Radiofrequency ablation of accessory pathways in the presence of atrial fibrillation

Radiofrequency catheter ablation was performed in 595 consecutive patients with Wolff-Parkinson-White syndrome. We attempted ablation of right and left accessory pathways, during sustained atrial fibrillation with rapid anterograde conduction over the accessory pathway in three patients. In other patient, who had an accessory pathway with anterograde decremental conduction properties, referred to as Mahaim atriofascicular fiber, originating from the right posterolateral atrium, who also had sustained atrial fibrillation during the electrophysiological study to assess accessory pathway conduction properties, was also submitted to ablation of the accessory pathway. At the successful ablation sites, a ventricular electrogram was consistently recorded preceding the onset of preexcitation, in the surface electrogram by 20 ms, during atrial fibrillation. All patients were successfully ablated with a single radiofrequency impulse. After successful ablation direct current cardioversion with 200 joules terminated the atrial fibrillation. In conclusion, radiofrequency catheter ablation of accessory pathways during sustained atrial fibrillation is feasible with a high success rate.     

Role of the surface electrocardiogram in the diagnosis of patients with supraventricular tachycardia

In this era of interventional electrophysiology, the accuracy of the electrocardiogram in diagnosis of supraventricular tachycardia could be improved by detailed endocardial mapping and confirmed by results of radiofrequency catheter ablation. This article describes the electrocardiographic characteristics for different types of supraventricular tachycardia: atrial fibrillation, atrial flutter, atrial tachycardia, atrioventricular reciprocating tachycardia using an accessory pathway, and atrioventricular node reentrant tachycardia. Several limitations, including the identification of P wave morphologies and polarities and separation between the terminal part of T wave and P wave during tachycardia, should be resolved before an accurate algorithm of the 12-lead surface electrocardiogram is developed for the diagnosis of supraventricular tachycardia.     

Atrial fibrillation in Wolff-Parkinson-White syndrome. Development and therapy

In patients with Wolff-Parkinson-White syndrome the accessory pathway may participate in various tachyarrhythmias thereby influencing symptoms and prognosis. Atrial fibrillation occurs in 10 to 32% of patients and may have life-threatening consequences by precipitating ventricular fibrillation in patients with rapid conduction due to an accessory pathway with short anterograde refractory period (< 250 ms). Pathogenesis of atrial fibrillation in the WPW syndrome and therapeutic options are reviewed in this presentation. Spontaneous degeneration of atrioventricular reentrant tachycardia has been reported to represent the most frequent mode of initiation of atrial fibrillation during electrophysiologic study (up to 64% of episodes). Hemodynamic changes during tachycardia may lead to increased sympathetic tone, hypoxemia or increased tension of the atrial wall, thus, triggering atrial fibrillation. Induction of reentrant tachycardia during electrophysiologic study also has shown to be strongly correlated to its clinical prevalence and is inducible in up to 77% of patients with atrial fibrillation. The pathogenesis and high incidence of atrial fibrillation in patients with WPW syndrome is related to presence and functional properties of the accessory pathway. After surgical excision or catheter ablation more than 90% of patients are free of this arrhythmia. Anterograde conduction properties of the pathway appear to be more important than retrograde properties. High incidence of atrial fibrillation is related to short anterograde refractory periods, and of note, this arrhythmia is rare (3%) in patients with concealed pathways. With intracardiac recordings, Jackman et al. could demonstrate atrial fibrillation due to micro-reentry originating in accessory pathway networks.(ABSTRACT TRUNCATED AT 250 WORDS)     

Isolated paralysis of the ramus marginalis mandibulae nervi facialis: clinical aspects, etiology, diagnosis and therapy. An overview]

