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.     

Impact of Right Ventricular Pacing Sites on Exercise Capacity during Ventricular Rate Regularization in Patients with Permanent Atrial Fibrillation

Background: The deleterious effects of right ventricular apical (RVA) pacing may offset the potential benefit of ventricular rate (VR) regularization and rate adaptation during an exercise in patient's atrial fibrillation (AF). Methods: We studied 30 patients with permanent AF and symptomatic bradycardia who receive pacemaker implantation with RVA (n = 15) or right ventricular septal (RVS, n = 15) pacing. All the patients underwent an acute cardiopulmonary exercise testing using VVI‐mode (VVI‐OFF) and VVI‐mode with VR regularization (VRR) algorithm on (VVI‐ON). Results: There were no significant differences in the baseline characteristics between the two groups, except pacing QRS duration was significantly shorter during RVS pacing than RVA pacing (138.9 ± 5 vs 158.4 ± 6.1 ms, P = 0.035). Overall, VVI‐ON mode increased the peak exercise VR, exercise time, metabolic equivalents (METs), and peak oxygen consumption (VO₂max), and decreased the VR variability compared with VVI‐OFF mode during exercise (P < 0.05), suggesting that VRR pacing improved exercise capacity during exercise. However, further analysis on the impact of VRR pacing with different pacing sites revealed that only patients with RVS pacing but not patients with RVA pacing had significant increased exercise time, METs, and VO₂max during VVI‐ON compared with VVI‐OFF, despite similar changes in peaked exercise VR and VR variability. Conclusion: In patients with permanent AF, VRR pacing at RVS, but not at RVA, improved exercise capacity during exercise.     

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.     

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.     

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.     

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.     

Acute Testing of the Rate-Smoothed Pacing Algorithm for Ventricular Rate Stabilization

We evaluated the capability of a new pacemaker-based rate-smoothing algorithm (RSA) to reduce the irregular ventricular response of AF. RSA prevents sudden decreases in rate using a modified physiological band and flywheel feature. Twelve patients (51 ± 21 years) with hemodynamically tolerated AF of 4 months to 20 years duration were studied. Atrial and ventricular leads were connected to the external pacemaker device in the electrophysiology laboratory. Consecutive RR intervals during AF were measured at baseline and after ventricular pacing with RSA ON. Ventricular pacing with the rate smoothing algorithm reduced maximum RR intervals (1,207 ± 299 vs 855 ± 148 ms, P = 0.0005), with no significant change in the minimum RR interval (401 ± 55 vs 393 ± 74 ms, P = 0.292). A small shortening of the mean RR interval (634 ± 153 vs 594 ± 135 ms, P = 0.007) was seen with no change in the median RR interval (609 ± 153 vs 595 ± 143 ms, P = 0.388). There was a 43% reduction in RR standard deviation (145 ± 52 vs 82 ± 28, P = 0.0005), 49% reduction in mean absolute RR interval difference (MAD) (152 ± 64 vs 77 ± 34, P = 0.0005) and MAD/mean RR ratio (0.23 ± 0.05 vs 0.13 ± 0.04, P = 0.0005). We conclude that rate-smoothed pacing effectively reduces RR variability of AF in the acute setting.     

Rate-Responsive Ventricular Pacing: Clinical Experience With the RS4-SRT Pacing System

Eighteen patients (11 men and 7 women) with symptomatic second or third degree atrioventricular block underwent implantation of the rate-responsive RS4-SRT pacing system. Exercise tolerance in RS4 mode was compared to that in VVI mode by randomized double-blind treadmill stress testing. Following hospital discharge, HS4 function was assessed by repeat exercise testing and 24-hour Holter monitoring. Difficulty in obtaining satisfactory P-wave amplitudes at implonfation (mean 3.1 ±1.5 mV) resulted in prolonged implantation times (mean 79.4 ± 26.4 minutes). Following implantation, 10 patients (58%) showed a significant ventricular rate response to exercise, seven did not, and one remained in sinus rhythm. For responders, peak ventricular paced rate and double product were significantly greater in RS4 than in VVI mode, being 101.8 ± 5.8 vs. 74.3 ± 0.4 beats per minute and 20.1 ± 2.9 vs. 15.5 ± 3.7 beats per minute ± mmHg ± 10⁻³, respectively (p < 0.001). However, treadmill times (10.5 ± 2.6 vs. 9.7 ± 3.3 minutes) and work done (5.51 ± 2.01 vs. 4.97 ± 2.33 joules ± 10⁻⁵) were not significantly different (p = 0.22). Following hospital discharge, repeat exercise testing and 24-hour Holter monitoring demonstrated RS4 junction in 11 of 16 and 15 of 18 patients, respectively. We conclude that, due to unreliable atrial sensing, the RS4-SRT pacing system does not provide the reliable rate-responsiveness required to improve exercise tolerance.     

