Christine C. Chiu

Are Implantable Loop Recorders Useful in Detecting Arrhythmias in Children with Unexplained Syncope

Introduction: Syncope and presyncope are symptoms that occur infrequently in children, are unpredictable, and represent a diagnostic challenge to the physician. Conventional diagnostic investigations are often unable to establish a diagnosis, making it difficult to determine patient risk and direct appropriate therapy. The implantable loop recorder (ILR) is a medical device that was created for prolonged monitoring of heart rate and rhythm and has been used in a limited number of pediatric studies in which the cause of the syncope is unknown.

A Comparison of Two Stab-On Unipolar Epicardial Pacing Leads in Children

The Oscor MP52V and Medtronic 4951 leads have similar construction and intended application. To determine if one of these designs was more suited to pediatric pacing, we reviewed implant, 3 month, and 12 months follow‐up thresholds for all 18 MP52V implants at our institution from December 1989 to April 1991 and compared them to the 4951 implants from fanuary 1982 to October 1989. Lead suirival for tbe MP52V implants was compared to the most recent 36 4951 implants. Patients ranged in ages from 2 days–16 years (median = 4 years) and required antibradycardia pacing for congenital or acquired heart disease. Patients were compared for weigbt and proportion ofatrial leads in each group by t‐test and Fisher exact tests respectively. Energy thresholds were assessed in μJ and compared by t‐test. Lead survival was defined hy abandonment or replacement for any reason. Kaplan 8‐ Meier survival curves were plotted and compared by Gehans Wilcoxan Test There were no significant differences between the MP52V and 4951 groups for age at implant (53 months vs 80 months) or proportion of atrial implants (5/18 vs 11/36). Lead survival was poor but did not differ significantly (70% vs 78% cumulative survival at 3 vears), usuallv failing by exit block. Implant and follow‐up thresholds did not differ significantly between leads. The MP52V did not provide significant improvement in performance over the 4951. New epicardial lead designs are needed to improve lead survival and thresholds in children.

Evolution of Heart Rate Control After Transplantation: Conduction Versus Autonomic Innervation

In cardiac transplantation, the donor organ is not initially innervated and demonstrates decreased heart rate variability (HRV). However, HRV may improve after several months. The mechanism for HRV improvement has not been elucidated; autonomic “reinnervation” of the donor heart has been proposed. The role of atrioatrial conduction from recipient to donor organ has not been evaluated. We prospectively evaluated cardiac transplant patients with a limited electrophysiology study at the time of their surveillance biopsies. Recordings were made of recipient and donor signals, observing conduction properties between recipient and donor atria. Holter recordings were analyzed and HRV was determined using spectral analysis techniques, recording mean RR interval, low-frequency power (LF), high-frequency power (HF), and the LF/HF ratio. These were compared to published norms. From November 1999 to May 2000, 21 patients (6 female) who underwent cardiac transplantation participated at a median age of 101 months (range, 4.1–217 months). Time posttransplant ranged from 26 days to 71 months. Holter data were available for 20 patients and demonstrated dissociated P waves in 13 (65%). The mean heart rate on Holter was 111 beats per minute (bpm) (range, 85–161 bpm). We were able to record distinct recipient atrial signals in 16 of 21 (76%) patients. The average recipient tissue heart rate was 55% that of the donor heart rate. We documented atrioatrial association in only 1 patient. HRV did not reach normal values for most patients and did not increase with time posttransplantation. The LF values were in the normal range for most patients, whereas 3 patients had normal HF values and 2 patients had values just below normal. Recipients of heart transplantation have a predominantly sympathetic influence of HRV. These preliminary data suggest that atrioatrial conduction does not play a role in reestablishing normal heart rate control following pediatric cardiac transplantation.

Clinical use of permanent pacemaker for conversion of intraatrial reentry tachycardia in children.

