Oral Albuterol Treatment in Three Pediatric Patients with Bradycardia: A Novel Therapy.

Clinically significant bradycardia is an uncommon problem in children, but one that can cause significant morbidity and sometimes necessitates implantation of a pacemaker. The most common causes of bradycardia are complete heart block (CHB), which can be congenital or acquired, and sinus node dysfunction, which is rare in children with structurally normal hearts. Pacemaker is indicated as therapy for the majority of children with CHB, and while early mortality is lower in postnatally diagnosed CHB than in fetal CHB, it is still up to 16%. In young children, less invasive transvenous pacemaker systems can be technically challenging to place and carry a high risk of complications, often necessitating surgical epicardial pacemaker placement, which usually entails a median sternotomy. We report three cases of pediatric patients referred for pacemaker implantation for different types of bradycardia, treated at our institution with oral albuterol with therapeutic results that avoided the need for surgical pacemaker implantation at that time.

Expanded Newborn Screening Using Genome Sequencing for Early Actionable Conditions.

Importance: The feasibility of implementing genome sequencing as an adjunct to traditional newborn screening (NBS) in newborns of different racial and ethnic groups is not well understood. Objective: To report interim results of acceptability, feasibility, and outcomes of an ongoing genomic NBS study in a diverse population in New York City within the context of the New York State Department of Health Newborn Screening Program. Design, Setting, and Participants: The Genomic Uniform-screening Against Rare Disease in All Newborns (GUARDIAN) study was a multisite, single-group, prospective, observational investigation of supplemental newborn genome screening with a planned enrollment of 100 000 participants. Parent-reported race and ethnicity were recorded at the time of recruitment. Results of the first 4000 newborns enrolled in 6 New York City hospitals between September 2022 and July 2023 are reported here as part of a prespecified interim analysis. Exposure: Sequencing of 156 early-onset genetic conditions with established interventions selected by the investigators were screened in all participants and 99 neurodevelopmental disorders associated with seizures were optional. Main Outcomes and Measures: The primary outcome was screen-positive rate. Additional outcomes included enrollment rate and successful completion of sequencing. Results: Over 11 months, 5555 families were approached and 4000 (72.0%) consented to participate. Enrolled participants reflected a diverse group by parent-reported race (American Indian or Alaska Native, 0.5%; Asian, 16.5%; Black, 25.1%; Native Hawaiian or Other Pacific Islander, 0.1%; White, 44.7%; 2 or more races, 13.0%) and ethnicity (Hispanic, 44.0%; not Hispanic, 56.0%). The majority of families consented to screening of both groups of conditions (both groups, 90.6%; disorders with established interventions only, 9.4%). Testing was successfully completed for 99.6% of cases. The screen-positive rate was 3.7%, including treatable conditions that are not currently included in NBS. Conclusions and Relevance: These interim findings demonstrate the feasibility of targeted interpretation of a predefined set of genes from genome sequencing in a population of different racial and ethnic groups. DNA sequencing offers an additional method to improve screening for conditions already included in NBS and to add those that cannot be readily screened because there is no biomarker currently detectable in dried blood spots. Additional studies are required to understand if these findings are generalizable to populations of different racial and ethnic groups and whether introduction of sequencing leads to changes in management and improved health outcomes. Trial Registration: ClinicalTrials.gov Identifier: NCT05990179.

Long-Term Follow-Up of Second-Degree Heart Block in Children.

Little is known about the outcomes of children with second-degree heart block. We aimed to determine whether children with structurally normal hearts and Mobitz 1, 2:1 block or Mobitz 2 are at increased risk for progressing to complete heart block (CHB) or requiring a pacemaker (PM) at long-term follow-up. We searched our institutional electrophysiology database for children with potentially concerning second-degree block on ambulatory rhythm monitoring between 2009 and 2021, defined as frequent episodes of Mobitz 1 or 2:1 block, episodes of Mobitz 1 or 2:1 block with additional evidence of conduction disease (i.e. first-degree heart block, bundle branch block), or episodes of Mobitz 2. Ambulatory rhythm monitor, ECG, and demographic data were reviewed. The primary composite outcome was CHB on follow-up rhythm monitor or PM placement. 20 patients were in the final analysis. Six (30%) patients either developed CHB but do not have a PM (4 = 20%) or have a PM (2 = 10%). Median follow-up was 5.8 years (IQR 4.4-7.0). Patients with CHB or PM were more likely to have second-degree block at maximum sinus rate (67% vs. 0%, p = 0.003), a below normal average heart rate (67% vs. 14%, p = 0.04), and 2:1 block on initial ECG (50% vs. 0%, p = 0.02). In this study of children with potentially concerning second-degree block, 30% of patients progressed to CHB or required a PM. Second-degree block at maximum sinus rate, a low average heart, and 2:1 block on initial ECG were associated with increased risk of disease progression.

