Acute complications of electrophysiology and pacing procedures: identification and management.

Non-pharmacologic interventional techniques for treatment and management of almost all cardiac arrhythmias have greatly expanded over the past decade. These newer interventional electrophysiologic techniques continue to demonstrate increasing success at achieving their targeted goals, and enhancing the patient's quality of life. However, like all interventional procedures, complications may result. In this article we provide the reader with an overview of the more common and significant adverse events that may follow electrophysiologic and pacing procedures, and how best to recognize and manage these complications. After providing the reader with an overview of the complications inherent to all electrophysiologic procedures, we will detail the adverse events intrinsic to specific therapeutic electrophysiologic interventions (DC cardioversion, pharmacologic-based cardioversion, antitachycardia pacing, and ablation of specific arrhythmias). In the last part of the review, we will delineate complications associated with pacing procedures (pacemaker and defibrillator implantation, biventricular pacing and pacing lead extraction).

Pacemaker troubleshooting: improved efficacy using a new diagnostic digital Holter recording system.

Asymptomatic dysfunction of cardiac pacing systems is not uncommonly detected using long-term ambulatory monitoring techniques. We report two patients with atrial and ventricular sensing abnormalities noted only on Holter monitoring. Multiple empirical attempts at pacemaker reprogramming based on deductive analysis of the pacing anomaly were unsuccessful. Through the use of a new digital recording system that allowed collection of surface electrocardiographic data, intracardiac electrograms, and Marker Channel data a correct diagnosis was made (pacing lead insulation failure). This new recording system has the advantage of significantly improving diagnostic sensitivity and resulting in cost savings.

Case report: spontaneous atriofascicular pathway automaticity simulating ventricular tachycardia.

Atriofascicular pathways most commonly present electrocardiographically as an antidromic reciprocating AV reentrant tachycardia. We report the case of a child who presented in infancy with a wide QRS complex tachycardia thought to be supraventricular tachycardia with aberrant conduction, associated with tachycardia-induced cardiomyopathy. Later in life the same patient represented with episodes of palpitations secondary to a wide QRS complex tachycardia, thought to be ventricular tachycardia. Electrophysiologic mapping demonstrated the origin of the wide QRS complex tachycardia was from automatic activity originating from a right anterolateral atriofascicular pathway, which also participated in a reentrant antidromic AV reciprocating tachycardia. Radiofrequency ablation of the atriofascicular pathway successfully eliminated both arrhythmias. The mechanism of the wide QRS complex tachycardia appeared to result from spontaneous automaticity of the atriofascicular pathway.

Congenital heart block: development of late-onset cardiomyopathy, a previously underappreciated sequela.

OBJECTIVE: We report 16 infants with complete congenital heart block (CHB) who developed late-onset dilated cardiomyopathy despite early institution of cardiac pacing. BACKGROUND: Isolated CHB has an excellent prognosis following pacemaker implantation. Most early deaths result from delayed initiation of pacing therapy or hemodynamic abnormalities associated with congenital heart defects. METHODS: A multi-institutional study was performed to identify common clinical features and possible risk factors associated with late-onset dilated cardiomyopathy in patients born with congenital CHB. RESULTS: Congenital heart block was diagnosed in utero in 12 patients and at birth in four patients. Ten of 16 patients had serologic findings consistent with neonatal lupus syndrome (NLS). A pericardial effusion was evident on fetal ultrasound in six patients. In utero determination of left ventricular (LV) function was normal in all. Following birth, one infant exhibited a rash consistent with NLS and two had elevated hepatic transaminases and transient thrombocytopenia. In the early postnatal period, LV function was normal in 15 patients (shortening fraction [SF] = 34 +/- 7%) and was decreased in one (SF = 20%). A cardiac pacemaker was implanted during the first two weeks of life in 15 patients and at seven months in one patient. Left ventricular function significantly decreased during follow-up (14 days to 9.3 years, SF = 9% +/- 5%). Twelve of 16 patients developed congestive heart failure before age 24 months. Myocardial biopsy revealed hypertrophy in 11 patients, interstitial fibrosis in 11 patients, and myocyte degeneration in two patients. Clinical status during follow-up was guarded: four patients died from congestive heart failure; seven required cardiac transplantation; one was awaiting cardiac transplantation; and four exhibited recovery of SF (31 +/- 2%). CONCLUSIONS: Despite early institution of cardiac pacing, some infants with CHB develop LV cardiomyopathy. Patients with CHB require close follow-up not only of their cardiac rate and rhythm, but also ventricular function.

