiac surgery (p = 0.009), and multiple devices (p = 0.03). Cases were somewhat more likely to have pulmonary hypertension (p = 0.09), ventricular dysfunction (p = 0.09), and nonatrial septal defects (p = 0.10). Patients were less likely to have device arm fractures (p = 0.05). The following were not related to sudden death: age, weight, gender, low systemic cardiac index, end-diastolic pressure, major noncardiac disease, serious adverse events, maximum device size, malposition, and residual leak. This study suggests that sudden death was more likely to occur in device-implanted patients who had severe underlying cardiac disease and/or multiple devices. No other device-related variables were associated with sudden death.

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.

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.

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.

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

BACKGROUND: Intraatrial reentrant tachycardia (IART) is a common problem in patients with congenital heart disease (CHD). The progression of clinical symptoms of IART and their response to radiofrequency (RF) ablation are not yet well described. OBJECTIVES: The objective of the study was to determine the early and midterm success rates of RF ablation in effecting a reduction of clinical arrhythmic events in patients with IART and CHD. METHODS: Clinical records of patients undergoing early, successful RF ablation were analyzed retrospectively to document the occurrence and frequency of documented IART, cardioversion and arrhythmia-related hospital visits before and after ablation. RESULTS: Fifty-five catheterizations for intended RF ablation of IART were performed in 45 patients (mean [+/-SD] age 24.5 +/- 10.5 years, 40 after surgical palliation of CHD). Early success was achieved for one or more IART circuits in 33 patients (73%). Mean clinical follow-up of those patients with successful ablation is 17.4 +/- 11.3 months (total 574 patient-months). Documented IART recurrence was noted after 21 (53%) of 40 early, successful catheterizations in 17 (52%) of 33 patients, with a mean time to recurrence of 4.1 months, often with electrocardiographically novel configurations. A more prolonged and frequent history of IART was a univariate risk factor for recurrence. Seven patients underwent repeat RF ablations, and eight patients were restarted on antiarrhythmic medications after ablation. Two patients who had severe ventricular dysfunction before RF ablation died 1.5 and 11 months after RF ablation without known arrhythmia recurrence. Clinical events related to IART increased steadily in frequency for 24 months before RF ablation. Radiofrequency ablation resulted in a reduction of event frequency to levels significantly lower than those in the 12-month period before RF ablation and not significantly different from those levels observed at baseline 3 to 4 years before RF ablation. CONCLUSIONS: In patients with successful RF ablation, the frequency of subsequent events was reduced compared with the 2 preceding years. However, recurrence of IART in patients who showed clinical improvement was frequent, and often revealed the presence of new IART configurations.

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

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