The "Automatic Mode Switch" Function in Successive Generations of Minute Ventilation Sensing Dual Chamber Rate Responsive Pacemakers

Automatic mode switch (AMS) from DDDR to VVIR pacing is a new algorithm, in response to paroxysmal atrial tachyarrhythmias. With the 5603 Programmer, the AMS in the Meta DDDR 1250 and 1250H (Telectronics Pacings Systems, Inc.) operates when VA is shorter than the adaptable PVARP. With the 9600 Programmer, an atrial protection interval can be defined after the PVARP. The latest generation, Meta DDDR 1254, initiates AMS when 5 or 11 heart cycles are > 150, 175, or 200 beats/min. From 1990 to 1993, 61 patients, mean age 61 years, received a Meta DDDR: in 24 a 1250, in 12 a 1250H and in the remaining 25 a 1254 model. Indication for pacing was heart block in 39, sick sinus syndrome in 15, the combination in 6, and hypertrophic obstructive cardiomyopathy in 1. Paroxysmal atrial tachyarrhythmias were present in 43. All patients had routine pacemaker surveillance, including 52 Holter recordings. In 32 patients, periods of atrial tachyarrhythmias were observed, with proper AMS to VVIR, except during short periods of 2:1 block for atrial flutter in 4. In two others, undersensing of the atrial arrhythmia disturbed correct AMS. With the 1250 and 1250H model, AMS was observed on several occasions during sinus rate accelerations in ten patients. This was never seen with the 1254 devices. Final programmation was VVIR in 2 (chronic atrial fibrillation), AAI in 1 (fracture of the ventricular lead), VDDR in 1 (atrial pacing during atrial fibrillation), DDD in 5, and DDDR in 53, 48 of whom had AMS programmed on. The AMS detection algorithm in the successive models of the Meta DDDR appears to have become more specfic.     

Atrial Arrhythmia Management with Sensor Controlled Atrial Refractory Period and Automatic Mode Switching in Patients with Minute Ventilation Sensing Dual Chamber Rate Adaptive Pacemakers

Although a long postventricular atrial refractory period fPVARP) may prevent the occurrence of pacemaker mediated tachycardias and inadvertent tracking of atrial arrhythmias in dual chamber (DDD) pacing, the maximum upper rate will necessarily be compromised. We tested the feasibility of using minute ventilation sensing in a dual chamber rate adaptive pacemaker (DDDR) to shorten the PVARP during exercise in 13 patients with bradycardias (resting PVARP = 463 ± 29 msec) to avoid premature upper rate behavior. Graded treadmill exercise tests in the DDD and DDDR modes at this PVARP resulted in maximum ventricular rates of 98 ± 8 and 142 ± 3 beats/min, respectively (P < 0.0001), due to chronotropic incompetence and upper rate limitation in the DDD mode, both circumvened with the use of sensor. In order to simulate atrial arrhythmias, chest wall stimulation was applied for 30 seconds at a rate of 250 beats/min at a mean unipolar atrial sensitivity of 0.82 mV. Irregular ventricular responses occurred in the DDD mode fthe rates at a PVARP of 280 and 463 ± 29 msec were, respectively 92 ± 5 and 66 ± 3 msec; P < 0.0001). In the DDDR mode at a PVARP of 463 ± 29 msec, regular ventricular pacing at 53 ± 2 beats/min occurred due to mode switching to VVIR mode in the presence of repetitive sensed atrial events within the PVARP. One patient developed spontaneous atrial fibrillation on follow-up, which was correctly identified by the pacemaker algorithm, resulting in mode switch from DDDR to regular VVIR pacing and preservation of rate response. In conclusion, sensor controlled PVARP allows a long PVARP to be used at rest without limiting the maximum rate during exercise. In addition, to offer protection against retrograde conduction, a long PVARP and mode switching also limit the rate during atrial arrhythmias and allow regular ventricular rate responses according to the physiological demands.     

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.     

