© 2004 by European Society of Cardiology
Long-term clinical performance of AAI pacing in patients with sick sinus syndrome: a comparison with dual-chamber pacing
aDepartment of Cardio-thoracic Surgery, Nagoya University School of Medicine 65 Turumai-cho, Syowa-ku, Nagoya City, Japan; bDepartment of Cardiology, Nagoya-Ekisaikai Hospital 66-4 Shonen-Cho, Nakagawa-ku, Nagoya City, Japan
Manuscript submitted 9 October 2003. Accepted after revision 17 May 2004.
* Corresponding author. Tel.: +81-52-744-2376; fax: +81-52-744-2383. E-mail address: hmasu{at}catvmics.ne.jp (H. Masumoto).
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Abstract |
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AIMS: In this clinical study, we compared two groups of age-matched patients, AAI and DDD, to evaluate the clinical benefits of AAI pacing in patients with sick sinus syndrome (SSS) and normal atrioventricular (AV) conduction.
METHODS AND RESULTS: Ninety-five patients with SSS implanted with AAI pacemakers were compared with 101 SSS patients implanted with DDD pacemakers. Mortality, chronic atrial fibrillation, lead survival rates, and reoperation rates were compared by Kaplan–Meier analysis. Eight AAI devices were switched to DDD due to high-degree (grade 2–3) AV block. The incidence of high-degree AV block was 1.104%/year, with a freedom rate of 88.6% at 10 years. There were no significant differences between the two groups in survival rates (87.8% in AAI vs. 93.4% in DDD at 10 years), freedom from atrial fibrillation (93.6% vs. 90.6%), or freedom from reoperation (71.3% vs. 76.3%). On the other hand, lead failure was twice as frequent in the DDD group than in the AAI group (relative risk=2.045, P=0.0382).
CONCLUSION: AAI pacing, a simple system using a single lead and single-chamber pacemaker, can achieve a clinical outcome similar to that of the DDD mode in patients with SSS and normal AV conduction.
Key Words: sick sinus syndrome, AAI pacing, DDD pacing, long-term follow up
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Introduction |
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Among patients with sick sinus syndrome (SSS), those managed by atrial pacing (AAI) reportedly suffer from lower rates of atrial fibrillation [1–
4], arterial thromboembolism [2–4], and mortality [1,3–5] compared with those treated by ventricular pacing (VVI). It has also been reported that patients with SSS benefit more from dual-chamber pacing (DDD) than from VVI [6–8]. However, it remains controversial which pacing mode, AAI or DDD, is more favourable for patients with SSS and normal AV conduction [9]. The AAI mode is thought to be more physiological than DDD mode, and the preservation of normal intraventricular conduction without ventricular pacing in AAI is thought to impart better ventricular function. On the other hand, AAI might impose a risk of AV block. Few reports have compared the long-term follow-up results of AAI and DDD in patients with SSS [9]. We evaluated the long-term clinical performance of AAI mode in comparison with the results of DDD mode based on data from three institutions affiliated with Nagoya University. |
Patients and methods |
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In treating SSS patients who have normal AV conduction, our three institutions have generally applied AAI pacing. This strategy was introduced at our institutions in different years: in 1979 at Nagoya University, in 1990 at Nagoya National Hospital, and in 1999 at Nagoya Ekisaikai Hospital. Patients with the following findings on the resting electrocardiogram (ECG) were excluded from this study: spontaneous second or third degree AV block, complete left bundle branch block, or bifascicular block. Patients with first degree AV block (PR interval >0.22 s), right bundle branch block, or unifascicular block were not excluded.
Patient profiles
The AAI group was assigned 95 patients (30 males and 65 females) who had been implanted with an AAI pacemaker at one of the above three institutions between the years 1979 and 2000 (average age 63.1 ± 12.5 at implantation). The resting ECG before operation revealed unifascicular block in four patients, right bundle branch block in eight, and first degree AV block in one. The DDD group was assigned 101 consecutive patients (46 males and 55 females) who had been implanted with DDD pacemakers at one of the same institutions before the introduction of the strategy of using AAI (average age 60.9 ± 14.1 at implantation). The resting ECG showed unifascicular block in six patients, right bundle branch block in nine, and first degree AV block in six. There were no significant differences between two groups other than gender (Table 1).
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Follow-up
All patients were carefully followed up at our pacemaker clinic every 3–6 months. The average follow-up period and range of follow-up were 8.7 (±6.2) and 0.5–21 years in the AAI group, versus 7.6 (±4.7) and 0.8–18 years in the DDD group. Five patients (2.6%) were lost to follow-up after 2 years (three AAI patients and two DDD patients).
