Pacemaker programming in patients with first‐degree AV‐block: Programming pattern and possible consequences

Abstract Background The optimal way of pacing in patients with an indication for pacing and concomitant first‐degree atrioventricular (AV)–block is not known, and consequently, firm guidelines on this topic are lacking. This study explored the current pacemaker programming pattern in patients with first‐degree AV‐block who have a dual chamber pacemaker without cardiac resynchronization. Methods The study was a retrospective chart review conducted at Duke University Hospital. Patients receiving a pacemaker due to sinus node dysfunction with coexistent first‐degree AV‐block were studied. Baseline demographics and characteristics, as well as pacemaker programming parameters and follow‐up data, were collected through chart review. Preimplantation and postimplantation electrocardiograms were analyzed. Results A total of 74 patients were included (mean age, 75 ± 11 y; 53% men). The mean ± SD preimplant PR interval and QRS duration was 243 ± 46 and 110 ± 30 milliseconds, respectively. A history of atrial fibrillation was present in 49% of the patients, and 77% had a normal left ventricular ejection fraction. The majority of patients (65%) had their pacemakers programmed to atrial pacing (AAI/DDD +/−R), whereas 32% and 2.7% of the pacemakers were programmed to AV‐sequential pacing (DDD) and ventricular pacing (VVI), respectively. There were no significant differences in baseline characteristics or electrocardiogram measures between patients programmed to the 3 pacing modes. Patients with pacemakers programmed to AAI had a lower ventricular pacing percentage at follow‐up (8 vs 55, and 46% [DDD and VVI, respectively]; P < .001). Conclusions There was no evident association between baseline characteristics and programmed pacing mode in patients with first‐degree AV‐block. The choice of pacing mode affects long‐term pacing burden, which in turn has been shown to influence outcome.


| INTRODUCTION
According to current guidelines, the sole presence of first-degree atrioventricular (AV)-block is, in most instances, not an indication for pacemaker treatment. 1 However, first-degree AV-block is commonly seen in patients with other indications for pacemaker therapy such as sinus node dysfunction or transient high degree of AV-block. Optimal pacing under these circumstances is unclear, and the existing literature does not provide any firm guidance. It is well known that right ventricular pacing may have negative long-term effects, regardless of underlying AV-conduction. 2,3 On the other hand, atrial pacing (AAI) has been shown to be potentially detrimental when compared with either backup ventricular pacing (VVI) or AV-sequential pacing (DDD) in patients with first-degree AV-block, specifically because atrial pacing at higher rates (in rate responsive modes) can further prolong the PR interval. 2,4,5 This makes programming particularly challenging in patients with bradycardia when first-degree AV-block is part of the problem.
The present study sets out to explore how electrophysiologists at a tertiary referral center choose to program pacemakers in patients with a first-degree AV-block and sinus node dysfunction and whether or not there are any patient or clinical characteristics that help guide them in their decision making.

| Statistical analysis
Normally distributed data are expressed as mean ± SD. Median and range are used when normal distribution could not be assumed.
Student t test was used for comparison between samples. Chi-square was used for discrete variables. All tests were 2-sided, and P < .05 was considered statistically significant. All statistical analyses were performed using IBM SPSS Statistics software (version 25 running on Mac OS X, IBM Corporation, Armonk, New York).
Apart from first-degree AV-block and sinus node dysfunction, 25% (n = 18) of the patients had a history of syncope or presyncope.  Table 1). The final programmed parameters at baseline are summarized in Table 2.
The delta PR was longer (ie, more pronounced prolongation) in patients with atrial pacing, but the difference was not statistically significant (−9.6 ± 36 vs 7 ± 34 ms compared with baseline, P = .090).

| DISCUSSION
The presence of first-degree AV-block in patients scheduled for a pacemaker due to sinus node dysfunction is a common finding. In the present study, one in 5 of these patients had a prolonged PR interval. The optimal way of treating patients with an indication for pacing and with a concomitant first-degree AV-block is presently unknown. In the DANPACE (The Danish multicenter randomised trial on single lead atrial versus dual chamber pacing in sick sinus syndrome) study, AAIpacing was compared with DDD-pacing in patients with sick sinus syndrome. 6 Patients with first-degree AV-block were found to fare worse than patients with normal AV-conduction, and a higher incidence of atrial fibrillation was observed. 4 This was particularly evident in patients randomized to AAI-pacing. In keeping with this, analyses of the Managed Ventricular Pacing trial revealed that the presence of first-degree AV-block was, in essence, the driver of the negative effects observed in patients with AAI-pacing when compared with backup VVI-pacing. 5 Both of these studies indicated that AAI-pacing may be unfavorable in patients with first-degree AV-block. However, reports from the Dual Chamber and VVI Implantable Defibrillator trial, in which DDD-pacing (with a high burden of RV-pacing) was compared with VVI-backup pacing (with a low burden of RV-pacing) in patients with heart failure and treatment with implantable cardiac defibrillator, indicate that DDDpacing was worse than VVI-backup even if the patients had first-degree AV-block and/or sinus bradycardia. 2 On the other hand, it is well known that excessive pacing of the right ventricle is associated with poor outcome, 7,8 making pacing programming in patients with first-degree AVblock challenging.
The lack of guidance and scientific evidence is echoed in the seemingly random choice of pacing mode in patients with first-degree AV-block and sinus node dysfunction seen in this study. Single chamber devices (VVI-pacing) are rarely used to treat patients with an indication for pacing and concomitant first-degree AV-block. One of the 2 patients with VVI devices in the current study was known to have persistent atrial fibrillation (albeit not at the time of implantation), and the other had a single chamber device implanted decades before the inclusion in the study (generator change).