Benefits and Limitations of Rate Adaptive Pacing Under Laboratory and Daily Life Conditions in Patients with Minute Ventilation Single Chamber Pacemakers

Rate adaptive pacing has been shown to improve hemodynamic performance and exercise tolerance during acute testing. However, there remain concerns about its benefit in daily life and possible complications incurred by unnecessary pacing. This double-blind crossover study compared the benefit of rate adaptive (SSIR) versus fixed rate (SSI) pacing under laboratory and daily life conditions in 20 rate incompetent patients with minute ventilation single chamber pacemakers (META II). The heart rate (HR) response during three different exercise tests (treadmill, bicycle ergomctry, walking test) was correlated with the Holler findings during daily life in either pacing mode. The maximal HR was significantly higher in the SSIR-mode compared to the SSI-mode, both during laboratory testing (treadmill: 123 ± 15 vs 93 ± 29 beats/min: ergometry: 118 ± 15 vs 89 ± 27 beats/min; walking test: 127 ± 9 vs 95 ± 26 beats/min, all P values < 0.01) as well as during daily life (Holter: 126 ± 13 vs 103 ± 24 beats/min, P < 0.01). On Holter, the average HR (71 ± 14 vs 71 ± 8 beats/min) and the percentage of paced rhythm (54 % vs 62%, SSI- vs SSIR-mode, P = NS) were not different in either mode. However, despite a 30% rate gain in the SSIR-mode, the exercise capacity remained unchanged, and only 38% of patients preferred the SSIR-mode. Minute ventilation pacemakers provide a physiological rate response to exercise. Irrespective of the protocol used, the findings of laboratory testing are comparable to those during daily life. However, patient selection for rate adaptive single chamber pacing should be made with caution, since the objective benefit of restoring normal chronotropy may subjectively be negligible for most patients.     

Follow-Up of a Minute Ventilation Rate Adaptive Pacemaker

Although rate adaptive pacemakers are now frequently prescribed, there is limited information regarding long-term follow-up of patients with a pacemaker capable of rate adaptation. We have examined our patients in whom a pacemaker capable of rate adaptation via a sensor that determines minute ventilation has been implanted. After following a group of 42 patients for a mean of 13.2 months we have found this to be a reliable rate adaptive pacing system. The sensor was reliable long term, the system is easy to program, and sensor settings were changed infrequently.     

Rate Responsive Cardiac Pacing Using a Minute Ventilation Sensor

A minute ventilation sensing rate responsive pacemaker was implanted in 15 patients (8 males and 7 females)with bradycardia. The mean age was 72.8 ± 8.7 years. The single chamber system measures transthoracic impedance between the tip electrode of a standard bipolar lead and the pulse generator case. In the adaptive mode the pulse generator calculates a rate responsive factor or slope during maximal exercise but /unctions as in the VVI mode. The patients exercised maximally on an upright cycle ergometer with the pacemaker programmed to VVI mode, adaptive mode, and rate responsive mode. Exercise and gas exchange data were collected continuously and analyzed using an automated breath-by-breath system. The slope, heort rate, and ventilation were measured every 20 seconds. Heart rate in pacemaker dependent patients correlated well to minute ventilation (correlation coefficient ranging from 0.72–0.95, P < 0.0001). This study demonstrates that minute ventilation is a good metabolic sensor in rate responsive pacing.     

