Reliability of the Evoked Response in Determining the Paced Ventricular Rate and Performance of the QT or Rate Responsive (TX) Pacemaker

The TX pacemaker uses a conventional transvenous electrode to sense T-waves of paced ventricular complexes and it adapts the pacing rate to varying physiological demands by responding to changes in the QT or, more correctly, the stimulus artifact-to-T-wave (stimulus-T) interval. This pacing system was assessed in 13 patients. The relation between heart rate and stimulus-T interval and the effect of programming on the performance of this pacemaker were studied on several occasions in each patient. Treadmill exercise performance during TX pacing mode was compared with atrial synchronized ventricular (VAT) and asynchronous ventricular demand (VOO and VVI--70 beats per minute) pacing modes. T-wave sensing problems arose in three patients. In one, this was overcome by reducing the pulse amplitude from 5.0 to 2.5 V. In another patient, spontaneous recovery of T-wave sensing occurred 5 months after pacemaker implantation. T-wave sensing deteriorated with the passage of time in most patients. Satisfactory rate response as assessed by treadmill exercise testing and Holter monitoring was achieved in 12 patients through adjustments of two programmable parameters: the slope that defines the alteration in heart rate in response to a millisecond change in stimulus-T interval and the "sensing window" that is the interval during which T-waves can be sensed and a rate response is possible. Exercise performance was significantly better during rate responsive pacing (TX) mode as compared with VVI pacing but was comparable to that during VAT pacing. The resting heart rate/stimulus-T interval can be described by the following linear regression equation: stimulus-T interval = 466 - 1.68 X paced-rate, r2 = -0.62. This relation, however, was subject to wide inter- and intra-patient variation. Consequently, given identical programmed parameters and exercise protocol, the chronotropic response differed significantly from patient to patient and in the same patient from one occasion to another. Our results show that a physiologically beneficial chronotropic response can be achieved in most patients. However, reprogramming, based on results of exercise tests and Holter monitoring, may be necessary to adjust for changes in T-wave sensing and the heart rate/stimulus-T interval relation and, thus to ensure that the pacemaker continues to function optimally.     

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.     

Rate-Responsive Pacing: Clinical Experience

Single chamber, rate-responsive pacing is emerging as a new modality in cardiac pacing and in ihe near future, dual chamber rule-responsive pacing may be the optimal solution for most pacemaker patients. In this report we describe our short- and long-term clinical experience with two different rate-responsive pacemakers: the RS4, an asynchronous atrial sensing ventricular pacemaker, and the TX-pacemaker, which senses the evoked QT after a ventricular paced beat, as an indicator of metoholic demand. Both systems use a single ventricular lead. Nine palients received RS4 and 10 palients received TX units. All of these patients had AV block and good ventricular function except for three patients with sinas node disease in the TX group. Between 1 and 3 months after implantation, a 24-hour Holter monitoring was performed, durifig which two maximal symptom-limited treadmill exercise tests (Bruce protocol) were conducted in VVI (70 bpm) and rate-responsive modes, in a random fashion. The mean follow-up was 25 months in RS4 group and 10 months in TX group. Significant improvements in patient exercise tolerance were found in the rate-responsive mode (9.0 vs. 6.6 METs in VVI) with similar results in both groups (RS4 and TX) despite higher ventricular pacing rates in the TX group (721 bpm vs. 102 bpm in RS4). An autolimited rate-responsive pacemaker-mediated tachycardia, induced by retrograde ventriculoatrial conduction, was observed in a patient with an RS4. There are still many problems with these units; at the end of follow-up, only 4 out of 9 with the RS4 unit and 9 out of 10 with the TX unit have pacers that are functioning properly. Single chamber rate-responsive pacing should be considered as a step forward in cardiac pacing.     