Holter ECG recordings were taken before generator exchange, and when the patients developed undiagnosed arrhythmia or any kind of pacing failure. The following events were noted: death, development of chronic atrial fibrillation, any kind of lead failure, reoperation, development of 2 or 3° AV block, operational pacing mode, prescription of antiarrhythmic drugs, and cost. Cause of death was obtained by interviewing the doctors who had care of the patient and by review of hospital records. Chronic atrial fibrillation was defined as atrial fibrillation found on three consecutive visits to a pacemaker clinic. A reoperation was defined as surgery for pacemaker infection, lead reimplantation for lead failure, or additional ventricular lead implantation. Generator exchange due to battery depletion was not classified as a reoperation. The pacemakers were set to the following programmes: the lower rate limit was set to 
60 bpm and the upper rate limit was 120 or 130 bpm in both groups. Rate adaptive function was adjusted for each patient based on his or her activities. In the DDD group, AV delay was principally programmed to 250 ms. However, the AV delay was reprogrammed to 150 ms, when the QRS was completely paced with 250 ms AV delay. Cost was defined as the price of all leads and generators during the follow-up period. The charge for both an operation and hospital accommodation was not classified as a cost. The price of pacemaker systems is regulated by the government in Japan. All the prices of leads and generators were defined as the present Japanese government regulated prices to compare the two groups.
Statistics
Continuous variables are expressed as mean (±SD) values. Groups were compared with the chi-square test for discrete variables and the unpaired t-test for continuous variables. Survival rates and event free rates were calculated with Kaplan–Meier analysis, and statistical significance was assessed with the log-rank test. The first event was counted as an event in each case. Predictors of mortality, chronic atrial fibrillation, and lead longevity were evaluated by the Cox proportional hazard regression method. The data were evaluated using StatView J5.0. A P value < 0.05 was considered significant. The results were expressed with 95% confidence limits (CLs) and P values.
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Results |
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Mortality
There were 18 late deaths (11 in the AAI group and 7 in the DDD group). Survival rates were not significantly different between the two groups (P=0.57, log-rank test, 87.8% in AAI vs. 93.4% in DDD at 10 years) (Fig. 2). Causes of death in the AAI group were malignancy in three patients, stroke in two, infection in two, sudden death in one, cardiac disease in one, and miscellaneous in two. Causes of death in the DDD group were malignancy in three patients, stroke in one, sudden death in one, and miscellaneous in two. The sudden deaths had a previous history of cardiovascular disease in both groups; namely, prior myocardial infarction in the AAI group and type A aortic dissection treated with Cabrol operation in the DDD group.
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Follow-up of the AAI group
Among the 95 patients in the AAI group, 8 were switched to the DDD mode due to the development of high-degree AV block, which appeared at 8.2 ± 4.1 years (range 5–17 years) after the first implantation, in patients 64.3 ± 11.4 years. One patient complained of dizziness and another was found to have asymptomatic second degree AV block on resting ECG at a pacemaker clinic. The other six patients were free of symptoms and showed no signs of high-degree AV block on resting ECG at follow-up visits. When these six patients attended for generator exchange or reoperation, the Holter ECG revealed transient 2:1 AV block (n=4) or Wenckebach block (n=2) only during the night. The approximate incidence of high-degree AV block was 1.10%/year. The event-free rates for high-degree AV block were 98.4% at 5 years, 88.6% at 10 years, and 85.1% at 15 years (Fig. 1). The Wenckebach block point was measured in 81 cases in the AAI group. In our multivariate Cox regression analysis, a Wenckebach block point of <120 bpm was a significant predictor of the development of high-degree AV block (relative risk 13.48 [95% CI 2.06–88.1], P=0.0066), whereas gender, age, supraventricular tachyarrhythmia, right bundle branch block, and antiarrhythmic drugs were not. Two of eight patients who developed high-degree AV block had been taking digoxin, but the AV block persisted after the drug was terminated: one of these patients suffered from sarcoidosis. Another three cases required additional ventricular leads during follow-up, due to atrial sensing failure in one case and high atrial stimulation threshold in two cases.
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Follow-up of the DDD group (operational pacing mode)
Recently used pacing modes in the DDD group have included DVI in 30 patients, AAI in 45, sinus rhythm in 9, VDD in 4, and VVI in 13. More than half of the patients in the DDD group could be treated without ventricular pacing leads. Moreover, fusion QRS was observed in 6 of 30 patients even in DVI mode operation at the last follow-up. Eight patients who developed chronic atrial fibrillation and four patients with paroxysmal atrial fibrillation were eventually treated with the VVI pacing mode.
