Europace Advance Access originally published online on January 16, 2008
Europace 2008 10(2):134-137; doi:10.1093/europace/eum290
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PACING
Long-term reliability of AAI mode pacing in patients with sinus node dysfunction and low Wenckebach block rate
1 Department of Cardiovascular Medicine, Tottori University Hospital, 36-1 Nishimachi, Yonago 683-8504, Japan; 2 Division of Regenerative Medicine and Therapeutics, Department of Genetic Medicine and Regenerative Therapeutics, Institute of Regenerative Medicine and Biofunction, Tottori University Graduate School of Medical Science, Yonago, 683-8504, Japan
Manuscript submitted 12 October 2007. Accepted after revision 11 December 2007.
* Corresponding author. Tel: +81 859 386517; fax: +81 859 386519. E-mail address: oigawa{at}grape.med.tottori-u.ac.jp
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Abstract |
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Aims: To compare the risk of atrioventricular (AV) conduction disturbance between patients with sinus node dysfunction on AAI pacing who had a low or high Wenckebach block rate (WBR).
Methods and results: Patients with sinus node dysfunction and normal AV conduction those underwent an electrophysiological study were studied. The patients were classified into two groups: Group L was with the patients with a WBR of 100 to 129 per minute and Group H was with the patients with a WBR 
130 per minute. All patients followed up every 3–6 months after an AAI pacemaker implantation. A total of 102 patients, including 35 Group L and 67 Group H, were followed for 90 ± 44 months. Six patients died from non-cardiac cause and five patients required a new atrial lead implantation due to lead failure during follow-up. Symptomatic bradycardia requiring a new ventricular lead implantation developed in four patients (annual incidence 0.5%). In Group L, two patients developed AV block (annual incidence 0.7%). In Group H, two patients developed bradycardic atrial fibrillation (annual incidence 0.4%). Kaplan–Meier analysis revealed no significant difference between the two groups (P = 0.2983).
Conclusion: These results suggest that a long-term risk of developing AV conduction disturbance is low even in patients with a WBR of 100 to 129 per minute.
Key Words: Sinus node dysfunction, Atrial pacing, Atrioventricular block, Atrial fibrillation, Pacemaker, Wenckebach block
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Introduction |
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Previous studies have shown that single-chamber atrial (AAI) pacing is safe and reliable for patients with sinus node dysfunction and normal atrioventricular (AV) conduction.1
–7 AAI pacing is superior to dual-chamber (DDD) pacing because there is a lower incidence of atrial fibrillation (AF)8 and better preservation of left ventricular function.8,9 In addition, ventricular pacing increases the risk of hospitalization for heart failure in patients with sinus node dysfunction.10 However, there is a risk of the occurrence of AV conduction disturbance that may require alteration of the pacemaker system in patients with AAI pacing. It remains controversial whether the baseline Wenckebach block rate (WBR) of AV node can be used to predict the risk of AV conduction disturbance.7,11 Accordingly, the present study was performed to compare the risk of AV conduction disturbance during long-term AAI pacing in patients with a low or high WBR. |
Methods |
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Consecutive patients who underwent AAI mode pacemaker implantation for symptomatic sinus node dysfunction from January 1991 to September 2003 at Tottori University Hospital were studied. All patients gave their informed consent before the study. Medical history, physical examination and 12-lead standard electrocardiogram (ECG) were done before implantation. And furthermore, patients underwent an electrophysiological study (EPS) and were checked an AV node WBR and His bundle electrograms. We considered that AAI pacing was contraindicated in patients with the following criteria: (i) A PQ interval > 0.26 s on the ECG; (ii) a history of second- or third-degree AV block; (iii) a history of symptomatic bradycardic AF; (iv) left bundle branch block or bifascicular block on the ECG; (v) detection of intra- or infra-Hisian block by the electrophysiological study; (vi) a WBR < 100 per minute or (vii) refusing an electrophysiological study. Right bundle branch block, unifascicular block and non-symptomatic AF were not contraindicated. We classified the subjects into two groups. Group L included the patients who had a WBR of 100 to 129 per minute and Group H with the patients who had a WBR
130 per minute. All patients were followed up at our pacemaker clinic every 3–6 months and the following events were noted: death, non-fatal stroke, non-fatal coronary event, syncopal event, heart failure hospitalization, development of permanent AF, symptomatic high-degree AV block, symptomatic bradycardic AF, lead or generator malfunction, and implantation of an additional ventricular lead.
