Demonstrating responsiveness of the pediatric cardiac quality of life inventory in children and adolescents undergoing arrhythmia ablation, heart transplantation, and valve surgery.

PURPOSE: Pediatric Cardiac Quality of Life Inventory (PCQLI) is a disease-specific pediatric cardiac health-related quality of life (HRQOL) instrument that is reliable, valid, and generalizable. We aim to demonstrate PCQLI responsiveness in children undergoing arrhythmia ablation, heart transplantation, and valve surgery before and after cardiac intervention. METHODS: Pediatric cardiac patients 8-18 years of age from 11 centers undergoing arrhythmia ablation, heart transplantation, or valve surgery were enrolled. Patient and parent-proxy PCQLI Total, Disease Impact and Psychosocial Impact subscale scores were assessed pre- and 3-12 months follow-up. Patient clinical status was assessed by a clinician post-procedure and dichotomized into markedly improved/improved and no change/worse/much worse. Paired t-tests examined change over time. RESULTS: We included 195 patient/parent-proxies: 12.6 ± 3.0 years of age; median follow-up time 6.7 (IQR = 5.3-8.2) months; procedural groups - 79 (41%) ablation, 28 (14%) heart transplantation, 88 (45%) valve surgery; clinical status - 164 (84%) markedly improved/improved, 31 (16%) no change/worse/much worse. PCQLI patient and parent-proxies Total scores increased (p ≤ 0.013) in each intervention group. All PCQLI scores were higher (p < 0.001) in the markedly improved/improved group and there were no clinically significant differences in the PCQLI scores in the no difference/worse/much worse group. CONCLUSION: The PCQLI is responsive in the pediatric cardiac population. Patients with improved clinical status and their parent-proxies reported increased HRQOL after the procedure. Patients with no improvement in clinical status and their parent-proxies reported no change in HRQOL. PCQLI may be used as a patient-reported outcome measure for longitudinal follow-up and interventional trials to assess HRQOL impact from patient and parent-proxy perspectives.

It is important to have quality of life (QOL) measures that are sensitive to change in QOL before and after procedures and to be sensitive to change over time. The Pediatric Cardiac Quality of Life Inventory (PCQLI) is a QOL measure specifically developed for children with cardiac disease. This study assessed the responsiveness of the PCQLI to detect change in QOL over time. QOL in Children and adolescents who were being treated for abnormal heart rhythms, heart transplantation, and aortic, pulmonary, or mitral valve surgery were assessed before and after their procedure. Children and adolescents with improved clinical status post-procedure, and their parents, reported better QOL after the procedure. Patients with no improvement from a cardiac standpoint and their parents reported no change in QOL after their procedure. The PCQLI may be used to assess QOL before and after cardiac procedures or medical treatment and follow QOL over time.

How we do it: Cardiac implantable devices are not a contraindication to MRI: time for a paradigm shift.

Magnetic resonance imaging (MRI) is now an indispensable diagnostic tool in medicine due to its outstanding contrast resolution and absence of radiation exposure, enabling detailed tissue characterization and three-dimensional anatomical representation. This is especially important when evaluating individuals with congenital heart disease (CHD) who frequently require cardiac implantable electrical devices (CIEDs). While MRI safety issues have previously limited its use in patients with CIEDs, new advances have called these limitations into question. However, difficulties persist in the pediatric population due to the continued lack of specific safety data both related to imaging young children and the specific CIED devices they often require. This paper discusses MRI safety considerations related to imaging patients with CIEDs, investigates pediatric-specific problems, and describes thorough methods for safe MRI access, highlighting the significance of specialized institutional guidelines.

Preliminary assessment of paediatric electrophysiology cardiac implantable electronic device resources around the world.

