Clinical Experience with a New Software-Based Antitachycardia Pacemaker for Recurrent Supraventricular and Ventricular Tachycardias

The Intermedics Intertach 262-12 tachycardia reversion pulse generator was implanted in 14 patients (six male, eight female, mean age at implantation 45 +/- 16 years) with recurrent symptomatic tachycardias. Six patients had atrioventricular (AV) nodal reentrant tachycardia, three patients had orthodromic tachycardia with Wolff-Parkinson-White syndrome, two had circus movement tachycardia via a concealed bypass tract, two had ventricular tachycardia, one patient had atrial flutter. Mean duration of symptoms before implantation was 8 +/- 4 years and mean number of antiarrhythmic drug trials was 3.5 +/- 1. The primary tachycardia response made consisted of autodecremental pacing in one patient, burst pacing in two patients, and adaptive scanning of the initial delay or burst cycle length in eleven patients. The secondary tachycardia response mode consisted of autodecremental pacing in four patients, burst pacing in three patients and burst scanning in four patients. Tachycardia response was automatic in all but one patient with ventricular tachycardia. During a follow-up period of 30.5 +/- 10.6 months, one patient with ventricular tachycardia died from a nonarrhythmic cause. Reinterventions were necessary due to electrode fracture in one patient and due to pacemaker software defect in another one. Two patients underwent surgical cure of their arrhythmia: one patient with atrial flutter and one patient with AV nodal reentry tachycardia, 24 months and 11 months postpacemaker implantation, respectively. Four patients required digitalis to prevent pacing induced atrial fibrillation. Other proarrhythmic effects were not encountered. The pacemaker proved to be a versatile system with reliable tachycardia detection and termination functions. It provided a valuable adjunctive therapy in these selected patients.     

Electrical Termination of Tachyarrhythmias by Discrete Pulses

Reentrant tachycardias can often be terminated by discrete pacing stimuli that penetrate the reentrant circuit. The ability of discrete stimuli to terminate an arrhythmia depends on the timing of the stimulus, the distance from the site of reentry where the stimulus is applied, the electrophysiologic properties of the myocardium between the site of stimulation and the site of reentry, and the size of the reentrant circuit.
Modes of pacing used to terminate tachycardia have included single or multiple timed extrastimuli, overdrive pacing, burst pacing and competitive asynchronous (underdrive) pacing. Patient-triggered devices that deliver asynchronous pacing stimuli are routinely available. Newer devices have been developed that automatically sense the onset of tachycardia and respond with pacing stimuli. These devices have been highly effective in selected patients with supraventricular tachycardia. The seriousness of occasional pacing-induced acceleration of ventricular tachycardia or conversion to ventricular fibrillation has limited the application of these devices in patients with ventricular arrhythmias. Pre-implantations electrophysiologic studies are necessary to document arrhythmia mechanisms and to determine the feasibility of various pacing modalities in treating the tachycardia. The potential for complicating arrhythmias (atrial fibrillation/flutter or ventricular fibrillation) must also be tested.
Future devices designed for terminating tachycardias with discrete pulses should be capable of being programmed to respond with one or more of the various modalities available. These devices should automatically and reliably sense both tachycardia onset and termination, and should adjust their responses appropriately if initial stimulation sequences fail to terminate the arrhythmia.     

Antitachycardia Pacing: A Comparison of Burst Overdrive, Self-Searching and Adaptive Table Scanning Programs

