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.     

New Integrated Sensor Pacemaker: Comparison of Rate Responses Between an Integrated Minute Ventilation and Activity Sensor and Single Sensor Modes During Exercise and Daily Activities and Nonphysiological Interference

A dual sensor DDDR pacemaker (DX2 Model 7970, Medtronic Inc.) has integrated the rate response of minute ventilation (MV) and activity (ACT) sensors. False rate acceleration by the ACT (constrained upper rate) and MV (cross-checked by ACT) is reduced. We examined the rate response profile and rate kinetics of the automatically optimized integrated sensor by comparing with the projected rate response of ACT and MV sensors alone in nine patients. After 1 month of sensor optimization using rate profile optimization (RPO), patients underwent maximal and submaximal treadmill exercises and performed activities of daily living (ADL). The integrated sensor mode gave a faster speed of rate response with a shorter delay time, time to 50% rate response and time to 90% of rate response compared to the MV sensor during hall walk (0.37 ± 0.08, 0.7 ± 0.09, 1.43 ± 0.19 vs 1.11 ± 0.1, 1.75 ± 0.14, 2.91 ± 0.17 min; P < 0.05), The average maximal sensor rates were significantly more proportional for the integrated sensor mode compared with either the ACT or MV mode. There was no significant difference in both the maximal pacing rate among the three sensor modes during maximal exercise and the rate decay during recovery. During interference studies by arm swinging (30–40 swings/min) and external tapping of the pacemakers (2 taps/s), there was only a moderate increase in pacing rate by 13 ± 9, 16 ± 5 beats/min. Hence, the new integrated sensor with the automatic rate profile optimization algorithm resulted in improved rate response profiles during submaximal exercise and ADL compared to the individual sensor response, and the sensor blending and cross-checking algorithm made the pacemaker relatively immune to false triggering of both the ACT and MV sensors.     

Clinical Study of a New Activity Sensor for Rate Adaptive Pacing Controlled by Electrical Signals Generated by the Kinetic Energy of a Moving Magnetic Ball

A new rate adaptive pacemaker (Sensorithm) controlled by an activity sensor providing electrical signals induced by a magnetic ball moving freely in an elliptical cavity surrounded by two copper coils, was implanted in ten patients; mean age of 75 years (range 64–89). Six patients had atrioventricular block and four had sinus node disease. In auto-set testing procedure during a 1-minute walk in the corridor, a slope resulting in a maximum rate of 95 beats/min was selected in every patient, and a medium reaction time was programmed. During graded treadmill exercise tests the heart rate increased 63 ± 7 beats/min to 135 ± 6 beats/min in rate adaptive pacing mode (VVIR), and 15 ± 6 beats/min (P < 0.0001) in ventricular pacing mode (VVI). The symptom-limited exercise time was 9.1 ± 1.1 minutes and 8.2 ±1.2 minutes (P = NS), and the exercise distance was 501 ± 95 meters and 428 ± 92 meters (P < 0.05) in VVIR and VVI pacing mode, respectively. The maximum oxygen uptake was 20.6 ± 2.6 mL/kg per minute in VVIR pacing and 18.1 ± 2.1 mL/kg per minute (P < 0.05) in VVI pacing. The delay time until the pacing rate increased 10% of the total rate increase at onset of treadmill exercise was 4.4 ± 0.7 seconds. Assuming a linear relation between metabolic workload and heart rate response from rest to the age predicted maximum heart rate, a deviation of heart rate ranging from 13.5 ± 11.2% to –1.6 ± 5.2% from the expected heart rate at mid-point and endpoint of each quartile of workload was observed during treadmill testing. Conclusions : By using a 1 -minute walk test for selecting an appropriate slope setting, Sensorithm provided a significant and proportional heart rate increase during exercise resulting in an improvement of exercise capacity during VVIR pacing compared to VVI pacing.     

