AAI Mode Research Articles

Impact of internal audit on pacemaker prescription and the immediate costs of pacing in the northern region: towards implementation of the recommendations of the British Pacing and Electrophysiology Group.

In September 1990 a working party of the British Pacing and Electrophysiology Group recommended the routine use of physiological pacing systems in patients with bradycardia. An audit of the impact of these recommendations on pacemaker prescription in the Freeman Hospital between March 1990 and August 1991 has previously been reported. This paper considers the effect of that internal audit on subsequent pacemaker prescription from September 1991 to February 1993. The records of 1228 patients who underwent first pacemaker implantation at the Freeman Hospital between March 1990 and February 1993 were audited retrospectively. The patient's age, indication for pacing, pacing mode, and cost of the generator and leads were recorded. The indications for pacing were sinus node dysfunction (24.9%) (including patients with coexistent sinus node dysfunction and atrioventricular block), atrioventricular block (57.2%), atrioventricular block and atrial fibrillation (12.2%), and carotid sinus syndrome (5.7%). There was an increase in carotid sinus syndrome (2.7% to 8.1%) between the two study periods but no other differences in the distribution of case mix or characteristics of patients. The cost of the working party's recommended optimal pacing mode was calculated from multiplication of the mean cost of the recommended unit over the second half of the study period by the number of patients who would have received that unit. Between March 1990 and August 1991 atrial pacing for sinus node dysfunction (AAI, AAIR, DDD, or DDDR) increased by 138% (from 25.0% to 59.6%), mainly because of increased use of AAI mode. Physiological pacing for atrioventricular block (DDD or VVIR) increased by 41% (from 17.0% to 24.0%), and VVIR pacing for atrioventricular block with atrial fibrillation increased by 111% (from 10.5% to 22.2%). After the internal audit (that is, between September 1991 and February 1993), physiological pacing for atrioventricular block increased by a further 126% (from 24.0% to 54.2%). Sixty three per cent of this increase was in the first six months after the internal audit. Pacemaker prescriptions in sinus node dysfunction and atrioventricular block with atrial fibrillation were unchanged (59.6% physiological pacing for sinus node dysfunction and 22.2% v 27.3% VVIR pacing for atrioventricular block with atrial fibrillation). These changes in practice were accompanied by an increase in the age of patients receiving physiological units. Costs of pacemaker hardware for the final six months of the audit (excluding carotid sinus syndrome) increased by 38% over the costs that would have accrued had pacing policy remained the same as for the initial six month period before the circulation of the recommendations of the working party. Adoption of the guidelines of the working party in full would lead to a further 66% increase in the costs of hardware. The principal effect of the recommendations of the working party alone was increased use of AAI pacing for sinus node dysfunction, with little change in the costs of hardware. The internal audit was followed by an increase in physiological pacing for atrioventricular block, and this has had important financial consequences. Internal audit was followed by closer adherence to the recommendations of the working party.

Atrial demand pacing in patients with symptomatic sick sinus syndrome.

Atrial demand pacing provides a physiological, simply implemented, and less costly alternative of cardiac stimulation in symptomatic sick sinus syndrome (SSS) patients. Hindrance from widespread use stems mainly from the potential development of high degree AV block and persistent atrial fibrillation. A reappraisal of atrial pacing is now justified as we gain more clinical information. In this study we examined retrospectively the clinical course of 22 well-selected SSS patients paced in AAI mode for 30 +/- 29 months. Two patients had infrequent short-run atrial tachyrhythmia before implantation. There was an early lead dislodgement which required repositioning later. Three acute threshold increments were noted which necessitated a change in atrial pacing site in one and short-term steroid use in the other two. No other sensing, pacing or operative complication occurred and all pacing systems performed well. AII patients survived during follow-up and no patient developed congestive heart failure, though depressed left ventricular function was found in three preoperatively. No high degree AV block was encountered. Four patients presented paroxysmal atrial fibrillation (PAF) 25 +/- 16 months after the procedure, of whom one developed chronic atrial fibrillation. No single factor predicted the development of PAF. Resumption of normal pacemaker function always occurred immediately in the pause following cessation of PAF and no revision of pacing mode was required in the patient with chronic AF. Symptomatic relief was obtained in all patients. In summary, single chamber, single rate atrial pacing remains a physiologic, reliable, economic and easily implemented pacing modality affordable to a number of sick sinus patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical Experience with a New DDD External Pacemaker

A multicenter trial of a new external DDD pacemaker was conducted to evaluate its clinical performance. Additionally, methods of temporary lead implantation were analyzed for best performance. The device was found to function with few complications. In only 16 of the 146 devices used was the DDD mode abandoned. Of these, 3 were changed to the AAI mode and 4 were for atrial fibrillation. Several methods of lead implantation proved satisfactory. However, a simple U stitch through the muscle functioned best for atrial application and either a U stitch or a tined stitch functioned best for ventricular application.

