A versatile pacemaker system for termination of tachycardias

Efficacy of a tiered therapy defibrillator system used to treat recurrent ventricular arrhythmias refractory to drugs

OBJECTIVE

To evaluate an implantable tiered therapy defibrillator system that delivered antitachycardia pacing treatment for slower well tolerated ventricular tachycardias and cardioversion or defibrillation for fast tachycardias or ventricular fibrillation.

METHODS

A tiered treatment device (Ventritex Cadence V-100) was implanted in 30 patients with ventricular tachycardia that was refractory to drugs. Efficacy was evaluated by the responses of induced or spontaneous arrhythmias to the treatments delivered.

RESULTS

Antitachycardia pacing successfully terminated 80% of episodes of ventricular tachycardia induced by non-invasive programmed stimulation, but acceleration was brought about by pacing in six patients in 10% of episodes. During a follow up of two to 17 (mean seven) months, 18 patients (60%) had recurrence of ventricular arrhythmias. Antitachycardia pacing terminated ventricular tachycardia in 17 of 18 patients in 87% of episodes. Twelve patients received shocks for ventricular tachycardia or fibrillation. Failure of pacing, with subsequent cardioversion, occurred in nine patients (50%) in one or more episodes. Acceleration of tachycardia by pacing occurred in 10 patients in 5% of episodes. Only two of these patients had experienced acceleration of previously induced arrhythmia. Five patients had spontaneous fast ventricular tachycardia or fibrillation treated by cardioversion or defibrillation. Spurious treatment was delivered in nine patients (30%), during atrial fibrillation in five, sinus tachycardia in two, and because of fracture of the sensing lead system in two patients. The retrieval of stored intracardiac electrograms was of clinical value in assessing spurious treatment.

CONCLUSIONS

Tiered treatment was effective in terminating recurrent ventricular arrhythmias in these selected patients. Most episodes were treated successfully by pacing, and resistant tachycardias, pacing induced acceleration, or haemodynamically compromising arrhythmias were treated by shocks.

Efficacy of automatic multimodal device therapy for ventricular tachyarrhythmias as delivered by a new implantable pacing cardioverter-defibrillator. Results of a European multicenter study of 102 implants

BACKGROUND

Third-generation implantable cardioverter-defibrillators are devices designed to treat ventricular tachycardia (VT) and ventricular fibrillation (VF) by means of overdrive pacing, cardioversion, or defibrillation. So far, the efficacy of tiered therapy has been documented only in small series. Therefore, a European multicenter clinical evaluation study of a new tachyarrhythmia control device, the Medtronic PCD pacer-cardioverter-defibrillator with epicardial patch-lead configuration, was undertaken.

METHODS AND RESULTS

We report on 102 patients (mean age, 55 +/- 13 years) from 11 European centers. PCD devices implanted between May 1989 and February 1991 were included. The patients suffered from hemodynamically significant ventricular tachyarrhythmias not suppressed by antiarrhythmic drug therapy and unrelated to acute myocardial infarction; one patient had nonsustained VT and severely depressed left ventricular function. Seventy patients had coronary artery disease with old myocardial infarctions, 23 had cardiomyopathies of various etiologies, and nine patients had no detectable heart disease. Mean ejection fraction was 36 +/- 14% (range, 10-76%). Mean intraoperative defibrillation threshold (51 patients) was 10.6 +/- 5.1 J (range, 2-18 J). The documented follow-up ranged from 1 to 21 months (mean, 9.4 +/- 5.8 months), or 79.9 cumulative patient-years. Perioperative mortality was 3.9%. The actuarial survival rate at 12 months was 91%. One sudden arrhythmic death occurred. Sixty patients (58%) received device therapy. Seventeen patients had therapies only for "VF" episodes, 16 patients only for VT, and 28 patients for VT and "VF" episodes. Based on device memory data, 1,235 spontaneous VT episodes were detected and treated in 43 patients. Twelve hundred four of these VT episodes received painless initial antitachycardia pacing therapy, restoring sinus rhythm in 91%. The 108 ongoing episodes received 209 multiple therapeutic attempts. Eighty-five additional overdrive pacing therapies restored sinus rhythm in 30%. Initial ineffective antitachycardia pacing therapies received 51 cardioversion pulses. The success rate was 61%. Seventy-three additional cardioversion pulses were delivered to backup ineffective pacing therapy as well as ineffective secondary cardioversion pulses. Their success rate was only 40%. Two hundred eighty-six spontaneous episodes were detected in 44 patients as "VF." Overall defibrillation efficacy was 97.6%.

