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.     

Pacemaker Syndrome with AAI Rate Variable Pacing: Importance of Atrioventricular Conduction Properties, Medication, and Pacemaker Programmability

A patient who received an AAI Activitrax rate variable pacemaker for treatment of symptomatic sinus bradycardia is described. disopyramide prolonged the anterograde effective refractory period of the fast conducting atrioventricular (AV) nodal pathway to such an extent, that conduction switched to the slow AV nodal pathway at low atrial pacing rates. This gave rise to symptoms of the pacemaker syndrome during moderate exercise because the paced atrial event was conducted with a long, spike to Q interval with occurrence of the paced atrial event just after the preceding QRS complex. A change of medication solved this problem. Programming a bipolar electrode configuration avoided sensing of far-field QRS signals with the associated problems of resetting the basic pacing interval as well as the upper rate interval. AAI rate variable pacing requires careful evaluation of AV conduction properties, AV conduction intervals as well as the influence of medication to be given. The use of multiprogrammable pacemakers with marker channel capability will significantly facilitate the understanding and resolution of anomalous behavior.     

Apparent P Wave Underselling in a DDD Pacemaker Post Exercise

Wencke-bach behavior of DDD pacemakers occurring when the P-P interval varies between the programmed upper rate interval and the total atrial refractory period is symmetrical in a sense that the pacemaker response during atrial rate acceleration is similar to the pacemaker response during atrial rate deceleration. This phenomenon can be observed in all patients with persistent AV block in whom a DDD pacemaker is implanted, during exercise testing when the spontaneous atrial rate exceeds the selected upper rate, i.e., the programmed upper rate interval. However, this phenomenon will not be observed in all patients with intermittent intact AV conduction during exercise. In this case report we describe a patient who showed an asymmetrical response during a bicycle exercise test. There was 1:1 atrial sensing ventricular pacing until the atrial rate exceeded the upper rate of 140 ppm, while atrial sensing was restored during recovery when the conducted sinus rhythm had decreased to 105 beats/min.     

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

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

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.     

Undesirable Mode Switching with a Dual Chamher Rate Responsive Pacemaker

The Telectronics 1250 Meta MV DDDR pacemaker is a new device featuring automatic mode switching from DDDH to VVIR pacing in the event of an atrial arrhythmia. Although mode switching is a valuable feature, sinus tachycardia can cause an undesirable mode switch to occur. Of 24 implants at this institution, 11 have been for an AV conduction disorder. Eight of these 11 patients were specificalJy evaiuated for undesirable mode switching. During exercise testing and/or Holter monitoring, mode switching was repeatediy seen in seven of the eight at low levels of exercise. Factors precipitating mode switching were a low rate response factor, low upper rate setting, long base postventricular atrial refractory period (PVARP) and a long AV delay. During Holter monitoring, patients spent up to 50% of the time in VVIR pacing as opposed to DDDR pacing. It is concluded that patients with intact sinus node function are at risk of undesirable mode switching and should probably be programmed to the DDD mode unless there is a specific indication for DDDR pacing. If the DDDR mode is chosen, careful selection of the aforementioned pacing parameters is required.     

Limitations to Activation of the Antitachycardia Burst Pacing Function of the Symbios 7008 Pacemaker in the Universal (DDD) Mode

The Symbios 7008 antitachycardia pacemaker was implanted in five patients for control of supraventricular tachycardia. Shortly after implantation in the first two patients, it was noted that the burst pacing sequence was not automatically activated by tachycardia when the pacemaker was in the DDD mode. Data from these two and the subsequent three patients were evaluated to explain this observation. The problem was primarily related to the operation of the device during the postventricular atrial refractory period. In all patients, the atrial electrogram encroached upon the programmed postventricular atrial refractory period because VA conduction during SVT was less than the lowest programmable interval (155 ms). Atrial events occurring during this interval will not trigger the tachycardia termination sequence. In all five patients, the size of the atrial electrogram decreased substantially (48 +/- 10%; mean +/- SD) during supraventricular tachycardia compared to sinus rhythm. In at least two of the five patients, decreased atrial size during supraventricular tachycardia may also have resulted in intermittent failure of atrial sensing during tachycardia, even at the most sensitive setting (0.6 mV). The latter may remain a problem even if the technical fault in SVT detection in the DDD mode were corrected. Two related problems were noted in the DDD mode: ventricular events during rapid SVT do not reset the low rate interval, resulting in random low rate pacing; and, automatic prolongation of atrial refractory period by two successive ventricular events without an intervening atrial sensed event compounds problems of atrial sensing. All of these problems were easily circumvented in all patients by noninvasive reprogramming to the DVI mode in which supraventricular tachycardia detection is based on ventricular sensing. These findings have implications for the future design of such devices.     

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.     

