Michael A. Lee

Catheter modification of the atrioventricular junction with radiofrequency energy for control of atrioventricular nodal reentry tachycardia.

BackgroundThe utility of transcatheter application of radiofrequency energy to eliminate atrioventricular nodal reentrant tachycardia (AVNRT) was investigated. Methods and ResultsThirty-nine patients (mean age, 53 ± 20 years; range, 14-86 years) with medically refractory AVNRT underwent perinodal ablation with radiofrequency energy. A custom-designed 6F catheter with a large (3-mm-long) distal electrode and interelectrode pacing of 2 mm was used in the majority of cases. The catheter used for ablation was initially positioned across the tricuspid anulus to obtain the largest His bundle electrogram, then withdrawn to obtain the largest atrial ventricular electrogram ratio, with a small His bundle electrogram (<100 μV). Each application of radiofrequency energy (350-550 kHz, 16.2 ± 5.2 W) was stopped after 60 seconds or if PR prolongation or an impedance rise was noted. The endpoints of the procedure were persistent modification of atrioventricular nodal conduction (either first-degree atrioventricular block or impairment of ventriculoatrial conduction) and noninducibility of AVNRT before and during isoproterenol administration. Radiofrequency energy was applied a mean of 6.8 ± 3.5 times per session. After a mean follow-up of 8 ± 3.0 months, 32 of the 39 patients (82%) have been free of AVNRT, and did not have high grade AV block. Three patients (8%) developed complete atrioventricular block and had pacemakers implanted. Two patients had unsuccessful initial procedures, and two patients had initially successful ablations but had recurrences of tachycardia 4-6 weeks later. Elimination ofAVNRT appeared to be due to effects on the retrograde fast pathway in most patients. ConclusionsRadiofrequency ablation of the perinodal right atrium appears to be safe and effective for treatment of typical AVNRT. (Circulation 1991;83:827–835)

Curative percutaneous catheter ablation using radiofrequency energy for accessory pathways in all locations: Results in 100 consecutive patients

Patients with accessory pathway-mediated supraventricular tachycardia have typically been treated with drugs or surgery. Although catheter ablation using high voltage direct current shocks has been used to treat patients with drug-refractory supraventricular tachycardia, there are associated disadvantages, including damage due to barotrauma as well as the need for general anesthesia. Recently, transcatheter radiofrequency energy has evolved as an alternative to direct current shock or surgery to ablate accessory pathways. Percutaneous catheter ablation of 109 accessory pathways with use of radiofrequency energy was attempted in 100 consecutive patients. Patient age ranged from 3 to 67 years. The patients had been treated for recurrent tachycardia with a mean of 2.7 +/- 0.2 antiarrhythmic agents that either proved ineffective or caused unacceptable side effects. In seven patients previous attempts at accessory pathway ablation with use of direct current shock had been unsuccessful. Forty-five (41%) of the pathways were left free wall, 43 (40%) were septal and 21 (19%) were right free wall. Eighty-nine (89%) of the 100 patients had successful radiofrequency ablation at the time of hospital discharge. In all but 12 patients the ablation was accomplished in a single session. Complications attributable to the procedure, but not to the ablation itself, occurred in four patients (4%). No patient developed atrioventricular block or other cardiac arrhythmias. Over a mean follow-up period of 10 months, nine patients had some return of accessory pathway conduction; a repeat ablation procedure was successful in all five patients in whom it was attempted. It is concluded that a catheter ablation procedure using radiofrequency energy can be performed on accessory pathways in all locations. The procedure is effective and safer, less costly and more convenient than cardiac surgery and can be considered as an alternative to lifelong medical therapy in any patient with symptomatic accessory pathway-mediated tachycardia.

