Continuous rapid atrial pacing to control recurrent or sustained supraventricular tachycardias following open heart surgery

Randomized comparison between Ramp and Burst+ atrial antitachycardia pacing therapies in patients suffering from sinus node disease and atrial fibrillation and implanted with a DDDRP device

AIMS

Atrial tachycardia and flutter frequently occur in association with atrial fibrillation and may be treated by overdrive pacing in patients who receive pacemakers with antitachycardia pacing (ATP) capabilities. The PITAGORA trial was a multi-centre, randomized, cross-over study aimed at comparing two different ATP modes for atrial tachyarrhythmia (AT) termination in patients suffering from sinus node disease (SND).

METHODS AND RESULTS

One hundred and seventy-six patients (72 M, age 71+/-9 years) received a Medtronic AT500 pacemaker. All patients were on class IC or III antiarrhythmic drugs. After a 5-month observation period, 170 patients were randomized to either Ramp or Burst+ ATP therapy; 4 months later they crossed over. One hundred and fifty-seven patients completed the 13 months of follow-up; 114 (72.6%) suffered 6088 AT episodes. In 75 patients, 1904 AT episodes were treated and 934 (49.1%) successfully terminated. The median value of individual patients' ATP efficacy was 60%. Burst+ terminated 387 out of 873 AT episodes (44%) in 58 patients. Ramp terminated 547 out of 1031 AT episodes (53%, P<0.001) in 56 patients. Ramp efficacy was significantly (P<0.01) and directly correlated with AT cycle length (ATCL), whereas Burst+ efficacy was not. Ramp showed higher (P<0.001) termination efficacy than Burst+ for ATCL >240 ms. Quality of life, as measured by the EuroQoL questionnaire, and number of symptoms significantly improved in the overall population. This improvement was significantly higher in patients with ATP efficacy >60%.

CONCLUSION

In patients suffering from SND and AT, Ramp therapy shows higher termination efficacy than Burst+ therapy in AT episodes with ATCL >240 ms. Further studies are required to show the impact of ATP on clinical outcomes.

Profound Independent Effects of Left Bundle Branch Block and Heart Rate During Supraventricular Tachycardia

Left bundle branch block (LBBB) has negative hemodynamic effects. In the same patient, profound hypotension occurs during supraventricular tachycardia with LBBB but not at the same rate in the absence of LBBB. At slower rates, blood pressure is similar with and without LBBB.

Mechanisms of Atrial Fibrillation

Mechanisms of Atrial Fibrillation. Based on experimental studies in the canine heart and an early computer model, atrial fibrillation (AF) has been thought to be due to multiple reentrant wavelets. However, subsequent studies in animal models are most consistent with a mechanism of AF due to a stable reentrant circuit of short cycle length or unstable reentrant circuits of short cycle length that drive the atria so fast that much or most of the atrial tissue manifests fibrillatory conduction. Limited mapping studies in patients during open heart surgery and during electrophysiologic studies using endocardial catheter electrodes also are most consistent with the concept of a driver, seemingly most often a focus in or near one or more of the pulmonary veins, precipitating and maintaining AF. However, a precise understanding of the mechanism(s) of AF in patients is not yet available.

Single site radiofrequency catheter ablation of atrial fibrillation: studies guided by simultaneous multisite mapping in the canine sterile pericarditis model

OBJECTIVES

To test the hypothesis that when activation of Bachmann's bundle (BB) is critical to the unstable reentrant circuits that maintain atrial fibrillation (AF) in the sterile pericarditis canine model, a lesion in BB would prevent induction of stable AF.

BACKGROUND

One mechanism of induced AF in this model is multiple unstable reentrant circuits, which frequently include BB as part of the reentrant pathway.

METHODS

Simultaneous multisite mapping studies during AF and after ablation of BB were performed by recording (384 to 396 electrodes) from both atria and the atrial septum during six induced AF episodes in six dogs with sterile pericarditis. Activation maps of AF (mean duration, 24 +/- 28 min) during 12 consecutive 100-ms windows were analyzed.

RESULTS

During AF, multiple unstable reentrant circuits (mean, 1.2 +/- 0.2 per window; range, 1 to 4) were observed, 68% involving BB. Nonactivation zones (mean duration, 57 +/- 16 ms in the right atrium and 53 +/- 23 ms in the left atrium) observed during AF were reactivated by a wave front most often coming from the atrial septum via BB (right atrium, 62%; left atrium, 67%). After successful radiofrequency catheter ablation of the midportion of BB, AF >5 s was not induced in all dogs. Mapping studies of transient AF (< or =5 s) induced after ablation showed neither reentrant circuits nor wave fronts activating the right atrium via BB.