Comparison of AliveCor KardiaMobile Six-Lead ECG with Standard ECG in Pediatric Patients.

The AliveCor KardiaMobile (ACKM) is a remote electrocardiogram (ECG) monitoring device. Little research has been conducted on its accuracy with pediatric patients. This prospective study aims to compare the ACKM six-lead device with a standard fifteen-lead ECG in measuring the QTc, QRS, and axis in pediatric patients. Pediatric patients ages 5 to 21 years were enrolled prospectively to have their ECG recorded using an ACKM six-lead device following a recording with the standard 15-lead ECG. A pediatric electrophysiologist measured the QTc, QRS interval, and QRS axis for both ECGs. Bland-Altman analysis was performed to assess agreement among measurements. The study included 141 patients. The mean age was 12.3 ± 4.4 years. Average heart rate was 79 ± 16 bpm. The mean difference in the QTc measurements for a paired standard ECG and ACKM was - 0.6 ms [95% confidence interval - 48 to 47 ms]. Of the ACKM QTc measurements, 117 (83%) were within 30 ms of the standard ECG. The mean difference in paired QRS measurements was - 1.3 ms [95% confidence interval - 23 to 21 ms]. Of the ACKM QRS measurements, 134 (95%) were within 20 ms of the standard ECG. The measured axis was the same for 84% of ACKM and standard ECGs. Over 80% of the ACKM six-lead ECGs produced QTc, QRS, and axis deviation measurements within a clinically useful range of the standard ECG. However, it is not accurate enough to be used consistently in place of a standard ECG for QTc and QRS measurement for pediatric patients.

Assessing the utility of atrial fibrillation induction to risk stratify children with Wolff-Parkinson-White syndrome.

BACKGROUND: Wolff-Parkinson-White syndrome is associated with sudden cardiac death from rapid conduction through the accessory pathway in atrial fibrillation. Adult patients are at higher risk for sudden cardiac death if the shortest-pre-excited-RR-interval in atrial fibrillation (SPERRI) is ≤250 milliseconds (msec) during electrophysiologic study. Exclusive conduction through the atrioventricular node in atrial fibrillation is presumed to convey lower risk. The shortest-pre-excited-paced-cycle-length with atrial pacing has also served as a marker for risk stratification. OBJECTIVE: To determine accessory pathway characteristic of patients undergoing induction of atrial fibrillation during electrophysiologic study. METHODS: We reviewed 321 pediatric patients that underwent electrophysiologic study between 2010 and 2019. Induction of atrial fibrillation was attempted on patients while on isoproterenol and SPERRI was measured if atrial fibrillation was induced. Shortest-pre-excited-paced-cycle-length (SPPCL) was determined while on isoproterenol. RESULTS: Atrial fibrillation was induced in 233 (73%) patients. Of those, 104 (45%) patients conducted exclusively through the atrioventricular node during atrial fibrillation (Group A). The remaining 129 (55%) patients had some conduction through the accessory pathway (Group B). In Group A, SPPCL was 260 msec with 48 (46%) conducting through the accessory pathway at ≤250 msec. In Group B, SPPCL was 240 msec with 92 patients (71%) conducting at ≤250 msec (p < 0.05). In Group B, SPERRI was 250 msec and had a positive correlation with SPPCL (p < 0.001, R2 = 0.28). Almost half (46%) of those with exclusive conduction through the atrioventricular node in atrial fibrillation had rapid accessory pathway conduction with atrial pacing. CONCLUSION: Conduction in atrial fibrillation during electrophysiologic study on isoproterenol via the atrioventricular node may not exclude high-risk accessory pathways in pediatric patients.

Supraventricular Tachycardia Without Preexcitation as a Cause of Sudden Cardiac Arrest in Pediatric Patients.

