Abstract
Background
Single chamber atrial pacemaker should be sufficient for patients with sinus node dysfunction (SND) with normal atrioventricular (AV) conduction. However, most patients undergo dual chamber pacemaker implantation because of concern of new onset AV block. The annual incidence of new AV block has been reported from 0.6 to 4.4 % in various studies.
Objectives
Our aim is to assess mode survival in sinus node dysfunction with normal AV conduction patients implanted with AAIR.
Methods
Patients who underwent single chamber atrial pacemaker implantation for SND with normal AV conduction between January 2014 and December 2021 were followed up for pacemaker device change, new onset AV block, bundle branch block, atrial fibrillation (AF), lead complications, reoperation and mortality rate.
Results
A total of 113 patients underwent single chamber atrial pacemaker implantation for SND during the study period. Mean age was 55.6 ± 12.7 years. During a mean follow up of 48.7 ± 24.9 months, none of the patients required pacemaker device change to VVIR/DDDR. Nine patients underwent reoperation, 5 for lead dislodgment, 1 for high threshold, 1 for pocket site erosion and 3 for pulse generator change. None developed AV block or AF with slow ventricular rate. Only 4 patients developed AF (3 paroxysmal,1 permanent). There were 3 deaths during follow up and none were sudden deaths.
Conclusion
Single chamber atrial pacing is an acceptable mode of pacing in patients with SND in developing countries. Development of AV conduction abnormalities is rare in this relatively younger population.
Keywords: Sinus node dysfunction, AAI, DDD, AV block, Atrial fibrillation
Abbreviations
- AAI/AAIR
Single chamber atrial pacing with or without rate modulation
- AF
Atrial fibrillation
- AV block
Atrioventricular block
- DDD/DDDR
Dual chamber pacing mode with or without rate modulation
- SND
Sinus node dysfunction
- VVI/VVIR
Single chamber ventricular pacing with or without rate modulation
1. Introduction
Sinus node dysfunction without atrioventricular (AV) conduction abnormalities can be treated with atrial pacing alone (AAIR), dual chamber pacing (DDDR) or with ventricular pacing alone (VVIR). Ventricular pacing alone has been shown to increase mortality in long-term1 compared to atrial pacing. It was also associated with increased risk of atrial fibrillation, thromboembolism1,2 and heart failure1 and therefore should be avoided in SND. However, it is not clear whether patients with SND should be treated with AAIR or DDDR. In a randomised trial of patients with SND, the risk of re-operation for high grade AV block was very low.3 Similar results were reported from other studies.4,5 However, guidelines suggest DDDR as default mode over AAIR for SND irrespective of age, because of concern for future development of AV block based on a randomized controlled trial, which showed increased re-operation in patients with AAIR mode of pacing with device change to VVIR/DDDR in 9.3 % at a mean follow up of 5.4 years.6,7 The mean age of patients in this study was 73 years, which is considerably higher compared to 57.6 years reported from South Asia8 and 58 years reported from Korea.4 Therefore the results of these studies may not be applicable in parts of the world where these patients are considerably younger. Apart from this, DDDR mode of pacing is costlier and may be associated with adverse consequences of ventricular dyssynchrony secondary to right ventricular pacing and higher rate of perioperative complications.9
2. Methods
This is a retrospective single centre observational study. All patients aged 18 and above who underwent implantation of a single chamber atrial pacemaker for sinus node dysfunction with normal AV conduction between January 2014 and December 2021 were identified from pacemaker clinic records. According to the usual practice at our center, patients with sinus node disease who had PR interval more than 200msec, bundle branch block or associated AV block underwent dual chamber pacemaker implantation. Atrial pacing for Wenckebach point was not performed during pacemaker implantation by us routinely. Wenckebach block point measured at time of implant has not been found to be a good predictor of AV conduction during follow up (10,11).
