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.     

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

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

Doppler Echocardiographic Studies in Sequential Atrioventricular Pacing

Six patients with sequential atrioventricular pacemakers were studied by Doppler echocardiography. A commercially available continuous wave system (transcutaneous aortovelography) was used and the transducer was placed in the suprasternal notch and angled to obtain peak aortic arch blood flow velocity. Changes in Doppler peak velocity have been previously shown to correlate closely and reliably with changes in hemodynamically measured stroke volume/cardiac output in the same patients following interventions, In all patients, the pacemaker was programmed from DVI mode to VVI (heart rate was kept constant) and then back to DVI, with the Doppler transducer held in a fixed position all the time, and peak velocities measured after the patient had been in any particular mode for at least 1 minute. Five of 6 patients showed reduction in peak velocities ranging from 13–25% (mean 18.4%) when the pacing mode was switched from DVI to VVI. Doppler peak velocity remained unchanged in 1 patient. Doppler echocardiography represents a simple, noninvasive method for estimating increments in stroke volume/cardiac output obtained with sequential AV pacing.     

Physiological Relationship Between AV Interval and Heart Rate in Healthy Subjects: Applications to Dual Chamber Pacing

The purpose of this paper is to specify the mathematical relationship between spontaneous AV interval (AVI) and heart rate (HR), the amplitude and rate of variation of AVI, and the physiological factors likely to affect these characteristics. Ten patients with healthy hearts were studied. Two catheter electrodes were positioned in the right atrium and at the tip of the right ventricle respectively, allowing the detection of endocardial signals. The AV and AA intervals for each heart cycle were digitized to on accuracy of ± 1 msec. Measurements were made at rest, then during a stress test on an exercise bicycle, and finally during the recovery phase. The results show that adaptation is very precise and takes place instantly. Any variation in heart rate causes an immediate, inversely proportional variation in AVI. Adaptation follows a linear pattern, generally with relatively low amplitude and an average AVI reduction of 27.5 ±11.2 msec for an average HR increase of 78.7 ± 22.5 bpm, i.e., a decrease of 4 ± 2.1 msec for an HR variation 0f 10 bpm. The amplitude and variation rate of AVI seem to be independent 0f the age and base value of the PR interval. These observations may be useful for designing new VDD or DDD pacemakers that automatically adapt the AV interval to the instantaneous heart rate. The hemodynamic benefits 0f this adaptation were also demonstrated.     

Atrioventricular Interval Optimization in the Right Atrial Appendage and Interatrial Septum Pacing: A Comparison Between Echo and Peak Endocardial Acceleration Measurements

PADELETTI, et al. : Atrioventricular Interval Optimization in the Right Atrial Appendage and Interatrial Septum Pacing: A Comparison Between ECHC and Peak Endocardial Acceleration. Interatrial septum pacing (IASP) reduces interatrial conduction time and consequently may interfere with atrioventricular delay (AVD) optimization. We studied 14 patients with an implanted BEST Living system device able to measure peak endocardial acceleration (PEA) signal. The aims of our study were to compare the (1) optimal AVD (OAVD) in right atrial appendage pacing (RAAP) and IASP, and (2) OAVD derived by the PEA signal versus OAVD derived by Echo/Doppler evaluation of the left ventricular filling time (LVFT) and cardiac output (CO). Measurements were performed in DDD VDD modes Eight patients (group A) had RAAP and six patients (group B) had IASP. In group A, OAVD measured by LVFT, CO, and PEA was 185 ± 23 ms , 177 ± 19 ms , and 192 ± 23 ms in DDD and 147 ± 19 ms , 135 ± 27 ms , and 146 ± 20 ms in VDD, respectively. OAVD measured by LVFT, CO, and PEA was significantly longer in DDD mode than in VDD (P < 0.01, P < 0.01, P < 0.001 ). In group B, OAVD measured by LVFT, CO, and PEA was 116 ± 19 ms , 113 ± 10 ms , and 130 ± 30ms in DDD and 106 ± 16 ms , 96 ± 15 ms , and 108 ± 26 ms in VDD, respectively. No statistical differences were observed between DDD and VDD. Significant correlations between OAVDs PEA derived and OAVDs LVFT and CO derived were observed (r = 0.71, r = 0.69, respectively ). When new techniques of atrial stimulation, as IASP, are used an OAVD shorter and similar in VDD and DDD has to be considered. The BEST Living system could provide a valid method to ensure, in every moment, the exact required OAVD to maximize atrial contribution to CO.     

Effect of Atrioventricular Sequential Pacing on Left Ventricular Flow Dynamics in a Patient with Mid-Ventricular Obstruction

The effect of dual chamber atrioventricular sequential pacing on the intraventricular pressure gradient was tested using Doppler echocardiography in a patient with hypertrophic mid-ventricular obstruction. Atrioventricular sequential pacing with relatively short atrioventricular delays reduced in the left ventricular pressure gradient at the mid-ventricular level. Also, atrioventricular sequential pacing affected the degree and profile of the isovolumetric relaxation flow. These results suggest that atrioventricular sequential pacing affects both systolic and diastolic left ventricular flow dynamics in mid-ventricular obstruction.     