DDIR Versus VVIR Pacing in Patients with Paroxysmal Atrial Tachyarrhythmias

Patients with sinus node dysfunction (SND) in particular those with tachycardia-bradycardia syndrome and patients undergoing atrioventricular nodal ablation procedures for refractory paroxysmal atrial tachyarrhythmias (PAT), are candidates for single chamber (VVIR mode) or dual chamber rate responsive (DDIR mode) systems. To evaluate the benefits and disadvantages of each pacing mode we retrospectively analyzed 33 patients with a history of frequent PAT who received a VVIR (22 patients); or a DDDR pacemaker (11 patients) programmed to the DDIR mode. The mean follow-up time was 25 and 18 months, respectively. Preimplant left atrial diameter was significantly smaller in the DDIR group. Chronic atrial fibrillation developed in 54% of the VVIR patients and 27% of the DDIR group, but this difference was not significant. Complications of patients with VVIR pacemakers included new mitral and tricuspid insufficiency, stroke, pacemaker inlolerance and aggravated congestive heart failure. Patients with DDIR pacemakers had a lower incidence of symptoms and complications. However, this group received more antiarrhythmic medication, required a closer follow-up, and their pacemakers needed frequent reprogramming. Our findings suggest that VVIR is a poor choice for patients with SND, congestive heart failure, and PAT, and that DDIR may be an acceptable alternative.     

Variability of Left Atrial Bloodflow Predicts Intolerance of Ventricular Demand Pacing and May Cause Pacemaker Syndrome

Variability of left and right atrial and left ventncular bloodflow was studied using transthoracic and transesophageal Doppler echocardiography and related to pacemaker mode preference during everyday activity. Bloodflow variability was less at all sites during dual chamber pacing compared to single chamber pacing. However, in patients suffering from pacemaker syndrome and whom prefer DDDR pacing, significantly increased variability of left atrial antegrade (but not retrograde) bloodflow during VVIR pacing compared to DDDR pacing was noted, which was not evident in patients tolerating VVIR mode pacing. This effect was not detected at any other site and suggests that adverse left atrial hemodynamics may result in intolerence to VVI/R mode pacing and might cause pacemaker syndrome.     

Predictors and clinical impact of atrial fibrillation after pacemaker implantation in elderly patients treated with dual chamber versus ventricular pacing

The Pacemaker Selection in the Elderly (PASE) trial was a prospective, multicenter, single blind, randomized comparison of single chamber, rate adaptive, ventricular pacing (VVIR) with dual chamber, rate adaptive pacing (DDDR) in 407 patients aged > or =65 years(mean 76 +/- 7 years, 60% male)with standard bradycardia indications for dual chamber pacemaker implantation. The incidence, predictors, and clinical consequences of atrial fibrillation (AF) developing after pacemaker implantation in the PASE trial were studied prospectively. During a median follow-up of 18 months, AF developed in 73 (18%) patients. Kaplan-Meier estimated cumulative incidences of AF in patients with sinus node dysfunction (n=176) at 18 months were 28% in the VVIR and 16% in the DDDR groups (P=0.08). After adjustment for other clinical variables using a Cox multivariate regression model, randomization to VVIR compared with DDDR pacing mode among patients with sinus node dysfunction was independently associated with a 2.6-fold increased relative risk (RR) of developing AF after pacemaker implantation (P=0.01). Other independent clinical risk factors for development of postimplant AF included a preimplant history of hypertension (P=0.02) or supraventricular tachyarrhythmias(P<0.04). Patients who developed AF had similar health related quality of life scores and cardiovascular functional status after 18 months of pacing as patients who remained free of AF. The RR of death, stroke, or heart failure hospitalization was not increased in patients who developed AF. Thus, in the elderly patients with sinus node dysfunction requiring permanent pacing, DDDR pacing mode protected against the development of AF. However, development of AF after pacemaker implantation in this population was not associated with a significant impact on quality-of-life, functional status, or other clinical endpoints during 18 months of follow-up.     

