Accelerometer-Based Adaptive-Rate Pacing: A Multicenter Study

A new adaptive rate pacemaker, using an acceleromeler to detect body motion as an indicator of metabolic demand, was evaluated in 13 centers located in five countries. During the study, 55 patients with a broad range of indications were implanted with the EXCEl™ VR single chamber pacemaker. One month evaluations were completed on a subgroup 0f 37 patients. The pacemaker response was optimized before discharge using a simple walking test. An "exercise test" recording feature in the programmer eliminated the need for ECG monitoring. At nominal settings, the mean (± SD) pacing rate increased 29 ± 9 ppm while walking slowly and 44 ± 11 ppm (n = 33) during a brisk walk. This information was used to optimize the parameter settings. Without further changes to the programmed settings the patients were subsequently tested 2–4 weeks postimplant with a symptom-limited treadmill test using the chronotropic assessment exercise protocol (CAEP). Mean pacing rate increased from 74.5 ±2.5 ppm (n = 24) at rest to 118.6 ± 12.2 ppm (n = 21) at 3 mph/6% grade to 143.5 ± 3.5 ppm [n = 2) at 3.8 mph/8% grade. Conclusion: The individual responses were proportional to the physical exertion imposed on the patients. Pacing rates were considered to be appropriate using the chronotropic response zone as a criterion for appropriate rate modulation. A simple walking test utilizing the exercise test facility, results in appropriate optimization of the pulse generator to the individual patient.     

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.     

Clinical Experience with an Activity Sensing DDDR Pacemaker Using an Accelerometer Sensor

The rate adaptive characteristics and pacemaker mediated tachycardia protection algorithm of an accelerometer based DDDR pacemaker were evaluated in 11 patients with bradycardia (seven atrioventricular block, four sick sinus syndrome). Rate adaptive programming was effected by collecting the acceleration level during a 3-minute moderate exercise ("tailoring" of sensor). In comparison with an externally attached piezoelectric sensor, the accelerometer sensor showed lower rate changes during external tapping of the pacemaker (16 +/- 3 vs 29 +/- 4 ppm, P less than 0.02) and applied direct pressure (1 +/- 1 vs 40 +/- 3 beats/min, P less than 0.001) on the pacemaker. At nominal setting, the accelerometer sensor showed improved rate stability and higher rate response to jogging and standing, although responses to other daily activities and treadmill exercise were similar. Apart from changing the rate responsive slope, rate response could be improved by repeat "tailoring" of the sensor at a lower exercise level, resulting in better overall rate response characteristics. The ability of the rate monitoring software to collect acceleration levels for an activity and profile the projected rate response at different rate responsive settings allowed programming to be effected with the minimum amount of exercise testing. The pacemaker also discriminated atrial tachyarrhythmias from normal sinus response using the sensor to judge the appropriateness of the atrial rate, which correctly identified and prevented rapid ventricular tracking in two patients during atrial flutter/fibrillation.     

A New Motion Responsive Pacemaker: First Clinical Experience with an Acceleration Sensor Pacemaker

A new accelerometer-based adaptive rate pacemaker (OEXCELVR^TM) was evaluated to investigate its behavior at nominal settings during treadmill exercise testing and postural changes. Eight patients with sinus rhythm were selected to compare intrinsic heart rate to sensor mediated rate. Throughout exercise treadmill testing, changes in the sensor mediated rate closely paralleled actual physiological changes. The Pearson product moment correlation of pacing rate with sinus frequency, calculated for all patients, was r = 0.82 (P = 0.001). Change in the patient's physical position resulted in immediate change in sensor rate, which corresponded appropriately to the type of position change and activity level. Average (± SD) pacing rate was 62.4 ± 2.7 beats/min supine; 67 ± 3.8 beats/min sitting; 69.8 ± 6.4 beats/min standing; 81.6 ± 8.7 beats/min slow walking; and 96.8 ± 1.3 beats/min fast walking. After 4 minutes of recovery, the average pacing rate dropped to 65 ± 3 beats/min. The interaction between the accelerameter and the pulse generator at nominal settings was accurate and infrequently required the use of its many programming options. The accelerometer sensor and pulse generator algorithm in this device during postural change and exercise resulted in physiological-like changes in sensor mediated heart rate.     

