Edward K. Rhee

A multicenter experience with novel implantable cardioverter defibrillator configurations in the pediatric and congenital heart disease population.

Both slowed and regularized ventricular rate provide hemodynamic benefits to patients with atrial fibrillation and thus constitute a primary therapeutic goal. The return to sinus rhythm obviously reaches this goal and has been the preferred strategy over several decades. Given that recurrence of atrial fibrillation is frequent in the face of both pharmacological and ablation-based invasive therapy, and that side effects may limit their use, rhythm control approaches may frequently fall short of expected clinical benefits. In that situation, rate control becomes the alternate strategy. In fact, a number of recent clinical trials comparing rhythm and rate control strategies consistently reported net benefits of rate control therapy (see1,2 for review). Accordingly, for many patients rate control is becoming the preferred strategy while rhythm control is being targeted when needed and/or possible.1 Rate control is primarily achieved by drug-induced conduction impairment of the AV node. When this approach fails, ablation-induced third-degree AV block coupled with ventricular pacing may be considered.3,4 Several other approaches are currently under scrutiny: ventricular pacing without AV block, slow pathway ablation, gene therapy, and selective ganglionic parasympathetic stimulation.3 The modulation of AV nodal function by cardiac ganglionic stimulation may prove to be of significant value in heart failure patients in whom antiarrhythmic drug-induced depression of ventricular function must be avoided.5-8 An added benefit is that a normal ventricular activation sequence is maintained. Selective ganglionic stimulation combined with ventricular pacing may provide further benefits by achieving a slowed and regularized ventricular rate in spite of persistent atrial fibrillation.9 The Soos et al. study in the current issue10 raises the possibility that ganglionic stimulation may be feasible with currently available pacemaker technology. The concept of rate control through parasympathetic stimulation is derived from pioneering experimental work showing that selective AV node conduction slowing can be achieved through local cardiac nerve stimulation.11-15 Effective parasympathetic ventricular rate slowing during atrial fibrillation has been reached in animals with nerve stimulation applied endocardially in the vicinity of AV node,16 transvenous catheter stimulation from the coronary sinus,5 and local electrical stimulation of inferior interatrial parasympathetic ganglionated plexus.7-10 In humans, transvenous

Cardiac Memory in Patients With Wolff-Parkinson-White Syndrome Noninvasive Imaging of Activation and Repolarization Before and After Catheter Ablation

Background— Cardiac memory refers to a change in ventricular repolarization induced by and persisting for minutes to months after cessation of a period of altered ventricular activation (eg, resulting from pacing or preexcitation in patients with Wolff-Parkinson-White syndrome). ECG imaging (ECGI) is a novel imaging modality for noninvasive electroanatomic mapping of epicardial activation and repolarization. Methods and Results— Fourteen pediatric patients with Wolff-Parkinson-White syndrome and no other congenital disease, were imaged with ECGI a day before and 45 minutes, 1 week, and 1 month after successful catheter ablation. ECGI determined that preexcitation sites were consistent with sites of successful ablation in all cases to within a 1-hour arc of each atrioventricular annulus. In the preexcited rhythm, activation-recovery interval (ARI) was the longest (349±6 ms) in the area of preexcitation leading to high average base-to-apex ARI dispersion of 95±9 ms (normal is ≈40 ms). The ARI dispersion remained the same 45 minutes after ablation, although the activation sequence was restored to normal. ARI dispersion was still high (79±9 ms) 1 week later and returned to normal (45±6 ms) 1 month after ablation. Conclusions— The study demonstrates that ECGI can noninvasively localize ventricular insertion sites of accessory pathways to guide ablation and evaluate its outcome in pediatric patients with Wolff-Parkinson-White syndrome. Wolff-Parkinson-White is associated with high ARI dispersion in the preexcited rhythm that persists after ablation and gradually returns to normal over a period of 1 month, demonstrating the presence of cardiac memory. The 1-month time course is consistent with transcriptional reprogramming and remodeling of ion channels.

Cryoablation of Accessory Pathways in the Coronary Sinus in Young Patients: A Multicenter Study from the Pediatric and Congenital Electrophysiology Society's Working Group on Cryoablation

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.

Experience and Results During Transition from Radiofrequency Ablation to Cryoablation for Treatment of Pediatric Atrioventricular Nodal Reentrant Tachycardia

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.

Cardiac resynchronization therapy in pediatric congenital heart disease: insights from noninvasive electrocardiographic imaging.