True Incidence of Pacemaker Syndrome

HELDMAN, D., ET AL.: True Incidence of Pacemaker Syndrome. Although the purported incidence of pacemaker syndrome according to the literature is only 5%–15%, this is based on a series of patients with VVI pacing. Increasing numbers of studies are being reported in which patients prefer the dual chamber mode despite little benefit being demonstrated on objective testing, suggesting that pacemaker syndrome may be more common than is generally reported. This study was designed to evaluate the reported symptoms in a series of patients programmed to both the VVI and one or more dual chamber modes. Forty unselected patients with dual chamber pacemakers were entered into a blind, randomized trial comparing the symptoms associated with VVI pacing to those associated with dual chamber pacing. Patients were randomized to either WI or dual chamber pacing. At the end of 1 week, questionnaires rating 16 different symptoms were completed. Blood pressure, LV function, presence of ventriculoatrial conduction, and ability to override the pacemaker were evaluated. The pacemaker was then programmed to the other mode. Overall, 12 of 16 symptoms were significantly worse in the VVI as compared to dual chamber mode. The most highly significant (p < 0.005) were shortness of breath, dizziness, fatigue, pulsations in the neck or abdomen, cough, and apprehension. Pacemaker syndrome was clinically recognized in 83% of patients paced in the WI mode with 65% of patients experiencing moderate to severe symptoms. There were no readily identified clinical, hemodynamic, or electrophysiological parameters that predicted which patients would develop pacemaker syndrome. Thus, when patients have an opportunity to experience both pacing modes in close proximity to one another, there is a high incidence of pacemaker syndrome in the VVI mode.     

Use of a New Fallback Function to Prevent Endless-Loop Tachycardias: First Clinical Results

The methods used for preventing endless-loop tachycardias (ELTs) most often consist of initiating a long postventricular atrial refractory period (PVARP) with the sensing of every event likely to induce ELTs, such as sensed premature ventricular contractions (PVCs). A new fallback function may be useful to prevent the initiation of ELTs. A window of atrial rate acceleration detection (WARAD) is initiated with the sensing of every sinus event and equals 75% of the preceding PP interval. If an atrial event is sensed during this period, as are premature atrial contractions (PACs), no atrioventricular (AV) delay is initiated, but an atrial puise output is delivered and a subsequent 31-msec AV delay is started. Theoretically retrograde P waves are premature compared to sinus rhythm. They are therefore detected as PACs, and do not initiate AV delay, thus prohibiting the induction of ELTs. This function was tested in six patients, using external or implanted Chorus 2 pacemakers. Short PVARP (203 msec) and high atrial sensibility were programmed. Retrograde conduction was induced either by inefficient atrial pacing or a long programmed AV delay. Two different dual chamber settings were tested: dual chamber pacing with the fallback function On or Off. In every situation, the function proved effective in preventing ELTs: the number of tachycardia episodes went from 124 with the function programmed Off to 5 with the function programmed On for comparable durations. More than 75 ELTs effectively prevented by fallback have been recorded.     

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.     

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.     

Pacemaker Syndrome Induced by the Mode Switching Algorithm of a DDDR Pacemaker

A patient with marked first-degree AV block and a DDDR pacemaker presented with a history of paroxysmal narrow QRS tachycardia, subsequently identified as sinus tachycardia (with a very long PR interval), causing a clinical problem similar to pacemaker syndrome because of loss of AV synchrony. The latter resulted from an excessively long postventricular atrial refractory period (PVARP) that prevented sensing of sinus P waves. The unfavorable hemodynamics caused reflex sinus tachycardia. The long PVARP was mandated by the mode switching algorithm of this particular device and was automatically set according to the selected tachycardia detection rate. The patient became asymptomatic when the mode switching function was turned off and the PVARP shortened.     

Sustained inhibition of a DDD pacemaker at rates below the programmed lower rate during automatic PVARP extension

A patient with a Pacesetter Paragon III DDD pacemaker exhibited sustained pacemaker inhibition at rates below the programmed lower rate during sinus rhythm with marked first degree AV block. In this device, a pacemaker defined ventricular extrasystole initiates automatic extension of the postventricular atrial refractory period to 480 ms and the atrial escape interval to 830 ms regardless of the programmed lower rate. Sustained pacemaker inhibition at rates below the programmed lower rate occurred because the P wave fell continually in the extended postventricular atrial refractory period, and the conducted QRS complex initiated a pacemaker ventricular extrasystole response with atrial escape interval extension. This process continued as long as the P wave stayed within the extended postventricular atrial refractory period, no ventricular extrasystole disrupted the sequence, and the R-R interval of spontaneous beats was shorter than the extended atrial escape interval. Such a pacemaker response should not be misinterpreted as device malfunction.     