Comparison of Continuously Recorded Sensor and Sinus Rates During Daily Life Activities and Standardized Exercise Testing: Efficacy of Automatically Optimized Rate Adaptive Dual Sensor Pacing to Simulate Sinus Rhythm

The normal sinus rhythm remains the gold standard to compare the rate response of a rate adaptive pacemaker. The aim of this study was to assess an automatically optimized dual sensor system by continuous comparison of the normal sinus (SR) and sensor indicated rates (SIR). Twelve patients with complete heart block (mean age 60 ± 9 years) with normal sinus rhythm received a dual sensor pacemaker driven by combined, automatically adaptive activity and QT sensors. After I month of automatic adaptation, patients performed a treadmill exercise in the VDD mode with simultaneous collection of SR and combined SIR. Thereafter the difference between SR and SIR was recorded over a 1-month period using a software downloaded into the pacemakers, with the patients ambulatory during this period. During exercise testing, the SR and SIR were significantly correlated (r =0.96 ± 0.02, P < 0.001), and the mean difference between SR and SIR was 4.01 ± 4.47 beats/mm. The percentages of paced beats, over the 1 month ambulatory period, that exhibited a difference between SR and SIR of 8 beats/mm were 98%± 2%, 90%± 4% and 67%± 8% for low, medium, and high workloads, respectively (P < 0.05, ANOVA). whereas > 95% of SIR were within 15 beats/min of SR independent of the level of activities. Thus, an automatically programmed dual sensor gives an accurate reflection of SR during exercise. SIR was less accurate for more vigorous daily life activities, but most of the SIR were within the normal SR variation of 15 beats/min.     

Effects of Sensor Selection on Exercise Stroke Volume in Pacemaker Dependent Patients

The effects of sensor selection and sensor blending on the cardiovascular response to graded exercise was evaluated in 10 patients (age 74 ± 2 yrs; 7 men and 3 women) implanted with a dual sensor rate adaptive VVIR pacemaker (Vitatron Topaz(tm) model 515). Patients underwent three graded exercise tests (GXT) with sensor programming randomly assigned. For a given graded exercise text the pacemaker was programmed into activity sensing (ACT), QT sensing, or dual sensing (ACT = QT). Data were recorded at rest and during each stage of the graded exercise text. Oxygen uptake (VO₂) was measured continuously using a Q Plex I system. Heart rate (HR), stroke volume (SV), and cardiac output (Qc) were measured by impedance cardiography. Systolic time intervals were calculated from simultaneous recordings of the ECG. phonocardiogram, and the impedance cardiogram. In response to the GXT no differences in peak VO₂ were observed across the three sensor settings. Regardless of the sensor setting Qc increased linearly with each increment in VO₂. The HR response to ACT only pacing was significantly higher than in the other two pacing conditions. During ACT only pacing SV failed to rise in response to exercise. The increased exercise Qc during QT and ACT = QT pacing were mediated by significant increases in both HR and SV. The QT and dual pacing conditions were also associated with longer diastolic filling times. The data indicate that the mechanisms responsible for the increase Qc during exercise were different for ACT versus ACT = QT or QT sensor-driven pacing.     

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.     

Assessment of pacemaker chronotropic response: implementation of the Wilkoff mathematical model

There are few practical guidelines for proper adjustment of rate responsive pacemaker sensor parameters. This study describes the application of the chronotropic assessment exercise protocol (CAEP) and the Wilkoff model of chronotropic response to assess the adjustment of pacemaker sensor parameters. In 31 patients implanted 1 month previously with a dual sensor pacemaker, pacemaker sensor parameters were adjusted to yield a peak sensor rate of 100 beats/min on a simple 6-minute walk (low intensity treadmill exercise [LITE] protocol); the maximum sensor rate was set to the age predicted maximum heart rate (220-age). The rate response behavior of the pacemaker was then assessed using the slope of metabolic-chronotropic relation (MCR) during CAEP exercise. After adjustments based on the LITE protocol, CAEP exercise yielded MCR slopes of 0.92 +/- 0.25 for the entire study group, which compares well with the predicted normal slope of 1. However, 7 of the 31 patients had sensor MCR slopes during CAEP exercise that were 2 SD or more below expected. To test the sensitivity of this approach to suboptimal pacemaker programming or suboptimal exercise, simulations were performed with the maximum sensor rate programmed below age-predicted maximum heart rate or with exercise truncated before maximum exertion; with these conditions, MCR slopes were sharply lower for the entire group. The authors conclude that a simple treadmill walk (LITE) allowed for optimum programming of sensor parameters in most patients, but in a minority the chronotropic behavior was underresponsive. Failure to appropriately adjust pacemaker maximum sensor rate or failure to achieve peak exercise sharply limits the accuracy of this methodology.     