Mortality following radiofrequency catheter ablation (from the Pediatric Radiofrequency Ablation Registry). Participating members of the Pediatric Electrophysiology Society.

Deaths have been reported following radiofrequency catheter ablation (RFCA), but the mortality rate in children has not been defined. This study sought to analyze the incidence and the factors associated with mortality related to RFCA. Ten of 4,651 cases (0.22%) reported to the Pediatric RFCA Registry resulting in death were reviewed and compared with a matched control group (n = 18). Death occurred in 5 of 4,092 children (0.12%, ages 0.1 to 13.3 years) with structurally normal hearts. Death was related to traumatic injury, myocardial perforation and hemopericardium, coronary or cerebral thromboembolism, and ventricular arrhythmia. All cases were left-sided (p = 0.019 vs right or septal) supraventricular arrhythmias with radiofrequency applications in the systemic atrium and/or ventricle, and all procedures were successful. Mortality occurred in 5 of 559 children (0.89%, p = 0.001 vs normals, ages 1.5 to 17.4 years) with structural heart disease. No new pathology except the mural radiofrequency lesions was seen at autopsy. Those with structurally normal hearts who died were smaller (32.7 vs 55.6 kg, p = 0.023) and had more radiofrequency applications (26.3 vs 8.7, p = 0.019) than those who survived. No differences were demonstrated for those with abnormal hearts. Operator experience was not different (deaths 103 +/- 106 vs controls 117 +/- 125, p = 0.41). Mortality associated with pediatric RFCA is rare, but is more frequent when there is underlying heart disease, lower patient weight, greater number of radiofrequency energy applications, and left-sided procedures. Operator experience does not appear to be a factor leading to mortality.

Case report: pulmonary vein stenosis following RF ablation of paroxysmal atrial fibrillation: successful treatment with balloon dilation.

Paroxysmal atrial fibrillation and atrial tachycardia may originate from a focal source in one or multiple pulmonary veins. A focal origin facilitates a potential cure amendable to radiofrequency ablation. Herein we report the case of a 16 year old adolescent male with a tachycardia induced cardiomyopathy who presented with very frequent paroxysmal episodes of atrial fibrillation, atrial flutter and atrial tachycardia. The origin of the arrhythmia was mapped to the secondary branches of the left lower pulmonary vein using an octapolar micro-mapping catheter. Immediately following application of three radiofrequency lesions, angiography of the left lower pulmonary vein revealed a region of focal stenosis at the site of energy application, with delayed pulmonary venous emptying. Attempts to relieve any element of spasm using direct administration of nitroglycerin were unsuccessful. Three months later repeat catheterization revealed an unchanged region of tight anatomical stenosis. Balloon dilation of two stenotic areas resulted in dramatic relief of the obstruction and improved venous drainage. Recatheterization 6 months later revealed mild restenosis that was successfully redilated. Intracardiac ultrasound demonstrated focal constriction. Care should be exercised in attempting RF ablation in distal arborization sites of the pulmonary veins in children, because of the small caliber compared to adult subjects. Radiofrequency induced focal areas of stenosis may be amenable to balloon catheter dilation.

Neurally mediated cardiac syncope: autonomic modulation after normal saline infusion.