BACKGROUND: The Pediatric and Congenital Electrophysiology Society (PACES) is a global organisation committed to the care of children and adults with CHD and arrhythmias. OBJECTIVE: To evaluate the global needs and potential inequities as it relates to cardiac implantable electronic devices. METHODS: ARROW (Assessment of Rhythm Resources arOund the World) is an online survey about cardiac implantable electronic devices, sent electronically to physicians within the field of Cardiology, Pediatric Cardiology, Electrophysiology and Pediatric Electrophysiology. RESULTS: ARROW received 42 responders from 28 countries, 50% from low-/middle-income regions. The main differences between low-/middle- and high-income regions include availability of expertise on paediatric electrophysiology (50% versus 93%, p < 00.5) and possibility to perform invasive procedures (35% versus 93%, p < 0.005). Implant of devices in low-income areas relies significantly on patient's resources (71%). The follow-up of the devices is on the hands of paediatric cardiologist/electrophysiologist in higher resources centres (93% versus 50%, p < 0.05). CONCLUSIONS: The ARROW survey represents an initial assessment of the geographical characteristics in the field of Pediatric Electrophysiology. The next step is to make this "state of the art" more extensive to other aspects of the expertise. The relevance of collecting this data before the World Congress of Pediatric Cardiology and Cardiac Surgery (WCPCCS) in 2023 in Washington DC was emphasised in order to share the resulting information with the international community and set a plan of action to assist the development of arrhythmia services for children within developing regions of the world.

Life-threatening cardiac arrhythmia and sudden death during electronic gaming: An international case series and systematic review.

BACKGROUND: Electronic gaming has recently been reported as a precipitant of life-threatening cardiac arrhythmia in susceptible individuals. OBJECTIVE: The purpose of this study was to describe the population at risk, the nature of cardiac events, and the type of game linked to cardiac arrhythmia associated with electronic gaming. METHODS: A multisite international case series of suspected or proven cardiac arrhythmia during electronic gaming in children and a systematic review of the literature were performed. RESULTS: Twenty-two patients (18 in the case series and 4 via systematic review; aged 7-16 years; 19 males [86%]) were identified as having experienced suspected or proven ventricular arrhythmia during electronic gaming; 6 (27%) had experienced cardiac arrest, and 4 (18%) died suddenly. A proarrhythmic cardiac diagnosis was known in 7 (31%) patients before their gaming event and was established afterward in 12 (54%). Ten patients (45%) had catecholaminergic polymorphic ventricular tachycardia, 4 (18%) had long QT syndrome, 2 (9%) were post-congenital cardiac surgery, 2 (9%) had "idiopathic" ventricular fibrillation, and 1 (after Kawasaki disease) had coronary ischemia. In 3 patients (14%), including 2 who died, the diagnosis remains unknown. In 13 (59%) patients for whom the electronic game details were known, 8 (62%) were war games. CONCLUSION: Electronic gaming can precipitate lethal cardiac arrhythmias in susceptible children. The incidence appears to be low, but syncope in this setting should be investigated thoroughly. In children with proarrhythmic cardiac conditions, electronic war games in particular are a potent arrhythmic trigger.

Cardiopulmonary Exercise Testing in Pediatric Patients With Hypertrophic Cardiomyopathy.

Background: Exercise stress testing (EST) in pediatric hypertrophic cardiomyopathy (HCM) patients has not well described in a large heterogenous cohort. Objectives: The objective of the study was to determine the clinical utility of EST in pediatric HCM. Methods: This was a retrospective single-center analysis of HCM patients younger than 21 years who had EST between January 1, 2000, and January 1, 2019. Clinical, demographic characteristics, and EST data were analyzed, using the last EST during the study or prior to the event in subjects with a primary outcome. The primary composite endpoint included cardiac death, transplant, or arrhythmia requiring implantable cardioverter-defibrillator placement. Outcome analysis was performed using Cox proportional hazard modeling. Results: The study cohort included 140 patients, 52% with a recognized genetic variant. There were 2 tests aborted due to safety concerns (ST-segment changes, ventricular ectopy). The median age at first EST was 13.6 years. Ninety percent of patients were tested using cycle ergometry, and 44% were on a beta-blocker. The median peak oxygen consumption was 37.1 mL/kg/min (IQR: 12.5 mL/kg/min) or 81.2% predicted, the mean anaerobic threshold was 21.8 Ml (IQR: 8.3 mL), and the median peak power was 2.6 ± 1.1 W/kg or 73.7% predicted. Ectopy during EST was seen in 44% of patients, and 8% had an abnormal blood pressure response to exercise. The endpoint was reached in 12 patients. The presence of any degree of ectopy was a predictor of the composite endpoint (hazard ratio: 5.8; 95% CI: 1.3-26.7). Conclusions: EST is clinically useful in select pediatric patients with HCM. Ectopy on EST is a risk factor for cardiac death, cardiac transplant, and arrhythmias requiring implantable cardioverter-defibrillator.