The follow up data was obtained from the pacemaker clinic records and in-person follow up. Patients are followed up in pacemaker clinic after implantation at 6 weeks, 6 months and then annually. During follow up visits patients were assessed clinically, device interrogation was performed and 12-lead electrocardiogram (ECG) was recorded. ECG was analysed for PR prolongation, 2nd or 3rd degree AV block and atrial fibrillation. Any device change, lead related complications and re-operations were also documented. Patients who did not report for follow up were contacted over telephone. In case of death of a patient, information regarding the final illness was obtained from review of hospital records, death certificate and information obtained from a close relative.
Primary objective was to study the incidence of pacemaker device change to DDDR/VVIR in patients who underwent single chamber atrial pacemaker implant for sinus node dysfunction. Secondary objectives were 1) to study the incidence and the reason for pacemaker reoperation, 2) to study the incidence of AV block (first or second- or third-degree AV block or bundle branch block) and AF with slow ventricular rate and 3) to study the mortality in these patients.
3. Results
A total of 142 patients underwent pacemaker implantation for SND between January 2014 and December 2021. In 29 patients, a VVIR/DDDR pacemaker was implanted because of BBB in 15 patients (pts), PR > 200 ms in 4 pts, intermittent AV block in 5 pts, atrial non-capture or high atrial thresholds in 3 pts, QT prolongation in 2 patients. The remaining 113 patients underwent implantation of a single chamber atrial pacemaker. Of them, 56 were male and mean age was 55.6 ± 12.7 years. Five patients had paroxysmal atrial fibrillation documented before implant and three patients had left ventricular systolic dysfunction with ejection fraction less than 55 %. Twenty-one patients had systemic hypertension and nine had diabetes mellitus (Table 1).
Table 1.
Baseline characteristics.
| Baseline characteristics | n = 113 |
|---|---|
| Age at implant (mean ± SD) | 55.6 ± 12.7 years |
| Male sex | 56 |
| Paroxysmal atrial fibrillation | 5 |
| Hypertension | 21 |
| Diabetes mellitus | 9 |
| Coronary artery disease | 2 |
| Chronic Kidney Disease | 3 |
| Ejection fraction<55 % | 3 |
| Lead type | |
| Active lead | 70 |
| Passive lead | 43 |
Mean follow up period was 48.6 ± 24.9 months and ranged from 4 months to 101 months. All patients were seen within the last one year of data collection except nine patients who did not visit the pacemaker clinic and could not be contacted over telephone. Results of these patients were taken from hospital records (Fig. 1).
Fig. 1.
Study consort diagram.
During a mean follow up of 48.6 months, none of the 113 patients required pacemaker device change to VVIR/DDDR. All study participants continued to remain in AAIR pacing mode at the end of study.
A total of nine patients had undergone reoperation after the initial AAIR implant. The most common reason for reoperation was lead repositioning due to either lead dislodgement or high threshold. Among the five patients with lead dislodgement, four had a passive fixation lead while one had an active fixation lead. One patient had undergone reoperation twice, once for high threshold and then for lead dislodgment. One patient had pocket site erosion six years after the implant and underwent device explant. After the explant, as patient's intrinsic sinus rate was adequate, he was managed conservatively. Three patients have undergone pulse generator change due to battery depletion (Table 2).
Table 2.
Reoperations after AAIR.
| Reasons for reoperation | n = 113 |
|---|---|
| Pacemaker mode change | 0 |
| Lead repositioning | 6 |
| Lead dislodgement | 5 |
| Lead repositioning for high threshold | 1 |
| Lead fracture | 0 |
| Device explant due to pocket site erosion | 1 |
| Pulse generator change | 3 |
| Total reoperations | 10a |
9 patients have undergone reoperations. One patient had undergone reoperations twice, once for high threshold and then for lead dislodgement.
A 12-lead electrocardiogram was analysed in 85 patients during follow up. None of the patients developed AV block, significant PR prolongation (PR interval >220msec) or atrial fibrillation with slow ventricular rate. During the follow up no one developed bundle branch block as well.
