Long-Term Pacing in Heart Transplant Recipients is Usually Unnecessary

The indications for and timing of permanent pacing were reviewed in all 17 of 154 adult heart transplant recipients at this center who have had permanent pacemakers implanted. Resting 12-lead ECGs recorded during routine follow-up were examined. A prospective study of pacing requirement was then undertaken. Holter monitoring was performed before and after reprogramming the pacemakers to VVI mode at 50 beats/min. Exercise responses in various pacing modes were then assessed in seven patients with rate responsive pacemakers using a standard Bruce protocol treadmill test. The indication for pacing was sinus node dysfunction in 59% (10/17) and atrioventricular (AV) block in 41% (7/17). The majority of pacemakers were implanted between seven and 21 days after transplantation. There was a progressive reduction in the frequency of pacing on 12-Jead ECGs with time after transplantation. Eight of 14 patients with empirically selected programming paced during Holter monitoring. After reprogramming to 50 beats/ min VVI mode only three of 14 patients, all with sinus node dysfunction, paced. Rate responsive pacing made no difference to exercise time. The requirement for long-term pacing in cardiac transplant recipients is small (3/154) and is limited lo patients with sinus node dysfunction. Rate responsive pacing did not increase exercise tolerance.     

Efficacy and Safety of Ventricular Rate Responsive Pacing in Children with Complete Atrioventricular Block

Single chamber rate responsive pacing offers many potential advantages over the more complex dual chamber atrial tracking pacing mode in children, and the preservation of atrioventricular synchrony could be unnecessary in selected groups of pediatric patients. Twenty-two pediatric patients (age range 9 months to 12 years; mean 6.5 years) had implantation of ventricular rate responsive (VVIR) pacemakers over a 2-year period. All patients had chronic third-degree atrioventricular block, and a normal ventricular function at rest. During the follow-up each patient underwent a 24-hour Holter monitoring, and ten performed a graded treadmill test in both ventricular fixed rate (VVI) and rate responsive (VVIR) pacing mode. Paced ventricular rates were found to be normal for age in all 22 patients; maximum rate did not reach the higher programmed rate during daily activities in any patient. Comparing the mean paced ventricular rate to the mean rates of blocked P waves, six patients showed a difference of more than 20 beats/min, which induced the pacemaker parameters to be reprogrammed. In all patients a significant correlation was found between variations of paced ventricular rate and variations of spontaneous blocked atrial rhythm (P < 0.05); this correlation persisted in the subsequent Holter controls in the ten patients with longer follow-up. Exercise tolerance resulted normal in the ten patients who performed a treadmill test either in VVIR or VVI mode, with increased maximal heart rates and maximal systolic blood pressure in VVIR mode (P < 0.0013). Rate responsive ventricular pacemakers seem to adequately respond to the physiological needs of daily life of this selected group of children requiring permanent pacing.     

VDD(R) Pacing: Short- and Long-Term Stability of Atrial Sensing with a Single Lead System

Background: Recent studies have shown that the atrial signal can reliably be sensed for VDD(R) pacing via atrial floating electrodes incorporated in a single-pass lead. However, there remains concern about the long-term stability of atrial sensing and proper VDD function under real-life conditions. This study investigated the long-term reliability of atrial sensing and atrioventricular synchronous pacing using a new single lead VDD(R) pacing system. Methods and Results: In 20 consecutive patients (ages 71 ± 14 years) with normal sinus node function and high-degree heart block, a single lead VDD(R) pacemaker (Unity(tm), Intermedics) was implanted, Atrial sensing was studied at implantation, at discharge, and at 1, 3, 6, 12, and 18 months of follow-up. At implant, the measured P wave amplitude was 2.3 ± 1.2 mV. By telemetry, the atrial sensing threshold was 0.79 ± 0.41 mV at discharge, 0.75 ± 0.43 mV at 1 month, 0.73 ± 0.43 mV at 3 months, 0.76 ± 0.41 mV at 6 months, 0.79 ± 0.41 mV at 12 months, and 0.77 ± 0.35 mV at 18 months of follow-up (P = NS). Appropriate VDD pacing was assessed by the percentage of correct atrial synchronization (PAS = atrial triggered ventricular paced complexes ± total number of ventricular paced complexes) during repeated Holters. PAS was 99.99%± 0.01 % at 1 month, 99.99%± 0.02% at 3 months, and 99.98%± 0.05% at 12 months of follow-up (P = NS). No atrial oversensing with inappropriate ventricular pacing was observed, neither during isometric arm exercise testing nor spontaneously during Holier monitoring. Conclusion: The long-term stability of atrial sensing with almost 100% correct atrial synchronous tracking and the lack of inappropriate pacing due to atrial oversensing make the new Unity VDD(R) system a highly reliable single lead pacing system. In view of the lower costs and the ease of single lead implantation, this system may offer an interesting alternative to DDD pacemakers in patients with normal sinus node function.     