A New Principle of Rate Adaptive Pacing in Patients with Sick Sinus Syndrome

The most "natural" rate adaptive pacemaker is VDD for patients with AV block. Nothing equivalent exists for patients with sick sinus syndrome (SSS). Even if they are paced in the AAI mode, the AV synchrony is often lost under exercise if nodal rhythms develop which cause the atria to contract against closed valves by retrograde conduction. We tried to develop a concept of rate adaptive pacing which is applicable in SSS patients by guaranteeing AV synchrony. It is known that AV delay shortens with increasing rate under exercise in normal subjects. Three AAI paced patients were evaluated to find out whether a similar correlation is valid between exercise and AV delay with constant rate. A nonconventional ECG was registered during the whole procedure by using an analog tape recorder. The pacing rate was changed with and without exercise on a bicycle to determine its influence on AV delay and by calculating the AV delay averaged over the last 8 beats. In all three patients a reproducible correlation existed between exercise and shortening of the AV delay. This effect was already detectable after 10 s. Increasing the pacing rate above "physiological" rates caused prolongation of the AV delay (over-stimulation phenomenon). We, therefore, concluded that measuring the AV delay in atrial paced patients with SSS by means of a ventricular electrode can be used as a fast parameter for rate adaptive pacing with AV synchrony. The "over-stimulation" phenomenon can additionally be utilized for controlling "physiological" rates depending on individual needs.     

Clinical Interest of a Sensor Driven Algorithm Limiting Ventricular Pacing Rate During Supraventricular Tachycardia in Dual Chamber Pacing

A sensor driven algorithm limiting ventricular pacing rate during supraventricular tachycardia (SVT) is included in a dual chamber rate modulated pacemaker sensitive to acceleration forces (Relay, 294-03, Intermedics Inc.). According to the intensity of concomitant exercise, the ventricular pacing rate is limited either to the programmed maximum pacing rate (MPR) or to an interim lower limit, called "conditional ventricular tracking limit" (CVTL). The MPR prevails over the CVTL when the sensor calculated pacing rate exceeds the minimal rate by more than 20 beats/mm. The purpose of the study is to determine the clinical safety and efficacy of this algorithm in patients with intermittent SVT. Method: a Relay was implanted in four patients with a bradycardia/tachycardia syndrome and in four patients with complete atrioventricular block (CAVB). All had episodes of paroxysmal atrial tachycardia. The units were programmed in DDDR: rate responsive parameters were adjusted by simulating the rate response during three levels of exercise to let the MPR override the CVTL only during strenuous exercise. Holter monitors and exercise testings were performed at 3-month follow-up. Results: in seven patients, Holter recordings showed Supraventricular arrhythmias at rest with a ventricular pacing rate limited to the CVTL. Appropriate rate increases during exercise testings were also demonstrated. Three devices had to be reprogrammed in DDIR tone patient suffering from nearly permanent atrial flutter and two patients not tolerating the CVTL pacing rate at rest). Conclusion: the CVTL algorithm is effective in protecting against high ventricular pacing rates during Supraventricular arrhythmias. It allows the selection of the DDDR mode even with a high MPR in patients with intermittent SVT.     

Changes in QT and Q-aT Intervals Induced by Mental and Physical Stress with Fixed Rate and Atrial Triggered Ventricular Inhibited Cardiac Pacing

We have investigated the influence of mental stress and physical stress, i.e., exercise, on the QT and Q-aT intervals (measured from the pacemaker stimulus to the end or the apex, respectively, of the T wave). The study was made on ten patients with high degree atrioventricular block treated with AV universal (DDD) pacemakers. These were programmed to a fixed rate ventricular (VVI) or an atrial triggered (VDD) function for different parts of the study. An arithmetic mental stress test and a bicycle exercise test were performed with each mode of pacing. In the VVI pacing mode, the atrial rate increased by 11% during mental stress and by 46% during exercise. There was a significant shortening of QT and Q-aT intervals with both types of stress. With VDD pacing, mental stress induced a 12% increase in rate and a significant shortening of QT and Q-aT. The paced rate increased by 50% during the exercise test. This increase in ventricular rate was associated with the most marked changes in QT and Q-aT intervals. Thus, both types of stress cause a significant shortening of the QT and Q-aT interval even in the absence of a simultaneous increase in ventricular rate. When the latter is allowed to increase during VDD pacing, both intervals shorten considerably more. There was a marked inter-individual variability in the response to both types of stress. These findings are of importance with regard to the QT sensing rate responsive pacemaker which can be expected to respond to mental stress in most patients, but that response might be unpredictable in the individual.     