CONCLUSIONS

The implanted device nearly eliminates sudden arrhythmic death in patients with documented, potentially fatal ventricular tachyarrhythmias. Automatic tiered therapy is highly effective to restore sinus rhythm, provided that an integrated two-zone tachycardia detection algorithm is used, assigning lower tachycardia rates to overdrive pacing and/or cardioversion and higher tachycardia rates to defibrillation. In general, spontaneous VTs can be terminated by automatic overdrive pacing, and painful or disturbing countershock therapies are not required to terminate the majority of spontaneous VT episodes.

Computer simulation of overdrive pacing during atrioventricular reentrant tachycardia

The study used a computer model of cardiac excitation to reproduce atrioventricular (AV) reentrant tachycardia and to evaluate the possibility of its termination by overdrive burst pacing. The model simulated activation waves radiating along a one-dimensional circular pathway, the portions of which represented the atrial, AV nodal, His-Purkinje, ventricular, and bypass parts of the tachycardia circuit. The pathway consisted of 289 elements. Only depolarised and resting states of elements were modelled. Differential refractoriness and conduction velocity for each element and the cycle length dependence of AV nodal decremental conduction were introduced. The experiments with the model examined the ability of overdrive 'on-circuit' pacing to terminate the tachycardia in order to determine the relevance of: (a) the coupling interval of the first beat in the burst; (b) the cycle length of the burst; (c) the number of stimuli in the burst; (d) His-Purkinje refractoriness; and (e) the degree of AV nodal decremental conduction. The results suggested that: (A) the general impression of a regular recovery wave and of a regular excitable window moving uniformly along the macro-reentrant circular path is incorrect; (B) the use of overdrive bursts of several stimuli with a short coupling interval has unpredictable effects; (C) the use of faster bursts with a cycle length only slightly shorter than the tachycardia cycle length is more safe (with respect to tachycardia reinitiation) and for certain combinations of the coupling interval and cycle length, prolonged bursts do not reinitiate the tachycardia; (D) the likelihood of tachycardia termination is increased by prolonging the refractoriness of the tachycardia circuit and by reducing AV nodal decremental conduction.

Atrial antitachycardia pacing in children and young adults

Atrial antitachycardia pacing was tested in 23 children and young adults. The majority of these patients had had operative repair of congenital cardiac defects and had both bradycardia and tachycardia. Pacemakers were usually implanted by the transvenous technique using bipolar leads. In each patient it was possible to find a tachycardia termination algorithm that successfully converted the tachycardia. In some patients very complex algorithms were necessary. In each patient it was also possible to find an algorithm that successfully differentiated the abnormal tachycardia from sinus tachycardia. Twelve patients required no antiarrhythmic drugs after pacemaker implantation, while 10 patients required one drug and one patient required two drugs. Eight of 23 patients had symptomatic tachycardias that required reprogramming the pacemaker to a different tachycardia termination sequence. Seven patients required reoperations, five for adapter problems and two for infection or erosion. Cardiac function improved in 15 of the 23 patients. Antitachycardia pacing is a viable option for management of tachycardias in children and young adults.

Characterization of spontaneous termination of sustained ventricular tachycardia associated with coronary artery disease

To characterize the change in cycle length and QRS morphology before spontaneous termination of sustained ventricular tachycardia (VT), electrocardiograms were recorded and VT cycle length measured for the periods 31 to 21 and 11 to 1 beats before termination in 55 episodes from 28 patients with coronary artery disease. Beats 31 to 21 were designated as a period of stable arrhythmia and served as a reference for changes occurring just before termination. Forty-four episodes of VT occurred in the setting of antiarrhythmic drug therapy; 11 episodes occurred in patients not treated with antiarrhythmic drugs. Variability in cycle length was indexed by the standard deviation of the mean cycle length and by the percentage of consecutive cycles varying by greater than or equal to 40 ms (% greater than or equal to 40 ms). There was greater variability just before termination (standard deviation of the mean cycle length, 25.8 ms; % greater than or equal to 40 ms, 16.7%) than during the stable period (standard deviation of the mean cycle length, 8.5 ms; % greater than or equal to 40 ms, 5.4%; p less than 0.001 for both). This was true irrespective of antiarrhythmic drug use, although the differences in the standard deviation of the mean cycle length for beats 11 to 1 and for beats 31 to 21 were greater for the antiarrhythmic drug group (29.6 vs 8.9 ms, p less than 0.001) than for the group not receiving antiarrhythmic drugs (11.0 vs 6.7 ms, difference not significant). No specific patterns of cycle length variability characteristic of VT termination were found.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Overview of the clinical electrophysiology study