Incidence of Atrial Fibrillation in Patients with Different Mode of Pacing. Long-term Follow-up

We evaluated the incidence of atrial fibrillation in 189 patients (92males, 97females, mean age 75 ± 12yrs, range 41–100yrs) with pacemaker, during a mean follow-up of 5.5yrs (range 1–24yrs). The indications for implant were: complete AV block (115pts), second degree Möbilz 2 AV block (51pts). bifascicular block (5pts). sick sinus syndrome (14pts), symptomatic bradycardia (4pts). The mode of stimulation considered were VVI (105pt), VVI rate responsive (21pts), single lead VDD (43pts), DDD (20pts). The occurrence of retrograde VA conduction in patients with VVI or VVI rate responsive pacing was also evaluated. Atrial fibrillation occurred in 40 pts (21%). The highest incidence was evidenced in patients with sick sinus syndrome (9pts, 64%), and in patients with VVI stimulation (28pts, 27%). On the contrary, the lowest incidence was found in single lead VDD stimulation (4pts, 9%). The patients with dual chamber pacing showed a relatively high incidence of the arrhythmia (5pts, 25%). Atrial fibrillation occurred in 9 out of 32 patients with retrograde VA conduction, and in 22 out of 94 patients without retrograde conduction (28% versus 23%, p=NS). In conclusion, it is confirmed that patients with sick sinus syndrome are at high risk for atrial fibrillation. Single lead VDD stimulation seems to be the better mode of pacing in preventing atrial fibrillation, while dual chamber pacing showed minor efficacy. The presence of retrograde VA conduction could not predict the occurrence of the arrhythmia.     

Early Clinical Experience with a Minute Ventilation Sensor DDDR Pacemaker

The new DDDR pacemaker META DDDR utilizes a minute veritilation sensor based on transthoracic impedance measurements. The sensor determines the metabolic indicated interval, the atrioventricular (AV) delay and the postventricular atrial refractory period (PVARP). The baseline PVARP must be carefully selected to define nonphysiological tachycardias. If a Pwave falls within the PVARP the pacemaker will automatically switch to the VVIR mode. This behavior prevents tracking of paroxysmal atrial tachyarrhythmias (PAT). Twenty-eight patients with sinus node dysfunction (n = 20), AV junction ablation (n = 5), complete or intermittent AV block (n = 3); who received a META DDDR pacemaker were studied. The mean age was 65 ± 13 years. Results: mode switching (reversion) to VVIR was observed in 57% of the patients. Forty-two percent had episodes of mode switching to VVIR during a stress test four related to PAT, and seven to sinus tachycardia. Fifty percent had episodes of mode switching to VVIR during a 24-hour Holter, four related to PAT, three to retrograde P wave sensing, and two to sinus tachycardia. At the last follow-up, 20 of the 26 patients initially programmed to the DDDR mode remained in the DDDR mode, while five were reprogrammed to the DDD and one to the VVIR mode. Mode switching has a high sensitivity but a low specificity for PAT. It appears to be a useful approach to prevent rapid tracking of atrial tachyarrhythmias. Careful PVARP programming is critical to appropriate reversion behavior, but further modifications of the algorithm are needed to improve its performance.     

Initial Experience with a New Algorithm for Automatic Mode Switching from DDDR to DDIR Mode

