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Introduction: Fasciculoventricular pathways (FVPs) are rare causes of preexcitation that do not mediate tachycardias. We report a two-center experience of pediatric patients with FVP and an unexpectedly high association of complex congenital heart defects (CHDs), chromosomal anomalies, and hypertrophic cardiomyopathy. Methods: A retrospective review of the electrophysiology database at two institutions was performed to identify patients with FVP from January 2000 to January 2011. Medical records of these patients were reviewed for clinical history and course, presence of comorbidities, and details of intracardiac electrophysiology (EP) study. Results: A total of 17 patients were identified. The primary indication for EP study was a preexcitation pattern on electrocardiogram. The majority of patients, 12/17 (71%), were found to have associated cardiac and genetic anomalies. Hypertrophic cardiomyopathy was found in 5/17 (29%) patients, with genetic testing in two patients demonstrating the lysosomal-associated membrane protein 2 mutation (Danon syndrome). Underlying complex CHDs were present in 3/17 (18%) patients. One patient (6%) was status post (s/p) cardiac transplant, one patient had hypertension, and another had Trisomy 21. Other electrophysiologic substrates mediating tachycardia were found in 3/17 (18%) patients. Only 5/17 patients (29%) were otherwise healthy with structurally normal hearts. Conclusions: In this largest reported series of FVP in children, there is an unusually high association of FVP with complex CHDs, chromosomal anomalies, and hypertrophic cardiomyopathy. Any patient with such disorders and manifest preexcitation should be evaluated with a high index of suspicion for a FVP. (PACE 2012;1-6) [ABSTRACT FROM AUTHOR]

Background: A wearable automated external defibrillator has been shown to be efficacious in the prevention of sudden death in adults who had a history of cardiac arrest but who did not have a permanent internal cardioverter/defibrillator (ICD) placed. The use of a wearable defibrillator has not been established in the pediatric population. Methods: We retrospectively reviewed the clinical database for the wearable external defibrillator from ZOLL Lifecor Corporation (Pittsburgh, PA, USA). We compared the use of the wearable defibrillator in patients ≤18 years of age to those aged 19–21 years. Results: There were 81 patients ≤18 years of age (median age = 16.5 years [9–18] and 52% male). There were 103 patients aged 19–21 years (median age = 20 years [19–21] and 47% male). There was no difference between groups in average hours/day or in total number of days the patients wore the defibrillator. In patients ≤18 years of age, there was one inappropriate therapy and one withholding of therapy due to a device–device interaction. In patients aged 19–21 years, there were five appropriate discharges in two patients and one inappropriate discharge in a single patient. Conclusion: It is reasonable to consider the wearable automated external defibrillator as a therapy for pediatric patients who are at high risk of sudden cardiac arrest but who have contraindications to or would like to defer placement of a permanent ICD. As there were no appropriate shocks in our patients ≤18 years of age, this study cannot address efficacy of the therapy. (PACE 2010; 33:1119–1124) [ABSTRACT FROM AUTHOR]

Background: Cryoablation with 4- and 6-mm tip ablation catheters has been demonstrated to be safe and effective in the treatment of atrioventricular nodal reentrant tachycardia (AVNRT) in pediatric patients, albeit with a higher rate of clinical recurrence. Limited information is available regarding efficacy, mid-term outcomes, and complications related to the use of the 8-mm Freezor Max Cryoablation catheter (Medtronic, Minneapolis, MN, USA) in pediatric patients. Methods: We performed a retrospective review of all pediatric patients with normal cardiac anatomy who underwent an ablation procedure for treatment of AVNRT using the 8-mm tip Cryoablation catheter at three large pediatric academic arrhythmia centers. Results: Cryoablation with an 8-mm tip catheter was performed in 77 patients for treatment of AVNRT (female n = 40 [52%], age 14.8 ± 2.2 years, weight 62.0 ± 13.9 kg). Initial procedural success was achieved in 69 patients (69/76, 91%). Transient second- or third-degree atrioventricular (AV) block was noted in five patients (6.5%). There was no permanent AV block. Of the patients successfully ablated with Cryotherapy, there were two recurrences (2/70, 2.8%) over a follow-up of 11.6 ± 3.3 months. Conclusion: Cryoablation with an 8-mm tip ablation catheter is both safe and effective with a low risk of recurrence for the treatment of AVNRT in pediatric patients. (PACE 2010; 33:681–686) [ABSTRACT FROM AUTHOR]