The A-R Interval as Exercise Indicator: A New Option for Rate Adaptation in Single and Dual Chamber Pacing

RUITER, J.H., ET AL.: The A-R Interval as Exercise Indicator: A New Option for Rate Adaptation in Single and Dual Chamber Pacing. We investigated the possibility to use the interval from an atrial stimulus to the Ventricular R wave [A-R interval) as an indicator of physical stress, in 16 patients with pacemakers implanted for severe atrial bradycardia but with intact AV conduction. The A-R interval was studied during incremental atrial pacing at rest and during exercise with a constant workload. In addition, the atrial pacing rate was kept constant just above spontaneous sinus rate and the dynamics of the A-R interval were studied during exercise with a low constant workload and during a maximal exercise test with increasing workload. Incremental atrial pacing prolonged the A-R interval and this response was blunted during exercise [p < 0.003). Atrial pacing at a constant rate and during a constant workload resulted in an almost direct shortening of the A-R interval. When the workload was increased but the atrial rate kept constant, a pronounced shortening of the A-R interval was noted [p < 0.0001). It is concluded that changes of the A-R interval during different kinds of exercise were prompt and predictable in patients with sinus node dysfunction but intact AV conduction. In these patients the shortening of the A-R interval during exercise may be a suitable indicator for rate adaptive atrial pacing.     

Safety of Slow Pathway Ablation in Patients with Long PR Interval: Further Evidence of Fast and Slow Pathway Interaction

Whether the presence of abnormal PR before selective slow pathway ablation for AV node reentrant tachycardia increased the risk of complete heart block remains controversial. We report our experience in seven patients with prolonged PR intervals undergoing catheter ablation for AV reentry tachycardia. Their mean age was 66 ± 12 years; four patients were female and three were male. RF ablation was performed using an anatomically guided stepwise approach. In six patients, common type AV node reentry was induced and uncommon type was observed in the remaining patient. In all seven patients, successful selective slow pathway ablation was associated with no occurrence of complete heart block and was followed by shortening of the AH interval in five patients. In all seven patients, successful ablation was achieved at anterior sites (M₁ in two patients and M₂ in five patients). Despite AH shortening after ablation, the 1:1 AV conduction was prolonged after elimination of the slow pathway, excluding either sympathetic tone activation or parasympathetic denervation. In conclusion, selective slow pathway ablation can be performed safely in the majority of patients with prolonged PR interval before the procedure. Because successful ablation is achieved at anterior sites in most patients, careful selection and monitoring of catheter position is required.     

Suppression of Torsades de Pointes by Biventricular Pacing in a Patient with Long QT Syndrome

This report describes a case of a patient with long QT syndrome (LQTS) with recurrent episodes of torsades de pointes (TdP). Use of biventricular pacing (BiVP) resulted in a shorter QT interval and a shorter T‐peak‐end interval and prevented further episodes of TdP. These findings suggest that BiVP may be helpful in patients with LQTS and refractory TdP.     

Differential Response of QTU Interval to Exercise, Isoproterenol, and Atrial Pacing in Patients with Congenital Long QT Syndrome

Sympathetic stimulation is well known to contribute to the genesis of QTU prolongation and ventricular lachyarrhythmias in patients with congenital long QT syndrome. In this study, we performed exercise treadmill testing, isoproterenol infusion (1–2 μg/min), and right atrial pacing (cycle length 500 msec) in 11 patients with congenital long QT (LQT) syndrome (LQT group) and in 12 age- and sex-matched controls (control group). The responses of the corrected QT (QT_c; Bazett's method) interval and the TU wave complex tvere evaluated. The QT_c interval was prolonged from 482 ± 63 msec^1/2 to 548 ± 28 msec^1/2 by exercise in the LQT group (n = 11; P < 0.005), and this was associated with fusion of the T waves with enlarged U waves, whereas the QT_c interval did not increase with exercise in the control group (n = 12; 402 ± 19 msec^1/2 vs 409 ± 22 msec^1/2). The QT_c interval was also prolonged from 466 ± 50 msec^1/2 to 556 ± 33 msec^1/2 by isoproterenol in the LQT group (n = 7; P < 0.005) in association with morphological changes of the TU wave complex like those seen with exercise, whereas it was only slightly increased from 399 ± 10 msec^1/2 to 436 ± 13 msec^1/2 by isoproterenol in the control group (n = 77; P < 0.001). However, the QT_c interval did not increase with atrial pacing in the LQT group (n = 8; 476 ± 57 msec^1/2 vs 486 ± 59 msec^1/2), whereas it was slightly increased from 400 ± 21 msec^1/2 to 426 ± 18 msec^1/2 by atrial paring in (he control group (n = 8; P < 0.005). These results suggest that sympathetic stimulation plays an important role in the QTU prolongation and marked TU wave complex abnormalities in patients with congenital long QT syndrome.     

