William H. Kou

Diagnosis and cure of the Wolff-Parkinson-White syndrome or paroxysmal supraventricular tachycardias during a single electrophysiologic test

BACKGROUND We conducted this study to determine the feasibility of an abbreviated therapeutic approach to the Wolff-Parkinson-White syndrome or paroxysmal supraventricular tachycardia, in which the diagnosis is established and radiofrequency ablation carried out during a single electrophysiologic test. METHODS One hundred six consecutive patients were referred for the management of documented, symptomatic paroxysmal supraventricular tachycardias (66 patients) or the Wolff-Parkinson-White syndrome (40 patients). All agreed to undergo a diagnostic electrophysiologic test and catheter ablation with radiofrequency current. No patient had had such a test previously. RESULTS Among the 66 patients with paroxysmal supraventricular tachycardias, the mechanism was found to be atrioventricular nodal reentry in 46 (70 percent) (typical in 44 and atypical in 2), atrioventricular reciprocating tachycardia involving a concealed accessory pathway in 16 (24 percent), atrial tachycardia in 2 (3 percent), and noninducible paroxysmal supraventricular tachycardia in 2 (3 percent). A successful long-term outcome was achieved in 57 of 62 patients (92 percent) with paroxysmal supraventricular tachycardia in whom ablation was attempted and in 37 of 40 patients (93 percent) with the Wolff-Parkinson-White syndrome. The only complications were one instance of occlusion of the left circumflex coronary artery, leading to acute myocardial infarction, and one instance of complete atrioventricular block. The mean (+/- SD) duration of the electrophysiologic procedures was 114 +/- 55 minutes. CONCLUSIONS The diagnosis and cure of paroxysmal supraventricular tachycardia or the Wolff-Parkinson-White syndrome during a single electrophysiologic test are feasible and practical and have a favorable risk-benefit ratio. This abbreviated therapeutic approach may eliminate the need for serial electropharmacologic testing, long-term drug therapy, antitachycardia pacemakers, and surgical ablation.

Radiofrequency catheter ablation of accessory atrioventricular connections in 250 patients. Abbreviated therapeutic approach to Wolff-Parkinson-White syndrome.

Background The purpose of this study was to report the results and complications of radiofrequency catheter ablation of accessory atrioventricular (AV) connections by using an abbreviated approach aimed at minimizing the duration of the procedure. Methods and Results Two hundred fifty consecutive patients with the Wolff-Parkinson-White syndrome or paroxysmal supraventricular tachycardia involving a concealed accessory AV connection underwent catheter ablation with the use of radiofrequency current. In 179 of the 250 patients, catheter ablation was performed at the time of an initial electrophysiology test. Two hundred thirty-five patients had one accessory AV connection and 15 patients had two or more. One hundred eighty-three accessory AV connections were manifest and 84 were concealed. One hundred sixty-one were located in the free wall of the left ventricle, 47 were in the right free wall, 44 were posteroseptal, 10 were anteroseptal, and five were intermediate septal. The time required for catheter placement, the diagnostic component of the electrophysiology test, and the ablation procedure was recorded for each patient, as was the total duration of fluoroscopy. A follow-up electrophysiology test was performed 2–3 months after the ablation procedure. Ninety-four percent of patients had all accessory AV connections successfully ablated and remained free of symptomatic tachycardia during a mean follow-up of 10±4 months. Two hundred nineteen patients (88%) had all accessory AV connections ablated during the initial attempt at catheter ablation. Mean duration of the entire procedure was 134±75 minutes. Procedure duration was longest in patients with multiple accessory AV connections, shortest in patients with intermediate septal accessory AV connections, and similar in all other locations. A nonfatal complication occurred in nine patients (4%). Conclusions The results of this study indicate that catheter ablation of accessory AV connections with radiofrequency current can be performed safely and expeditiously in a majority of patients and confirm in a large series the feasibility of catheter ablation at the time of an initial diagnostic electrophysiology test. This abbreviated therapeutic approach avoids the need for electropharmacological testing, long-term antiarrhythmic drug therapy, and surgical therapy in the majority of patients with the Wolff-Parkinson-White syndrome or with symptomatic tachycardias involving accessory AV connections.

Long-term results of catheter ablation of idiopathic right ventricular tachycardia.