OBJECTIVES: This study assessed the heart variability response to orthostatic stress during tilt table testing before and after normal saline administration. BACKGROUND: The efficacy of sodium chloride and mineralocortoid in the treatment of neurally mediated cardiac syncope is attributed to intravascular volume expansion; however, their modulation of autonomic nervous system activity has not been evaluated. METHODS: Heart rate variability analysis was performed on 12 adolescents with a history of syncope or presyncope (mean age 15.2+/-0.7 years) during tilt table testing. Subjects were upright 80 degrees for 30 min or until syncope. After normal saline administration, the patient was returned upright for 30 min. Heart rate variability analysis data were analyzed by an autoregression model (Burg method). RESULTS: All subjects reproducibly developed syncope during control tilt table testing; median time to syncope was 9.4+/-2.1 min. After normal saline infusion, none of the subjects developed syncope after 30 min upright. In the control tilt, there was an initial increase followed by a progressive decrease in low frequency power until syncope. Repeat tilt after normal saline administration demonstrates that low frequency power increased but the magnitude of initial change was blunted when compared with control. In addition, low frequency power increased during normal saline tilt sequence compared with the control tilt, during which it decreased. CONCLUSIONS: Normal saline blunted low frequency power stimulation and prevented paradoxical low frequency power (sympathetic) withdrawal. Increasing intravascular volume with normal saline alters autonomic responses that may trigger neurally mediated syncope reflexes.

Congenital heart disease caused by mutations in the transcription factor NKX2-5.

Mutations in the gene encoding the homeobox transcription factor NKX2-5 were found to cause nonsyndromic, human congenital heart disease. A dominant disease locus associated with cardiac malformations and atrioventricular conduction abnormalities was mapped to chromosome 5q35, where NKX2-5, a Drosophila tinman homolog, is located. Three different NKX2-5 mutations were identified. Two are predicted to impair binding of NKX2-5 to target DNA, resulting in haploinsufficiency, and a third potentially augments target-DNA binding. These data indicate that NKX2-5 is important for regulation of septation during cardiac morphogenesis and for maturation and maintenance of atrioventricular node function throughout life.

Radiofrequency ablation of arrhythmias in the pediatric patient.

Advances in management of pediatric arrhythmias using radiofrequency catheter ablation are reviewed. Discussion begins with the most frequent arrhythmia experienced in childhood, supraventricular tachycardia, and its variants. Subsequent consideration will center on progress made in using radiofrequency catheter ablation to manage ventricular tachycardia, both in the normal heart as well as in surgically repaired tetralogy of Fallot. Potential limitations to radiofrequency ablation in the infant age group are addressed. Technologic progress as it applies to pediatric patients is also examined. Lastly, an enhanced appreciation for the immense contribution that radiofrequency catheter ablation techniques have made will emerge for the reader after reviewing recent results obtained using surgical techniques for arrhythmia ablation.

Persistence of ventricular arrhythmia after resolution of occult myocarditis in children and young adults.

OBJECTIVES: We sought to examine whether resolution of occult myocarditis in children with associated ventricular arrhythmia correlated with the presence of arrhythmia at late follow-up. BACKGROUND: Complex ventricular arrhythmias have been documented in children with myocarditis. Therapy is aimed at controlling the arrhythmia and any associated ventricular dysfunction. However, no reported studies have documented whether resolution of myocarditis in children is associated with resolution of the associated arrhythmias. METHODS: We performed a retrospective analysis of 12 patients (mean age 12 years) with myocarditis. Ambulatory electrocardiographic (Holter) monitors were reviewed for ventricular arrhythmias at presentation and follow-up. Patients were assigned to Group I if they received corticosteroids in addition to any antiarrhythmic agents and to Group II if they did not receive steroids. Follow-up endomyocardial biopsy was performed in some patients, and results were analyzed in relation to the presence of arrhythmias at follow-up. RESULTS: Eleven patients had ventricular tachycardia, and one had multiform couplets. Corticosteroids were given to seven patients (Group I). Follow-up biopsy was performed in seven patients (six received steroids), with resolution of inflammation in all; four of the seven still had ventricular arrhythmias but with improved control. Of the five patients without follow-up biopsy, three had persistent arrhythmia. Absence of inflammation at follow-up biopsy did not correlate with loss of ventricular arrhythmias, and there was no difference between Group I and II patients with respect to resolution of arrhythmia (Fisher exact test, p = 0.70, power 11%). CONCLUSIONS: Complex ventricular arrhythmias persist after apparent resolution of occult myocarditis in children. Although these arrhythmias are easier to control after such resolution, the patients may require long-term antiarrhythmic therapy.

