Effects of cardiac growth on electrical dyssynchrony in the single ventricle patient.

Single ventricle patients, including those with hypoplastic left heart syndrome (HLHS), typically undergo three palliative heart surgeries culminating in the Fontan procedure. HLHS is associated with high rates of morbidity and mortality, and many patients develop arrhythmias, electrical dyssynchrony, and eventually ventricular failure. However, the correlation between ventricular enlargement and electrical dysfunction in HLHS physiology remains poorly understood. Here we characterize the relationship between growth and electrophysiology in HLHS using computational modeling. We integrate a personalized finite element model, a volumetric growth model, and a personalized electrophysiology model to perform controlled in silico experiments. We show that right ventricle enlargement negatively affects QRS duration and interventricular dyssynchrony. Conversely, left ventricle enlargement can partially compensate for this dyssynchrony. These findings have potential implications on our understanding of the origins of electrical dyssynchrony and, ultimately, the treatment of HLHS patients.

Use of the rate-corrected JT interval for prediction of repolarization abnormalities in children.

A prolonged rate-corrected QT interval (QTc) may be associated with an increased risk of developing ventricular arrhythmias and sudden death, particularly in patients with the hereditary long QT syndrome (LQTS), myocardial ischemia, or antiarrhythmic medication toxicity. It is known that there are some patients with LQTS who sometimes have a borderline or normal QTc (< or = 0.45 second). Although the QTc has been the standard measurement of ventricular repolarization, it includes both depolarization and repolarization and may not always be a sensitive indicator of the type of repolarization abnormalities seen in LQTS. Intraventricular conduction abnormalities complicate evaluation of the QTc interval. The rate-corrected JT interval (JTc) is a more accurate measurement of ventricular repolarization, and therefore may be a more sensitive means of assessing abnormalities. The QTc on a resting electrocardiogram was determined in 40 patients with LQTS and in 31 patients with right bundle branch block after tetralogy of Fallot repair. These were compared with 1,000 age-matched control subjects. The right bundle branch block group had normal JT and JTc measurements, despite having prolonged QT and QTc intervals compared with controls. The JTc identified 85% of patients affected with LQTS compared with only 58% identified using only the QTc as a marker for the syndrome. The JTc is a more specific measurement of ventricular repolarization than the QTc by eliminating QRS duration variability. It appears to be a more sensitive predictor of repolarization abnormalities, and may be helpful in identifying patients with LQTS who have borderline or normal QTc measurements on resting electrocardiograms.

Arrhythmias and thromboembolic complications after the extracardiac Fontan operation.

BACKGROUND: Late morbidity and mortality after the Fontan operation are largely due to atrial arrhythmias, ventricular failure, and thrombus formation. The extracardiac Fontan procedure avoids extensive atrial manipulation and suture lines, theoretically minimizing the impetus for these events. We examined our experience with the extracardiac Fontan operation with particular attention to thromboembolism and arrhythmias. METHODS AND RESULTS: We retrospectively reviewed the medical and surgical records of all 16 patients who underwent an extracardiac Fontan operation between July 1993 and May 1996. Fifteen patients (94%) were in sinus rhythm before the operation. In the immediate postoperative period, seven (44%) had arrhythmias consisting of accelerated junctional rhythm and ectopic atrial rhythm. No associated hemodynamic compromise and no early deaths occurred. Patients were followed up for 3 to 34 months after the Fontan operation. Arrhythmias were detected in eight patients (50%) on surface electrocardiograms, and seven (44%) showed evidence of sinus node dysfunction on 24-hour Holter monitor studies. Thrombi were found in three patients (19%). All patients were asymptomatic, with no evidence of conduit obstruction by echocardiogram. CONCLUSIONS: The incidence of hemodynamically significant tachyarrhythmias appears to be reduced after the extracardiac Fontan operation. A significant percentage of patients have evidence of sinus node dysfunction, suggesting the presence of other surgical or nonsurgical factors responsible for this finding. Our incidence of thrombotic events is similar to previous reports with other Fontan modifications. It appears to be a reasonable option to maintain these patients on anticoagulation indefinitely.