CONCLUSIONS

In this AF model, catheter ablation of BB terminates and prevents the induction of AF by preventing 1) formation of unstable reentrant circuits that involve BB, and 2) activation of the atrial-free walls after a nonactivation period.

Atrial fibrillation after minimally invasive coronary artery bypass grafting: A retrospective, matched study

BACKGROUND

Atrial fibrillation after cardiac operations is a source of morbidity and resource consumption. Various factors common to cardiac operations have been cited as causal. Comparison of the incidences of atrial fibrillation after conventional cardiac operations and minimally invasive cardiac operations may provide some insight into the mechanisms of this complication.

METHODS

All patients undergoing minimally invasive direct coronary artery bypass grafting from January 26, 1996, through September 17, 1997, were evaluated for the occurrence of in-hospital postoperative atrial fibrillation. Data from these 55 patients were compared with data from a control cohort of patients undergoing conventional, solitary coronary artery bypass grafting. Each patient undergoing minimally invasive direct coronary artery bypass grafting was matched by age (+/- 3 years) and date of operation (+/- 7 days) with a patient undergoing conventional coronary artery bypass grafting.

RESULTS

During the period since the advent of minimally invasive direct coronary artery bypass grafting at our institution, the incidence of postoperative atrial fibrillation has been slightly lower among the patients undergoing this form of coronary artery bypass grafting (26%) than among the total population of patients undergoing conventional coronary artery bypass grafting (34%). Comparison of the age-matched groups, however, showed the incidence to be slightly but not significantly greater in the minimally invasive direct coronary artery bypass grafting cohort (13/55, 24%) than in the conventional coronary artery bypass grafting cohort (11/55, 20%; P =. 6). The minimally invasive direct coronary artery bypass grafting group was less likely to be discharged with antiarrhythmic therapy than was the conventional coronary artery bypass grafting group (6 versus 10; P =.006).

CONCLUSIONS

According to these data, mechanisms traditionally implicated in atrial fibrillation after coronary artery bypass grafting, such as the use of cardiopulmonary bypass, mechanical manipulation of the atrium, and atrial ischemia, are not causal but may be related to the duration of the arrhythmic complication. Strategies directed toward management and reduction of the incidence of postoperative atrial fibrillation should be focused accordingly.

Atrial tachycardia originating from a single site with exit block mimicking atrial fibrillation eliminated with radiofrequency applications

We describe the case of a patient who has a right atrial tachycardia and atrial fibrillation who was found to have a single site responsible for both. We recorded a tachycardia from this site with exit block into the remainder of the atria.

Mechanisms and medical management of patients with atrial flutter

Type I atrial flutter is due to reentrant excitation, principally in the right atrium. The standard ECG remains the cornerstone for its clinical diagnosis. Acute treatment should be directed at control of the ventricular response rate and, if possible, restoration of sinus rhythm. Radiofrequency catheter ablation therapy provides the best hope of cure, although atrial fibrillation may subsequently occur after an ostensibly successful ablative procedure. Alternatively, antiarrhythmic drug therapy to suppress recurrent atrial flutter episodes may be useful, recognizing that occasional recurrences are common despite therapy. Radiofrequency ablation of the His bundle ablation with placement of an appropriate pacemaker system may be useful in selected patients.

Use of temporary atrial pacing in management of patients after cardiac surgery

The authors' clinical experience with temporary atrial pacing to evaluate its use in the management of patients after cardiac surgery was reviewed. A total of 339 patients undergoing cardiac surgery were studied with regard to postoperative pacing therapy. Postoperative pacing was performed in 186 of 339 patients to treat supraventricular bradycardia or tachyarrhythmias. Rapid atrial pacing was performed to interrupt re-entrant supraventricular tachyarrhythmias. In bradycardic patients, haemodynamics could be improved as the result of significant increase of blood pressure and oxygen saturation in the pulmonary artery (SVO2) caused by atrial pacing. Premature beats could be suppressed in 63% and supraventricular tachyarrhythmias could be interrupted in 66% of the patients only by atrial pacing. Temporary atrial pacing is safe, rapid and effective as the treatment of choice; it is believed that the technique should be applied in preference to pharmacological treatment in the management of patients after cardiac surgery.

