Antitachycardia Device Research Articles

207 Incidence and clinical significance of the asssociation of paroxysmal supraventricular and ventricular tachycardia

Fine-QRS complex tachycardia alternating with wide-QRS complex tachycardia can lead to an erroneous diagnosis of paroxysmal supraventricular tachycardia (SVT) with or without aberrancy. The purpose of the study was to evaluate the incidence and the significance of the association of SVT and ventricular tachycardia (VT) in the same patient. 898 patients aged from 11 to 88 years were consecutively admitted for a sustained VT; 818 patients had associated heart disease (history of myocardial infarction 374, idiopathic dilated cardiomyopathy 69, arrhythmogenic right ventricular dysplasia 86, miscellaneous 289) and 80 had no apparent heart disease. Electrophysiological study including programmed atrial and ventricular stimulation, 2D cardiac echocardiography, coronary angiography in patients older than 40 years, right ventricular angiography and cardiac RMI since 2002, were performed in these patients. Fifteen patients presented (2%) with either SVT or VT. All SVT's were related to an atrioventricular node reentrant tachycardia (AVNRT). The association of SVT and VT was significantly more frequent in patients without heart disease and with verapamil-sensitive VT (n=6/80, 7.5%)(<0.001), arrhythmogenic heart disease (n=4/86, 5%)(0.05) than in those with myocardial infarction (n=4/374, 0.1%) or dilated cardiomyopathy (n=0). Among 692 patients with AVNRT, 39 had associated heart disease and only 5 have both tachycardias. Radiofrequency ablation of AVNRT performed in all patients did not change the recurrence of VT which required ablation in 3 patients and the implantation of antitachycardia device with defibrillator in 2 patients. The association of SVT and VT is rare in patients with heart disease except in those with arrhythmogenic right ventricular dysplasia. The association is more frequent in patients without heart disease diagnosis and could be underestimated; fine QRS complex tachycardia alternating with wide QRS complex tachycardia leads generally to the erroneous diagnosis of SVT with or without aberrancy.

Multiarm spirals in a two-dimensional cardiac substrate.

A variety of chemical and biological nonlinear excitable media, including heart tissue, can support stable, self-organized waves of activity in a form of rotating single-arm spirals. In particular, heart tissue can support stationary and meandering spirals of electrical excitation, which have been shown to underlie different forms of cardiac arrhythmias. In contrast to single-arm spirals, stable multiarm spirals (multiple spiral waves that rotate in the same direction around a common organizing center) have not been demonstrated and studied yet in living excitable tissues. Here, we show that persistent multiarm spirals of electrical activity can be induced in monolayer cultures of neonatal rat heart cells by a short, rapid train of electrical point stimuli applied during single-arm-spiral activity. Stable formation is accomplished only in monolayers that show a relatively broad and steep dependence of impulse wavelength and propagation velocity on rate of excitation. The resulting multiarm spirals emit waves of electrical activity at rates faster than for single-arm spirals and exhibit two distinct behaviors, namely "arm-switching" and "tip-switching." The phenomenon of rate acceleration due to an increase in the number of spiral arms possibly may underlie the acceleration of functional reentrant tachycardias paced by a clinician or an antitachycardia device.