An Integrated Dual Sensor System Automatically Optimized by Target Rate Histogram

The use of combined sensors and advanced algorithms using different principles can improve rate performance over a single sensor system. Combinations of sensors and more sophisticated algorithms, however, invariably increase the complexity of pacemaker programming. An automatically optimized combined minute ventilation and activity DDDR pacemaker was developed to minimize repeated sensor adjustment. The device used subthreshold (below cardiac stimulation threshold) lead impedance to detect lead configuration at implantation automatically, followed by "implant management," including setting of lead polarity and initiation of DDDR pacing. Automatic sensor adaptation was achieved by programming a "target rate histogram" based on the patient's activity level and frequency of exertion, and the rate profile optimization process matched the recorded integrated sensor response to the target rate histogram profile. In nine patients implanted with the DX2 pacemakers, the implant management gave 100% accuracy in the detection of lead polarity. Rate profile optinuzation automatically increased the pacing rate during exercise between discharge and 3-month follow-up (hall walk: 78 ± 3 vs 98 ± 3 beats/min, and maximal treadmill exercise: 89 ± 6 vs 115 ± 5 beats/min, P < 0.001) with a significant increase in exercise duration during maximal exercise (7.18 ± 1 min vs 9.56 ± 2 min, P = 0.05). The accuracy of rate profile optimization versus manual programming was assessed at 1 month, and there was no significant difference between pacing rate kinetics and maximal pacing rate between the two methods of programming. In conclusion, pacemaker automaticity can be initiated at implantation and the self-optimized rate adaptive response appeared to be comparable to that derived from a manual programming procedure, which may reduce the need to perform time consuming sensor programming.     

Clinical Evaluation of a Dual Sensor, Rate Responsive Pacemaker

Dual sensor pacemakers should respond more appropriately during differing exercise modes than a single sensor device. The Topaz™ models 515 (QT and activity count [ACT] sensing) pacemaker shows appropriate rate response during treadmill exercise testing. We postulated that adjustments to relative sensor contribution should allow fine tuning of the onset of rate response. Eleven patients with this pacemaker were studied. Three standard exercise tests were performed with adjustment of sensor blending and activity threshold between each one. We also assessed the response to isometric exercise and a false positive activity signal. Results : Times to 100 ppm (3.7 ± 1.3, 4.4 ± 2.0, 5.3 ±1.5 mins), times to peak rate (6.1 ± 1.6, 5.6 ± 1.4, 6.5 ± 1.3 mins) and accelerations to peak (9.0 ± 2.4, 9.2 ± 5.3, 7.7 ± 2.8 ppm/min) were measured in all three different sensor settings (QT = ACT, QT 相似文献   

A Prospective Multicenter Study Demonstrating Clinical Benefit with a New Accelerometer-Based DDDR Pacemaker