Four patients developed atrial fibrillation during follow up period. Of them three patients had paroxysmal atrial fibrillation and one patient had permanent AF. All these patients who developed AF had adequate ventricular rate and hence remained in AAIR pacing mode.
Two (1.7 %) patients had stroke in our study and one of them expired 2 years after implant. The other patient developed permanent atrial fibrillation 6 years after implant following which she had a cerebellar stroke.
There were 3 deaths during the follow up. Two of them were non-cardiac deaths. One patient died due to stroke 2 years after implantation. Second patient died due to urosepsis and its complications. Third patient died due to heart failure with refractory cardiogenic shock and acute kidney injury.
4. Discussion
4.1. Summary of results
In this study of 113 patients with SND undergoing AAIR pacemaker implantation, we found that during a mean follow up of 49 months, no one required device change to VVIR/DDDR or developed AV block or bundle branch block. A total of nine patients underwent reoperation, most commonly for lead dislodgement. Four patients developed atrial fibrillation but none of them had slow ventricular rate requiring device change to VVIR/DDDR. There were three deaths.
According to 11th world survey of cardiac pacing, patients undergoing pacemaker implantation in developed countries are older with more than 80 % of them being more than 60 years compared to developing nations such as India where only 63 % of them are more than 60 years.12 Our findings of a mean age of 55.6 ± 12.7 years in our study is in agreement with this data that patients in India and other developing countries are significantly younger than those in the West.5,7,13,14
The superiority of AAIR pacemaker over VVIR pacemaker was shown in previous studies, with a lower incidence of heart failure, atrial fibrillation, thromboembolism, stroke and death.1,2,12,14 The choice between AAIR vs DDDR is still debated. Prospective studies by Masumoto et al15 from Japan and Kim et al4 from Korea with follow up over 5 yrs have shown AAIR pacing is safe compared to dual chamber pacing and was associated with less lead related complications15 and chronic atrial fibrillation.4 However, Nielsen et al7 reported reoperations at a rate of 1.7 % per yr for device change to DDDR in those with SND implanted with AAIR.
Although AAIR pacemaker preserves physiological ventricular contraction, the concern was that it doesn't protect against bradycardia if atrioventricular block develops subsequently. The annual incidence of AV block in patients with SND has been reported to vary widely from 0.6 % to 2.9 %.3,16
4.2. AV block in sinus node dysfunction
In our cohort of 113 patients with SND with an AAIR pacemaker, no patient developed AV block during a mean follow up of 49 months. Similar low incidence of AV block was reported by Andersen et al3 (0.6 % per year i.e, 4 out of 101) in a randomised study between AAIR and DDDR pacing. In this study, 2 of the 4 had underlying right bundle branch block at the time of implantation. Similar results were reported by Morinigo et al14 (0.8 % per year) and Kim et al4 (0.9 % per year). Mean age in their cohorts were 72yrs and 59yrs respectively. However, 17Kristensen et al17 and Nielsen et al7 reported 1.7 % per year incidence of AV block in a predominantly Danish population with a mean age of 71years and 73 years respectively. The contrasting results between our study and some of the western data may be related to younger age (mean age of 55.6 years) of our study population and exclusion of patients with significant PR prolongation or any bundle branch block at the time of implantation. Younger age of patients with SND in the Asian population has also been noted before. In a study from South Asia, involving predominantly Indian population, mean age at diagnosis was 58yrs8, similar age at diagnosis was reported from South Korea (58yrs)4 and Japan (63yrs).15 Also the overall mean age of patients undergoing pacemaker implantation was less compared to European countries.12 The younger age is likely due to overall younger population and differential healthcare seeking behaviour.8
4.3. Reoperation rates
Nine out of 113 patients (7 %) underwent reoperation for reasons other than device change to VVIR/DDDR. Of them, six were due to lead related problems, one was due to pocket infection and three due to pulse generator change. In a retrospective study, Masumoto et al15 reported reoperation rate of 18.5 % in the AAIR group and 16.8 % in DDDR group (excluding pacemaker generator change). However, lead failure was twice as frequent with DDDR (22.8 %) than with AAIR pacing (13.7 %). Nielsen et al7 and Morinigo et al14 reported reoperation rate of 4.7 % and 4.3 % for lead failures. The possible reasons were not reported by them. In our study, five of six lead failures were due to dislodgment of passive fixation leads, one lead was repositioned due to a high threshold and one reoperation was for pocket infection. Incidence of lead dislodgement has significantly reduced with more usage of active fixation leads in recent years.
