Natural history of sinus node chronotropy in paced patients

Influence of DDD rate response pacing with integrated double sensors on physical efficiency and quality of life

AIMS

The aim of this study was to evaluate whether the use of a double sensor gives additional benefits for patients in improving physical efficiency as well as quality of life (QoL) as compared to the accelerometer sensor alone.

METHODS AND RESULTS

The presented research is a prospective, randomized, single-blind clinical trial. Double-sensor (accelerometer and minute-ventilation) pacemakers (Guidant, Pulsar Max DR) were implanted in 20 patients with sinus node dysfunction (SND) and chronotropic incompetence. After randomization, patients were placed in one of two groups: 1, only the accelerometer sensor was activated; 2, both sensors were activated. After a 3-month follow-up, an initial cardio-pulmonary exercise test was performed, after which the patients were placed in the opposite group for a further 3 months. Finally, the second tests were performed. In 75% of the patients an improvement in QoL was observed in the double-sensor group (P = 0.0242) when compared with the single-sensor group. The addition of a ventilating sensor had no influence on the duration of exercise test (A: 11 +/- 3.19 vs. B: 11 +/- 2.92 P = 1.0000). The parameters of cardio-pulmonary exercise tests recorded in situations A and B before exertion, and 6 minutes after exertion were not statistically different.

CONCLUSION

The use of double-sensor pacemakers does not improve physical efficiency; however, it does improve QoL.

Is a Dual-Sensor Pacemaker Appropriate in Patients with Sino-Atrial Disease? Results from the DUSISLOG Study

BACKGROUND

Rate-responsive pacemakers (PMs) are often supplied with accelerometer (XL) and minute ventilation (MV) sensors to provide a physiologic rate response according to patient needs. No information is available about the real benefit of dual-sensor rate-responsive pacing on the daily life of patients.

METHODS

DUSISLOG (Dual Sensor vs Single Sensor comparison using patient activity LOGbook) is a two-arm prospective, randomized, multicenter study that enrolled 105 patients who received a rate-responsive PM (Insignia), Guidant Corp.). After 1 month of DDD pacing at 60 ppm lower rate, a single sensor (XL or MV, randomized) was activated for 3 months at the manufacturer's suggested nominal settings, followed by a 3-month period with dual sensors optimized with automatic response. During the last month of each period, the following data concerning patient physical activity were retrieved from PM diagnostics (Activity Log): mean percentage of physical activity, mean intensity of activity. Quality of life (QoL) scores and 6-minute walk test (WT) were also recorded.

RESULTS

Single-sensor rate-responsive pacing resulted in symptomatic benefit equally with XL and MV sensors while no additional benefit was found using dual sensor. In a subgroup analysis, patients (17%) with marked chronotropic incompetence and with 0% atrial sensing received benefits from single sensor with an additional advantage from sensor (QoL: +21 +/- 14% P < 0.05; WT: +17 +/- 7% P < 0.02).

CONCLUSION

In most patients with rate-responsive devices, a single sensor is sufficient to achieve a satisfactory rate response. A dual sensor combination and optimization provides an additional benefit only in a selected population with an advanced atrial chronotropic disease.

Development of sinus node disease in patients with AV block: implications for single lead VDD pacing

OBJECTIVE

To investigate the incidence of sinus node disease after pacemaker implantation for exclusive atrioventricular (AV) block.

DESIGN

441 patients were followed after VDD (n = 219) or DDD pacemaker (n = 222) implantation for AV block over a mean period of 37 months. Sinus node disease and atrial arrhythmias had been excluded by Holter monitoring and treadmill exercise preoperatively in 286 patients (group A). In 155 patients with complete AV block, a sinus rate above 70 beats/min was required for inclusion in the study (group B). Holter monitoring and treadmill exercise were performed two weeks, three months, and every six months after implantation. Sinus bradycardia below 40 beats/min, sinoatrial block, sinus arrest, or subnormal increase of heart rate during treadmill exercise were defined as sinus node dysfunction.

RESULTS

Cumulative incidence of sinus node disease was 0.65% per year without differences between groups. Clinical indicators of sinus node dysfunction were sinus bradycardia below 40 beats/min in six patients (1.4%), intermittent sinoatrial block in two (0.5%), and chronotropic incompetence in five patients (1.1%). Only one of these patients (0.2%) was symptomatic. Cumulative incidence of atrial fibrillation was 2.0% per year, independent of the method used for the assessment of sinus node function and of the implanted device.

CONCLUSIONS

In patients undergoing pacemaker implantation for isolated AV block, sinus node syndrome rarely occurs during follow up. Thus single lead VDD pacing can safely be performed in these patients.

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 AV 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 tachyarrhythmia, (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 > or = 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.

Atrial rate adaptive pacing: what happens to AV conduction?

To investigate if an nonphysiological prolongation of the AV interval is common during activity sensor modulated atrial rate adaptive (AAIR) pacing, 21 patients with sinus node disease treated with fixed rate atrial (AAI) or AAIR pacemakers were examined. Spike-Q intervals were compared at different heart 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 interval 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 AAIR 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.(ABSTRACT TRUNCATED AT 250 WORDS)

Exercise chronotropy in patients with normal and impaired sinus node function after cardiac transplantation

The chronotropic response during graded, symptom limited exercise was investigated in 32 cardiac transplant recipients a mean of 49 +/- 18 days after transplantation. All patients had systematic evaluation of postoperative donor sinus node (SN) function and the cardioacceleratory response was compared according to the SN function. Twenty-one patients had normal postoperative SN studies (corrected SN recovery time < 520 msec, group I) while the SN function was impaired postoperatively in the remainder (n = 11, group II; corrected SN recovery time 4,149 +/- 6,283 msec in 5 patients, junctional escape rhythm in 6 patients). All patients had regained sinus rhythm at time of the exercise test. Patients in group II had lower basal sinus rates at the beginning of exercise (91.5 +/- 11 vs 101.4 +/- 7 beats/min, P < 0.02). This lower chronotropy was maintained over every incremental step (F rate between groups = 30, P = 0.0001, F rate vs workload = 15, P = 0.0001 by two-way ANOVA) and resulted in a significantly lower heart rate at individual peak exercise (108.3 +/- 20 vs 124.2 +/- 13 beats/min, P < 0.02). A total of 14/16 patients in group I but only 2/16 patients in group II accomplished a peak heart rate > or = 120 beats/min (P = 0.009). The workload achieved did not differ between the groups (107 +/- 29 vs 102 +/- 32 watts, P > 0.5). These data show a lower SN chronotropy during rest and at peak exercise in cardiac transplant recipients with postoperative SN deficiency and apparent normalization of SN function.

AAI pacing mode: when is it indicated and how should it be achieved?

AAI pacing offers better hemodynamic characteristics than dual-chamber pacing and is the optimal mode for patients with sick sinus syndrome without AV conduction disorders. AAI pacing may be achieved by single-chamber atrial pacing, by programming a dual-chamber pacemaker to the AAI mode, or by programming a dual-chamber pacemaker to DDD mode with a long AV delay. The annual incidence of AV block development in patients with sick sinus syndrome is low, probably 1-5%, but there is no method of detecting patients immune or prone to future development of AV block. Chronotropic incompetence is often present in patients with sick sinus syndrome but the value of additional rate response is not yet firmly established. Our recommendations for the choice of the optimal method of pacing are discussed.

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.