BACKGROUND Electrocardiographic imaging (ECGI) is a novel electrophysiologic imaging modality that may help guide patient selection and lead placement for cardiac resynchronization therapy (CRT). OBJECTIVE The purpose of this study was to apply noninvasive ECGI to pediatric heart failure patients with congenital heart disease (CHD) undergoing evaluation for CRT. METHODS ECGI was applied in eight patients with CHD who were either being evaluated for CRT or undergoing CRT. An electrical dyssynchrony (ED) index was computed from the ECGI epicardial activation maps as the standard deviation of activation times at 500 epicardial sites of the systemic ventricle. A normal ED of 20 +/- 4 ms was calculated from a control group of normal pediatric patients. RESULTS Four patients had an ECGI assessment for ED but did not undergo CRT implant. Two other patients had ECGI assessment pre-CRT that demonstrated abnormal ED and went on to CRT implant. In both cases, the resynchronization lead was placed at the site of latest electrical activation (as determined by ECGI) in pre-CRT baseline rhythm. A total of four patients (two responders, two nonresponders) were studied with post-CRT in multiple rhythms. Responders had an average ED of 22 ms in optimal CRT conditions. The nonresponder had very elevated ED (37 ms) in all rhythms including optimal CRT settings. ED and ECG QRS duration showed weak correlation (r = 0.58). CONCLUSIONS ECGI can be used in pediatric heart failure patients to evaluate ventricular ED and identify suitable candidates for CRT. In addition, ECGI can guide resynchronization lead placement to the area of latest electrical activation. It could also be used in noninvasive follow-ups for assessing synchrony and the electrophysiological substrate over time.

Electrophysiologic substrate and intraventricular left ventricular dyssynchrony in nonischemic heart failure patients undergoing cardiac resynchronization therapy

BACKGROUND Electrocardiographic imaging (ECGI) is a method for noninvasive epicardial electrophysiologic mapping. ECGI previously has been used to characterize the electrophysiologic substrate and electrical synchrony in a very heterogeneous group of patients with varying degrees of coronary disease and ischemic cardiomyopathy. OBJECTIVE The purpose of this study was to characterize the left ventricular electrophysiologic substrate and electrical dyssynchrony using ECGI in a homogeneous group of nonischemic cardiomyopathy patients who were previously implanted with a cardiac resynchronization therapy (CRT) device. METHODS ECGI was performed during different rhythms in 25 patients by programming their devices to biventricular pacing, single-chamber (left ventricular or right ventricular) pacing, and native rhythm. The electrical dyssynchrony index (ED) was computed as the standard deviation of activation times at 500 sites on the LV epicardium. RESULTS In all patients, native rhythm activation was characterized by lines of conduction block in a region with steep activation-recovery interval (ARI) gradients between the epicardial aspect of the septum and LV lateral wall. A native QRS duration (QRSd) >130 ms was associated with high ED (≥30 ms), whereas QRSd <130 ms was associated with minimal (25 ms) to large (40 ms) ED. CRT responders had very high dyssynchrony (ED = 35.5 ± 3.9 ms) in native rhythm, which was significantly lowered (ED = 23.2 ± 4.4 ms) during CRT. All four nonresponders in the study did not show significant difference in ED between native and CRT rhythms. CONCLUSION The electrophysiologic substrate in nonischemic cardiomyopathy is consistent among all patients, with steep ARI gradients co-localizing with conduction block lines between the epicardial aspect of the septum and the LV lateral wall. QRSd wider than 130 ms is indicative of substantial LV electrical dyssynchrony; however, among patients with QRSd <130 ms, LV dyssynchrony may vary widely.

Modification to the Fontan procedure for the prophylaxis of intra-atrial reentrant tachycardia: short-term results of a prospective randomized blinded trial.

OBJECTIVES We evaluated the feasibility, safety, and short-term efficacy of an interventional atrial incision placed at the time of the Fontan operation to reduce the development of intra-atrial reentrant tachycardia. METHODS This prospective randomized blinded trial was conducted in patients with congenital heart disease undergoing an initial lateral tunnel Fontan. Intervention patients underwent a lateral tunnel Fontan with an interventional atrial incision/cryoablation from the atriotomy to the right atrioventricular annulus. Controls underwent a standard lateral tunnel Fontan. Safety of the intervention was monitored. Short-term efficacy was determined by comparisons of conduction block across the incision area and spontaneous or inducible atrial arrhythmias. RESULTS There were no significant differences between intervention (n = 21, median 2.4 years, range 0.8-3.9) and controls (n = 21, median 2.7 years, range 1.5-13.9) in age, type of heart disease, surgical parameters, or postoperative outcomes. Safety parameters showed no difference between groups in number or severity of adverse events. Short-term efficacy included evidence of conduction block with a longer conduction time across the incision area in intervention patients (median 97 ms, range 35-160) compared with controls (median 40 ms, range 8-77, P =.0001). No intervention patients had spontaneous or inducible intra-atrial reentrant tachycardia versus 2 controls (0/21 versus 2/21, P = NS). CONCLUSIONS An interventional atrial incision to reduce intra-atrial reentrant tachycardia in the Fontan operation was feasible and safe. The intervention changed the atrial substrate as shown by an increase in conduction time. Short-term results showed a low incidence of intra-atrial reentrant tachycardia in all patients. Longer follow-up is necessary to assess clinical efficacy.