Pacemaker Syndrome Evaluated by Cardiopulmonary Exercise Testing

Two patients who presented with dyspnea on effort, persisting after insertion of a fixed rate ventricular demand pacemaker (VVI) for sick sinus syndrome, were evaluated by cardiopulmonary exercise testing. During VVI pacing a heightened ventilatory response to exercise and a fluctuation of ventilation occurred. The high ventilatory equivalent for CO2 throughout exercise with VVI pacing suggests that the patients had ventilation-perfusion mismatching due to an increase in the pulmonary capillary wedge pressure caused by 1:1 ventriculoatrial conduction. Rate responsive ventricular (VVIR) pacing associated with intact 1:1 ventriculoatrial conduction exaggerated the exertional dyspnea, while rate responsive atrial (AAIR) pacing improved the ventilatory response to exercise. We suggest that a heightened ventilatory response to exercise due to ventilation-perfusion mismatching may be an important factor causing the pacemaker syndrome, and that cardiopulmonary exercise testing is useful in identifying the exercise-induced symptoms with ventricular pacing.     

Course of Symptoms and Spontaneous ECG in Pacemaker Patients: A 5-Year Follow-up Study

We investigated the course of symptoms and the spontaneous ECG retrospectively in 308 patients who had received a pacemaker because of atrioventricular (AV) block (n = 115), sick sinus syndrome (SSS, n = 107), bradyarrhythmic atrial fibrillation (bradyarrhythmia, n = 51), carotid sinus syndrome (CSS, n = 16), complete bifascicular block associated with 1st degree AV block (n = 13) and with other indications (n = 6). The mean implantation time was 63 months. The clinical state of 93% of all patients improved after pacemaker implantation; their symptoms decreased markedly. Persisting syncopy in some patients with SSS, however, supports a restricted implantation policy. We rarely saw improved AV conduction in patients with AV block (11%). Furthermore, in patients with SSS, atrial fibrillation occurred significantly more often (35%) than in those with AV block (17%; P less than 0.01). Only 3% of patients with SSS developed 2nd and 3rd degree AV block within the observation period. In all patients with initial bifascicular block and additional 1st degree AV block, pacing prevented further syncopal attacks; four of them showed 3rd degree AV block at control, indicating that pacemaker implantation is mandatory in symptomatic patients with bifascicular disease and 1st degree AV block.     

Pacemaker Mediated Tachycardia as a Complication of the Autointrinsic Conduction Search Function

The autointrinsic conduction search (AICS) option, featured on some DDD pacemakers, performs periodic assessments of atrioventricular (AV) conduction capability during a single beat AV delay extension. Demonstration of ventricular conduction during the prolonged AV delay, permits ongoing AV delay extension if the patient's intrinsic conduction is preferred to ventricular pacing. A case is presented where the wide separation of atrial and ventricular pacing during the conduction search permitted retrograde ventriculoatrial conduction, precipitating pacemaker mediated tachycardia (PMT) on seven occasions in one patient. Two onset patterns are reported, both attributable to the AICS option. Recommendations for prevention strategies are made. (PACE 2004; 27[Pt. I]:824–826)     

Clinical Experience with a New Multiprogrammable Dual Chamber Pacemaker

We evaluated the clinical performance of a new dual chamber pacemaker, ELA Chorus(tm), in 35 patients. This device incorporates linear rate adaptive AV delay (AVDR), rate smoothing, fallback, impedance telemetry, pacemaker mediated tachycardia (PMT) recognition and reprogramming software, intracardiac electrogram displays, aufothreshold testing, diagnostic data, battery depletion curves, and laptop computer programming. Mean patient age was 68 years; 18 patients had AV block, six had sinus node dysfunction (one with AV block), nine had carotid sinus hypersensitivity (three with AV block), and two had vagally mediated syncope. At hospital discharge, programming was DDD with a mean low rate of 60 (50–70) beats/min, mean high rate of 126 (120–154) beats/mm; AVDR was ON in 21 patients, rate smoothing ON in six patients, fallback ON in six patients, and PMT reprogramming algorithm ON in 27 patients, Pacemaker follow-up involved 500 clinic visits over 14.3 months (1–36). Three patients developed atrial fibrillation, reprogrammed to DDI mode (two patients) or fallback (one patient). Fallback was used 617 times. PMT occurred 427 times in six patients; the PMT algorithm reprogrammed AV delay and postventricular atrial refractory period (PVARPJ automatically, a function unique to the Chorus(tm). Intracardiac electrograms and autothreshold testing improved follow-up efficiency. This new dual chamber pacemaker enhances programming flexibility and improves diagnostic accuracy at follow-up.     

Pacemaker Electrocardiography of Rate Smoothing During DDD Pacing

A rate smoothing option is available in a new bipolar AV universal (DDD) pacemaker. In three patients, two with intact retrograde conduction and one with retrograde block, rate smoothing values of 3% and 6% were programmed. Irregular pacemaker-mediated tachycardia occurred in one patient and AV synchrony was temporarily lost in the other two patients. In this report, we describe the pacemaker electrocardiography of rate smoothing during DDD pacing.