Effects of long-term right ventricular apical pacing on left ventricular perfusion, innervation, function and histology

OBJECTIVES The purpose of this study was to better understand the effects of long-term right ventricular pacing on left ventricular perfusion, innervation, function and histology. BACKGROUND Long-term right ventricular apical pacing is associated with increased congestive heart failure and mortality compared with atrial pacing. The exact mechanism for these changes is unknown. In this study, left ventricular perfusion, sympathetic innervation, function and histologic appearance after long-term pacing were studied in dogs in an attempt to see whether basic changes might be present that might ultimately be associated with the adverse clinical outcome. METHODS A total of 24 dogs were studied. Sixteen underwent radiofrequency ablation of the atrioventricular (AV) junction to produce complete AV block. Seven of these underwent long-term pacing from the right ventricular apex (ventricular paced group), and nine had atrial and right ventricular apical pacing with AV synchrony (dual-chamber paced group). A control group of eight dogs had sham ablations with normal AV conduction. These dogs had atrial pacing only. Regional perfusion and sympathetic innervation were studied in all dogs by imaging with thallium-201 and [I123]metaiodobenzylguanidine, respectively. The degree of innervation was also determined by assay of tissue norepinephrine levels. Left ventricular function was assessed by radionuclide ventriculography. Cardiac histology was studied with both light and electron microscopy. RESULTS Mismatching of perfusion and innervation in the ventricular paced group was noted, with perfusion abnormalities of both the septum and free wall. Regional [I123]metaiodobenzylguanidine distribution was homogeneous. Tissue norepinephrine levels were elevated in both the ventricular and dual-chamber paced groups compared with the control group. No light or electron microscopic findings were noted in any groups. In the dual-chamber paced group, diastolic dysfunction was noted, with normal systolic function. CONCLUSIONS Ventricular pacing resulted in regional changes in tissue perfusion and heterogeneity between perfusion and sympathetic innervation. Both ventricular and dual-chamber pacing were associated with an increase in tissue catecholamine activity. The abnormal activation of the ventricles via right ventricular apical pacing may result in multiple abnormalities of cardiac function, which may ultimately affect clinical outcome.

Survival after implantation of the cardioverter defibrillator

The actuarial survival of 60 consecutive recipients of the implanted cardioverter defibrillator (ICD) were compared with 120 matched concurrent medically treated patients using a case-control design. All ICD patients and controls presented with either sustained ventricular tachycardia or ventricular fibrillation. Controls were matched to ICD recipients according to 5 variables: age, left ventricular ejection fraction, arrhythmia at presentation, underlying heart disease and drug therapy status. Mean ages were 58 and 59 years in ICD patients and controls, and the average ejection fractions were 36 and 35%. Coronary artery disease was present in 75 and 79% of ICD patients and controls, respectively. During follow-up, sudden deaths were fewer in ICD recipients than in controls (5 vs 10%, p less than 0.01). At 1 and 3 years, actuarial survival was 0.89 vs 0.72 and 0.65 vs 0.49 for ICD recipients and controls. The 5-year actuarial survival curves were significantly different by the Cox proportional hazards model (p less than 0.05). It is concluded that in this retrospective case-control study, the use of the ICD in the management of patients at risk for sudden death results in improved probability of survival.

Radiofrequency catheter ablation for treatment of bundle branch reentrant ventricular tachycardia: results and long-term follow-up.

Seven of 120 consecutive patients with inducible sustained ventricular tachycardia (from September 1, 1988 to January 1, 1991) had bundle branch reentrant tachycardia and underwent percutaneous radiofrequency ablation of the right bundle branch. The seven patients had been unsuccessfully treated with a mean of 3 +/- 1 drugs. Four patients presented with syncope and three with aborted sudden death. The baseline electrocardiogram revealed a left bundle branch block pattern in three patients and an intraventricular conduction defect in four. The baseline HV interval was prolonged in each case (79 +/- 2 ms). With use of programmed ventricular extrastimuli, sustained bundle branch reentrant tachycardia was inducible in all patients at a mean cycle length of 283 +/- 17 ms (range 230 to 350). Bundle branch reentrant tachycardia characteristics included atrioventricular dissociation, a His deflection that preceded each QRS complex and spontaneous His to His variation that preceded changes in ventricular tachycardia cycle length. A quadripolar catheter was positioned across the tricuspid valve with the distal electrode tip of the catheter near the right bundle branch. One to three applications of continuous unmodulated radiofrequency current at 300 kHz between the distal electrode and a large posterior skin patch resulted in complete right bundle branch block in all patients, after which none had inducible bundle branch reentrant tachycardia on restudy. On restudy, three of the seven patients had ventricular tachycardia of myocardial origin (not bundle branch reentry). One patient required no therapy; drug or defibrillator therapy was used in the others.(ABSTRACT TRUNCATED AT 250 WORDS)

Radiofrequency catheter ablation: the effect of electrode size on lesion volume in vivo.

