AAIR versus DDDR pacing in the bradycardia tachycardia syndrome: a prospective, randomized, double-blind, crossover trial

In 19 patients paced and medicated for bradycardia tachycardia syndrome (BTS), AAIR and DDDR pacing were compared with regard to quality of life (QoL), atrial tachyarrhythmia (AFib), exercise tolerance, and left ventricular (LV)function. Patients had a PQ interval < or = 240 ms during sinus rhythm, no second or third degree AV block, no bundle branch block, or bifascicular block. In DDDR mode, AV delay was optimized using the aortic time velocity integral. After 3 months, QoL was assessed by questionnaires, patients were investigated by 24-hour Holter, cardiopulmonary exercise testing (CPX) was performed, and LV function was determined by echocardiography. QoL was similar in all dimensions, except dizziness, showing a significantly lower prevalence in AAIR mode. The incidence of AFib was 12 episodes in 2 patients with AAIR versus 22 episodes in 7 patients with DDDR pacing (P = 0.072). In AAIR mode, 164 events of second and third degree AV block were detected in 7 patients (37%) with pauses between 1 and 4 seconds. During CPX, exercise duration and work load were higher in AAIR than in DDDR mode (423+/-127 vs 402+/-102 s and 103+/-31 vs 96+/-27 Watt, P < 0.05). Oxygen consumption (VO2), was similar in both modes. During echocardiography, only deceleration of early diastolic flow velocity and early diastolic closure rate of the anterior mitral valve leaflet were higher in DDD than in AAI pacing (5.16+/-1.35 vs 3.56+/-0.95 m/s2 and 69.2+/-23 vs 54.1+/-26 mm/s, P < 0.05). As preferred pacing mode, 11 patients chose DDDR, 8 patients chose AAIR. Hence, AAIR and DDDR pacing seem to be equally effective in BTS patients. In view of a considerable rate of high degree AV block during AAIR pacing, DDDR mode should be preferred for safety reasons.     

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

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

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.     

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.     

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.     

Preserving normal ventricular activation versus atrioventricular delay optimization during pacing: the role of intrinsic atrioventricular conduction and pacing rate

The purpose of the study was to compare the effects of DDD pacing with optimal AV delay and AAI pacing on the systolic and diastolic performance at rest in patients with prolonged intrinsic AV conduction (first-degree AV block). We studied 17 patients (8 men, aged 69 +/- 9 years) with dual chamber pacemakers implanted for sick sinus syndrome in 15 patients and paroxysmal high degree AV block in 2 patients. Aortic flow and mitral flow were evaluated using Doppler echocardiography. Study protocol included the determination of the optimal AV delay in the DDD mode and comparison between AAI and DDD with optimal AV delay for pacing rate 70/min and 90/min. Stimulus-R interval during AAI (ARI) was 282 +/- 68 ms for rate 70/min and 330 +/- 98 ms for rate 90/min (P < 0.01). The optimal AV delay was 159 +/- 22 ms. AV delay optimization resulted in an increase of an aortic flow time velocity integral (AFTVI) of 16% +/- 9%. At rate 70/min the patients with ARI < or = 270 ms had higher AFTVI in AAI than in DDD (0.214 +/- 0.05 m vs 0.196 +/- 0.05 m, P < 0.01), while the patients with ARI > 270 ms demonstrated greater AFTVI under DDD compared to AAI (0.192 +/- 0.03 m vs 0.166 +/- 0.02 m, P < 0.01). At rate 90/min AFTVI was higher during DDD than AAI (0.183 +/- 0.03 m vs 0.162 +/- 0.03 m, P < 0.01). Mitral flow time velocity integral (MFTVI) at rate 70/min was higher in DDD than in AAI (0.189 +/- 0.05 m vs 0.173 +/- 0.05 m, P < 0.01), while at rate 90/min the difference was not significant in favor of DDD (0.149 +/- 0.05 m vs 0.158 +/- 0.04 m). The results suggest that in patients with first-degree AV block the relative impact of DDD and AAI pacing modes on the systolic performance depends on the intrinsic AV conduction time and on pacing rate.     

