Efficacy of Ventricular Rate Stabilization by Right Ventricular Pacing During Atrial Fibrillation

To assess the effect of right ventricular pacing on rate regularity during exercise and daily life activities, 16 patients with sinoatrial disease and chronic atrial fibrillation (AF) were studied. Incremental ventricular pacing was commenced at 40 beats/min until > 95% of ventricular pacing were achieved during supine, sitting, and standing. Thirteen patients also underwent randomized paired submaximal exercise tests in either a fixed rate mode (VVI) or a ventricular rate stabilization (VRS) mode in which the pacingrate was set manually at 10 beats/min above the average AF rate duringthe last minute of each exercise stage. The pacing interval for rate regularization was shortest during standing (692 ± 26 ms) compared with either supine or sitting (757 ± 30 and 705 ± 26 ms, respectively, P < 0.05). During exercise, VRS pacing significantly increased the maximum rate (119 ± 5.2 vs 106 ± 4.2 ms, P < 0.05), percent of ventricular pacing (85%± 5% vs 23%± 7%, P < 0.05), rate regularity index (5.8%± 1.6% vs 13.4%± 1.9%, P < 0.05), and maximum level of oxygen consumption (12.4 ± 0.5 vs 11.3 ± 0.5 ml/kg, P < 0.05) compared with VVI pacing. There was no change in oxygen pulse or difference in symptom scores in this acute study between the two pacing modes. It is concluded that right ventricular pacing may significantly improve rate regularity and cardiopulmonary performance in patients with chronic AF. This may be incorporated in a pacing device for rate regularization of AF using an algorithm that is rate adaptive to postural and exercise stresses.     

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.     

The Effects of Rate-Adaptive Atrial Pacing Versus Ventricular Backup Pacing on Exercise Capacity in Patients with Left Ventricular Dysfunction

Background: Atrial rate-adaptive pacing may improve cardiopulmonary reserve in patients with left ventricular dysfunction.
Methods: A randomized, blinded, single-crossover design enrolled dual-chamber implantable defibrillator recipients without pacing indications and an ejection fraction ≤40% to undergo cardiopulmonary exercise treadmill stress testing in both atrial rate-adaptive pacing (AAIR) and ventricular demand pacing (VVI) pacing modes. The primary endpoint was change in peak oxygen consumption (VO₂). Secondary endpoints were changes in anaerobic threshold, perceived exertion, exercise duration, and peak blood pressure.
Results: Ten patients, nine males, eight with New York Heart Association class I, mean ejection fraction 24 ± 7%, were analyzed. Baseline VO₂ was 3.6 ± 0.5 mL/kg/min. Heart rate at peak exercise was significantly higher during AAIR versus VVI pacing (142 ± 18 vs 130 ± 23 bpm; P = 0.05). However, there was no difference in peak VO₂ (AAIR 23.7 ± 6.1 vs VVI 23.8 ± 6.3 mL/kg/min; P = 0.8), anaerobic threshold (AAIR 1.3 ± 0.3 vs VVI 1.2 ± 0.2 L/min; P = 0.11), rate of perceived exertion (AAIR 7.3 ± 1.5 vs VVI 7.8 ± 1.2; P = 0.46), exercise duration (AAIR 15 minutes, 46 seconds ± 2 minutes, 54 seconds vs VVI 16 minutes, 3 seconds ± 2 minutes, 48 seconds; P = 0.38), or peak systolic blood pressure (AAIR 155 ± 22 vs VVI 153 ± 21; P = 0.61) between the two pacing modes.
Conclusion: In this study, AAIR pacing did not improve peak VO_2, anaerobic threshold, rate of perceived exertion, or exercise duration compared to VVI backup pacing in patients with left ventricular dysfunction and no pacing indications.     

