The most common site of success and its predictors in radiofrequency catheter ablation of the slow atrioventricular nodal pathway in children.

BACKGROUND: Locating ablation targets on the slow pathway in children as one would in adults may not accommodate the dimensional changes of Koch's triangle that occur with heart growth. We investigated the most common site of success and the effect of a variety of variables on the outcome of slow pathway ablation in children. METHODS: A total of 116 patients (ages 4-16 years) with structurally normal hearts underwent radiofrequency ablation of either the antegrade or the retrograde slow pathway. Ablation sites were divided into eight regions (A1, A2, M1, M2, P1, P2, CS1, and CS2) at the septal tricuspid annulus. RESULTS: Ablation was successful in 112 (97%) children. The most common successful ablation sites were at the P1 region. The less the patient weighed, the more posteriorly the successful site was located (P = 0.023, OR 0.970, 95% CI 0.946-0.996), and the more likely the slow pathway was eliminated rather than modified: median weight was 46.7 kg (range, 14.5-94.3 kg) in the eliminated group and 56.5 kg (range, 20-82.6 kg) in the modified group (P = 0.021, OR 1.039, 95% CI 1.006-1.073). CONCLUSIONS: The most common site of success for slow pathway ablation in children is at the P1 region of the tricuspid annulus. The successful sites in lighter children are more posteriorly located. Weight is also a predictor of whether the slow pathway is eliminated or only modified.

Clinical and electrophysiological characteristics of fasciculoventricular fibers in children.

INTRODUCTION: Fasciculoventricular (FV) fiber is a rare cause for ventricular preexcitation. It is usually described as an innocent bystander pathway. There is only limited data on FV fiber in children. Hence we evaluated the clinical and electrophysiological features of FV fiber in a group of 11 children. METHODS AND RESULTS: Of 215 children with manifest preexcitation who had electrophysiological studies at the University of Miami, 11 (5.1%) had characteristics of FV fiber. FV fiber was not directly responsible for any arrhythmias in these children. Three children had supraventricular tachycardia due to associated left sided Kent fiber and FV fiber was identified after the ablation of Kent fiber. One child had associated hypertrophic cardiomyopathy, another child had atrial septal defect and a third child had ventricular septal defect. The electrophysiological testing of FV fiber revealed AH interval of 40-95 ms and H-delta interval of 15-40 ms. Mapping study showed that the FV fiber was located on the right side of the heart in all patients: right anteroseptal in 9, right midseptal in 1 and it could not be mapped well in 1 as the delta wave was intermittent. We identified a discrete FV fiber depolarization spike in 9 patients, with a local FV fiber depolarization to delta wave interval of 5-20 ms (11+4 ms). CONCLUSION: FV fiber is an uncommon cause for ventricular preexcitation in children and it can be associated with other conduction abnormalities and heart defects. FV fibers are commonly located at the right anteroseptal region and are not usually involved in any tachycardia. Discrete local FV fiber potential can be identified during electrophysiological testing of these patients.

Carvedilol in children with cardiomyopathy: 3-year experience at a single institution.

BACKGROUND: Carvedilol reduces mortality and hospitalization in adults with congestive heart failure. Limited information is available about its use in children. METHODS: We reviewed the medical records of 24 children with dilated cardiomyopathy and left ventricular ejection fraction of

Effects of a blocked atrial beat on the atrioventricular nodal recovery property in patients with dual nodal pathways.

Dual AVN physiology can be demonstrated by a variety of maneuvers. To determine whether AVN recovery times following a blocked extrastimulus facilitate or obscure detection of dual AVN physiology, 11 patients (9-17 years) were studied with dual AVN pathways by using single and double atrial extrastimuli. With a single atrial extrastimuli, the premature atrial stimulus (A2) was coupled to basic atrial beats (A1). The fast and slow AVN recovery curves were constructed with plots of the nodal conduction time against the recovery time (A1A2,A2H2). With double atrial extrastimuli, a fixed blocked A2 beat (A2B) was followed by a scanning atrial beat (A3). The nodal recovery property post-A2B was studied by plots of A2BA3,A3H3. In all patients the recovery curve of the fast pathway post-A2B had a leftward shift when compared to that of the pre-A2B curve (i.e., the AH was shortened at the same recovery time). The window of slow pathway conduction post-A2B disappeared totally in five patients and decreased significantly in six patients (post-A2B: 26 +/- 42 ms; pre-A2B: 80 +/- 65 ms, P < 0.05). In the six patients that still had slow pathway conduction post-A2B, the slow pathway effective refractory period post-A2B was significantly less than that of pre-A2B (215 +/- 38 vs 268 +/- 16 ms, P < 0.05). The fast pathway effective refractory period post-A2B was also diminished significantly (235 +/- 62 vs 357 +/- 76 ms, P < 0.0001). The authors conclude that blocked atrial beats decrease the visibility of the slow pathway conduction.