Comparison of Intrinsic Versus Paced Ventricular Function

There is increasing evidence supporting the benefits of providing optimum AV delay in cardiac pacing, though controversy exists regarding its value and the benefits of intrinsic versus paced ventricular activation. This study compared various AV delays at rest in patients whose native AV delays were 200 msec. Only patients with DDD pacemakers who had intact AV conduction and normal ventricular activation were included in the study. Nine patients were studied. Methods: Ten studies were performed. Evaluation was done in AAI and DDD modes at paced heart rates of 60/min or as close as possible to the intrinsic heart rate if this was > 60/min. Stroke volume (SV) and cardiac output (COJ were measured. Results: When AV sequential pacing in the DDD mode with an optimum AV delay was compared to AAI pacing with a prolonged AV interval, the average optimum AV delay in the DDD mode was 157 msec and ranged from 125 to 175 msec. The average AV interval in the AAI mode was 245 msec and ranged from 212 to 300 msec. In the DDD mode, there was an overall significant improvement in CO of 11% and SV of 9%. Patients with intrinsic AV conduction times of > 220 msec showed an overall significant improvement in CO of 13% and SV of 11%. In patients with intrinsic AV conduction times of < 220 msec, an improvement in CO of 6% and SV of 4% was seen. Conclusions: (1) An optimum AV delay is an important component of hemodynamic performance; and (2) AV sequential pacing at rest with an optimum AV delay may provide better hemodynamic performance than atrial pacing with intrinsic ventricular conduction when native AV conduction is prolonged > 220 msec.     

Determination of the optimal atrioventricular interval in sick sinus syndrome during DDD pacing

BACKGROUND: Although the AAI pacing mode has been shown to be electromechanically superior to the DDD pacing mode in sick sinus syndrome (SSS), there is evidence suggesting that during AAI pacing the presence of natural ventricular activation pattern is not enough for hemodynamic benefit to occur. Myocardial performance index (MPI) is a simply measurable Doppler-derived index of combined systolic and diastolic myocardial performance. The aim of this study was to investigate whether AAI pacing mode is electromechanically superior to the DDD mode in patients with SSS by using Doppler-derived MPI. METHODS: Thirty-nine SSS patients with dual-chamber pacing devices were evaluated by using Doppler echocardiography in AAI mode and DDD mode. The optimal atrioventricular (AV) interval in DDD mode was determined and atrial stimulus-R interval was measured in AAI mode. The ratio of the atrial stimulus-R interval to the optimal AV interval was defined as relative AV interval (rAVI) and the ratio of MPI in AAI mode to that in DDD mode was defined as relative MPI (rMPI). RESULTS: The rMPI was significantly correlated with atrial stimulus-R interval and rAVI (r = 0.57, P = 0.0002, and r = 0.67, P < 0.0001, respectively). A cutoff point of 1.73 for rAVI provided optimum sensitivity and specificity for rMPI >1 based on the receiver operator curves. CONCLUSIONS: Even though the intrinsic AV conduction is moderately prolonged, some SSS patients with dual-chamber pacing devices benefit from the ventricular pacing with optimal AV interval. MPI is useful to determine the optimal pacing mode in acute experiment.     

The Use of Implantable Sensors for the Control of Pacemaker Mediated Tachycardias: A Comparative Evaluation Between Minute Ventilation Sensing and Acceleration Sensing Dual Chamber Rate Adaptive Pacemakers