INTRODUCTION: Little is known about the predictors of recurrent atrial flutter or fibrillation after successful radiofrequency ablation of typical atrial flutter. In addition, there is only limited evidence suggesting that elimination of atrial flutter would modify the natural history of atrial fibrillation in patients who experienced both of these arrhythmias. The aims of the present study were to investigate the long-term results of radiofrequency catheter ablation and to examine the predictors for late occurrence of atrial fibrillation in a large population with typical atrial flutter. METHODS AND RESULTS: The study population consisted of 144 patients (mean age 56 +/- 18 years) with successful ablation of clinically documented typical atrial flutter. In the first 50 patients, successful ablation was defined as termination and noninducibility of atrial flutter; for the subsequent 94 patients, successful ablation was defined as achievement of bidirectional isthmus conduction block and no induction of atrial flutter. The clinical and echocardiographic variables were analyzed in relation to the late occurrence of atrial flutter or fibrillation. Over the follow-up period of 17 +/- 13 months, 14 (9.7%) patients had recurrence of typical atrial flutter. In the first 50 patients, 8 (16%) had recurrence of atrial flutter, compared with only 6 (6%) of the following 94 patients. Patients with incomplete isthmus block had a significantly higher incidence of recurrent atrial flutter than those with complete isthmus block (6/16 vs 0/78, P < 0.0001) in the following 94 patients. There was no predictor for recurrence of atrial flutter after successful ablation as determined by univariate and multivariate analysis. Although successful ablation of atrial flutter eliminated atrial fibrillation in 45% of patients with a prior history of atrial fibrillation, 31 (21.5%) of 144 patients undergoing this procedure developed atrial fibrillation during the follow-up period. Univariate analysis revealed that three clinical variables were related to the occurrence of atrial fibrillation: (1) the presence of structural heart disease; (2) a history of atrial fibrillation before ablation; and (3) inducible sustained atrial fibrillation after ablation. By multivariate analysis, only a history of atrial fibrillation and inducible sustained atrial fibrillation could predict the late development of atrial fibrillation after atrial flutter ablation. CONCLUSION: Radiofrequency catheter ablation of typical atrial flutter is highly effective and associated with a low recurrence rate of atrial flutter, but atrial fibrillation continues to be a long-term risk for patients undergoing this procedure. The presence of structural heart disease and prior spontaneous or inducible sustained atrial fibrillation increases the risk of developing atrial fibrillation.     

Complex atrial dysrhythmias in a patient with congestive cardiomyopathy

A patient with primary cardiomyopathy and long standing atrial fibrillation presented with atrial tachycardia and AV block. Atrial pacing sequentially converted the atrial tachycardia to atrial flutter (biatrial) and to the dissimilar atrial rhythms of right atrial fibrillation with left atrial flutter, right atrial flutter with left atrial electrical standstill and right atrial fibrillation with left atrial standstill. The clincial milieu and intracardiac recordings are presented.     

Lessons from animal models of atrial arrhythmias

This article presents selected lessons from experimental studies of atrial fibrillation and atrial flutter that pertain to the mechanisms and predisposing factors for flutter and fibrillation and approaches to treatment by antiarrhythmic drugs. Experimental studies also provide lessons for the effects of ablation and surgical lesions on prevention or facilitation of atrial fibrillation and flutter.     

Coronary sinus pacing initiates counterclockwise atrial flutter while pacing from the low lateral right atrium initiates clockwise atrial flutter. Analysis of episodes of direct initiation of atrial flutter

INTRODUCTION: Rapid atrial pacing in sinus rhythm may directly induce atrial flutter without provoking intervening atrial fibrillation, or initiate atrial flutter indirectly, by a conversion from an episode of transient atrial fibrillation provoked by rapid atrial pacing. The present study was performed to examine whether or not the direct induction of clockwise or counterclockwise atrial flutter was pacing-site (right or left atrium) dependent. METHODS AND RESULTS: We analyzed the mode of direct induction of atrial flutter by rapid atrial pacing. In 46 patients with a history of atrial flutter, rapid atrial pacing with 3 to 20 stimuli (cycle length = 500 - 170 ms) was performed in sinus rhythm to induce atrial flutter from 3 atrial sites, including the high right atrium, the low lateral right atrium, and the proximal coronary sinus, while recording multiple intracardiac electrograms of the atria. Direct induction of atrial flutter by rapid atrial pacing was a rare phenomenon and was documented only 22 times in 15 patients: 3, 11, and 8 times during stimulation, respectively, from the high right atrium, low lateral right atrium, and the proximal coronary sinus. Counterclockwise atrial flutter (12 times) was more frequently induced with stimulation from the proximal coronary sinus than from the low lateral right atrium (8 vs 1, P = .0001); clockwise atrial flutter (10 times) was induced exclusively from the low lateral right atrium (P = .0001 for low lateral right atrium vs proximal coronary sinus, P = .011 for low lateral right atrium vs high right atrium). CONCLUSIONS: Direct induction of either counterclockwise or clockwise atrial flutter was definitively pacing-site dependent; low lateral right atrial pacing induced clockwise, while proximal coronary sinus pacing induced counterclockwise atrial flutter. Anatomic correlation between the flutter circuit and the atrial pacing site may play an important role in the inducibility of counterclockwise or clockwise atrial flutter.     

