Adequacy of Pacing Rate During Exercise in Rate Responsive Ventricular Pacing

Our objective was to determint; the adequate pacing rate during exercise in ventricular pacing by measuring exercise capacity, cardiac output, and sinus node activity. Eighteen patients with complete AV block and an implanted pacemaker underwent cardiopulmonary exercise tests under three randomized pacing rates: fixed rate pacing (VVJ) at 60 beats/min and ventricular rate-responsive pacing (VVIR) programmed to attain a heart rate of about 110 beats/min ar 130 beats/min (VVIR 110 and VVIR 130, respectively) at the end of exercise. Compared with VVI and VVIR 130, VVIR 110 was associated with an increased peak oxygen uptake(VVIR 110:20.3 ± 4.5 vs VVI: 16.9 ± 3.1; P < 0.01; and VVIR 130: 19.0 ± 4.1 mL/min per kg, respectively; P < 0.05) and a higher oxygen uptake at anaerobic threshold (15.3 ± 2.7, 12.7 ± 1.9; P < 0.01, and 14.6 ± 2.6 mL/min per kg; P < 0.05). The atrial rate during exercise expressed as a percentage of the expected maximal heart rate was lower in VVIR 110 than in VVI or VVIR 130 (VVIR 110: 75.9%± 14.6% vs VVI: 90.6%± 12.8%; P < 0.01; VVIR 110 vs VVIR 130: 89.1%± 23.1%; P < 0.05). There was no significant difference in cardiac output at peak exercise between VVIR 110 and VVIR 130. We conclude that a pacing rate for submaximal exercise of 110 beats/min may be preferable to that of 130 beats/min in respect to exercise capacity and sympathetic nerve activity.     

Activity-Sensing Rate Responsive Versus Conventional Fixed-Rate Pacing: A Comparision of Rate Behavior and Patient Well-Being During Routine Daily Exercise

Rate responsive single chamber pacing (WIR) may be the pacemaker of choice in pafients who are not suitable candidates for a dual chamber system. Several studies, most of them performed in an exercise laboratory, have shown a significantly higher exercise capacity demonstrating an improvement in cardiac output and anaerobic threshold compared to conventional fixed rate pacing (VVT). Expressing our idea that stress testing in an “artificial environment” on a bicycle or motor driven treadmill has its limitations and may be difficult to extend into patient's daily life, we designed an outdoor study imitating patient's daily activity. Twenty-one patients with an activity-sensing rate responsive pacemaker performed in a double blind fashion in VVI and VVIR mode the following test circuit: walking 170 meters on flat ground, 210 meters incline, climbing a flight of stairs, and the same circuit in reverse order, and therefore “downhill”. Heart rate behavior was recorded by Holter monitoring and patients subjective feelings of well-being, i.e. fatigue and dyspnea were also evaluated, VVIR pacing responded promptly to exercise, i.e., walking on a flat ground, but no further significant increase in pacing rate was observed in relationship to the strength of physical activity while walking inclined or climbing stairs. While patients became exhausted, a nonphysiological decrease in heart rate sometimes occurred. Despite these limitations 6 of 12 patients who had a paced-only rhythm while exercising in both VVI and VVIR mode reported feeling significantly belter in the VVIR mode, expressing less dyspnea and fatigue. In contrast, two of nine patients having only intermittently paced rhythm preferred the VVIR mode. Patients with lower ejection fraction (EF) were more likely to show subjectively a benefit while exercising in VVIR mode, compared to those with less reduced or normal EF. Despite the technical limitations of using a piezo crystal for rate adaptation, WIR pacing is an important option in paced-only patients, but it seems less beneficial in patients with only intermittent paced rhythm.     

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.     