Electrocardiographic findings in Rett syndrome: an explanation for sudden death?

Girls with Rett syndrome had significantly longer corrected QT intervals (p < 0.001) and more T-wave abnormalities (p < 0.001) than were found in age-matched healthy girls. With advancing stages of the syndrome, the proportion of corrected QT interval prolongations and T-wave changes increased. The findings suggest a possible cardiac basis for sudden, unexpected death in Rett syndrome.

Successful closure of a previously unsuspected atrial septal defect by an implantable Clamshell device and subsequent transvenous pacemaker implantation.

Implantation of transvenous leads for a permanent cardiac pacing system usually requires the absence of intracardiac shunts. We report the case of an asymptomatic atrial septal defect in an 11-year-old boy who required permanent pacing. We implanted an atrial septal defect closure (Clamshell) device prior to implantation of transvenous leads. This new device makes transvenous implantation possible and may reduce the risk of stroke in patients with these anomalies.

Potassium currents of neurons isolated from medical nucleus tractus solitarius.

Voltage-dependent potassium currents of neurons enzymatically isolated from the medial and dorsal subnuclei of the solitary tract (mNTS) of adult guinea pig have been characterized with respect to their voltage dependence, time dependence, and sensitivity to specific blocking agents. This region of the medulla receives baroreceptor afferent input and is involved in cardiovascular regulation. Our results showed the presence of three types of potassium currents. First, in all neurons studied (n = 58) a slowly developing outward current was present at potentials more positive than -30 mV. The time to half-peak current decreased with depolarization [24.8 ms at 0 mV; 19.2 ms at +10 mV; 12.5 ms at +20 mV; 9.9 ms at +30 mV (n = 4)]. This current required 20 mM tetraethylammonium (TEA) for full block and failed to show significant inactivation for voltage commands up to 300 ms. Second, a rapidly activating, 4-aminopyridine (4-AP)-sensitive transient outward potassium current was present in 83% of the cells examined (n = 39/47). Threshold for activation was -30 mV. The current relaxation consisted of three components: tau 1 = 14-49 ms; tau 2 = 174-362; tau 3 = 1.1-2.4 s. Finally, in all cells tested calcium activated a large nontransient outward potassium current that was inhibited by charybdotoxin. The studies reported here will be used in conjunction with studies describing sodium and calcium currents to understand the basis for generation of activity in the mNTS in response to baroreceptor input.

Late ventricular arrhythmia and sudden death following direct-current catheter ablation of the atrioventricular junction.

Early reports of direct-current catheter ablation (DCCA) of the atrioventricular (AV) junction for resistant AV tachycardias documented efficacy of DCCA with little morbidity. Nine patients underwent DCCA at our institution 4 to 9 years ago: 3 patients had DCCA in the coronary sinus for permanent junctional reciprocating tachycardia, 2 patients had His ablation, 2 had coronary sinus and His ablation for permanent junctional reciprocating tachycardia, and 2 had DCCA for congenital tachycardia, and 2 had DCCA for congenital junctional ectopic tachycardia. Shocks (total 1 to 5) ranged from 12.5 to 400 J. Five patients had pacemaker implant at the time of DCCA. During follow-up, 3 patients developed clinical ventricular tachycardia: all 3 had DCCA of the His bundle. One asymptomatic patient with ventricular tachycardia, who had DCCA of the bundle of His, died suddenly 6 years later with ventricular fibrillation. Autopsy revealed 2 ventricular scars: 1 extending from the AV junction and 1 in the outflow tract. No patient with DCCA limited to the coronary sinus developed ventricular tachycardia. DCCA of the His bundle can result in late ventricular arrhythmias, possibly a result of extension of the DCCA lesion into the ventricle. These late findings should be considered in evaluating the safety and efficacy and follow-up for patients undergoing radiofrequency ablation.