QT dispersion predicts ventricular arrhythmia in pediatric cardiomyopathy patients referred for heart transplantation.

BACKGROUND: QT dispersion has been used in stratifying risk for sudden death in adults with dilated cardiomyopathy, but its role in the pediatric population has not been delineated. METHODS: We reviewed electrocardiograms in pediatric patients with dilated cardiomyopathy referred for heart transplantation, to evaluate the role of QT dispersion in predicting malignant arrhythmias in these patients. Three groups were defined: Group I (n = 13) had dilated cardiomyopathy and malignant ventricular arrhythmias, Group II (n = 13) had dilated cardiomyopathy with no ventricular arrhythmias and Group III (n = 30) consisted of normals. QT dispersion was defined as the duration of the shortest QT subtracted from that of the longest. In addition, the standard deviation of the QT intervals was calculated for each ECG, using 12 leads. RESULTS: QT dispersion was significantly prolonged in Group I (97 +/- 33 msec) compared to Group II (74 +/- 19 msec) and Group III (42 +/- 17 msec). QT standard deviation was also prolonged in Group I (30 +/- 11 msec) vs Group II (22 +/- 5 msec) and Group III (13 +/- 4 msec). Using a threshold value of 90 msec for QT dispersion or 25 msec for QT standard deviation, a sensitivity of 78% and a specificity of 70% was obtained for identifying patients who would subsequently develop ventricular arrhythmias. CONCLUSIONS: In pediatric heart transplant candidates with dilated cardiomyopathy, QT dispersion and QT standard deviation identify patients at higher risk for the development of malignant ventricular arrhythmia. This simple test can be helpful in the evaluation and management of these patients awaiting transplantation.

Outcome while awaiting heart transplantation in children: a comparison of congenital heart disease and cardiomyopathy.

BACKGROUND: Outcomes for children who undergo heart transplantation differ for children with congenital heart disease as compared to those with structurally normal hearts. Similar data have not been reported for these groups of patients for the morbidity and mortality associated with waiting for a donor. We report these data. METHODS: A retrospective review was performed for all pediatric patients who were listed for heart transplantation at Stanford from 1977 to 1996, comparing mortality and major morbidity for patients with congenital heart disease and those with cardiomyopathy and structurally normal hearts. RESULTS: There were 96 patients who met study criteria, of whom 67 were successfully transplanted. The median waiting time was 23 days. Survival at 30 days was 93% and at 90 days was 81%, with no difference between groups. Major complications were identified in 38% of patients with structurally normal hearts, vs 9% of patients with congenital heart disease (p < 0.001). CONCLUSIONS: Overall mortality is similar for patients with congenital heart disease and those with structurally normal hearts while listed for heart transplantation, but patients with congenital heart disease have fewer episodes of major morbidity during this time.

Reentrant tachycardia using two discrete atrioventricular nodes and a concealed atriofascicular pathway.

We describe a case of reentrant supraventricular tachycardia using two discrete atrioventricular (AV) nodes in the antegrade direction and a concealed atriofascicular pathway in the retrograde direction in a 21-year-old woman with superior-inferior ventricles and ventricular inversion. Using the Carto endocardial mapping system, two discrete AV nodes were identified as well as a separate decremental AV pathway located midway between the two nodes. Ablation of the separate pathway resulted in elimination of inducible tachycardia without loss of either AV node.

Radiofrequency catheter ablation: indications and complications.

Radiofrequency catheter ablation was first described in pediatric patients in the early 1990s. Since then, multiple advances in the technology and understanding of radiofrequency ablation have allowed this technique to blossom into one of the most powerful therapeutic tools available to the pediatric electrophysiologist. This treatment has, in the majority of cases, replaced arrhythmia surgery as the definitive cure for most arrhythmias. Ablation therapy is commonly implemented as an elective procedure to treat paroxysmal reentrant supraventricular tachycardia. There are several advantages to this therapy when used in the common indications: no exercise restrictions, no need for chronic drug therapy, and the avoidance of hospital visits for breakthrough episodes. This review will discuss the indications for radiofrequency ablation in the current era. In order to fully discuss this issue, this review will include the prior treatment of arrhythmias, current success rates, complications, and potential long-term issues.