Improved Accelerometer-Based Rate Adaptive Pacing by Means of Second-Generation Signal Processing

Accelerometer-based rate adaptive pacing has gained widespread clinical use. Limitations exist for the distinction between walking upstairs and downstairs. It was the aim of this study to evaluate a new signal processing algorithm for more physiological rate adaptation. A custom-made pacemaker incorporating an accelerometer was randomly fixed to the left or right chest of 16 pacemaker patients (7 females, age: 64 ± 11 years), 18 elderly study participants (6 females, age: 62 ± 11 years), and 15 students (7 females age: 23 ± 2 years). Study participants walked on level ground, upstairs and downstairs at five different step rates (72, 84, 96, 108, and 120 steps/min) controlled by an acoustic quartz metronome. The accelerometer signals, recorded on a portable data recorder, were analyzed with respect to frequency content, peak average of the mean acceleration, and morphology characteristics of the acceleration signal above and belowzero baseline. By calculating the quotient of the signal's duration above and below zero baseline, a reliable discrimination between walking upstairs and downstairs was possible. A correction of the Leaky integrator signal by the new quotient yielded a more adequate rate adaptation to walking up and downstairs to represent at the patient's daily life activities. A more physiological rate adaptation can be achieved when using not only the accelerometer signal's amplitude, but applying additionally the morphology criterium of the acceleration signal's content in the positive and negative direction.     

New Concept in Activity-Controlled Pacemakers: Clinical Results With an Accelerometer-Based Rate Adaptive Pacing System

An accelerometer-based rate adaptive generator (EXCEL VR) has been introduced. A preclinical group of 22 subjects with strap-on devices was observed and reported. A clinical protocol including observation of rate adaptive response to typical daily activities and incremental exercise on a treadmill was administered in seven implanted patients. Indications for implantation in these patients was either second- or third-degree atrioventricular block (five patients, VVIR pacing mode) and sick sinus syndrome (two patients, AAIR pacing mode). Mean pacing rates were 50 ppm (supine), 56 ppm (standing), 77 ppm (descending the stairs), 81 ppm (slow walk), 83 ppm (slow stair climb), 91 ppm (fast walk), and 92 ppm (fast stair climb). When the arm proximal to the pulse generator was exercised, the rate rose to 92 ppm. When the distal arm was strained, the rate was 63 ppm. During treadmill testing, rates between 82 ppm (2 km/hour) and 104 ppm (5 km/hour) were observed. This accelerometer-based rate adaptive pulse generator provided a proportional response to graded activities of treadmill exercise and daily living in these groups of preclinical and clinical subjects.     

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.     

Practical Aspects of Rate Adaptive Atrial (AAI,R) Pacing: Clinical Experiences in 44 Patients

Forty-four patients with sinus node disease and chronotropic incompetence but no evidence of AV conduction disturbances were treated with rate adaptive atriul (AAI,R) pacemakers. Medtronic Activitrax and Siemens Sensolog activity sensing single chamber pulse generators were used. Twentyfour patients (55%) had the bradycardia-tachycardia syndrome. The mean folloiw-up time is 20 ± 14 months (range 1–48, median 17 months). All patients remain alive. Two patients were reoperated upon for lead problems without change of pacing mode. One patient developed symptomatic: srecond-degree Wenckebach block during follow-up, and received a DDD,R system. Although 22 of the patients were treated with antiarrhythmic drugs postoperatively, no further cases of significant AV conduction disturbances were seen. During rapid atrial pacing, exercise-induced enhancement of AV conduction was a consistent finding, although less pronounced in patients treated with beta-blocking drugs. One patient developed permanent atrial fibrillation with an adequate ventricular rate. By systematic reprogramming procedures, QRS complex sensing through the atrial electrode could be demonstrated in 25 patients (23/28 with unipolar and 2/16 with bipolar leads). it could be counteracted effectively by pulse generator program selection in all cases. Forty-two of 44 patients (95%) remain in AAI,R pacing with normal function, Rate adaptive atrial pacing can be successfully applied in this patient group.     

A blended sensor restores chronotropic response more favorably than an accelerometer alone in pacemaker patients: the LIFE study results