Spontaneous onset of type I atrial flutter in patients

OBJECTIVES

This study sought to characterize the spontaneous onset of atrial flutter in patients.

BACKGROUND

Temporary epicardial electrodes are routinely placed on the atria of patients at the time of open heart surgery and brought out through the anterior chest wall for potential diagnostic and therapeutic use in the postoperative period. We utilized these electrodes to study the spontaneous onset of type 1 atrial flutter in 16 patients in the postoperative period after open heart surgery.

METHODS

Twenty-seven episodes of the spontaneous onset of type I atrial flutter from sinus rhythm were studied in these 16 patients by recording bipolar atrial electrograms simultaneously with at least one electrocardiographic lead during each episode.

RESULTS

In all 27 episodes, the onset of type I atrial flutter was through a transitional rhythm of variable duration (mean 9.3 s) precipitated by a premature atrial beat. In 21 episodes, the transitional rhythm was atrial fibrillation; in 3 episodes it was type II atrial flutter that appeared to generate atrial fibrillation; and in 3 episodes it was a brief (3 to 6 beats), rapid, irregular arrhythmia.

CONCLUSIONS

Type I atrial flutter does not start immediately after a premature atrial beat. Rather, it starts after a transitional rhythm that is usually atrial fibrillation. Extrapolating from mapping studies of the onset of atrial flutter in the canine pericarditis model, we suggest that a transitional rhythm is required for the initiation of type I atrial flutter because during that rhythm, the requisites for development of the atrial flutter reentry circuit evolve.

Pacing therapy for atrial tachyarrhythmias

The use of pacing techniques for the treatment of atrial tachyarrhythmias has been advocated for more than 30 years. Although it has played a beneficial role in the management of paroxysmal supraventricular tachycardia (PSVT) in drug-refractory patients, tachycardia acceleration and development of atrial fibrillation has been the major drawback. With the availability of radiofrequency catheter ablation therapy, the use of implantable antitachycardia devices for PSVT is currently negligible. From retrospective and small control studies it has been shown that atrial or dual-chamber pacing in patients with sick sinus syndrome has been associated with a lower incidence of paroxysmal atrial flutter or fibrillation than in those who received a ventricular pacemaker. Furthermore, recent studies have reported the potential benefit of reducing frequency of paroxysmal atrial flutter and fibrillation with multisite atrial pacing. As a result, there is a resurgence of research interest in antitachycardia pacing for prevention of atrial tachyarrhythmias. This paper briefly describes the basic aspects of antitachycardia pacing, reviews the data on the use of implantable antitachycardia devices for PSVT and the selection of patients, and assesses the current status of research on atrial pacing for prevention of paroxysmal atrial flutter and fibrillation.

A comparison of transoesophageal atrial pacing and direct current cardioversion for the termination of atrial flutter: a prospective, randomised clinical trial

OBJECTIVE

To compare the safety and efficacy of transoesophageal atrial pacing (TAP) with an easily swallowed pill electrode and direct current cardioversion (DCC) in patients with atrial flutter that was refractory to appropriate medical treatment.

DESIGN

Prospective, randomised clinical trial.

SETTING

Community based United States naval hospital.

SUBJECTS

Twenty one consecutive patients with refractory atrial flutter selected consecutively from the inpatient cardiology consultation service. All patients were haemodynamically stable and medical treatment with a class IA or IC antiarrhythmic agent had failed. Eleven patients were treated with TAP and 10 patients were treated with DCC.

INTERVENTIONS

Digoxin was given to all patients to control the ventricular rate to < 100/minute.

MAIN OUTCOME MEASURE

Conversion to normal sinus rhythm and arrhythmias after cardioversion.

RESULTS

Conversion to normal sinus rhythm was similar in both groups (TAP 8/11, DCC 9/10, p = 0.31). Arrhythmias after cardioversion including third degree heart block and non-sustained ventricular tachycardia were more frequent in the DCC group (TAP 0/11, DCC 6/10, p = 0.02).

CONCLUSION

Transoesophageal atrial pacing with an easily swallowed pill electrode is safe, well tolerated, and is as efficacious as DCC for refractory atrial flutter.