Rate Responsive Pacing Using a Minute Ventilation Sensor

Minute ventilation, the product of respiratory rate and tidal volume, correlates directly with oxygen consumption, cardiac output, and heart rate. An implantable pacemaker has been developed which allows variation in pacing rate in response to measured changes in minute ventilation. This single chamber system measures transthoracic impedance between the tip electrode of a standard bipolar lead and the pulse generator case. Low amplitude current pulses (1 mA for 15 μsec) are generated each 50 msec between the ring electrode and the case. In the adaptive mode, the pulse generator calculates a rate response factor or slope after maximal exercise. This slope, which describes the relationship between pacing rate and minute ventilation together with the pacing rate limits are the only programmable rate responsive features. Minute ventilation rate responsive systems have been implanted in 12 patients (8/emales, 4 males), of mean age 63 years. Indications were His bundle ablation (6), acquired complete heart block (4), and sick sinus syndrome (2). At post-implant exercise testing, pacing rate rose within the first minute. Peak rate and time to upper rate were dependent on workload. After exercise, pacing rate remained at peak for up to 2 minutes before a gradual fall to resting rate. Comparative studies of the minute ventilation and the activity sensor pacing systems in the same patients confirmed that the minute ventilation system more closely parallels normal sinus response to activity. The minute ventilation rate responsive pacing system is simple to programme, no special lead is required and the system is highly physiologic.     

Reliability of Minute Ventilation as a Parameter for Rate Responsive Pacing

A minute ventilation sensing rate responsive pacemaker was implanted in 11 patients with bradycardias. Their mean age was 59 +/- 4 years (mean +/- SEM). The pacemaker measures minute ventilation by sensing intravascular impedance using a standard bipolar electrode. The rate responsive programming was simple: apart from ascribing an upper and lower rate, the only programmable parameter was the slope of rate response. This could be derived approximately by assessing the suggested slope value during an exercise test in the 'adaptive VVI' mode. Compared with exercise in the VVI mode, symptom limited treadmill tests in the rate responsive mode showed a 33% improvement of exercise capacity and a 44% improvement of cardiac output as determined noninvasively by continuous wave Doppler measurements of the ascending aortic blood flow. The pacing rate was appropriately increased during a variety of daily activities such as walking at different speeds and gradients, and ascending and descending stairs. Voluntary interference of the respiratory pattern such as during coughing and hyperventilation increased the pacing rate from a resting rate of 70 bpm to 111 +/- 10 and 86 +/- 4 bpm respectively. Continuous talking during exercise attenuated the expected rate response. The pacemaker can sense activity induced by arm swinging. In conclusion, the Meta pacemaker improved cardiac output and exercise capacity in patients with bradycardias. Its rate response was related to workload. Although voluntary interference affected the pacing rate, excessive rate acceleration was not encountered.     

Rate Responsive Pacing with a Minute Ventilation Sensing Pacemaker during Pregnancy and Delivery

A minute ventilation sensing rate responsive pacemaker was implanted in a 29-week pregnant woman with symptomatic complete atrioventricular (AV) block under echocardiographic and electrocardiographic (ECG) guidance. Satisfactory rate responses during a submaximal treadmill exercise test and daily activities were achieved. The course of pregnancy and cesarean section is discussed. During the cesarean section and after the delivery of the baby, changes in the ventilator settings confirmed that the pacing rate was closely correlated with both the tidal volume (r = 0.94, P less than 0.01) and the respiratory rate (r = 0.93, P less than 0.05).     

A Simultaneous, Noninvasive Comparison with Sinus Rhythm, of two Activity Sensing, Rate Adaptive Pacemakers, in an Elderly Population

We compared the rate response to low level work, arm exercise, step testing, and treadmill exercise between the Siemens Sensolog 703 S (Sg) and the Medtronic Activitrax (Ax) pacemakers, and simultaneous sinus rhythm (SR) in an elderly population. In ten subjects mean age 70.6 years, range 49-81 years, the pacemaker responses were noninvasively compared by strapping the units to the chest wall under constant and equal pressure applied by an adjustable belt. Pacemaker rates and SR were recorded simultaneously on a three-channel ECG recorder. The units were programmed in situ to give an increase in rate from 70 beats/min sitting, to 100 beats/min after walking at a normal pace for 30 seconds. Programming took three times longer for Sg (P less than 0.02). The response to standing and bending was poor for both units (Ax mean 75.7 beats/min, Sg mean 77.6 beats/min), when compared to SR (mean 90.3 beats/min). A 20-step test resulted in a greater rate response from Ax (mean 105.3 beats/min) than from Sg (mean 96.3 beats/min [P = 0.09]), though both were still less than SR (116.3). There were significant differences between the two pacemakers on treadmill testing, at peak rate achieved (Ax mean 112.5 beats/min; Sg mean 102.7 beats/min [P less than 0.005], SR mean 122.5 beats/min) and at end exercise (Ax mean 112.5 beats/min; Sg mean 92.9 beats/min [P less than 0.002], SR mean 121.3 beats/min). Arm exercise, however, resulted in a significantly greater response from Sg than Ax (105.1 and 88.5 beats/min, respectively; P less than 0.01, SR 98.7 beats/min).(ABSTRACT TRUNCATED AT 250 WORDS)     