Background: Adaptive rate sensors used in permanent pacemakers incorporate an accelerometer (XL) to increase heart rate with activity. Limited data exists regarding the relative benefit of a blended sensor (BS) (XL and minute ventilation) versus XL alone in restoring chronotropic response (CR) in chronotropically incompetent (CI) patients. Methods: One thousand five hundred thirty‐eight patients from the limiting chronotropic incompetence for pacemaker recipients (LIFE) study were implanted with a pacemaker and 1,256 patients had data collected at 1 month. Patients performed a treadmill test 1‐month postimplant while programed in nonrate responsive mode (DDD‐60) to determine CI. Only patients who completed at least three exercise stages and achieved a peak perceived exertion ≥16 were included in the analyses. The metabolic chronotropic relationship (MCR) slope was used to evaluate CR in 547 patients. Patients were randomized to XL or BS with a conservative fixed rate response factor (XL = 8, MV = 4). CI patients performed a follow‐up 6‐month treadmill test. Results: CI prevalence in this patient population (n = 547) was 34%. No differences in baseline characteristics existed between groups. Although both groups showed significant within‐group improvements in MCR slope from 1 to 6 months (both P < 0.001), the BS group had a significantly higher MCR slope at 6 months compared to the XL group (P = 0.011). Improvement in quality of life (QOL) did not differ between groups . Conclusions: In this general pacemaker population with CI, a BS programed empirically restores CR more favorably than an XL sensor programed nominally. Further studies are needed to determine if individual sensor optimization would lead to improvement in functional capacity, higher MCR slopes, and QOL.     

Peak Endocardial Acceleration-Based Clinical Testing of the "BEST" DDDR Pacemaker

The peak endocardial acceleration (PEA, unit g) shows a near correlation with myocardial contractility during the isometric systolic contraction of the heart (dP/dtmax), with sympathetic activity and, thus, with physiological heart rate modulation. The (Biomechanical Endocardial Sorin Transducer (BEST) sensor is incorporated in the tip of a pacing lead and measures PEA directly near the myocardium. In an international study, the lead was implanted with the dual chamber pacemaker Living-1 (Sorin) in 105 patients. The behavior of the PEA signal was tested under conditions of physical and mental stress and during daily life activities by 24-hour recordings of PEA (PEA Holter) at 1 to 2 months and approximately 1 year after implantation. Implantation of the BEST lead was performed without complications in all patients. The sensor functioned properly in the short- and long-term in 98% of patients. Although PEA values differed from patient to patient, the values closely reflected the variations in sympathetic activity due to physical and mental stress in each patient. During exercise and during daily life activities a close correlation between PEA and heart rate was observed among patients with normal sinus rhythm. Peak endocardial acceleration allows a nearly physiological control of the pacing rate.     

Behavior of Different Activity-Based Pacemakers During Treadmill Exercise Testing with Variable Slopes: A Comparison of Three Activity-Based Pacing Systems

A new generation of activity-based pacemakers incorporates an accelerometer sensitive to low frequency acceleration signals in the anteroposterior direction for sensing of bodily stress. The purpose of our investigation was to test a representative model of these new activity-based pacemakers (Relay) and compare it with current vibrationand housing pressure-sensing systems. We tested ten pacemaker patients with implanted Activitrax, Sensolog, and Relay systems during treadmill exercise testing with variable slopes. Devices from the three systems were also strapped externally to the chest of each patient and to ten normal test subjects in the control group. Exercise tests were conducted with changes of treadmill speed and/or treadmill slope. For comparable workloads during constant speed/variable slope and constant slope/variable speed, Relay had similar rate responses (difference not significant). Significant differences (P < 0.05) in rate adaptation attributable to the kind of treadmill exercise (change in treadmill speed or slopes) were observed in the housing pressure- and vibration-based pacemakers. Activity-based pacemakers with an acceleration sensor adapt pacing rates during treadmill exercises independent of treadmill speed or slope better than those controlled by a conventional housing pressure or vibration sensor.     

Temperature May Be an Appropriate Sensor for Chronotropically Incompetent Patients with Postural Syncope

Chronotropically incompetent patients benefit most from sensor driven rate response during exercise. Postural syncope may occur despite the chronotropic response because of the failure of currently available sensors to respond physiologically to postural changes. Seven chronotropically incompetent patients with postural syncope who had a dual chamber rate adaptive pacemaker (Circadia^R) that modulates heart rate in response to temperature change were studied with respect to: (1) response to exercise: and (2) head-up tilt (HUT). During exercise, continuous-wave Doppler of aortic velocities and two-dimensional echocardiographic derived measurements of left ventricular systolic function were used to assess cardiac function. Patients exercised longer (by an average of 168 sec) in the DDDF/compared to the DDl mode (P = 0.013). Increase in exercise duration was due mostly to the sensor driven increase during DDDH pacing. During DDDR pacing, heart rate increased from 71 ± 6 to 121 ± 17 ppm compared to 70 ± 1 to 103 ± 21 ppm for the DDl pacing (P = 0.038). Stroke volume as assessed by Doppler derived stroke distance (SD) contributed more significantly to the cardiac output increase during exercise in the DDl mode (SD increased from 13.4 ± 4 to 18 ± 7 cm in DDl compared to 13 ± 4 to 14 ± 2 cm in DDDR mode), although these mechanisms were insufficient to fully compensate for failure of appropriate chronotropic response. In response to the HUT, right ventricular temperature increased from 36.78°C ± 0.29°C to 36.89±± 0.28°C (P = 0.0002), and heart rate increased from 54 ± 3 to 71 ± 8 ppm (P = 0.0003) in the DDDR mode. No significant change in heart rate occurred in the DDl mode in response to the HUT. Strong positive correlation of temperature and heart rate was noted in all patients in response to HUT (P = 0.001, R²= 0.755–0.976). We conclude that temperature sensor responds physiologically to exercise and HUT. Therefore, temperature sensing rate adaptive dual chamber pacing may be appropriate for chronotropically incompetent patients with posture related syncope.     

