2.1 Bradycardia is a slow heart rate, defined as a heart rate of less than 60 beats per minute. Bradycardia can be caused by a range of factors, including diseases such as:
sick sinus syndrome – a number of abnormal heart rhythms caused by an irreversible dysfunction of the sinus node (the heart's natural pacemaker), including:
sinus arrest or pause, in which the sinus node occasionally does not generate electrical impulses, from a period lasting a couple of seconds to several minutes
sinoatrial exit block, in which the sinus node generates electrical impulses normally, but the signal is blocked before it leaves the sinus node
alternating bradyarrhythmias and tachyarrhythmias (a fast heart rate), such as bradycardia‑tachycardia syndrome
atrioventricular block (a condition in which electrical impulses from the sinus node are slowed or blocked). Atrioventricular block can occur independently from sick sinus syndrome, and so people with symptomatic bradycardia due to sick sinus syndrome may also have or develop atrioventricular block.
2.2 The most commonly identified causes of abnormal heart rhythms are age, ischaemic heart disease, heart valve disorders and heart failure. If untreated, symptomatic bradycardia may lead to fatigue, fainting, palpitations, dizziness, heart failure and an increased risk of mortality.
2.3 Sick sinus syndrome is difficult to diagnose because of the intermittent symptoms, and also because symptoms are usually non‑specific and observed in other disorders. Diagnosis is made using electrocardiograms (ECGs). Because abnormalities may be intermittent, Holter monitoring (ECG monitoring for 24 to 48 hours) or event recorders may be used.
2.4 The prognosis of individuals with sick sinus syndrome is variable and difficult to predict, depending on the underlying cause and the presence and severity of comorbidities (such as ischaemic heart disease). For most people, the disease is idiopathic (that is, the cause is unknown) and progressive. People whose disease is not symptomatic do not need therapy; however, once the disease becomes symptomatic, it can have a significant impact on quality of life, and the only effective treatment is permanent implantation of a pacemaker. Most people who need a pacemaker implanted are older than 60 years.
2.5 The prevalence of sick sinus syndrome is thought to be about 0.03% of the whole population, and increases with age. However, both the prevalence of bradyarrhythmias due to sick sinus syndrome needing permanent pacemaker implant, and the prevalence of sick sinus syndrome with atrioventricular block, is unknown. Hospital episode statistics data from October 2012 to September 2013 included 2490 patients with a primary diagnosis of sick sinus syndrome in NHS hospitals in England. Sick sinus syndrome usually occurs in older adults, but it can affect people of any age, and affects men and women equally. The incidence of atrioventricular conduction abnormalities also increases with increasing age.
2.6 Pacemakers are electrical devices that consist of a small battery‑powered generator and 1 or more pacing leads that are in contact with the inner wall of the right atrium and/or the right ventricle. The primary aim of permanent pacing is to prevent the heart from beating too slowly. An important secondary aim is to reproduce, as far as possible, the function of the heart's normal electrical conduction system, which coordinates the way the heart muscle contracts. Pacemaker devices may be broadly classified as single‑ or dual‑chamber, depending on whether leads are applied to 1 or 2 heart chambers. Dual‑chamber pacemaker devices are attached to both chambers of the heart and may be used in either dual‑chamber pacing mode (in which both the right atrium and ventricle are paced, which mimics the natural pacing rhythm of the heart) or single‑chamber pacing mode (where only 1 chamber of the heart is paced, either the atrium or the ventricle). Single‑chamber pacemaker devices may be either single‑chamber atrial devices or single‑chamber ventricular devices, and may only be used in the mode (that is to pace the chamber) where the lead was originally placed. Pacemakers may also be rate modulating (that is, able to sense and adapt the rate of pacing to the level of physical exertion).
2.7 NICE technology appraisal guidance 88 (hereafter referred to as TA88) recommended the use of single‑chamber atrial pacemakers for treating sick sinus syndrome in people in whom, after full evaluation, there was no evidence of impaired atrioventricular conduction. The purpose of this part review is to update this recommendation because the DANPACE trial, which was published after the publication of TA88, has provided additional evidence comparing dual‑ with single‑chamber atrial pacemakers for this population.
2.8 In 2012/13 in England, more than 20,000 people had a single‑ or a dual‑chamber pacemaker fitted. Sick sinus syndrome was the fourth most prevalent primary diagnosis (9.5%) after atrial fibrillation and flutter (22.5%), complete atrioventricular block (18.8%) and second degree atrioventricular block (10.6%). For people with a primary diagnosis of sick sinus syndrome (2490 patients), 67.5% had implantation of a dual‑chamber pacemaker, 14.8% had implantation of a single‑chamber pacemaker and 2.2% had a re‑operation of an existing implanted pacemaker.