Correlation of Impedance Minute Ventilation with Measured Minute Ventilation in a Rate Responsive Pacemaker

Although rate responsive pacing based on impedance minute ventilation (IMV) is now standard, there is almost no data confirming the relationship between IMV from an implanted pacemaker and measured minute ventilation (VE) during exercise. Nineteen completely paced adults implanted with Medtronic Kappa 400 pacemakers underwent symptom-limited maximal metabolic treadmill testing using a modified Minnesota Pacemaker Response Protocol. Minute ventilation (VE, L/min) was simultaneously measured using the flowmeter of a respiratory metabolic gas analysis system and the transthoracic impedance minute ventilation circuitry of the pacemaker. Correlation coefficients (r) were used to find the best fit line to describe the relationship between the two measurements. Mean (+/- SD) r values for the first, second, and third order polynomial equations and for log and exponential equations were: 0.92 +/- 0.08, 0.94 +/- 0.04, 0.95 +/- 0.04, 0.91 +/- 0.06, and 0.91 +/- 0.07, respectively. None of the r values were statistically different from the first order equation. Transthoracic IMV as measured by the Medtronic Kappa 400 is closely correlated to measured minute ventilation and is represented well by a first order (linear) equation.     

Inappropriate Rate Change in Minute Ventilation Rate Responsive Pacemakers Due to Interference by Cardiac Monitors

Observations of inappropriate rate increase in five patients with minute ventilation rate responsive implanted pacemakers (Telectronics Meta) are reported. Pacing rate increases were observed immediately upon connection of the resting patients to two brands of widely used cardiac monitors, and one commonly used echocardiograph. In some circumstances, the rate increase remained until monitor disconnection; in others the rate increase was transient, lasting about 20 seconds. A hardware thoracic resistance variation simulator was constructed and connected to one of the pacemakers to test sensitivity to rate modifying interference from external sources. This demonstrated that the sensitivity to interference is dependent upon the frequency of the interfering signal and is highest in the range 10–60 kHz. that peak currents as low as 10 μA can cause maximum rate increase, and that the signals injected into patients by several cardiac monitors, for purposes of lead-off detection or respiratory monitoring, fall into the frequency range at which the pacemaker is most susceptible to interference.     

New Algorithms to Increase the Initial Rate Response in a Minute Volume Rate Adaptive Pacemaker

Background : Minute volume is a truly physiological sensor for rate adaptive pacing that correlates with metabolic expenditure throughout the range of physical activity. Criticism has centered on the slow initial response compared to less physiological sensors. A new algorithm, consisting of rate augmentation factor and programmable speed of response, has been incorporated in the 1206 META III pacemaker generator and was designed to improve the rate response at lower levels of exertions. Rate augmentation factor increases the programmed rate response factor by 3, 6, or 10 when set to low, medium, or high, respectively; this augmentation lasting to 50% of the maximum programmed rate. Response time can be programmed to medium or fast. Methods : Nine patients were studied during the first 3 minutes of an exercise test (Bruce protocol) in a single blind manner. The pacemaker generator was randomly programmed with rate augmentation factor at off, low, or high and speed of response to medium or fast, giving six possible combinations. Heart rates were recorded continuously for the duration of the test and until resting heart rate was achieved during recovery. The test was repeated until all six combinations had been tested. Results : During exercise significant differences appeared in response time from 30 seconds onward. Fast response and rate augmentation factor contributed to an improved rate response with greatest speed of response seen with fast response time and high rate augmentation factor. During recovery decreases in recovery time were seen with fast response time but rate augmentation factor prolonged recovery. Conclusions : Rate augmentation factor improves initial rate response in the early stages of exercise. Fast response gives an improved time to initial rate increase and shortens the duration of inappropriate postexercise tachycardia. These features improve the pattern of response of the minute ventilation sensor.     