Evaluation by Cardiopulmonary Exercise Test of DDDR Versus DDD Pacing

In eight patients (age 62 ± 6 years) a DDDR pacemaker was implanted for sick sinus syndrome (three cases) or second- and third-degree AV block (five cases). In five subjects chronotropic incompetence (maximal heart rate on effort < 110 beats/min) was present before implantation. One month after implantation the patients were randomized to DDDR or DDD pacing for 3 weeks each, with subsequent crossover, and at the end of each period a symptom limited Cardiopulmonary exercise test (25 watts/2 min) was performed and the patients were requested to fill a symptoms questionnaire. Results: DDDR pacing, compared to DDD, was associated with higher maximal heart rates (127 ± 20 vs 110 ± 27 beats/min, P < 0.02), higher (VO₂ max (25.4 ± 6.1 vs 21.5 ± 7.8 mL/kg/per min, P < 0.03) and higher VO₂ at the anaerobic threshold (20.3 ± 5.0 vs 15.8 ± 4.9 mL/kg per min, P < 0.03), without significant differences in mean exercise time (526 ± 193 vs 472 ± 216 sec, NS). The increase in VO₂ max obtained in DDDR versus DDD was significantly related to the increase in maximal heart rate (r = 0.72, P < 0.05) and the increase in VO₂ at the anaerobic threshold obtained in DDDR versus DDD was related to the increase in heart rate at the anaerobic threshold (r = 0.81, P < 0.02). In patients with chronotropic incompetence the improvement obtained in DDDR versus DDD was even more significant (VO₂ max = 22.7 ± 5.9 vs 16.1 ± 4.4 mL/kg per min, P < 0.03; VO₂ at the anaerobic threshold = 18.4 ± 5.1 vs 13.2 ± 2.8 mL/kg per min, P < 0.05; exercise time = 438 ± 132 vs 352 ± 150 sec, P < 0.02). In the population as a whole, no significant differences were found relative to subjective symptoms, meanwhile in patients with chronotropic incompetence a better subjective tolerance was apparent with DDDR than with DDD pacing. In conclusion, DDDR pacing induces a significant improvement of exercice capacity, in comparison to DDD pacing, related to the ability to reach higher heart rates during exercise. This phenomenon is particulary evident in patients with chronotropic incompetence in whom DDDR pacing also is subjectively better tolerated.     

Superior Cardiac Hemodynamics of Atrioventricular Synchrony Over Rate Responsive Pacing at Submaximal Exercise: Observations in Activity Sensing DDDR Pacemakers

LAU, C.-P., ET AL.: Superior Cardiac Hemodynamics of Atrioventricular Synchrony Over Rate Responsive Pacing at Submaximal Exercise: Observations in Activity Sensing DDDR Pacemakers. The relative hemodynamic profile between dual chamber pacing (DDD) and activity sensing rate responsive pacing (VVIR) was compared in ten patients with dual chamber rate responsive pacemakers (Synergist 11). With a double blind, randomized exercise protocol, DDDR pacemakers were programmed into VVI, VVIR, and DDD (AV interval 150 msec) modes and in seven patients the test in the DDD mode was repeated with the AV interval programmed at 75 msec. A treadmill exercise test of 6-minutes duration (2 stages, Stage 1 at 2 mph, 0% gradient and Stage II at 2 mph, 15% gradient) was performed at each of the programmed settings, with a rest period of 30 minutes in between tests. Cardiac output was assessed using continuous-wave Doppler sampling ascending aortic flow and expressed as a percentage of the value achieved during VVI pacing. During exercise, pacing rate between DDD and VVIR pacing was similar but was higher with DDD at the first minute of recovery (91 ± 4vs 81 ± 3 beat/min, respectively). Cardiac output was significantly higher at rest, during low level exercise, and recovery with DDD pacing compared with VVIR pacing (resting: 21 ± 14 vs -2 ± 7%; Stage I: 36 ± 6 vs 16 ± 7%; Stage II: 25 ± 15 vs 10 ± 8%; recovery: 26 ± 12 vs 4 ± 9%; p < 0.05 in all cases). Systolic blood pressure was significantly higher during low level of exercise in the DDD mode. Shortening of the AV interval to 75 msec did not significantly affect cardiac output during exercise, but cardiac output after exercise was reduced (2 ± 6 vs 23 ± 6% at an AV interval of 150 msec, p < 0.02). By enhancing the stroke volume, DDD pacing improves cardiac hemodynamics at rest, during low level exercise, and early postexercise recovery.     