Echocardiographic factors predicting the maintenance of sinus rhythm one year after cardioversion for non-valvular atrial arrhythmias]

Echocardiographic factors predictive of the maintenance of sinus rhythm after successful cardioversion were investigated in 94 patients with non-valvular atrial arrhythmias of recent onset. Seventy-five patients with atrial fibrillation and 19 with atrial flutter admitted for reduction of their arrhythmias underwent transthoracic and transoesophageal echocardiography. After excluding a thrombus in the left atrial appendage or checking that it had disappeared (5 patients), and electrical (n = 74) or pharmacological (n = 20) cardioversion was successfully performed. The maintenance of sinus rhythm (n = 44) or recurrence of arrhythmia (n = 50) were controlled every 3 months for one year. The mean value of the peak positive blood flow in the left atrial appendage was 38 +/- 20 cm/s for the whole group. It was not possible to identify an echocardiographic parameter predictive of maintenance of sinus rhythm at one year either in the whole group or in the subgroups with atrial flutter or atrial fibrillation. In the group in atrial flutter, the mean value of the peak positive blood flow in the left atrial appendage was significantly greater than in the group with atrial fibrillation: 49 +/- 22 cm/s vs 35 +/- 18 cm/s, respectively; p < 0.05. The peak of positive flow in the left atrial appendage was statistically related to indirect parameters of left atrial function and of left ventricular function in the group with atrial fibrillation but only with parameters of left ventricular function in the smaller group with atrial flutter.     

Effectiveness of digitalis with or without acebutolol in preventing atrial arrhythmias after coronary artery surgery

In this study, a beta-adrenergic blocker in combination with digoxin provided marginal protection against atrial fibrillation/flutter after coronary artery surgery. The economic comparison of patients who did and did not develop atrial fibrillation/flutter indicates that prevention of these arrhythmias can have a significant impact on length of hospital stay and cost of this common surgical procedure.     

Dependency on atrial electrophysiological properties of appearance of paroxysmal atrial fibrillation in patients with Wolff-Parkinson-White syndrome: evidence from atrial vulnerability before and after radiofrequency catheter ablation and surgical cryoablation

The pathogenesis of paroxysmal atrial fibrillation in patients with Wolff-Parkinson-White syndrome and the effects of elimination of accessory pathways on the appearance of atrial fibrillation are still controversial. Fifty-four patients with Wolff-Parkinson-White syndrome were classified into three groups: a No AF group (n = 24), patients without paroxysmal atrial fibrillation; an RF-AF Group (n = 12), patients with paroxysmal atrial fibrillation whose accessory pathways were eliminated using radiofrequency catheter ablation; and a Cryo-AF Group (n = 18), patients with paroxysmal atrial fibrillation whose accessory pathways were eliminated with surgical cryoablation. The electrophysiological characteristics of each group were evaluated prior to and following the elimination of their accessory pathways. As indices of atrial vulnerability, the presence of fragmented atrial activity and repetitive atrial firing zones were assessed. Inducibility of atrial fibrillation was significantly reduced following ablation of accessory pathways in the Cryo-AF group (83.3%-5.6%, P < 0.0001), while it was unchanged in the RF-AF group (83.3%-75%). In preablation studies, the effective refractory periods of the atrium in the RF-AF group and the Cryo-AF group were significantly shorter compared with the No AF group (204 +/- 18 ms, 197 +/- 16 ms vs 246 +/- 44 ms, respectively, P < 0.0001). Following ablation, the effective refractory period for patients in the Cryo-AF group was significantly prolonged compared with before ablation (197 +/- 16 ms to 232 +/- 24 ms, P < 0.0001). As a result of this prolongation of the effective refractory period of the atrium, the fragmented atrial activity and repetitive atrial response zones narrowed following ablation in the Cryo-AF group, but not in the RF-AF group. Therefore, the pathogenesis of atrial fibrillation in patients with Wolff-Parkinson-White syndrome may depend on the refractory period of the atrium rather than on the presence of accessory pathways.     

