Difficulties with invasive risk stratification performed under anesthesia in pediatric Wolff-Parkinson-White Syndrome.

BACKGROUND: Children with Wolff-Parkinson-White Syndrome (WPW) are at risk for sudden death. The gold standard for risk stratification in this population is the shortest pre-excited RR interval during atrial fibrillation (SPERRI). OBJECTIVE: The purpose of this study was to determine how closely measurements made in the electrophysiology laboratory in patients with WPW compared to SPERRI obtained during an episode of clinical pre-excited atrial fibrillation (Clinical-SPERRI). METHODS: This was a subgroup analysis of a multicenter study of children with WPW. Subjects in our study (N = 49) were included if they had Clinical-SPERRI measured in addition to 1 or more of 3 surrogate measurements: SPERRI obtained during electrophysiological study (EP-SPERRI), accessory pathway effective refractory period (APERP), or shortest pre-excited paced cycle length with 1:1 conduction (SPPCL). RESULTS: Seventy percent of electrophysiological measurements were made with patients under general anesthesia. Clinical-SPERRI moderately correlated with EP-SPERRI (r = 0.495; P = .012). However, 24% of our patients with Clinical-SPERRI ≤250 ms would have been misclassified as having a low-risk pathway based on EP-SPERRI >250 ms. Clinical-SPERRI did not correlate with APERP or SPPCL (r < 0.3; P >.1). Mean EP-SPERRI, APERP, and SPPCL all were greater than Clinical-SPERRI. CONCLUSION: Electrophysiology laboratory measurements of pathway characteristics made with patients under general anesthesia do not correlate well with Clinical-SPERRI. Of APERP, SPPCL, and EP-SPERRI, only EP-SPERRI had moderate correlation with Clinical-SPERRI. This study questions the predictive ability of invasive risk stratification with patients under general anesthesia, given that 24% of patients with high-risk Clinical-SPERRI (≤250 ms) had EP-SPERRI that may be considered low risk (>250 ms).

Effect of electrical dyssynchrony on left and right ventricular mechanics in children with pulmonary arterial hypertension.

BACKGROUND: Electrical and right ventricular (RV) mechanical dyssynchrony has been previously described in pediatric pulmonary arterial hypertension (PAH), but less is known about the relationship between electrical dyssynchrony and biventricular function. In this study we applied cardiac magnetic resonance (CMR) imaging to evaluate biventricular size and function with a focus on left ventricular (LV) strain mechanics in pediatric PAH patients with and without electrical dyssynchrony. METHODS: Fifty-six children with PAH and comprehensive CMR evaluation were stratified based on QRS duration z-score, with electrical dyssynchrony defined as z-score ≥2. Comprehensive biventricular volumetric, dyssynchrony, and strain analysis was performed. RESULTS: Nineteen PAH patients had or developed electrical dyssynchrony. Patients with electrical dyssynchrony had significantly reduced RV ejection fraction (35% vs 50%, p = 0.003) and greater end-diastolic (168 vs 112 ml/m2, p = 0.041) and end-systolic (119 vs 57, ml/m2, p = 0.026) volumes. Patients with electrical dyssynchrony had reduced RV longitudinal strain (-14% vs -19%, p = 0.007), LV circumferential strain measured at the free wall (-19% vs -22%, p = 0.047), and the LV longitudinal strain in the septal region (-10% vs -15%, p = 0.0268). LV mechanical intraventricular dyssynchrony was reduced in patients with electrical dyssynchrony at the LV free wall (43 vs 19 ms, p = 0.019). CONCLUSIONS: The electrical dyssynchrony is associated with the reduced LV strain, enlarged RV volumes, and reduced biventricular function in children with PAH. CMR assessment of biventricular mechanical function with respect to QRS duration may help to detect pathophysiologic processes associated with progressed PAH.

Perioperative electrophysiology study in patients with tetralogy of Fallot undergoing pulmonary valve replacement will identify those at high risk of subsequent ventricular tachycardia.