Heart rate turbulence and heart rate variability in patients with atrial synchronous ventricular pacing

Background: Heart rate turbulence (HRT) and heart rate variability (HRV) have been shown to be independent and powerful predictors of mortality in a specific group of cardiac patients. Pacing has unfavorable effects on autonomic function. Our aim is to investigate autonomic responses to atrial synchronous ventricular pacing (VDD) by evaluating HRT and HRV parameters.
Methods and Results: The study groups comprised 12 control and 12 patients without organic heart disease and with normal sinus function who were implanted with a permanent VDD pacing system for high-degree atrioventricular block. The HRV and HRT analysis were assessed from a 24-hour Holter recording. There was no statistically significant difference between the two groups for HRV parameters. When HRT parameters were compared, turbulence onset was significantly higher in the cardiac paced group than the controls group (2.729 ± 8.818 vs –1.565 ± 8.301, P = 0.006), but no statistically significant difference was found between the two groups for turbulence slope (11.166 ± 10.034 vs 31.675 ± 28.107, P = 0.68). The number of patients who had abnormal HRT onset was significantly higher in the paced group than controls (9 vs 2, P = 0.004).
Conclusion: Atrial synchronous pacing has unfavorable effects on autonomic function. Altered ventricular depolarization sequence may lead to changes in autonomic response. Although we found no difference in HRV parameters between the control and VDD patient groups, the HRT onset and number of patients with abnormal HRT onset was significantly higher in VDD patients. HRT onset can be a better way of noninvasive autonomic response predictor in VDD patients.     

A Multicenter Evaluation of a Single-Pass Lead VDD Pacing System

Since June 1985 until April 1989, 237 patients (130 males, 107 females, aged 22 to 95 years, mean 71) with symptomatic AV conduction disturbances and competent sinus node, were implanted with a single-pass lead VDD pacing system in 30 centers and followed-up for at least 6 months. The ventricular pacing lead incorporated two atrial ring 3-cm apart electrodes, positioned within the right atrial cavity without contact with the heart wall, in order to detect the atrial activity, which is differentially processed by the pacemaker. At implant, mean atrial electrogram amplitude, derived from a custom pacemaker system analyzer (PSA) with the same input filter of the pacemaker was 1.7 +/- 0.8 mV (n = 93). In all cases, atrial sensitivity at implant was the default value +/- 0.15 mV. The atrial tracking capability of the pacing systems was assessed within the month and every 6 months after implantation by means of clinical evaluation, resting ECG, 24-hour Holter monitoring and the following tests: exercise stress testing, mental stress, isometric exercise, and nifedipine test. These tests evoke an increase of atrial rate in consequence of metabolic needs or as a reflex response. The criterion used to evaluate the correct operation of the system was the percentage of atrial synchronization. This was defined as the ratio between atrial triggered ventricular paced complexes and all ventricular paced complexes. All monitorings showed a ratio higher than or equal to 98% in a percentage of patients not lower than 95%. Mean follow-up was 385 days (range 183-1,370 days).(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Pacemakers of the 1980s. An overview

