AV conduction with atrial rate adaptive pacing in the bradycardia tachycardia syndrome

AV conduction with atrial rate adaptive pacing (AAIR) during exercise was investigated in 43 patients (28 men, 15 female, mean age 68 +/- 7 years) who were paced and medicated with antiarrhythmic drugs for the bradycardia tachycardia syndrome (BTS). Patients were included if they had no second- or third-degree AV block, no complete bundle branch or bifascicular block, and a PQ interval < or = 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 (R) with maximum AAI pacing rate (Fmax) achieved below the Wenckebach point (SQ-R-Fmax). Bicycle ergometry was performed using the Chronotropic Assessment Exercise Protocol, and AAI pacing rate was increased stepwise by programming load-adapted increments. Seven patients showed intrinsic rhythm during exercise. In those 36 patients who were atrially paced throughout ergometry (E), SQ was measured with 70 beats/min on the lowest CAEP stage (SQ-E-70) and with Fmax at maximum work load (SQ-E-Fmax). During exercise, no second-degree AV block was observed, but 28 of 36 patients (78%) showed a nonphysiological increase of the SQ interval, and the average SQ-E-Fmax was significantly longer than SQ-E-70 (250 +/- 31 versus 228 +/- 32 ms, P < 0.01). There was only a weak correlation between SQ-R-Fmax and SQ-E-Fmax (r = 0.35824, P < 0.05). When Fmax obtained during exercise was kept during recovery, 14 patients (39%) developed a second-degree AV block between 15 and 240 seconds after ergometry, 8 patients within 90 seconds. Patients who had exhibited a P on T wave in the ECG with Fmax at the end of exercise (11 of 36 patients) were reevaluated by Doppler echocardiography. Using the same exercise protocol and identical, load-adapted rate increments, only 3 of 11 patients showed premature mitral valve closure. It is concluded that patients paced and medicated for BTS are prone to a nonphysiological prolongation of AV conduction with AAIR pacing during and after exercise. As this risk can hardly be predicted by rapid atrial pacing at rest, the pacing system should be dual chamber in this subset of patients. This especially applies to the patients in whom mechanical AV timing is affected by the conduction delay.     

A New Principle of Rate Adaptive Pacing in Patients with Sick Sinus Syndrome

The most "natural" rate adaptive pacemaker is VDD for patients with AV block. Nothing equivalent exists for patients with sick sinus syndrome (SSS). Even if they are paced in the AAI mode, the AV synchrony is often lost under exercise if nodal rhythms develop which cause the atria to contract against closed valves by retrograde conduction. We tried to develop a concept of rate adaptive pacing which is applicable in SSS patients by guaranteeing AV synchrony. It is known that AV delay shortens with increasing rate under exercise in normal subjects. Three AAI paced patients were evaluated to find out whether a similar correlation is valid between exercise and AV delay with constant rate. A nonconventional ECG was registered during the whole procedure by using an analog tape recorder. The pacing rate was changed with and without exercise on a bicycle to determine its influence on AV delay and by calculating the AV delay averaged over the last 8 beats. In all three patients a reproducible correlation existed between exercise and shortening of the AV delay. This effect was already detectable after 10 s. Increasing the pacing rate above "physiological" rates caused prolongation of the AV delay (over-stimulation phenomenon). We, therefore, concluded that measuring the AV delay in atrial paced patients with SSS by means of a ventricular electrode can be used as a fast parameter for rate adaptive pacing with AV synchrony. The "over-stimulation" phenomenon can additionally be utilized for controlling "physiological" rates depending on individual needs.     

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.     

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.     

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.     

Pacemaker Syndrome with AAI Rate Variable Pacing: Importance of Atrioventricular Conduction Properties, Medication, and Pacemaker Programmability

A patient who received an AAI Activitrax rate variable pacemaker for treatment of symptomatic sinus bradycardia is described. disopyramide prolonged the anterograde effective refractory period of the fast conducting atrioventricular (AV) nodal pathway to such an extent, that conduction switched to the slow AV nodal pathway at low atrial pacing rates. This gave rise to symptoms of the pacemaker syndrome during moderate exercise because the paced atrial event was conducted with a long, spike to Q interval with occurrence of the paced atrial event just after the preceding QRS complex. A change of medication solved this problem. Programming a bipolar electrode configuration avoided sensing of far-field QRS signals with the associated problems of resetting the basic pacing interval as well as the upper rate interval. AAI rate variable pacing requires careful evaluation of AV conduction properties, AV conduction intervals as well as the influence of medication to be given. The use of multiprogrammable pacemakers with marker channel capability will significantly facilitate the understanding and resolution of anomalous behavior.     