BACKGROUND: Ventricular tachyarrhythmias are the most common cause of death in patients with repaired tetralogy of Fallot (TOF), but predicting those at risk remains a challenge. An electrophysiology study (EPS) has been proposed to risk stratify patients with TOF. OBJECTIVE: We sought to evaluate a perioperative EPS-guided approach to risk stratify patients with TOF undergoing pulmonary valve replacement (PVR) and guide concomitant cryoablation. METHODS: A prospective cohort study of patients with TOF undergoing an EPS at the time of PVR from 2006 to 2017 was conducted at 2 centers. Patients inducible at the time of pre-PVR had undergone concomitant cryoablation in addition to PVR. A repeat post-PVR EPS was performed in those initially inducible to guide implantable cardioverter-defibrillator (ICD) implantation. RESULTS: Of 70 patients who underwent a pre-PVR EPS, 34 (49%) had inducible sustained ventricular tachycardia (VT): 25 monomorphic VT and 9 polymorphic VT. Among patients undergoing cryoablation, 14 (45%) had inducible VT and underwent ICD implantation. During a mean follow-up period of 6.1 ± 3.2 years, 3 patients (21%) had appropriate ICD shocks for symptomatic VT. There was an average of 2.3 shocks (range 1-4 shocks), and the mean time to first shock post-device implantation was 3.6 years (range 2.9-4.3 years). Among patients with negative pre- or post-PVR EPS results, 2 had VT requiring radiofrequency ablation and/or subsequent ICD implantation. There were no arrhythmic deaths. CONCLUSION: A pre-PVR EPS identified patients with higher-risk TOF undergoing PVR. Despite empirical VT cryoablation at the time of PVR, a high percentage of patients remained inducible for VT. In this high-risk cohort, post-PVR EPS evaluation is important to identify patients at risk of VT despite cryoablation.

Noninvasive predictors of perioperative atrial arrhythmias in patients with tetralogy of Fallot undergoing pulmonary valve replacement.

BACKGROUND: Patients with tetralogy of Fallot (TOF) have increased risk of atrial arrhythmias. HYPOTHESIS: A measure of atrial dispersion, the P-wave vector magnitude (Pvm), can identify patients at risk for perioperative atrial flutter (AFL) or intra-atrial re-entrant tachycardia (IART) in a large TOF cohort. METHODS: We performed a blinded, retrospective analysis of 158 TOF patients undergoing pulmonary valve replacement between 1997 and 2015. History of AFL/IART was documented using electrocardiogram, Holter monitor, exercise stress test, implanted cardiac device, and electrophysiology study. P-R intervals, Pvm, QRS duration, and QRS vector magnitude were assessed from resting sinus-rhythm 12-lead electrocardiograms and identification of those with AFL/IART was determined. RESULTS: Fourteen patients (8.9%) were found to have AFL/IART. Pvm, QRS duration, and QRS vector magnitude significantly differentiated those with AFL/IART from those without on univariate analysis: 0.09 ± 0.04 vs 0.18 ± 0.07 mV, 161.3 ± 21.9 vs 137.7 ± 31.4 ms, and 1.2 (interquartile range, 1.0-1.2) vs 1.6 mV (1.0-2.3), respectively (P < 0.05 for each). The Pvm had the highest area under the ROC curve (0.88) and was the only significant predictor on multivariate analysis, with odds ratio of 0.02 (95% confidence interval: 0.01-0.53). P-R duration, MRI volumes, and right-heart hemodynamics did not significantly differentiate those with vs those without AFL/IART. CONCLUSIONS: In TOF patients undergoing pulmonary valve replacement, Pvm has significant value in predicting those with perioperative AFL/IART. These clinical features may help further evaluate TOF patients at risk for perioperative atrial arrhythmias. Prospective studies are warranted.

Management of pediatric tachyarrhythmias on mechanical support.

