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....................................................................................................................................................................... 5.1.1.2 Bradycardiatachycardia form of sinus node dysfunction The bradycardiatachycardia variant of SND is the most common form, and is characterized by progressive, age-related, degenerative fibrosis of the sinus node tissue and atrial myocardium. Bradyarrhythmias can be associated with various forms of atrial tachyarrhythmias, including AF.125 In this form of SND, the bradyarrhythmias may correspond to atrial pauses due to sinoatrial blocks or may be due to overdrive suppression after an atrial tachyarrhythmia.135

Atrial tachyarrhythmias may be present at the time of diagnosis, typically with sinus arrest and asystolic pauses at the termination of atrial tachyarrhythmias or after device implant. Control of atrial tachyarrhythmias in patients presenting with high ventricular rates may be difficult before implant, as drugs prescribed for rate control may worsen bradyarrhythmias. Ablation of the atrial tachyarrhythmia, mainly AF, has been proposed in lieu of pacing and continuing medications for selected patients,136138 but no data are available from RCTs to show whether catheter ablation of AF is non-inferior to cardiac pacing with respect to bradycardia-related symptoms in patients with bradycardiatachycardia syndrome.139 If drug treatment is chosen, bradyarrhythmias during drug treatment for rate or rhythm control may be managed by dose reduction or discontinuation as an alternative to cardiac pacing, but in many cases bradyarrhythmias persist.

5.1.2 Pacing mode and algorithm selection In patients with SND, controlled studies found that DDD was superior to single-chamber ventricular pacing in reducing the incidence of AF. These studies also showed some effect of DDD pacing on the occurrence of stroke.140,141 Dual-chamber pacing reduces the risk of pacemaker syndrome, which may occur in more than a quarter of patients with SND.21,142 Pacemaker syndrome is associated with a reduction in quality of life and usually justifies the preference for DDD vs. ventricular rate-modulated pacing in SND, when reasonable.143 Potential exceptions are very elderly and/or frail patients with infrequent pauses who have limited functional capacity and/or a short expected survival. In these patients, the benefit of DDD(R) vs. VVIR pacing is expected to have limited or no clinical impact, and the incremental risk of complications related to the second atrial lead required in DDD(R) implants should also be considered when choosing the pacing mode. In patients with SND treated with a DDD pacemaker, programming of the AV interval and specific algorithms for minimizing RV pacing may further reduce the risk of AF and particularly of persistent AF.144 Dual-chamber pacing is safer and more sustainable than atrial-only pacing modes used in the past,127 even though single-lead atrial pacing was found to be superior to singlelead ventricular pacing.145,146 The results of studies that evaluated different pacing modes in bradyarrhythmias, including in some cases both SND and AVB, are shown in Supplementary Table 6. With regard to the choice between DDD(R) and atrial pacing atrial sensing inhibited-response rate-adaptive (AAIR) pacing, an RCT with only 177 patients suggested a reduced risk of AF with AAIR.147 However, the most recent DANish Multicenter Randomized Trial on Single Lead Atrial PACing vs. Dual Chamber Pacing in Sick Sinus Syndrome (DANPACE), which enrolled 1415 patients followed for a mean of 5.4 years, found no difference between DDD(R) and AAIR pacing in all-cause mortality.127 The DANPACE trial also found a higher incidence of paroxysmal AF [hazard ratio (HR) 1.27] and a two-fold increased risk of pacemaker reoperation with AAIR, with AVB developing in 0.61.9% of patients every year.127 These findings support the routine use of DDD(R) rather than AAIR pacing in patients with SND.

In view of these data, DDD(R) is the pacing mode of first choice in SND (Figure 5). Unnecessary RV pacing should be systematically avoided in patients with SND, because it may cause AF and deterioration of HF, particularly if systolic function is impaired or borderline.144,148 This can be achieved by programming of the AV interval or using specific algorithms for minimizing RV pacing. Programming an excessively long AV interval to avoid RV pacing in patients with prolonged AV conduction may be disadvantageous from a haemodynamic point of view by causing diastolic mitral regurgitation, which may lead to symptoms and/or AF.144,149,150 Pacing algorithms for minimizing ventricular pacing are often used in SND.144,151 A meta-analysis of algorithms for minimizing RV pacing failed to show a significant effect compared with conventional DDD pacing in patients with normal ventricular function with regard to endpoints such as incidence of persistent/permanent AF, all-cause hospitalization, and all-cause mortality.152 However, the rationale for reducing unnecessary RV pacing remains strong and is coupled with the benefits of extending device longevity.151,152 Some manufacturerspecific algorithms are more effective in minimizing ventricular pacing, but may confer disadvantages in allowing decoupling between atria and ventricles.153,154 Rarely, algorithms designed to minimize ventricular pacing can cause life-threatening ventricular arrhythmias that are pause dependent or pause triggered.155158 No direct comparison of these algorithms has been performed so far, but pooled data from randomized trials do not show clear-cut superiority of any specific algorithm in improving clinical outcome.152,159 In patients with severely reduced LVEF and a SND indication for pacing, in whom a high percentage of ventricular pacing is expected, an indication for CRT or HBP should be evaluated (see section 6 on CRT and section 7 on HBP). The role of pacing algorithms for preventing AF has been the subject of controversy. A series of algorithms for preventing/suppressing AF has been tested, such as dynamic atrial overdrive pacing, atrial pacing in response to atrial premature beats, pacing in response to exercise, and post-mode-switch pacing. The clinical evaluation of these algorithms, also applied at different atrial pacing sites, is not convincing and no clinical benefit with regard to major clinical endpoints has been demonstrated.160,161 Atrial antitachycardia pacing [ATP; i.e. delivery of atrial stimuli at high frequencies to convert an atrial tachyarrhythmia to sinus rhythm (SR)] has also been tested for reducing the atrial tachyarrhythmia burden and counteracting the tendency over time towards progression to permanent AF.162 Conventional delivery of atrial ATP in a way that mirrors the delivery of ventricular ATP (bursts/ramp at arrhythmia onset) has a relatively low success rate, and indeed the trials based on conventional atrial ATP showed no benefit on AF burden or clinical events.163 A new form of ATP delivery has been Downloaded from academic.oup.com/eurheartj/article/42/35/3427/6358547 by guest on 07 October 2026