Long-Term Pacing in Heart Transplant Recipients is Usually Unnecessary

The indications for and timing of permanent pacing were reviewed in all 17 of 154 adult heart transplant recipients at this center who have had permanent pacemakers implanted. Resting 12-lead ECGs recorded during routine follow-up were examined. A prospective study of pacing requirement was then undertaken. Holter monitoring was performed before and after reprogramming the pacemakers to VVI mode at 50 beats/min. Exercise responses in various pacing modes were then assessed in seven patients with rate responsive pacemakers using a standard Bruce protocol treadmill test. The indication for pacing was sinus node dysfunction in 59% (10/17) and atrioventricular (AV) block in 41% (7/17). The majority of pacemakers were implanted between seven and 21 days after transplantation. There was a progressive reduction in the frequency of pacing on 12-Jead ECGs with time after transplantation. Eight of 14 patients with empirically selected programming paced during Holter monitoring. After reprogramming to 50 beats/ min VVI mode only three of 14 patients, all with sinus node dysfunction, paced. Rate responsive pacing made no difference to exercise time. The requirement for long-term pacing in cardiac transplant recipients is small (3/154) and is limited lo patients with sinus node dysfunction. Rate responsive pacing did not increase exercise tolerance.     

The Development of Sinoatrial Dysfunction in Pacemaker Patients with Isolated Atrioventricular Block

The purpose of this paper is the assessment of sinus node competence over time in patients with isolated atrioventricular block (AV block). Patients implanted with AV synchronous pacemakers for isolated A V block between December 1993 and June 1995 were prospectively evaluated at predischarge, 6 weeks, and subsequent 6 months follow-up with respect to atrial rate monitors/24-hour Holter and modified exercise test. Patients unable to maintain AV synchronous pacing or complete a modified exercise test were excluded. Sinus node competency is interpreted as: (1) absence of atrial brady- or tach-yarrhythmia, (2) ability to achieve a minimum heart rate of 100 beats/min with modified exercise test or during daily activities. There were 58 patients (22 women), mean age 71.0 ± 13.8 with an average follow-up of 30.4 months (11–40). Three patients did not complete a modified exercise test, 4 patients were lost to follow-up, and 2 patients were unable to maintain AV synchronous pacing. Of the remaining 49 patients, 3 developed chronic or paroxysmal atrial fibrillation. No patient developed significant bradyarrhythmias. All patients achieved a heart rate of ≥ 100 beats/min modified exercise test. In our group of patients with isolated AV block within a moderate follow-up period, development of Sinoatrial dysfunction was rare (6%). A longer follow-up is required to delineate the natural history of Sinoatrial dysfunction in patients with isolated AV block.     

Respiratory-Dependent Atrial Pacing, Management of Sinus Node Disease

The effectiveness of respiratory-dependent atrial pacing (AAI-RD) was assessed in 23 patients (11 male, 12 female; 68 ± 10 years) with symptomatic isolated sinus node disease (SND). Follow-up was performed at 3 month intervals and included history taking, physical examination, ECG recording and 24-hour Holter monitoring. An incremental treadmill exercise test was performed in 21/23 patients before pacemaker implantation, in 23/23 patients after implantation (at least two tests with different programmed settings of respiratory rate/paced rate ratio); 21/23 patients underwent treadmill tests during both fixed rate 70 bpm and AAI-RD pacing. Physiological sensitivity of AAI-RD pacing was found excellent in 34 tests (85%) and fair in six (15%). Spontaneous heart rate was significantly higher after pacemaker implantation fbpm 115 ± 20 vs 98 ± 24, P < 0.001). In 10/21 patients paced rate was significantly higher during AAI-RD vs AAI pacing (131 ±9 vs 106 ± 16, P < 0.001) with better total work time (min 9.9 ± 4 AAI-RD vs 6.8 ± 2.6 AAI, P < 0.002), higher oxygen consumption at anaerobic threshold (ml/min 1137 ± 406 AAI-RD vs 882 ± 268 AAI-RD vs 5.5 ± 2.6 AAI, P - 0.001). No significant difference was found in 7/21 patients (overlap between spontaneous and paced rate during both AAI-RD and AAI programming); 4/21 patients did not reach anaerobic threshold owing to osteomuscular limitations. AV block was detected in 1/23 patients, Biorate circuital failure in 1/23, sporadic undersensing in 5/23, short and symptom-free myopotential inhibitions in 10/23. We concluded that AAI-RD pacing is a reliable, safe and useful modality in pacemaker management of isolated SNA, especially in patients with abnormal rate response to exercise.     