Multiple accessory pathways in pediatric patients with Wolff-Parkinson-White syndrome.

The characteristics of multiple accessory pathways in children have not been previously studied. Records were reviewed of 317 consecutive pediatric patients with Wolff-Parkinson-White syndrome who underwent electrophysiologic study and radiofrequency catheter ablation at our institution. Twenty-eight patients (9%) had multiple pathways (a total of 64 pathways: 21 patients had 2, 6 had 3, and 1 patient had 4 pathways). The locations were left free wall (22 pathways), right free wall (19 pathways), posteroseptal (17 pathways), and anteromidseptal (6 pathways). Of these 64 pathways, 55 were ablated successfully without complications, 5 failed ablation, and 4 fasciculoventricular fibers did not require treatment. Three patients had a newly found pathway at the repeat session. Three patients had atrioventricular nodal reentrant tachycardia and the slow pathway area was modified. One patient had failed initial ablation and had a successful ablation using a 3-dimensional electroanatomic mapping system. Compared with patients with a single pathway, those with multiple pathways exhibited a higher incidence of antidromic tachycardia, a shorter anterograde accessory pathway effective refractory period (<250 ms), a longer fluoroscopic time (65 +/- 43 vs 39 +/- 46 minutes, p <0.05), and a larger number of unsuccessful attempts (9 +/- 16 vs 5 +/- 8, p <0.05). Success rate (92% vs 93%) and recurrence rate (1.7% vs 2.1%) were similar in both groups. This study demonstrates that multiple pathways are not rare in pediatric patients and that multiple pathways contrast with a single pathway in a variety of conduction properties.

Usefulness of tissue Doppler echocardiography for evaluating ventricular function in children without heart disease.

Tissue Doppler echocardiographic imaging (TDI) is a novel method for accurately evaluating ventricular function. Currently, scant data are available on the distribution of tissue Doppler indexes in healthy children in the age range of 1 to 18 years. The aims of this study were to assess the distribution of tissue Doppler indexes of systolic and diastolic ventricular function in healthy children, to assess the influence of age on these indexes, and to compare them with conventional Doppler indexes. A total of 151 consecutive children aged 1 to 18 years were enrolled in the study. Nine different (7 diastolic and 2 systolic) TDI parameters were assessed. Peak velocities of systolic and diastolic excursions of the mitral and tricuspid annuli were obtained from the apical 4-chamber view. Mean velocities of early diastolic recoil of mitral and tricuspid annuli were measured from the apical 4-chamber view. The mean velocity of early diastolic relaxation of the left ventricular posterior wall was measured in the parasternal long-axis view. Results showed a statistically significant difference in some of the TDI indexes among the different pediatric age groups. Most of the TDI indexes showed a very weak correlation with age. There was no significant correlation (p >0.05) between peak velocities of the early diastolic mitral inflow Doppler pattern (E wave) and the corresponding TDI index. In contrast, there was a significant (p <0.001) correlation between the corresponding Doppler indexes in the tricuspid annulus. We conclude that TDI is a valuable tool for assessing ventricular function, particularly diastolic function. Establishment of normative data for TDI in the pediatric age group should broaden the clinical applicability of this useful modality for assessing ventricular function.

Quantitative assessment of the recovery property of atriofascicular/atrioventricular-type Mahaim fiber.

INTRODUCTION: One of the characteristics of the Mahaim fiber is that it possesses a decremental property related to the slow rate of recovery of its excitability similar to that of AV node. The aim of this study was to evaluate the recovery property of the atriofascicular/atrioventricular-type Mahaim fiber and compare it with that of the AV node. METHODS AND RESULTS: Nine patients with a Mahaim fiber were studied; 8 of the patients had atriofascicular/atrioventricular-type fiber. Different models were used to analyze the relationship between conduction time for the Mahaim fiber and the corresponding coupling intervals. The simplest model with the best fit was found to be the linear regression of the natural log of conduction time on corrected coupling intervals. The individual R2 values ranged between 0.43 and 0.98 for the Mahaim fiber and between 0.79 and 0.98 for AV node. The final model chosen for the log transformed data for the Mahaim fiber and for the AV node was the line with parameter estimates defined as a weighted average, over patients, of the corresponding individual line parameters. The weight used for each parameter was the inverse of its variance. The slopes of the lines of the transformed data were not significantly different between the Mahaim fiber and the AV node. Thus, the best fitting curve for the recovery property of the AF-type Mahaim fiber is a simple exponential curve similar to that of the AV node. CONCLUSION: The atriofascicular/atrioventricular-type Mahaim fiber has a quantitative recovery property very similar to that of the AV node.