Long-Term outcomes of cardiac pacing in adults with congenital heart disease

ObjectivesThe purpose of this retrospective study was to define long-term outcomes after pacemaker therapy in adults with congenital heart disease (CHD). BackgroundAdults with CHD represent a unique and expanding population. Many will require pacemaker or implantable defibrillator therapy, with a lifelong need for re-intervention and follow-up. They pose technical and management challenges not encountered in other groups receiving pacing, and the complication and re-intervention rates specific to this population are not well-defined. MethodsWe reviewed outcomes of 168 adults with CHD, 89 females, mean age 40 years, in whom a pacemaker or anti-tachycardia device was implanted. ResultsMean age at implant was 28 years with mean pacing duration 11 years at follow-up (range, 0.5 to 38.0). Seventy-two (42%) received initial dual-chamber devices and remained in this mode, while 23 (14%) went from ventricular to dual-chamber pacing in follow-up. Initial mode of pacing did not have a significant effect on subsequent atrial arrhythmia. Patients receiving an initial epicardial system were younger than those paced endocardially (17 ± 12 years vs. 35 ± 16 years, p < 0.001) and more likely to undergo re-intervention (p = 0.019). Difficulty with vascular access was encountered in 25 patients (15%), while 45 (27%) experienced lead-related complications. No significant predictors of lead complications were identified. ConclusionsLead complications were not significantly different for epicardial versus endocardial, nor physiologic versus ventricular pacing, but a trend toward improved lead survival in patients receiving endocardial leads at first implant was observed. Adults with CHD remain at risk for atrial arrhythmias regardless of pacing mode.

Predictors of Device Activation for Ventricular Arrhythmias and Survival in Patients with Implantable Pacemakers/Defibrillators

Predictors of survival and arrhythmia recurrence for patients with implanted defibrillators have been reported but patients with sustained, well-tolerated ventricular tachycardia were often excluded from these trials. Arrhythmia recurrence and survival in populations including these patients have been less well studied. The purpose of the present study was to examine predictors of spontaneous ventricular arrhythmias and mortality in patients who received a tiered therapy antitachycardia pacemaker/defibrillator for ventricular tachycardia, fibrillation, or both. Three hundred thirty-seven patients who received a Ventritex CADENCE tiered therapy antitachycardia device at one of 19 participating centers between July 11, 1989 and March 4, 1991 are included in this retrospective analysis. Diagnostic summary data and stored electrograms telemetered from the implanted device were assessed to determine characteristics of recurrent arrhythmias. Mean follow-up was 360 +/- 10 (SEM) days. Thirty-three patients died during follow-up. At least one recurrent ventricular arrhythmia was observed in 205 patients (61%). A total of 7,539 episodes were observed with a mean of 37 +/- 5 per patient. Patients with recurrent ventricular arrhythmias were slightly but significantly older (64 +/- 0.7 vs 59 +/- 1.2 years; P < 0.001) but were not distinguished by gender or underlying structural disease. Patients whose presenting arrhythmia was monomorphic ventricular tachycardia were more likely to experience recurrent ventricular arrhythmias (69% recurrence rate) than patients presenting with ventricular fibrillation or polymorphic ventricular tachycardia (46% recurrence rate; P < 0.001). Cycle length of spontaneous tachycardia was also a predictor of arrhythmia recurrence. Patients having slower ventricular arrhythmias were less likely to remain recurrence free. Mean left ventricular ejection fraction was similar for patients with and without recurrences. Younger age and absence of arrhythmia recurrence but not presenting arrhythmia were predictors of survival. We conclude that age and presentation with monomorphic ventricular tachycardia are important predictors of arrhythmia recurrence for this patient population. Exclusion of patients with monomorphic ventricular tachycardia underestimates the rate of recurrent ventricular arrhythmias and utilization of device therapy.

Prolonged monitoring for detection of symptomatic arrhythmias after slow pathway ablation in AV-nodal tachycardia

To study the incidence of symptoms and recurrences of AV-nodal re-entrant tachycardia (AVNT) after treatment with radio-frequency ablation of the slow pathway, event recording with transtelephonic transmission was performed for at least 3 weeks in 19 patients out of a series of 25. Follow-up with an implanted antitachycardia device was possible in two other patients, making the total number under continued surveillance 21 25 . The period of monitoring was prolonged as complaints remained or became present after 1 month in eight patients. During a mean follow-up of 10 months, late recurrence of AVNT was observed in this way in 4 25 patients; they were submitted to a second procedure. Symptoms were present in many others and were explained by the recordings. Sinus tachycardia was recorded in three patients, intermittent AV-block of the first degree in another, and frequent atrial or ventricular premature beats in six patients. These minor arrhythmias tended to decrease over time. A coexistent atrial tachycardia was redetected in two patients. Thus, event recording is useful to distinguish recurrence of AVNT, sinus tachycardia, other types of supraventricular tachycardia, and atrial or ventricular premature beats, which all may be a reason of complaints during the first weeks after ablation. It provided a feeling of safety for symptomatic patients who often suffered from anxiety before the ablation.