Methods and devices for permanent cardiac pacing remained relatively stable for over two decades with use of the single-chamber ventricular demand (VVI) pacemaker. However, changes have occurred in the 1980s and are expected to continue with the availability of more advanced technology and with increasing knowledge about cardiac pacing. The physiologic benefit of the newer dual-chamber atrial synchronous (VDD) and fully automatic, universal (DDD) pacemakers over the VVI pacemaker in patients with permanent complete heart block and normal sinus node function has been established. These newer units not only reestablish atrioventricular synchrony but also are physiologically rate-responsive. The VDD pacemaker is expected to be phased out in favor of the DDD pacemaker. When the atrial rate or interval is lower than the lower rate limit, the VDD pacemaker functions as a VVI, whereas the DDD pacemaker functions as an atrioventricular sequential (DVI) pacemaker to maintain continuous atrioventricular synchrony. Contrary to general belief, patients with complete heart block and normal sinus node function may gain very little physiologic benefit, if any, from DVI pacing. The sinus node will compete with the pacemaker's atrial stimulation when the sinus rate is faster than the DVI pacemaker rate (which usually occurs during activity). Also, the ventricular pacing rate will not vary with physiologic change. The DVI and atrial demand (AAI) pacemakers have been used in some patients with sinus node dysfunction. Increasing exercise tolerance should not be expected in the majority of patients because they are not pacemaker-dependent during activity, ie, their heart rate is higher than the pacemaker rate. However, these pacemakers appear to help in eliminating pacemaker syndrome, which does not infrequently occur with VVI pacemakers. Patients with sinus node dysfunction but without atrioventricular block do not gain more physiologic benefit with a DDD than with a DVI pacemaker. Whether these patients have severe sinus node dysfunction all the time or adequate sinus node function most of the time during follow-up, the DDD pacemaker will function as a noncommitted DVI with atrial sensing (DDI). The early report of DVI pacemaker-induced atrial fibrillation during follow-up has been refuted by more recent works. If the DDD pacemaker is significantly more expensive than the DVI pacemaker, the latter type may be a good alternative for this condition.     

Non-invasive Evaluation of Ventricular Function and Volumes During Atrioventricular Sequential and Ventricular Pacing

Thirteen patients who all had previously inserted temporary or permanent pacemakers (6, VVI; 7, A-V sequential) were studied by two-dimensional echocardiography and radionuclide gated blood pool ventriculography (RVG) for non-invasive evaluation of cardiac performance. Patients were paced in both the VVI mode and during sinus/atrial or A-V sequential pacing. Although there was no objective change of the ejection fraction during V-pacing and atrial/A-V sequential pacing or sinus rhythm, as has been previously reported, A-V sequential pacing did result in significant improvement in overall cardiac function and output as judged by radionuclide ventriculography and blood pressure response in most of our patients. An appropriately timed atrial contribution to ventricular systole resulted in improved ventricular function in those individuals with pre-existing systolic or diastolic myocardial dysfunction and/or sick sinus syndrome in whom pacemaker therapy was indicated. Radionuclide ventriculography appears to be a reliable, accurate, non-invasive method that can be used to evaluate patients before implantation of a permanent ventricular or atrioventricular pacemaker in order to decide which pacing mode is best for that particular individual.     

Efficacy and Safety of Bipolar Sensing with High Atrial Sensitivity in Dual Chamber Pacemakers

In dual chamber pacemakers, atrial sensing performance is decisive for maintenance of AV synchrony. Particularly, the efficacy of mode switching algorithms during intermittent atrial tachyarrhythmias depends on the sensitive detection of low potential amplitudes. Therefore, a high atrial sensitivity of 0.18 mV, commonly used in single lead VDD pacemakers, was investigated for its efficacy and safety in DDD pacing. Thirty patients received dual chamber pacemakers and bipolar atrial screw‐in leads for sinus node syndrome or AV block; 15 patients suffered from intermittent atrial fibrillation. Pace makers were programmed to an atrial sensitivity of 0.18 mV. Two weeks, 3, 9, and 15 months after implantation, P wave sensing threshold and T wave oversensing thresholds for the native and paced T wave were determined. The myopotential oversensing thresholds were evaluated by isometric contraction of the pectoral muscles. Automatic mode switch to DDIR pacing was activated when the mean atrial rate exceeded 180 beats/min. The patients were followed by 24‐hour Holter monitoring. Two weeks after implantation, mean atrial sensing threshold was 1.81 ± 0.85 mV (range 0.25–2.8 mV) without significant differences during further follow‐up. Native T wave sensing threshold was < 0.18 mV in all patients. In 13% of patients, paced T waves were perceived in the atrial channel at the highest sensitivity. This T wave sensing could easily be avoided by programming a postventricular atrial refractory period exceeding 300 ms. Myopotential oversensing could not be provoked and Holter records showed no signs of sensing dysfunction. During a 15‐month follow‐up, 1,191 mode switch events were counted by autodiagnostic pacemaker function. Forty‐two of these events occurred during Holter monitoring. Unjustified mode switch was not observed. In DDD pacemakers, bipolar atrial sensing with a very high sensitivity is efficient and safe. Using these sensitivity settings, activation of the mode switch algorithm almost completely avoids fast transmission of atrial rate to the ventricle during atrial fibrillation.     