The role of implantable sensors to control pacemaker mediated tachycardias was investigated in 16 patients with two different dual chamber rate adaptive (DDDR) pacemakers, which sensed eiter minute ventilation (DDDR-Meta, nine patients) or body acceleration (Relay, seven patients). Successive atrial sensed events beyond a programmable rate occurring in the absence of detection of exercise by the sensors were considered to represent retrograde conduction or atrial arrhythmias, and the pacemakers responded by either a mode shift from DDDR to ventricular rate adaptive (VVIR) pacing (DDDR-Meta) or by tracking at an interim rate, the so-called conditional ventricular tracking limit (CVTL, Relay). In the unipolar atrial sensing mode, myopotential sensing (MPI) and external chest wall stimulations (CWS) at 250 beats/min were induced to be preferentially sensed by the atrial channel to simulate the conditions of atrial arrhythmias. In the DDD mode, these maneuvers resulted in ventricular responses of 88 +/- 3 beats/min and 110 +/- 3 beats/min for MPI and CWS, respectively. The pacing rate was significantly reduced in the DDDR mode with the sensors correctly detecting and responding to the sensed abnormal atrial signals (68 +/- 5 beats/min during MPI and 71 +/- 5 beats/min during CWS, P less than 0.005 compared with the corresponding DDD rate). One patient with a Relay pacemaker developed spontaneous atrial flutter and the ventricular tracking responses were 140 and 85 beats/min in the DDD and DDDR pacing modes, respectively. Thus MPI and CWS are useful bedside testing methods to assess pacemaker response during atrial arrhythmias. The use of implantable sensors to judge the appropriateness of atrial rate is a new approach to the management of pacemaker mediated tachycardias.     

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

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

Initial Clinical Experience with a New Dual Sensor SSIR Pacemaker Controlled by Body Activity and Minute Ventilation

Fourteen patients were implanted with a single chamber dual sensor pacemaker (Legend Plus®) that measures minute ventilation (VE) via variations in impedance between a bipolar lead and the pacemaker case, and activity via a piezoelectric crystal bonded to the pacemaker case. Chronotropic incompetent patients were exercised an a treadmill and a bicycle in dual sensor mode. Activity only indicated pacing rate was measured using a strap-on pacemaker. Both implanted and strap on pacemakers were adjusted to yield a steady-state pacing rate of 100 beats/min during hall walk. Pacing rate, VE, and oxygen uptake (VO₂) were measured continuously. Linear curve fit analysis slopes for plots of VE versus pacing rate during exercise (1.33-1.49) compared favorably to values reported in normals. Peak pacing rates achieved for treadmill and bicycle testing for dual sensor mode were higher than activity mode alone. Slopes of heart rate to VE or VO₂ were not significantly different (P < 0.05) for dual sensor mode in contrast to activity alone. In conclusion, the Legend Plus dual sensor rate adaptive pacing therapy delivered pacing rates more proportional to VE and VO₂ under different types of exercise than rates indicated by a strap-on pacemaker in activity mode.     

Atrial Arrhythmia Management with Sensor Controlled Atrial Refractory Period and Automatic Mode Switching in Patients with Minute Ventilation Sensing Dual Chamber Rate Adaptive Pacemakers

Although a long postventricular atrial refractory period fPVARP) may prevent the occurrence of pacemaker mediated tachycardias and inadvertent tracking of atrial arrhythmias in dual chamber (DDD) pacing, the maximum upper rate will necessarily be compromised. We tested the feasibility of using minute ventilation sensing in a dual chamber rate adaptive pacemaker (DDDR) to shorten the PVARP during exercise in 13 patients with bradycardias (resting PVARP = 463 ± 29 msec) to avoid premature upper rate behavior. Graded treadmill exercise tests in the DDD and DDDR modes at this PVARP resulted in maximum ventricular rates of 98 ± 8 and 142 ± 3 beats/min, respectively (P < 0.0001), due to chronotropic incompetence and upper rate limitation in the DDD mode, both circumvened with the use of sensor. In order to simulate atrial arrhythmias, chest wall stimulation was applied for 30 seconds at a rate of 250 beats/min at a mean unipolar atrial sensitivity of 0.82 mV. Irregular ventricular responses occurred in the DDD mode fthe rates at a PVARP of 280 and 463 ± 29 msec were, respectively 92 ± 5 and 66 ± 3 msec; P < 0.0001). In the DDDR mode at a PVARP of 463 ± 29 msec, regular ventricular pacing at 53 ± 2 beats/min occurred due to mode switching to VVIR mode in the presence of repetitive sensed atrial events within the PVARP. One patient developed spontaneous atrial fibrillation on follow-up, which was correctly identified by the pacemaker algorithm, resulting in mode switch from DDDR to regular VVIR pacing and preservation of rate response. In conclusion, sensor controlled PVARP allows a long PVARP to be used at rest without limiting the maximum rate during exercise. In addition, to offer protection against retrograde conduction, a long PVARP and mode switching also limit the rate during atrial arrhythmias and allow regular ventricular rate responses according to the physiological demands.     