Contribution of Atrioventricular Synchrony to Left Ventricular Systolic Function in a Closed-Chest Canine Model of Complete Heart Block: Implications for Single-Chamber Rate-Variable Cardiac Pacing

This study assessed the impact of atrioventricular (AV) synchrony on characteristics of left ventricular (LV) systolic function during ventricular pacing over a wide heart rate range in a conscious closed-chest canine model of complete AV block. Ten healthy adult dogs underwent thoracotomy during which complete AV block was created by formaldehyde injection, and paired ultrasonic sonomicrometers were positioned on the LV anterior-posterior minor axis. Following recovery from surgery, peak and end-diastolic LV transmural pressure, maximum dP/dt, stroke work, end-diastolic minor axis dimension, and maximum velocity of shortening, were quantitated at heart rates of 80, 100, 120, 140, and 160 beats per minute (bpm) during both ventricular pacing alone and AV sequential pacing with increasing AV intervals (0, 50, 100, 150, 200, 250, and 300 ms). Over the heart rate range tested, parameters of LV systolic function did not differ significantly during ventricular pacing with or without AV synchrony. For example, during ventricular pacing alone maximum LV dP/dt varied from 2110 +/- 70 mmHg/s to 2463 +/- 567 mmHg/s, a range essentially identical to that observed in the presence of AV synchrony. On the other hand, although the impact on LV performance of varying AV interval from 0 to 300 ms was small, differences tended to become more pronounced at higher pacing rates. At 80 bpm, neither stroke work nor maximum LV dP/dt were affected by change in AV interval, while at heart rates greater than or equal to 120 bpm both stroke work and LV dP/dt tended to maximize at AV intervals of 50 and 100 ms and thereafter declined.(ABSTRACT TRUNCATED AT 250 WORDS)     

Efficacy of single lead VDD pacing in patients with impaired and normal left ventricular function

Atrial synchronous ventricular pacing seems to be the best pacing mode for patients with advanced AV block and impaired LV function. The long-term follow-up of single lead VDD pacing was studied in 33 patients with impaired LV function and compared to 42 patients with normal LV function. All patients received the same VDD lead and VDDR pacemaker. The lead model with 13-cm AV spacing between the atrial and ventricular electrode was implanted in 89% of the patients. Follow-ups were 1, 3, 6, and 12 months after implantation. The percentage of atrial sensing and the P wave amplitude were determined at each follow-up. Minimal P wave amplitude at implantation was 2.0 +/- 1.4 mV in patients with impaired and 1.7 +/- 0.9 mV with normal LV function (not significant). At the 12-month follow-up, 33 patients with normal and 23 patients with depressed LV function remained paced in the VDD mode. The remaining patients died in five (impaired LV function) and seven cases (normal LV function) or their pacemakers were programmed to the VVI/VVIR pacing mode in four (impaired LV function) and three cases (normal LV function). P wave amplitude did not differ in the two groups (e.g., at month 12: impaired: 1.17 +/- 0.42 mV; normal: 1.09 +/- 0.49 mV). The atrial sensitivity was programmed in most patients to sensitive settings with no differences between the two groups (e.g., at month 12: impaired: 0.13 +/- 0.06 mV; normal: 0.13 +/- 0.05 mV). The diagnostic counters indicated nearly permanent atrial sensing (e.g., at month 12: impaired: 99.3 +/- 2.2%; normal: 99.0 +/- 1.0 mV). In conclusions, single lead VDD pacing restored AV synchronous ventricular pacing in patients with normal and with impaired LV function indicating that it could be an alternative to DDD pacemakers, but not to dual-chamber pacing.     

Atrial Epicardial Pacing with Long Stimulus to P Wave Interval in a Patient with Arrhythmogenic Right Ventricular Dysplasia Complicated by Right Atrial Thrombosis

Atrial epicardial pacing with a long stimulus to P wave interval in a patient with arrhythmogenic right ventricular dysplasia complicated by right atrial thrombosis is discussed. Arrhythmogenic right ventricular dysplasia (ARVD) is associated with a high incidence of malignant ventricular arrhythmias. Most patients with ARVD need antiarrhythmic drugs, catheter ablation, or an implantable cardioverter defibrillator. We report a patient with ARVD in whom effective treatment with sotalol caused severe, symptomatic sinus bradycardia requiring permanent pacing. Due to leftward displacement of the right ventricle and the presence of two thrombi in the right atrium, an epicardial atrial lead and AAI pacemaker were implanted. A long stimulus to P wave interval caused by severe dilatation of the right atrium was recorded. During a 6 months of follow-up on sotalol treatment there were neither ventricular tachycardia (VT) attacks nor pacing problems.