Effects of Chronotropic Responsive Cardiac Pacing on Ventilatory Response to Exercise in Patients with Complete AV Block

To identify the effect of chronotropic responsive cardiac pacing on the ventilatory response to exercise, ten selected patients with complete atrioventricular block underwent paired cardiopulmonary exercise tests in fixed rate ventricular (WI) and dual chamber (DDD) or rate responsive ventricular (VVIR) pacing modes. Compared to VVI pacing, DDD or VVIR pacing increased peak oxygen uptake (P < 0.005) and augmented anaerobic threshold (P < 0.001), In eight patients, dyspnea was the major symptom limiting exercise with VAT pacing and this was markedly attenuated with DDD or VVIR pacing. In all patients, ventilation (VE) and the ratio of ventilation to CO₂ production (VE/VCO₂) were consistently higher with VVI pacing during exercise. To compare the response of the two pacing modes at the same workloads in an aerobic condition, we measured ventilatory variables 1 minute prior to the anaerobic threshold obtained with VVI pacing. When DDD or VVIR pacing was compared with VVI pacing, VE and VE/VCO₂ significantly decreased from 20.5 ± 5.3 L/min to 18.3 ± 5.0 L/min (P < 0.005) and from 35.9 ± 5.8 to 31.9 ± 5.0 (P < 0.003), respectively. Respiratory frequency rose significantly more with VVI pacing (P < 0.001) despite an unchanged tidal vohame. Although peak VE did not differ between the two pacing modes, VE/VCO₂ at the peak exercise increased significantly more with VVI pacing (P < 0.005). Respiratory frequency also rose more with VVI pacing (P < 0.005) and tidal volume did not change. This study suggests that chronotropic responsive cardiac pacing attenuates the exertional dyspnea by improving the ventilatory response to exercise as well as increasing the cardiac output in patients with complete atrioventricular block.     

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.     

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.     

Comparison of Low Rate Dual Chamber Pacing to Activity Responsive Rate Variable Ventricular Pacing

A study was undertaken to evaluate exercise performance in 18 dual chamber pacemaker patients believed to be chronotropically incompetent. All patients were paced in a DDD AV synchronous mode at 80 beats per minute (beats/min) as well as an externally triggered, activity responsive VVIR mode. Patients underwent two single blind, randomized symptom-limited treadmill tests (Sheffield protocol). Four of the 18 patients achieved intrinsic rates greater than 100 beats/min and were deleted from the primary study. It was noted that all four of these patients performed best with intrinsic rate response and AV synchrony. Thirteen of the remaining 14 patients demonstrated improved exercise tolerance in the VVIR mode. Average exercise time in the VVIR mode (7:25 +/- 3:12 min) was significantly greater (P less than 0.05) than the DDD mode (6:01 +/- 2:27 min). Work performed was significantly greater (P less than 0.05) in the VVIR mode (4.77 +/- 1.97 METS) than in the DDD mode (3.78 +/- 0.77 METS). Maximum heart rates were 83.86 +/- 5.11 beats/min in DDD mode versus 116.00 +/- 10.56 beats/min in VVIR mode. The results demonstrated that improved exercise tolerance can be achieved with single chamber rate variable pacing compared to DDD pacing in patients with chronotropic incompetence. However, potential symptoms associated with loss of AV synchrony should be ruled out.     

Benefit of Single Setting Rate Responsive Ventricular Pacing Compared with Fixed Rate Demand Pacing in Elderly Patients