Noninvasive electrocardiographic imaging (ECGI) of epicardial activation before and after catheter ablation of the accessory pathway in a patient with Ebstein anomaly

Ebstein’s anomaly (1) is characterized by abnormal development of the tricuspid valve with the septal (and often posterior) leaflets of the valve displaced into the right ventricle (RV). The abnormal development of the tricuspid valve is often associated with several conduction abnormalities, including delayed intra-atrial conduction, right bundle branch block (RBBB) (2, 3), and ventricular pre-excitation (4). Absence of a RBBB pattern during sinus rhythm on a baseline ECG suggests the presence of an atrio-ventricular accessory pathway (AP) in patients with Ebstein’s anomaly. Often, successful catheter ablation of an AP results in a complete or partial RBBB pattern on the post-ablation 12-lead ECG in 94% of cases (5). However, changes in the activation of the heart following a successful catheter ablation of AP in a patient with Ebstein’s anomaly have never been studied with epicardial activation imaging techniques. Electrocardiographic imaging (ECGI) (6, 7) is a novel noninvasive imaging modality for cardiac electrophysiology. ECGI can image cardiac activity on the epicardial surface of the heart from body-surface potentials measured with 250 electrodes together with heart-torso anatomic information obtained from a thoracic ECG-gated CT. It has been validated with intra-operative mapping data in humans (8). It has also been applied in humans to image the electrophysiologic substrate and cardiac excitation under normal and various pathophysiologic conditions (6–11).

Noninvasive Electrocardiographic Imaging (ECGI) of a univentricular heart with Wolff-Parkinson-White syndrome

Electrocardiographic imaging (ECGI) is a noninvasive functional imaging modality which reconstructs epicardial potentials, electrograms, and activation and recovery maps from body-surface ECG potentials. For this purpose, up to 256 ECGs are recorded by a 256-channel body surface potential mapping (BSPM) system and the heart-torso geometry is obtained using thoracic computed tomography (CT)1,2. This technique was developed and validated extensively in normal and abnormal canine hearts3–11. More recently, ECGI was validated in humans by comparison with direct intra-operative epicardial mapping in patients undergoing open-heart surgery12. To date, ECGI has been applied in adult human subjects for the following purposes: 1. To study cardiac electrophysiology of the normal adult human heart2. 2. To image electrophysiologic responses to pacing in heart failure patients undergoing cardiac resynchronization therapy13 (pacing sites were localized with an accuracy better than 10 mm)14. 3. To guide catheter ablation of focal ventricular and atrial tachycardias15,16. 4. To image typical atrial flutter prior to catheter ablation1 and atypical atrial flutter prior to a surgical Cox-Maze procedure17. Here we describe for the first time, a case where ECGI was applied to a pediatric patient with a congenital structural heart defect. The patient had a univentricular heart and Wolff-Parkinson-White syndrome, and ECGI was used to localize the accessory pathway and help guide catheter ablation. To date, there have been no reported cases of ECGI in the pediatric population.

Management of Pediatric Tachyarrhythmias on Mechanical Support

Background—Pediatric patients with persistent arrhythmias may require mechanical cardiopulmonary support. We sought to classify the population, spectrum, and success of current treatment strategies. Methods and Results—A multicenter retrospective chart review was undertaken at 11 sites. Inclusion criteria were (1) patients <21 years, (2) initiation of mechanical support for a primary diagnosis of arrhythmias, and (3) actively treated on mechanical support. A total of 39 patients were identified with a median age of 5.5 months and median weight of 6 kg. A total of 69% of patients were cannulated for supraventricular tachycardia with a median rate of 230 beats per minute. A total of 90% of patients were supported with extracorporeal membrane oxygenation for an average of 5 days. The remaining 10% were supported with ventricular assist devices for an average of 38 (20–60) days. A total of 95% of patients were treated with antiarrhythmics, with 43% requiring >1 antiarrhythmic. Amiodarone was the most frequently used medication alone or in combination. A total of 33% patients underwent electrophysiology study/transcatheter ablation. Radiofrequency ablation was successful in 9 patients on full flow extracorporeal membrane oxygenation with 3 radiofrequency-failures/conversion to cryoablation. One patient underwent primary cryoablation. A total of 15% of complications were related to electrophysiology study/ablation. At follow-up, 23 patients were alive, 8 expired, and 8 transplanted. Conclusions—Younger patients were more likely to require support in the presented population. Most patients were treated with antiarrhythmics and one third required electrophysiology study/ablation. Radiofrequency ablation is feasible without altering extracorporeal membrane oxygenation flows. There was a low frequency of acute adverse events in patients undergoing electrophysiology study/ablation, while on extracorporeal membrane oxygenation.