Statistical analysis
Continuous variables are reported as the mean ± SD. The mean age was calculated at the time of initial pacemaker implantation. The two groups were compared with the 
2 test for discrete variables and the unpaired t-test for continuous variables. Event-free rates were calculated by the Kaplan–Meier method, and the significance of differences in these rates was assessed with the log-rank test. Predictors of AV conduction disturbance were evaluated by the Cox proportional hazard regression method. Analyses were done using Stat-View J5.0 Software (SAS Institute Inc. Cary, NC, USA) and P < 0.05 was considered significant.
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Results |
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Hundred and sixty three patients with sinus node dysfunction underwent a pacemaker implantation during study period at Tottori University hospital. However, 32 of 163 patients were excluded due to following criteria: a long PQ interval was found in five, a history of advanced AV block in one, a left bundle or bifascicular block in five, an intra- or infra-Hisian block in four, a WBR < 100 per minute in nine, and a refusing EPS in eight. Because 29 patients were referred to some other hospitals after an AAI mode implantation, they were excluded from this study. Then, a total of 102 patients with sinus node dysfunction and normal AV conduction were studied. A mean follow-up time until death, pacemaker mode change, or the end of the study, was 90 ± 44 months (range: 9–188 months). Among them, 35 patients (25 women and 10 men) with a mean age of 71 ± 10 years (range: 53–99 years) were classified into Group L and their mean WBR was 116 ± 11 per minute. Patient characteristics were described in Table 1. An anti-arrhythmic medication was given to six patients for the treatment of paroxysmal AF (One flecainide, two pilsicainide, one cibenzoline and two amiodarone). Low-dose beta-blockers were given to four patients (two patients with ischaemic heart disease, one patient with heart failure and one patient with tachycardic AF). These medications were continued after a pacemaker implantation, but the anti-arrhythmic medication was stopped in a patient when he developed permanent AF. A mean follow-up period of Group L was 92 ± 43 months (range: 14–188 months). The other 67 patients (41 women and 26 men) with a mean age 73 ± 9 years (range: 46–93 years) formed Group H and their mean WBR was 159 ± 18 per minute. Patient characteristics were also described in Table 1. An anti-arrhythmic medication was given to 10 patients for the treatment of paroxysmal AF (six pilsicainide, two pirmenol and two amiodarone). Beta-blockers were given to six patients (one patient with ischemic heart disease, three patients with heart failure and two patients with tachycardic AF). These medications were continued after a pacemaker implantation, but the anti-arrhythmic medication was stopped in six patients when they developed permanent AF. A mean follow-up period of Group H was 90 ± 44 months (range: 9–184 months). Clinical features were similar between the two groups, except for the WBR and the number of the patients with right bundle branch block (Table 1).
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Symptomatic bradycardia
The number of patients requiring addition of a ventricular lead for any reason was six (annual incidence 0.8%). It included two patients requiring AV junctional ablation and VVI mode pacemaker implantation to manage tachycardic AF that was refractory to medical therapy (one in each group). Therefore, the number of patients requiring pacemaker mode revision for the development of bradycardia was four (annual incidence 0.5%). In Group L, symptomatic bradycardia occurred in two patients (annual incidence 0.7%) due to advanced AV block. One patient was a 75-year-old man with a preoperative WBR of 110 per minute and right bundle branch block. Because he needed a medication for paroxysmal AF, he had received pilsicainide. He presented with dizziness at 69 months after pacemaker implantation and the ECG showed advanced AV block. The second patient was a 73-year-old woman with a preoperative WBR of 120 per minute who was readmitted to our hospital with dizziness at 34 months after pacemaker implantation. Her ECG also showed advanced AV block. In both cases, a ventricular lead was added and pacing was changed to the DDD mode. Symptomatic bradycardic AF developed in two patients of Group H (annual incidence 0.4%). The first patient was a 77-year-old man with a preoperative WBR of 135 per minute who was readmitted due to chest discomfort at 53 months after pacemaker implantation. His ECG showed bradycardic AF. The second patient was a 72-year-old man with a preoperative WBR of 145 per minute who was readmitted to hospital with an easy fatigability at 18 months after pacemaker implantation. His ECG also showed bradycardic AF. In both cases, because several defibrillation therapies were tried but failed, a new lead was advanced into the right ventricle and a new VVI mode pacemaker was implanted (Table 2). All events were detected at the outpatient clinic. According to Kaplan–Meier analysis, there was no significant difference in the incidence of symptomatic bradycardia between Group L and Group H (log-rank test, P = 0.2983, Figure 1). The Cox proportional hazard regression analysis showed that clinical features, ECG findings, anti-arrhythmic medications, and electrophysiological data had no predictive value for symptomatic bradycardia (Table 3).