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.     

Optimization of Ventricular Function by Improving the Activation Sequence During Ventricular Pacing

Abnormal electrical activation occurring during ventricular pacing reduces left ventricular (LV) pump function. Two strategies were compared to optimize LV function using ventricular pacing, minimal asynchrony and optimal sequence of electrical activation. ECG and hemodynamics aortic flowpmbe, thermodilution cardiac output, LV pressure and its maximal rates of rise (LVdP/dtpos) and fall (LVdP/dtneg) were measured in anesthetized open-chest dogs (n = 7) with healthy hearts. The QRS duration (a measure of asynchrony of activation) was 47 ± 5 ms during sinus rhythm and increased to 110 ± 12 ms during DDD pacing at the right ventricular (RV) apex with a short AV interval. During pacing at the LV apex and LV base, the QRS duration was 8%± 7% and 15%± 7% (P < 0.05) longer than during RV apex pacing, respectively. Stroke volumes, LVdP/dtpos and LVdP/dtneg, however, were higher during LV apex(15%± 16%, 10%± 12% [P<0.05], and 15%± 10%, respectively) and LV base pacing (11%± 12% [P<0.05], 3%± 12%, and 3%± 11%, respectively) than during RV apex pacing. Systolic LV pressure was not influenced significantly by the site of pacing. Biventricular pacing (RV apex together with one or two LV sites) decreased the QRS duration by approximately 20% as compared with RV apex pacing, however, it did not improve stroke volumes, LVdP/dtpos and LVdP/dtneg beyond those during pacing at the LV apex alone. In conclusion, the sequence of electrical activation is a stronger determinant of ventricular function than the synchrony of activation. For optimal LV function the selection of an optimal single pacing site, like the LV apex, is more important than pacing from multiple sites.     

Is Atrial Sensing of Ventricular Far-Field Signals Important in Single-Lead VDD Pacing?

In single-lead VDD pacing the atrial sensitivity frequently is programmed to sensitive values. Atrial sensing of ventricular far-field signals should be reduced by differential atrial sensing. The aim of the study was to evaluate the effectiveness of this approach. Methods: The study included 10 patients with a single-lead VDD pacemaker (Thera 8948, Lead 5032). The atrial sensitivity was set to its most sensitive value of 0.18 mV and the telemetered intraatrial EGM was continuously recorded. After atrial tracked ventricular pacing, VVI pacing was performed with pacing rates from 100 to 160 beats/min in steps of 10 beats/min and up to 165 beats/min. The peak-to-peak amplitudes of P waves (P) and ventricular far-field signals (VFFS) were measured from the recordings. The ratio P/VFFS that defines the atrial signal-to-noise ratio was calculated, and the time from stimulus to maximum of the far-field signals amplitude (Tmax) was measured. Results: P measured 0.98 ± 0.76 mV. A VFFS was visible in the atrial channel in all patients with an amplitude of 0.45 ± 0.25 mV (range 0.01–1.0 mV), independent of the pacing rate. The ratio P/VFFS was 3.9 ± 4.2 (range 0.9–21.0). Tmax measured 99.4 ± 15.2 ms during sinus rhythm. A rate dependent shortening of Tmax to 92.7 ± 11.2 ms at 140 beats/min was observed (P = 0.001). At rates above 140 beats/min no further shortening occurred. Conclusion: Ventricular far-field signals are measurable in the atrial channel of VDD systems and may reach considerable amplitudes, which are not rate dependent. Although differential sensing provides favorable P waves to ventricular far-field signal ratios, refractory periods are needed to avoid far-field sensing. The rate dependent shortening of the ventricular signal can be detected in the atrial channel in VDD pacing.     

Optimized Standby Rate Reduces the Ventricular Rate Variability in Pacemaker Patients with Atrial Fibrillation