From November 1994 to October 1995, 63 patients (average age 66 years; 41 men) from 15 centers implanted with the Biotronik Dromos DR and Ergos TC 03 pulse generators were prospectively screened with an exercise test in the DDD mode for the presence of chronotropic incompetence (CI). Both pulse generators incorporate an identical accelerometer-based motion sensor. CI was defined as a maximum heart rate < 60% of age predicted maximum heart rate or 100 beats/min. Twenty-five patients (40%) met the criteria for CI. Two weeks later, CI patients were required to complete paired metabolic exercise testing in the DDD and DDDR modes on consecutive days with a 24-hour rest period. The order of testing was randomized and performed double blinded to minimize potential biases. Three patients who did not reach the anaerobic threshold (AT) and one patient who was unable to perform the metabolic testing were excluded from the analysis. Compared to the DDD mode, there were statistically significant improvements in the DDDR mode for all five endpoints: heart rate (84 ± 3.6 vs 113 ± 3.5 beats/min; P < 0.0001); total exercise time (8.23 ± 0.71 vs 9.15 ± 0.65 min; P = 0.0005); maximum VO₂ (17.76 ± 1.36 vs 20.43 ± 1.75 mL/kg per min; P = 0.0001); V0₂ at AT (13.1 ± 0.87 vs 14.59 ± 0.79 mL/kg per min; P < 0.01); and exercise time to AT (5.65 ± 0.61 vs 6.33 ± 0.53 min; P = 0.02). In conclusion, the results of paired metabolic exercise tests with the Dromos DR and Ergos TC 03 pulse generators demonstrate a clear clinical benefit using the accelerometer-based sensor in the CI patient     

Rate responsive pacemakers: a rapid assessment protocol

Background: Rate responsive (RR) pacemakers are commonly implanted with nominal conservative factory-set responsiveness, which is usually accepted because established exercise protocols are time-consuming. We aimed for efficient assessment of RR pacemaker settings.
Methods: We tested exercise heart rates in controls and paced patients using a brief exercise test that approximates real-life levels of exertion. The test used a nonmotorized treadmill: 30 seconds walking at patient-determined speed followed by 15 seconds brisk exertion. Subjects totaled 110: 26 with RR pacemakers; 22 with non-RR pacers; 27 "sick" nonpaced control patients; and 35 healthy controls. Heart rate (HR) was measured prior to exercise, after 30 seconds of casual walk, after 15 seconds of brisk walk, and 1 minute into recovery. Testing required <5 minutes from set-up to recovery.
Results: The 26 RR pacer patients had a mean HR at rest = 74 ± 10 beats per minute (bpm), walk = 87 ± 14, and brisk = 94 ± 18 (increase 27%). Non-RR pacer patients (n = 22): rest = 73 ± 12 bpm, walk = 88 ± 14, and brisk = 94 ± 17 (increase 24.3%, P = 0.60 vs RR patients). "Sick" controls (n = 27): rest = 78 ± 14 bpm, walk = 102 ± 17, and brisk = 117 ± 18 (increase 51.9%, P< 0.001 vs RR pts). For the healthy controls, HRs were at rest 83+/11 bpm, walk = 104 ± 12, and brisk = 117 ± 13 (P< 0.001 compared to both paced groups; P = NS vs sick controls).
Conclusions: Nominal RR settings may be suboptimal for many patients. The nonmotorized treadmill test allows quick and inexpensive assessment of RR programming, with the potential for efficient RR optimization.     

Evaluation of a New Rate Adaptive Ventricular Pacemaker Controlled by Double Sensors

The LEGEND-PLUS, a new rate adaptive pacemaker that combines activity and minute ventilation sensing for automatic rate adaptation was implanted in the right ventricle (VVIR) in 11 patients (mean age 62 ± 9 years). Initial programming was performed using the Programmer Exercise Protocol (a 3-minute walk). This programming was evaluated by treadmill tests, up-stairs and down-stairs walking, and Holier recordings. Results: Following the final programming of LEGEND-PLUS, the mean upper activity rate was 102 ± 7 beats/rain (range 90–120 beats/min), while the mean upper minute ventilation rate was 125 ± 16 beats/min (range 100–150 beats/min). The mean rate responses during the exercise protocol and the final programming in minute ventilation and activity sensing modes were 5.4 ± 2.3 (range 1–9), versus 4 ± 2.4 (range 1–8; P < 0.01) and 7.6 ±1.1 (range 5–9), versus 7.5 ± 0.8 (range 6–9; P = 0.8), respectively. In the combined sensing mode, the acceleration rate was identical to the activity rate response and the deceleration rate mimicked the minute ventilation. Conclusion: Dual sensor VVIR pacemakers have the potential to improve rate adaptation to exercise. The rate response to exercise in patients fitted with activity and minute ventilation sensors, VVIR pacemakers closely mimics the physiological rate response.     