Atrial flutter--update on the mechanism and treatment

Atrial flutter is a common and usually benign but symptomatic supraventricular tachycardia. There is a striking similarity between patients with atrial flutter suggesting a common substrate despite the presence or absence of underlying heart disease. In man, the mechanism is a single reentrant circuit originating in the right atrium whose center appears to be functional within the anatomical constraints of the right atrium. The reentrant circuit of atrial flutter contains an area of slow conduction in the inferior right atrium but the size and exact location is uncertain. Drug therapy directed at terminating and preventing atrial flutter has been available for many years. The efficacy and safety of this therapy is not as well tested as is the same therapy for atrial fibrillation. The most effective way to terminate atrial flutter is a nonpharmacological approach. Several nonpharmacological methods provide new treatment options in the management of patients with drug resistant or hemodynamically unstable atrial flutter. The use of anticoagulation for this disorder is still evolving. There is a risk of clinically apparent thromboemboli in some patients with atrial flutter although the risk appears less than that for atrial fibrillation. In the future, refinements and improvements in therapy for atrial flutter will likely be derived from a better understanding of its mechanism.

The effect of chronic atrial overdrive suppression pacing on the incidence of supraventricular tachyarrhythmias

Chronic overdrive suppression pacing has been suggested as an effective adjunctive method for reducing the incidence of cardiac tachyarrhythmias. Documentation of effectiveness during prolonged monitoring is lacking, however. To assess more accurately the long-term utility of this treatment modality for medically refractory supraventricular tachyarrhythmias (SVTs), 10 patients with atrially implanted Intermedics Intertach pacemakers were randomly assigned to either a low or a high bradycardia (back-up) pacing rate. SVT counts were performed during matching follow-up periods both at the initial rate and after rate crossover. The primary antitachycardia modality of this pacemaker (P mod) provides burst pacing to terminate tachycardia episodes, and P mod counters were utilized to quantitate SVT episodes. Tachycardia termination algorithms were programmed to "no restart" and were not changed during the study. The P mod use counter, therefore, reflected the number of discrete episodes of SVTs. Pacemaker implantation diagnoses include atrial flutter, concealed bypass tract, AV nodal reentry, intraatrial reentry, and Wolff-Parkinson-White associated tachycardia. Patient age was 59 +/- 18 yrs. The average pacemaker back-up low rate was 45.7 +/- 4 versus a back-up high rate of 85.1 +/- 2 beats/min. Follow-up was for 57.4 days +/- 33 days at the low rate and 57.3 days +/- 34 days at the high rate (r = 0.99). There was no difference in SVT incidence with a P mod usage of 98.4 +/- 106 at the low rate and 100.8 +/- 94 at the high rate (p = NS). In this blinded, randomized cross-over trial, chronic atrial overdrive suppression pacing did not reduce the overall incidence of SVT episodes during prolonged monitoring.

Temporary external DDD pacing after cardiac operations

Temporary atrial and ventricular pacing in the DVI, VVI, and AOO modes using atrioventricular sequential DVI devices is routinely used in cardiac operations. This study evaluated a new temporary external DDD pacemaker (Medtronic 5345 External Pulse Generator) capable of ten pacing modes. Thirty-nine devices have been applied to 38 adult patients (27 male, 11 female) after a variety of open heart procedures. Group 1 had atrial pacing wires placed 1.5 to 2.0 cm apart superiorly on the right atrium, group 2 had atrial wires placed 1.0 to 1.5 cm apart on the right atrial free wall, and group 3 had atrial wires placed on the right atrial free wall 0.8 cm apart, using a Silastic ring for fixation. Ventricular wires were placed on the free wall (group 1) or the diaphragmatic surface (groups 2 and 3) of the right ventricle. Postoperative atrial and ventricular sensing and pacing thresholds were obtained on return to the intensive care unit; analysis of variance demonstrated a significantly greater atrial sensing threshold in group 3. Four patients in group 1 permanently lost atrial sensing, 1 patient in group 2 intermittently lost atrial sensing at 24 hours with return at 36 hours postoperatively, and 1 patient in group 1 lost ventricular sensing capability. All other patients had adequate atrial and ventricular sensing capability documented until elective pacemaker removal (mean, 166 hours; range, 17 to 667.5 hours). Nineteen patients required some form of temporary pacing postoperatively; 11 patients demonstrated hemodynamic benefit from a pacing mode that is not available on the currently used DVI devices, and 7 of these required true DDD pacing capability. Six patients benefited from atrial pacing with adequate atrial sensing and simultaneous ventricular backup. Burst pacing with the device was used successfully to treat postoperative atrial flutter in 2 patients. We conclude that temporary external DDD pacing is feasible and effective in postoperative cardiac surgical patients. Atrial sensing is possible in most patients but electrode positioning is important for adequate thresholds. In some patients, hemodynamic as well as electrophysiologic improvement can be demonstrated with universal DDD pacing capability as compared with standard DVI pacing.

