Importance of Pacemaker Noise Reversion as a Potential Mechanism of Pacemaker-ICD Interactions

Numerous types of interactions between pacemakers and implantable cardioverter defibrillators (ICDs) have been described. Pacemaker outputs preventing appropriate detection of ventricular tachycardia or ventricular fibrillation by the ICD is one of the more serious. Asynchronous pacemaker activity during ventricular arrhythmias maybe caused by either nonsensing of the arrhythmia or by noise reversion, which is an algorithm that causes the pacemaker to switch to asynchronous pacing when repetitive sensing at a high rate occurs. We analyzed the mechanisms underlying asynchronous pacemaker activity in ventricular arrhythmias using pacemaker telemetry during the arrhythmia. Thirty-nine induced arrhythmias from 26 different procedures in 19 patients with both pacemakers and ICDs were analyzed. Of the 39 arrhythmias, asynchronous pacemaker activity occurred in 16. The underlying mechanism was nonsensing in 4 episodes and noise reversion in 12 episodes. Clinically significant interference with detection arose on three occasions. Conditions favoring the occurrence of noise reversion include specific pacemaker models, arrhythmia cycle lengths in the range causing noise reversion of the individual pacemaker model, long noise sampling periods, and VVI pacing mode. Noise reversion can be diagnosed by telemetering the pacemaker marker channel during ventricular arrhvthmias as a part of routine pacemaker-ICD interaction evaluation. It can be prevented or minimized by programming short ventricular refractory periods or using pacemakers with shoii retriggerable refractory periods.     

Intermittent Pacemaker Syndrome: Revision of VVI Pacemaker to a New Cardiac Pacing Mode for Tachy-Brady Syndrome

A patient with tachy-brady syndrome manifested by paroxysmal atrial fibrillation and symptomatic sinus bradycardia and treated by VVI pacing developed pacemaker syndrome during episodes of ventricular pacing. His cardiac pacemaker was revised to a dual chamber system utilizing the new AV sequential DDI pacing mode which eliminated pacemaker-related tachycardias and totally abolished the pacemaker syndrome symptoms. There have been no further episodes of atrial fibrillation, possibly due to elimination of temporal dispersion of refractory periods during bradycardia. The propensity for atrial fibrillation has also been minimized by excluding competitive atrial stimulation during DVI pacing. The DDI mode provides the clinician increased utility and flexibility in the use of AV sequential pacing therapy.     

A New Pacemaker for Paroxysmal Atrial Fibrillation Treated with Radiofrequency Ablation of the AV Junction

Atrial fibrillation is a relative contraindication to atrial synchronous pacing because of the risk of the tracking of rapid atrial rhythms by the pacemaker. In this study, we describe the clinical results of an AV synchronous rate responsive pacemaker with an original algorithm, which is able to sense pathological increments in atrial rate and automatically to switch into a non-AV synchronous mode of pacing. This pacemaker was implanted in 12 patients who had undergone radiofrequency ablation of the A V junction in order to cure severely symptomatic, drug refractory, paroxysmal atrial fibrillation. In an acute, intrapatient comparison between the standard AV synchronous mode and the automatic switching mode, ventricular tracking of atrial fibrillation occurred in 35% and 4% of total beats at rest and in 24% and 2% of total beats during exercise, respectively (P < 0.001). During 5 ± 4 months of follow-up, no further tachyarrhythmia related symptoms occurred. In conclusion, the standard DDDR mode is unable to eliminate ventricular tracking of atrial fibrillation, thus undermining the efficacy of AV junction ablation therapy. The automatic switching mode eliminates this adverse effect of dual chamber pacing.     

Pacemaker Induced Mitral Regurgitation: An Alternative Form of Pacemaker Syndrome

A patient in atrial fibrillation was referred for mitral valve replacement due to severe mitral regurgitation. A cardiac pacemaker had previously been implanted. Cardiac catheterization demonstrated large V waves in the wedge pressure tracing during ventricular pacing, which were not present during native conduction. A left ventriculogram demonstrated severe mitral regurgitation during ventricular pacing, but not during native conduction. This patient, in atrial fibrillation, had severe mitral regurgitation induced by ventricular pacing and not by native conduction. Pacemaker syndrome may be caused by mitral regurgitation that is probably not secondary to AV dissociation, but rather the result of dyssyn-chronous ventricular contraction.     