Rate Responsive Pacing Using the Evoked QT Principle. A Physiological Alternative to Atrial Synchronous Pacemakers

We have evaluated clinically a rate-responsive pacemaker which uses the evoked QT principle as indicator of physiological demand. This pacemaker is microprocessor-based and fully programmable noninvasively through radiofrequency coupling to an external microcomputer. To date this system has been implanted in 15 patients. With this QTsensing pacemaker the ra te response to exercise was smooth and progressive, and gradually returned to the basic paced rate after termination of activity. Physiologic rate responsive pacing resulted in significant improvement in exercise tolerance and a 40% increase in cardiac output when compared to fixedrate pacing in 8 patients. This initial experience confirms the possibility of obtaining a physiological response to exercise using a pacing system dependent only on a unipolar electrode which is independent of the problems of atrial activity and sensing. Rate responsive pacing might prove to be a useful alternative to atrial synchronous systems, and particularly advantageous in those patients whose sinoatrial function is abnormal or who suffer from atrial arrhythmias.     

Cardiopulmonary Responses to Exercise in Children with Activity Sensing Rate Responsive Ventricular Pacemakers

The physiological benefits of activity sensing rate responsive ventricular pacing)VVIR) over fixed rate pacing)VVI) were investigated in 14 children during incremenlal cycle exercise. Based on their heart rhythm response during exercise, children were divided into two groups. Group I patients)13 ± 4 years) remained in a paced-only rhythm when exercised. Group II patients)16 ± 7 years) were paced at rest but converted to sinus rhythm with exercise. In Group I patients, the significant physioJogicol benefits of VVIR over VVI pacing were evidenced hy a 51% increase in peak heart rate)HRmax) and a 16% increase in exercise duration and maximum oxygen uptake)VO₂max). Additionally, a 27% reduction in peak oxygen pulse)O₂Pmax) was found, reflecting a similar decrease in stroke volume. The cardiorespiraiory responses of Group I and 11 patients were compared in terms of percent of predicted normal values. Although Group I patients in the VVIR mode attained a better exercise performance than in the VVI mode and a normal O₂Pmax)108% pred). their HRmax)62% pred) and VO₂max)70% pred) fell far below normal values. In comparison. Group II patients, who went into sinus rhythm, achieved normal values for HRmax)84% pred), VO₂max)90% pred), and O₂Pmax)97% pred). The higher pacing rates attained by Group I patients in the VVIR mode may have allowed them to reach not only a higher cardiac output but also a more normal stroke volume at peak exercise than in the VVI mode. However, the overall exercise performance of children paced in the VVI and VVIR modes were significantly diminished compared to the performance of children who went into sinus rhythm with exercise.)     

Temporal Relationship Between Exercise and QT Shortening in Patients with QT Pacemakers

The present study was undertaken to examine the temporal relationship between exercise and QT interval shortening as one of the principal determinants for the functioning of QT pacemakers. Ten patients (mean age of 72.6 years) with implanted QT pacemakers were subjected to supine bicycle exercise with two different slopes, 90% and 80%. The QT interval as seen by the pacemaker was monitored by telemetry and stored on magnetic tape. After the beginning of exercise QT prolongation of a few msec occurred up to 40 sec in most patients. The earliest QT shortening of 4 msec was noted after 63.4 sec with 90% slope and 75.7 sec with 80% slope. The difference was not significant. The further time course was dependent on slope and pacemaker algorithm. Maximal QT shortening was 65.9 msec with 90% and 69.8 msec with 80% slope. It was seen 29.2 sec after termination of exercise with 90% slope and 69.5 sec with 80% slope (P < 0.05). There was no correlation of the measured delays with age. Earliest rate response in QT driven pacemakers is determined by earliest QT shortening on one hand and by the slope setting of the pacemaker on the other, where the limiting parameter appears to be QT shortening, which occurs after the first minute of exercise.     