Radiofrequency current is a promising alternative to high voltage direct current defibrillator discharges for catheter ablation of arrhythmias. However, lesions produced with radiofrequency current are relatively small and use of high power is limited by the impedance rise that occurs with desiccation of tissue and coagulum formation. The effect of electrode size on radiofrequency ablation was assessed by comparing results of radiofrequency application using a standard 6 French electrode catheter (distal electrode 2 mm in length) to those using catheters modified with longer distal electrodes (3, 4, 6, 8, and 10 mm in length). Radiofrequency ablation was performed at 47 left ventricular endocardial sites in 20 anesthetized dogs. A constant power of 13.3 ± 1.3 watts at 550 kHz was applied between the distal catheter electrode and a skin electrode until a total of 500 joules had been delivered or a rise in impedance occurred. Increasing electrode length from 2 to 4 mm more than doubled lesion volume from a mean of 143 to 326 mm3 (P = 0.025). Increasing electrode length beyond 4 mm produced progressively smaller lesions (157 mm3, 155 mm3, and 67 mm3 for 6‐, 8‐, and 10‐mm electrode lengths, respectively). Impedance rise was significantly less likely with larger electrodes and took longer to occur. Increasing the size of electrodes used for radiofrequency ablation allows application of higher power without an impedance rise. Optimizing electrode size (3 or 4 mm in this study) results in larger lesions and may improve the effectiveness of radiofrequency ablation of arrhythmias.

Long-term follow-up of patients after transcatheter direct current ablation of the atrioventricular junction

The long-term follow-up study (41 +/- 23 months) of 47 patients undergoing direct current ablation because of drug-resistant supraventricular arrhythmias is reported. Significant early complications occurred in four patients and included hypotension, pericarditis, nonsustained polymorphic ventricular tachycardia and one sudden death. In 42 patients (86%), complete atrioventricular (AV) block was initially achieved. During the follow-up period, AV conduction resumed in 2 of these 42 patients. Of the seven patients in whom ablation was unsuccessful, two developed late complete AV block and three had symptomatic improvement. An improved activity level was reported among 83% of the patients with successful ablation. Health care utilization manifest as the number of hospital admissions per year before and after ablation decreased significantly after ablation (2.4 +/- 2.0 versus 0.3 +/- 0.5, p less than 0.001). Echocardiographic evaluation in five patients with a depressed left ventricular ejection fraction (27 +/- 7%) before ablation showed a significant increase (45 +/- 14%, p less than 0.05) after an average follow-up period of 31 months. New onset of congestive heart failure occurred after ablation in four patients, of whom two had no structural heart disease. The total mortality rate, including the one patient with sudden death, was 17% and was significantly higher among patients with underlying structural heart disease. Transcatheter direct current ablation is an effective treatment in patients with drug-resistant supraventricular tachycardia, providing a beneficial long-term outcome including an improved quality of life and a decrease in health care utilization.(ABSTRACT TRUNCATED AT 250 WORDS)

Ablation of the atrioventricular junction with radiofrequency energy using a new electrode catheter

Percutaneous catheter ablation using radiofrequency energy can be used to interrupt atrioventricular (AV) conduction in patients with supraventricular tachycardia refractory to drugs. Results of radiofrequency ablation of the AV junction using a custom-designed catheter with a large, 3-mm-long distal electrode, 2-mm interelectrode spacing, and a shaft with increased torsional rigidity were compared with those using a standard quadripolar electrode catheter (Bard EP). An electrocoagulator (Microvasive Bicap 4005) supplied unmodulated radiofrequency current at 550 kHz, which was applied between the distal electrode of the ablation catheter and a large skin electrode. With use of the modified catheter, 12 of 13 patients (92%) had persistent complete AV block induced with 7 +/- 5 applications of 18 +/- 6 W of radiofrequency power. In contrast, complete AV block was produced in only 9 of 18 (50%) historical control patients treated with the standard catheter, despite a similar number of applications (7 +/- 5) and power output (16 +/- 4 W). A rise in impedance, due to desiccation of tissue and coagulum formation, occurred earlier (28 +/- 18 vs 52 +/- 24 seconds, p less than 0.001) and more frequently (54 vs 40% of applications, p = 0.047) in patients treated with the standard catheter than in patients treated with the modified catheter. The use of a catheter designed to increase the surface area of electrode-tissue contact allows more radiofrequency energy to be delivered before a rise in impedance occurs and appears to increase the effectiveness of radiofrequency ablation of the AV junction.