Ten consecutive patients with recurrent episodes of symptomatic, idiopathic, sustained monomorphic ventricular tachycardia (VT) originating in the right ventricle underwent an attempt at catheter ablation of the ventricular tachycardia. There were seven women and three men, with a mean age of 39 +/- 14 years (+/- SD). None of the patients had any evidence of structural heart disease. The VT had a left bundle branch block configuration and an inferior axis in each patient, and the mean cycle length was 313 +/- 75 msec. Based on the methods of induction of the VT and the response of the VT to verapamil, the VT mechanism was presumed to be reentry in six patients, triggered activity in three patients, and catecholamine-sensitive automaticity in one patient. Sites for ablation were guided by pace mapping, and an appropriate target site was identified in the right ventricular outflow tract in each patient. From one to three shocks of 100-360 J (mean total, 336 +/- 195 J) were delivered from a defibrillator between the tip of the ablation catheter (cathode) and a patch electrode on the anterior chest (anode). An electrophysiology test 7-9 days after ablation demonstrated that VT was still inducible in only one patient, who was treated with amiodarone. One other patient had a recurrence of VT 3 weeks after ablation and was treated with verapamil. Eight of 10 patients were not treated with antiarrhythmic medications and have had no episodes of symptomatic VT during 15-68 months of follow-up (mean follow-up, 33 +/- 18 months). There were no acute or long-term complications.(ABSTRACT TRUNCATED AT 250 WORDS)

Concealed entrainment as a guide for catheter ablation of ventricular tachycardia in patients with prior myocardial infarction

Fifteen consecutive patients with drug-refractory, recurrent, sustained, monomorphic ventricular tachycardia and a history of remote myocardial infarction underwent catheter ablation of ventricular tachycardia. Shocks of 100 to 300 J were delivered to sites at which pacing during ventricular tachycardia resulted in concealed entrainment, in which the ventricular tachycardia accelerated to the pacing rate, there was a long stimulus to QRS interval and there was no change in the configuration of the QRS complex during pacing at several rates compared with the configuration during ventricular tachycardia, thus identifying a zone of slow conduction in the reentrant circuit. Concealed entrainment was demonstrated in nine (60%) of 15 patients, and the stimulus to QRS intervals were 90 to 400 ms. At sites of concealed entrainment, the endocardial activation time relative to the QRS complex during ventricular tachycardia ranged from -125 to +50 ms, the timing of the local electrogram relative to the QRS complex was the same during entrainment as during ventricular tachycardia and the pace map during sinus rhythm was discordant with that of the ventricular tachycardia in seven patients. In the six patients in whom a site of concealed entrainment could not be identified, the target site for ablation was selected on the basis of identification of an isolated mid-diastolic potential, activation mapping and pace mapping. The mean (+/- SD) cumulative number of joules delivered to the target site was 306 +/- 140. A successful long-term clinical outcome was achieved in 9 of the 15 patients (mean follow-up 20 +/- 7 months). The clinical success rate was the same whether the target site was selected on the basis of concealed entrainment (five of nine, 56%) or on the basis of the other mapping techniques (four of six, 67%). In conclusion, the responses to pacing suggest that sites at which there is concealed entrainment may be located within a zone of slow conduction in the ventricular tachycardia reentry circuit, although not necessarily in an area critical for the maintenance of reentry. The long-term clinical efficacy of catheter ablation targeted to sites of concealed entrainment is about 60%, similar to the results achieved when conventional mapping techniques are used.

Identification and catheter ablation of a zone of slow conduction in the reentrant circuit of ventricular tachycardia in humans

Three patients who had incessant ventricular tachycardia and in whom a zone of slow conduction was identified are presented. Each patients tachycardia was refractory to multiple antiarrhythmic drugs and was being treated with amiodarone at the time of the electrophysiologic study. The ventricular tachycardia cycle length was 500 to 580 ms. In Patients 1 and 2, a single site at the posterolateral wall or low septum in the left ventricle was identified at which overdrive pacing during ventricular tachycardia resulted in ventricular capture with a stimulus to QRS interval of 280 to 400 ms and with little or no change in the configuration of the QRS complexes during pacing as compared with during ventricular tachycardia. In Patient 3, the same phenomenon was observed at two areas in the left ventricle: at the inferior wall, overdrive pacing during ventricular tachycardia resulted in a stimulus to QRS interval of 440 to 470 ms, whereas at the posterolateral wall, the stimulus to QRS interval was 320 to 360 ms. Transcatheter shocks of 100 to 240 J delivered at the pacing sites have been successful in preventing recurrences of ventricular tachycardia over a follow-up period of 10 to 11 months. These observations may be explained by the pacing site being located within a reentrant circuit in a zone of slow conduction bounded by inexcitable tissue between the pacing site and the exit site of the reentrant circuit. In Patient 3, the variable stimulus to QRS intervals are explained by variable proximity of the pacing sites within the slow conduction zone to the exit site of the reentrant circuit.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term results of catheter ablation of a posteroseptal accessory atrioventricular connection in 48 patients.