Automated analysis of spontaneously occurring arrhythmias by implantable devices: Limitations of using rate and timing features alone

Real-time automated systems for arrhythmia analysis by implantable antitachycardia devices have been designed to incorporate two-channel rate criteria with intracavitary atrial and ventricular electrogram morphology. Because the power requirements for morphologic analysis substantially limit antitachycardia device longevity, the authors sought to develop an alternative algorithm that relies solely on rate and three newly developed timing features: onset (median ventricular rate filtering to detect abrupt onset), loss of atrioventricular (AV) sequency (premature ventricular depolarizations), and regularity-multiplicity (minimal median cycle length variation concurrent with integral [n:1] AV periodicity). This system was assessed using spontaneously occurring arrhythmias in patients undergoing electrophysiology studies. Electrograms were captured on FM tape (1–500 Hz) using bipolar catheters in the high right atrium and the left ventricular apex. In 11 patients, 25 distinct arrhythmias were analyzed, which included sinus tachycardia (ST) (1 passage), supraventricular tachycardia (SVT) (6 passages), ventricular tachycardia (VT) with concurrent sinus rhythm (16 passages), VT with concurrent atrial flutter (VT/AFl) (2 passages), and ventricular fibrillation (VF) (1 passage). The algorithm correctly diagnosed 1 of 1 episode of ST, 4 of 6 episodes of SVT, 15 of 16 episodes of VT with concurrent sinus rhythm, 0 of 2 episodes of VT/AFl, and 1 of 1 episode of VF. Ventricular tachycardia episodes were misdiagnosed as SVT because of absence of loss of AV sequency in VT onset (1 episode), presence of multiplicity between VT and AFl (1 episode), and absence of VT regularity during AFl (1 episode). Algorithms that are confined to rate and timing features alone are capable of correctly diagnosing most spontaneously occurring tachyarrhythmias. Misdiagnosis of VT may occur, however, despite the integration of multiple timing features.

Use of telemetry functions in the assessment of implanted antitachycardia device efficacy

Twenty patients (aged 50 ± 21 years and mean left ventricular ejection fraction 37 ± 17%) with recurrent ventricular arrhythmias were treated with an investigational, implantable combined antitachycardia-pacing cardioverter defibrillator. The device's telemetry capabilities include both stored (1-second snapshots) and real-time display of endocardial and device-circuit signals. The device can store these before, during and after up to 50 tachycardia and antitachycardia pacing episodes. All stored events are indexed to a 24-hour internal clock. During 10.1 ±5.1 months of follow-up, the device was used in 11 of 20 patients. In the entire group, antitachycardia pacing was activated on 44 ± 14 occasions per patient (total 874) and shock delivery occurred on 8 ± 14 occasions per patient (total 156). Reconstruction by stored telemetry of all device-therapy episodes was possible. Twenty-six percent of all shocks delivered were not appropriate and were due to atrial arrhythmias in 2 patients and dysfunction of the sensing lead in 3. The absence of a relation between symptoms and appropriate shock delivery was documented in 1 patient. Antitachycardia pace acceleration occurred in 5.3% of cases; 7% of attempts at pacing were unsuccessful and needed shock therapy. It is concluded that the enhanced telemetry available in newer antitachycardia devices enables more accurate assessment of device use and enhances diagnosis of inappropriate therapy delivery.