In order to assess the value of a simple, single setting rate response option to VVI pacing, 12 patients (mean age 75.1 ± 6,2, range 62–83 years, seven males, five females) with symptomatic complete heart block were entered into a double-blind, randomized crossover trial of VVI versus VVIR (single setting rate responsive) pacing using Medtronic Activitrax pacemakers. Assessment was by time taken in seconds (sec) and Borg scale symptom score (6–20) for simple activities (standing from chair x 30; walking 800 meters; 52 steps on stairs [slow and fast pace], and incremental, noninclined maximal treadmill exercise), performed after a 4-week period with the patient in each pacing mode. Times were significantly improved in VVIR mode for standing from chair [mean ± SD] (78.7 ± 22.5 vs 70.7 ± 19.5 sec; P < 0.05), for 800 m walk (1032 ± 80 vs 885 ± 59 sec; P < 0.05), fast ascent of stairs (29.5 ± 7.7 vs 26.5 ± 5.6 sec; P < 0.02), and treadmill exercise (626.7 ± 189.5 vs 741.0 ± 170.2 sec, P < 0.005) although no difference in time for slow stair ascent was demonstrated. Symptom scores were significantly less in VVIR for standing from chair (12.7 ± 2.8 vs 10.3 ± 1.8; P < 0.01), 800 m walk (10.9 ± 2.7 vs 9.0 ± 2.4; P < 0.01), slow ascent of stairs (11.6 ± 2.1 vs 10.0 ± 2.0; P < 0.01), and fast ascent of stairs (13.0 ± 2.0 vs 11.7 ± 1.9; P < 0.02) but unchanged for treadmill exercise. Single setting VVIR pacing increases maximum exercise capacity and decreases perceived difficulty of submaximal exercise in elderly patients with symptomatic heart block. This would be a beneficial addition to most limited and multiprogrammable VVI systems for use in the elderly.     

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

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

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.     

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.     

Rate Modulated Pacing Based on Right Ventricular dP/dt: Quantitative Analysis of Chronotropic Response

Right ventricular contractility increases in response to catecholamine stimulation and greater ventricular preload, factors that increase with exercise workload. Thus, the maximum systolic dP/dt may be a potentially useful sensor to control the pacing rate of a permanent pacing system. The present study was designed to test the long-term performance of a permanent pacemaker that modulates pacing rate based on right ventricular dP/dt and to quantitatively analyze the chronotropic response characteristics of this sensor in a group of patients with widely varying structural heart diseases and degrees of hemodynamic impairment. A permanent pacing system incorporating a high fidelity pressure sensor in the lead for measurement of right ventricular dP/dt was implanted in 13 patients with atrial arrhythmias and AV block, including individuals with coronary artery disease, hypertension, severe obstructive pulmonary disease with prior pneumonectomy, atrial septal defect, dilated cardiomyopathy, restrictive cardiomyopathy, and mitral stenosis. Patients underwent paired treadmill exercise testing in the VVI and VVIR pacing modes with measurement of expired gas exchange and quantitative analysis of chronotropic response using the concept of metabolic reserve. The peak right ventricular dP/dt ranged from 238–891 mmHg/sec with a pulse pressure that ranged from 19–41 mmHg. There was a positive correlation between the right ventricular dP/dt and pulse pressure (r = 0.70, P = 0.012). The maximum pacing rate and VO_2max were 72 ± 6 beats/min and 12.61 ± 4.0 cc O₂/kg per minute during VVI pacing and increased to 124 ± 18 beats/min and 15.89 ± 5.9 cc 0₂/kg per minute in the VVIR pacing mode (P < 0.0003 and P < 0.002, respectively). The integrated area under the normalized rate response curve was 96.7 ± 45.7% of expected during exercise and 100.1 ± 43.4% of expected during recovery. One patient demonstrated an anomalous increase in pacing rate in response to a change in posture to the left lateral decubitus position. Thus, the peak positive right ventricular dP/dt is an effective rate control parameter for permanent pacing systems. The chronotropic response was proportional to metabolic workload during treadmill exercise in this study population with widely varying forms of structural heart disease.     

Importance of Heart Rate Response During Exercise in Patients Using Atrioventricular Synchronous and Ventricular Pacemakers