Atrial permanent pacing for sinus node dysfunction with absent right superior vena cava

In patients with sinus node dysfunction and normal atrioventricular conduction, single chamber atrial pacing (AAI or AAIR mode) represents the most physiological treatment. Sinus node dysfunction is recognised in association with an absent right superior vena cava, and we present a case in which complete resolution of symptoms was achieved with endocardial atrial permanent pacing.

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.

Cardiac pacing in neonates, infants, and preschool children.

A series of 37 children < 5 years old at pacemaker implant were followed from 1 to 105 months. Five of 37 patients required reoperation for battery depletion while two required reoperation for exit block of epicardial ventricular leads. Each patient paced in the DDD or AAI mode was still in the original mode at the end of follow up.

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.

Atrioventricular Wenckebach Point and Progression to Atrioventricular Block in Sinoatrial Disease.

The value of measurement of the atrioventricular (AV) Wenckebach point at rest as a predictor of progression to AV block was investigated prospectively. Twenty-four patients with sinoatrial disease without evidence of conduction disturbance on 12-lead ECG or 24-hour ambulatory monitoring were paced with Medtronic Activitrax II, Medtronic Legend, or Telectronics Meta MV systems in AAI or AAIR modes. Patients were monitored for symptoms and evidence of AV block on 24-hour tapes. The mean age of the patients was 67 years (range: 42-88). There were 11 males and 13 females. The mean follow-up time was 10.7 +/- 5 months. Four patients required revision of pacing system as a result of development of AV block during follow-up. One other patient manifested intermittent second-degree AV block and remains in AAI. The AV Wenckebach points measured at 1 month postimplantation in the four patients who developed AV block requiring revision of system were 140, 125, 165, and 60 (mean 123 +/- 4). The mean AV Wenckebach point at first assessment in the remaining 20 patients was 153 +/- 24. The mean age of those requiring revision of system was 71 +/- 7 compared with 67 +/- 14 in those who did not. In this small series the frequency of development of significant AV block was 17%. This is markedly higher than in other recently reported series. The study demonstrates that an AV Wenckebach point above 120/min does not confer immunity from progression to AV block.

Relation of prognosis in sick sinus syndrome to age, conduction defects and modes of permanent cardiac pacing

A large population of sick sinus syndrome (SSS) patients was analyzed to determine whether age of patients, presence of conduction disturbances and mode of permanent pacing are related to the occurrence of supraventricular tachyarrhythmias, cerebral embolism and cardiac mortality. Three hundred thirty-nine patients permanently paced (135 AAI, 79 DDD, 125 VVI) because of SSS were followed for a mean period of 5 years (range 2 to 10). Patients were divided into 4 groups according to age (<70 or > 70 years) and the presence or absence of an associated conduction disturbance. Sixty-eight percent of VVI, 55% of AAI and 40.5% of DDD patients were > 70 years of age. In the VVI and DDD groups a conduction disturbance was present in 67 of 204 (33%) patients; conduction disturbances were more common in patients > 70 years old (46 of 111, 41%) than in those <70 years old (21 of 93, 22%). The Wenckebach threshold (>140 beats/min) remained unchanged during the follow-up period in 82% of AAI patients. In 9% of these patients, the Wenckebach threshold showed some degree of deterioration, but only in 2 patients was it <100 beats/min (1.5%). Spontaneous second-degree atrioventricular block was observed in 7 patients (5%); it disappeared in 6 of these patients when drug therapy was discontinued. The incidence of atrial fibrillation was higher in the VVI group (47%) than in the DDD (13%, p < 0.05) and the AAI (4%, p < 0.001) patients without conduction disturbance. It was still higher in VVI patients with conduction disturbance (44%) compared to that of DDD patients with conduction disturbance (11.5%, p < 0.01). A higher incidence of stable atrial fibrillation in the VVI group was also observed, regardless of age or conduction disturbance. Overall mortality rates were 30% in VVI, 16% in DDD and 13% in the AAI mode (p < 0.001). Cardiac mortality was significantly higher in the VVI group (13%) compared to that of the AAI group (3%) (p < 0.001) regardless of age. It was also higher in the VVI group >70 years old (15%) than in the DDD group > 70 years (p > 0.03). The presence of conduction disturbance did not influence cardiac mortality. The stroke mortality rates were 8% in the VVI, 2% in the AAI and 2.5% in the DDD group (difference not significant). The difference in stroke mortality became statistically significant in the subgroup of patients > 70 years old between the VVI (17%) and AAI (3%) modes (p < 0.001). Our data indicate that the AAI and DDD modes should always be preferred to the VVI mode in treatment of SSS, particularly in patients > 70 years of age.