Chronic atrial fibrillation
Chronic atrial fibrillation developed in four patients in the AAI group and eight patients in the DDD group. However, there was no significant difference between the two groups in the event-free rate for chronic atrial fibrillation (P=0.574: log-rank test, 93.6% in AAI, 90.6% in DDD at 10 years) (Fig. 3). These four AAI patients who developed chronic atrial fibrillation required no additional pacing therapy. Preoperative supraventricular tachyarrhythmia was a predictor of chronic atrial fibrillation in multivariate Cox regression analysis (relative risk = 0.186 [95% CI 0.043–0.813], P=0.0253). At the last follow-up visits, 36 of 95 patients in the AAI group and 37 of 101 patients in the DDD group were treated with more than one antiarrhythmic drug. The antiarrhythmic drugs were digoxin, ß-blocker, calcium channel blocker, or other antiarrhythmic drugs.
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Lead failure
Lead failure was observed in 14 patients (13.7%) in the AAI group and 23 patients (22.8%: 5 atrial leads, 14 ventricular leads, and 4 both leads) in the DDD group. Leads failures were twice as frequent in the DDD group than in the AAI group in univariate Cox regression analysis (relative risk = 0.489 [95% CI 0.249–0.962], P=0.0382). The actuarial lead survival curve was significantly better in the AAI group than in the DDD group (P=0.0335, log-rank test, 77.4% in AAI and 62.8% in DDD at 10 years) (Fig. 4). Twelve of 14 patients in the AAI group and 14 of 23 patients in the DDD group required additional pacing leads due to lead failures. Two AAI patients and six DDD patients were treated with unipolar leads converted from bipolar leads, and three DDD patients were switched to the AAI mode.
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Reoperation
Eighteen patients in the AAI group and 17 patients in the DDD underwent reoperations (excluding generator exchange). Causes of reoperation in the AAI group were lead failure in 12 patients, development of high-degree AV block in seven, infection in one, and miscellaneous in three (there was some overlap). Causes of reoperations in the DDD group were lead failure in 14 patients and infection in three patients. Freedom from reoperation was not significantly different between the two groups (P=0.859: log-rank test, 71.3% in AAI, 76,3% in DDD at 10 years) (Fig. 5).
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Cost
The present Japanese government regulated prices of pacemaker systems are as follows. The atrial lead, ventricular lead, single chamber generator, and dual chamber generator cost 289,000 yen, 289,000 yen, 1,330,000 yen, and 1,480,000 yen, respectively. The mean costs in the AAI and DDD groups were 466,900 ± 392,900 and 594,700 ± 463,500 yen/year, respectively (P=0.062, unpaired t-test). Costs were not significantly different between the two groups. However, the cost of DDD during follow-up was relatively more expensive than that of AAI.
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Discussion |
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TopAbstractIntroductionPatients and methodsResultsDiscussionConclusionReferences |
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AAI pacing has been reported to produce better results than VVI pacing in SSS patients with normal AV conduction. Documented advantages have included a lower mortality [1
,3–5], a lower rate of thromboembolism [2–4], less frequent development of atrial fibrillation [1–4], and a relatively low incidence of high-degree AV block (range 0.5–2.0%/year) [3,10–14]. While few reports have presented long-term follow-up results comparing AAI and DDD modes, cardiac function in AAI mode has been reported to be more physiological and superior to DDD mode when atrioventricular conduction is intact [15,16]. Moreover, long-term ventricular stimulation has been reported to be potentially harmful [17,18]. On the other hand, several questions remained unanswered. It remains unclear, for example, how these findings affect the clinical long-term performance, especially in patients with DDD pacemakers. The simplicity of AAI mode and the use of a single pacing lead are additional advantages of AAI pacing. However, the development of high-degree AV block must be considered when comparing the merits and demerits of AAI and DDD pacing for patients with SSS. This complication may necessitate implantation of an additional ventricular lead in order to switch to DDD or VVI pacing. The expected incidence and predictors of high-degree AV block should be clarified.
In the present study, eight patients in the AAI group required additional ventricular leads due to onset of second degree AV block. The incidence of second-degree AV block was calculated at 1.104%/year, slightly higher than that reported in the recent literature (<1.0%) [13,14]. However, only one of the eight patients had symptoms, and six were diagnosed incidentally by Holter ECG showing 2° AV block during sleep before generator exchange or reoperation. The timing of conversion from AAI to DDD is still unclear. Rosenqvist et al. [11] reported that asymptomatic episodes of high-degree AV block could reflect changes in autonomic tone rather than degeneration of the AV node, especially during sleep. We made the switch to DDD somewhat early in order to prevent symptomatic bradycardia due to high-degree AV block, but we could have postponed the procedure until symptoms appeared. In fact, our seven asymptomatic cases might never have received the DDD mode. If we had not made this upgrade, the incidence of high-degree AV block and the freedom rate from reoperation would have been lower in the AAI group.