Sudden cardiac arrest in pediatric patients is a rare occurrence. Supraventricular tachycardia without the presence of ventricular preexcitation in pediatric patients with a structurally normal heart is generally considered benign. Previous literature in adults reported a subset of patients in whom SVT was suspected to be the primary trigger of sudden cardiac arrest. We performed a single-center, retrospective cohort study of pediatric patients without known heart disease, 1-21 years of age, presenting with aborted SCA between 2009 and 2019. We collected diagnostic studies in all patients to identify the etiology of the aborted SCA. Thirty patients met the inclusion criteria. The median age at the time of SCA was 15.2 years. The etiology of SCA was identified in 23 (77%) patients. Of the seven patients with unknown diagnosis after initial diagnostic studies, three patients subsequently developed fast SVT that was presumed to be the etiology of the initial SCA. These three patients had varying diagnoses of atrioventricular nodal reentry tachycardia, ectopic atrial tachycardia, and a concealed accessory pathway with atrioventricular reentrant tachycardia. After ablation or medical treatment of the SVT substrate, no further tachyarrhythmias were observed. Pediatric patients presenting with an aborted SCA of unknown etiology ought to be considered for electrophysiology testing to elicit occult SVT substrates that may lead to a malignant ventricular tachyarrhythmia.

Anodal stimulation in pediatric patients with permanent epicardial ventricular pacemakers.

OBJECTIVES: We aimed to measure the frequency and factors associated with anodal stimulation in a pediatric population with epicardial pacing leads. BACKGROUND: In bipolar pacemakers, capture of the myocardium typically occurs at the cathode. However, AS with capture at the anode has been described. This has not been described in epicardial pacemakers. METHODS: Retrospective data were collected from patients ≤ 21 years of age with permanent bipolar epicardial ventricular pacemakers from 1/2017 to 1/2018. AS was defined as a clear change on surface ECG in at least one of the 12 leads assessed by two blinded pediatric electrophysiologists. RESULTS: Twenty-four bipolar leads in 23 patients were included in the study. One patient had both biventricular leads tested. Median age was 7.1 years (IQR 5.0-10.9), weight was 20.9 kg (IQR 16.5-33.5), and 65% were male. Testing was performed at a median of 2.8 years (IQR 1.6-6.1) after implant. Congenital heart disease was present in 57%. Complete heart block was the pacemaker indication in 78%. AS was identified in 16/24 (67%) of leads tested. Identification of AS was associated with presence of congenital heart disease (p = 0.004) and 3DD between electrodes (p = 0.04). CONCLUSIONS: AS is common in pediatric patients and was associated with a history of congenital heart disease and greater estimated 3DD between electrodes. The prevalent nature of AS may allow clinicians to utilize existing pacemakers as multisite pacing systems.

Conduction Properties and Ablation of Adenosine Sensitive Accessory Pathways in Children.

Block in accessory pathway (AP) conduction with adenosine has been previously described. However, conduction characteristics of these APs has not been well defined to date. All patients with APs

Long-Term Patient Experience Following Acutely Successful Ablation of Supraventricular Tachycardia Substrate in Children.

Definitive treatment of supraventricular tachycardia (SVT) substrate involves catheter ablation. While objective success rates have been well established, long-term subjective patient experiences have not been well described. We quantify a subjective cure rate and characterize long-term patient experience after acutely successful ablation. A cross-sectional survey of pediatric patients with accessory pathways or atrioventricular nodal reentrant tachycardia who underwent acutely successful ablation from 2008 to 2012 was performed. Data were obtained from medical records and patient surveys. Patients with congenital heart disease other than patent ductus arteriosus, patent foramen ovale, or coronary artery abnormalities were excluded. Statistical analyses included Student's t-test and χ2 analysis for continuous and categorical variables, respectively. Surveys were sent to 153 patients of which 147 responded with median follow-up of 7.2 (IQR 6.1-8.5) years. Of the 147 responders, 124 (84%) patients reported cure with a male predominance. Symptoms were present in 130/147 (88%) patients pre-ablation and in 53/147 (36%) post-ablation. Among those with post-ablation symptoms, 50/53 (94%) reported symptomatic improvement. Recurrence occurred in 23/147 (16%) patients and was more prevalent following cryoablation. Ablation of SVT substrate can be curative with excellent long-term results and patient satisfaction. Long-term subjective cure rate is high and there is a substantial decrease in symptoms post-ablation. Many patients continue to have symptoms following ablation; however, the majority of these patients consider themselves cured and symptoms can be attributed to other etiologies. Recurrence is uncommon and occurs more frequently following cryoablation.