Diagnosis of Atrial Undersensing in Dual Chamber Pacemakers: Impact of Autodiagnostic Features

Atrial undersensing occurs in a considerable number of patients, both with single lead VDD pacemakers and with DDD devices. The aim of this study was to investigate the diagnostic efficacy of electrocardiographic methods and autodiagnostic pacemaker features to detect atrial sensing dysfunction. Two hundred and thirty-one patients with AV block received single lead VDD pacemakers or DDD devices. Atrial sensitivity was programmed to 0.1 or 0.18 in VDD devices and to 0.5 mV in DDD devices; the rate limits were set to 40 and 160 beats/min. Twelve-lead ECG recording for 1 minute during deep respiration and change of body position, 24-hour Holter ECG recording, and treadmill exercise were performed 2 weeks and 15 months after pacemaker implantation. AV synchrony and, if available, P wave amplitude histogram were sampled by autodiagnostic pacemaker features and compared to electrocardiographic findings. Atrial undersensing was assumed, if AV synchrony was below 100% or if minimal P wave amplitude (PWA) was equal to the programmed atrial sensitivity. Intermittent atrial undersensing occurred in 20.7% of patients. The diagnostic sensitivities of the various methods used to detect atrial sensing failures were: 24-hour Holter monitoring 97.5%, P wave amplitude histogram 90.0%, stored AV synchrony 68.0% without significant difference between the various devices, treadmill exercise testing 58.8%, and 12-lead ECG recording 21.3%. In one patient, atrial undersensing was exclusively detected by exercise testing. In conclusion, autodiagnostic pacemaker features facilitate the evaluation of atrial sensing performance. However, to exclude intermittent atrial malsensing, routine Holter monitoring and treadmill exercise are still needed .     

Usefulness of Echocardiography to Predict Inappropriate Atrial Sensing in Single-Lead VDD Pacing

Reliable atrial sensing is the prerequisite for restoration of atrioventricular synchrony in patients with single-lead VDD pacing systems. To determine echocardiographic variables associated with inappropriate atrial sensing, 21 consecutive patients with symptomatic second- or third-degree AV block and normal sinus node function were studied. Prior to implantation echocardiographic measurements of end-systolic and end-diastolic dimensions and volumes of the right atrium and right ventricle were performed. All patients underwent implantation of a Medtronic Thera VDD(d) pacemaker with a bipolar Medtronic Capsure electrode. A minimal amplitude of the unfiltered atrial electrocardiogram of > or =0.5 mV was required for permanent lead position and the atrial sensitivity was programmed below the lowest recorded value. Appropriate atrial sensing (atrial triggered ventricular paced complexes/total number of ventricular paced complexes) was assessed during 24-hour Holter monitoring and treadmill exercise testing 3 to 6 weeks after implantation. Inappropriate atrial sensing (<95% correct atrial synchronization during Holter registration and/or <97.5% during exercise testing) was present in nine patients. Right atrial volumes and the right ventricular end-diastolic volume was significantly higher, as compared to patients without inappropriate sensing (12 patients). The right atrial and diastolic volumes had the highest correlation with correct atrial sensing r = 0.83, P<0.0001). Using a postdefined cut-off value of > or =80 mL for the end-diastolic right atrial volume, sensitivity and specificity for inappropriate sensing was 100% and 92%, respectively. These findings show that preimplant echocardiography can identify patients with inappropriate sensing during VDD pacing, in whom DDD pacing should be considered.     