Implantation of dual chamber devices in patients with paroxysmal atrial tachyarrhythmias who require permanent pacemakers may lead to significant complications due to an inappropriately triggered ventricular response. VVI/VVIR units cause loss of AV synchrony in the presence of sinus activity. A new DDDR device (THERA DR, model 7940), with an automatic mode switching (AMS) algorithm, was evaluated. When the mean atrial rate is > 182 beats/min, atrial tachyarrhythmia is detected, and AMS is activated. Twenty-three patients (12 males, mean age 71 ± 7 years) underwent implantation of a THERA DDDR device with the AMS algorithm. Seventeen patients had AV block and/ or sick sinus syndrome (SSS) and atrial arrhythmias, and 6 patients (2 with hypertrophic obstructive cardiomyopathy) had SSS and paroxysmal atrial fibrillation (PAF). The follow-up period was from 1–9 months. During follow-up, Holter monitoring and treadmill tests were performed. Results : Eighty-seven episodes of AMS were recorded. Telemetered AMS recordings demonstrated episodes in which the DDDR mode switched to the DDIR mode in the presence of PAF, and reverted to DDDR when sinus rhythm returned. Paroxysmal supraventricuiar arrhythmias with a heart rate < 182 beats/min did not activate tbe mode switch. Conclusions : This early, short-term clinical experience with a DDDR device capable of AMS from DDDR to DDIR demonstrated appropriate clinical function and response to PAF. These preliminary results suggest that DDDR pacemakers with AMS to DDIR may significantly extend the current indications for dual chamber pacing.     

Quality-of-Life During DDD and Dual Sensor VVIR Pacing

Twenty-one patients (mean age 68 ± 8 years) with dual-sensor (QT + activity) DDDR pacemaker were randomly assigned to a crossover, double-blind study in order to evaluate their quality-of-life scores. All pacemakers were implanted for sick sinus syndrome (8 patients) or complete heart block (13 patients). The pacemakers were randomly programmed to VVIR or DDD pacing modes for 2-week periods and then the pacing mode was switched for another 2-week period. At the end of each period, the quality-of-life was evaluated by a questionnaire with regard to cardiovascular symptoms, physical activity, psychosocial and emotional functioning, and self-perceived health. Nineteen questions were scored 0–5 points each. Significant improvement in the mean total quality-of-life score (20.5 ± 14.9 vs 34.8 ± 17.4) as well as in dyspnea on effort, dizzy spells, palpitation, sweating, fatigue, lethargy, emotional functioning, and self-perceived health was observed during DDD compared to VVIR pacing. No question was scored in favor of VVIR pacing mode. Significant improvements during DDD pacing was demonstrated in all subgroups of patients (sick sinus syndrome, chronotropically competent and incompetent patients, and patients with high degree AV block). Eighteen patients preferred DDD pacing mode, while only one preferred WIR pacing mode. Two remaining patients expressed no preference. The results suggest that DDD pacing offers better quality-of-life than dual sensor VVIR pacing in all subgroups of patients commonly indicated for pacemaker implantation.     

Pacemaker Upgrade for Recurrent Pacemaker Syndrome Using a Redundant Contralateral Electrode in a Patient with Bilateral Venous Stenoses

Following His-bundle ablation and VVIR pacemaker implantation, severe pacemaker syndrome developed and was treated with DDDR pacing, in a 70-year-old woman. Due to bilateral subclavian vein stenoses, DDDR pacing could not be maintained and an unusual method of restoring atrioventricular synchrony is described using the contraiateral redundant atrial electrode connected to the ipsilateral dual chamber pacemaker and ventricular electrode.     

The Use of Implantable Sensors for the Control of Pacemaker Mediated Tachycardias: A Comparative Evaluation Between Minute Ventilation Sensing and Acceleration Sensing Dual Chamber Rate Adaptive Pacemakers