The Effects of Rate Responsive Pacing on Exercise Performance in the Postoperative Univentricular Heart

Following the Fontan operation for definitive palliation of the univentricular heart, sinus node dysfunction, and/or atrioventricular block requiring pacemaker therapy is common. In previous studies ventricular rate responsive pacing (VVI, R) resulted in improved exercise performance over VVI pacing in anatomically normal hearts with either sinus node disease or atrioventricular block. In this study, the usefulness of both VVI, R and DDD, R pacing are evaluated in the postoperative univentricular heart following the Fontan operation. Eight postoperative Fontan patients with sinus node disease or atrioventricular block underwent exercise testing using a treadmill protocol. Six patients had single chamber ventricular pacemakers and two patients had dual chambered rate responsive pacemakers. Median age at exercise testing was 14 years. Patients were tested in the VVI, VVI, R, and DDD, R modes acting as their own controls. Heart rate, work rate, oxygen consumption, and respiratory exchange ratio were monitored continuously. Heart rate was significantly increased in the rate responsive modes compared to the VVI mode. In spite of the significant increase in heart rate, there was no change in maximal work rate or oxygen consumption. There was also no significant change in oxygen consumption at ventilatory anaerobic threshold. From these data we would conclude that VVI, R pacing in postoperative univentricular hearts does not result in improved exercise performance and that further study with DDD, R pacing is needed to determine its usefulness in this group of patients.     

Rate Responsive Pacemakers: Assessment after Two Years

Rate responsive pacemakers (RRPM) for patients without sufficient response of the heart rate (HR) to exercise represent an alternative to improve cardiac output (CO) and capacity for exercise via an increase of HR. From 1983 until December 1985, we implanted 30 QT-related (TX), 25respiratory dependent (RDP), and 35 body activity directed (ACT) pacemakers. The follow-up examination consisted of Holter-ECG, treadmill and/or bicycle workload, and determination of CO (TX: thermodilution technique, n = 11; 6 months after implantation. RDP: equilibrium radionuclide ventriculography, n = 13; 1 month after implantation). The capacity for exercise of patients with ACT was studied using a climbing step. Adaptation of HR could be achieved with TX. RDP, and ACT. There was a significant increase in CO during exercise TX or RDP versus VVI-mode (TX: δ= 1.7l/min, RDP: δ= 2.1 l/min).Although all systems exhibited weak points, RRPM are reliable devices. We abide by using these pacemakers.     

The Effect of Rate Responsive Pacing in Patients with Angina Pectoris on the Extent of Ischemia on 201-Thallium Exercise Scintigraphy

VAN CAMPEN, L.C.M.C., et al. : The Effect of Rate Responsive Pacing in Patients with Angina Pectoris on the Extent of Ischemia on 201-Thallium Exercise Scintigraphy. In patients with coronary artery disease (CAD), rate responsive pacing is considered to be contraindicated because an increase in heart rate may increase oxygen demand. Although previous studies have shown no subjective increase in ischemia during rate responsive pacing, data from objective assessment have not been documented. The goal of this study was to determine if there was an increase in ischemia on 201-Thallium (²⁰¹TI) exercise scintigraphy in this mode of pacing in patients with CAD and angina. Eighteen consecutive patients with chronic atrial fibrillation and symptomatic bradyarrhythmias with a pacemaker for more than 6 months participated in the study. In VVI and VVIR modes a symptom-limited exercise ²⁰¹TI scintigram was performed in a single blind randomized crossover fashion. Exercise duration, anginal attacks, use of nitroglycerine (NTG) tablets, blood pressure, and analysis of the scintigrams were assessed during each pacing mode. Fifteen men and three women were included (  age 65.9 ± 4.9 years, LVEF 0.44 ± 0.07  ). Four were in Class III angina pectoris, and 14 in class II. The mean exercise duration increased 28% in the VVIR group without an increase in anginal attacks per week or the use of NTG tablets. On scintigrams, no differences were seen between the two groups. One patient was withdrawn from the study because of an increase in angina pectoris (AP) attacks during VVIR pacing. Rate responsive pacing is safe and effective in patients with CAD without an increase in subjective and objective signs of ischemia.     