Comparison of Normal Sinus Rhythm and Pacing Rate in Children with Minute Ventilation Single Chamber Rate Adaptive Permanent Pacemakers

Rate adaptive pacemakers are used to achieve a better cardiac performance during exercise by increasing the heart rate and cardiac output. The ideal rate adaptive sensor should be able to mimic sinus node modulation under various degrees of exercise and other metabolic needs. Minute ventilation sensing has proven to be one of the most accurate sensor systems. In this study, alterations in sinus rhythm and pacing rates during daily life conditions in 11 children (median age 11 years, range 6–14 years) with minute ventilation single chamber pacemakers were investigated. Correlation of sinus rhythm with pacing rates was assessed. ECG records were obtained from 24–hour Holter monitoring. Average rates of five consecutive P waves and pace waves were determined every half hour. The average of the two values was then used to determine hourly rates. Correlation coefficients between the sinus rhythm and pacing rates were calculated. In nine patients, pacing rates correlated well to sinus rhythm (range 0.6793–0.9558. P < 0.001 and P < 0.05), whereas in two cases correlation was not sufficient (P > 0.05). Most of the patients, in whom rate response factor (RRF) measurements during peak exercise by treadmill with cnronotropic assessment exercise protocol were performed and pacemakers were programmed to these parameters, had more appropriate ventricular rates compared to spontaneous sinus rates. In these patients mean RRF value was 15.3 ± 2.7 (range 12–20, median 15). This study shows that during daily activities minute ventilation rate adaptive pacemakers can achieve pacing rates well correlated to sinus rhythm that reflects the physiological heart rate in children.     

Incidence of atrial tachyarrhythmias in pacemaker patients: results from the Balanced Evaluation of Atrial Tachyarrhythmias in Stimulated patients (BEATS) study

OBJECTIVES: The prospective Balanced Evaluation of Atrial Tachyarrhythmias in Stimulated patients (BEATS) study compared atrial tachyarrhythmia (AT) detection by means of serial ECG recordings versus device detection. BACKGROUND: The annual incidence of AT in patients with dual-chamber pacemakers may be significantly underestimated based on ECG and Holter recordings. METHODS: A DDD(R) device capable of AT-triggered dual-channel electrogram (EGM) storage was implanted in 254 patients (70 +/- 11 years, 159 men) with a class I pacing indication. Patients were seen at 6, 26, and 52 weeks after pacemaker implantation. At all visits, symptoms were checked, surface ECGs were recorded including a 24-hour Holter recording at 6 weeks, and the pacemakers were interrogated. Primary study endpoint was AT documentation by surface ECG/Holter versus stored EGMs. Secondary endpoints consisted of the association between patients' symptoms and AT documentation, and of the AT incidence depending on pacing indication and a history of AT. RESULTS: ATs were documented by ECG/Holter recordings in 37 patients (15%) and by stored EGMs in 137 patients (54%) (P < 0.0001). Symptoms were absent in 108 of 137 patients (79%) with device-documented AT but present in 70 of 117 patients (60%) without AT documentation. AT documentation was more frequent in patients with a history of AT but not in patients with sinus node compared to AV node disease. CONCLUSION: ATs occur in pacemaker patients significantly more frequently than estimated by ECG/Holter recordings. Only the analysis of device-stored EGMs allows reliable assessment of the AT burden.     

Sinus Arrest in Diaphragmatic Myocardial Infarction: Treatment of Power Failure with Atrial Pacing

Sinus arrest occurred in a patient with acute diaphragmatic myocardial infarction associated with right ventricular infarction. Cardiac output fell dramatically despite maintenance of a junctional rate of 72. Ventricular pacing at rate 82 and dopamine administration resulted in only slight hemodynamic improvement. Atrial pacing at rate 84 restored normal cardiac output until resumption of sinus node activity. These results suggest that atrial contraction is important for the maintenance of ventricular function in some patients with acute infarction, and may be of particular importance in the presence of right ventricular infarction. Temporary atrial or atrioventricular sequential pacing may be of great hemodynamic benefit in selected patients with conduction defects complicating myocardial infarction.     