Eight patients with the Siemens Elema "Tachylog" generator implanted for management of paroxysmal reentrant tachycardia were studied to assess the safety and efficiency of three antitachycardia programs. The programs investigated were burst overdrive, self-searching, and adaptive table scanning. There were five males and three females aged 19-62 years. Seven had Wolff-Parkinson-White syndrome, and one had dual atrioventricular nodal pathways. Four had right atrial electrodes and four had right ventricular electrodes. Patients were studied lying, standing, and exercising in all three modes, and the appropriate long-term programs were chosen. The generator remained in a program for 1 month, it was interrogated and the memory was read, and then it was reprogrammed to a different antitachycardia mode. Burst overdrive was unsuitable for long-term use in four patients, producing atrial fibrillation in one and ventricular arrhythmias in three. In this group, self-searching and adaptive table scanning were safe and equally effective (mean number of attempts/tachycardia 6.97 and 6.3, respectively). In the four patients in whom all three programs could be used, burst overdrive proved to be most efficient, the mean number of attempts/tachycardia were 2.4 (cf 9.6 and 9.0 for self-searching and adaptive table scanning). Thus, burst overdrive was only suitable for long-term use in 50% of our patients, but when safe it was more efficient than the other two programs, especially in those with narrow termination windows on exercise.     

Termination and Acceleration of Ventricular Tachycardia with Autodecremental Pacing, Burst Pacing, and Cardioversion in Patients with an Implantable Cardioverter Defibrillator

This multicenter study reports the outcome of ventricular tachycardia (VT) therapy (conversion or acceleration) and the relationship to initial tachycardia cycle length and other clinical variables using an implantable device with the capability of autodecremental or burst pacing, Cardioversion, and defibrillation. The device was implanted in 444 patients (mean age 58 ± 15 years) with 1,240 episodes of VT induced with noninvasive programming and reported in a multicenter database. Only the first sequence attempted for conversion by pacing or Cardioversion was assessed, and Cardioversion energies were 0.2–5 J. Autodecremental pacing was used to treat 700 induced episodes of VT during titration of pacing therapies (57% converted and 12% accelerated), burst pacing to treat 357 episodes (49% converted and 11% accelerated), and Cardioversion to treat 183 episodes (82% converted and 4% accelerated). Cardioversion was the most effective treatment and had the lowest acceleration rate. Shorter VT cycle lengths were more likely to accelerate with burst pacing and longer VT cycle lengths to convert with both burst and autodecremental pacing. Patients with higher ejection fractions were more likely to convert with autodecremental and burst pacing. Use of Cardioversion, higher ejection fraction, absence of unrepaired aneurysm, longer VT cycle lengths, coronary artery disease, and use of autodecremental pacing predicted conversion. Lower ejection fraction and VT cycle lengths ± 300 msec predicted tachycardia acceleration.     

Long-Term Therapy of Antitachycardia Pacing for Supraventricular Tachycardia

Long-term antitachycardia pacing therapy with the InterTach 262-12 and 262-16 was evaluated in 32 consecutive patients (mean age 50 +/- 13 years) with recurrent, drug refractory supraventricular tachycardia. AV nodal reentrant tachycardia was present in 20 patients, Wolff-Parkinson-White syndrome in ten patients, and a reentrant tachycardia due to Mahaim fibers in one patient. During follow-up of 39 +/- 17 months, 250 persistent tachycardia episodes occurred in 22 patients. By adjusting detection and termination mode, recurrent supraventricular tachycardia could be controlled in 19 of 32 patients (60%) by antitachycardia pacing alone. Concomitant antiarrhythmic drug therapy was required in ten of 32 patients (30%). During follow-up antitachycardia pacing became ineffective in three patients (10%). Thus, chronic antitachycardia pacing proved to be safe and effective in selected patients with drug refractory supraventricular tachycardia and could significantly improve quality of life by rapid termination of recurrent supraventricular tachycardia episodes.     