Prospective evaluation of transesophageal pacing for the interruption of atrial flutter

PURPOSE

Although transesophageal pacing has been used successfully for the interruption of cardiac arrhythmias, the efficacy of this technique for the interruption of spontaneous atrial flutter remains poorly defined. The utility of transesophageal pacing to interrupt atrial flutter that was persistent despite standard antiarrhythmic drug therapy (mean duration: 70.3 days; range: one day to more than 365 days) was studied prospectively in 39 consecutive patients.

PATIENTS AND METHODS

After written informed consent was obtained from each patient, transesophageal pacing was performed with a programmable stimulator, using the distal electrode as the cathode and the proximal electrode as the anode. All patients continued to receive a type 1 antiarrhythmic drug or amiodarone throughout the period of transesophageal pacing. The response to transesophageal pacing was classified as follows: (1) direct conversion; (2) indirect conversion; or (3) failure to interrupt atrial flutter.

RESULTS

The mean stimulus amplitude and pulse duration required for atrial capture were 19.8 +/- 7.5 mA and 18.4 +/- 7.9 msec. Atrial flutter was successfully converted to sinus rhythm by transesophageal pacing in 82% of patients. In 38% of patients, atrial flutter was converted directly to sinus rhythm without another intervening arrhythmia (direct conversion). The mean pacing rate required for direct conversion was 341 +/- 27 beats/minute. In 44% of patients, the cycle length of atrial flutter was accelerated to less than 180 msec or was converted to atrial fibrillation with spontaneous conversion to sinus rhythm within 24 hours (mean 8.4 +/- 9.3 hours, indirect conversion). The mean pacing rate inducing accelerated atrial flutter or transient atrial fibrillation was 372 +/- 61 beats/minute (p = NS compared to direct conversion). Atrial flutter was not interrupted or atrial fibrillation was induced that did not spontaneously convert to sinus rhythm within 24 hours in an additional seven patients (18%). The underlying cardiac disease, age, previous drug therapy, atrial size, atrial flutter cycle length, history of prior atrial fibrillation, left ventricular function, and concomitant medical illnesses did not predict the efficacy of transesophageal pacing.

CONCLUSION

The present study suggests that transesophageal pacing is highly effective for interrupting spontaneous atrial flutter that does not terminate with standard antiarrhythmic drug therapy.

Chronic rapid atrial pacing to maintain atrial fibrillation: use to permit control of ventricular rate in order to treat tachycardia induced cardiomyopathy

LR was a patient, followed over a 16-year period, who presented with an atrial tachycardia which was initially intermittent, but became incessant. Neither the atrial tachycardia nor the associated rapid ventricular response rate could be treated successfully with available drug therapy, resulting in a dilated cardiomyopathy and New York Heart Association (NYHA) class III-IV congestive heart failure. Acute induction of atrial fibrillation with rapid atrial pacing demonstrated that the associated ventricular rate could be satisfactorily slowed with digitalis therapy. Initially, short bursts from an implanted, radiofrequency controlled, patient activated pacemaker programmed to a rate of 600 bpm and connected to a permanent endocardial atrial J lead successfully interrupted the tachycardia and precipitated atrial fibrillation. Over a period of 3 months, this therapy changed the patient's heart failure to NYHA class II status. Subsequently, precipitation of atrial fibrillation with this technique failed, resulting in return to NYHA class III-IV congestive heart failure. Therefore, a custom-designed, high rate, rate-programmable pacemaker was implanted to pace the atria rapidly and continuously to maintain atrial fibrillation. A pacing rate of 375 bpm plus digoxin slowed the ventricular rate to 70-80 bpm, with stabilization of the congestive heart failure to NYHA class II. The pacemaker generator was replaced 6 months later, and after another 5 months, pacing was discontinued. The patient's subsequent rhythm remained stable atrial fibrillation with clinically successful control of both the ventricular rate and heart failure (NYHA class II) until the patient's death 72 months later. This unique case demonstrates another form of chronic therapy which, in selected cases, can be used for the long term control of rapid ventricular response rates to supraventricular arrhythmia.