Initial Experience with Mode Switching in a Dual Sensor, Dual Chamher Pacemaker in Patients with Paroxysmal Atrial Tachyarrhythmias

Mode switching algorithms have been developed to avoid tracking of atrial fibrillation (AF) or flutter (AFL) during DDD(R) pacing. Upon recognition of AF or AFL, the mode is switched to a nontracking, sensor driven mode. The Vitatron Diamond model 800 pacemaker does this on a beat-to-beat basis. Atrial events occurring within a “physiological range” (± 15 beats/min) calculated from a running average of the atrial rate are tracked. When atrial events are not tracked the escape interval is either determined by the sensor(s) or by a fallback algorithm thereby preventing large increases in V-V interval during mode switching. Loss of atrioventricular (AV) synchrony by atrial premature beats and after an episode of AF or AFL is prevented by atrial synchronization pulses (ASP), which are delivered after a safe interval (timed out from the sensed premature atrial event) has expired and before delivery of the next ventricular stimulus. We implanted 26 such devices in 18 men and 8 women with symptomatic second- or third-degree AV block and paroxysmal AF or AFL. Their ages ranged from 18–84 years (mean 60), and the follow-up ranged from 2–13 months (mean 8). During pacemaker check-up, exercise testing or 24-hour Holter monitoring one or more episodes of mode switching was documented in 8 patients. In these 8 patients a smooth transition (ventricular rate) from sinus rhythm to AF or AFL was documented on one or more occasions, without inappropriate increase in ventricular rate in the DDDR mode. None of the patients complained of palpitations. Appropriate rate response was seen in all patients during Holter monitoring and exercise. Restoration of AV synchrony with ASP was documented many times. In 2 patients the DDIR mode was programmed due to intermittent synchronization of ventricular stimuli to near incessant supraventricular tachycardia, which sometimes gave rise to asymptomatic slightly irregular ventricular paced rhythms below WO beats/min. Recognition of AF or AFL was reliable. No inappropriate increases in ventricular pacing rate were seen at the onset of or during AF or AFL. ASP is an effective method of maintaining AV synchrony and avoiding competitive atrial pacing.     

Atrial Inhibited Pacing in the Sick Sinus Node Syndrome: Clinical Value and the Demand for Rate Responsiveness

A consecutive series of 66 patients (males = 32; mean age +/- SD = 71 +/- 9 years) given atrial inhibited pacemakers for sick sinus nodes were followed to study the incidence of lead failures, chronic atrial tachyarrhythmias, and atrioventricular conduction disturbances. The need for rate responsive pacing was also assessed. Pre and postoperative investigation could include carotid sinus massage, Holter monitoring, exercise testing, and invasive electrophysiology. The mean follow-up time +/- SD was 32 +/- 29 months (median = 26 months). Three patients (5%) had their pacemakers replaced due to lead failures (loss of sensing = 2; exit block = 1). Two pacemakers (3%) were replaced after 5 and 22 months due to atrial fibrillation. Four patients (6%) received new pacemakers because of development of second-degree or complete atrioventricular block after 1, 6, 12, and 31 months, respectively. During exercise, most patients (76%) responded with an increase in sinus rate at least as marked as that achievable with the currently available rate responsive pacemakers. Assuming careful patient selection, atrial inhibited pacing is well suited for many patients with sinus node dysfunction and preserved atrioventricular conduction. There is a limited need for rate responsive pacemakers in these patients.     

Electrophysiology and Indications for Pacing in the ''8O''s*

Newer electrophysiological studies have improved our understanding of the pathogenesis of cardiac arrhythmias. Bradycardias originate either from a dysfunction of impulse formation in the sinoatrial node or from a disturbed conduction of the impulse. Different pathogenetic mechanisms are discussed as causes of tachyarrhythmias: circus movement (re-entry) is primarily due to pathological changes in conduction and refractoriness. Focal impulse formation results from local disturbances of depolarization and repolarization of the cell membrane: increased automaticity, abnormal automaticity, triggered activity. Symptomatic bradycardias still represent the standard indication for cardiac pacing particularly with implantable pacemakers. Based on clinical electrophysiology, various types of pacemakers are available at present: atrial triggered and atrial pacing pacemakers, AV-sequential pacemakers, ventricular demand-pacemakers, stand-by pacemakers, and fixed rate pacemakers. The multiprogrammability of newer pacemaker devices is a very useful tool in avoiding secondary interventions. For antitachycardia pacemaker therapy there are essentially three methods in use: 1. overdrive pacing to prevent re-entry phenomena and automaticity and also to suppress tachyarrhythmias based on increased or abnormal automaticity; 2. competitive stimulation for termination of tachycardias by means of single impulses; and 3. rapid atrial stimulation to convert atrial flutter into atrial fibrillation and consequently to normal sinus rhythm. In very rare cases rapid ventricular stimulation is mandatory. The positive results achieved with temporary stimulation methods have led to the development of permanent (implantable) antitachycardia pacemakers for long-term therapy, which have proven to be a low-risk alternative in drug-resistant tachyarrhythmias.     