Evaluation of Rate-Responsive Pacemakers by Transesophageal Holter Monitoring of Spontaneous Atrial Rate

BONGIORNI, M.G., ET AL.: Evaluation of Rate-Responsive Pacemakers by Transesophageal Holter Monitoring of Spontaneous Atrial Rate. One of the most important problems in rate responsive (RR) pacing is the clinical experimental evaluation of the reliability of various sensors. In particular, it is difficult to test their sensitivity and specificity during daily activity of the patients. Atrial rate, when present and normal, is the most physiological marker of metabolic requirements, but sometimes it is impossible to analyze the P wave in ventricular paced rhythm during routinely performed tests (e.g., ergometric test and 24-hour Holter monitoring). During various physical activities, we monitored atrial electrograms on an esophageal lead on the first channel of a standard Holter tape recorder; on the second channel a surface ECG lead was recorded. We selected 10 patients with high grade heart block and normal sinus node function paced in RR-VVI mode. RR pacing was obtained using various sensors (body activity, blood temperature, spike-T interval, minute ventilation). The good quality of recording allowed an easy evaluation of atrial and ventricular rates. In four cases an appropriate increase in heart rate was documented; sensitivity threshold and/or rate response slope were reprogrammed when indicated. The pacing rate of one patient did not parallel the atrial rate during walking only. In three cases, we observed a delay in the ventricular rate increase, with ventricular rate decreasing at peak exercise despite further atrial rate increase. In the last two patients, we observed inappropriate pacing response; pacing rate increased later and to a lower level than the atrial one. This new method is applied easily and appears reliable to evaluate the response of RR pacemakers to individual metabolic needs. Its applicability is, however, limited by the need for a normal sinus node function. In conclusion, transesophageal atrial rate recording is a useful tool for the clinical evaluation of RR pacemakers, and it can be proposed as a new method for testing new sensors.     

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.     

A Double-Blind Study of Submaximal Exercise Tolerance and Variation in Paced Rate in Atrial Synchronous Compared to Activity Sensor Modulated Ventricular Pacing

To assess the variation in paced rate during everyday activity and the importance of atrioventricular synchronization (AV synchrony) for submaximal exercise tolerance, atrial synchronous (DDD) and activity rate modulated ventricular (VVI,R) pacing were compared in 17 patients with high degree AV block. The patients were randomly assigned to either mode and evaluated by treadmill exercise to moderate exertion and by 24-hour Holter monitoring after 2 months in the DDD and VVI,R modes, respectively. At the end of the study, the patients were programmed to the pacing mode corresponding to the preferred study period. During the treadmill test, the mean exercise time to submaximal exertion (Borg 5/10), exertion ratings and respiratory rate did not differ between pacing modes despite a significantly lower ventricular rate in the VVI,R mode. The atrial rate during VVI,R pacing was significantly higher than the ventricular rate, but did not differ from the ventricular rate during DDD pacing. There was a diurnal variation in paced rate in both pacing modes. Paced ventricular rate was, however, higher and variation in paced rate greater in DDD compared to VVI,R pacing. Nine patients preferred the DDD mode, three patients preferred the VVI,R mode, while five subjects did not express any preference. The results from this study indicate that the variation in paced rate during activity sensor-driven VVI,R pacing does not match that during DDD pacing neither during everyday activities nor during submaximal treadmill exercise. Nevertheless, no differences in exercise time, Borg ratings, and respiratory rate during submaximal exercise were found. Thus, for most patients with high degree AV block, DDD and VVI,R pacing seem equally satisfactory for submaximal exercise.     

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.     

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.     