Impact of dipyridamole on adenosine dosing in pediatric and young adult patients after heart transplantation.

BACKGROUND: Relative contraindications to adenosine use have included heart transplant and dipyridamole. We previously demonstrated the safety and efficacy of adenosine-induced atrioventricular (AV) block in healthy young heart transplant recipients while suspending dipyridamole therapy (dual antiplatelet agent). This prospective follow-up study evaluated the safety and efficacy of adenosine use in the same cohort of heart transplant recipients while on dipyridamole. METHODS: Adenosine was incrementally dosed until AV block occurred (maximum 200 mcg/kg up to 12 mg). The primary outcome was clinically significant asystole (≥12 seconds). Secondary outcomes included maximal adenosine dose, AV block duration, dysrhythmias, and clinical symptoms. Outcomes were compared to the parent study. RESULTS: Thirty of 39 eligible patients (5-24 years) were tested. No patient (0%, CI 0%-8%) experienced clinically significant asystole. AV block occurred in 29/30 patients (97%, CI 86%-100%). The median dose causing AV block was 50mcg/kg (vs 100 mcg/kg off dipyridamole; P = .011). Seventeen patients (57%, CI 39%-72%) required less adenosine to achieve AV block on dipyridamole; six (20%) required more. AV block occurred at doses ≥25 mcg/kg in all patients. In pairwise comparison to prior testing off dipyridamole, no significant change occurred in AV block duration, frequency of cardiac ectopy, or incidence of reported symptoms. No atrial fibrillation/flutter occurred. CONCLUSIONS: AV block often occurs at twofold lower adenosine doses in healthy young heart transplant recipients taking oral dipyridamole, compared with previous testing of this cohort off dipyridamole. Results suggest that initial dosing of 25 mcg/kg (maximum 0.8 mg) with stepwise escalation poses low risk of prolonged asystole on dipyridamole.

COVID-19 reveals Brugada pattern in an adolescent patient.

A diagnosis of Brugada pattern in paediatric or adolescent patients is rare. COVID-19 is characterised by fevers and a pro-inflammatory state, which may serve as inciting factors for Brugada pattern. Recently described in two adult patients, we report the first case of Brugada pattern in an adolescent with COVID-19.

Cardiac workup and monitoring in hospitalised children with COVID- 19.

Approximately, 1.7 million individuals in the United States have been infected with SARS-CoV-2, the virus responsible for the novel coronavirus disease-2019 (COVID-19). This has disproportionately impacted adults, but many children have been infected and hospitalised as well. To date, there is not much information published addressing the cardiac workup and monitoring of children with COVID-19. Here, we share the approach to the cardiac workup and monitoring utilised at a large congenital heart centre in New York City, the epicentre of the COVID-19 pandemic in the United States.

Advanced Heart Block in Children with Lyme Disease.

BACKGROUND: The clinical course of children with advanced heart block secondary to Lyme disease has not been well characterized. OBJECTIVE: To review the presentation, management, and time to resolution of heart block due to Lyme disease in previously healthy children. METHODS: An IRB approved single-center retrospective study was conducted of all patients < 21 years old with confirmed Lyme disease and advanced second or third degree heart block between 2007 and 2017. RESULTS: Twelve patients (100% male) with a mean age of 15.9 years (range 13.2-18.1) were identified. Six patients (50%) had mild to moderate atrioventricular valve regurgitation and all had normal biventricular function. Five patients had advanced second degree heart block and 7 had complete heart block with an escape rate of 20-57 bpm. Isoproterenol was used in 4 patients for 3-4 days and one patient required transvenous pacing for 2 days. Patients were treated with 21 days (n = 6, 50%) or 28 days (n = 6, 50%) of antibiotics. Three patients received steroids for 3-4 days. Advanced heart block resolved in all patients within 2-5 days, and all had a normal PR interval within 3 days to 16 months from hospital discharge. CONCLUSION: Symptomatic children who present with new high-grade heart block from an endemic area should be tested for Lyme disease. Antibiotic therapy provides quick and complete resolution of advanced heart block within 5 days, while steroids did not appear to shorten the time course in this case series. Importantly, no patients required a permanent pacemaker.