Guidance for Rebooting Electrophysiology Through the COVID-19 Pandemic From the Heart Rhythm Society and the American Heart Association Electrocardiography and Arrhythmias Committee of the Council on Clinical Cardiology: Endorsed by the American College of Cardiology.

Coronavirus disease 2019 (COVID-19) has presented substantial challenges to patient care and impacted health care delivery, including cardiac electrophysiology practice throughout the globe. Based upon the undetermined course and regional variability of the pandemic, there is uncertainty as to how and when to resume and deliver electrophysiology services for arrhythmia patients. This joint document from representatives of the Heart Rhythm Society, American Heart Association, and American College of Cardiology seeks to provide guidance for clinicians and institutions reestablishing safe electrophysiological care. To achieve this aim, we address regional and local COVID-19 disease status, the role of viral screening and serologic testing, return-to-work considerations for exposed or infected health care workers, risk stratification and management strategies based on COVID-19 disease burden, institutional preparedness for resumption of elective procedures, patient preparation and communication, prioritization of procedures, and development of outpatient and periprocedural care pathways.

Frequency of Ventricular Arrhythmias and Other Rhythm Abnormalities in Children and Young Adults With the Marfan Syndrome.

Patients with the Marfan syndrome (MFS) are at risk for sudden death. The contribution of arrhythmias is unclear. This study examines the prevalence of arrhythmias in children with the MFS and their relation to clinical and/or echocardiographic factors. Data from the Pediatric Heart Network randomized trial of atenolol versus losartan in MFS were analyzed (6 months to 25 years old, aortic root diameter z-score > 3.0, no previous aortic surgery and/or dissection). Baseline 24-hour ambulatory electrocardiographic monitoring was performed. Significant ventricular ectopy (VE) and supraventricular ectopy (SVE) were defined as ≥10 VE or SVE/hour, or the presence of high-grade ectopy. Three-year composite clinical outcome of death, aortic dissection, or aortic root replacement was analyzed. There were 274 analyzable monitors on unique patients from 11 centers. Twenty subjects (7%) had significant VE, 13 (5%) significant SVE; of these, 2 (1%) had both. None had sustained ventricular or supraventricular tachycardia. VE was independently associated with increasing number of major Ghent criteria (odds ratio [OR] = 2.13/each additional criterion, p = 0.03) and greater left ventricular end-diastolic dimension z-score (OR = 1.47/each 1 unit increase in z-score, p = 0.01). SVE was independently associated with greater aortic sinotubular junction diameter z-score (OR = 1.56/each 1 unit increase in z-score, p = 0.03). The composite clinical outcome (14 events) was not related to VE or SVE (p ≥ 0.3), but was independently related to heart rate variability (higher triangular index). In conclusion, in this cohort, VE and SVE were rare. VE was related to larger BSA-adjusted left ventricular size. Routine ambulatory electrocardiographic monitoring may be useful for risk stratification in select MFS patients.

Development and impact of arrhythmias after the Norwood procedure: A report from the Pediatric Heart Network.