Active fixation of endocardial pacing leads: the preferred method of pediatric pacing.

Pacing system failure due to lead related problems may necessitate repositioning or explantation of the problem lead. Pediatric patients with permanent pacemakers have additional considerations that necessitate revision or explantation of pacing leads. Active fixation type leads appear to offer the physician advantages over passive fixation leads that may make them the lead of choice for use in children. We reviewed our experience with active fixation type leads to determine whether the ease with which these leads could be revised or explanted justified recommending their use in our patients. Eleven patients underwent 13 lead revisions. The time from implant to revision was a mean of 12.3 months. Six patients had previously undergone repair of a congenital heart defect. Modes of pacing were: DDD (seven); AAI (three); and VVI (one). Exposed, isodiametric leads accounted for 11/13 leads. Leads were successfully explanted in nine cases and repositioned in four cases. The only lead that could not be revised and resulted in retention was a nonisodiametric, retractable helix lead at the junction of the subclavian vein and clavicle. We conclude isodiametric active fixation leads can be safely repositioned or explanted in children and should be considered the preferred method for endocardial pacing in children.

Clinical course of idiopathic dilated cardiomyopathy in children.

Previous studies in adults with dilated cardiomyopathy suggest that the presence of arrhythmia, especially ventricular tachycardia, correlates with increased mortality. We performed a retrospective analysis of 63 children with idiopathic dilated cardiomyopathy to determine the prognostic significance of arrhythmias and other findings with respect to mortality. The mean age at diagnosis of the cardiomyopathy was 4.96 +/- 5.3 years. The overall mortality rate was 16% over a 10 year follow-up period. Persistent congestive heart failure and ST-T wave changes correlated with increased mortality (p less than 0.05). No other variables affected outcome. Arrhythmias were found in 46% of the patients; of the arrhythmias, 48% were atrial arrhythmias. Ventricular tachycardia was present in six patients. Death occurred in 4 (14%) of 29 patients with known arrhythmia; 1 of the 5 died suddenly. The remaining 6 deaths in the series occurred in the 34 patients without a documented arrhythmia. It is concluded that 1) arrhythmias are frequently seen in children with dilated cardiomyopathy but are not predictive of outcome; 2) sudden death in children with this disease is rare; and 3) persistent congestive heart failure portends a poor prognosis.

Bradycardia and syncope in children not controlled by pacing: beta-adrenergic hypersensitivity.

Cardiac pacing is frequently employed in the therapy of children with syncope and documented bradycardia. This report describes two children, ages 7 and 9 years, who underwent placement of demand ventricular pacing systems for documented bradycardia and syncope. Cardiac catheterization and intracardiac electrophysiological studies failed to show evidence of structural abnormalities, sinus node or conduction system disease, inducible arrhythmias, or VA conduction in each patient. Both patients had persistent symptoms after pacemaker implantation. Autonomic function testing with continuous heart rate and blood pressure monitoring revealed exaggerated beta-adrenergic responses to simple standing and small doses of isoproterenol. Symptoms were completely eliminated with atenolol. In these two children, cardiac pacing alone was not adequate for relief of symptoms. Autonomic mechanisms of bradycardia and hypotension should be considered prior to implantation of permanent pacing systems in children.