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.     

AAIR Versus DDDR Pacing in Patients with Impaired Sinus Node Chronotropy: An Echocardiographic and Cardiopulmonary Study

The aim of this study was to compare AAIR and DDDR pacing at rest and during exercise. We studied 15 patients (10 men, age 65 ± 6 years) who had been paced for at least 3 months with activity sensor rate modulated dual chamber pacemakers. All had sick sinus syndrome (SSS) with impaired sinus node chronotropy. The patients underwent a resting echocardiographic evaluation of systolic and diastolic LV function at 60 beats/min during AAIR and DDDR pacing with an AV delay, which ensured complete ventricular activation capture. Cardiac output (CO) was also measured during pacing at 100 beats/min in both pacing modes. Subsequently, the oxygen consumption (VO₂at) and VO₂at pulse at the anaerobic threshold were measured during exercise in AAIR mode and in DDDR mode with an AV delay of 120 ms. The indices of diastolic function showed no significant differences between the two pacing modes, except for patients with a stimulus-R interval > 220 ms, for whom the time velocity integral of LV filling and LV inflow time were significantly lower under AAI than under DDD pacing. At 60 beats/min, CO was higher under AAI than under DDD mode only when the stimulus-R interval was below 220 ms. For stimulus-R intervals longer than 220 ms, and also during pacing at 100 beats/min, the CO was higher in DDD mode. The stimulus-R interval decreased in all patients during exercise. The time to anaerobic threshold, VO₂at ond VO₂at pulse showed no significant differences between the two pacing modes. Our results indicate that, at rest, although AAIR pacing does not improve diastolic function in patients with SSS, it maintains a higher CO than does DDDR pacing in cases where the stimulus-R interval is not excessively prolonged. On exertion, the two pacing modes appear to be equally effective, at least in cases where the stimulus-R interval decreases in AAIR mode.     

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.     

Clinical Experience with an Activity Sensing Pacemaker

During clinical evaluation of the Medtronic * Activitrax pacemaker in a worldwide multicenter study, implant and follow-up data were provided by 61 investigators on 222 patients. Pacing indications included two- and three-degree AV block in 149 and atrial arrhythmias in 174 patients; 16 patients received atrial pacing. Average and longest documented follow-up periods were 7.5 and 16 months respectively. Paired treadmill tests, one in Activity mode and one in VVI/AAI mode, were performed by 120 patients. At peak exercise, average heart rate was 95 bpm in VVI/AAI mode and 118 bpm in Activity mode (p < 0.0001). Average exercise time was 9.4 minutes in VVI/AAI mode and 10.8 minutes in Activity mode (p < 0.0001). In 54 patients who exclusively had paced rhythm during both treadmill tests, average heart rates and exercise times were 70 ppm and 8.1 minutes in VVI/AAI mode and 111 ppm and 10.3 minutes in Activity mode respectively (p < 0.0001). 24-hour Holter recordings typically demonstrated pacing at or near basic rate during periods of rest and appropriate increase in pacing rate during daily activities. Patients had significantly fewer problems with physical effort in daily life during a week of Activity mode pacing than during a week of VVI/AAI mode pacing (p < 0.05) as assessed from the symptom scores recorded by 62 patients in special diaries.     

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.     