Introduction: Coronary sinus accessory pathways (CSAPs), atrioventricular connections formed by the coronary sinus myocardial coat, have been described in adult patients, but not systematically described in pediatric patients. Methods: Patients who underwent CSAP ablation were compared to patients with right posteroseptal (RPS) pathway ablation (control group) from November 2004 to June 2007. Retrospective reviews of preablation 12-lead electrocardiogram (EKG), fluoroscopic, and intracardiac electrogram data were then performed to identify electrophysiologic markers of CSAP. Results: A total of 23 patients were identified: 13 with CSAP and 10 with RPS pathways. Preablation EKGs demonstrated preexcitation in 8/10 (80%) patients with RPS pathways versus 9/13 (69%) patients with CSAP (P = 0.66). Preexcitation with a negative delta wave in lead II was seen in 5/9 (56%) patients with CSAP versus 0/8 in RPS (P = 0.029), and preexcitation with a positive delta wave in augmented vector right (aVR) was seen in 9/9 (100%) patients with CSAP versus 3/8 (37.5%) with RPS (P = 0.009). Accessory pathway (AP) potentials were seen on the coronary sinus (CS) catheter in 6/13 (46%) of CSAP and in 0 RPS ablations (P = 0.019). Recurrence of tachycardia occurred in 5/13 (38%) of patients with CSAP and 1/10 (10%) of patients with RPS pathways (P = 0.18). Conclusions: CSAPs should be considered when preablation EKG demonstrates preexcitation with a negative delta wave in lead II and a positive delta wave in aVR, and if an AP potential is seen on the CS catheter. Recurrence of tachycardia postablation or the need for multiple ablations should raise suspicion for a CSAP. [ABSTRACT FROM AUTHOR]

We report a fatal device-device interaction between a wearable automated defibrillator (WAD; LifeVest - LifeCor, Inc., Pittsburgh, PA, USA) and a unipolar pacemaker that occurred in an 18-year-old patient listed for cardiac transplantation due to his failing Fontan. The patient developed ventricular tachycardia that was initially detected by the WAD. However, large unipolar pacing artifacts and specific WAD arrhythmia detection algorithms caused the WAD to revert to nonrecognition of the arrhythmia, which lead to the patient's death. We identify likely causes of the failure and suggest methods of preventing such occurrences in the future. [ABSTRACT FROM AUTHOR]

Background: The potential advantages of using a 4Fr lumenless pacing lead (3830 SelectSecure™, Medtronic Inc, Minneapolis, MN, USA) in children are largely negated due to the large size of the delivery system. Here we describe an innovative, sheath guided, delivery technique using conventional 5F sheaths. Methods: Transvenous access was obtained via the left cephalic or axillary vein. A 5Fr introducer set with a 45° curved tip (CheckFlo® Performer® Introducer Set with the Children's Hospital Boston Modification, Cook Medical Inc, Bloomington, IN, USA) was placed over a wire into the right atrium (RA) or right ventricle (RV). The sheath was modified by cutting off the valved end and a SelectSecure™ lead was introduced through the sheath. Rotating the sheath provided steerability and allowed for precise placement of the lead. After successful lead placement, the sheath was removed with a universal sheath splitter. Results: We placed seven atrial and six ventricular leads in eight patients during nine separate cases with this method. Patient ages and weights ranged from 5 to 16 years and 16 to –59 kg respectively. Pacing thresholds were excellent at implant. Leads were placed successfully in all attempts. There were no procedural complications. One patient had leads placed twice; both lead systems were removed for suspected infection. Over short-term follow-up in five patients, lead position and characteristics have remained stable. Conclusion: Delivery of the SelectSecure™ lead in children can be successfully and precisely performed using a modified 5Fr sheath obviating the need for a large steerable delivery system. [ABSTRACT FROM AUTHOR]