BACKGROUND: Pediatric patients with persistent arrhythmias may require mechanical cardiopulmonary support. We sought to classify the population, spectrum, and success of current treatment strategies. METHODS AND RESULTS: A multicenter retrospective chart review was undertaken at 11 sites. Inclusion criteria were (1) patients <21 years, (2) initiation of mechanical support for a primary diagnosis of arrhythmias, and (3) actively treated on mechanical support. A total of 39 patients were identified with a median age of 5.5 months and median weight of 6 kg. A total of 69% of patients were cannulated for supraventricular tachycardia with a median rate of 230 beats per minute. A total of 90% of patients were supported with extracorporeal membrane oxygenation for an average of 5 days. The remaining 10% were supported with ventricular assist devices for an average of 38 (20-60) days. A total of 95% of patients were treated with antiarrhythmics, with 43% requiring >1 antiarrhythmic. Amiodarone was the most frequently used medication alone or in combination. A total of 33% patients underwent electrophysiology study/transcatheter ablation. Radiofrequency ablation was successful in 9 patients on full flow extracorporeal membrane oxygenation with 3 radiofrequency-failures/conversion to cryoablation. One patient underwent primary cryoablation. A total of 15% of complications were related to electrophysiology study/ablation. At follow-up, 23 patients were alive, 8 expired, and 8 transplanted. CONCLUSIONS: Younger patients were more likely to require support in the presented population. Most patients were treated with antiarrhythmics and one third required electrophysiology study/ablation. Radiofrequency ablation is feasible without altering extracorporeal membrane oxygenation flows. There was a low frequency of acute adverse events in patients undergoing electrophysiology study/ablation, while on extracorporeal membrane oxygenation.

Percutaneous transhepatic access for catheter ablation of cardiac arrhythmias.

AIMS: Femoral venous access may be limited in certain patients undergoing electrophysiology (EP) study and ablation. The purpose of this study is to review a series of patients undergoing percutaneous transhepatic access to allow for ablation of cardiac arrhythmias. METHODS AND RESULTS: Six patients with a variety of cardiac arrhythmias and venous abnormalities underwent percutaneous transhepatic access. Under fluoroscopic and ultrasound guidance, a percutaneous needle was advanced into a hepatic vein and exchanged for a vascular sheath over a wire. Electrophysiology study and radiofrequency ablation was then performed. All tachycardias, including atrial tachycardia, atrial flutter, atrioventricular nodal tachycardia, and atrial fibrillation, were ablated. Procedural times ranged from 227 to 418 min. Fluoroscopy times ranged from 32 to 95 min. There were no complications. All six patients have been arrhythmia-free in follow-up (5-49 months, mean 23.1 months). CONCLUSION: Percutaneous transhepatic access is safe and feasible in patients with limited venous access who are undergoing EP study and ablation for a range of cardiac arrhythmias.

Cryoablation of the slow atrioventricular nodal pathway via a transbaffle approach in a patient with the Mustard procedure for d-transposition of the great arteries.

The ablation of atrioventricular (AV) nodal reentrant tachycardia in patients with the Senning or Mustard procedure is quite challenging because these atrial baffle procedures isolate the AV node from systemic venous access. Cryoablation is commonly utilized for AV nodal slow pathway modification in patients with structurally normal hearts. The cryoablation technique offers the advantage of monitoring AV nodal conduction during lesions, with the ability to terminate a lesion prior to permanent injury to the AV node. This case describes the successful cryoablation of the slow AV nodal pathway via the transbaffle approach in a patient with d-transposition of the great arteries status post the Mustard procedure.

Use of cryoablation for treatment of tachyarrhythmias in 2010: survey of current practices of pediatric electrophysiologists.