Rate Adaptive Atrial Pacing in the Bradycardia Tachycardia Syndrome

In 42 patients (26 men, 16 women; mean age 69 ± 10 years), who were paced and medicated with antiarrhythmic drugs for the bradycardia tachycardia syndrome, chronotropic response and AV conduction with rapid atrial pacing during exercise were studied. Patients were included if they had no second- or third-degree AV block, no complete bundle branch or bifascicular block, and a PQ interval ≤ 240 ms during sinus rhythm at rest. The interval between the atrial spike and the following Q wave (SQ) was measured in the supine position at rest with an AAI pacing rate of 5 beats/min above the sinus rate (SQ-R+5), and at the end of exercise with 110 beats/min (SQ-E110). Bicycle ergometry was performed using the Chronotropic Assessment Exercise Protocol with the pacemakers being programmed to AAI with a fixed rate of 60 beats/min. Chronotropic incompetence was defined as peak exercise heart rate: (1) < 100 beats/min; (2) < 75% of the maximum predicted heart rate; or (3) the heart rate at half the maximum workload < 60 + 2 beats/min per mL O₂/kg per minute (calculated O₂ consumption). During exercise, one patient developed atrial fibrillation. Chronotropic incompetence was present in 71 % (29/41) of the patients according to definition 2, and in 76% (31/41) according to definition 1 or 3. Ten out of 41 patients (24%) exhibited a second-degree AV block with atrial pacing at 110 beats/min at the end of exercise. Only 9 out of the remaining 31 patients (29%) showed a physiological adaptation of the SQ-E110, and 21 patients (68%) exhibited a paradoxical increase of the SQ interval with rapid atrial pacing at the end of exercise as compared to the SQ-R+5. These observations indicate that the pacing system to be used in most patients paced and medicated for the bradycardia tachycardia syndrome should be dual chamber, and the option of rate adaptation should be considered.     

A Randomized Double-Blind, Cross-Over Study of the Linear and Nonlinear Algorithms for the QT Sensing Rate Adaptive Pacemaker

BAIG, M.W., ET AL.: A Randomized Double-Blind, Cross-Over Study of the Linear and Nonlinear Algorithms for the QT Sensing Rate Adaptive Pacemaker. We have compared the pacing rate responses during cardiopulmonary exercise testing in 11 patients (mean 59 years, six female) with implanted QT sensing rate adaptive pacemakers who were randomly programmed to 1-month periods in the linear and nonlinear algorithms using a double-blind, cross-over design. Exercise testing was performed at the end of each month block and symptoms were scored with the MacMaster questionnaire. With exercise, the time to a 10 beats/min increment in rate was significantly less with the nonlinear compared to the linear algorithm (126 sec vs 255 sec, P = 0.02) but there were no significant differences in exercise duration, the peak pacing rate, the peak VO₂, the VO₂ at the anaerobic threshold or the mean correlation coefficients of the pacing rate VO₂ relationship. Rate oscillation occurred in seven patients in the linear algorithm and in two patients in the nonlinear setting. Initial deceleration of the pacing rate at the onset of exercise occurred in seven patients in the linear algorithm and in four patients in the nonlinear setting. The nonlinear algorithm is associated with a faster response time during exercise and fewer instances of rate instability. However, it has not overcome the problem of a dip in the pacing rate at the beginning of exercise. The major difference in the function of the two algorithms is faster initial acceleration with the nonlinear algorithm. This is explained by the significantly higher values of the slope setting at the lower rate limit for the nonlinear versus the linear algorithm (6.3 ms/ms vs 5.1 ms/ms).     

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.     