Background: Cryoablation has emerged as a new, theoretically safer, modality for treating atrioventricular nodal reentrant tachycardia (AVNRT). The purpose of this study is to compare procedural aspects and outcomes during the transition from radiofrequency (RF) ablation to cryoablation for pediatric AVNRT. Methods: Data were obtained retrospectively from 80 consecutive pediatric patients who underwent AVNRT ablation from 10/2001– 4/2006 (RF n = 42, Cryo n = 38). Statistical analysis was performed using unpaired t-test, chi-square test, and analysis of variance. Results: RF ablations were performed anatomically in NSR while three different mapping techniques were used during cryoablation: ablation during AVNRT (26%), anatomic in NSR (48%), and anatomic with S1 S2 pacing (26%). There was no difference in the number or duration of lesions between the three cryo subgroups. Acute success was obtained in 95% of RF and 97% of cryo cases. There was no difference in the number of total, mapping, or full-duration lesions between the RF and cryogroups. Despite accounting for longer cryolesion time, total ablation time (P < 0.001), mapping time (P = 0.002), and full duration lesion time (P < 0.001) were longer in the cryogroup. There was no significant difference in total procedure time; fluoroscopy time was shorter in the cryoablation group (P = 0.049). There was one confirmed recurrence of tachycardia in each group with a 2% recurrence rate. Conclusions: Cryoablation for treatment of pediatric AVNRT is as safe and efficacious as RF ablation. Although cryolesions are intrinsically longer in duration, total procedure times were not increased and fluoroscopy times were decreased compared to RF. [ABSTRACT FROM AUTHOR]

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 transeptal 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. [ABSTRACT FROM AUTHOR]

Introduction: In pediatric and congenital heart disease patients, transvenous ICD implantation may be limited secondary to patient size, venous, or cardiac anatomy. Epicardial patches require a thoracotomy, and may lead to a restrictive pericardial process. Because of these issues, we have explored novel ICD configurations. Methods: Retrospective review at 10 centers implanting ICDs without a transvenous shocking coil or epicardial patches. Results: Twenty-two patients underwent implant at a mean age of 8.9 years (range: 0.3–43.5), with a mean weight of 25.5 kg (range: 5.2–70). Diagnoses included complex CHD, intracardiac tumors, cardiomyopathy, idiopathic VT, LV noncompaction, and long QT syndrome. Three configurations were used: subcutaneous array, a transvenous design ICD lead placed on the epicardium, or a transvenous design ICD lead placed subcutaneously. Difficulties were found at implant in 8 patients: 4 had difficulty inducing VT/VF, and 4 had high DFTs. Over a mean follow-up of 2.2 years (range: 0.2–10.5), 7 patients had appropriate shocks. Inappropriate shocks occurred in 4 patients. System revisions were required in 7 patients: 2 generator changes (in 1 patient), 3 pace-sense lead replacement, 1 additional subcutaneous coil placement due to increased DFT, 1 upgrade to a transvenous system, and 1 revision to epicardial patch system. Conclusions: ICD implantation can be performed without epicardial patches or transvenous high-energy leads in this population, using individualized techniques. This will allow ICD use in patients who have intracardiac shunting or are deemed too small for transvenous ICD leads. The long-term outcome and possible complications are as yet unknown in this population, and they should be monitored closely with follow-up DFTs. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Skeletal muscle has been used for biomechanicol assist in experimental and clinical studies. Central to the success of these procedures is the generation of sufficient muscle force for the lifetime of the subject. Burst (tetanic) stimulation results in summation of individual twitches and generates higher power output. However, the superiority of paroneural versus intramuscular as well as proximal versus middle and distal intramuscular stimulations remains unclear. Electrophysiological mapping and mechanical performance of seven canine latissimus dorsi muscles were analyzed. The mechanism of higher tension generation produced by: (1) increased temporal summation; (2) greater motor units activated; or (3) result of both were determined. The parameters primarily dependent on the number of activated motor units are significantly greater following paraneural and proximal intramuscular stimulations. The parameters mainly related to temporal summation ore not different between various electrode configurations. For intramuscular stimulation, it is the location of interelectrode field rather than the locution of the cathode per se that determines the mechanical performance of the skeletal muscle. Furthermore, tension development of skeletal muscle is primary nerve activation rather than direct muscle stimulation. The higher tension generation that resulted from different electrode configurations is produced by activating a higher number of muscle fibers through the neuromuscular junctions. [ABSTRACT FROM AUTHOR]