Clinical electrophysiology testing is now a standard, useful technique for assessing patients with bradyarrhythmias or tachyarrhythmias. The technique requires specialized training and equipment. The recording equipment and program stimulator have evolved to sophisticated devices allowing accurate reproduction of intracardiac electrograms and timing of programmed extrastimuli. Electrophysiologic studies are useful for determining the mechanisms of a tachycardia or bradycardia and identifying the most appropriate therapy, whether it be pacing, antiarrhythmic medications, transvenous ablation, or electrosurgery.

Devices for tachycardia termination

Remarkable advances have been made over the last 2 decades in the management of tachyarrhythmias. Simultaneous developments have provided new drugs, new surgical and catheter ablation techniques and new implantable devices. Initial enthusiasm with antitachycardia pacemakers was tempered by the realization of dangers and difficulties associated with their use, particularly in the treatment of ventricular tachycardia. However, progress has been made along several lines: (1) improvements in the automatic detection of target tachyarrhythmias; (2) the development of termination algorithms that are more adaptable to spontaneous changes in the tachycardia termination zone; (3) improvements in the safety of termination algorithms; (4) development of automatic cardioversion or defibrillation for the management of malignant ventricular arrhythmias; and (5) incorporation of multiple pacing facilities in single implantable units.

Treatment of cardiac arrhythmias: when, how and where?

Despite major advances in the understanding of mechanisms, better diagnostic methods and a wide array of new modes of therapy, management of cardiac arrhythmias continues to be a challenge. Because of possible deleterious effects of antiarrhythmic therapy, the decision about when and how to treat should be weighed carefully with emphasis on symptoms and the prognostic significance of the arrhythmia. When possible, the high risk patient should be referred to a center where expertise and diagnostic and therapeutic possibilities allow optimal treatment.

Implantable electrical devices in the management of tachyarrhythmias

Electrical therapy for tachyarrhythmias attempts to achieve one or more of three aims: a) prevention of tachycardia; (b) control of the hemodynamic effect of tachycardia; (c) termination of tachycardia. In practice, long term control of tachycardia in selected patients can be achieved with implantable devices which can automatically recognize and terminate tachycardias. Termination can be achieved with a number of pacing modalities. These pacing modalities are reviewed in this article and some guidelines to the choice of modality are given. Patients with supraventricular tachycardia are often more appropriately treated with drugs or surgery but some can be effectively treated with antitachycardia pacing. Some patients with ventricular tachycardia can be successfully treated with these devices but this group is at risk of tachycardia acceleration or degeneration in response to pacing. An implantable cardioverter-defibrillator should be used as a backup in these patients. Present generation devices now incorporate antitachycardia pacing, low energy cardioversion, and higher energy defibrillation in the same unit.

Changes in cycle length at the onset of sustained tachycardias--importance for antitachycardiac pacing

We analyzed changes in the spontaneous cycle length of sustained tachycardia during the first 100 beats after electrophysiologic initiation of sustained monomorphic ventricular tachycardia (VT), atrioventricular nodal tachycardia (AVNT), and circus movement tachycardia incorporating an accessory pathway (CMT). The mean cycle length of VT was 288 +/- 75 msec, for AVNT this value was 388 +/- 63 msec, and for CMT this value was 348 +/- 76 msec. After initiation, in all three types of tachycardia changes in cycle length of up to +/- 15% to 25% were observed. The changes in cycle length ranged from +12% to -18% in patients with VT, from +17% to -15% in patients with AVNT, and from +17% to -15% in patients with CMT. The mean percentage of changes during the first 100 beats of tachycardia was 7.0 +/- 4.7% (VT), 9.5 +/- 5.4% (AVNT) and 8.3 +/- 5.4% (CMT). Patients with VT and AVNT showed both a constant increase or decrease or alteration of the rate of tachycardia. In no patient with CMT was there a constant decrease in cycle length after initiation. The mean time to achieve the maximal increase or decrease in cycle length was 13 +/- 6 and 11 +/- 9 seconds in patients with VT and 16 +/- 3 and 20 +/- 7 seconds in patients with AVNT. In patients with CMT, the mean time to achieve the maximal increase (10 +/- 7 seconds) or decrease (20 +/- 9 seconds) varied markedly.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrical devices for treatment of arrhythmias