AV block and changes in pacing mode during long-term follow-up of 399 consecutive patients with sick sinus syndrome treated with an AAI/AAIR pacemaker

This retrospective study included a large cohort of consecutive patients primarily implanted at Skejby University Hospital with an AAI/AAIR pacemaker because of sick sinus syndrome (SSS) from July 1981 to July 1999. The primary aim of the study was to analyze the risk of developing AV block during long-term follow-up. A secondary aim was to study the incidence and reasons for changes in pacing mode caused by other than AV block. A total of 399 patients (231 women, mean age 71 +/- 13.5 years) were identified. Mean follow-up was 4.6 +/- 3.4 years and occurred at death, reoperation with mode change, pacemaker explant, or end of study. During follow-up, 44 patients had a ventricular lead implanted with a mean delay of 2.8 +/- 3.1 years (range 1 day-10.4 years) after the primary implantation. A total of 30 patients received a ventricular lead because of AV block or AF with bradycardia (annual incidence 1.7%). Another 14 patients received a ventricular lead without having documented AV block or AF with pauses (annual incidence 0.8%). The present observational study documents that in patients with SSS treated with AAI/AAIR pacing, AV block requiring implantation of a ventricular lead occurs at a rate of 1.7% per year. It is considered that AAI/AAIR pacing is safe and reliable as treatment for patients with SSS and normal AV conduction.     

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.     

Atrial Rate Adaptive Pacing: What Happens to AV Conduction?

To investigate if an nonphysiological prolongation of the AV inteii-al is common during activity sensor modulated atrial rate adaptive (AAIR) pacing, 21 patients witb sinus node disease treated with fixed rate atrial (AAI) or AAIR pacemakers were examined. Spike-Q intervals were compared at different beaii: rates obtained by overdrive pacing at rest and during exercise (Study I), measured during exercise at unresponsive (AAI), optimal (AAIR) and over responsive programming (AAIR +) of the activity sensor (Study II), and finally examined by 24-hour Holter recording in AAI and AAIR pacing modes (Study III). Study I: The spike-Q interval increased significantly with increasing heart rate at rest, but not during exercise. At rest the spike-Q interval was significantly higher at all heart rates compared to exercise. There was a significant positive correlation between the maximal spike-Q interval at rest and the maximal spike-Q inteival during exercise (r = 0.63). Study II: The spike-Q interval was shortest in the AAI and longest in the AAIR+ mode in all patients. Study III: During AAI or AAIR pacing the spike-Q interval was longest at night and shortest in the morning. The mean spike-Q interval was longer in AAIB than in AAI pacing. No statistical difference between the maximal spike-Q intervals observed during the two modes was, however, found. Variations in spike-Q interval are generally caused by changes in autonomic tone or medication with drugs with antiarrhythmic effect. Our results indicate that the risk for an nonphysiological prolongation of the AV interval during AAIR pacing is rather small and can be predicted by studying the spike-Q interval at rest during overdrive pacing.     

Full Ventricular Capture Indicated by the QT Interval Function

The atrioventricular (AV) interval is critical in dual chamber (DDD) pacing in patients with hypertrophic obstructive cardiomyopathy (HOCM) to obtain full ventricular capture (FVC) with maximal reduction of the left ventricular (LV) outflow gradient and optimal LV diastolic filling. We studied the relationship of FVC, fusion, spontaneous AV conduction, and the QT interval. Methods: 11 patients with various cardiac diseases and stable AV conduction received a QT sensing Diamond (tm) Vitatron, DDD pacemaker. Software was downloaded into the pacemaker. In the DDD pacing mode, with the QT interval measured from the ventricular pacing stimulus to the end of the T wave, the AV interval was shortened from 400 ms, in 20-ms steps, to 90 ms. At 90 ms the stimulation rate was increased by 30 beats/mm and the AV interval was increased stepwise. FVC and fusion was examined on the surface ECG, Results: At 400 ms interval, spontaneous AV conduction inhibited the pacemaker. Shortening the AV interval resulted in pacing with a short QT interval. Further reduction of the AV interval resulted in a longer QT interval up to a point where the QT interval became stable. This point, the bending point in the plot of measured QT interval versus shortened AV intervals, coincided with the point of FVC. The relation of the QT-AV interval plot and the point of fusion was comparable when lengthening the AV interval at a 30 beats/mm faster stimulation rate. Conclusion: The bending point in the QT interval versus AV interval plots showed a good correlation with the FVC and fusion points observed on ECG. The results suggest that automatic discrimination between fusion and full capture using QT interval measurements may be feasible.     

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.