AV node ablation and pacemaker implantation after withdrawal of effective rate-control medications for chronic atrial fibrillation: effect on quality of life and exercise performance

We assess whether AV node ablation and pacemaker implantation after discontinuation of effective rate-control medical therapy for chronic atrial fibrillation had a positive impact on quality of life and exercise performance. To assess the possibility of a placebo effect following pacemaker implantation, the study included three groups of patients. Group 1 underwent an echocardiogram, treadmill exercise, and quality of life measurement 1 month prior to and 6 months following AV node ablation and pacemaker implantation associated with discontinuation of rate-control medications. Group 2 underwent AV node ablation and pacemaker implantation without discontinuation of antiarrhythmic rate-control drugs. Group 3 underwent pacemaker implantation without performing AV node ablation and continuing rate-control medical therapy. At the 1- and 6-month evaluation, the patients in group 1 showed a significant improvement of left ventricular ejection fraction, quality of life, and activity scores. The exercise duration and the maximal VO2 consumption, however, did not change significantly. A slight improvement of the quality of life and physical activity scores was observed in the group undergoing AV node ablation without withdrawal of medications. However, no significant changes were observed in the group receiving only the pacemaker without modification of medical therapy and with intact AV node conduction. In conclusion, in patients with chronic atrial fibrillation, discontinuation of effective rate-control medical therapy followed by AV node ablation and permanent pacing appeared to improve quality of life and activity scores despite no change in exercise duration. The improvement observed does not seem to reflect a placebo effect.     

Atrial Fibrillation Induced by Testing Magnet Applied to VVI Pacemaker

The first known case of testing magnet-induced atrial fibrillation in a patient with a VVI pacemaker is reported. A macrore-entry mechanism is postulated, involving retrograde conduction from the ventricle through the AV node to the atrium following an asynchronous pacemaker stimulus.     

Paroxysmal Atrial Fibrillation and High Degree AV Block: Use of Single-Lead VDDR Pacing with Mode Switching

Dual chamber rate responsive pacing incorporating a mode switching option is increasingly listed in patients with chronic paroxysmal atrial fibrillation and high degree AV block. Single-lead VDDR pacemakers have been rarely used for this indication. The purpose of this study was to determine thnir reliability of atrial sensing during atrial fibrillation, the percentage of at rial synchronous ventricular pacing, and the behavior of the sinus rate outside the phases of atrial fibrillation. We studied ten patients with a single-lead VDDR pacemaker implanted for this indication. Follow-up visits were performed at predischarge and after 1, 3, 6, 12. 18, and 24 months. During the mean follow-up period of 18.9 ± 6.9 months, the atrial sensing thresholds in sinus rhythm remained stable. Atrial synchronous ventricular stimulation was achieved in 68,7 ±31.2% (median 82.5%) of the whole follow-up time. All patients showed an adequate atrial rate response during sin us rhfthm. Atrial fibrillation was detected by the pacemakers in 24.0 ± 29.8% of time. In 3 of 10 patients the duration of atrial fibrillation showed a steady increase from visit to visit. The sensed amplitudes of atrial fibrillation ranged from 0.1–1.0 mV. A programmed atrial sensitivity of 0.1 mV was necessary to achieve complete sensing of atrial fibrillation. None of the patients experienced tachycardias with optimized pacemaker programming. Single-lead VDDR pacing incorporating a mode-switching option is useful in patients with high degree AV block and paroxysmal atrial fibrillation, since it provides atrial synchronous ventricular pacing in more than two-thirds of follow-up time. In a subgroup of patients, a progressive increase of the time during atrial fibrillation was demonstrated. A reliable detection of paroxysmal atrial fibrillation requires the programming of the atrial sensitivity to its most sensitive value.     