Electrical devices can be used for preventing and terminating tachycardia and for achieving hemodynamic improvement during a continuing tachycardia. Conventional approaches to tachycardia prevention include pacing at physiologic rates to prevent brady-cardia-related tachycardia or tachycardias associated with prolonged QT-interval syndromes. More exotic techniques, such as those involving stimulation during the refractory period, are undergoing investigation. Some tachycardias cannot be easily terminated or recur incessantly. Hemodynamics can be improved by pacing methods that result in a narrower QRS complex by coupled pacing and, in supraventricular tachycardias, by pacing rapidly enough to create atrioventricular block. Most clinical tachycardias are caused by reentry. Careful analysis of the timing of individual stimuli that successfully terminate tachycardias indicate that critical relations exist in the conduction velocity, refractoriness and physical properties and dimensions of the reentry circuit and the remaining myocardium. Elucidating these relations has permitted inferences into the mechanisms by which pacing terminates or accelerates tachycardias. A vast number of pacing patterns have evolved for use in tachycardia termination. None of these appear to be foolproof. There is widespread and justified concern about the risk of acceleration of tachycardia when antitachycardia pacing is used in the ventricle. Experience indicates that only a few patients are suitable for termination of ventricular tachycardia by pacing, but these carefully selected patients may do well. Both the results and the potential for widespread use may be better with pacing for termination of supraventricular tachycardia. Life-threatening tachycardias or fibrillation can be terminated by direct-current countershock. Although many technical problems remain, implantable cardioverter-defibrillators, possibly combined with antitachycardia pacemakers, will play an increasing role in the management or serious arrhythmias.

Implantable pacers for tachycardia termination: stimulation techniques and long-term efficacy

The long-term efficacy of pacing for termination of supraventricular tachycardia (SVT) and ventricular tachycardia (VT) was reviewed. Increasingly complex and sophisticated antitachycardia pacing stimulation patterns have evolved, and are outlined. Although excellent results are reported with simple patterns, it may be that the more complex algorithms increase the percentage of tachycardia patients who may be candidates for implantation of a device. In the papers reviewed, there were 460 patients, 268 with SVT, and 192 with VT. Results were judged to be good-excellent in 96.5% of both VT and SVT groups.

Analysis of the resetting phenomenon in sustained uniform ventricular tachycardia: incidence and relation to termination

Although the phenomenon of resetting has been studied in several experimental and clinical rhythms, it has not been systematically analyzed in ventricular tachycardia. To define the incidence and determinants of resetting as well as its relation to ventricular tachycardia termination, the response to programmed stimulation was prospectively studied during 78 electrically induced episodes of sustained, uniform ventricular tachycardia (mean cycle length 365 +/- 59 ms) in 53 patients. Single and double ventricular extrastimuli were introduced during 78 and 39 episodes of ventricular tachycardia, respectively. Rapid ventricular pacing was performed during 27 episodes. Resetting occurred in response to single ventricular extrastimuli in 43 (55%) of 78 ventricular tachycardias, to double extrastimuli in 31 (79%) of 39 ventricular tachycardias and to rapid pacing in 23 (85%) of 27 ventricular tachycardias. No ventricular tachycardia characteristic distinguished those tachycardias that were reset from those not reset. Termination of ventricular tachycardia occurred in 7 (9%) of 78 episodes with single ventricular extrastimuli, 14 (36%) of 39 episodes with double ventricular extrastimuli and 13 (48%) of 27 episodes with rapid pacing. Termination was less frequent than resetting with both single (9 versus 55%) and double (36 versus 79%) extrastimuli, as well as rapid pacing (48 versus 85%). Resetting preceded termination in 7 of 7 ventricular tachycardias terminated with single ventricular extrastimuli, 12 of 14 terminated with double ventricular extrastimuli and 9 of 13 terminated by rapid pacing. Ventricular tachycardias that were terminated could not be differentiated from those that were reset without termination.