Atrioventricular synchronous pacing offers advantages over fixed-rate ventricular (VVI) pacing both at rest and during exercise. This study compared the hemodynamic effects at rest and exercise of ventricular pacing at a rate of 70 beats/min, ventricular pacing where the rate was increased during exercise and dual chamber pacing. Ten patients, age 63 +/- 8 years, with multiprogrammable DDD pacemakers were studied using supine bicycle radionuclide ventriculography. Radionuclide data during dual chamber pacing was acquired at rest and during a submaximal workload of 200-400 kpm/min. The pacemakers were then programmed to VVI pacing at a rate of 70 beats/min, and 1 week later, studies were repeated in the VVI mode at rest, during exercise at a rate of 70 beats/min, and during exercise with the VVI pacemaker programmed to a rate adapted to the DDD pacing exercise rate. At rest, the cardiac output was lower in the VVI compared with the AV sequential mode (4.1 +/- 1.1 vs 5.7 +/- 1.1 1/min, P less than 0.01). During exercise, the cardiac output increased from resting values in the DDD and VVI pacing modes, however cardiac output in the rate-adapted VVI mode was higher than in the VVI mode with the rate maintained at 70 beats/min (8.1 +/- 1.5 vs 6.3 +/- 1.1 1/min, P = 0.02). Three patients completed lower workloads with VVI pacing at 70 beats/min compared with AV synchronous pacing. At rest, AV sequential pacing was superior to VVI pacing, suggesting the importance of the atrial contribution to ventricular filling. With VVI pacing during exercise, cardiac output was improved with an increased pacemaker rate, suggesting that the heart rate response during exercise was the major determinant of the higher cardiac output.     

Efficacy and Safety of Ventricular Rate Responsive Pacing in Children with Complete Atrioventricular Block

Single chamber rate responsive pacing offers many potential advantages over the more complex dual chamber atrial tracking pacing mode in children, and the preservation of atrioventricular synchrony could be unnecessary in selected groups of pediatric patients. Twenty-two pediatric patients (age range 9 months to 12 years; mean 6.5 years) had implantation of ventricular rate responsive (VVIR) pacemakers over a 2-year period. All patients had chronic third-degree atrioventricular block, and a normal ventricular function at rest. During the follow-up each patient underwent a 24-hour Holter monitoring, and ten performed a graded treadmill test in both ventricular fixed rate (VVI) and rate responsive (VVIR) pacing mode. Paced ventricular rates were found to be normal for age in all 22 patients; maximum rate did not reach the higher programmed rate during daily activities in any patient. Comparing the mean paced ventricular rate to the mean rates of blocked P waves, six patients showed a difference of more than 20 beats/min, which induced the pacemaker parameters to be reprogrammed. In all patients a significant correlation was found between variations of paced ventricular rate and variations of spontaneous blocked atrial rhythm (P < 0.05); this correlation persisted in the subsequent Holter controls in the ten patients with longer follow-up. Exercise tolerance resulted normal in the ten patients who performed a treadmill test either in VVIR or VVI mode, with increased maximal heart rates and maximal systolic blood pressure in VVIR mode (P < 0.0013). Rate responsive ventricular pacemakers seem to adequately respond to the physiological needs of daily life of this selected group of children requiring permanent pacing.     

Two-Year Experience with Rate-Modulated Pacing Controlled by Mixed Venous Oxygen Saturation