Irregular Ventricular Stimulation in the DDI Mode of a Dual Chamber Pacemaker With Atrial-Based Lower Rate Timing

This report describes two patients with atrial fibrillation in whom an implanted CHORUS DDD pacemaker programmed to the DDI mode produced an irregular ventricular stimulation rate. The lower rate timing of these devices is atrial-based only when an atrial event opens an AV interval shorter than the programmed AV delay. In the DDI mode, if Api represents the time when an atrial paced event (Ap) would have occurred if it had not been inhibited by a previous atrial sensed event (As), then Api-Vp constitutes the implied AV interval where Vp is a paced ventricular event. Although the As-Vp interval (As-Api+Api-Vp) generates an atrial refractory period during its entire duration, the pacemaker can sense an atrial event (A r ) during the implied AV interval. A r cannot start another AV delay, but it can initiate the atrial-based lower rate interval. This timing mechanism can cause irregular prolongation of Vp-Vp intervals to a value longer than the programmed lower interval with a maximal extension equal to the programmed AV delay. Such behavior of the CHORUS pacemaker should not be interpreted as malfunction.     

Rate Responsive Dual Chamber Pacing

We report about a new pacemaker, which simultaneously offers dual chamber pacing in DDD Mode and activity controlled rate response. The system also uses activity-sensing to differentiate true sinus tachycardia from ectopic atrial activity or atrial fibrillation and therefore prevents pacemaker mediated arrhythmias. The clinical experience proves appropriate functioning of all technical aspects of the device. Preliminary noninvasive hemodynamic assessments confirm improvement in cardiacjunction with AV synchronous pacing mode and demonstrate the ouporiority of rate-responsive dual chamber versus single ventricular pacing.     

Characterization of pacemaker arrhythmias due to normally functioning AV demand (DVI) pulse generators

Normally functioning DVI pulse generators with different electronic characteristics may cause complex cardiac arrhythmias that must not be interpreted as pacemaker malfunction. When there is no refractory period after the atrial output, a DVI pulse generator may deliver atrial pacemaker impulses at irregularly shortened intervals and produce an increase in the atrial pacemaker rate compared with the programmed free-running AV sequential rate. Theoretically this variation of the atrial cycle length can occur only within a well-defined range that represents the difference between the ventricular and atrial output escape intervals. In reality, the interplay of the spontaneous sinus rate, duration of AV conduction, time of sensing the ventricular electrogram in relation to the surface QRS complex, and the programmed AV sequential time all influence the atrial pacemaker rate. DVI pulse generators may also create interesting arrhythmias such as pseudopseudofusion beats (delivery of an atrial spike within the QRS complex), double pseudofusion beats, and double pacemaker impulses within the QRS complex according to the electrophysiologic circumstances and specifications of the pulse generator.     

Electrocardiograms from the turtle to the elephant that illustrate interesting physiological phenomena

This article describes a collection of ECGs from many species obtained over the past 50 years. Presented are ECGs of species in which the pacemaker is a separate contractile chamber with its own action and recovery potentials. In such species, pacemaker atrial and AV block can be produced. Shortening of the atrial refractory period and the negative inotropic effect can be produced by vagal stimulation. The cardiac electrogram and stroke volume are recorded from the turtle heart. The ECG and respiration were recorded from the snake. ECG records were obtained from the anesthetized and decapitated housefly. ECG records of the rabbit show slowing when the nose encountered irritating vapors. Records from a dog with atrial fibrillation exhibit rhythmic fibrillation frequency changes correlated with respiration. In addition, in a morphinized dog with atrial fibrillation, impulses crossed the AV node only during inspiration. The ECGs of a cow and camel exhibit long P-R intervals and biphasic P waves. Finally the elephant ECG shows a clear U wave following the T wave.     