IN CONCLUSION

Resetting with programmed extrastimuli is common in hemodynamically stable sustained ventricular tachycardia.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical intracardiac electrophysiologic testing: technique, diagnostic indications, and therapeutic uses

Clinical cardiac electrophysiologic testing has evolved rapidly since 1968, when the technique was first described. In an electrophysiologic study, electrode catheters are positioned within the heart to record electrical activity from the atrium, atrioventricular conduction tissue, and ventricle. Programmed stimulation is then performed, which involves pacing of the atrium or ventricle and introducing critically timed premature stimuli during sinus rhythm or paced rhythm. The use of programmed stimulation in conjunction with intracardiac recordings in electrophysiologic studies has facilitated the diagnosis of mechanisms of arrhythmias and the assessment of therapy. Electrophysiologic testing is useful in selected patients with sinus node dysfunction, conduction system disorders, supraventricular tachycardia, ventricular tachycardia, or ventricular fibrillation and in survivors of out-of-hospital cardiac arrest and patients with symptomatic but unsubstantiated rhythm disturbances. Therapeutic approaches that can be assessed by electrophysiologic testing include serial drug testing to determine the effectiveness of antiarrhythmic agents, antitachycardia pacing, the implantable defibrillator, transcatheter ablation, and electrophysiologically guided surgical procedures. In this review, we discuss the methods of electrophysiologic testing, its clinical applications in diagnosing the various cardiac rhythm disturbances, and its use in assessing various therapeutic modalities.

Is there a universal antitachycardia pacing mode?

A pacing mode using automatically increasing number of stimuli with adaptive coupling intervals was evaluated prospectively as a possible universal pacing mode, because a universal mode would save extensive testing and tailoring time. In group 1, which included 7 patients with implanted antitachycardia pacemaker systems, the test mode was compared with the previously tested and tailored mode. In group 2, which included 11 patients undergoing invasive electrophysiologic study, the test mode was compared with the scanning and asynchronous burst mode. There were 4 patients in group 3. The mode was tested prospectively in these 4 patients. Three of these patients were tested after pacemaker implantation (in supine and upright body position and after moderate exercise). The fourth patient had recurring episodes of VT, which were terminated with the test mode via an external lead. Of 209 tachycardias (156 supraventricular tachycardia [SVT] and 53 with VT) studied with the test mode, 1 episode of nonsustained atrial fibrillation was induced from the ventricle and 1 episode of VT was not terminated using the test mode and long coupling intervals. Two episodes of VT in patients with a recent myocardial infarction (MI) required direct-current countershock: due to acceleration in 1 patient and due to VF in 1. All other tachycardias were terminated promptly by the test mode without prior knowledge about successful coupling intervals or number of stimuli. Of the remaining 106 tachycardias studied (69 SVT, 37 VT) the scanning mode failed to terminate 2 episodes of SVT with up to 4 atrial premature beats and induced acceleration of VT in 1 patient with a recent MI.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of pacemaker performance using computer simulation

A description is given of a mathematical model of impulse conduction through the heart. The model can be used to evaluate the best pacing mode for the individual patient and to develop new pacemakers. This allows study of the influence of different parameters related to the behavior of the heart or pacemaker. Two examples using a model of a DDD pacemaker and two examples describing simulation of an antitachycardia pacing system are given to illustrate how the performance of pacemakers under different conditions can be simulated.

Programmable extrastimulus pacing for long-term management of supraventricular and ventricular tachycardias: clinical experience in 16 patients

Sixteen patients with recurrent, drug-resistant supraventricular (13 patients) or ventricular (3 patients) tachycardia were treated chronically by programmable extrastimulus pacing; either a fully automatic device (Telectronics PASAR 4151: eight patients with supraventricular tachycardia) or a patient--activated device (Medtronic Interactive Tachy System) was used. During a follow-up period of 5 to 30 months, five of the subjects treated with the fully automatic device showed successful results, one had recurrent tachycardia, and two had their units explanted for system-related problems. The patients treated with the externally activated device were, on the whole, very well controlled. This mode of treatment, if applied in well-selected cases, is promising; it seems safe and considerably reduces the number of hospital admissions.

Automatic pacemaker termination of two different types of supraventricular tachycardia

A new antitachycardia pacemaker system was used in a 58 year old woman to terminate two different types of supraventricular tachycardia by a single automatic pacing mode. During the invasive electrophysiologic study before pacemaker implantation (in the absence of medication), sustained episodes of atrioventricular (AV) nodal reentrant tachycardia and two short-lasting episodes of nonsustained atrial tachycardia were induced. After implantation, sustained episodes of both AV nodal tachycardia and atrial tachycardia were initiated. Both arrhythmias could be terminated reproducibly by a single pacing mode.