Permanent Overdrive Atrial Pacing in the Chronic Management of Recurrent Postoperative Atrial Reentrant Tachycardia in Patients with Complex Congenital Heart Disease

This study investigated the value of permanent atrial pacing as an adjunct to the current therapy in the chronic management of recurrent postoperative atrial reentrant tachycardia in patients with complex congenital heart disease. We studied the postpacing clinical course in 18 patients with recurrent atrial reentrant tachycardias unresponsive to conventional therapy who had an implanted atrial pacemaker. The pacemaker was programmed at a lower pacing rate 20% faster than the spontaneous mean daily rate previously determined with 24-hour Holter monitoring. Serial Holter recordings and pacemaker programming sessions were subsequently performed trying to mantain a paced atrial rhythm overdriving the spontaneous rhythm as long as possible. Twenty-four hour Holter monitoring documented a prevalent (> 80%) paced rhythm during the daily hours in all patients during the follow-up; all patients, however, required at least once a variation In programmed mode and pacing rate. Antiarrhythmic medications were discontinued after 6 months if the patient remained arrhythmia free while on pacing. Recurrences of atrial reentrant tachycardia occurred in five patients (29%) during the initial 6 months interval after the pacemaker implantation, while late recurrences occurred in only two patients (11 %). One patient died suddenly 10 months after the pacemaker implant. At the end of the follow-up, 15 patients (83%) were arrhythmia-free and only 2 of them were still on antiarrhythmic drugs. We conclude that permanent atrial overdrive pacing can be an important tool in the management of patients with atrial reentrant tachycardia following repair of congenital heart disease.     

Autodecremental Pacing—A Microprocessor Based Modality for the Termination of Paroxysmal Tachycardias

Autodecremental pacing—A microprocessor based modality for the termination of paroxysmal tachycardias. Five patients aged between 27 and 48 years were referred for investigation of recurrent paroxysmal tachycardias. EJectrophysiological studies revealed concealed ventriculoatrial accessory pathways in two patients, possible atrionodal pathways in two patients and dual intranodal pathways in one patient. During electrophysiologicol study, particular attention was paid to methods of terminating tachycardia by pacing techniques including single or double atrial and ventricular extrastimuli, atriaJ or ventricular underdrive, atriaJ overdrive pacing, and in two patients, rapid ventricular pacing. Autodecremental' atrial pacing was employed in all five patients and autodecremental ventricular pacing in two patients. This system is controlled by a microprocessor interfaced with a stimulator. When tachycardia of a cycle length less than 375 ms is sensed the system initiates pacing sequences. The initial stimulus is introduced at an interval less than the tachycardia cycle determined by a preset decremental value D. Each subsequent pacing interval is reduced by the value of D resulting in a gradual acceleration of pacing. The total duration of pacing is limited by the value of the pacing period (P). The final pacing rate is determined by P but cannot exceed 275 bpm (cycle length of 218 ms). Both P and D are operator programmable variables. Tachycardias of a cycle length less than 218 ms do not activate the pacemaker. The postpacing sensing deadtime of the system is set at 50 ms. In three patients, double atrial extrastimuli or atrial overdrive initiated atrial flutter or fibrillation. Autodecremental atrial pacing was successful in converting tachycardia to sinus rhythm in all five patients without initiation of other tachyarrhythmias. Autodecremental ventricular pacing was successful in one of the two patients in which it was used. This new modality of pacing has several theoretical advantages over conventional methods: the decremental mode may avoid stimulation in the vulnerable period and minimizes the rislt of initiating other tachyarrhythmias; gradual acceleration of pacing over a short period results in stimulation at different phases of the tachycardia cycle length; and the operator variables D and P provide a flexible system which may be adjusted to suit a particular patient and tachycardia. The development of a fully implantable programmable system is made attractive by the simplicity and adaptability of this technique.     

Termination Of Sustained Tachycardia By External Noninvasive Pacing

Invasive cardiac pacing has proved useful in the induction and termination of reentrant sustained tachycardias. In one of our two cases, programmed ventricular extra-stimulation was used to induce sustained ventricular tachycardia from the endocardial surface of the right ventricle. Induced ventricular tachycardia was terminated by burst ventricular pacing with an external cardiac pacemaker. In our second patient, external pacing was effective at inducing and terminating sustained supraventricular tachycardia. These patients illustrate that the principles of terminating sustained reentrant tachycardia with invasive pacing may also apply to noninvasive external pacing. The usefulness of this approach in treating reentrant tachycardias needs further evaluation.     