Sustained ventricular tachycardia associated with sarcoidosis: Assessment of the underlying cardiac anatomy and the prospective utility of programmed ventricular stimulation, drug therapy and an implantable antitachycardia device

The presentation, cardiac anatomy and utility of programmed ventricular stimulation in seven patients with sustained ventricular tachycardia associated with sarcoidosis are described. The mean patient age was 38 ± 8 years. Pulmonary involvement was apparent in three patients and no systemic manifestations of sarcoidosis were present in one patient. All patients had electrocardiographic abnormalities at rest and six had a left ventricular ejection fraction <45%. All seven patients had left ventricular wall motion abnormalities and five had mitral valve dysfunction.Sustained ventricular tachycardia was easily induced in all patients. Spontaneous sustained ventricular tachycardia was not prevented with corticosteroid administration. Despite antiarrhythmic drug therapy, two patients had sudden cardiac death and an additional four had recurrence of ventricular tachycardia. Four patients had an automatic cardioverter-defibrillator implanted and received drug therapy: all four received appropriate shocks.This report represents the largest descriptive series of consecutive patients with sustained ventricular tachycardia associated with sarcoidosis. Antiarrhythmic drug therapy of ventricular tachycardia in patients with sarcoidosis, even when guided with programmed ventricular stimulation, is associated with a high rate of arrhythmia recurrence or sudden death, or both. Thus, implantation of an automatic antitachycardia device (cardioverter-defibrillator) should be considered as primary therapy in such patients. Furthermore, sarcoidosis should be excluded, with Kveim skin testing if necessary, in any patient with sustained ventricular tachycardia of unknown origin.

Mixed venous oxygen saturation for differentiating stable from unstable tachycardias

Current antitachycardia systems are incapable of adequately distinguishing stable from unstable tachycardias. Previously, integration of a pressure sensor or an impedance sensor, together with electrogram analysis, has been investigated as an improved method of identifying unstable arrhythmias. A mixed venous oxygen saturation sensor was investigated for differentiating stable from unstable paced and induced tachycardias in 10 patients. During rapid pacing at 600, 500, 400, 350, 300, and 250 msec cycle lengths, mixed venous oxygen saturation decreased as cycle length decreased. For any given cycle length, rapid ventricular pacing tended to result in greater mixed venous oxygen desaturation compared with atrial pacing. Mixed venous oxygen saturation decreased similarly during induced ventricular tachycardias at cycle lengths > 230 msec. However, ventricular tachycardias at cycle lengths ≤230 msec and ventricular fibrittation had no effect on mixed venous oxygen saturation until after termination. Subsequently, a mixed venous oxygen saturation-tiered therapy algorithm (cycle length ≤230 msec = unstable; cycle length >230 msec and MVO 2 ≥6% over 30 seconds = unstable) was developed and was tested retrospectively in 113 paced and induced tachyarrhythmias in these 10 patients for detecting unstable tachycardias (defined as a decrease from baseline systolic arterial pressure of ≥50 mm Hg at 15 seconds). The mixed venous oxygen algorithm had 93% sensitivity and 96% specificity compared with rate-only (rate ≥170 beats/min) detection with 93% sensitivity and 71% specificity. Therefore a tiered therapy antitachycardia device could integrate zoned rate detection with mixed venous oxygen saturation to improve detection specificity of current antitachycardia systems.

Identification of Ventricular Tachycardia Using Intracardiac Electrograms: A Comparison of Unipolar Versus Bipolar Waveform Analysis

Implantable antitachycardia devices suffer a high false-positive rate of delivery of therapy because current detection schemes based upon ventricular rate and rate variations are excessively sensitive at the cost of specificity. Several methods have been proposed for providing complementary information derived from morphologic analysis of intraventricular electrograms in order to increase specificity. The majority of these techniques have utilized bipolar electrogram analysis to detect changes in ventricular activation indicative of ventricular tachycardia. Whether bipolar or unipolar intracardiac electrogram analysis might be preferred for discriminating ventricular tachycardia from sinus rhythm has not been determined. In this study, a previously demonstrated method for identification of ventricular tachycardia using intracardiac electrograms, correlation waveform analysis, was used to analyze both unipolar and bipolar signals during sinus rhythm and ventricular tachycardia recorded during electrophysiology studies of 15 patients with inducible sustained monomorphic ventricular tachycardia. Correlation waveform analysis consistently discriminated between all depolarizations during ventricular tachycardia in 14/15 patients (93%) using either electrogram configuration; 13 of the 14 patients were common to both groups. Of these patients, 8/15 (53%) had greater separation between sinus rhythm and ventricular waveforms with bipolar electrogram analysis while 7/15 (47%) had greater separation with unipolar electrogram analysis. We conclude that morphologic analysis of unipolar and bipolar electrograms may be equally effective in distinguishing ventricular tachycardia from sinus rhythm. For individual patients, either a unipolar or bipolar ventricular configuration may be preferable, and should be chosen on a patient-specific basis during electrophysiology study prior to antitachycardia device implantation.