Mixed venous oxy-hemoglobin saturation (M_VO₂) is a physiological variable with several features that might be desirable as a control parameter for rate adaptive pacing. Despite these desirable characteristics, the long-term reliability of the M_VO₂ sensor in vivo is uncertain. We, therefore, designed a study to prospectively evaluate the long-term performance of a permanently implanted M_VO₂ saturation sensor in patients requiring VVIR pacing. Under an FDA approved feasibility study, eight patients were implanted with a VVIR pulse generator and a right ventricular pacing lead incorporating an M_VO₂ sensor. In order to accurately assess long-term stability of the sensor, patients underwent submaximal treadmill exercise using the Chronotropic Assessment Exercise Protocol (CAEP) at 2 weeks, 6 weeks, and 3, 6, 9, 12, 18, and 24 months following pacemaker implantation. Paired maximal exercise testing using the CAEP was also performed with the pacing system programmed to the VVI and VVIR modes in randomized sequence with measurement of expired gas exchange after 6 weeks and 12 months of follow-up. During maximal treadmill exercise the peak exercise heart rate (132 ± 9 vs 71.5 ± 5 beats/min, P < 0.00001) and maximal rate of oxygen consumption (1,704 ± 633 vs 1382 ± 407 mL/min, P = 0.01) were significantly greater in the VVIR than in the VVI pacing mode. Similarly, the duration of exercise was greater in the VVIR than the VVI pacing mode (8.9 ± 3.6 min vs 7.6 ± 3.7 min, P = 0.04). The resting M_VO₂ and the M_VO₂ at peak exercise were similar in the VVI and VVIR pacing modes (P = NS). However, the M_VO₂ at each comparable treadmill exercise stage was significantly higher in the VVIR mode than in the VVI mode (CAEP stage 1 (P = 0.005), stage 2 (P = 0.04), stage 3 (P = 0.008), and stage 4 (P = 0.04). The correlation between M_VO₂ and oxygen consumption (VO₂) was excellent (r = -0.93). Telemetry of the reflectance of red and infrared light and M_VO₂ in the right ventricle during identical exercise workloads revealed no significant change over the first 12 months of follow-up (ANOVA, P = NS). The chronotropic response to exercise remained proportional to VO₂ in all patients over the first 12 months of follow-up. The time course of change in M_VO₂ during maximal exercise was significantly faster than for VO₂. At the 18- and 24-month follow-up exercise tests, a significant deterioration of the sensor signal with attenuation of chronotropic response was noted for 4 of the 8 subjects with replacement of the pacing system required in one patient because of lack of appropriate rate modulation. Rate modulated VVIR pacing controlled by right ventricular M_VO₂ provides a chronotropic response that is highly correlated with VO₂. This parameter responds rapidly to changes in workload with kinetics that are more rapid than those of VO₂. Appropriate rate modulation provides a higher M_VO₂ at identical workloads than does VVI pacing. Although the M_VO₂ sensor remains stable and accurate over the first year following implantation, significant deterioration of the signal occurs by 18–24 months in many patients.     

Direct His-Bundle Pacing:

Direct His-bundle pacing (DHBP) produces rapid sequential multisite synchronous ventricular activation and, therefore, would be an ideal alternative to right ventricular apical (RVA) pacing. In 54 patients with cardiomyopathy, ejection fraction (EF) 0.23 ± 0.11, persistent atrial fibrillation, and normal QRS < 120 ms. DHBP was attempted. This was successful in 39 patients. In seven patients, the effect of increasing heart rate on contractility (Treppe effect) was investigated. Twelve patients who also received a RVA lead underwent cardiopulmonary testing. After a mean follow-up of 42 months, 29 patients are still alive with EF improving from 0.23 ± 0.11 to 0.33 ± 0.15. Functional class improved from 3.5 to 2.2. DP/dt increased at each pacing site (P < 0.05) as the heart rate increased to 60, 100, and 120 beats/min. Rise in dP/dt by DHBP pacing at 120 beats/min was at least 170 ± mmHg/s, greater than any other site in the ventricle (P < 0.05). Cardiopulmonary testing revealed longer exercise time (RVA 255 ± 110 s) (His 280 ± 104 s) (P < 0.05), higher O₂ uptake (RVA 15 ± 4 mL/kg per minute) (His 16 ± 4 mL/kg minute) (P < 0.05), and later anaerobic threshold (RVA 126 ± 71 s) (His 145 ± 74 s) (P < 0.05) with DHBP compared to RVA pacing. Long-term DHBP is safe and effective in humans. DHBP is associated with a superior Treppe effect and increased cardiopulmonary reserve when compared to RVA pacing. (PACE 2004; 27[Pt. II]:862–870)     

Long-Term Clinical Performance of a Central Venous Oxygen Saturation Sensor for Rate Adaptive Cardiac Pacing