The effect of flecainide, 0.3 mg/L and 1.0 mg/L, on inducible nonsustained reentry was studied, in vitro, in the canine tricuspid ring. Nonsustained reentry was engineered by cutting the ring and reconnecting it with an adjustable electronic delay. Delays were used that produced reentry lasting 1-3 beats (group A), 4-10 beats (group B), and 11-25 beats (group C). Reentry was initiated multiple times at each selected delay. A proarrhythmic effect, defined as a significant increase in the duration of reentry, was observed in all 14 trials at the law dose and in two of 15 trials at the high dose in seven experiments. In four mare trials a transient proarrhythmic response was seen initially during exposure to the high dose. In five of seven experiments, reentry became sustained after at least one dose of flecainide. Proarrhythmic responses resulted when flecainide increased the tachycardia cycle length more than the effective refractory period and there was less cycle length oscillation after initiation. Antiarrhythmic responses resulted either from a marked increase in effective refractory period at the site of block or production affixed block. [ABSTRACT FROM AUTHOR]

Introduction: Fasciculoventricular pathway has been described as an unusual variant of preexcitation. Electrocardiographic imaging (ECGI) is a novel imaging modality for noninvasive electroanatomic mapping of epicardial activation and repolarization. Case: We present a case of an 18-year-old male with hypertrophic cardiomyopathy (HCM) and an electrocardiogram (ECG)-based diagnosis of Wolff-Parkinson-White (WPW) syndrome, who underwent a noninvasive ECGI study to image ventricular activation, followed by an electrophysiology study (EPS). The ECGI electroanatomic isochrone map showed early activation of the epicardial aspect of the atrioventricular (A-V) groove and an aberrant posterior-base-to-apex progression of activation in the left ventricular (LV) epicardium. The EPS showed a likely fasciculoventricular pathway (FVP) without any inducible tachycardia. Conclusion: While FVP has been described before, this is the first report of detailed quantitative three-dimensional characterization of electrical activation sequence of a heart with this type of preexcitation, using a novel noninvasive imaging modality (ECGI). In spite of abnormal ventricular activation, the EPS demonstrated that the FVP is not capable of supporting reentrant supraventricular tachycardia or rapidly conducted atrial fibrillation. [ABSTRACT FROM AUTHOR]

The article focuses on the use of implantable cardioverter defibrillators (ICD) in pediatric patients. Several studies in adults with nonthoracotomy ICD systems have suggested routine postimplant ICD testing is unnecessary if there is no suspicion of device or lead malfunction, and one editorial has suggested defibrillation testing at the time of ICD implant may not even be necessary at all. At least three prospective studies have examined the stability of the defibrillation threshold (DFT) with respect to minimal safety margins in adult ICD patients. In the Post Implant Testing Study, 764 routine postimplant DFT tests were analyzed.