Sensor-Driven Rate Smoothing in a DDDR Pacemaker

DDD pacemakers may have large cycle-to-cycle variations in rate at the upper rate limit because of 2:1 block or Wenckebach-type block. Rate smoothing was introduced as an option to eliminate these large variations. Now, DDDR pacemakers can produce similar electrocardiographic displays through a different mechanism that uses an activity sensor. This is termed "sensor-driven rate smoothing" because it occurs only when the activity sensor is driving the pacemaker. In the case described, as the atrial rate exceeded the maximum tracking rate and reverted to Wenckebach-type block, the RR interval varied only from 600 msec to 680 msec (13.3% rate-smoothing value) because of sensor-driven pacing. Maximal sensor-driven rate smoothing requires optimal programming of the rate response indicators. This sensor-driven rate-smoothing effect is an electrocardiographic manifestation that will undoubtedly be seen more frequently as DDDR devices come into widespread clinical use.     

A New Feature for Control of Inappropriate High Rate Tracking in DDDR Pacemakers

LEE, M.T., ET AL. A New Feature for Control of Inappropriate High Rate Tracking in DDDR Pacemakers. A limitation of current DDD and DDDR pacemakers is the inability to distinguish between inappropriate high rate atrial sensed events that are physiologically appropriate to track (e.g., elevated sinus rates resulting from exercise, emotional responses, etc.) and those that are physiologically inappropriate to track (e.g., paroxysmal atrial dysrhythmias, myopotentials, retrograde conduction, etc.). The sophistication of sensing circuitry is not yet sufficiently advanced to permit a pacemaker to distinguish appropriate atrial events by morphology. The addition of an independent sensor to a DDD pacemaker (i.e., DDDR) gives more information about the patient's condition, especially with respect to exercise. This information can be used to judge the appropriateness of a high sensed atrial rate, and to modulate the pacemaker's response. If the sensor input is below a specified level, indicating lack of exercise, the DDDR can track sensed atrial events only to a tolerably low limit-the conditional ventricular tracking limit (CVTL). Wenckebach-type behavior ensues at the CVTL until the sensor input increases, indicating that exercise is occurring, or until the sensed atrial rate decreases. If the sensor input indicates exercise, the DDDR pacemaker can track up to the programmed maximum rate. Two DDDR systems have been developed that incorporate this feature; one based on temperature, the other on activity. Currently the CVTL is set at a value about 30 ppm above the pacing rate, as a compromise to support emotional needs not seen by the sensor. Improved sensors could cause the decision to raise the tracking limit (i-e., recognition of physiological need for higher rates) to be more accurate, perhaps making the CVTL proportional to the sensor signal.     

Chronotropic incompetence in patients with an implantable cardioverter defibrillator: prevalence and predicting factors

Chronotropic incompetence (CI), which has not been systematically examined in the ICD patient population, may have implications for device programming. A total of 123 ICD patients were classified into three groups: single-chamber ICD with sinus rhythm, dual-chamber ICD with sinus rhythm, and single-chamber ICD with permanent atrial fibrillation. Heart rate response, maximum oxygen uptake, and oxygen uptake at the anaerobic threshold were measured during treadmill exercise testing. In addition, clinical variables such as antiarrhythmic drug therapy, underlying heart disease, and left-ventricular (LV) ejection fraction were recorded. Of the patients studied, 38% were chronotropically incompetent (47/123). Significant predictors of CI were as follows: presence of a coronary disease (P = 0.036), prior cardiac surgery (P = 0.037), chronic drug therapy with beta-blockers (P = 0.032), administration of amiodarone (P = 0.025), and a combination of these two forms of treatment (P = 0.01). Spiroergometry revealed reduced exercise capacity (P = 0.041) and lessened VO2max (P = 0.034) among chronotropically incompetent patients. A large percentage of ICD patients demonstrates CI with subsequently reduced physical stress tolerance. In light of the DAVID study, we believe that a closer examination of rate-adaptive modes for ICD patients is warranted under enhanced conditions: (1) optimized AV interval programming; (2) utilization of new algorithms to reduce ventricular pacing in combination with rate-adaptive atrial pacing, with the goal of addressing CI while minimizing ventricular pacing; and (3) an optimized upper heart-rate limit.     