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.     

Single chamber atrial pacing: a realistic option in sinus node disease: a long-term follow-up study of 213 patients

BACKGROUND: Despite several decades of experience with atrial pacing, many centers do not apply this mode to any greater extent, mainly because of concerns for the development of future atrioventricular (AV) block or atrial fibrillation. Recent studies have emphasized possible negative effects of right ventricular stimulation, even when AV-synchrony is preserved, and have thus given rise to renewed interest in single chamber atrial pacing for sinus node disease. METHODS: This study presents the results of up to 19 years' follow-up of 213 patients with sinus node disease treated with atrial pacing with respect to survival and causes of death, development of atrial fibrillation and AV block, and total mode survival. Patients were divided into two groups: with or without associated atrial tachyarrhythmias at the time of implant. Results are given for all patients and for the two groups separately. RESULTS: The mean follow-up time was 10.1 years. The survival of the entire group was lower after 10 years than that of an age and gender-matched general Swedish population. This was caused by patients with the brady-tachy syndrome (BT) having a significantly higher mortality rate than controls, whereas those with bradycardia only (B) had survival comparable to the general population. Permanent atrial fibrillation (AF) developed in 20% of patients and was significantly more common in patients with BT. The majority of patients with AF (78%) no longer needed any pacing, i.e., did not require ventricular stimulation due to slow ventricular rate. The annual incidence of high grade AV block was 1.8%. If patients with preexisting bundle branch block were excluded, the incidence was 1.6%. No fatal episode of AV block was seen. The overall mode survival at the end of follow-up was 75%, with 155 patients still with atrial pacemakers. CONCLUSION: Atrial pacing is a safe and reliable mode of pacing in patients with sinus node disease, even in the very long-term.     

DDD Pacing: An Effective Treatment Modality for Recurrent Atrial Arrhythmias

We performed atrial EP studies (atrial substrate evaluation) on 10 patients. These patients had evidence of paroxysmal, sustained, recurrent atrial arrhythmias (7 men and 3 women with a mean age of 64 ± 15 years). All patients combined a brady-tachy syndrome; 7 patients had a sick sinus syndrome (SSS) and 3 patients a typical vagally induced atrial arrhythmia. No anti-arrhythmic drug was allowed in 3 patients with SSS, 1 drug failed in 4 patients and the combination of 2 drugs failed in 3 patients during the first to eighth years prior to pacemaker implantation. Atrial substrate evaluation was feasible in all these patients off anti-arrhythmic therapy and showed important abnormalities of atrial loco-regional conduction parameters and long refractory periods (RP). The remarkable point was, in 7 patients, a paradoxical improvement in intra-atrial conduction delay at rapid pacing rate. The DDD pacing mode was chosen in all patients. No technical problem occurred during implantation. Atrial pacing rate was programmed to be slightly higher than the mean diurnal heart rate calculated on Holter monitoring. After implantation, the mean follow-up period was 18 ± 25 months with an average of one Holter every 4 months during the first 2 years. The 7 patients who improved intra-atrial conduction at rapid pacing rate were controlled without drugs, 2 patients were controlled with 1 drug, and 1 patient with 2 drugs. Atrial pacing in the DDD mode in a selected group of patients prevents paroxysmal and drug-resistant atrial arrhythmias. Atrial substrate evaluation is a sensitive tool for assuring the long-term benefit of atrial pacing. In this subset of patients, maintenance of AV synchrony by DDD pacing is preferable to catheter ablation of the His bundle.