A Double-Blind Study of Submaximal Exercise Tolerance and Variation in Paced Rate in Atrial Synchronous Compared to Activity Sensor Modulated Ventricular Pacing

To assess the variation in paced rate during everyday activity and the importance of atrioventricular synchronization (AV synchrony) for submaximal exercise tolerance, atrial synchronous (DDD) and activity rate modulated ventricular (VVI,R) pacing were compared in 17 patients with high degree AV block. The patients were randomly assigned to either mode and evaluated by treadmill exercise to moderate exertion and by 24-hour Holter monitoring after 2 months in the DDD and VVI,R modes, respectively. At the end of the study, the patients were programmed to the pacing mode corresponding to the preferred study period. During the treadmill test, the mean exercise time to submaximal exertion (Borg 5/10), exertion ratings and respiratory rate did not differ between pacing modes despite a significantly lower ventricular rate in the VVI,R mode. The atrial rate during VVI,R pacing was significantly higher than the ventricular rate, but did not differ from the ventricular rate during DDD pacing. There was a diurnal variation in paced rate in both pacing modes. Paced ventricular rate was, however, higher and variation in paced rate greater in DDD compared to VVI,R pacing. Nine patients preferred the DDD mode, three patients preferred the VVI,R mode, while five subjects did not express any preference. The results from this study indicate that the variation in paced rate during activity sensor-driven VVI,R pacing does not match that during DDD pacing neither during everyday activities nor during submaximal treadmill exercise. Nevertheless, no differences in exercise time, Borg ratings, and respiratory rate during submaximal exercise were found. Thus, for most patients with high degree AV block, DDD and VVI,R pacing seem equally satisfactory for submaximal exercise.     

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.     

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.     

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.     

Practical Aspects of Rate Adaptive Atrial (AAI,R) Pacing: Clinical Experiences in 44 Patients

Forty-four patients with sinus node disease and chronotropic incompetence but no evidence of AV conduction disturbances were treated with rate adaptive atriul (AAI,R) pacemakers. Medtronic Activitrax and Siemens Sensolog activity sensing single chamber pulse generators were used. Twentyfour patients (55%) had the bradycardia-tachycardia syndrome. The mean folloiw-up time is 20 ± 14 months (range 1–48, median 17 months). All patients remain alive. Two patients were reoperated upon for lead problems without change of pacing mode. One patient developed symptomatic: srecond-degree Wenckebach block during follow-up, and received a DDD,R system. Although 22 of the patients were treated with antiarrhythmic drugs postoperatively, no further cases of significant AV conduction disturbances were seen. During rapid atrial pacing, exercise-induced enhancement of AV conduction was a consistent finding, although less pronounced in patients treated with beta-blocking drugs. One patient developed permanent atrial fibrillation with an adequate ventricular rate. By systematic reprogramming procedures, QRS complex sensing through the atrial electrode could be demonstrated in 25 patients (23/28 with unipolar and 2/16 with bipolar leads). it could be counteracted effectively by pulse generator program selection in all cases. Forty-two of 44 patients (95%) remain in AAI,R pacing with normal function, Rate adaptive atrial pacing can be successfully applied in this patient group.     

Incidence and Significance of Chronotropic Incompetence in Patients with Indications for Primary Pacemaker Implantation or Pacemaker Replacement

This prospective study was undertaken to evaluate the incidence and significance of chronotropic incompetence in 211 patients [age 71.1 6 10.6 years (mean 6 SD)] by means of maximum exercise test in order to determine the indication for rate-responsive pacing before primary pacemaker implantation (147 patients) or pacemaker replacement (64 patients). There were 112 (53%) patients with second- or third-degree AV block, 63 (30%) with sick sinus syndrome, and 36 (17%) with chronic atrial fibrillation. Chronotropic incompetence was defined as maximum heart rate lower than age-adjusted norm calculated by the formula: 0.7x(220 - age) and its significance as the difference between the two rates. The overall incidence of chronotropic incompetence was 42%. The incidence was significantly higher in patients with atrial fibrillation (67%, P<0.0005) and sick sinus syndrome (49%, P<0.012) than in those with AV block (30%). The mean difference between maximum heart rate and the age-adjusted norm was 18% (range 2%-63%). The mean difference was significantly higher in patients with atrial fibrillation (27%, range 8-63%) than in those with sick sinus syndrome (19%, range 2%-45%, P<0.01), or with AV block (12%, range 6%-26%, P<0.000001). The rate-responsive pacemakers were implanted in 44% of 211 patients studied and in 43% of 196 patients excluded from the study due to the apparent (contra)indication of rate-responsive pacing (NS). Thus, chronotropic incompetence seems to be common in the pacemaker patient population. The highest incidence and significance was found in patients with chronic atrial fibrillation. Systematic evaluation of chronotropic competence can double the rate of implantation of rate-responsive pacemakers; however, further studies are needed to clarify relation between the significance of chronotropic incompetence and functional benefit of rate-responsive pacing.