Lack of Physiological Adaptation of the Atrioventricular Interval to Heart Rate in Patients Chronically Paced in the AAIR Mode

Seventeen consecutive patients, aged 56 +/- 12, were chronically paced in the AAIR mode for a symptomatic sinus node disease with atrial chronotropic incompetence defined by a peak exercise heart rate (HR) less than 75% of the maximal predicted heart rate (MPHR) mean = 65 +/- 10%). Sensors used were activity sensing (n = 7), minute ventilation (n = 6), or respiratory rate (n = 4). Basic pacing rate was programmed at 71 +/- 5 beats/min and the maximal sensor rate at approximately 85% MPHR (143 +/- 10); other sensor parameters were programmed individually. Six months after implant, two standardized and symptom limited exercise tests were performed in random order, AAI and AAIR modes, respectively. AAIR pacing significantly improved peak exercise HR (139 +/- 14 vs 112 +/- 30 beats/min; P less than 0.01), maximal sustained workload (132 +/- 42 vs 110 +/- 38 watts; P less than 0.02), and total exercise duration (724 +/- 299 vs 594 +/- 245 sec; p less than 0.02) compared to the AAI mode. In all 17 patients, HR was continuously sensor driven in the AAIR mode, making it possible to precisely study the adaptation of the stimulus-R interval and of the stimulus-R:RR ratio during exercise. Six patients normally adapted with a progressive shortening. Six others did not adapt at all without any variation of interval. Five patients paradoxically increased their stimulus-R interval (286 +/- 10 msec at peak E vs 220 +/- 19 msec at rest) and their stimulus-R:RR ratio (67 +/- 20% vs 29 +/- 4%), producing P waves occurring immediately after, or even within the R wave of the preceding cycle; two patients complained of severe exercise related symptoms corresponding to the so-called "AAIR pacemaker syndrome." The principal factors involved in the nonadaptation of AV interval to HR were related to the patient (organic heart disease, with the particular problem of the denervated heart; the bradytachy syndrome; and the use of drugs, especially beta blockers and Class I antiarrhythmic drugs) or to the pacemaker ("overstimulation" phenomenon). These observations constitute an additional argument for wider indications of implanting DDDR units in these patients.     

Heart Rate Recovery and Chronotropic Incompetence in Patients with Subclinical Hypothyroidism

Background: Heart rate recovery (HRR) and chronotropic incompetence (CI) in patients with subclinical hypothyroidism (SCH) has not been explored previously. The aim of the present study was to evaluate the HRR and CI in patients with SCH.
Methods: Twenty-five patients (11 men, 14 women with a mean age of 36 ± 10 years) who were diagnosed SCH determined by an increased serum thyrothrophine (TSH) concentration (>4.0 ng/mL) and the normal free triiodothyronine (fT3) and free thyroxin (fT4) levels, were included in the study. The control group of healthy individuals with normal TSH (12 males, 15 females) with a mean age of 36 ± 3 years was also included. Two groups were well matched for age, sex, and body mass index. Medical history, physical examination, electrocardiogram, treadmill exercise testing, and chest radiogram were performed for all participants.
Results: The characteristics of SCH patients and control cases were similar with regard to age, sex, and BMI except for TSH levels. Serum TSH levels were significantly higher in SCH patients than the controls (P < 0.001). No significant differences were observed in the changes of heart rate (HR), exercise tolerance (metabolic equivalents) , or systolic and diastolic blood pressures at rest or during exercise between the groups, whereas HRR and CI were significantly lower during exercise testing in the SCH patients compared to controls (P < 0.003; P < 0.03, respectively).
Conclusion: The results of the present study demonstrated that SCH can cause impaired cardiovascular autonomic function and attenuated HR response to exercise. (PACE 2010; 2–5)     

Assessment of the Chronotropic Response at the Anaerobic Threshold: An Objective Measure of Chronotropic Function