Long-Term Antitachycardia Pacing Experience for Supraventricular Tachycardia

A pacemaker was used to control drug-resistant reentrant supraventricular tachycardia (SVT) in 40 patients. An antitachycardia pacemaker was implanted in 37 for SVT; in one for ventricular tachycardia that could also be used to terminate SVT; in one SVT could be terminated with an activity rate variable pacemaker; and in one a DDD pacemaker was used for prevention and termination of SVT. Twenty patients had AV nodal reentrant tachycardias, eight had tachycardias due to a concealed accessory pathway, eight had a Wolff-Parkinson-White syndrome, three had reentrant atrial tachycardias, and one had atrial flutter. Twenty-two patients were paced from the right atrium, five from the coronary sinus, ten from the right ventricle, and three had a DDD pacemaker. During a total follow-up period of 1,503 (mean 38) months an estimated 16,240 episodes of tachycardia were terminated promptly at home, 58 required several attempts, 57 episodes lasted longer than 30 minutes but did not require medical attention, and 11 required hospital admission. Hospital admission for SVT decreased from one per patient-month (in the 3 months before implantation) to 1 per 137 patient-months after implantation. Additional reentrant tachycardias occurred in 13 patients. Antiarrhythmic drug therapy in combination with a conservative antitachycardia pacing mode was required in four patients paced from the atrium to avoid pacing induced atrial fibrillation. Antiarrhythmic drug therapy was used in 42% of patients to help control SVT. Conclusions: (1) Drug-resistant SVTs can be safely and effectively managed on the long-term with antitachycardia pacemakers. (2) Rapid termination of SVT improved the quality-of-life significantly by avoiding prolonged episodes of tachycardia and repetitive hospital admissions.     

Randomized Cross-Over Evaluation of Two Adaptive Pacing Algorithms for the Termination of Ventricular Tachycardia

Objective: In a randomized, cross-over study we evaluated the efficacy of rate adaptive constant cycle length (BURST)and autodecremental (RAMP)pacing for termination of sustained monomorphic ventricular tachycardia. Methods: An external device capable of delivering the same types ofantitachycardia pacing as the newer generation implantable cardioverter defibrillators wos used. Thirty-one patients with ischemic and nonischemic cardiomyopathy and documented clinical ventricular tachycardia or ventricularfibrillation were examined during routine invasive electrophysiological studies. RAMP and BURST pacing were each attempted in 54 matched pairs of induced ventricular tachycardia. After a therapy was applied, the tachycardia was reinitiated and the other therapy applied during the second episode so that a total of 108 ventricular tachycardia episodes were studied. Results: Overoll efficacy of ventricular tachycardia pace termination was 69% and the time required to stop ventricular tachycardia was 14.1 ± 11.3 seconds. The ability to terminate ventricular tachycardia by RAMP (72%)or BURST (65%)pacing was not significantly different. However, time to terminate ventricular tachycardia by HAMP (It.8 ± 8.5 sec)was significantly shorter than by BURST (16.4 ± 13.5), P < 0.001. Acceleration of ventricular tachycardia was uncommon with both pacing modes, 7/108 (7%). The ability to pace terminate ventricular tachycardia was cycle length dependant. The highest success was with ventricular tachycardia cycle length between 300 and 350 msec. The success rate decreased with faster and also slower ventricular tachycardia. Conclusions: 1. Rate adaptive pacing methods for ventricular tachycardia termination are effective and safe. 2. Autodecremental fiAMP pacing afford quicker ventricular tachycardia termination than constant cycle length BURST pacing. 3. The ability to terminate ventricalar tachycardia is cycle length dependent with cycle length range of 300–350 msec being most responsive to pace termination     