The role of implantable sensors to control pacemaker mediated tachycardias was investigated in 16 patients with two different dual chamber rate adaptive (DDDR) pacemakers, which sensed eiter minute ventilation (DDDR-Meta, nine patients) or body acceleration (Relay, seven patients). Successive atrial sensed events beyond a programmable rate occurring in the absence of detection of exercise by the sensors were considered to represent retrograde conduction or atrial arrhythmias, and the pacemakers responded by either a mode shift from DDDR to ventricular rate adaptive (VVIR) pacing (DDDR-Meta) or by tracking at an interim rate, the so-called conditional ventricular tracking limit (CVTL, Relay). In the unipolar atrial sensing mode, myopotential sensing (MPI) and external chest wall stimulations (CWS) at 250 beats/min were induced to be preferentially sensed by the atrial channel to simulate the conditions of atrial arrhythmias. In the DDD mode, these maneuvers resulted in ventricular responses of 88 +/- 3 beats/min and 110 +/- 3 beats/min for MPI and CWS, respectively. The pacing rate was significantly reduced in the DDDR mode with the sensors correctly detecting and responding to the sensed abnormal atrial signals (68 +/- 5 beats/min during MPI and 71 +/- 5 beats/min during CWS, P less than 0.005 compared with the corresponding DDD rate). One patient with a Relay pacemaker developed spontaneous atrial flutter and the ventricular tracking responses were 140 and 85 beats/min in the DDD and DDDR pacing modes, respectively. Thus MPI and CWS are useful bedside testing methods to assess pacemaker response during atrial arrhythmias. The use of implantable sensors to judge the appropriateness of atrial rate is a new approach to the management of pacemaker mediated tachycardias.     

Pacemaker Upgrade for Recurrent Pacemaker Syndrome Using a Redundant Contralateral Electrode in a Patient with Bilateral Venous Stenoses

Following His-bundle ablation and VVIR pacemaker implantation, severe Pacemaker syndrome developed and was treated with DDDR pacing in a 70-year-old woman. Due to bilateral subclavian vein stenosis, DDDR pacing could not be maintained and an unusual method of restoring atrioventricular synchrony is described using the contralateral redundant atrial electrode connected to the ipsilateral dual chamber pacemaker and ventricular electrode.     

Long-Term Survival of Chosen Atrial-Based Pacing Modalities

Atrial-based cardiac pacing modalities were chosen in 341 of 684 (50%) patients selected for permanent cardiac pacing at the Grey Nuns Community Health Center between 1989 and 1995. There were 183 males and 158 females. Mean age was 70 years (range 8–97 years). The indications for atrial-based pacing were: advanced atri- oventricular (AV) block (n = 166) 49%; sick sinus syndrome (n = 153) 45%; hypersensitive carotid sinus syndrome (n = 11) 3%; neurocardiac syncope (n = 10) 2.9%; and hypertrophic cardiomyopathy (n = 1) 0.3%. Forty-eight patients had a known history of paroxysmal atrial arrhythmias. All patients had routine follow-up performed at 24 hours, 7 days, 6 weeks, 3 months, and then 6 biannuallv. Mean follow-up was 6.5 years (range 1 month to 12 years). Observed survival of the programmed atrial-based modality was compared to the original mode chosen at the time of implantation. Thirty-five of 37 (95%) chosen for AAIR modes remain programmed AAIR. Twenty-two of 24 (92%) chosen for VDDR modes remain programmed VDDR. Two hundred and fifty-five of 280 (91 %) chosen for DDD or DDDR modes remain programmed DDDR. Two of 37 (5%) patients originally implanted with AAI pacing systems were upgraded to DDDR mode due to new onset AV block. One of 24 (4%) patients originally implanted with a VDDR pacing system was upgraded to DDDR due to loss of atrial sensing of the single pass lead. Twenty-six of 304 (8.5%) patients originally implanted with DDD/DDDR (n - 25) and VDDR (n = 1) pacing systems were reprogrammed to VVI or WIR: 16 (62%) due to sustained refractory atrial arrhythmias; 5 (19%) due to atrial lead malfunction; and 5 (19%) due to reasons unrelated to the pacing system. With careful review of the patients' conduction disorder and appropriate selection of pacing modality, the observed survival of long-term atrial-based pacing remains at 92% when compared to the chosen modality at the time of implantation. Atrial-based pacing may be used to reduce the incidence of atrial dysrhythmia with careful programming of the base atrial pacing rates.     