Prospective Study of Adenosine on Atrioventricular Nodal Conduction in Pediatric and Young Adult Patients After Heart Transplantation.

BACKGROUND: Supraventricular tachycardia is common after heart transplantation. Adenosine, the standard therapy for treating supraventricular tachycardia in children and adults without transplantation, is relatively contraindicated after transplantation because of a presumed risk of prolonged atrioventricular block in denervated hearts. This study tested whether adenosine caused prolonged asystole after transplantation and if it was effective in blocking atrioventricular nodal conduction in these patients. METHODS: This was a single-center prospective clinical study including healthy heart transplant recipients 6 months to 25 years of age presenting for routine cardiac catheterization during 2015 to 2016. After catheterization, a transvenous pacing catheter was placed and adenosine was given following a dose-escalation protocol until atrioventricular block was achieved. The incidence of clinically significant asystole (≥12 seconds after adenosine) was quantified. The effects of patient characteristics on adenosine dose required to produce atrioventricular block and duration of effect were also measured. RESULTS: Eighty patients completed adenosine testing. No patient (0%; 95% confidence interval, 0-3) required rescue ventricular pacing. Atrioventricular block was observed in 77 patients (96%; 95% confidence interval, 89-99). The median longest atrioventricular block was 1.9 seconds (interquartile range, 1.4-3.2 seconds), with a mean duration of adenosine effect of 4.3±2.0 seconds. No patient characteristic significantly predicted the adenosine dose to produce atrioventricular block or duration of effect. Results were similar across patient weight categories. CONCLUSIONS: Adenosine induces atrioventricular block in healthy pediatric and young adult heart transplant recipients with minimal risk when low initial doses are used (25 µg/kg; 1.5 mg if ≥60 kg) and therapy is gradually escalated. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier: NCT02462941.

The "hidden" concealed left-sided accessory pathway: An uncommon cause of SVT in young people.

BACKGROUND: Concealed left-sided accessory pathways (CLAP) are a cause of supraventricular tachycardia (SVT) in the young. Most are mapped with right ventricular (RV) apical/outflow pacing. Rarely, alternative means of mapping are required. We review our experience from three pediatric electrophysiology (EP) centers with a rare form of "hidden" CLAP. METHODS: All patients <21 years undergoing EP study from 2008 to 2014 with a "hidden" CLAP (defined as an accessory pathway [AP] for which RV pacing at cycle lengths [CL] stable for mapping did not demonstrate eccentric retrograde conduction) were included. EXCLUSION CRITERIA: preexcitation. Demographic, procedural, and follow-up data were collected. RESULTS: A total of 23 patients met the criteria (median age, 14.3 years [range 7-21], weight, 51 kg [31-99]). 21 (96%) had SVT and one AFIB (4%). APs were adenosine sensitive in 7/20 patients (35%) and VA conduction was decremental in six (26%). CLAP conduction was demonstrable with orthodromic reentrant tachycardia in all patients, with RV extrastimulus testing in seven (30%) and with rapid RV pacing (

Wolff-Parkinson-White syndrome: a single exercise stress test might be misleading.

Risk stratification of patients with Wolff-Parkinson-White syndrome for sudden death is a complex process, particularly in understanding the utility of the repeat exercise stress test. We report a case of an 18-year-old patient who was found to have a high-risk pathway by both invasive and exercise stress testing after an initial exercise stress test showing beat-to-beat loss of pre-excitation.

QT prolongation and torsades de pointes in a patient with heart block and a pacemaker.

Prolongation of the QT interval and development of torsades de pointes are known in patients with complete heart block and profound bradycardia. We report the case of a patient with complete heart block and torsades, with long QT seen during a period of junctional tachycardia at a rate faster than the minimum pacemaker rate.

Implantation of permanent pacemaker and ICD leads in children using a three-dimensional electroanatomic mapping system as an aid to fluoroscopy.