OBJECTIVES: The study objective was to determine the predictors of new-onset arrhythmia among infants with single-ventricle anomalies during the post-Norwood hospitalization and the association of those arrhythmias with postoperative outcomes (ventilator time and length of stay) and interstage mortality. METHODS: After excluding patients with preoperative arrhythmias, we used data from the Pediatric Heart Network Single Ventricle Reconstruction Trial to identify risk factors for tachyarrhythmias (atrial fibrillation, atrial flutter, supraventricular tachycardia, junctional ectopic tachycardia, and ventricular tachycardia) and atrioventricular block (second or third degree) among 544 eligible patients. We then determined the association of arrhythmia with outcomes during the post-Norwood hospitalization and interstage period, adjusting for identified risk factors and previously published factors. RESULTS: Tachyarrhythmias were noted in 20% of subjects, and atrioventricular block was noted in 4% of subjects. Potentially significant risk factors for tachyarrhythmia included the presence of modified Blalock-Taussig shunt (P = .08) and age at Norwood (P = .07, with risk decreasing each day at age 8-20 days); the only significant risk factor for atrioventricular block was undergoing a concomitant procedure at the time of the Norwood (P = .001), with the greatest risk being in those undergoing a tricuspid valve procedure. Both tachyarrhythmias and atrioventricular block were associated with longer ventilation time and length of stay (P < .001 for all analyses). Tachyarrhythmias were not associated with interstage mortality; atrioventricular block was associated with mortality among those without a pacemaker in the unadjusted analysis (hazard ratio, 2.3; P = .02), but not after adding covariates. CONCLUSIONS: Tachyarrhythmias are common after the Norwood procedure, but atrioventricular block may portend a greater risk for interstage mortality.

Radiation safety protocol using real-time dose reporting reduces patient exposure in pediatric electrophysiology procedures.

Radiation exposure during pediatric catheterization is significant. We sought to describe radiation exposure and the effectiveness of radiation safety protocols in reducing exposure during catheter ablations with electrophysiology studies in children and patients with congenital heart disease. We additionally sought to identify at-risk patients. We retrospectively reviewed all interventional electrophysiology procedures performed from April 2009 to September 2011 (6 months preceding intervention, 12 months following implementation of initial radiation safety protocol, and 8 months following implementation of modified protocol). The protocols consisted of low pulse rate fluoroscopy settings, operator notification of skin entrance dose every 1,000 mGy, adjusting cameras by >5 at every 1,000 mGy, and appropriate collimation. The cohort consisted of 291 patients (70 pre-intervention, 137 after initial protocol implementation, 84 after modified protocol implementation) at a median age of 14.9 years with congenital heart disease present in 11 %. Diagnoses included atrioventricular nodal reentrant tachycardia (25 %), atrioventricular reentrant tachycardia (61 %), atrial tachycardias (12 %), and ventricular tachycardia (2 %). There were no differences between groups based on patient, arrhythmia, and procedural characteristics. Following implementation of the protocols, there were significant reductions in all measures of radiation exposure: fluoroscopy time (17.8 %), dose area product (80.2 %), skin entry dose (81.0 %), and effective dose (76.9 %), p = 0.0001. Independent predictors of increased radiation exposure included larger patient weight, longer fluoroscopy time, and lack of radiation safety protocol. Implementation of a radiation safety protocol for pediatric and congenital catheter ablations can drastically reduce radiation exposure to patients without affecting procedural success.

An international multicenter study comparing arrhythmia prevalence between the intracardiac lateral tunnel and the extracardiac conduit type of Fontan operations.