Electromagnetic compatibility aspects of active robotic systems for surgery: the robotic prostatectomy experience

This case describes ventricular proarrhythmia as a result of a synchronized internal atrial defibrillation shock in a 29-year-old man with Ebstein's anomaly referred for radiofrequency ablation of a right posterior accessory pathway. During the electrophysiologic study, atrial fibrillation was induced and 3/3 msec shocks of various strengths were delivered between two decapolar defibrillation catheters in the coronary sinus and right atrial appendage. A 2.0-J biphasic shock synchronized to an R wave after a short-long-short ventricular cycle length pattern with a preshock coupling interval of 245 msec induced ventricular fibrillation, which was externally defibrillated with 200 J. This observation has implications for the development of implantable atrial defibrillators.     

Conversion efficacy and safety of intravenous ibutilide compared with intravenous procainamide in patients with atrial flutter or fibrillation

OBJECTIVES: This multicenter study compared the efficacy and safety of ibutilide versus procainamide for conversion of recent-onset atrial flutter or fibrillation. BACKGROUND: Ibutilide fumarate is an intravenous (IV) class III antiarrhythmic agent that has been shown to be significantly more effective than placebo in the pharmacologic conversion of atrial flutter and fibrillation to sinus rhythm. Procainamide is commonly used for conversion of recent-onset atrial fibrillation to normal sinus rhythm. METHODS: One hundred twenty-seven patients (age range 22 to 92 years) with atrial flutter or fibrillation of 3 h to 90 days' (mean 21 days) duration were randomized to receive either two 10-min IV infusions of 1 mg of ibutilide fumarate, separated by a 10-min infusion of 5% dextrose in sterile water, or three successive 10-min IV infusions of 400 mg of procainamide hydrochloride. RESULTS: Of the 127 patients, 120 were evaluated for efficacy: 35 (58.3%) of 60 in the ibutilide group compared with 11 (18.3%) of 60 in the procainamide group had successful termination within 1.5 h of treatment (p < 0.0001). Seven patients were found to have violated the protocol and were not included in the final evaluation. In the patients with atrial flutter, ibutilide had a significantly higher success rate than procainamide (76% [13 of 17] vs. 14% [3 of 22], p=0.001). Similarly, in the atrial fibrillation group, ibutilide had a significantly higher success rate than procainamide (51% [22 of 43] vs. 21% [8 of 38], p=0.005). One patient who received ibutilide, which was found to be a protocol violation, had sustained polymorphic ventricular tachycardia requiring direct current cardioversion. Seven patients who received procainamide became hypotensive. CONCLUSIONS: This study establishes the superior efficacy of ibutilide over procainamide when administered to patients to convert either atrial fibrillation or atrial flutter to sinus rhythm. Hypotension was the major adverse effect seen with procainamide. A low incidence of serious proarrhythmia was seen with the administration of ibutilide occurring at the end of infusion.     

Direct conversion of atrial flutter to sinus rhythm with low-output, short-duration transesophageal atrial pacing

BACKGROUND AND HYPOTHESIS: Transesophageal atrial pacing (TAP) is useful for terminating paroxysmal non-self terminating atrial flutter (PAF); however, high output pacing of long stimulus duration causes severe symptoms such as chest pain. The objective of this study was to investigate the effect of low-output, short-duration TAP on the conversion of PAF. METHODS: We applied low-output (within 15 mA with a pulse duration of 10 ms), short-duration (within 4 s) TAP in 31 patients (50 +/- 19 years) with PAF. Transesophageal pacing was delivered with 10 pulses of burst pacing at intervals that were 20 ms shorter than those of the flutter wave length. When the conversion was unsuccessful, we delivered 20 pulses of burst pacing. RESULTS: Sixteen patients (52%) were converted directly to sinus rhythm and 12 (38%) to atrial fibrillation. Transesophageal pacing was ineffective in 3 (10%) patients. The duration of atrial flutter, maximum flutter wave amplitude, effective pacing intervals, underlying heart diseases, and cardiac function were not different between patients who had direct conversion to sinus rhythm and those converted to atrial fibrillation. The patients who had direct conversion to sinus rhythm had longer flutter wave cycle lengths than those converted to atrial fibrillation (248 vs. 221 ms, p < 0.005). No patient had complications and complained of any symptoms. CONCLUSION: Low-output, short-duration TAP was useful to convert PAF directly to sinus rhythm without side effects.     