''Long-Term Results of Antitachycardia Pacing in Patients with Supraventricular Tachycardia

Between 1979 and 1984 the Cybertach-60, (Intermedics, Inc. Model 262-01), a programmable, automatic antitachycardia pacemaker was implanted in 11 patients who had drug-refractory supraventricular tachycardia (SVT). The patients have been followed for a total of 64-108 (mean 84 months). All patients were symptomatic and had failed two or more drugs and six patients had required prior DC cardioversion. The mechanism of supraventricular tachycardia was atrioventricular (AV) nodal reentry in six patients, AV reentry in four patients, and atrial tachycardia in one patient. Preoperatively all patients had reliable termination of the tachycardia without induction of atrial fibrillation by pacing methods available to Cybertach-60. Postimplant, Cybertach-60 reliably terminated all episodes of tachycardia without ancillary drug therapy. Nevertheless, at long-term follow-up antitachycardia pacing was effective and safe in the minority (36%), with only four patients out of eleven still using a pacemaker for supraventricular tachycardia. One of these four patients required additional drug therapy. In one of the patients, the Cybertach-60 was replaced after 78 months by a more advanced device, (Intertach, Intermedics, Inc.) because of a depleted Cybertach-60 battery. In seven patients who no longer use antitachycardia pacing for termination of tachycardia, one patient developed atrial fibrillation during tachycardia termination (at 58 months postimplant). Three patients experienced induction of tachycardia or atrial fibrillation by the pacemaker due to undersensing of sinus P waves (at 36, 48, and 51 months).(ABSTRACT TRUNCATED AT 250 WORDS)     

Treatment of Ventricular and Supraventricular Tachyarrhythmias by Transcutaneous Cardiac Pacing

The efficacy of noninvasive transcutaneous cardiac pacing (TCP) in the treatment of tachyarrhythmic events was tested in 24 patient: 14 with ventricular tachycardia, seven with supraventricular tachycardia and three with atrial flutter. Six (42.9%) ventricular tachycardias were interrupted: in two of the ten patients on whom underdrive pacing was attempted and in all four cases in which overdrive stimulation was possible. Five of the six supraventricular tachycardias utilizing an atrioventricular bypass tract were interrupted, while the TCP was unsuccessful on the only patient with atrioventricular nodal reentrant tachycardia. TCP failed to interrupt the arrhythmia in the three cases of atrial flutter. No clinically significant untoward effects (in particular tachycardia acceleration or ventricular fibrillation) were observed, except for a tolerable thumping sensation on the chest during pacing. In four patients, TCP effects on cardiac activation was evaluated by endocavitary recording: while the mean ventricular threshold was 70 mA, atrial capture was possible on only two patients at a current intensity of 140 and 150 mA. We consider our preliminary experience with TCP in the treatment of tachycardias encouraging. The technique was easily and rapidly usable and it was immediately successful in the majority of atrioventricular reentrant tachycardias and in a relevant percentage of ventricular tachycardias. In this latter setting TCP was mostly effective in the slower tachycardias where overdrive pacing was possible. A further experience with devices provided by higher pacing rates is warranted.     

Clinical Experience with the Intertach 262-12 Pulse Generator in Patients with Recurrent Supraventricular and Ventricular Tachycardia

FROMER, M., ET AL.: Clinical Experience with the Intertach 262-12 Pulse Generator in Patients with Recurrent Supraventricular and Ventricular Tachycardia. An antitachycardia pulse generator, the Intermedics Intertach 262-12 was implanted in 16 patients (14 patients with supraventricular tachycardia of various origins and two patients with recurrent ventricular tachycardia), who were not responsive to various antiarrhythmic drug regimens. The follow-up was from 6–49 months (mean 30.9 ± 13.8). Five patients had a follow-up of over 3 years. The device was used in all patients. One patient with ventricular tachycardia died from a nonarrhythmic cause. Loss of responsiveness to burst pacing was observed in 1/14 patients with supraventricular tachycardia and nontolerance of antitachycardia pacing in one patient. Overall clinical success of pacing was observed in 13/16 patients = 81%. The pacemaker proved to be a versatile system with reliable tachycardia detection and termination functions.     