BACKGROUND: Cryoablation for arrhythmia substrates in pediatrics has been available since 2003. The purpose of this study was to evaluate the current approach of pediatric electrophysiologists to the use of cryoablation in the current era. METHODS: We sent an Internet link to an online survey to all members of the Pediatric and Congenital Electrophysiology Society. Individuals and not institutions were surveyed. RESULTS: A total of 70 responses were received. Responding physicians were largely invasive pediatric electrophysiologists (94%) who practice at mid- to high-volume centers (>50 ablation procedures/year). Survey responders report that cryoablation was utilized for <50% of the ablation volume, and most utilize it for only 10%. With respect to specific arrhythmia substrates, 41% of responders use cryoablation as first-line therapy for atrioventricular nodal reentrant tachycardia. For accessory pathways, 94% report that cryoablation would only be utilized after mapping the accessory pathway to a "high-risk location." Other arrhythmia substrates considered for cryoablation would be accessory pathways mapped to high-risk areas, junctional ectopic tachycardia, a parahisian ectopic atrial tachycardia, or an atrial tachycardia near the phrenic nerve. CONCLUSION: For pediatric electrophysiologists who responded to the survey, radiofrequency energy remains the primary energy source for ablation. The current use of cryoablation technology is directed at arrhythmia substrates near the normal conduction system or other "high-risk" areas.

Ventricular ectopy following successful cryoablation for Wolff-Parkinson-White syndrome in the right posterior septum: a case report.

We report a case of new onset ventricular ectopy following cryothermal ablation of a right posterior septal accessory pathway. To our knowledge, this is the first report of secondary arrhythmias from cryothermal ablation of atrial arrhythmias.

Cryothermal catheter ablation of atrioventricular nodal reentrant tachycardia in a pediatric patient after atrioventricular canal repair.

Anatomic displacement of the atrioventricular node and associated conduction tissue in atrioventricular septal defects has been previously described. In spite of the increasing use of cryothermal catheter ablation in the pediatric population, there remains very little literature regarding its use in congenital heart disease. We describe successful cryothermal modification of the slow atrioventricular nodal pathway in a 12-year-old patient with a previously repaired partial atrioventricular septal defect and inducible atrioventricular nodal reentrant tachycardia. The use of a steerable catheter to locate the displaced His signal combined with the use of cryothermal energy allowed for the safe and effective treatment of this patient's tachycardia.

Cryoablation of accessory pathways in the coronary sinus in young patients: a multicenter study from the Pediatric and Congenital Electrophysiology Society's Working Group on Cryoablation.

INTRODUCTION: This is a multicenter retrospective study evaluating the immediate- and mid-term outcomes of cryoablation of accessory pathways in the coronary sinus in children or in patients with congenital heart disease. METHODS AND RESULTS: Twenty-one patients (median age 13.0 years, range 2-40) from six institutions were included. The accessory pathways were concealed in 11 and manifest in 10. Of 12 patients who had coronary sinus angiography, two had large coronary sinus diverticula, one had a dilated coronary sinus due to a left superior vena cava to coronary sinus, and one had a "pouch" at the mouth of the coronary sinus. Six patients underwent ablation procedures with cryoablation alone, while in the remaining 15 patients, both cryoablation and radiofrequency ablation were utilized. The ablation procedure included left-sided endocardial mapping via a retrograde or transseptal approach in 13 (62%). Procedural success was achieved with cryoablation in the coronary sinus in 15/21 (71%). Four patients (19%) had successful radiofrequency ablation at the right or left posterior septum. Two patients (10%) had unsuccessful procedures. Of the 15 patients with initially successful cryoablation procedures, six (40%) had arrhythmia recurrences at a median of 17 days (range 1-120). Recurrences could not be explained by differences in patient or procedural variables. CONCLUSION: Cryoablation in the coronary venous system in young patients is feasible but associated with a high arrhythmia recurrence rate. Cryoablation techniques and/or equipment need to be improved in order to safely create more permanent lesions in this arrhythmia substrate.

Characterizing dual atrioventricular nodal physiology in pediatric patients with atrioventricular nodal reentrant tachycardia.