Patients with chronic atria! fibrillation (AF) and symptomatic bradycardia often receive ventricular-based pacemakers. However, many of these patients continue to have symptoms of palpitations, which may be due to ventricular rate variability. It has previously been shown that contin uous ventricular pacing during AF has a stabilizing effect on the ventricular rate. Hence, a study was initiated to determine whether a patient-specific optimal ventricular standby rate that reduces the ventricular rate variability, without over-pacing, could be predicted. A ventricular rate stabilization (VRS) pacing algorithm that increases the pacing rate until instability is reduced below a threshold was developed. The VRS algorithm was utilized to determine a patient-specific standby rate in 15 patients with chronic AF, intact AV nodal conduction, and implanted pacemakers. The computer algorithm controlled a pacemaker programmer to automatically change the pacemaker's ventricular pacing rate via telemetry. Patients were studied for 15 minutes with VRS and for 15 minutes with 50 ppm fixed rate pacing (control). The results were as follows: (1) VRS versus control = P < 0.05; (2) mean ventricular pacing rate (ppm): 77 ± 13 versus 50 ± 0; (3) mean ventricular rate (beats/mm); 82 ± 13 versus 79 ± 12; (4) ventricular rate coefficient of variation (%): 11 ± 1 versus 22 ± 5; (5) percent pacing: 75 ± 8 versus 6 ± 8; (6) percent of RR intervals less than minimum pacing interval eliminated: 58 ± 12; (8) regression analysis: mean VRS pacing rate (beats/min) = 0.96 X mean control ventricular rate + 2.3, r²= 0.85. We concluded that: (1) a moderate increase in the ventricular pacing rate was required to substantially stabilize the ventricular rate; (2) the resulting mean ventricular rate increased marginally: (3) a majority of RR cycles less than each patient's minimum pacing interval were eliminated; and (4) there was a linear relationship between the mean ventricular rate during control and the optimal ventricular pacing rate. Thus, a ventricular pacing rate close to the mean ventricular rate during control consistently reduced the ventricular variability. Although pacing at an increased ventricular standby rate reduces variability at rest, the optimal solution would likely be an adaptive rate algorithm that changes the ventricular standby rate as the mean intrinsic rate varies.     

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.     

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.     

Sinus Node Dysfunction and Impairment of Global Atrial Conduction Time After High Rate Atrial and Ventricular Pacing in Dogs

ZUPAN, I., et al .: Sinus Node Dysfunction and Impairment of Global Atrial Conduction Time After High Rate Atrial and Ventricular Pacing in Dogs. It has been shown in animals and humans that AF shortens the atrial refractory period and impairs its rate adaptation. The aim of the study was to evaluate the effects of high rate pacing on sinus node function and intraatrial conduction. Eight dogs were subjected to rapid atrial pacing (AP) at a rate of 400 beats/min for 16 days. After a complete recovery of left ventricular function, they underwent rapid ventricular pacing (VP) at 240 beats/min of equal duration. Sinus node recovery time (SNRT) was measured after pacing at 150, 160, and 170 beats/min. P wave duration was measured on a surface ECG recorded at a paper speed of 200 mm/s. Measurements were performed at baseline, immediately after AP or VP, and four weeks after termination of AP or VP. SNRT immediately after AP and VP was significantly prolonged at all three pacing rates   (P < 0.03)   . P wave duration increased significantly after either type of pacing   (AP: 74.3 ± 6.4 ms, VP: 70.0 ± 3.8 ms)   compared with baseline values   (60.6 ± 6.2 ms, P < 0.05)   . Rapid AP and VP induces sinus node dysfunction and prolongs intraatrial conduction time. The effects of sustained AP and VP on sinus node function and atrial myocardium returned toward control values 4 weeks after cessation of pacing. The authors hypothesize that reversible electrical remodeling occurs both in the sinus node and in the atrial myocardium. (PACE 2003; 26[Pt. II]:507–510)     

The Effect of Posture on the Response to Atrioventricular Synchronous Pacing in Patients with Underlying Cardiovascular Disease

In order to determine whether the hemodynamic benefit of atrioventricular synchronous pacing is maintained in the upright position, 14 patients with dual chamber pacemakers were paced in VVI mode and DDD mode in both the supine and standing position. The hemodynamic response was assessed by measuring the velocity time integral derived from the pulsed-wave Doppler signal in the left ventricular outflow tract during VVI pacing and dual chamber pacing at three different AV delays (125, 200, 250 ms). In the supine position, the velocity time integral during VVI pacing was 14.6 ± 3.0 cm and this increased during DDD pacing at all three AV delays (17.7 ± 3.3, 17.9 ± 3,0, 17.5 ± 3.5 cm). In the upright position, the velocity time integral during VVI pacing was 12.9 ± 3.5 cm and this increased with DDD pacing (15.5 ± 3.3, 15. 1 ± 4.0, 15.1 ± 3.9 cm). It was concluded that although stroke volume decreases when assuming the upright position, the beneficial response to dual chamber pacing is maintained and equals that observed in the supine position.     