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Mortality and other complications
Five patients required an additional implantation of a new atrial lead due to lead failure. A generator malfunction was not found during follow-up. Permanent AF developed in seven patients (annual incidence 0.9%) and six of the seven patients belonged to Group H. Non-fatal ischaemic heart event also developed in four (three in Group L and one in Group H), and non-fatal strokes in three (all in Group H). Heart failure hospitalization occurred in five (two in Group L and three in Group H). There were six non-cardiac deaths during follow-up (two in Group L and four in Group H). Three patients died of malignant neoplasm, two of cerebral infarction and one of cerebral breeding. The incidence of these events did not differ between the two groups.
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Discussion |
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Main findings
The present study showed that patients with sinus node dysfunction on AAI pacing with the study inclusion criteria have a low risk of AV block requiring the addition of a ventricular lead, and this low risk refers to not only patients with WBR
130 per minute but also patients with WBR of 100 to 129 per minute.
Risk of atrioventricular block
Previous studies have shown that there are the several benefits of AAI mode pacing in patients with sinus node dysfunction.1–6 First, it reduces the risk of AF compared with DDD mode pacing.8 Other advantages of AAI mode pacing are reported to be: (i) preservation of ventricular synchrony and function;9,10 (ii) use of a simple and low-cost generator; (iii) a single-lead system, and (iv) a long battery life. However, a major potential disadvantage is the risk of high-degree AV block. Previous studies have found that the annual incidence of AV block requiring insertion of an additional ventricular lead is 
1% in patients with sinus node dysfunction on AAI pacing.6,8,12–14 In the present study, annual incidence of AV block was 0.5%. This low risk of AV block might be owing to the preoperative EPS.
Wenckebach block rate
An atrial pacing test and the measurement of the WBR are routinely performed to determine the indications for AAI mode pacing. However, the reported cut-off value of the WBR that allows use of an AAI mode pacemaker varies between 100 and 130 per minute,6,8,12–14 and it remains unclear whether the WBR can actually be used to predict high-degree AV block. Masumoto et al.14 reported that a WBR < 120 per minute is a predictor of high-degree AV block. On the other hand, Andersen et al.7 reported that the WBR showed large spontaneous variations during follow-up, making it of little value for identifying patients at risk of high-degree AV block. In these studies, however, the number of patients who had a WBR < 130 per minute was small and the duration of follow-up was short. In present study, we followed 35 patients with a WBR of 100 to 129 per minute for 92 ± 43 months, and found only two symptomatic AV block (annual incidence 0.7%). There was no statistical difference of the incidence of AV block between patients with a WBR of 100 to 129 per minute and patients with a WBR 130 per minute or higher. These results suggest that a development of symptomatic bradycardia during AAI mode pacing is rare in patients with sinus node dysfunction, even if they have a WBR of 100 to 129 per minute. It seems that a WBR has little predictive value.
Limitations
Because this study is retrospective and the patient numbers are relatively small, further study is required for determining whether AAI pacing is truly safe in patients with sinus node dysfunction and a low WBR. Unfortunately, we could not find a useful predictor of AV block. Further study is also required.
Conflict of interest: none declared.
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Funding |
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Funding to pay the Open Access publication charges for this article was provided by the author.
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References |
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