Atrioventricular and Ventriculo-Atrial Conduction in Patients with Symptomatic Sinus Node Dysfunction

In 14 patients with symptomatic sinus node dysfunction—sinus bradycardia, sino-atrial exit block, or sinus arrest—electrophysiological studies were performed before implantation of a pacemaker. In 8 patients incremented high right atrial pacing showed AV-nodal Wenckebach at pacing rates equal to or above 130/min (group I); in 6 patients AV-nodal Wenckebach was reached at pacing rates Jess than 130/min (group II). During ventricular pacing at a rate 10–15% faster than the existing sinus rate, ventriculo-atrial (VA) conduction was present in all patients of group I, while VA conduction was present in only 2 patients of group II (p < 0.05). Patients with symptomatic sinus node dysfunction but with intact AV conduction frequency show VA conduction during ventricular pacing and thus are particularly at risk for developing a pacemaker syndrome when a ventricular demand (VVI) pacemaker is implanted. This complication can be avoided by atrial demand (AAI) pacing or A V sequential (DVI) pacing. When adequate experience has been gathered with A V universel (DDD) pacemakers, the indications for selection of a pacemaker in patients with symptomatic sinus node dysfunction will probably change.     

Sinus and paced P wave duration and dispersion as predictors of atrial fibrillation after pacemaker implantation in patients with isolated sick sinus syndrome

The aim of this study was to prospectively evaluate the sinus and the paced P wave duration and dispersion as predictors of AF after pacemaker implantation in patients with isolated sick sinus syndrome (SSS). The study included 109 (69 women, mean age 72 +/- 11 years) patients with SSS, 59 with bradycardia-tachycardia syndrome (BTS). A 12-lead ECG was recorded before pacemaker implantation and during high right atrial and septal right atrial pacing at 70 and 100 beats/min. The ECGs were scanned into a computer and analyzed on screen. The patients were treated with AAIR (n = 52) or DDDR pacing. The P wave duration was measured in each lead and mean P wave duration and P wave dispersion were calculated for each ECG. AF during follow-up was defined as: AF in an ECG at or between follow-up visits; an atrial high rate episode with a rate of > or =220 beats/min for > or =5 minutes, atrial sensing with a rate of > or =170 beats/min in > or =5% of total counted beats, mode-switching in >/=5% of total time recorded, or a mode switching episode of > or =5 minutes recorded by the pacemaker telemetry. The ECG parameters were correlated to AF during follow-up. Mean follow-up was 1.5 +/- 0.9 years. None of the ECG parameters differed between patients with AF and patients without AF during follow-up, nor was there any difference between groups after correction for BTS and age. BTS was the strongest predictor of AF during follow-up (P < 0.001). P wave duration and dispersion measured before and during pacemaker implantation were not predictive of AF after pacemaker implantation in patients with isolated SSS.     

Atrial pacing should be used more frequently in sinus node disease

BACKGROUND: Single lead atrial (AAI(R)) pacing for sick sinus syndrome provides physiological pacing and is less expensive than a dual chamber system. Compared with ventricular-based pacing, it maintains the normal cardiac depolarization sequence, is associated with less atrial fibrillation and heart failure, and avoids pacemaker syndrome. We sought whether it is possible to select patients for AAI(R) pacing with a low likelihood of subsequent ventricular pacing, and whether this approach was cost-effective. METHODS: A retrospective review was conducted of AAI(R) pacemaker implantations. Patients requiring a further procedure for insertion of a ventricular lead (for DDD(R) or VVI(R) pacing) were compared with those who remained atrially paced. RESULTS: 2.7% (117 of 4,366) of implants were AAI(R), compared with less than 1% overall for New Zealand and Australia. During follow-up of 3.5 (2.3, 7.7) years, insertion of a ventricular lead was required in 14 (12%), and was more likely in those with pre-existing PR interval >0.20 seconds (odds ratio 7.8, P = 0.003) or left bundle branch block (LBBB, odds ratio 17, P = 0.037). Right bundle branch block, left anterior fascicular block, or history of paroxysmal atrial fibrillation were not more frequent in the group requiring ventricular pacing, and preimplantation Wenckebach point was not different. The most efficient strategy was initial AAIR implantation in all except those with LBBB or PR interval >0.20 seconds. Compared with routine DDDR implantation, cost was reduced by 20%, with a 1.4% annual incidence of further procedures. CONCLUSION: AAIR is the appropriate pacing choice for sick sinus syndrome without LBBB or PR interval >0.20 seconds.     