Critical dose of digoxin for treating supraventricular tachycardias after heart surgery

This study was conducted to ascertain if critical peak body stores of digoxin were needed to protect patients from the debilities that result from supraventricular tachycardias occurring after open heart operations. We gave digoxin peak body stores of 15 micrograms/kg of lean body weight to 100 consecutive patients after open heart operations. If supraventricular tachycardias persisted four hours, we increased peak body stores to 17 or 19 micrograms/kg. The operations included coronary artery bypass grafts, heart valve replacements, and congenital defect correction. After operation, 18 patients had atrial fibrillation or flutter. During supraventricular tachycardias, ventricular rates were 150 beats per minute or slower. In the 100 patients, the median hospital stay after operation was four days. No patient required rehospitalization. The patients who had supraventricular tachycardias stayed in the hospital no longer than the patients who were at all times in regular sinus rhythm. All patients who entered the hospital with regular sinus rhythm went home with regular sinus rhythm. The critical safe peak body stores of digoxin needed to prevent debilities resulting from supraventricular tachycardias after open heart operations were 15 to 19 micrograms/kg of lean body weight.

Esmolol: safety and efficacy in postoperative cardiothoracic patients with supraventricular tachyarrhythmias

Esmolol, an intravenous, ultrashort-acting beta-blocker, was studied for its ability to safely control supraventricular arrhythmias up to 24 hours in 15 postoperative cardiothoracic surgery patients with atrial fibrillation or flutter and rapid ventricular response. Esmolol obtained an initial therapeutic response in nine (60 percent) patients. Mean heart rate for the 15 patients was reduced from 139 +/- 12 beats/min before therapy to 106 +/- 21 beats/min during esmolol infusion (p less than 0.01). The mean time to a therapeutic response after initiation of therapy, using a multistep titration regimen (500 micrograms/kg/min loading infusions over one minute, prior to incremental titration steps from 50 to 300 micrograms/kg/min over 4 to 14 minutes), was 22 +/- 9 minutes, and therapy was continued for 17 +/- 9 hours in responders. Esmolol significantly lowered blood pressure in the group studied and resulted in mild supine or orthostatic hypotension in ten (67 percent) patients. Side effects, including hypotension (10/15 patients), gastrointestinal disturbances (2/15), and weakness or somnolence (6/15), were transient and were not associated with serious clinical sequelae. We conclude that esmolol is effective for rate control in a majority of postoperative cardiothoracic surgery patients with atrial fibrillation or flutter. Side effects, although mild, occur relatively frequently, limiting prolonged infusions and warranting close surveillance of patients.

Use of procainamide with rapid atrial pacing for successful conversion of atrial flutter to sinus rhythm

Rapid atrial pacing is a useful technique and often the therapy of choice to terminate atrial flutter in patients. However, interruption of atrial flutter by rapid atrial pacing may not always produce sinus rhythm, but rather may result in atrial fibrillation. Twelve patients with spontaneous atrial flutter that had been present for greater than 24 h were studied to assess the efficacy of atrial pacing, alone and in combination with procainamide, to convert atrial flutter to normal sinus rhythm. Rapid atrial pacing for greater than or equal to 15 s from selected atrial sites at selected pacing rates were performed during atrial flutter. The initial pacing rate was always at a cycle length 10 ms shorter than the atrial flutter cycle length. If atrial flutter persisted after cessation of pacing, it was repeated at progressively shorter cycle lengths until either a rate of 400 beats/min was achieved or atrial fibrillation was induced. In two patients, atrial flutter was converted to sinus rhythm with pacing alone. Three patients developed sustained atrial fibrillation as a result of the rapid atrial pacing, this rhythm ultimately reverting back to atrial flutter in two. Ten patients received procainamide and 9 of the 10 had lengthening of the atrial flutter cycle length by a mean of 68 ms (1 patient continued to have atrial fibrillation). Then, using the same atrial pacing protocol, high right atrial pacing alone at a mean cycle length of 227 ms interrupted atrial flutter in all these patients, returning their rhythm to sinus rhythm. It is concluded that intravenous procainamide effectively augments the efficacy of rapid atrial pacing to convert atrial flutter to sinus rhythm.

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.