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)     

Multicenter Clinical Evaluation of a New SSIR Pacemaker

A multicenter clinical evaluation of Sorin Swing 100, a new SSIR pacemaker with a gravimetric sensor, was performed by seven different centers enrolling a total of 89 patients, 56 men and 33 women, mean age 73.1 years, for pacemaker implantion (73 patients) or pacemaker replacement (16 patients). Pacing mode was VVIR in 73 patients and AAIR in 16. The behavior of pacing rate was evaluated 3 months after the implant by performing a 24-hour Holter monitor, an exercise stress test, and tests for the assessment of mechanical external interference (MEI). A physiological behavior of the paced rate was always observed during Holter monitoring. In 52 completely paced patients mean diurnal, nocturnal, and maximal heart rate were, respectively, 74.9 ± 5.7 ppm, 58.1 ± 5.8 ppm, and 113.4 ± 12.7 ppm; a paced rate exceeding 100 ppm was reached on the average 5.6 times/Holter monitor. In all but two patients the sleep rate (55 ppm) was reached during the night or long resting time. During exercise stress test a direct correlation between the increase in pacing rate and the increase in workload was observed; the mean maximal heart rate reached in 49 completely paced patients was, respectively, 102.8 ± 9 ppm in 17 patients who accomplished stage 1, 116.2 ± 13.6 ppm in 28 patients who accomplished stage 2, and 133 ± 6.7 ppm in 10 patients who accomplished stage 3 of the Bruce protocol. MEI testing never increased the pacing rate over the noise rate (10 ppm over the basic rate). In only seven patients the results obtained suggested to change the nominal set up of the pacemaker. Our experience clearly indicates that Swing 100 is an effective, reliable, and easy to use SSIR pacemaker. The availability of the sleep rate allows a more physiological pattern of pacing rate and can lead to significant energy saving.     

Initial Clinical Experience with a Minute Ventilation Sensing Rate Modulated Pacemaker: Improvements in Exercise Capacity and Symptomatology

A minute ventilation sensing rate modulated pacemaker was implanted in nine patients with bradycardia. Minute ventilation is sensed in this pacemaker by means of a standard bipolar pacing electrode. Compared with exercise in the constant rate ventricular pacing (WI) mode at 1 month after pacemaker implantation, rate responsive pacing resulted in an improvement of exercise capacity of 33 ± 5% (from 437 ± 42 s in the WI mode to 593 ±57 s in the rate modulated mode, P < 0.01, Bruce protocol). This improvement was maintained in the seven patients in whom an exercise test was repeated at 3 months after implantation. The pacing rate was significantly correlated with oxygen consumption (r = 0.8A ± 0.04) and measured minute ventilation (r = 0.76 ± 0.06), Symptomatology in these patients was assessed by means of self-assessment questionnaires in a double blind, randomized cross-over study in which the pacemaker was alternatively programmed into the WI and rate modulated modes. Significant improvements in "shortness of breath" and "energy during daily activities" were documented during rate modulated pacing and "palpitations" and "chest pain" were not worsened. Most patients preferred the rate modulated mode during the study. In conclusion, rate modulated pacing by sensing minute ventilation resulted in better exercise capacity and symptomatology. The pacing rate also showed good correlation with the individual's oxygen requirement.     

Respiratory-Dependent Atrial Pacing, Management of Sinus Node Disease

The effectiveness of respiratory-dependent atrial pacing (AAI-RD) was assessed in 23 patients (11 male, 12 female; 68 ± 10 years) with symptomatic isolated sinus node disease (SND). Follow-up was performed at 3 month intervals and included history taking, physical examination, ECG recording and 24-hour Holter monitoring. An incremental treadmill exercise test was performed in 21/23 patients before pacemaker implantation, in 23/23 patients after implantation (at least two tests with different programmed settings of respiratory rate/paced rate ratio); 21/23 patients underwent treadmill tests during both fixed rate 70 bpm and AAI-RD pacing. Physiological sensitivity of AAI-RD pacing was found excellent in 34 tests (85%) and fair in six (15%). Spontaneous heart rate was significantly higher after pacemaker implantation fbpm 115 ± 20 vs 98 ± 24, P < 0.001). In 10/21 patients paced rate was significantly higher during AAI-RD vs AAI pacing (131 ±9 vs 106 ± 16, P < 0.001) with better total work time (min 9.9 ± 4 AAI-RD vs 6.8 ± 2.6 AAI, P < 0.002), higher oxygen consumption at anaerobic threshold (ml/min 1137 ± 406 AAI-RD vs 882 ± 268 AAI-RD vs 5.5 ± 2.6 AAI, P - 0.001). No significant difference was found in 7/21 patients (overlap between spontaneous and paced rate during both AAI-RD and AAI programming); 4/21 patients did not reach anaerobic threshold owing to osteomuscular limitations. AV block was detected in 1/23 patients, Biorate circuital failure in 1/23, sporadic undersensing in 5/23, short and symptom-free myopotential inhibitions in 10/23. We concluded that AAI-RD pacing is a reliable, safe and useful modality in pacemaker management of isolated SNA, especially in patients with abnormal rate response to exercise.     