Programming a Long Paced Atrioventricular Interval May Be Risky in DDDR Pacing

In patients with intermittent AV block and dual chamber pacemakers, a long paced AV interval of 200 msec or more can be selected to prolong pulse generator life (by avoiding the ventricular pace output) and to enable a more physiological and hemodynamically superior activation sequence. This case report describes the potential risks of programming a long paced AV interval in a patient with a DDDR pacemaker. T wave pacing, as described here, can occur if the conducted QRS complex is not sensed because it occurs during the ventricular blanking period (delivery of the atrial stimulus). This can be initiated by the mechanisms that induce apparent and actual P wave undersensing of the conducted QRS complex. In this case report apparent P wave undersensing and subsequent T wave pacing with ventricular capture (in a patient with intermittent AV block) occurred frequently during an exercise test done in the DDDR mode with a paced AV interval of 200 msec, according to the clinical evaluation protocol.     

Predictive Value of the P Wave at Implantation for Atrial Fibrillation After VVI Pacemaker Implantation

This study assesses the value of P wave measurements on the surface EGG at implantation, in the prediction of atrial fibrillation in VVI paced patients. From a consecutive series of 320 pacemaker implantations 172 WI paced patients for symptomatic atrioventricular block (AVB) (n = 126; mean age 69 ± 14) or sick sinus syndrome (SSS) (n = 56; mean age 68,6 ± 12] and in sinus rhythm at implantation were used in this study. P wave duration in VI is correlated with the incidence of atrial fibrillation during 5 years of follow-up. VI at implantation was significantly longer (114.6 ± 2.7 msec) in the patients who developed atrial fibrillation than in those who did not (91.9 ± 2.7 msec) (P < 0.001). Although positive predictive accuracy increases progressively for higher VI values for AVB and SSS, the negative predictive and diagnostic accuracy of V1 criteria were Jess in SSS. Application of the Bayes' theorem showed that in SSS the probability to develop atrial fibrillation is 33% for V1 < 110 msec and is for V1 < 90 msec still higher than that reported in DDD paced patients. In the AVB group the probability to develop atrial fibrillation is 8% for V1 < 110 msec and 6% for V1 < 100 msec. It seems, therefore, that atrial stimulation (AAI or DDD) is always indicated in SSS. In AVB with V1 < 100 msec, DDD pacing, if not needed for other indications, apparently does not offer much benefit in the prophylaxis of atrial fibrillation.     

The Safety and Efficacy of Chronic Ventricular Pacing at 1.6 Volts Using a Steroid Eluting Lead

Steroid eluting leads may allow for lower chronic pacing thresholds and therefore lower pacing outputs. Twenty-two patients (15 presenting with syncope) were implanted with VVI or VVIR pacemakers and transvenous steroid eluting leads and followed for a mean of 20.6 months while being paced at 1.6 V and 0.6 msec. Mean acute voltage pacing thresholds were 0.40 V at 0.5 msec and chronic pulse width thresholds were 0.21 msec at 0.8 V. Pacemaker function was documented with one to three 24-hour Holter monitors, attached during the 2-6 week postimplant period, bimonthly transtelephonic monitoring, and monthly pacemaker clinic visits. No patient developed recurrent symptoms and consistent capture was verified in all patients on every 24-hour Holter recording and transtelephonic monitor. Chronic ventricular pacing at an output of 1.6 V at 0.6 msec is safe and effective when using a steroid eluting lead and potentially has implications for pacemaker longevity.