Forty-eight patients with a posteroseptal accessory atrioventricular (AV) connection underwent catheter ablation of the accessory AV connection with 200-400 J shocks delivered by a standard defibrillator. Cathodal shocks were delivered through the proximal pair of electrodes of a 6F quadripolar electrode catheter positioned in the coronary sinus such that the proximal electrodes straddled the ostium (12 patients) or the third electrode from the tip was at the ostium (36 patients). A 16-cm patch electrode positioned on the back or anterior chest served as the anode. Two to 4 shocks were delivered (total, 635 +/- 198 J, mean +/- SD). The cathether ablation procedure was clinically successful in eliminating symptomatic tachycardias in in 32 of 48 patients (67%) during a mean follow-up of 26 +/- 19 months. A long-term follow-up electrophysiology study was performed in 27 of the 32 patients who had a successful clinical outcome, and this showed that conduction through the accessory AV connection was completely absent in 25 patients and present but impaired in two patients. The success rate was significantly higher in patients with a concealed accessory AV connection (13 of 13, 100%) than in patients with manifest preexcitation (19 of 35, 54%; p less than 0.001). Among the 12 patients in whom the proximal electrodes of the ablation catheter straddled the ostium of the coronary sinus, one patient developed cardiac tamponade requiring needle pericardiocentesis; there were no instances of cardiac tamponade among the 36 patients in whom the third electrode from the tip was at the ostium of the coronary sinus. Other complications were AV block requiring a permanent pacemaker and transient atrial tachycardia in one patient each and an asymptomatic pericardial effusion in three patients. In conclusion, with the catheter ablation technique described in this study, a successful clinical outcome may be achieved in approximately two thirds of patients who have a posteroseptal accessory AV connection, and the risk of serious complications is low. This technique is particularly well suited to patients with a concealed posteroseptal accessory AV connection, in whom the success rate is higher than in patients with manifest preexcitation.

Effect of shock polarity on ventricular defibrillation threshold using a transvenous lead system

OBJECTIVES The purpose of this study was to determine whether the polarity of a monophasic shock used with a transvenous lead system affects the defibrillation threshold. BACKGROUND The ability to implant an automatic defibrillator depends on achieving an adequate defibrillation threshold. METHODS A transvenous defibrillation lead with distal and proximal shocking electrodes was used in this study. In 29 consecutive patients, the defibrillation threshold, using a stepdown protocol was determined twice in random order: 1) with the distal coil as the anode, and 2) with the polarity reversed. Only the 20 patients in whom an adequate defibrillation threshold could be obtained with the transvenous lead alone were included in this study. These patients were 61 +/- 14 years old (mean +/- SD) and had a mean ejection fraction of 28 +/- 12%. RESULTS The mean defibrillation threshold was 11.5 +/- 5.0 J with the distal coil as the anode versus 16.9 +/- 7.7 J with the distal coil as the cathode (p = 0.04). The defibrillation threshold was lower by a mean of 9 +/- 7 J with the former configuration in 14 patients and was lower by a mean of 7 +/- 6 J with the latter configuration in 3 patients; in 3 patients it was the same with both configurations. Use of a subcutaneous patch was avoided in five patients by utilizing the distal electrode as the anode. CONCLUSIONS Defibrillation thresholds with monophasic shocks are approximately 30% lower with the distal electrode as the anode. The use of anodal shocks may obviate the need for a subcutaneous patch and allow more frequent implantation of a transvenous lead system.