Clinical Comparison of Acute Single to Dual Chamber Pacing in Chronotropically Incompetent Patients with Left Ventricular Dysfunction

Dual chamber, rate responsive (DDDR) pacing is felt to be superior to ventricular, rate responsive (VVIR) pacing since it more closely mimics the normal electrical and hemodynamic activity of the heart. This reasoning has been used to justify the higher initial costs and increased complexity of dual chamber systems. This study was designed to determine if objective criteria could be identified during acute testing to justify implanting a dual chamber instead of a single chamber system in patients with left ventricular dysfunction. Eight patients with DDDR pacemakers (implanted for chronotropic incompetence) and left ventricular dysfunction underwent exercise radionuclide angiography and graded exercise treadmill testing. Each patient performed the tests in the single (VVIR) and dual (DDDR) chamber modes in a randomized, blinded fashion. We found that objective parameters such as ejection fraction (31%± 13% vs 31%± 10%), exercise tolerance (6.1 ± 2.7 min vs 6.3 ± 2.9 min), oxygen consumption (VO₂) (941 ± 286 mL/min vs 994 ± 314 mL/min), carbon dioxide production (VCO₂) (995 ± 332 mL/min vs 1054 ± 356 mL/min), and maximum attainable workload (43 ± 24 W vs 46 ± 22 W) did not differ between the single and dual chamber pacing modes. These findings suggest that in the acute setting, the additional cost and complexity of dual chamber, rate responsive pacing cannot be justified by objective improvements in exercise tolerance in patients with underlying left ventricular dysfunction.     

P Wave Tracking Above the Maximum Tracking Rate in a DDDR Pacemaker

Dual-chamber, rate-modulated pacemakers have recently become available. These devices, whose rate response is determined by the combined input from the intrinsic atrial rate and the sensor-driven rate, have led to some unexpected upper rate behaviors. In the case presented, with the maximum sensor pacing rate at 150 ppm, multiple episodes of apparent P wave tracking occurred above the maximum P wave iracking rate of 100 ppm. This behavior is explained by P waves thai inhibit sensor-driven atrial output; inhibition may result in variable maximum tracking rates that are equal to the current sensor-driven rate. This effect appears to have minimal physiological consequence. Its importance lies in its recognition as normal DDDR function so that searches for pacemaker malfunction will not be made.     

Incidence and Significance of Chronotropic Incompetence in Patients with Indications for Primary Pacemaker Implantation or Pacemaker Replacement

This prospective study was undertaken to evaluate the incidence and significance of chronotropic incompetence in 211 patients [age 71.1 6 10.6 years (mean 6 SD)] by means of maximum exercise test in order to determine the indication for rate-responsive pacing before primary pacemaker implantation (147 patients) or pacemaker replacement (64 patients). There were 112 (53%) patients with second- or third-degree AV block, 63 (30%) with sick sinus syndrome, and 36 (17%) with chronic atrial fibrillation. Chronotropic incompetence was defined as maximum heart rate lower than age-adjusted norm calculated by the formula: 0.7x(220 - age) and its significance as the difference between the two rates. The overall incidence of chronotropic incompetence was 42%. The incidence was significantly higher in patients with atrial fibrillation (67%, P<0.0005) and sick sinus syndrome (49%, P<0.012) than in those with AV block (30%). The mean difference between maximum heart rate and the age-adjusted norm was 18% (range 2%-63%). The mean difference was significantly higher in patients with atrial fibrillation (27%, range 8-63%) than in those with sick sinus syndrome (19%, range 2%-45%, P<0.01), or with AV block (12%, range 6%-26%, P<0.000001). The rate-responsive pacemakers were implanted in 44% of 211 patients studied and in 43% of 196 patients excluded from the study due to the apparent (contra)indication of rate-responsive pacing (NS). Thus, chronotropic incompetence seems to be common in the pacemaker patient population. The highest incidence and significance was found in patients with chronic atrial fibrillation. Systematic evaluation of chronotropic competence can double the rate of implantation of rate-responsive pacemakers; however, further studies are needed to clarify relation between the significance of chronotropic incompetence and functional benefit of rate-responsive pacing.     

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.