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.     

Myopotential Interference in Unipolar Rate Responsive Pacemakers

The effects of myopotential interference on unipolar rate responsive pacemakers were assessed in 22 patients. Six types of pacemakers (from four manufacturers) were studied: five TX2 (QT sensing), seven Biorate (five RDP3 and two MB-1, respiratory rate sensing), seven Activitrax (activity sensing), two Medtronic 2503 (dP/dt sensing), and one Sensolog P703 (activity sensing). Provocative tests using arm exercises were performed in both VVI and rate responsive modes. At nominal sensitivity settings (1.8-2.5 mV), 55% of these patients were myopotential positive for at least 1 provocative test. Pressing the palms together was found to be the most sensitive provocative test. Rate response was achieved with treadmill exercise (all patients), hyperventilation (RDP3 and MB-1) and tapping (Activitrax) or wobbling the pacemaker in its pocket (Sensolog). During continued rate acceleration, myopotential interference was induced by arm exercises. The duration of inhibition was shorter when the provocative tests were performed during rate response compared to that occurred at rest. Short periods of myopotential interference resulted in temporary inhibition of pacing but rate response continued immediately on removal of the interference. In one patient with a RDP3 pacemaker, a prolonged episode of myopotential interference during treadmill exercise resulted in reversion of the pacemaker to the interference mode. Appropriate adjustment of the sensitivity setting effectively controlled the symptoms in most patients. However, one patient with a QT sensing pacemaker and symptomatic myopotential interference required programming to the VVT pacing mode. Two out of five patients with RDP3 required pacemaker replacement because of uncontrolled myopotential interference.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of Body Constitution and Age on Maximum Pacing Rate of Activity-Modulated Rate Responsive Pacemakers

The pacing rate of activity-modulated pacemakers is triggered by vibrations running through the body. Whether the body constitution predicts maximum pacing rate and may facilitate rate response programming was studied in 16 patients with Activitrax pacemakers. Rate response parameters were programmed to a fixed setting in VVIR/VOOR mode (lower pacing rate 60 ppm, upper pacing rate 125-130 ppm, activity threshold medium/7). Body vibrations were induced by a treadmill exercise test with increasing speed. Maximum pacing rates were measured at the stage of symptom-limited tolerance. Exercise tests with a duration of 7.3 +/- 2.9 minutes resulted in a maximum pacing rate of 98 +/- 22 ppm ranging from 60-122 ppm. Maximum pacing rates did not differ between male (n = 10; 102 +/- 21 ppm) and female (n = 6; 92 +/- 24 ppm). Correlations between maximum pacing rates and body constitutional factors were not significant with r = -0.15 (weight), r = 0.39 (height), r = 0.07 (body surface area), and r = -0.27 (skin-fold thickness). The correlations with body mass index (r = -0.53) and age (r = -0.53) were initially significant, but not after Bonferroni-Simes-Hommel correction. The age-dependent relationship may be caused by the shorter exercise duration of older patients indicated by the correlation between exercise duration and maximum pacing rate (r = 0.77), as well as with age (r = -0.73). Conclusions: body constitution did not modify body vibrations and did not allow prediction of maximum pacing rates; therefore, it is no aid for the programming of rate response parameters.     