OBJECTIVE: The study objective was to determine whether the extracardiac conduit Fontan confers an arrhythmia advantage over the intracardiac lateral tunnel Fontan. METHODS: This multicenter study of 1271 patients compared bradyarrhythmia (defined as need for pacing) and tachyarrhythmia (defined as needing antiarrhythmic therapy) between 602 patients undergoing the intracardiac Fontan and 669 patients undergoing the extracardiac Fontan. The median age at the time of the Fontan procedure was 2.1 years (interquartile range, 1.6-3.2 years) for the intracardiac group and 3.0 years (interquartile range, 2.4-3.9) for the extracardiac group (P < .0001). The median follow-up was 9.2 years (interquartile range, 5-12.8) for the intracardiac group and 4.7 years (interquartile range, 2.8-7.7) for the extracardiac group (P < .0001). RESULTS: Early postoperative (<30 days) bradyarrhythmia occurred in 24 patients (4%) in the intracardiac group and 73 patients (11%) in the extracardiac group (P < .0001). Early postoperative (<30 days) tachyarrhythmia occurred in 32 patients (5%) in the intracardiac group and 53 patients (8%) in the extracardiac group (P = not significant). Late (>30 days) bradyarrhythmia occurred in 105 patients (18%) in the intracardiac group and 63 patients (9%) in the extracardiac group (P < .0001). Late (>30 days) tachyarrhythmia occurred in 58 patients (10%) in the intracardiac group and 23 patients (3%) in the extracardiac group (P < .0001). By multivariate analysis factoring time since surgery, more patients in the extracardiac group had early bradycardia (odds ratio, 2.9; 95% confidence interval, 1.8-4.6), with no difference in early tachycardia, late bradycardia, or late tachycardia. CONCLUSIONS: Overall arrhythmia burden is similar between the 2 groups, but the extracardiac Fontan group had a higher incidence of early bradyarrhythmias. There was no difference in the incidence of late tachyarrhythmias over time between the 2 operations. Therefore, the type of Fontan performed should be based on factors other than an anticipated reduction in arrhythmia burden from the extracardiac conduit.

Do LQTS gene single nucleotide polymorphisms alter QTc intervals at rest and during exercise stress testing?

BACKGROUND: The impact of harboring, genetic variants or single nucleotide polymorphisms (LQT-PM) on the repolarization response during exercise and recovery is unknown. OBJECTIVE: To assess the QTc interval adaptation during exercise stress testing (EST) in children with LQT polymorphisms compared to a group of age and gender matched normal controls. METHODS: One hundred forty-eight patients were age and gender matched into two groups: LQT-PM and control. Each patient underwent a uniform exercise protocol employing a cycle ergometer followed by a 9 minute recovery phase with continuous 12-lead electrocardiogram (ECG) monitoring. Intervals (RR, QT and QTc) at rest (supine), peak exercise and in recovery (1, 3, 5, 7, and 9 minutes) were measured. RESULTS: Forty-three patients were positive for LQT-PM and the control group consisted of 105 patients. A total of 83 SNPs were identified: SCN5A n = 31 (37%), KCNE1 n = 29 (35%), KCNH2 n = 20 (24%), KCNQ1 n = 2 (2%) and KCNE2 n = 1 (1%). The QTc interval measurements of the LQT-PM were longer at rest, peak exercise and all phases of recovery when compared to the control group. Neither group demonstrated abnormal QTc interval adaptation in response to exercise. Patients with homozygous SNPs had longer resting QTc intervals when compared to patients with only heterozygous SNPs (435 ± 23 ms vs. 415 ± 20 ms, respectively, P value <0.006). CONCLUSIONS: Individuals with LQT-PM may have longer QTc intervals at rest as well as at peak exercise and all phases of the recovery period compared to normal controls. Additionally, subjects with homozygous SNPs had longer resting QTc intervals when compared to those with only heterozygous SNPs.

Efficacy of ventricular pacing in the treatment of an arrhythmic storm associated with a congenital long QT mutation.

Long QT syndrome in the infant with 2:1 atrioventricular block is a malignant form of disease associated with frequent torsade de pointes in some cases. Those patients that do not respond to antiarrhythmic therapy are particularly challenging to manage. Ventricular pacing in this patient population has been shown to reduce arrhythmic events. We report a case of a newborn with frequent torsade de pointes requiring defibrillation and cardiopulmonary resuscitation with immediate shortening of the QTc interval with ventricular pacing and subsequent resolution of torsade de pointes.

Genotype- and mutation site-specific QT adaptation during exercise, recovery, and postural changes in children with long-QT syndrome.