PACTOT: a reprogrammable software pacing system

The long battery life in modern pacemakers has created the need for pacemakers in which all the parameters can be changed and updated. The availability of such a system has potential advantages: new pacing techniques can be programmed without reoperation; the number of different pacemaker systems in stock in a hospital can be reduced to this reprogrammable unit; and, finally, this system can be of great help in designing and evaluating new pacing strategies.

Externally activated antitachycardia pacemaker with noninvasive electrophysiologic re-testing capability

An Omni Orthocor 234A special device pacemaker was implanted in nine patients for treatment of drug-resistant supraventricular tachycardia (three patients) or ventricular tachycardia (six patients). This device is activated using a special external unit, which delivers from six to 15 stimuli at preselected coupling intervals ranging from 195 to 500 ms. Serial noninvasive electrophysiology studies were performed either in the hospital or on an outpatient basis using the triggered mode, which can respond to programmed chest wall stimulation. Three patients with reciprocating supraventricular tachycardia were treated effectively by this device during an average follow-up of 2.2 years. Of the six patients with stable ventricular tachycardia amenable to pacemaker termination, only four remained successful during an average follow-up of 1.9 years. Such devices may find important use in serial noninvasive electrophysiologic testing during long-term clinical follow-up. The present form of this device is inadequate for widespread application, but may be useful for highly selected individuals.

Arrhythmias induced during termination of supraventricular tachycardia

Pacing is being used frequently for the treatment of drug-resistant, paroxysmal supraventricular tachycardias (SVT). SVT can usually be terminated by pacing, but arrhythmias may be induced which interfere with the safety of antitachycardia pacing. To quantify these pacing-induced arrhythmias, 453 attempts to terminate SVT in 111 patients were analyzed. The patients were 6 to 73 years old (mean 41); 62 were male. Seventy-six patients had SVT using an accessory atrioventricular bypass, and 35 patients had intranodal SVT. Single and then, if required, multiple ventricular and atrial premature beats and overdrive pacing were delivered from the atrium and ventricle. A pacing-induced arrhythmia occurred in 9% of all attempts (34% of patients). Atrial flutter or fibrillation (AF) was the most frequent arrhythmia (in 8% of all attempts and sustained in 75%). Atrial vs ventricular pacing resulted in a 12% vs 2% incidence of AF. AF was unrelated to age, sex, atrial size and SVT type, and was predominantly induced by multiple premature beats. In 6 patients a different SVT and in 2 patients a nonsustained ventricular tachycardia was induced. In 6 patients SVT could only be terminated by initiating another arrhythmia. Thus, AF is frequently induced during attempted pacing termination of SVT. To limit the risk of AF, a single premature beat should preferentially be used to terminate SVT. In 6% of patients, SVT can only be terminated by inducing another arrhythmia.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of invasive electrophysiologic studies in the evaluation and treatment of supraventricular tachycardia

Electrophysiologic studies have provided new insights into the mechanisms responsible for supraventricular arrhythmias and have enabled investigators to evaluate with precision the acute effects of pharmacologic, physiologic, electrical, and surgical interventions. Not all patients with supraventricular arrhythmias require invasive studies, however, since empiric drug trials will often be adequate for management. At present, the clinical indications for study include the following: (1) for diagnosis of tachycardia mechanism when scalar ECG analysis is uncertain; (2) for assessment of risk of future life-threatening arrhythmia; and (3) as a rapid means of assessing future therapy when sporadic arrhythmias are likely to be poorly tolerated. Innovations that include surgical and catheter ablations of tachycardia pathways and antitachycardia pacing devices hold great promise and in the future, will provide nonpharmacologic options for patients poorly controlled by or intolerant of drug therapy.

A case report demonstrating spontaneous change in tachycardia terminating window

A patient who received a patient-activated pacemaker system for termination of paroxysmal, drug-resistant, ventricular tachycardia is described. During the pre-implant invasive electrophysiological (EP) study and the three post-implant non-invasive EP studies, tachycardias were easily and reproducibly terminated by two stimuli using the interval scanning mode. On the fourth day post-implant, this pacing mode no longer terminated tachycardia at rest. A new pacing mode using more stimuli was then found to terminate the tachycardia reproducibly under various physiological conditions. This case report demonstrated a spontaneous change in the tachycardia terminating window and the usefulness of versatility in antitachycardia pacemaker systems.