A New Mechanical Sensor for Detecting Body Activity and Posture, Suitable for Rate Responsive Pacing

In the past, thought about rate responsive pacing mainly focused on rate increase with exercise but did not consider that a rate increase with postural changes also is mandatory in order to prevent orthostatic reactions. A nightly decrease in pacemaker rate when the body is at rest and in a supine position is a further advantage for the patient's sleep and recovery. Therefore, we developed a sensor that could detect not only rest and body activity but also discriminate between a supine and an upright position. This sensor is a muiticontact tilt switch containing a small mercury ball, as shown in the left panel of the figure below. The principle of discrimination between rest and low and high body activity is realized by the movement of the mercury ball resulting from body motion, which causes openings and closures within the sensor as the ball touches the numerous sensor contacts. In the upright position, a distinct number of contacts at the bottom of the tilt switch are closed. In the supine position, there is no closure of the bottom contacts and a postural discrimination can he achieved. We studied 12 volunteers and 10 pacemaker patients with this new device both at rest and during physical exercise. The right panel of the figure illustrates that the contacts per second correlate to the increase of physical exercise, such as walking on the treadmill. Further studies with an external pacemaker containing a small sensor suitable to fit into the pacemaker are in preparation.     

Physiological Benefits of a Pacemaker with Dual Chamber Pacing at Low Heart Rates and Single Chamber Rate Responsive Pacing During Exercise

Dual chamber rate responsive pacing may be an ideal mode but may result in high current drain and premature battery depletion. To minimize battery drain during exercise, this study compared a combination pacing mode of IDDD and ventricular rate responsive pacing (WIR). Nine patients were studied who had complete heart block, sinus rhythm, DDD pacemakers, and a reduced mean left ventricular ejection fraction of 44%. Patients were exercised in DDD, WIR, and a combination of DDD at low heart rates and WIR at mean heart rates over 89 bpm. Blood pressure, heart rate, exercise duration, work rate, oxygen uptake, anaerobic threshold, and oxygen pulse were measured. There was no difference in symptoms or in mean cardiopulmonary function indices including exercise duration 10.7. 10.3. 10.3 minutes; heart rate 127. 133. 136 bpm; oxygen uptake 1.4. 1.5. 1.5 L/minute; or anaerobic threshold 5.6, 5.5, 5.7 minutes (p > 0.05) in any mode. A pacemaker that provides atrioventricular synchrony at low heart rates with ventricular rate responsiveness at high heart rates may be an alternative mode for some patients.     

Evaluation of the Temperature Response to Exercise Testing in Patients with Single Chamher, Rate Adaptive Pacemakers: A Multicenter Study

Temperature responsive pacemakers were implanted in 45 patients (ages 44 to 90); 31 patients were evaluated by randomized, paired treadmill exercise tests 1 month postimplant. Of 28 males and 17 females, 19 had coronary artery disease; 8 had congestive heart failure. Pacing indications included sinus node disease (26), atrial fibrillation (15), AV block (10), and brady/tachy syndrome (10); some had multiple indications. Blood temperature (every 10 seconds, resolution = 0.004 degrees C) and pacing rate (every minute) were telemetered from the pacemaker. Average heart rate, exercise duration (5.7 min VVI; 6.7 min VVIR), VVIR response time (22 sec), initial temperature drop (0.23 degrees C) and maximum rate of drop (0.65 degrees C/min), temperature rise (0.31 degrees C VVI; 0.38 degrees C VVIR) and rate of rise (0.27 degrees C/min) were studied in a subset of patients. In pacer-dependent patients, average paired increases in exercise duration and heart rate was 56% and 34%, respectively. Including all (31) patients, some with intermittent sinus rhythm, increases were 28% and 9%, respectively. Because exercise duration increased, temperature rise was higher with rate adaptation. Rate adaptation was obtainable in all patients and patients averaged 99 +/- 48 increases above basic pacing rate per day at nominal temperature sensitivity. Conclusion: Beneficial rate adaptation is achievable using blood temperature to modify rate in a sensor based system.     