Automatic Adaptation of the Basic Pacing Rate in Response to Minute Ventilation

Rate responsive pacing based on minute ventilation (VE) correlates highly with metabolic demand. This type of sensing also recognizes extended periods of rest. The Chorum pacemaker includes a rate responsive algorithm that modulates the basic rate according to phases of activity versus sleep. Forty-six patients (mean age 78 ± 15), received a Chorum pacemaker for atrioventricular block in 17 cases, sick sinus syndrome in 25, and mixed disorders in 4. Holter monitoring was performed to analyze heart rate and to examine the circadian adaptation of the minimal pacing rate. The mean basic rate was programmed at 63 ± 5 beats/min, and the sleep rate at 52 ± 4 beats/min. Seventeen patients had spontaneous heart rates consistently above the programmed basic rate, and 6 had sustained supraventricular tachyarrhythmias. One-half of the patients had periods of pacing at the programmed sleep rate. The mean diurnal pacing rate was 68 ± 5 beats/min compared to a mean nocturnal rate of 60 ± 4 beats/min (P < 0.0001). The average time spent at the basic rate was 37 ± 30 min (0–110) during daytime (4%), versus 242 ± 153 min (20–477) at night (45%, P < 0.0001). No adverse effect was observed in this patient population. VE allows a reliable detection of the sleeping periods as well as an adjustment of the basic rate in accordance. Caution is advised in cases of bradycardia dependent tachyarrbythmias.     

Single Versus Double Chamber Rate Responsive Cardiac Pacing: Comparison by Cardiopulmonary Noninvasive Exercise Testing

A new double chamber rate responsive cardiac pacemaker (DDDMR) bas been implanted in seven patients (four males and three females) with a mean age of 62 years. Indication for pacemaker treatment was complete AV block in two patients, complete AV block associated to sinus node disease in three patients and sinus node disease alone in two patients. Six patients underwent two maximal stress tests on a cycloergometer performed twice randomly starting with WIMR or DDDMR. Basic work load of 50 watts was increased by steps of 25 watts every 2 minutes. Heart rate, respiratory frequency, blood pressure, exercise duration, maximal charge developed, oxygen consumption, rate pressure product, efficiency and Borg scale were compared. Our results show a general trend but no significant differences between ail the measured parameters except for efficiency which was significantly higher with DDDMR. These results prove a slight improvement of cardiopulmonary performance in DDDMR pacing compared to WIMR and also confirm the importance of atrial contribution to cardiac output on exercise.     

Pacemaker Mediated Tachycardias In Single Chamber Rate Responsive Pacing

LAU, C.-P., ET AL.: Pacemaker Mediated Tachycardias In Single Chamber Rate Responsive Pacing. Although pacemaker mediated tachycardias are classically associated with dual chamber pacemakers, single chamber rate responsive pacemakers are also susceptible to such tachycardias under special circumstances. A unipolar activity sensing rate responsive pacemaker (Activitrax 8403) was implanted in an 83-year-old man with complete atrioventricular block. The pacemaker was programmed at an output of 5 V, activity threshold medium, rate response 5, and lower and upper rates of 70 and 125 beats/min, respectively. He presented with palpitations at rest and muscle twitching of the pacemaker pocket 4 months after implantation. Examination confirmed that the pacemaker had flipped over, resulting in pocket pacing which in turn activated the activity sensor, resulting in a rate response. The increase in pacing rate lead to a higher frequency of pocket pacing, thus leading to positive feedback increase in rate. With the patient at rest, pacemaker mediated rates were 106, 91, and 74 beats/min at low, medium and high thresholds, respectively. Decreasing the output to 2.5 V eliminated pocket pacing and the tachycardia. As a result of the reversal of the pacemaker, a similar rate response during exercise could only be achieved at a more sensitive rate responsive setting. Thus, pacemaker mediated tachycardia can complicate pacemaker "flipping" in single chamber activity sensing rate responsive pacemakers. Methods for the avoidance and treatment of pacemaker flipping are discussed. A review of other sensor mediated tachycardias is also presented.     