CHIU, C.C., et al.: Clinical Use of Permanent Pacemaker for Conversion of Intraatrial Reentry Tachycardia in Children. The use of the implanted atrial‐based pacemaker to overdrive postsurgical intraatrial reentry tachycardia (IART) was evaluated in a large group of pediatric patients over a 14‐year study period. The authors sought to determine the feasibility of this noninvasive technique in the management of this specialized population and to determine factors associated with successful conversion. They examined 128 manual overdrive attempts performed on 22 consecutive patients. There were 10 patients with post‐Fontan repair, 7 with post‐Mustard/Senning procedure, and 5 with miscellaneous lesion types. The number of IART episodes for overdrive pacing per patient ranged from 1 to 15. The first overdrive pacing attempt was successful in 63% (14/22) of the patients. The mean IART cycle length was 278 ± 59 ms. The mean pacing rate for effective conversion of IART was 66 ± 10% faster than the IART rate. By controlling for repeated measures for individual patients, three factors were found to be independently associated with a successful outcome: (1) lesion type other than Fontan surgery (P = 0.007), (2) lack of acceleration of IART with the overdrive attempt (P < 0.001), and (3) patient use of amiodarone with attempt (P = 0.005). There were three procedural complications: two inadvertent overdrive pacing episodes, and one episode of acceleration of IART cycle length and conduction resulting in need for cardioversion. Manual pacemaker overdrive conversion of IART is a useful adjunct in the management of postsurgical IART in the pediatric population and should be considered as an initial treatment option.

Unusual electrophysiological findings in atrioventricular node reentrant tachycardia.

Introduction (AVNRT) was made based on the demonstration of inducible supraventricular tachycardia with a The tracings are from an 8-year-old boy with septa1 retrograde atrial activation sequence; and recurrent paroxysmal supraventricular tachycarthe inability to preexcite the atria when a ventricudia who had frequent recurrences despite antiarlar premature beat was introduced when the His rhythmic medication. Combined electrophysiolbundle was refractory. ogy study and ablation was planned. A diagnosis Figure 1, left side, was taken prior to applying of atrioventricular node reentrant tachycardia pressure with the ablation catheter in the vicinity

Impact of Programmed Sensitivity Safety Factor on Atrial Sensing in Children

The relationship between the pacemaker sensitivity safety factor (PSSF) and atrial under‐ or oversensing as documented by 24‐hour Holter monitoring was examined. Our study comprised 78 transvenous fixed atrial leads implanted between 1983–1995 in 71 children. Overall, 210 Holter reports identified 143 (68%) Holters with normal atrial sensing function, 31 (15%) with undersensing, 32 (15%) with oversensing, and 4 (2%) with both problems. From 161 Holter reports in which the PSSF was available, the incidence of undersensing at a PSSF of 2.0 (range 1.5–2.4) was 25% (14/57). There was a dramatic decline in undersensing when the PSSF was 3 (3%) compared to a FSSF < 3 (21 %) (P < 0.001). A PSSF cut‐off point of 2.0 best predicted occurrence of undersensing with a sensitivity of 79% and a specificity of 67%. Other variable were also examined by multiple logistic regression analysis, but only PSSF remained highly associated with undersensing (odds ratio [OR] = 0.6, P = 0.03). In contrast, PSSF did not have a significant role in predicting oversensing, but presence of sick sinus syndrome (OR = 10.5) or unipolar lead (OR = 5.6) were significantly associated with oversensing (P = 0.0001). The majority of undersensing problems can be avoided by routinely allowing for at least a threefold or more programmed sensitivity margin. Other factors may increase the risk of oversensing, regardless of the PSSF.

Simultaneous Wide and Narrow QRS Complex Tachycardias in a Child: What Is the Mechanism?

Case Presentation An 8-year-old boy was referred for recurrent wide complex tachycardia. At 4 years of age, his initial presentation to another facility was notable for acute heart failure due to a wide complex tachycardia (260 bpm) with right bundle block (RBBB) morphology and left axis deviation resistant to adenosine and to DC shocks and finally converted to sinus rhythm (SR) after i.v. amiodarone. Cardiac work-up ruled out structural heart disease. On the present admission the heart rate was 215 beats/minute and the QRS morphology was identical to the previous episode (Fig. 1). Adenosine rapid bolus was given