Determinants of the ventricular rate during atrial fibrillation

Determinants of the ventricular cycle length during atrial fibrillation were examined in 52 patients. Thirty-three patients had structural heart disease and none had an accessory atrioventricular (AV) connection. The AV node effective and functional refractory periods, the shortest atrial pacing cycle length associated with 1:1 conduction, the AV node conduction time and indexes of concealed conduction in the AV node were measured in the baseline state (36 patients) and after modification of sympathetic tone by infusion of isoproterenol or propranolol (8 patients each). Atrial fibrillation was then induced with rapid atrial pacing, and the mean, shortest and longest ventricular cycle lengths were measured. Variables that correlated most strongly with the mean RR interval during atrial fibrillation were the AV node effective refractory period (r = 0.93; p less than 0.001), AV node functional refractory period (r = 0.87; p less than 0.001) and shortest atrial pacing cycle length associated with 1:1 conduction (r = 0.91; p less than 0.001). The AH interval during sinus rhythm (r = 0.74; p less than 0.001) and during atrial pacing at the shortest cycle length with 1:1 conduction (r = 0.52; p less than 0.001) had weaker correlations. Measures of concealed conduction did not improve the prediction of the mean or longest ventricular cycle length during atrial fibrillation. In conclusion, the refractory periods and conductivity of the AV node are the best indicators of the potential of the node to transmit atrial impulses to the ventricles during atrial fibrillation. The degree of concealed conduction in the AV node is a less important determinant of the mean ventricular rate during atrial fibrillation.

Incidence of loss of consciousness during automatic implantable cardioverter-defibrillator shocks

OBJECTIVE To determine the incidence of loss of consciousness occurring in association with shocks delivered by automatic implantable cardioverter-defibrillators (AICD) in patients who had undergone implantation as treatment for ventricular tachycardia or ventricular fibrillation. DESIGN Cohort study. SETTING Two major tertiary medical care facilities. PATIENTS A total of 180 patients who had undergone implantation of an AICD for treatment of ventricular tachycardia or ventricular fibrillation. INTERVENTION Implantation of an AICD that delivered only high-energy shock. MEASUREMENTS During a mean (+/- SD) follow-up period of 16 +/- 12 months, the incidence of loss of consciousness occurring in association with spontaneous AICD shocks was determined. Various clinical factors were analyzed to identify predictors of loss of consciousness that occurred during AICD shocks. MAIN RESULTS Of the 180 patients who received an AICD, 106 patients (59%) experienced AICD shocks during follow-up. Sixteen of the 180 patients (9%) experienced loss of consciousness; 13 of these 16 patients had syncope and 3 died suddenly, in association with AICD shocks. The absence of syncope during one AICD shock did not always predict the absence of syncope during subsequent shocks. Syncope could not be predicted by age, sex, history of syncope, left ventricular function, type of underlying heart disease, electrophysiologic findings, rate of ventricular tachycardia, antiarrhythmic medications, and type of pulse generator implanted. CONCLUSIONS Patients with sustained ventricular tachycardia or ventricular fibrillation who receive an AICD that delivers only high-energy shock therapy are at moderate risk for experiencing loss of consciousness during AICD shocks. No clinical variables were found to be predictors of syncope. Therefore, driving and other activities that require patients to be extra vigilant should not be assumed to be safe after implantation of an AICD that delivers only high-energy shock.

Natural history of patients with unexplained syncope and a nondiagnostic electrophysiologic study

The purpose of this study was to define the natural history of 99 patients with unexplained syncope who underwent an electrophysiologic test that either was entirely normal or demonstrated nonspecific abnormalities that were nondiagnostic (inducible polymorphic ventricular tachycardia or ventricular fibrillation, a mildly prolonged sinus node recovery time of less than 2 s, a His-ventricular interval of 55 to 99 ms or supraventricular tachycardia not associated with hypotension). The mean age (+/- SD) of the patients was 56 +/- 19 years; structural heart disease was present in 47 patients and absent in 52. Complete follow-up was available in 95 patients. During 20 +/- 11 months of follow-up, 2 patients (2%) died suddenly, 19 patients (20%) had recurrent syncope and 74 patients (78%) had no further episodes of syncope. Among the 19 patients who continued to have syncope after the electrophysiologic testing, the cause of syncope was established clinically in 4 and was found to be high degree atrioventricular (AV) block (2 patients) or sinus node dysfunction (2 patients). No clinical or laboratory findings distinguished patients who had sudden death or syncope during follow-up from patients who did not. In conclusion, in patients with unexplained syncope who undergo an electrophysiologic test that is nondiagnostic 1) the incidence of sudden death is low (2%); 2) the remission rate of syncope is high (80%); 3) the electrophysiologic test may be documented to have been falsely negative in greater than or equal to 20% of patients who continue to have syncope, syncope in these patients being caused by AV block or sinus node dysfunction; and 4) patients at risk of sudden death or recurrent syncope, or both, cannot be readily identified prospectively.