Measurement of Minute Ventilation with Different DDDR Pacemaker Electrode Configurations

A rate responsive minute ventilation (VE) pacemaker was implanted in 49 patients (70.8 ± 40.0 years). A Chorus RM 7034 pacemaker was implanted in 43 patients and an Opus RM 4534 in six patients. Four sensor configurations were compared: atrial configuration (bipolar atrial lead) in 34 patients; ventricular configuration (bipolar ventricular lead) in 6 patients; unipolar configuration (double unipolar leads) in 6 patients; and floating configuration (VDD single-pass lead) in 3 patients. The patients carried out 57 exercise tests in all with cardiopulmonary recording (CPX). Real VE and oxygen consumption (VO₂) were recorded by the CPX, the VE measured by the sensor (VEsensor) was recorded in the pacemaker memory. The mean correlation between VE and VEsensor was 0.90 ± 0.08 (P < 0.001) and between VO₂ and VEsensor was 0.86 ± 0.10 (P < 0.001). The mean correlation between VE and VEsensor by configuration type were as follows: atrial configuration = 0.89 ± 0.08; ventricular configuration = 0.95 ± 0.05; unipolar configuration = 0.87 ± 0.14; and floating configuration = 0.88 ± 0.05. In conclusion, VE may be reliably measured using different electrode configurations. A study conducted in a larger population should allow one to conclude that uniploar electrodes can be used in VDDR, AAIR, VVIR, or DDDR modes to measure VE.     

Rate-Adaptive Cardiac Pacing in Children Using a Minute Ventilation Biosensor

YABEK, S.M., ET AL.: Rate-Adaptive Cardiac Pacing in Children Using a Minute Ventilation Biosensor. Chronotropic integrity is required for a normal cardiac output response to exercise. We evaluated a rate-adaptive ventricular demand pacemaker (Telectronics, META-MV) which uses minute ventilation as the sensed physiological variable for adjusting pacing rate, in seven young patients with a mean age of 11.4 years. All patients had clinically significant bradycardia related to complete heart block (n = 4) or sinus node dysfunction (n = 3). For the entire group, paced heart rates increased from 70 ± 10 beats/min to 151 ± 19 beats/min with exercise testing. The onset of rate adaptation took < 30 seconds. Changes in paced rate were linearly related to workload, VO₂ (5.9 to 20.7 mL/min/kg) and minute ventilation (8–65 L/min). The decline in pacing rate after exercise was related directly to the gradual decrease in minute ventilation and VO₂. Our data show that minute ventilation closely and accurately reflects the metabolic demands of varying workloads in children and can be used to achieve physiological, rate-adaptive pacing.     

The "Low Intensity Treadmill Exercise" Protocol for Appropriate Rate Adaptive Programming of Minute Ventilation Controlled Pacemakers