Cardiac surgery for arrhythmias

Cardiac arrhythmia surgery was initiated in 1968 with the first successful division of an accessory AV connection for the Wolff-Parkinson-White Syndrome. Subsequent surgical procedures included the left atrial isolation procedure and the right atrial isolation procedure for automatic atrial tachycardias, discrete cryosurgery of the AV node for AV nodal reentry tachycardia, the atrial transection procedure, corridor procedure and Maze procedure for atrial fibrillation, the right ventricular disconnection procedure for arrhythmogenic right ventricular tachycardia, the encircling endocardial ventriculotomy, subendocardial resection procedure, endocardial cryoablation, the Jatene procedure, and the Dor procedure for ischemic ventricular tachycardia. Because of monumental strides in the treatment of most refractory arrhythmias by endocardial catheter techniques during the past decade, the only remaining viable surgical procedures for cardiac arrhythmias are the Maze procedure for atrial fibrillation and the Dor procedure for ischemic ventricular tachycardia. Nevertheless, the 25-30 years of intense activity in the field of cardiac arrhythmia surgery provided the essential foundation for the development of these catheter techniques and represent one of the most exciting and productive eras in the history of medicine. In one short professional career, we have witnessed the birth of arrhythmia surgery, its adolescence as an "esoteric" specialty, its prime as an enlightening yet exhausting period, and finally its waning years as a source of knowledge and wisdom on which better methods of treatment have been founded. One could hardly ask for a more rewarding experience.     

Radiofrequency Catheter Ablation and Modulation of Atrioventricular Conduction in Patients with Atrial Fibrillation

We attempted radiofrequency ablation of the AV junction with a sequential right- and left-sided approach in 78 patients affected by severely symptomatic, drug refractory atrial fibrillation. Stable third-degree A V block was obtained in 99% of cases and, after 3 months, persisted in 92% of cases. Single session, stepwise, radiofrequency modulation of the AV node was attempted in 13 patients with paroxysmal atrial fibrillation. During sinus rhythm, ablation of the slow and fast AV node pathways was performed in order to increase the nodal refractory period or to slow conduction. Clinically successful modulation of AV conduction was achieved in 15% of cases and persisted during a 3-month follow-up. In conclusion. AV junction ablation is a well-established means of treating atrial fibrillation, but implies the implant of a permanent pacemaker. AV node modulation avoids the pacemaker implant, but is efficacious only in a minority of patients. Thus, in patients affected by paroxysmal atrial fibrillation, AV modulation should be attempted first; if this is ineffective. AV ablation can be performed during the same session.     

Long-Term Follow-Up of Patients Treated By Radiofrequency Ablation of the Atrioventricular Junction

JENSEN, S.M., et al .: Long-Term Follow-Up of Patients Treated By Radiofrequency Ablation of the Atrioventricular Junction . Radiofrequency ablation of the AV conduction tissue (His-bundle ablation) is an accepted treatment for therapy resistant atrial fibrillation/flutter. However, data on the long-term effects of the procedure are limited. We followed 50 patients for a mean of 17 months after AV junction ablation. The indication was treatment resistant atrial fibrillation or flutter. The patients underwent a standardized interview performed by two nurses. Health care was studied via the in-patient register. Subjective improvement was reported by 88% and the number of days in hospital per year was reduced from 17 to 7. The use of antiarrhythmic drugs was reduced by 75%. If the reduction in costs of drugs and days in hospital is compared with the cost of the ablation and the pacemaker implantation, breaking even is achieved after 2.6 years. We could not confirm that patients with paroxysmal atrial fibrillation note less improvement than those with chronic fibrillation. Conclusion: Ablation of the AV junction is a cost effective treatment with good long-term results and relatively few complications. Recommendations: Chronic atrial fibrillation: If sinus rhythm cannot be established and in cases in which heart rate regulating drugs have been ineffective, ablation of the AV junction with implantation of a VVIR pacemaker is recommended. Paroxysmal atrial fibrillation: If the patient despite treatment with antiarrhythmic drugs continues to have symptomatic episodes of atrial fibrillation, then AV junction ablation with implantation of a permanent pacemaker is recommended. Patients who have self-limiting episodes of atrial fibrillation should be given a DDDR pacemaker with an automatic mode switch. Patients who do not have self-limiting attacks and require DC conversion, should receive a VVIR pacemaker     

Reduction of right ventricular pacing in patients with sinus node dysfunction through programming a long atrioventricular delay along with the DDIR mode