The only significant predictor of high-degree AV block in the present study was a Wenckebach block point of <120 bpm. Right bundle branch block was not a predictor of high-degree AV block, while some reports have recommended DDD pacing in patients with right bundle branch block [4,12]. Left bundle branch block and bifascicular block were not evaluated in our study. First degree AV block also lacked predictive power, but our data was limited as only one AAI patient showed this abnormality. Several groups have reported that slight prolongation of the PR interval is not a predictor of high-degree AV block [12,19–22]. Even antiarrhythmic drugs lacked power in predicting high-degree AV block in the present study. On this point, it should be noted that most AV conduction disturbances are due to antiarrhythmic drug therapy rather than degeneration of the conduction system [11,20,21].
In the limited number of patients in whom the Wenckebach block point was measured (n=81), a Wenckebach block point of <120 bpm significantly predicted the development of high-degree AV block. Andersen et al. [14] showed that a Wenckebach block point of over 100 bpm did not predict the development of AV block. Rosenqvist et al. [11] also reported that there were no correlations among Wenckebach block points in a range of 110–150 bpm in 15 papers reviewed. Although it remains controversial whether the Wenckebach block point is predictive of high-degree AV block [22], the ease and simplicity of taking the measurement has compelled us to perform it routinely and use it as an index when selecting AAI or DDD. Three of our cases required additional ventricular leads due to two additional problems sometimes encountered in long-term AAI pacing; namely, elevated atrial stimulation threshold and failure to sense atrial potentials. Fortunately, future improvements in lead design and technique are likely to minimize these two problems.
Chronic atrial fibrillation has been reported to appear more frequently in SSS patients treated with VVI than those with AAI pacing [1–4]. Yet, DDD pacing may also prevent the progression to chronic atrial fibrillation by driving the atria. Atrial overdrive stimulation is somewhat effective in suppressing atrial ectopic activity and atrial fibrillation [23]. The present study also failed to show any significant difference between groups in the development of chronic atrial fibrillation. However, a recent well-organized study by Nielsen et al. [24] concluded that atrial fibrillation was significantly less common during AAIR pacing than during DDDR pacing. This discrepancy may be due to the lack of statistical power in our study and the differential definition of atrial fibrillation. In our present study, however, even among the AAI patients who developed chronic atrial fibrillation, none required additional ventricular pacing due to bradycardia. This was identical to the result reported by Andersen et al. [4].
Lead failure is one of the most important complications during long-term follow-up after pacemaker implantation. The relative risk for lead failure in DDD pacing is calculated to be 2.045 higher than that in AAI pacing, since twice the number of pacing leads is implanted. Hauser et al. [25] reported a 6% incidence of ventricular lead failure during 5 years of dual-chamber pacing. Helguera et al. [26] reported that leads in older patients (>65 years old) and leads in the atrial position had fewer verified failures. The number of pacing leads remaining in the body is also important. Multiple pacing leads may be associated with infection, venous occlusion [27,28], tricuspid valve regurgitation [29], and lead migration [30]. The lead extractions, sometimes required, entail either a specific transvenous procedure or a thoracotomy and carry a risk of life-threatening complications such as haemothorax or cardiac tamponade. Although the rates of complications and mortality are low (<1.5% and <1.0%, respectively) [31–33], any risk whatsoever makes the procedure undesirable. Our AAI group had a reoperation rate similar to that of the DDD group when all aspects, including high-degree AV block, were taken into account. Nevertheless, the smaller number of pacing leads implanted still gives AAI pacing an advantage. Although the appearance of high grade atrioventricular block in SSS patients is not frequent, in order to make allowances for every circumstance, a dual chamber pacemaker may be implanted and programmed so as to permit native ventricular depolarization, although this may not be successful [34]. In younger patients, AAI should be implanted to avoid lead failure in the future.
Our study is a non-randomized retrospective cohort with a relatively small patient population. While this limits the value of interpretation of our findings for the present, our long-term follow-up results should facilitate comparisons between AAI and DDD pacing in patients with SSS.
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Conclusion |
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There were no significant differences between our two groups in mortality, reoperation rates, or causes of death. Our institutions have adopted the following strategy in treating patients with SSS. Patients with SSS and normal AV conduction should be treated with AAI pacing. Normal AV conduction can be confirmed with a Wenckebach block point of more than 120 bpm measured at operation. AAI pacing should be changed to DDD pacing when symptomatic high-degree AV block develops. Our clinical results with this clinical strategy showed no significant differences between the two groups in the rates of survival, chronic atrial fibrillation, or reoperation. However, the AAI mode showed better lead survival. AAI pacing is a simple system that can achieve a clinical outcome similar to that of DDD pacing in patients with SSS.
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References |
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