Observations on Induction and Termination of Paroxysmal Supraventricular Tachycardia by External Pacing

Paroxysmal Supraventricular tachycardia (PSVT) can be reproducibly induced and terminated by critically timed atrial or ventricular depolarizations. In this study, noninvasive trans-cutaneous (external) cardiac pacing (NTCPJ was compared to endocardial ventricular pacing for the termination and induction of PSVT. In 24 patients, either atrioventricular (AV) nodal reentrant tachycardia or AV reciprocating tachycardia was reproducibly terminated with either critically timed ventricular depolarizations or overdrive ventricular pacing from an endocardial right ventricular site. There were 32 trials of NTCP attempts to interrupt PSVT in the 24 patients. External pacing was successful at terminating PSVT in 23 patients and in 30 of 32 (94%) trials. In 20 patients, there were 26 trials of external pacing attempts to induce PSVT. External pacing initiated PSVT in 21 of 26 trials (81%). The pacing sequences used to induce and terminate PSVT with external pacing were copied from the endocardial sequences. The external pacing threshold averaged 77 ± 22 mA but the current needed to terminate PSVT was about 1.5 greater than threshold at 117 ± 27 mA. Serial external pacing studies were performed in seven patients. The thresholds for external pacing were similar from trial to trial as were the mode of termination and induction between the endocardial and external methods. External pacing can terminate most AV reciprocating tachycardias and many AV nodal reentrant tachycardias. It appears promising as a means of inducing PSVT. However, the high stimulation amplitudes needed will prohibit wide acceptance of external pacing for induction and termination of PSVT.     

室上性心动过速161例食管心房调搏资料分析

对161例SVT食管心房调搏资料的分析表明:1.预激综合征(包括隐匿性)是SVT最常见的原因,本组占50%(81/161);其次是房室结双径路,占43%(70/161)。2.食管心房调搏诱发SVT 112例(诱发率70%),其电生理机制以AVRT为第一位,占54%;AVNRT为第二位,占38%,证实国人SVT电生理机制情况与国外相比有不同的特点。3.用食管心房调搏可对SVT进行电生理分型,并作出无创性鉴别诊断。     

Comparison of Fixed Burst Versus Decremental Burst Pacing for Termination of Ventricular Tachycardia

The objective of this study was to compare prospectively the efficacy of fixed burst pacing with that of decremental hurst pacing in terminating VT. Forty-four patients with inducible sustained monomorphic VT were studied. The efficacy of fixed burst and decremental burst pacing in terminating 57 distinct types of VT were compared during 50 eiectrophysiology tests fmean VT cycle length = 334 ± 84 msec. Termination of each type of VT was attempted with fixed burst and decremental burst pacing, Both pacing algorithms were delivered in an adaptive fashion with an increasing number of stimuli with each successive attempt at VT termination. Seventy percent of VT episodes were successfully terminated with fixed burst pacing, The mean number of stimuli required for VT termination was 5 ± 2. Seventy-two percent of VT episodes were successfully terminated with decremental burst pacing. The mean number of stimuJi required for VT termination ivas 5 ± 2. For fixed burst and decremental burst pacing, the efficacy of VT termination was greater for VTs with a cycle length > 300 msec than for faster VTs (P < 0.05). The efficacy of VT termination and the incidence of VT acceleration were no different for the two pacing algorithms (P > 0.1). The results of this study demonstrate that fixed burst and decrementai burst pacing are equally effective in terminating VT and that a single adaptive pacing algorithm is effective in terminating nearly three fourths of VTs.     