Termination of spontaneous atrial flutter by transesophageal pacing

Transesophageal atrial pacing using the constant-rate technique was performed in 26 patients presenting with spontaneous atrial flutter (atrial cycle length between 180 and 270 ms). All but one patient had been treated with one or more antiarrhythmic agents (digoxin, quinidine, procainamide, propranolol, verapamil, diltiazem, and propafenone) within the previous 12 hours. Transesophageal atrial pacing at cycle lengths between 80 and 180 ms was successful in terminating atrial flutter in 22 patients: immediate reversion to sinus rhythm in 16, following transient sinus pause in one, following a brief period of atrial fibrillation in three, and following longer periods of atrial fibrillation in another two. No post-conversion ventricular arrhythmia and no other complications were observed. All patients experienced only a mild burning discomfort during the procedure. It is concluded that atrial pacing via the esophagus is a safe and noninvasive technique of terminating spontaneous atrial flutter. The effectiveness of this technique is comparable to endocardial or epicardial atrial pacing.

Use of the pill electrode for transesophageal atrial pacing

The pill electrode, which was developed for esophageal electrocardiography, has found application in transesophageal atrial pacing during procedures such as conversion of tachycardia, electrophysiologic measurement, and acceleration of heart rate to produce stress during cardiac imaging studies. This paper presents theoretical studies that examine the relationship of interelectrode distance, current level, and pulse duration to the achievement of successful capture. Theoretical results agree with our clinical findings, i.e., current levels of 25 mA are effective to sustain capture; increased pulse duration reduces current requirements; and close bipolar spacing combines efficacy with safety. Results of animal studies performed to assess the extent of esophageal burn injury reveal that current levels in excess of 75 mA are required to produce lesions in short-term (under 30 minutes) pacing, and greater than 60 mA in long-term (4 hours) pacing. These results are based on experiments using a pulse duration of 2 ms, and the current levels that produce injury will be considerably lower if longer pulse durations are used. Typical current levels and pulse durations for successful capture are presented for 46 subjects in several new clinical applications. Termination of tachycardia, basic electrophysiologic measurements, and controlled acceleration of heart rate can be performed noninvasively with this technique.

Advances in the management of cardiac arrhythmias in children

The authors discuss several recent developments in the diagnosis and management of cardiac arrhythmias in the young, focusing on areas in which the greatest progress has been made so that the pediatrician can incorporate these developments into his practice and participate more fully in the management of the patient requiring tertiary care.

Diagnosis and treatment of arrhythmias during and following open heart surgery

The ability to record electrograms directly from the atria and to pace the atria and/or ventricles provides an effective, rapid, easy, and remarkably safe way to treat most disorders of rhythm and conduction in patients during and following open heart surgery. This article reviews various applications of those techniques.

Temporary epicardial wire electrodes in the diagnosis and treatment of arrhythmias after open heart surgery

The demonstrated safety, efficacy, and ease of utilization of the temporarily placed epicardial wire electrodes strongly support their routine use. By having temporary stainless steel wire electrodes available in the postoperative period, the diagnosis of arrhythmias after open heart surgery is greatly facilitated. Furthermore, because of the clinical advantages of cardiac pacing, it has become the treatment of choice for many, if not most, arrhythmias in the postoperative period.

Verapamil therapy in the treatment of supraventricular arrhythmias following open heart surgery

Certain general conclusions suggest themselves on the basis of our extensive experience with treating arrhythmias in patients following open heart surgery, our specific results with verapamil therapy in the treatment of atrial fibrillation and atrial flutter in patients following open heart surgery, and the results of verapamil therapy administered in other groups of patients. First, verapamil can provide highly effective, rapid, and safe control of the ventricular response in the treatment of atrial fibrillation and atrial flutter in patients following open heart surgery. Usually, it should be used in concert with digitalis therapy. Second, extrapolation from the data of others suggests that verapamil has an important role to play in the treatment of most other supraventricular arrhythmias in patients following open heart surgery, particularly if temporary wire electrodes are not available.