Rate adaptive ventricular pacemakers using central venous oxygen saturation (O₂Sat) to control the pacing rate have been implanted in 14 patients (mean age 71 years), with a mean follow-up period of 44 months (range 2–63 months). In eight patients the pacemakers were replaced due to signs of battery depletion after an implant duration of 39–58 months. During bicycle exercise testing the O₂Sat decreased on average from 61%± 4% at rest to 36%± 4% (P < 0,0001) at peak exercise, and the maximum pacing rate was 122 ± 5 beats/min. The time delay until the O₂Sat bad dropped 10%, 65%, and 90% of the total reduction during exercise was 4.8 ± 0.9 seconds, 39.8 ± 3.8 seconds, and 71.3 ± 7.5 seconds, respectively. The O₂Sat decreased 9.4%± 2% (P <0.005) from resting supine to resting sitting. Oxygen breathing increased the telemetered O₂Sat from the pacemaker by 8.4 %± 1 % (P < 0.001). During follow-up the O₂Sats were relatively stable in 50% of the patients, but demonstrated significant fluctuations in the others. At 1-year invasive follow-up O₂Sat measured by the pacemaker decreased 22%± 2%, and in blood samples from the right ventricle 22%± 2% from rest to 3 minutes exercise at 25 watts. There was a significant correlation between O₂Sat measured by the pacemaker and in blood samples from right ventricle (n = 105; r = 0.73; P < 0.001). In two patients the O₂Sat dropped significantly during pneumonia. In another patient episodes of angina pectoris was associated with low O₂Sat and a concomitant fast pacing rate.     

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.)     

Efficacy and Safety of Rate Responsive Pacing in Patients with Coronary Artery Disease and Angina Pectoris

The present study included 17 patients with angina pectoris and coronary artery disease in whom a rate responsive ventricular pacemaker (Medtronic Activitrax) had been implanted. All patients had an exclusively paced rhythm. Single blinded, random, cross-over treadmill tests in the rate responsive pacing mode (VVIR) and in the fixed-rate demand mode (VVI) were performed, with an interval of 4-6 weeks. Mean exercise duration increased by 25% during VVIR pacing. Maximal heart rate increased significantly during VVIR compared to VVI pacing (VVI = 74 +/- 2 bpm, VVIR = 116 +/- 8 bpm, P less than 0.001) as did the rate-pressure product (VVI = 10.850 +/- 1,124, VVIR = 16.628 +/- 2,110, P less than 0.001). Despite improved performance, the number of anginal attacks per week and the nitroglycerin consumption did not show a significant difference between the two pacing modes. It is concluded that rate responsive pacing is beneficial and safe in patients with angina pectoris and coronary artery disease.     

Beat-to-Beat Variability in Stroke Volume During VVI Pacing as Predictor of Hemodynamic Benefit from DDD Pacing

To determine whether the magnitude of Beat-to-Beat variability in stroke volume (SVJ during VVI pacing can predici hemodynamic benefit from DDD pacing, we undertook Doppier recordings of systolic and diastolic LV flow during VVI and DDD pacing in 20 patients (age 54 ± 9 years)with DDD pacemakers implanted due to AV block. SV increased by 19%± 10% from VVI to DDD (P < 0.01). This increase was greater (29%± 9%)in patients with a ratio of early (E)/late (A) filling < 1 compared to those with E/A > 1 (10%± 9%) (P < 0.001). Beat-to-Beat variability in SV was greater in VVI (13%± 8%)compared to DDD (4%± 1%) (P < 0.001). Patients with E/A < 1 showed greater Beat-to-Beat variability in SV during VVI pacing (19 ± 6%)compared to those with E/A > 1 (8%± 4%) (P < 0.001). Beat-to-Beat variability in SV during VVI pacing correlated with both percent change in SV from VVI to DDD (r = 0.89, P < 0.001)and E/A (r = -0.71, P < 0.001). In conclusion, patients with E/A < 1 derive greater hemodynamic benefit at rest from DDD pacing compared with E/A > 1. In addition, patients with complete AV block who show large variations in SV during VVI pacing may obtain greater hemodynamic benefit at rest from DDD pacing than patients with small variations.