Termination of Tachycardias by Transesophageal Electrical Pacing

To evaluate the therapeutic significance of noninvasive transesophageal pacing for termination of tachycardias the method of rapid atrial or ventricular transesophageal pacing was used in 233 patients with different tachycardiac arrhythmias. We were able to terminate atrial flutter in 136 of 162 patients by transesophageal rapid atrial stimulation (conversion to sinus rhythm in 75 cases, induction of atrial fibrillation in 61 cases). Atrial tachycardias were interrupted in 17 of 23 patients (sinus rhythm in 11 cases, atrial fibrillation in six cases). AV reciprocating/AV nodal supravenrricular reentry tachycardias were terminated in 62 of 63 patients (sinus rhythm in 58 cases, atrial fibrillation in four cases). By transesophageal rapid ventricular pacing ventricular tachycardias could be terminated in ten of 15 patients. The success rate of transesophageal pacing was influenced by the pacing rate, by the type of tachycardiac arrhythmia inclusive by the type of atrial flutter and by the tachycardia's cycle length. Because the success rates are comparable with invasive technique and the procedure is simpler, the noninvasive transesophageal antitachycardiac pacing should be respected as the method of the first choice in patients with supraven-tricular tachycardias.     

Benefits and Potential Risks of Atrial Antitachycardia Pacing After Repair of Congenital Heart Disease

Atrial reentry tachycardia is common after surgical repair of congenital heart disease. The arrhythmia is often difficult to treat and is occasionally life-threatening. This study reports experience with atrial antitachycardia (AAIT mode) pacing for the management of atrial reentry tachycardia, with emphasis on the risks and benefits of automatic pacing therapy. Eighteen patients (2–32 years of age) with a variety of congenital heart lesions underwent atrial antitachycardia pacemaker placement for recurrent atrial tachycardia that was amenable to pace termination prior to the implantation procedure. An appropriate antitachycardia program was determined by repeated induction and termination of atrial tachycardia using the noninvasive programmed stimulation mode of the pacemaker. Over 4–30 months of follow-up, 6 patients had 189 episodes of tachycardia successfully converted with AAI-T pacing, 4 patients had 8 episodes of tachycardia detected hut not successfully converted, and 8 patients had no episodes of tachycardia with antibradycardia pacing alone. The number of patients receiving pharmacological therapy other than digoxin or beta blockade fell from 12 to 6, Two subjects died suddenly, 1 while wearing a Holter monitor. In both, tachycardia was detected and pace cardioversion attempted. Conclusions: Atrial antitachyardia pacing is a useful tool in the management of patients with congenital heart disease and atrial arrhythmias; however, in selected cases, it may not prevent and may even exacerbate the lethal complications of the tachycardia. Antitachycardia function evaluation is recommended under varying levels of autonomic stress prior to institution of automatic therapy.     

Relation between Spontaneous Atrial Fibrillation and Atrial Vulnerability in Patients with Wolff-Parkinson-White Pattern

An intracavitary electrophysiological study was carried out on 103 patients with Wolff-Parkinson-White (WPW), 23 symptomatic patients had documented episodes of atrial fibrillation, 54 symptomatic patients had atrioventricular reentrant tachycardias, and 26 asymptomatic. Patients were examined for the relation between spontaneous atrial fibrillation and atrial vulnerability, defined as the possibility to induce sustained (greater than 1 minute) episodes of atrial fibrillation with a stimulation protocol excluding atrial bursts. Atrail fibrillation induction was attempted by single and double atrial extrastimuli during pacing at two different cycle lengths and incremental atrial pacing. Sustained atrail fibrillation was induced in 65% of the patients with spontaneous atrial fibrillation, and in 13% of the symptomatic patients with documented episodes of atrioventricular reentrant tachycardias and in 15% of the asymptomatic patients (P less than 0.0005). Atrial vulnerability was higher in patients with spontaneous atrial fibrillation than in patients without this arrhythmia. No significant difference was observed between symptomatic without atrial fibrillation and asymptomatic patients.