Current status of antitachycardia devices.

With the limitations of currently available modalities for treating clinically important tachycardias, the role of implanted antitachycardia devices will continue to expand. The challenge of the future will not only involve continued technological advances but the socioeconomic impact of this efficacious but expensive mode of therapy in an era of increasing financial restraints. Further studies to definitively prove the efficacy of more widespread use of antitachycardia device therapy will be needed.

Atrial Pacing: Who do We Pace and What do We Expect? Experiences with 100 Atrial Pacemakers

The records of 100 patients with permanent atrial pacemakers implanted over a 7-year period were reviewed to assess the role and results of this mode of pacing. Indications for pacing were sick sinus syndrome in 91, carotid sinus hypersensitivity in 3, and use of an antitachycardia device in 6 patients. The mean follow-up period was 32.9 months. Symptomatic relief was good. Lead dislodgment occurred in 11 patients (usually in the first week). Threshold rises not amenable to reprogramming occurred in three patients and loss of sensing occurred in seven patients but only one required intervention. Overall, 21 patients required reoperation. The type of lead did not influence the need for reoperation that appeared to be related to the experience of the operator. Complete atrioventricular block occurred in three patients, two of whom had carotid sinus hypersensitivity and one had sick sinus syndrome. Chronic atrial fibrillation occurred in five patients, none of whom required revision of the pacemaker system. Atrial pacing is a satisfactory pacing mode in patients with sick sinus syndrome. Provided satisfactory atrioventricular conduction has been shown by incremental atrial pacing to at least 120 beats/min and carotid hypersensitivity is absent, progression to complete atrioventricular block is uncommon. Greater implanting skills are required for good results.

Problems of Sensing Tachyarrhythmias by an Antitachycardia Pacemaker (Symbios 7008)

Atrial burst pacing is an effective method of terminating supraventricular tachycardia. In the patient presented in this report, a Symbios 7008 pacemaker (Medtronic Inc., Minneapolis, MN, USA) was implanted for two reasons: (1) severe AV conduction defect (AH, 230 msec; HV, 150 msec) and bifascicular block following anterior myocardial infarction; and (2) paroxysmal atrial flutter. The conduction defect ruled out programming other than atrial burst in DDD mode. Activation of burst pacing required appropriate programming of the "tachycardia detection window" on the basis of the cycle length of the flutter waves. In the case reviewed, episodes of atrial flutter with variable cycle lengths of 230 to 280 msec necessitated reprogramming of the AV interval, the refractory period, and the upper rate interval. The use of an antitachycardia device in automatic mode may be limited by variations in tachycardia cycle length.

Identification of Ventricular Tachycardia Using Intracavitary Ventricular Electrograms: Analysis of Time and Frequency Domain Patterns