The objective of rate adaptive pacemakers that measure minute ventilation by tmnsthoracic impedance is to simulate the physiological relationship of the sensed signal to the sinus node response during exercise, thus achieving an appropriate matching of heart rate with patient effort. The purpose of this study was to determine the physiological relationship between heart rate and minute ventilation (HR/VE) during peak exercise testing in order to develop a database for appropriate rate adaptive slope programming of minute ventilation controlled pacemakers. Due to several clinical limitations of peak exercise testing, it was additionally determined whether the 35-watt “low intensity treadmill exercise” (LITE) protocol can be used as a substitute for peak exercise test using the “ramping incremental treadmill exercise” (RITE) protocol in order to assess the correct HR/VE slope below the anaerobic threshold. The stress tests were performed on a treadmill with the collection of breath-by-breath gas exchange. Linear regression analysis was used to determine the HR/VE slope below and above the anaerobic threshold and during the early, dynamic phase of low intensity exercise with the RITE and LITE protocols, respectively. The results of this testing in 41 healthy subjects demonstrated that the HR/VE relationship throughout treadmill exercise using the RITE protocol was not linear but curvilinear in nature, with a steeper HR/VE slope of 1.54 ± 0.51 below versus 1.15 ± 0.37 above the anaerobic threshold (P < 0.005). The HR/VE slope determined during the early, dynamic phase of the LITE protocol (1.58 ± 0.88) did not differ from the HR/VE slope from rest to anaerobic threshold obtained using the peak exercise RITE test (1.54 ± 0.51; P = 0.79), Rate adaptive pacing should simulate the curvilinear relationship between heart rate and minute ventilation from rest to peak exercise. The HR/VE slope determined during the early, dynamic phase of low intensity exercise represents the HR/VE slope derived from the RITE protocol below the anaerobic threshold. According to the peak exercise database, the slope above anaerobic threshold can easily be calculated as a percentage of the slope below the anaerobic threshold. The LITE protocol can, therefore, be effectively performed as a substitute for peak exercise stress tests to determine the correct pacemaker rate response factor in order to obtain a physiological heart rate to minute ventilation relationship for the appropriate matching of paced heart rate with patient effort.     

The Safety of Digital Mobile Cellular Telephones with Minute Ventilation Rate Adaptive Pacemakers

In vitro tests suggest that rate adaptive pacemakers using changes in transthoracic impedance to vary pacing rate may be affected by digital mobile telephones. Electromagnetic fields generated by digital mobile telephones (Global System for Mobile [GSM]) represent a potential source of electromagnetic interference (EMI) for the Telectronics META rate adaptive pacemakers, which use transthoracic impedance as a sensor to determine changes in minute ventilation. Sixteen implanted Telectronics META pulse generators were exposed to 25-W simulated GSM transmissions (900-MHz carrier pulsed at 2, 8, and 217 Hz with a pulse width of 0.6 ms) and the antenna of a 2-W digital mobile telephone (900-MHz, 217-Hz pulse. 0.6-ms pulse width). The 12 dual and four single chamber devices were programmed to maximum sensitivity and assessed in unipolar and bipolar settings and rate adaptive and nonrate adaptive modes. In all cases of EMI, testing was repeated at lower, more routinely set bipolar sensitivity levels. At maximum sensitivity, 11 of 16 devices displayed no evidence of EMI. Brief ventricular triggering occurred in 2, a brief pause in 1, a combination of both in 1, and a brief episode of pacemaker-mediated tachycardia in 1. With pulse generators programmed to more routine sensitivities, only one device displayed rare single beat ventricular triggering. No changes in minute ventilation rate adaptive pacing were observed. At maximum unipolar sensitivities, the META series of rate adaptive pacemakers are resistant to clinically important EMI from digital mobile telephones. Set at routine sensitivities, these devices perform reliably in the presence of digital mobile telephones.     

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.     

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.     

Quality of Life in Patients with Rate Responsive Pacemakers: A Randomized, Cross-Over Study

Eleven patients with rate responsive pacemakers (7 men, 4 women, mean age 41 years with a range of 23-60) were randomly assigned to a cross-over study in order to assess their overall exercise capacity and quality-of-life (QOL) scores. All of the pacemakers were implanted for complete AV block or sick sinus syndrome. The pacemakers were randomly programmed into VVI or rate responsive (VVIR) pacing modes for 3-week study periods in each mode. At the end of each period, an exercise test was performed and the QOL was evaluated by the "Hacettepe Quality-of-Life Questionnaire". All patients exercised longer in the VVIR mode (mean 10.54 ± 0,73 min) than in the VVI mode (mean 7.81 ± 0.62 min) (P < 0.05). QOL scores were also found to be significantly higher in the VVIR mode (mean 173.81 ± 16.22 points) compared to the VVI mode (mean 156.27 ± 21.22 points) (P < 0.01). In conclusion, our results suggest that VVIR pacing offers a better QOL in addition to an improved exercise capacity, compared to the single chamber nonrate modulated pacing (VVI).