INTRODUCTION: Dual atrioventricular (AV) nodal physiology, defined as an AH jump > or =50 msec with a 10 msec decrease in A1A2, is the substrate for atrioventricular nodal reentrant tachycardia (AVNRT) and yet it is present in a minority of pediatric patients with AVNRT. Our objective was to characterize dual AV nodal physiology as it pertains to a pediatric population. METHODS/RESULTS: We retrospectively reviewed invasive electrophysiology studies in 92 patients with AVNRT (age12.1 +/- 3.7 yrs) and in 46 controls without AVNRT (age 13.3 +/- 3.7 yrs). Diagnoses in controls: syncope (N = 31), palpitations (N = 6), atrial flutter (N = 3), history of atrial tachycardia with no inducible arrhythmia (N = 3), and ventricular tachycardia (N = 3). General anesthesia was used in 49% of AVNRT and 52% of controls, P = 0.86. There were no differences in PR, AH, HV, or AV block cycle length. With A1A2 atrial stimulation, AVNRT patients had a significantly longer maximum AH achieved (324 +/- 104 msec vs 255 +/- 67 msec, P = 0.001), and a shorter AVNERP (276 +/- 49 msec vs 313 +/- 68 msec P = 0.0005). An AH jump > or =50 msec was found in 42% of AVNRT versus 30% of controls (P = 0.2). Using a ROC graph we found that an AH jump of any size is a poor predictor of AVNRT. With atrial overdrive pacing, PR > or = RR was seen more commonly in AVNRT versus controls, (55/91(60%) vs 6/46 (13%) P = 0.000). CONCLUSIONS: Neither the common definition of dual AV nodes or redefining an AH jump as some value <50 msec are reliable methods to define dual AV nodes or to predict AVNRT in pediatric patients. PR > or = RR is a relatively good predictor of AVNRT.

Cryoablation in pediatric atrioventricular nodal reentry: electrophysiologic effects on atrioventricular nodal conduction.

BACKGROUND: Cryoablation for treatment of atrioventricular nodal reentrant tachycardia (AVNRT) is safe and efficacious. Information on the effects of cryoablation on atrioventricular (AV) nodal conduction is limited. OBJECTIVES: The purpose of this study was to evaluate the effects of cryoablation on AV nodal conduction in pediatric patients with AVNRT. METHODS: We retrospectively analyzed electrophysiologic studies before and after successful cryoablation. Patients were divided into two groups: group 1 (n = 22, age 14 +/- 3 years) had baseline discontinuous atrial-to-His interval (AH) conduction curves; and group 2 (n = 13, age 12 +/- 4 years, P = .054) had continuous curves. RESULTS: At baseline, group 1 had longer measurements of maximal AH with A1A2, AV nodal effective refractory period, and AV block cycle length. Postcryoablation, both group 1 and group 2 showed decreases in maximal AH with A1A2 pacing or atrial overdrive pacing and in the finding of PR > or = RR with atrial overdrive pacing (group 1: 55% vs 5%, P < .001; group 2: 69% vs 0%, P < .001). A significant increase in overall AV effective refractory period and a decrease in AV block cycle length were found in group 1 but not group 2. Fifty percent of group 1 patients had complete abolition of slow pathway conduction. CONCLUSION: Successful cryoablation for treatment of AVNRT is associated with a reduction in PR > or = RR and with decreases in maximal AH with A1A2 pacing or atrial overdrive pacing. Further study is needed to determine the usefulness of these parameters for assessment of ablation efficacy or as proxies for AVNRT inducibility.

Cryoablation versus radiofrequency ablation for treatment of pediatric atrioventricular nodal reentrant tachycardia: initial experience with 4-mm cryocatheter.