Advances in the treatment of cardiac rhythm disturbances.

Many advances in the care of children with cardiac rhythm disturbances have been made in the past year. From the fetus with supraventricular tachycardia to the adolescent with vasovagal syncope, new and effective therapies have evolved. Molecular genetics has led to monumental leaps in the understanding of long QT syndrome, and a new pharmacologic alternative to cardioversion has been introduced. There have also been new and noteworthy developments in the more established area of radiofrequency ablation. These concern safety and also touch on one of today's most controversial areas, cost effectiveness. This article discusses each of these advances in the realm of pediatric cardiac electrophysiology.

Quality-of-life in patients receiving implantable cardioverter defibrillators at or before age 40.

As the use of ICDs increases, more young patients will be eligible to receive these devices. Such patients may have different concerns than older patients who more commonly receive ICDs. We investigated quality-of-life issues in patients followed by the Yale electrophysiology service who were < or = 40 years old (mean = 28) at the time of ICD implant. Mean time since ICD placement was 3.3 years. Each patient received a modified SF-36 health questionnaire; 16 (88%) of 18 responded. Nine were women; ten were married. The highest education level attained was high school for 6 (37%), and college or beyond for 10 (63%). Ten patients were employed; eight held the same job before and after ICD placement. Four women conceived after ICD implantation; one experienced ICD discharge during pregnancy. All delivered healthy infants. All patients felt their health was good to excellent, with 6 (38%) reporting an improvement in health since ICD placement. All felt capable of performing the activities of daily living, while 68% engaged freely in moderate physical activities. All patients felt they were average to very attractive. However, 63% worried about how their clothes fit with the ICD. Three quarters of the patients felt the ICD interfered with social interactions, while 50% were concerned about sexual encounters. Thus, even though these young patients have body image concerns and may limit their activities to some degree, they are productive, active members of society who have benefitted from ICD placement.

Using 12-lead ECG and synthesized VCG in detection of right ventricular hypertrophy with terminal right conduction delay versus partial right bundle branch block in the pediatric population.

In pediatric electrocardiogram (ECG) analysis, mild right ventricular hypertrophy (RVH) and especially mild RVH with terminal right conduction delay (RVHtcd) are often confused with partial right bundle branch block (PRBBB). This is problematic for computer ECG analysis algorithms and even for most experienced pediatric cardiologists. This study was designed to achieve better classification of mild RVHtcd and PRBBB by combining the 12-lead synthesized vectocardiogram (VCG) transverse plane measurements with scalar ECG measurements. Pediatric ECGs used in the study were recorded with 15 leads and a 500 Hz sampling rate at the Lucile Salter Packard Children's Hospital, Stanford University Medical Center. Out of 4,200 ECGs collected consecutively over a period of 18 months, 447 RVH, 335 RBBB and 589 Normal were interpreted by expert pediatric cardiologists, and were included in the study. Statistical comparison of ECG and VCG measurements were done in stratified ECG sets (412) that have a visually indistinguishable waveform pattern, 117 RVHtcd, 96 PRBBB and 199 normal, showed significant differences in initial and terminal vectors in the transverse plane. The mean angle of the initial vector was anterior (57.2 degrees +/- 41.8) in the normal group, left anterior in the PRBBB group (34.4 degrees +/- 39.5) and in the RVHtcd group (31.9 degrees +/- 41.0) and. The mean angle of the terminal vector was right anterior (158.3 degrees +/- 36.8) in the PRBBB group, rightward (179.7 degrees +/- 29.9) in the RVHtcd group and right posterior (212.6 degrees +/- 37.8) in the normal group. These are clearly applicable features for a classification algorithm. Significantly improved classification results were obtained from a new algorithm using combined ECG and VCG measurements versus an existing algorithm. The limitation of this study stems from the unavailability of a more reliable gold standard. It may be necessary to used body surface potentials obtained with a large number of electrodes to accurately differentiate the study groups.