4.4. Atrial fibrillation
New onset atrial fibrillation occurred in four patients (3.96 %) in our study, which is notably less compared to previously reported studies.1,3,7,13 Rate of developing atrial fibrillation after pacemaker implant was much lower with isolated atrial pacing compared to isolated ventricular pacing.1,2 Andersen et al,1 reported 46 % relative risk reduction in incidence of atrial fibrillation and 65 % relative risk reduction of chronic atrial fibrillation with atrial pacing. Connolly et al18 reported 18 % relative reduction in atrial fibrillation with atrial based pacing compared to VVIR. In a meta-analysis of comparison between atrial pacing and isolated ventricular pacing, atrial pacing is associated with highly significant 20 % reduction in atrial fibrillation.2 Lower incidence of atrial fibrillation with atrial based pacing is due to preservation of atrioventricular synchrony and normal atrial mechanics compared to isolated ventricular pacing.
Majority of studies comparing AAIR versus DDDR pacing have found either reduced incidence of atrial fibrillation with AAIR or similar incidence between them. Kim et al4 reported lower incidence of AF with AAIR (2.8 %) compared to DDDR (15.2 %). Fored et al13 in a large registry follow up reported atleast 14 % higher risk of admission for atrial fibrillation with DDDR compared to AAIR. Contrary to others, Nielsen et al7 (DANPACE) reported more paroxysmal atrial fibrillation with AAIR (28.4 %) compared to DDDR (23 %). There was no difference in chronic atrial fibrillation between two groups. According to them, this may be due to longer baseline PQ interval in a subgroup of AAIR patients which lead to prolonged AV conduction with atrial pacing, resulting in mitral regurgitation then subsequently atrial fibrillation. Lesser incidence of atrial fibrillation in our study cohort 31474may be related to younger age.
4.5. Mortality
All-cause mortality in our study was 2.6 % over a mean follow up of 48.6 mths (0.7 % per year) and none of them were sudden deaths. This is similar to 0.48 % annual mortality in the AAIR group reported by Kim et al,4 but was less than 5.5 % per year in the AAIR cohort reported by Nielsen et al7 and 3.5 % per year reported by Kuniewicz et al.5 The higher mortality in these studies is likely related to older age of included population and comorbid status.
5. Limitations
Retrospective analysis, relatively short duration of follow-up and small number of patients are the main limitations of our study. However, no requirement of device change to VVIR/DDDR in 458 patient-years of follow up strongly supports that the incidence is very low. Etiology of sinus node dysfunction was not extensively evaluated, although reversible causes including hypothyroidism, infectious causes and electrolyte abnormalities were excluded before implanting pacemaker.
6. Conclusion
In younger patients with sinus node dysfunction and normal AV conduction, the risk of future development of AV block is very low. Single chamber atrial pacing is sufficient and safe as the mode of pacing in these patients.
Clinical perspectives
-
1.
Symptomatic SND without AV conduction abnormalities can be treated with AAIR alone, but most are treated with DDDR/VVIR
-
2.
Primary reason for this is concern of future development of AV block, but the incidence of AV block in older studies may not apply in a more carefully selected, younger population.
-
3.
We found no AV block during medium term follow up in our cohort and suggest that AAIR pacing is an appropriate mode of pacing for SND in appropriately selected patients.
Informed consent
Informed consent has been obtained from all patients.
Declaration of competing interest
None for any of the authors.
Acknowledgements
None.
References
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