BACKGROUND: Initial reports have shown cryoablation to be safe and efficacious for treatment of atrioventricular nodal reentrant tachycardia (AVNRT). No direct comparisons of cryoablation vs radiofrequency (RF) catheter ablation in pediatric patients have been made. OBJECTIVES: The purpose of this study was to compare the outcomes of cryothermal vs RF catheter ablation for treatment of AVNRT in pediatric patients. METHODS: We retrospectively reviewed consecutive ablation procedures for treatment of AVNRT at a single arrhythmia center. The RF group consisted of patients who underwent RF ablation from 2002 until cryothermy became available. The cryoablation group consisted of patients who underwent cryothermal ablation from 2004 to 2005. The groups were compared for procedural and electrophysiologic outcomes. RESULTS: RF (n = 60, age 14 +/- 4 years) and cryoablation (n = 57, age 14 +/- 4 years) groups had similar demographic and baseline parameters. Procedural times were shorter in the RF group (RF ablation 112 +/- 31 minutes vs cryoablation 148 +/- 46 minutes, P < .001). Fluoroscopy times were comparable (RF ablation 21 +/- 15 minutes vs cryoablation 20 +/- 13 minutes, P = .77). In an intention-to-treat analysis, success of the procedure was 100% for RF ablation and 95% for cryoablation (P = .11). No permanent AV block occurred in either group. Recurrence rates were higher for the cryoablation group, but this did not reach statistical significance (RF ablation 2% vs cryoablation 8%, P = .19). CONCLUSION: Cryoablation appears to be similar to RF for ablation of AVNRT with respect to short-term efficacy and safety of the procedure in a pediatric population. Recurrence rates are higher with cryoablation.

Usefulness of a ventricular extrastimulus from the summit of the ventricular septum in diagnosis of septal accessory pathway in patients with supraventricular tachycardia.

To compare usefulness of a ventricular extrastimulus (VES) from the right ventricular (RV) apex versus the RV septum in patients with a septal accessory pathway (AP), VES was applied from the RV apex and the summit of the RV septum in patients with septal APs. A VES from the RV apex and from the summit was diagnostic of the presence of an AP in 13 of 28 patients (83%) and in 10 of 12 patients, respectively (46% p <0.05), and VES proved an AP as a part of the tachycardia circuit in 5 of 28 patients (18%) and 6 of 12 patients, respectively (50%, p <0.05). A VES during His bundle refractoriness from the RV summit increases the diagnostic yield for both the presence of an AP and its participation in the tachycardia circuit with respect to RV apical VES.

Significance of bundle branch block during atrioventricular nodal reentrant tachycardia.

There are very limited data on the effects of bundle branch block (BBB) in patients with atrioventricular nodal reentrant tachycardia (AVNRT). Studies in a total of 155 patients with 162 episodes of AVNRT were retrospectively analyzed. A total of 38 patients (25%) developed spontaneous right BBB, whereas 5 (3%) developed left BBB during tachycardia. Five of the 38 (13%) with right BBB showed near identical prolongation of both the ventriculoatrial (VA) (15 +/- 5 ms; 10 to 23) and His to atrial intervals (HA) (14 +/- 4 ms; 10 to 20) with an identical atrial activation sequence for both right BBB or normal QRS tachycardia complexes. In contrast, all 5 patients with left BBB showed a decrease in the VA (-18 +/- 11 ms; 10 to 36) with unchanged HA comparing left BBB to normal QRS patterns during AVNRT. The magnitude of prolongation of the His to ventricular interval (HV) during left BBB (19 +/- 12 ms; 10 to 40) was nearly identical to the decrease in the VA. In conclusion, prolongation of VA and HA with unchanged HV in patients with AVNRT and right BBB suggests that right BBB is due to a block in the fibers in close proximity to the His recording site. The data suggest that fibers in the His bundle are predestined to activate the right bundle branch, and in AVNRT the lower turnaround point may be within the His bundle.

Survey of current practice of pediatric electrophysiologists for asymptomatic Wolff-Parkinson-White syndrome.