A New Algorithm for Closed-Loop Stimulation: A Feasibility Study

PIERAGNOLI, P., et al .: A New Algorithm for Closed-Loop Stimulation: A Feasibility Study. Closed-loop stimulation (CLS) is a physiological system for adaptive rate pacing based on monitoring and processing of the intracardiac impedance. The "standard" CLS algorithm (SCLS) requires continuous ventricular pacing. A new, enhanced CLS algorithm (ECLS) provides rate modulation during sensed and paced ventricular depolarizations. The aim of this study was to validate ECLS and to compare its effectiveness with that of SCLS. Ten patients received Inos²⁺ CLS pulse generators. SCLS and ECLS were uploaded to the device and evaluated in a randomized, crossover fashion at 30 and 45 days after pacemaker implantation. At each follow-up visit, ambulatory and posture tests were performed. Heart rate (HR) during daily activity was evaluated based on 24-hour Holter recordings. During all phases of the ambulatory test, both algorithms provided physiologically appropriate rates in all patients. The proportion of sensed ventricular events was significantly higher in ECLS (93.9%) than in SCLS (0.7%). The proportion of paced ventricular events during 24 hours was substantially lower with ECLS (25.7%) than with SCLS (98.4%). Postural changes did not influence HR with either algorithm. The Holter recordings indicated prompt, safe, and effective rate modulation appropriate to patient activity. In conclusion, analysis of these clinical data demonstrated the safety and effectiveness of the ECLS algorithm. Moreover, with this algorithm the ventricle is paced only when required, which may be expected to retard battery depletion and retain the natural ventricular activation pattern whenever possible. (PACE 2003; 26[Pt. II]:229–232)     

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.     

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.     

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.     

Prolonged paced QRS duration as a predictor for congestive heart failure in patients with right ventricular apical pacing

BACKGROUND: The recent studies showed that right ventricular (RV) pacing was associated with worsening of heart failure. The aim of this study is to clarify the clinical significance of paced QRS duration during RV pacing to predict congestive heart failure (CHF) patients. METHODS AND RESULTS: This study enrolled in 92 patients with atrioventricular block who underwent initial pacemaker implantation. The paced QRS duration was automatically obtained by electrocardiography immediately after pacemaker implantation and then by routine attendance at a pacemaker clinic every 3 months. The paced QRS duration was positively correlated with left ventricular end-diastolic dimension (P < 0.05) and left ventricular end-systolic dimension (P < 0.05), and tended to negatively correlate with left ventricular ejection fraction (P = 0.0507). The paced QRS duration immediately after pacemaker implantation was 170.4 +/- 18.9 ms. During a mean follow-up period of 53 +/- 16 months, 16 patients developed CHF. We selected as a cut-off value the nearest whole number (190 ms) that was one standard deviation greater than the mean, and divided into two groups according to baseline paced QRS duration. Patients with a paced QRS duration of <190 ms comprised group A (n = 77, nine of which developed CHF) and the remainder comprised group B (n = 15, seven of which developed CHF). Prolonged paced QRS duration (> or =190 ms) was associated with a significant increase in the overall morbidity of CHF (P < 0.05). Additionally, paced QRS duration significantly prolonged during the follow-up period among group A patients with CHF (P < 0.05), but did not change among patients without CHF. CONCLUSION: We concluded that paced QRS duration can be a useful indicator of impaired left ventricular function in patients with RV pacing. Even in patients whose paced QRS duration is relatively shorter, progressive prolongation of paced QRS duration can predict the development of CHF.