MEINE, M., et al. : Assessment of the Chronotropic Response at the Anaerobic Threshold: An Objective Measure of Chronotropic Function. The evaluation of the heart rate response to exercise is important for the diagnosis of chronotropic incompetence and the assessment of a rate responsive algorithm of sensorcontrolled pacemakers. The aim of the present study was to examine a classification of the chronotropic response at an individually moderate exercise level. Sixteen pacemaker patients (patient group, age 62.9 ± 7.6 years ) with sick sinus syndrome and 15 age‐matched healthy subjects (control group, age 57.6 ± 9.4 years ) underwent a maximum cardiopulmonary exercise test on a treadmill after a protocol with individually selected incremental steps. To analyze the patients' intrinsic heart rate response, the rate responsive mode of the pacemaker was switched off. Chronotropic incompetence was diagnosed in eight patients whose maximal heart rate was < 80% of the age‐predicted heart rate. The heart rate at the anaerobic threshold was significantly lower in the chronotropically incompetent subgroup than in the chronotropically competent patients and the healthy subjects (85.9 ± 6.6 beats/min vs 100.3 ± 9.9 beats/min and 112.9 ± 11.7 beats/min , respectively). The chronotropic slope of the heart rate reserve as a function of the metabolic reserve was significantly higher in the control group than in the patient groups with either mild or severe chronotropic incompetence (0.94 ± 0.17 vs 0.64 ± 0.08 and 0.43 ± 0.14 , respectively). Furthermore, the chronotropically incompetent response could be divided into a linear type with and without a threshold, an exponential, and a logarithmic type. The anaerobic threshold was an objectively detectable breakpoint at an individually moderate exercise level that could be used for characterization of chronotropic function. At the anaerobic threshold, a physiological heart rate response was about 220 ‐ age – 50 beats/min. A deviation of more than 10 beats/min below this physiological value characterized chronotropic incompetence.     

Exercise Chronotropy in Patients with Normal and Impaired Sinus Node Function After Cardiac Transplantation

The chronotropic response during graded, symptom limited exercise was investigoted in 32 cardiac transplant recipients a mean of 49 ± 18 days after transplantation. All patients had systematic evaluation of postoperative donor sinus node (SN) function and the cardioacceleratory response was compared according to the SN function. Twenty-one patients had normal postoperative SN studies (corrected SN recovery time < 520 msec, group I) while the SN function was impaired postoperatively in the remainder (n = 11, group II; corrected SN recovery time 4,149 ± 6,283 msec in 5 patients, junctionai escape rhythm in 6 patients). All patients had regained sinus rhythm at time of the exercise test Patients in group II had lower basal sinus rates at the beginning of exercise (91.5 ± 11 vs 101.4 ± 7 beats/min, P < 0.02). This lower chronotropy was maintained over every incremental step (F_{rato between groups}= 30, P = 0.0001, F_{rate vs workload}= 15, P = 0.0001 by two-way ANOVAJ and resulted in a significantly lower heart rate at individual peak exercise (108.3 ± 20 vs 124.2 ±13 beats/min, P < 0.02). A total of 14/16 patients in group I but only 2/16 patiejils in group 11 accomplished a peak heart rate ± 120 beats/min (P = 0.009). The workload achieved did not differ between the groups (107 ± 29 vs 102 ± 32 watts, P > 0.5). These data show a lower SN chronotropy during rest and at peak exercise in cardiac transplant recipients with postoperative SN deficiency and apparent normalization of SN fundion.     