Catheter ablation for atrial flutter and fibrillation. An effective alternative to medical therapy

Atrial flutter and atrial fibrillation are common arrhythmias that can be difficult to manage clinically. In many patients, these conditions are refractory to pharmacologic therapy because of drug failure or intolerance. Radiofrequency catheter ablation may be a reasonable alternative in patients with typical atrial flutter. The procedure has a high initial success rate and a low complication rate. However, recurrence after ablation is common, and a second treatment session may be needed. In selected patients with atrial fibrillation, radiofrequency ablation can be useful for rate control. However, its use in curing chronic fibrillation is still experimental. The procedure involves insertion of a pacemaker, anticoagulation therapy is still needed in most patients, and the need for antiarrhythmic medication may not be obviated.     

Right-sided maze procedure for right atrial arrhythmias in congenital heart disease

BACKGROUND: Atrial fibrillation and flutter, commonly associated with congenital heart anomalies that cause right atrial dilatation, may cause significant morbidity and reduction of quality of life, even after surgical repair of the anomalies. METHODS: In an effort to reduce the incidence of atrial tachyarrhythmias after repair of right-sided congenital heart disease, we performed a concomitant right-sided maze procedure. RESULTS: Eighteen patients with paroxysmal atrial fibrillation or flutter (n = 12) or chronic atrial fibrillation or flutter (n = 6) aged 10.9 to 68.4 years (mean 34.9 years) underwent a right-sided maze in association with repair of Ebstein's anomaly (n = 15), congenital tricuspid insufficiency (n = 2), and isolated atrial septal defect (n = 1). There were no early deaths, reoperations, or complete heart block. Discharge rhythm was sinus (n = 16) or junctional (n = 2). Follow-up was complete in all 18 patients and ranged from 3.1 to 17.2 months (mean 8.1 months); all are in New York Heart Association class I. Early postoperative arrhythmias developed in 3 patients (all were converted to sinus rhythm by antiarrhythmic drugs). There were no late deaths or reoperations. CONCLUSIONS: The inclusion of a right-sided maze procedure with cardiac repair in patients having congenital heart anomalies that cause right atrial dilatation and associated atrial tachyarrhythmias is effective in eliminating or reducing the incidence of those arrhythmias.     

Multiple accessory pathways in patients with the pre-excitation syndrome

We have studied 135 patients with the pre-excitation syndrome and have demonstrated evidence of multiple accessory pathways in 20 patients. Five patients had two distinct accessory atrioventricular (A-V) connections, associated with enhanced A-V node conduction in one patient. Twelve patients had a single accessory A-V connection associated with enhanced A-V conduction. In one of these there was an additional fasciculo-ventricular connection. One patient had an accessory A-V connection associated with a nodoventricular bundle. Two patients had fasciculo-ventricular connections combined with enhanced A-V conduction. The latter two patients had electrocardiograms suggestive of a complete accessory A-V connection. Patients with enhanced A-V conduction had shorter cycle lengths during reciprocating tachycardia, primarily because of a short A-H during the dysrhythmia, than those without such conduction. In addition, patients with enhanced A-V conduction demonstrated more rapid conduction from atrium to His bundle during induced atrial fibrillation and two developed life-threatening ventricular responses during atrial fibrillation. A nodo-ventricular pathway was documented to participate in reciprocating tachycardia in one patient. Surgery was undertaken in 13 patients. In 11, the intraoperative mapping studies confirmed the preoperative predictions. In two patients, the presence of a second accessory A-V connection was documented after ablation of one.     