Tachycardia detection by implantable antitachycardia devices using rate alone has major limitations. Several alternative methods have been proposed to distinguish ventricular tachycardia or ventricular fibrillation from normal sinus rhythm using intracardiac electrograms. These methods have not been tested, however, for recognition of ventricular tachycardia in patients with abnormal surface QRS conduction during sinus rhythm or with antiarrhythmic drug therapy. In this study, three techniques for the identification of ventricular tachycardia from intracavitary bipolar ventricular electrograms were examined and compared: correlation waveform analysis, amplitude distribution analysis, and spectral analysis using Fast Fourier transformation. Thirty episodes of induced monomorphic ventricular tachycardia were analyzed and compared sinus rhythm in four groups of patients with: I. Normal surface QRS conduction during sinus rhythm without antiarrhythmic drug therapy (five episodes); II. Intraventricular conduction delay or bundle branch block during sinus rhythm without antiarrhythmic drug therapy (nine episodes); III. Normal surface QRS conduction during sinus rhythm with antiarrhythmic therapy (six episodes); and IV. Intraventricular conduction delay or bundle branch block during sinus rhythm with antiarrhythmic drug therapy (ten episodes). Correlation waveform analysis had 100% sensitivity and specificity in distinguishing ventricular tachycardia from sinus rhythm, even in the presence of an intraventricular conduction delay, bundle branch block, and antiarrhythmic drug therapy. In contrast, amplitude distribution analysis differentiated 15/30 episodes (50.0%) of ventricular tachycardia from sinus rhythm, and a maximum of 18/30 episodes (60.0%) of ventricular tachycardia were identified by special analysis using Fast Fourier transformation. Correlation waveform analysis appears to be a reliable technique to discriminate ventricular tachycardia from sinus rhythm using intracavitary ventricular electrograms. Its computational demands are modest, making it suitable for consideration in an implantable antitachycardia device.

Fatal and nonfatal cardiac arrest in patients with an implanted antitachycardia device for the treatment of supraventricular tachycardia

P aroxysmal supraventricular tachycardia (SVT) is a frequent and disabling condition, sometimes unresponsive to medical therapy.l Tachycardia termination pacing is a useful alternative treatment in patients with SVT. The use of antitachycardia pacing has been shown to have acceptable long-term efficacy.2 However, in patients with ventricular tachycardia it is known to carry a risk of tachycardia acceleration3 or induction of ventricular fibrillation.4 Therefore, for the treatment of ventricular tachycardia it is recommended that such pacemakers be physician activated (a manual nonautomatic mode] or used in association with an automatic implantable defibrillator.5 The potential danger of tachycardia termination pacing for SVT is less well defined. We report 4 cases of fatal and 1 case of nonfatal cardiac arrest in patients fitted with an antitachycardia pacemaker, the Programmable Automatic Scanning Arrhythmia Reversion (PASAR) pacemaker (model 4151). The data were collected in the form of questionnaires filled out by implanting physicians and returned to the pacemaker manufacturer (Telectronics). On a worldwide basis, a total of 122 patients (139 devices] had been implanted for the control of SVT. The follow-up period was 4 to 65 months [mean 34). Most patients (55%] had accessory pathways and 36% had atrioventricular nodal reentrant tachycardia. Sixtyone percent of the patients were paced from the right ventricular apex. Four cases of sudden unexplained cardiac deaths and I case of near sudden death were identified. The PASAR model 4151 was a prototype, implantable, bipolar pulse generator that was designed to sense the occurrence of a tachycardia by programmable high rate criteria. After 4 consecutive tachycardia beats, I or 2 timed premature stimuli were deiivered in an attempt to revert the tachycardia to sinus rhythm. How this device functions in tachycardia termination is shown in Figure 2. Jf tachycardia termination failed, the initial coupling interval between the

An approach to therapy for paroxysmal supraventricular tachycardia

A variety of options are available for managing recurrent paroxysmal supraventricular tachycardia. These options include empirical drug therapy on a trial and error basis, drug therapy based on the results of electrophysiologic testing and nonpharmacologic treatment including operative therapy, catheter ablation and antitachycardia devices. Empirical drug therapy is appropriate when the tachycardia is relatively well tolerated and the patient has access to a medical facility. Therapy guided by electrophysiologic testing is more appropriate for patients with severe symptoms during tachycardia, patients with a potential for more serious arrhythmias such as atrial fibrillation in the Wolff-Parkinson-White syndrome and in patients who have failed to respond to empirical trials of drug therapy. Electrophysiologic testing usually provides information about the precise mechanism responsible for the tachycardia and allows verification of drug efficacy. It is a strict prerequisite for operative, ablative or antitachycardia device therapy. The choice of therapy depends a great deal on local expertise, patient preference and individual considerations. Operative therapy is very successful in patients with supraventricular tachycardia associated with the Wolff-Parkinson-White syndrome and should be given high priority as an option in younger patients facing a lifelong commitment to antiarrhythmic drugs.