BACKGROUND: Three-dimensional electroanatomic mapping systems (3D mapping) allow the creation of an anatomic representation of the cardiac anatomy and real-time monitoring of transvenous pacing catheters. Their use to facilitate pacemaker (PM) and implantable cardioverter defibrillator (ICD) lead placement in the pediatric population has not been well defined. We sought to review our experience using 3D mapping as an adjunct to fluoroscopy for positioning of permanent PM and ICD leads in pediatric patients. METHODS: We performed a retrospective review of all patients ≤21 years of age who underwent PM or ICD implantation with the aid of the Ensite Velocity system (Ensite) from May 2012 to September 2014. Fluoroscopy was utilized in addition to 3D mapping to aid obtaining vascular access, to visualize fixation of the lead to the myocardium, and to evaluate lead length within the vasculature. RESULTS: Nineteen patients (mean age 14.6 ± 4.4 years) underwent placement of active fixation PM leads (N = 17) and/or ICD leads (N = 10) with the aid of Ensite. All leads were successfully placed (eight atrial, 19 ventricular). Fluoroscopic exposure was a mean of 3.2 minutes (± 2.8, 0.1-10.5). There was one lead dislodgement. CONCLUSIONS: Ensite was used successfully as an adjunct to fluoroscopy in all patients in whom it was attempted to aid the placement of permanent transvenous PM and ICD leads. Future evaluation could focus on the use of 3D mapping systems to further minimize or eliminate fluoroscopy from PM and ICD implantations.

A Smartphone Application to Diagnose the Mechanism of Pediatric Supraventricular Tachycardia.

Smartphone applications that record a single-lead ECG are increasingly available. We sought to determine the utility of a smartphone application (AliveCor) to record supraventricular tachycardia (SVT) and to distinguish atrioventricular reentrant tachycardia (AVRT) from atrioventricular nodal reentrant tachycardia (AVNRT) in pediatric patients. A prior study demonstrated that interpretation of standard event and Holter monitors accurately identifies the tachycardia mechanism in only 45 % of recordings. We performed an IRB-approved prospective study in pediatric patients undergoing an ablation for SVT. Tracings were obtained by placing the smartphone in three different positions on the chest (PI-horizontal, PII-rotated 60° clockwise, and PIII-rotated 120° clockwise). Two blinded pediatric electrophysiologists jointly analyzed a pair of sinus and tachycardia tracings in each position. Tracings with visible retrograde P waves were classified as AVRT. The three positions were compared by Chi-square test. Thirty-seven patients (age 13.7 ± 2.8 years) were enrolled in the study. Twenty-four had AVRT, and 13 had AVNRT. One hundred and eight pairs of tracings were obtained. The correct diagnosis was made in 27/37 (73 %) with position PI, 28/37 (76 %) with PII, and 20/34 (59 %) with PIII (p = 0.04 for PII vs. PIII and p = NS for other comparisons). A single-lead ECG obtained with a smartphone monitor can successfully record SVT in pediatric patients and can predict the SVT mechanism at least as well as previously published reports of Holter monitors, along with the added convenience of not requiring patients to carry a dedicated monitor.

Defining the electrocardiogram in the neonate with hypoplastic left heart syndrome.

Hypoplastic left heart syndrome (HLHS) is a severe form of congenital heart disease characterized by underdevelopment of the left heart. There has been no previously defined "classic" ECG pattern in a large homogenous population of patients with HLHS. We performed a retrospective review of ECGs from neonates with HLHS from 2001 to 2011 with electrocardiograms available prior to surgical intervention. Eighty-nine neonates met the inclusion criteria and were compared to a control population. HLHS patients had a longer PR interval 108 ± 18 versus 98 ± 11 ms (p < 0.05), a wider QRS complex 84 ± 17 versus 54 ± 5 ms (p < 0.05), lower voltage S waves in V1 2.0 ± 3.3 versus 5.8 ± 4.6 mm (p < 0.001) or absent S waves in V1 52 versus 4 % (p < 0.001) and lower voltage R waves in V6 7.8 ± 4.8 versus 9.3 ± 4.2 mm (p < 0.05). Patients with HLHS were more likely to have absent Q waves in the lateral precordial leads 78 versus 0 % (p < 0.001) and inferior leads 20 versus 1 % (p < 0.001) and an abnormal frontal plane QRS axis 26 versus 11 % (p < 0.05). HLHS patients were more likely to have a preexcited appearance 11 versus 0 % (p = 0.001). Despite these findings, 20 % of patients with HLHS had a normal ECG. Compared to age-matched controls, patients with HLHS were more likely to exhibit a longer PR interval, a wider QRS complex, decreased left-sided forces, an absence of septal Q waves in the inferior and lateral leads, an abnormal frontal plane QRS axis and a preexcited appearance.