Bradycardia-mediated tachyarrhythmias in congenital heart disease and responses to chronic pacing at physiologic rates

The coexistence of bradycardia and a tachyarrhythmia may preclude effective pharmacologic treatment of 1 arrhythmia without paradoxic aggravation of the other. This study evaluated the potential relation between the 2 types of arrhythmias and the effect of conventional modes and rates of pacing for bradycardia on the frequency of the associated tachyarrhythmias. Twenty-one young patients, aged 2 to 19 (mean 11) years with congenital heart disease and a tachyarrhythmia occurring in the setting of chronic bradycardia were studied. The effects of pacing were evaluated by comparison of the number of episodes of clinical tachycardia during the 12-month intervals before and after pacemaker implantation. During these intervals, antiarrhythmic drug therapy was not altered. Patients were analyzed as independent groups, based on the type of tachyarrhythmia: supraventricular (n = 5), atrial flutter (n = 9) and ventricular (n = 7). The modes of chronic pacing were AAI (n = 4), DDD (n = 6) and VVI (n = 11). The prevention of bradycardia by pacing was associated with a significant decrease in the frequency of supraventricular (p = 0.008) and ventricular (p = 0.02) tachyarrhythmias. However, the frequency of atrial flutter was not altered. Prevention of tachycardia was more frequently associated with the AAI and DDD modes of pacing compared to VVI (p = 0.08). Pacing represents an effective therapy for certain tachyarrhythmias associated with chronic bradycardia, although critical modes may be required.

Sinus Node Dysfunction Associated with Isolated Left Superior Vena Cava

The absence of the right superior vena cava with persistance of the left is a rare venous anomaly, which occurs in 0.05% of general population. This anomaly has been associated with other congenital cardiac defects but rarely with sinus node dysfunction. We report the case of a 52‐year‐old woman who suffered from symptomatic bradycardia that was associated with supraventricular arrhythmias, and refractory to drugs. Implantation of a pacemaker was necessary and an AAI mode possible because of normal atrioventricular conduction. Insertion of the PM lead was performed via the right cephalic vein, then conducted through the innominate vein into the left persistent superior vena cava, leading to the right atrium via the coronary sinus. The electrode was fixed to the right atrial lateral wall; stimulation threshold was within normal limits. Digital angiography of superior venous inflow confirmed complete absence of the right superior vena cava and described a dilated coronary sinus. No other structural heart disease was present. In accordance with reports in the literature, we found the absence of right superior vena cava complicated by sick sinus syndrome and suggest an etiologic link between these two afflictions. Sinus node function should be studied whenever this venous anomaly is discovered in presence of evocated symptoms.

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.

What Is the Most Appropriate Stimulation Mode in Patients with Sinus Node Dysfunction?

Sinus node disease (SND) has caused many controversies about the appropriate stimulation mode. We compared the advantages and disadvantages of VVI, AAI, DDD, and DDI mode. In an additional study, left ventricular function at rest (R) and during exercise (E) was investigated in dual chamber and ventricular stimulation mode with a stimulation rate of 70 ppm (R) and 110 ppm (E). A total of 223 patients (pts) was investigated (67 AAI, 87 VVI, 69 DDI). Hemodynamic disadvantages in VVI mode resulted in a 55% actuarial incidence of atrial fibrillation after five years. In AAI mode, we found another 25% complication rate due to impaired AV conduction (n = 9) or a bradyarrhythmia (n = 6) with slow ventricular response. DDI mode implies the possibility of sustaining a pacemaker mediated tachycardia. Single ventricular stimulation with a high stimulation rate (110 ppm) under E showed a worse left ventricular performance as compared to dual chamber stimulation. DDI mode shows none of the aforementioned disadvantages. To sum it up: Until a dual chamber rate responsive pacemaker becomes available, the DDI mode represents the best stimulation mode for patients with a SND.