OBJECTIVE: To determine the approach that pediatric electrophysiologists use as they evaluate asymptomatic patients with Wolff-Parkinson-White (WPW) syndrome regarding electrophysiologic testing and radio frequency ablation. METHODS: A 21-question survey was mailed to 66 pediatric electrophysiologists who had voluntarily submitted patient data at any time to the Pediatric Radio Frequency Ablation Registry since its inception in 1990. The survey addressed issues regarding physician experience with electrophysiologic testing and radio frequency ablation, risk assessment, electrophysiology study, and factors that influence the decision to perform radio frequency ablation in asymptomatic patients. RESULTS: Returned surveys (43 of 66 [65%]) were analyzed blindly. The 43 physicians who responded were experienced, with 37 reporting >5 years of performing radio frequency ablation and 30 having performed >200 radio frequency ablation procedures. Thirty-six of the 43 electrophysiologists used invasive electrophysiologic study for risk stratification in asymptomatic patients with WPW. Electrophysiologic findings guided selection of patients for radio frequency ablation procedures. Expected radio frequency ablation outcome quotes to the family were consistent with recently published data from the Electrophysiology Society regarding current-era experience with radio frequency ablation. CONCLUSION: The majority of responding electrophysiologists use invasive electrophysiologic study both to stratify risk for asymptomatic WPW and to select appropriate patients for radio frequency ablation. This current practice should be communicated to other pediatric cardiologists and pediatricians.

Use of electrophysiologic testing to assess risk in children with Wolff-Parkinson-White syndrome.

In adults with Wolff-Parkinson-White syndrome, the likelihood of sudden death can be estimated based upon the presence or absence of symptoms. Comparable data in children do not exist. To date, therefore, invasive risk stratification has been used to guide management regarding radiofrequency ablation in symptomatic children. As the safety of electrophysiology study and radiofrequency ablation in children has improved, asymptomatic patients have been referred more commonly for invasive risk stratification. We sought to compare the findings from electrophysiologic studies in symptomatic children with Wolff-Parkinson-White syndrome to the findings in asymptomatic children with Wolff-Parkinson-White pattern on their electrocardiogram. Thus, we compared the findings from electrophysiologic studies carried out in patients seen at Stanford University and University of California, San Francisco, from April 1999 to February 2001 with a preexcitation pattern on their electrocardiogram. The patients were divided into three groups: 23 asymptomatic patients studied for risk stratification, 19 patients who presented with syncope, and 77 patients presenting with documented supraventricular tachycardia. Data were collected for commonly accepted invasive criterions for stratification of risk: an effective refractory period of the accessory pathway less than 270 ms, multiple pathways, septal location of pathway, and inducibility of supraventricular tachycardia. Groups were compared by chi-square. No differences were found between the groups for any of the variables. These data suggest that risk factors for sudden death, developed in studies of adult patients, are not clearly applicable to children. Further studies are needed better to define the indications for study and ablation in children.

Invasive electrophysiology in children: state of the art.

While noninvasive techniques, including esophageal recording and pacing, clearly have advantages in the pediatric population; they also have significant limitations. Invasive electrophysiology (EP) in children now encompasses the use of many advanced engineering applications, which contribute to the efficacy of such procedures. This is particularly true with respect to the performance of radiofrequency catheter ablation. First, microcatheters (eg, Cardima) offer advantages as diagnostic catheters in small hearts, and allow pacing and recording from both atrium and ventricle in even the smallest infants using limited venous access. In addition, there is the possibility of mapping the distal coronary sinus, and the right atrioventricular groove via the right coronary artery. Second, electroanatomic mapping using the CARTO system (Biosense Webster) allows complex maps to be constructed in patients with congenital heart disease and a history of cardiac surgery. Although somewhat laborious to construct, such maps offer great detail to guide ablation, and also provide voltage information to guide identification of patches and scars. Similarly, non-contact mapping systems (eg, EnSite, Endocardial Solutions) are available which record far-field potentials and employ solutions to the inverse problem to reconstruct endocardial potentials. Three-dimensional mapping based on a single beat is possible, and the success of ablation in creating conduction block in unique channels can be evaluated. Both of these three-dimensional mapping systems have the potential to improve outcomes in patients with complex disease undergoing ablation. Finally, patients are now undergoing combined procedures with interventional catheterization (eg, device closure, stenting) along with EP procedures (eg, ablation, device implant) in the same laboratory session. The state of the art in invasive pediatric EP increasingly involves the use of advanced technology adapted for use in pediatric and congenital heart disease applications.