Radiofrequency catheter ablation in type I atrial flutter: preliminary experience of 10 cases

Common atrial flutter results from macroreentry in the right atrium. Catheter ablation of slow conduction, between tricuspid annulus and inferior vena cava (TA-IVC) or tricuspid annulus and coronary sinus ostium (TA-CS os) has been reported to terminate and prevent recurrence of this arrhythmia. We reported 10 consecutive patients, 7 men and 3 women, who underwent radiofrequency catheter ablation of common atrial flutter. The mean age was 59.4 +/- 11.2 years (range 42-82 years). During the paroxysmal atrial flutter, all patients had palpitation, 4 had dyspnea on exertion, 3 patients had syncope and 1 patient had presyncope. The mean duration of symptoms was 5.7 +/- 4.9 years (range 0.5-13 years). Two patients had dilated cardiomyopathy, 1 Ebstein's anomaly and 1 chronic obstructive pulmonary disease. Four patients (40%) had history of atrial fibrillation (AF) before ablation. The mean cycle length of atrial rhythm was 257.2 +/- 36.6 ms. Ablation was done by anatomical approach and could terminate arrhythmia in 9 patients (90%), 7 from TA-IVC, 2 from TA-CS os without major complication. The mean number of applications was 20.4 +/- 16.9 and turned atrial flutter to normal sinus rhythm in 13.5 +/- 10.7 seconds. Fluoroscopic and procedure times were 38.4 +/- 31.4 and 157.2 +/- 68.8 minutes, respectively. During the follow-up period of 24.0 +/- 28.7 weeks, 2 patients had recurrent atrial arrhythmia, 1 atrial fibrillation and 1 atrial flutter type I, giving the final success rate of 70 per cent. All patients who had recurrence or failure had a history of paroxysmal AF before ablation. In conclusion, radiofrequency catheter ablation in atrial flutter type I, using anatomical approach, is an effective treatment to terminate and prevent this arrhythmia in short term follow-up. It may be considered as an alternative treatment in patients with atrial flutter who were refractory to antiarrhythmic agents.     

Tachyarrhythmias in old age

The electrocardiograms of 1,171 patients above the age of 65 in a predominantly geriatric institution were reviewed to determine the incidence of tachyarrhythmias. Data on the overall incidence and the individual types of arrhythmias are presented. Atrial fibrillation was the most common arrhythmia observed, followed by atrial flutter and supraventricular tachycardia. Atrial fibrillation often was associated with other evidence of myocardial damage. The significance of sinus bradycardia and grade I A-V block in the pathogenesis of atrial fibrillation and the significance of the tachyarrhythmias are discussed.     

Atrial tachyarrhythmias in acute myocardial infarction

Causative factors, clinical consequences and treatment of atrial tachyarrhythmias were reviewed in 917 monitored patients with definite acute myocardial infarction. Significant atrial tachyarrhythmias were found in 104 (11 per cent) of them and included atrial fibrillation in 67, atrial flutter in 29 and paroxysmal atrial tachycardia in 33. These episodes were single in 79 patients and multiple in 25, and began within the first four days of acute myocardial infarction in 90 per cent of the patients. Fifty per cent of these atrial tachyarrhythmias were heralded by premature atrial contractions. The incidence of atrial tachyarrhythmia was not related to the location of the acute myocardial infarction or to the presence or degree of power failure; however, atrial tachyarrhythmias were significantly more frequent in patients with pericarditis. Atrial tachyarrhythmias were well tolerated in almost one fifth of the patients, caused marginal compromise in almost two thirds and led to severe clinical deterioration in one fifth. Paroxysmal atrial tachycardia rarely required specific treatment, atrial fibrillation was best managed with intravenous administration of digoxin except when associated with severe clinical compromise, and atrial flutter generally required cardioversion or rapid intravenous therapy and usually caused severe clinical deterioration. Over-all, atrial tachyarrhythmia was not associated with a significantly increased mortality, and in those who died, death was not related specifically to the atrial tachyarrhythmia but rather to the severity of the underlying acute myocardial infarction. However, persisting atrial tachyarrhythmias, particularly atrial flutter which tends to be refractory to both heart rate control and cardioversion, may contribute indirectly to morbidity and mortality.     

Mechanisms and medical management of patients with atrial flutter

Type I atrial flutter is due to reentrant excitation, principally in the right atrium. The standard ECG remains the cornerstone for its clinical diagnosis. Acute treatment should be directed at control of the ventricular response rate and, if possible, restoration of sinus rhythm. Radiofrequency catheter ablation therapy provides the best hope of cure, although atrial fibrillation may subsequently occur after an ostensibly successful ablative procedure. Alternatively, antiarrhythmic drug therapy to suppress recurrent atrial flutter episodes may be useful, recognizing that occasional recurrences are common despite therapy. Radiofrequency ablation of the His bundle ablation with placement of an appropriate pacemaker system may be useful in selected patients.