BACKGROUND: Exercise stress testing has shown diagnostic utility in adult patients with long-QT syndrome (LQTS); however, the QT interval adaptation in response to exercise in pediatric patients with LQTS has received little attention. METHODS AND RESULTS: One-hundred fifty-eight patients were divided into 3 groups: Those with LQTS type 1 (LQT1) or LQTS type 2 (LQT2) and normal control subjects without cardiovascular disease. Each patient underwent a uniform exercise protocol with a cycle ergometer followed by a 9-minute recovery phase with continuous 12-lead ECG monitoring. Each patient underwent a baseline ECG while resting in the supine position and in a standstill position during continuous ECG recording to determine changes in the QT and RR intervals. Fifty patients were gene-positive for LQTS (n=29 for LQT1 and n=21 for LQT2), and the control group consisted of 108 patients. QT interval adaptation was abnormal in the LQT1 patients compared with LQT2 and control patients (P<0.001). A corrected QT interval (QTc) >460 ms in the late recovery phase at 7 minutes predicted LQT1 or LQT2 versus control subjects with 96% specificity, 86% sensitivity, and a 91% positive predictive value. A recovery ΔQTc((7 min-1 min)) >30 ms predicted LQT2 versus LQT1 with 75% sensitivity, 82% specificity, and a 75% positive predictive value. The postural ΔQT was significantly different between LQTS and control groups (P=0.005). CONCLUSIONS: Genotype-specific changes in repolarization response to exercise and recovery exist in the pediatric population and are of diagnostic utility in LQTS. An extended recovery phase is preferable to assess the repolarization response after exercise in the pediatric population.

Abnormalities of cardiac repolarization in Williams syndrome.

Williams syndrome (WS) affects 1 in 8,000 live births and has a high risk of sudden death. No previous studies have evaluated corrected QT (QTc) prolongation in WS. Retrospective review of all patients with WS evaluated at our institution from January 1, 1980 to December 31, 2007 was performed. WS was diagnosed by a medical geneticist and/or by fluorescence in situ hybridization. Patients with ≥1 electrocardiogram (ECG) with sinus rhythm and measurable intervals were included. Normal control ECGs were identified from a large clinical database. Corrected JT (JTc) interval was calculated when QRS and QTc intervals were prolonged. QTc interval ≥460 ms and JTc interval >340 ms were defined as prolonged. Prevalence comparisons were made using Fisher's exact test. Statistical probability of <0.05 was considered significant. Of 270 patients identified, 188 had ECGs for review. Complete data were present in 499 of 517 ECGs (patients' mean age 10.3 ± 9.9 years); 1,522 normal ECGs of age-similar patients composed the control group. QTc prolongation prevalences were 2.0% in controls and 13.6% in WS (p <0.0001); in those, JTc prolongation prevalences were 1.8% in controls and 11.7% in WS (p <0.0001). Four patients died during follow-up; 2 had QTc prolongation and 1 died during noncardiac surgery. Another patient with QTc prolongation sustained cardiac arrest during a procedure. In conclusion, cardiac repolarization is prolonged in WS. Presence of prolonged cardiac repolarization may contribute to the high incidence of periprocedural mortality in these patients. All patients with WS should be screened for cardiac repolarization abnormalities, especially before surgery.

Outcome of high-risk neonates with congenital complete heart block paced in the first 24 hours after birth.

OBJECTIVE: Risk factors for poor outcome with congenital complete heart block include prematurity, low birth weight, hydrops, low ventricular rates, and congenital heart disease. In this group, medical therapy is often ineffective, pacing is technically challenging, and mortality exceeds 80%. The purpose of this study is to assess outcomes of patients with congenital complete heart block who were paced in the first 24 hours after birth owing to the presence of known risk factors. METHODS: We performed a retrospective review of patients with congenital complete heart block paced in the first 24 hours after birth at our institution between November 1, 1995, and July 31, 2007. RESULTS: Thirteen patients were identified, 4 of whom had heterotaxy syndrome. Eleven patients had temporary epicardial pacing wires placed; 2 received permanent pacemakers as the initial mode of pacing. There were 7 deaths (54% mortality) at a mean age of 19.9 +/- 19 days. Among 7 patients with structural heart disease, there was 1 survivor. Among 6 patients with structurally normal hearts, there were 5 survivors (P = .025). Patients with temporary wires who survived to permanent pacemaker implantation (6/11) used their temporary leads for 33.8 +/- 18.3 days. CONCLUSIONS: In the severely affected fetus with congenital complete heart block and significant structural heart disease, outcomes remain poor; however, neonates with congenital complete heart block and structurally normal hearts who are monitored antenatally and delivered in a planned fashion at an institution capable of early pacing can have favorable outcomes. The use of temporary pacing wires is an option in the management of these patients.