A Special Outpatient Clinic for Following Patients with Implanted Tachyarrhythmia Devices

Implantable anti-tachycardia devices have become an additional therapeutic option for those patients afflicted with life-threatening tachyarrhythmias. Follow-up of these complex devices are time-consuming and, if mismanaged, may be dangerous to the patient. For these reasons, a special anti-tachycardia device clinic was started at Newark Beth Israel Medical Center in July 1984. From the inception of the clinic to September 1985, 24 patients were followed. Seventy-five percent had antitachycardia devices (ATDs) implanted for treatment of ventricular tachyarrhythmias (VT/VF) with the remaining 25% for supraventricular tachycardias. All patients were seen every 3 months or more often if clinically required. Of 112 clinic examinations, 102 (91%) were scheduled appointments (group I) while the remaining 10 visits (group II) were unscheduled and preceded by symptomatic episodes. The problems detected in clinic (groups I and II) ranged from sudden failure of an AICD to apprehension. Appropriate nonoperative treatment was given during clinic evaluation for 60% of the problems detected in group II, while the remaining 40% required eventual surgical intervention. Compliance throughout the 15-month follow-up period was 100%. Major benefits of the clinic cited by patients and their families were continuity of care, the time allotted to meet the individual needs, and management of most problems on an out-patient basis.

Differentiation of Sinus Tachycardia from Paroxysmal 1:1 Tachycardias Using Single Late Diastolic Atrial Extrastimuli

Existing antitachycardia devices do not discriminate perfectly between sinus tachycardia and paroxysmal tachycardias with 1:1 atrioventricular relationship (paroxysmal 1:1 tachycardias). The present study tested the hypothesis that the nature of the ventricular response to atrial extrastimulation might distinguish between sinus tachycardia and selected paroxysmal 1:1 tachycardias. In 15 patients, atrial extrastimuli were delivered during sinus tachycardia and in 13 patients during various types of paroxysmal 1:1 tachycardia, and the timing of the next ventricular beat was measured. During sinus tachycardia, in 14 of 15 patients, atrial extrastimuli which were, in turn, early by 80 and 100 ms made the next ventricular beat premature by at least 30 and 50 ms, respectively. In all 13 patients, during paroxysmal 1:1 tachycardia, atrial extrastimuli that were early by 80 and 100 ms failed to make the next ventricular beat premature by more than 10 ms. Single atrial extrastimuli that were premature by less than or equal to 100 ms did not provoke faster tachycardias in any of the patients. In this study, a technique that used single late extrastimuli during tachycardia safely distinguished sinus tachycardia from paroxysmal tachycardias. This technique might be suitable for incorporation into an antitachycardia device. Further investigation of this technique is warranted in a larger number of patients with a wider variety of tachycardias. Patients with Gemini 415As having dual anodal rings, which can be identified radiographically, are at risk for this design-dep design-dependent cross-talk and merit close observation.

An implantable antitachycardia pacemaker with back-up pacing and scanning burst mode.

We used an automatically triggered antitachycardia device (PASAR 4171) which is able to provide up to 7 stimuli in the atrium of three patients with AV-nodal tachycardia. A PASAR 4172 was implanted in a patient with WPW which gave two stimuli in the right ventricle. One revision was needed due to exit block. Temporary undersensing occurred in one patient. Atrial fibrillation occurred for the first time postoperatively in the WPW patient, without major side-effects. Treatment with low dosage amiodarone was initiated to prevent recurrence. At follow-up, magnet application was useful to induce supraventricular tachycardia in the three 4171 patients with 4171 devices, proving effective termination of tachycardia. Back-up pacing or concertina mode were used in 3 of 4 patients.