Background  

Right ventricular (RV) pacing increases the incidence of atrial fibrillation (AF) and hospitalization rate for heart failure. Many patients with sinus node dysfunction (SND) are implanted with a DDDR pacemaker to ensure the treatment of slowly conducted atrial fibrillation and atrioventricular (AV) block. Many pacemakers are never reprogrammed after implantation. This study aims to evaluate the effectiveness of programming DDIR with a long AV delay in patients with SND and preserved AV conduction as a possible strategy to reduce RV pacing in comparison with a nominal DDDR setting including an AV search hysteresis.     

Effects on Cardiac Performance of Atrioventricular Node Catheter Ablation Using Radiofrequency Current for Drug-Refractory Atrial Arrhythmias

Patients with atrial fibrillation or atrial flutter (AF) are candidates for radiofrequency (RF) catheter ablation of the atrioventricular (AV) node with the aim being to control heart rate. As patients wilh AF can have markedly impaired ventricular function, information concerning the hemodynamic effects of AV node ablation using RF current would be valuable. Fourteen consecutive patients (mean age 65 ± 3 years) with drug-resistant AF underwent AV node catheter ablation with RF current and had permanent pacemaker implantation. The mean left ventricular ejection fraction (FFJ by two-dimensional echoeardiography immediately before ablation was 42 ± 3% (range 14%–54%) and their mean exercise time was 4.4 ± 0.4 minutes. Complete AV block was achieved in all 14 patients with 6 ± 2 RF applications (range 1–18). There was no evidence of any acute cardiodepressant effect associated with delivery of RF current, and EF 3 days after ablation was 44 ± 4%. By 6 weeks after ablation, the left ventricular EF was significantly improved compared to baseline (47 ± 4% postablation vs 42 ± 3% preahlation; P < 0.05), and this modest increase in EF was accompanied by an improvement in exercise time (5.4 ± 0.4 min). In conclusion, delivery of RF current for AV node catheter ablation in patients with AF and reduced ventricular function is not associated with any acute cardiodepressant effect. On the contrary, improved control of rapid heart rate following successful AV node ablation is associated with a modest and progressive improvement in cardiac performance.     

Automatic Tachycardia Recognition

A microcomputer algorithm for tachycardia identification, suitable for use in un implanted antitachycardia pacemaker, is described. The system employs an atrial and ventricular electrogram, detects a sustained fast rate in either chamber, and awakens the main program to perform detailed analysis of the tachycardia and its immediately preceding beats. The algorithm distinguishes atrial, ventricular, and AV nodal and re-entrant tachycardia from high rates due to sinus tachycardia. For testing of the program, we used a data base of twenty-two tape-recorded and documented arrhythmias provoked during electrophysiologic studies in which atrial and ventricular bipolar electrodes were in place; twenty-one of twenty-two wave successfully detected. These included atrial fibrillation, atrial flutter, atrial tachycardia, AV nodal re-entrant tachycardia, AV re-entrant tachycardia using an accessory pathway, and ventricular tachycardia with and without ventriculo-atrial conduction.     

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

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

Radiofrequency Modification of Atrioventricular Conduction by Selective Ablation of the Low Posterior Septal Right Atrium in a Patient with Atrial Fibrillation and a Rapid Ventricular Response

A case is presented of a 58-year-old woman with atrial fibrillation and uncontrolled ventricular responses up to 180 beats/min despite therapy with digoxin. Radiofrequency energy was applied to the low posteroseptai right atrium in an attempt to modify "slow fiber" conduction. This resulted in a decrease in ventricular rate from 125 to 50 beats/min. Follow-up Holter monitor demonstrated an average heart rate of 64 beats/min (range 43–112). On exercise tolerance test, the maximum heart rate was 126. Modification of the low posterosepta right atrium may prove to be an alternative to AV node or His bundle ablation and pacemaker implantation in patients with poorly controlled atrial fibrillation and rapid ventricular response. The mechanism by which this approach was effective may be ablation of slow conducting AV nodal fibers with a short refractory period.