Time and temperature profile of catheter cryoablation of right septal and free wall accessory pathways in children.

INTRODUCTION: The overall acute success with cryoablation for accessory pathways (APs) has been reported to be lower than with radiofrequency ablation. Generally, prior cryomapping (limited to -30 degrees C) has been used to test for loss of AP conduction and absence of atrioventricular (AV) node impairment. However, the temperature at which loss of AP conduction occurs may be variable. The purpose of this study was to evaluate the time and temperature profile at which loss of AP conduction occurs. METHODS AND RESULTS: A retrospective study evaluated 25 patients (mean age 13.3 +/- 3.6 years) who underwent cryoablation for right-sided APs (22 manifest/3 concealed). Direct cryoablation (-80 degrees C) without cryomapping was performed using a "time to success" strategy. If AP conduction was successfully interrupted within 25 seconds of the onset of cryoablation, the lesion was continued for 240 seconds; otherwise it was terminated and further mapping was performed. Cryoablation was successful in 24/25 (96%) patients. Temperature at loss of AP conduction was -66.2 +/--16.7 degrees C (range +32 to -84 degrees C) with conduction block at temperatures lower than -30 degrees C for all but 3 APs. Critical time to success (interval from cryoadherence to loss of AP conduction) was significantly shorter for permanently successful cryolesions, compared with transiently successful lesions (6.3 +/- 4.1 vs. 11.2 +/- 2.2 sec; P < 0.001). There were no major complications. CONCLUSIONS: Cryothermal energy required for successful ablation may be variable and restricting test applications to -30 degrees may limit its efficacy. A "time to success" strategy may improve outcome of cryoablation for right-sided APs in children without compromising safety.

Substrate characterization of ventricular tachycardia in a porcine model of tetralogy of Fallot using noncontact mapping.

BACKGROUND: Ventricular tachycardia (VT) in patients following tetralogy of Fallot (TOF) repair is challenging to map because of the presence of scar, patch material, and hemodynamic residua of surgery. This study investigates whether noncontact mapping can identify the arrhythmia substrate in a porcine model that involves a right ventricular outflow tract (RVOT) patch and either chronic volume or pressure load on the right ventricle. METHODS: Nine infant pigs (3-5 kg) underwent surgery involving an RVOT patch and creation of pulmonary insufficiency (PI, n = 4) or pulmonary stenosis (PS, n = 5). After a mean of 4.2 months, pigs underwent invasive electrophysiology studies (EPS) with noncontact mapping (Ensite, St. Jude Medical, St. Paul, MN USA) of the right ventricle. Automated, unipolar voltage maps (VM) were constructed during sinus rhythm. Threshold for substrate was set at -0.5 mV and incrementally adjusted to higher values until a contiguous region of low voltage was delineated. Programmed stimulation was performed to induce VT. VT activation was correlated to location of VM defined substrate. Three control pigs underwent EPS and VM. RESULTS: Free-wall RVOT substrate was identified in each of the model animals, correlating to location of the patch. The mean voltage threshold was -1.1 mV. VT was induced in 6/9 animals. Diastolic activation approximated the inferior or lateral border of the substrate in all animals. No RVOT substrate was identified in the control pigs. CONCLUSION: Automated voltage mapping of sinus beats identifies substrate for VT in a porcine model of TOF. Consistent diastolic activation of the substrate border was found during VT. Targeting this area may be useful in the ablation of VT after repair of TOF.

Cryoablation of congenital familial ectopic tachycardia with preservation of atrioventricular nodal function in an infant.

A 1-year-old child weighing 8 kg with familial congenital junctional ectopic tachycardia that was difficult to treat with antiarrhythmic medications underwent successful cryoablation with preservation of atrioventricular (AV) nodal function. This report describes a strategy of cryoablation in conjunction with a 3-D mapping system and the use of atrial overdrive pacing during cryothermal application to assess AV nodal function.