Comparison of Ventricular Function in Atrial Rate Adaptive Versus Dual Chamber Rate Adaptive Pacing During Exercise

The hemodynamic effects of two different pacing modes—rate adaptive atrial (AAIR) versus dual chamber (DDDR) pacing—were assessed in 12 patients with DDDR pacemakers during upright bicycle exercise first-pass radionuclide angiography using a multiwire gamma camera with tantalum-178 as a tracer. All patients had sinus node disease with intact AV conduction. Patients exercised to the same heart rate in random order in these two different pacing modes, AAIR and DDDR with AV delay (of 100 msec) selected to maintain 100% ventricular capture. Cardiac output in creased significantly above baseline values during exercise in both pacing modes: 154 ± 41% (mean ± SEM, P = 0.002) with AAIR, versus 95 ± 24% (P = 0.004) with DDDR (P = NS between the two modes). The peak filling rate, likewise, increased in both pacing modes (2.3 ± 0.21 end-diastolic volumes/sec to 3.8 ± 0.31 end-diastolic volumes/sec in AAIR [P = 0.0004] and 2.2 ± 0.18 end-diastolic volumes/sec to 3.4 ± 0.27 end-diastolic volumes/sec in DDDR [P = 0.0008]). LV ejection fraction was normal at rest (60 ± 4%, SEM) and did not significantly change with submaximal exercise in either pacing mode (both 56%, P = NS). No significant changes in end-diastolic volume or stroke volume indexes occurred with exercise in either pacing mode. Our study demonstrates that in patients with normal resting LV function, AAIR and DDDR pacing are equally effective in attaining appropriate increases in cardiac output and LV filling during exercise.     

Rate Adaptive Pacing—Clinical Experience with Three Different Pacing Systems

Physiological stimulation can be achieved by either bifocal or rate responsive pacing. The latter pacemakers adapt the heart rate to physical activity by biological signals. Out of many possible approaches only three pacemaker systems for rate responsive pacing are available: the QT-pacemaker (Tx or Quintech), the respiratory biorate pacemaker, and the activity detecting Activitrax. Our own experiences (8 QT, 6 Biorate, 8 Activitrax pacemakers) and a survey of 95 QT- and 37 Biorate pacemakers from 11 centers are reported. The Biorate pacemaker functions without any problems; its present disadvantage is limited programmability. With the Tx pacemaker failing, frequency adaptation (26%) was found more often in the early series, mostly due to voltage polarization at the tip of the electrode. The Activitrax pacemaker gives satisfactory frequency adaptation, largely depending on the activity of the muscles of the shoulder and pectoral region.     

Influence of Exercise Induced Myocardial Ischemia on Right Ventricular dP/dt: Potential Implications for Rate Responsive Pacing

Background : Right ventricular (RV) dP/dt_max has been used as a simple parameter for rate responsive pacing to simulate the normal sinus node function. However, the effect of acute myocardial ischemia on RV dP/dt_max has not yet been evaluated. Methods : RV high fidelity pressure was measured in 21 patients at rest and during supine bicycle exercise. Nine patients (Group 1 = controls) had no or only minimal alterations of the coronary arteries and 12 (Group 2 =CAD) had significant coronary artery disease with exercise induced left ventricular (LV) wall-motion abnormalities (n = 10) and/or angina pectoris (n = 6). RV pressure and its first derivative (RV dP/dtj were determined by an 8 French micromanometer catheter. The time constant of RV pressure decay (Tau) was calculated from the negative reciprocal of RV pressure versus negative dP/dt during isovolumic relaxation. RV volumes and ejection fraction were calculated from RV biplane angiograms (multiple slice method) at rest and during exercise. Results : Heart rate (HR), RV dP/dt_max and dP/dt_min increased significantly during exercise, whereas Tau decreased. There were no significant differences between the two groups, although RV ejection fraction increased from 67% to 72% in the control group but decreased from 63% to 51% in the CAD group (P < 0.05). An exponential relationship was found between HR and dP/dt_max with a correlation coefficient of 0.82 (P < 0.01; SEE = 7% of the mean value). Conclusions : Acute exercise induced myocardial ischemia does not significantly influence RV dP/dt_max during sinus rhythm. Consequently, this index of RV contractility may be used in patients with coronary artery disease as a simple parameter for rate responsive pacing.