Developmental cellular electrophysiologic effects of d-sotalol on canine cardiac Purkinje fibers.

d-Sotalol may be a clinically useful class III antiarrhythmic agent for controlling ventricular arrhythmias in children. Because age-related differences in repolarization currents may contribute to developmental differences in response to antiarrhythmic agents that primarily affect repolarization, the electrophysiologic effects of d-sotalol were compared in Purkinje fibers from neonatal and adult dogs. Significant age-related changes characterized the antiarrhythmic profile of d-sotalol. d-Sotalol (10(-4) M) significantly prolonged the action potential duration of adult Purkinje fibers (310 +/- 8 to 380 +/- 7 ms, p less than 0.01) and neonatal fibers (247 +/- 5 to 342 +/- 9 ms, p less than 0.01). However, the lengthening of action potential duration was significantly greater in the immature age group. d-Sotalol had no significant effect on maximum diastolic potential, action potential amplitude, or phase zero upstroke velocity in normally polarized fibers. In contrast, different electrophysiologic effects were observed in K(+)-depolarized Purkinje fibers. Superfusion of adult K(+)-depolarized fibers with d-sotalol suppressed excitability in five (38%) of 13 fibers and significantly decreased action potential amplitude (88 +/- 2 to 83 +/- 1 mV, p less than 0.05) and phase zero upstroke velocity (180 +/- 14 to 105 +/- 3 V/s, p less than 0.01) in the other eight fibers. The membrane depressant effects observed in the younger age group were significantly less [no suppression of excitability and a smaller decrease in phase zero upstroke velocity (121 +/- 22 to 101 +/- 23 V/s, p less than 0.05). The magnitude of action potential duration prolongation by d-sotalol in K(+)-depolarized fibers was less than in normally polarized fibers.(ABSTRACT TRUNCATED AT 250 WORDS)

Epicardial mapping: how to measure local activation?

UNLABELLED: Epicardial ventricular mapping was performed in 5 dogs during sinus rhythm with a sock array containing 41 electrodes. Maps were generated with a computer-assisted mapping system using four different definitions of local epicardial activation: (1) maximal negative slope (intrinsic deflection) of the unipolar electrogram, (2) maximal slope of the bipolar electrogram, (3) maximal amplitude of the bipolar electrogram, and (4) first onset by 45 degrees from the baseline of the bipolar electrogram. The site of earliest and latest epicardial activation was identical with maximal negative slope in the unipolar electrogram and maximal slope and maximal amplitude of the bipolar electrogram in all five animals. Times of earliest and latest epicardial activation calculated with maximal amplitude of the bipolar electrogram were most similar to those evaluated with maximal negative slope of the unipolar electrogram. Using onset of the bipolar electrogram, activation times were measured 10 to 12 msec earlier than with each of the other three definitions of local activation, and in two of the five animals, first epicardial breakthrough was mapped to a different site than with the three other methods. CONCLUSIONS: (1) Maximal amplitude of the bipolar electrogram coincided with maximal negative slope of the unipolar electrogram; (2) Using onset of the bipolar electrogram, timing and location of earliest epicardial activation may be misinterpreted.

Surgical treatment of arrhythmias in children.

Primary surgical treatment of many tachyarrhythmias in children is now possible. In those with life-threatening arrhythmias not responsive to any form of medical treatment, the choice for surgery is clear. These arrhythmias include atrial fibrillation with the Wolff-Parkinson-White syndrome, PJRT, or atrial ectopic tachycardia with severe congestive cardiomyopathy, incessant ventricular tachycardia in infancy, and recurrent sustained ventricular tachycardia in postoperative congenital heart disease. In the majority of patients, however, surgical treatment remains an option to be weighed carefully against chronic medical treatment. Surgery is now possible with very low mortality for infants and children with Kent bundles, atrial ectopic tachycardia, and the permanent form of junctional reciprocating tachycardia. The mortality, morbidity, and likelihood of eventual resolution of the arrhythmia with each type of management plan should be considered. With possible direct surgical ablation of atrial flutter and newer forms of catheter treatment of arrhythmias, the future looks promising.