Hemodynamic Benefits of Right Ventricular Outflow Tract Pacing: Comparison with Right Ventricular Apex Pacing

To assess optimal hemodynamics in relation to stimulation site during right ventricular pacing, 17 consecutive patients who underwent cardiac catheterization were studied. In all patients, right ventricular apex and right ventricular outflow tract stimulation was performed at 85, 100, and 120 beats/min. Cardiac index at both pacing sites was compared using the left ventricular outflow tract continuous wave Doppler technique. Comparison of the two stimulation sites demonstrated that right ventricular outflow tract pacing resulted in a higher cardiac index at 85 beats/min (2.42 ± 1.2 vs 2.04 ±1.0 L/min per m², P < 0.002) at 100 beats/min (2.78 ± 1.4 vs 2.35 ± 1.1 L/min perm², P < 0.001) and 120 beats/min (3.00 ± 1.5 vs 2.61 ± 0.9 L/min perm², P < 0.001). From a total of 51 paired observations, 45 showed an increase in cardiac index during outflow tract pacing as compared to apex pacing. Right ventricular outflow tract pacing at 120 beats/min resulted in a lower cardiac index than right ventricular apex pacing in patients with significant coronary artery disease and/or impaired left ventricular function (ejection fraction ≤ 50%), whereas right ventricular outflow tract pacing produced higher cardiac indices in the absence of these abnormalities. Right ventricular outflow tract pacing resulted in higher cardiac indices as compared to apex pacing in all other subgroups at all other pacing sites tested. It is concluded that stimulation of the right ventricular outflow tract offers a significant hemodynamic benefit during single chamber pacing as compared to conventional apex pacing, particularly in the absence of significant coronary artery disease and/or left ventricular dysfunction.     

Comparison of the Effects of AV Nodal Ablation Versus AV Nodal Modification in Patients with Congestive Heart Failure and Uncontrolled Atrial Fibrillation

Radiofrequency (RF) catheter ablation of the atrioventricular node (AVN) and implantation of a ventricular pacemaker can improve cardiac performance in patients with congestive heart failure (CHF) and uncontrolled atrial fibrillation (AF). Alternatively. RF catheter modification of the A VN has been proposed to slow ventricular response during AF without requirement for permanent pacing. Among 44 consecutive patients (mean age 69.7 ± 10.2 years) with drug resistant chronic AF, 22 (group I) had AVN ablation with permanent ventricular pacemaker implantation, while 22 patients had attempted AVN modification. Complete AV block was obtained in all group I patients while only seven (32 %) A VN modification patients (group II) had permanent slowing of ventricular rate. Among patients in group I, mean left ventricular ejection fraction (EF) increased from 32.2%± 8.8% before ablation to 41.9%± 14.6% 4-weeks postablation (P < 0.01); exercise tolerance time (ETT) increased from 2.9 ± 2.2 minutes to 4.5 ± 2.9 minutes (P < 0.01); and quality-of-life score decreased from 66.1 ± 22.6 to 36.9 ± 17.1 (P < 0.01). By comparison, there was only a small increase in ETT in the seven successful group II patients (2.4 ± 1.8 minutes to 3.0 ± 1.9 minutes; P < 0.05) and there was no significant change in EF or quality-of-life. While AVN ablation can occasionally have transient adverse effects, it is more effective than AVN modification for improving cardiac performance in selected patients with CHF and AF.     

Comparative Functional Effects of Chronic Ventricular Demand and Atrial Synchronous Ventricular Inhibited Pacing

We compared the effects of chronic ventricular inhibited (VVI) and atrial synchronous ventricular inhibited (VDD) pacing on functional capacity in 8 patients with complete atrioventricular heart block. Permanent VDD (Medtronic #2409, ASVIP) pacemakers were implanted in four men and four women (age range 27-76 years, mean 58.9 +/- 18.4 years), and randomly assigned to a three-month period of VDD or VVI pacing in this single blinded, crossover study. Functional capacity was assessed by questionnaire, graded treadmill exercise testing and radionuclide angiocardiography prior to pacemaker implant and following each pacing period. Following 3 months of pacing in each of VVI and VDD pacing modes, maximum heart rate (83.4 +/- 14 vs 134.9 +/- 16.4 beats/min, p less than 0.001) and double product (147.5 +/- 58.3 vs 218.9 +/- 52.7, p less than .001) were greater with VDD pacing. Although exercise duration on treadmill exercise testing (5.3 +/- 2.9 vs 6.9 +/- 3.1 minutes, p less than 0.1) was greater in the VDD mode, the difference was not significant. Similarly, there was no significant difference in functional capacity as measured by questionnaire scores (50.1 +/- 8.4 vs 46.9 +/- 8.9, p less than 0.1) or in left ventricular ejection fraction for the two pacing modes (.54 vs .55, p less than .5). Only one patient reported a subjective improvement with physiologic (VDD) pacing, whereas the remaining patients stated no preference. We conclude that VDD pacing offers improved maximal cardiac work during exercise compared to VVI pacing.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.