Improvement of exercise tolerance by single lead VDD pacemaker: evaluation using cardiopulmonary exercise test

We used a cardiopulmonary test to assess the physiological benefit of single lead VDD pacing in ten patients (six men, four women; aged 32-84 years, mean 69 years) with atrioventricular block. Maximal symptom-limited treadmill exercise test using a ramp protocol was performed under VDD and VVIR or VVI pacing (VVI) in random sequence. The pacemaker was then programmed to the VDD mode, and Holter ECG was recorded in nine patients. Compared with findings during the VVI, the VDD mode had a greater chronotropic response (mean maximal heart rate, VDD 106 +/- 17 beats/min vs VVI 79 +/- 19 beats/min, P = 0.03), and was associated with prolongation of exercise duration (VDD 11.2 +/- 2.9 minute vs VVI 10.5 +/- 3.1 minute; P = 0.01), and the onset of anaerobic threshold at a higher oxygen uptake (VDD 12.4 +/- 3.4 mL/min per kilogram vs VVI 10.0 +/- 2.1 mL/min per kilogram; P < 0.01). Atrial sensing was recognized in almost all normal sinus P waves for all cases examined using Holter ECG. Thus, chronotropic response during exercise by VDD pacemaker improved exercise tolerance, indicating that a VDD pacemaker might be useful for patients requiring physical activity.     

Delayed Exercise Rate Response Kinetics Due to Sensor Cross-Checking in a Dual Sensor Rate Adaptive Pacing System: The Importance of Individual Sensor Programming

By cross-checking the relative sensor activation between a nonspecific and specific sensor during extraneous interference, a multisensor rate adaptive pacemaker may he able to limit inappropriate rate responses. The effects of activity (ACT) sensor programming on rate response kinetics of a QT and ACT dual sensor VVIR pacemaker with sensor cross-checking algorithm were studied in four patients with atrial fibrillation and complete heart block. The rate adaptive setting of each sensor was individually optimized, and an equal rate contribution for the QT and ACT sensors (QT = ACT) was used in the dual sensor VVIR mode. Three maximal treadmill exercise tests were performed in random order in three different VVIR modes driven by QT only, QT = ACT, and in the dual sensor mode with the most sensitive (low threshold) ACT setting. In the two dual sensor modes, the time for onset of rate response (delay time) was reduced (both < 15 sec) compared with QT only VVIR mode (233 ± 70 sec). However, the time to 50% of rate response in the low ACT threshold dual sensor mode was delayed compared with to QT = ACT (450 ± 110 [95% confidence interval 234–666] vs 311 ± 103 [109–513]sec, P < 0.05) and was similar to the QT only mode (401 ± 120 [l66–636]sec). The time to reach 90% of rate response was similar in the three modes tested. The resting activity counts registered by the ACT sensor were < 5 and 16 ± 2 counts/mm in the optimally programmed and low threshold ACT settings, respectively. This resulted in sensor cross-checking at rest in the overprogrammed dual sensor VVIR mode, thereby limiting the rate response. Thus, the combined sensor system provides a faster initial response to exercise than the QT only sensor. Programming the ACT threshold to low will prevent this faster response because of sensor cross-checking.     

Aerobic Capacity in Rate Modulated Pacing

Whether heart rate or AV synchrony is the most important factor for an increase in aerobic capacity was evaluated in a comparative study between sinus bradycardia, VVIR, DDD, and DDDR stimulation. Sixteen patients (mean age 67 years) with chronotropic incompetence and impJanted DDDR pacemaker (Telectronics META 1250) were randomly studied by cardiopulmonary exercise testing. All patients were exercised to their anaerobic threshold (ATJ with the following heart rates: DDD 84 ± 3, WIR 110 ± 5, and DDDR 116 ± 6 beats/min. Mean oxygen uptake (VO₂, mL/kg per min) at AT was 7.4 ± 0.3 in DDD and WIR modes. A 12% increase was measured in DDDR mode (8.3 ± 0.4). Compared to VVIR work capacity in the DDDR mode was improved by 17% (41 vs 48 W/min). In patients with isolated sinus node disease (n = 9) the increase of VO₂ and work capacity at AT during DDDR mode was more pronounced (16% and 20%, respectively, compared to VVIR). In patients with intermittent second or third degree AV block (n = 7) the differences between the pacing modes were not significant. This might partly be due to a lesser degree of chronotropic incompetence in this subgroup. In conclusion only the conjunction of heart rate increase and preservation of AV synchrony provides a significant improvement in aerobic capacity during exercise.     

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.