Clinical electrophysiology--a decade of progress

During the past 14 years there have been major advances in the field of clinical electrophysiology. This progress is a result of a more extensive use of intracardiac electrode catheters with recordings from multiple sites in the right and left cardiac chambers, the introduction of programmed electrical stimulation techniques and the use of antiarrhythmic drugs for diagnostic and therapeutic purposes during acute electrophysiologic testing. This article examines the pioneering studies and the subsequent developments in the field of clinical electrophysiology. The specific topics that are reviewed include the sinus node and atrium, atrioventricular conduction, supraventricular tachycardia and ventricular tachycardia. The therapeutic implications of each topic are also discussed. Clinical electrophysiology in its initial stages was a descriptive technique, but has since become an important diagnostic and therapeutic tool. However, electrophysiologic testing is an intensive process, requiring specialized training and a substantial commitment of human and physical resources.

Role of implantable pacemakers in control of recurrent ventricular tachycardia

Implanted pacemakers can provide a viable alternative to pharmacologic therapy or surgical management of patients with recurrent ventricular tachycardia. An increasing variety of pacemaker techniques are proving useful for preventing, controlling the effective rate of or terminating ventricular tachycardia. To assess the role of permanent pacing in the treatment of ventricular tachycardia, a consecutive series of 160 patients undergoing electrophysiologic testing for recurrent ventricular tachycardia were analyzed. Thirty-nine patients received implantable pacemakers, of which 13 were intended for bursts of rapid ventricular pacing. No adverse responses were attributed to these burst pacemakers, but concern for possible acceleration of tachycardia and appropriate identification of the arrhythmia were among factors limiting more widespread use of antitachycardia pacing. Some of these limitations may be resolved with further advances in electrophysiologic understanding of arrhythmias combined with strides in medical electronics, which will permit the development of new generations of highly sophisticated antitachycardia pacemakers.

The mechanism of flutter electrical alternans

We have had the opportunity to observe the occurrence of flutter electrical alternans in which two distinct populations of flutter waves are present and which alternate in 1:1 and 2:1 patterns. The flutter alternans whether 2: or 3:1, was concordant with the pattern of preceding ventricular conduction (ventriculophasic variation). This concordance occurred reproducibly and remained consistent. Our example of flutter alternans probably represents mechanical artefact caused by catheter movement during ventricular mechanical systole. We reproduced this pattern consistently at a slower rate during coronary sinus pacing. These findings appear to suggest an explanation for certain types of so-called atrial flutter electrical alternans.

Use of atrial epicardial electrodes to diagnose and treat postoperative arrhythmias in children

Temporary Teflon-coated stainless steel wires were placed on the right atrium of 100 consecutive infants and children undergoing open heart surgery. The patients' ages ranged from 1 day to 17 years. The wires were used for diagnosis or treatment 40 times in 30 patients. Atrial electrograms were recorded 14 times to diagnose arrhythmias and conduction disturbances that were unsuspected or misdiagnosed from the standard electrocardiogram. In 10 patients, atrial pacing was used to treat postoperative arrhythmias. Atrial pacing was also used as an adjunct to therapy in 16 children with postoperative low cardiac output and bradycardia with intact atrioventricular conduction. The wires were removed before discharge and no complications resulted from their use. Previous studies have demonstrated the usefulness of temporary atrial wires after cardiac surgery in adults. This experience confirms that the technique is easy and safe and can be of great diagnostic and therapeutic value in children.

Ventricular tachycardia and ventricular fibrillation in patients with short P-R intervals and narrow QRS complexes

Eleven patients with short P-R intervals and narrow QRS complexes had ventricular tachycardia due to organic heart disease: mitral valve prolapse with mitral insufficiency (2 patients); alcoholic (?) cardiomyopathy (2 patients); and coronary artery disease (7 patients). Intracardiac studies showed short A-H intervals during sinus rhythm in all cases. The onset of ventricular fibrillation (which, to our knowledge, has not been observed in patients having short P-R and A-H intervals coexisting with narrow QRS complexes) was documented in 4 cases. Only 1 patient (with quinidine syncope) had been premedicated. In the 3 other patients the episodes of ventricular fibrillation appeared during bouts of atrial fibrillation with rapid ventricular rates which could have been an exprerssion of the "enhanced A-V conduction" that had been manifested in sinus beats by short P-R and A-H intervals. In clinical settings and physiological conditions proven to be hemodynamically unstable (such as transient ischemia or acute myocardial infarction) these rapid ventricular rates could have led to ventricular fibrillation; directly because of the R-on-T phenomenon, and/or indirectly due to decreased coronary perfusion. Ventricular tachycardia and ventricular fibrillation due to organic heart disease probably occur more often than suggested by the few reported cases in the literature. Its significance, however, has to be clarified by further prospective studies.