The Effect of Radiofrequency Catheter Ablation on Permanent Pacemakers: An Experimental Study

Radiofrequency current is being investigated as an alternative to direct current shock for transcatheter abJation of cardiac arrhythmias. Permanent pacemakers are known to be susceptible to high frequency electromagnetic interference. This study was performed to examine the effects of Imnscatheter radiofrequency ablation on permanent pacemakers in a worst‐case scenario. Nineteen pulse generators representing 16 models from seven manufacturers were acutely implanted in 12 dogs to assess (heir function during and after ablation. Pulse generators were implanted subcutaneously in the neck and connected to a transvenous permanent pacing lead positioned in the right ventricular apex. A 6F quadri‐polar electrode catheter was positioned approximately 1 cm from the tip of the permanent pacing lead. Radiofrequency current from an electrosurgical unit was applied between the distal electrode of the catheter and a large diameter skin electrode placed below the left scapula. Three additional ablation sessions were performed with the catheter situated 4‐5 cm from the permanent pacing lead. Each ablation consisted of 35 W of radiofrequency power, delivered for up to 30 seconds. Twelve pulse generators were falsely inhibited during radiofrequency ablation while programmed to (he WI or DDD mode, nine of which continued to be inhibited while programmed to the VOO or DOO mode. Five pulse generators paced at abnormal rates, including three examples of one pulse generator model that displayed pacemaker runaway. Runaway was observed during eight ablations, resulting in two episodes of ventricular fibrillation. Eleven pulse generators reverted to noise mode behavior during ablation. Only three pulse generators were unaffected during ablation. No reprogramming or pacing system malfunctions were observed after cessation of radiofrequency current application or during ablations > 4 cm from the permanent lead. No changes in lead impedance, sensing, or capture threshold were observed. In conclusion, transcatheter radiofrequency ablation within close proximity of a permanent pacing lead may falsely inhibit implanted pulse generators, induce pacemaker runaway, or cause pulse generators to revert to noise mode behavior. Radiofrequency ablation performed in patients with permanent pacemakers requires careful monitoring as well as backup external pacing. A complete pacing system analysis should be performed following each ablation.

Electrophysiological findings and long-term follow-up of patients with the permanent form of junctional reciprocating tachycardia treated by catheter ablation.

Background The permanent form ofjunctional reciprocating tachycardia (PJRT) commonly presents as recurrent drug-refractory, narrow-complex tachycardia. We studied the efficacy and safety of catheter ablation in treating these patients. Methods and Results Six patients with the diagnosis of PJRT were treated at our institution with direct-current catheter ablation. The study cohort comprised three men and three women with a mean age of 33.8±4.5 years. The mean time from onset of symptoms to ablation was 129±44.7 months. All failed multiple drug therapy (mean number of drugs failed was 5.3±0.5). The left ventricular ejection fractions were calculated by echocardiography and were greater than 60% in all except two patients, whose ejection fractions were 25% and 32%. Symptom duration was significantly longer in those with depressed ejection fraction compared with normal patients (258 versus 64.5 months, p < 0.01). Electrophysiological findings revealed evidence of an atrioventricular reciprocating tachycardia involving retrograde decremental conduction over an accessory pathway localized to the posteroseptal area. Five patients received two direct-current shocks (250±16.7 J per shock) via paired electrodes from a catheter positioned just outside the coronary sinus os to a patch placed between the scapulae or on the anterior chest wall. One patient received a single direct-current shock of 300 J. The only complication was the development of complete atrioventricular block in one patient. This patient had previously undergone permanent pacemaker insertion for the sick sinus syndrome. The mean hospital stay after ablation was 2.2 days. Mean peak creatinine phosphokinase after ablation was 352±58.1 units/I and the MB fraction was 12±2%. Follow-up echocardiograms or gated nuclear studies showed improvement of ejection fraction in the two patients who presented with depressed ejection fractions. After a mean follow-up of 35.8±10.3 months, all patients remained free of tachycardia without antiarrhythmic drugs. Conclusions We conclude that catheter ablation by using direct current energy appears to be an effective treatment in patients with PJRT.