From the Guidelines
Sick sinus syndrome is a disorder where the heart's natural pacemaker (sinus node) doesn't function properly, causing abnormal heart rhythms, and the most effective treatment for symptomatic bradycardia is permanent cardiac pacing, as stated in the 2013 guidelines 1.
Definition and Causes
Sick sinus syndrome refers to a broad array of abnormalities in sinus node and atrial impulse formation and propagation, including persistent sinus bradycardia and chronotropic incompetence without identifiable causes, paroxysmal or persistent sinus arrest with replacement by subsidiary escape rhythms in the atrium, AV junction, or ventricular myocardium 1. This condition occurs when the sinus node becomes damaged, often due to age-related fibrosis, heart disease, or other conditions affecting heart tissue.
Symptoms and Diagnosis
Symptoms of sick sinus syndrome include fatigue, dizziness, fainting, shortness of breath, chest pain, and palpitations 1. The clinical manifestations of SND are diverse, reflecting the range of typical sinoatrial rhythm disturbances, and the most dramatic presentation is syncope, which is caused by a sudden pause in sinus impulse formation or sinus exit block, either spontaneously or after the termination of an atrial tachyarrhythmia 1.
Treatment
The decision to implant a pacemaker for SND is often accompanied by uncertainty that arises from incomplete linkage between sporadic symptoms and ECG evidence of coexisting bradycardia, but permanent cardiac pacing is the only effective treatment for symptomatic bradycardia 1. Medications like beta-blockers or calcium channel blockers may need to be discontinued as they can worsen bradycardia, and anticoagulants might be prescribed if atrial fibrillation is present to prevent blood clots and stroke 1.
Quality of Life and Mortality
The condition is more common in older adults and can progressively worsen over time, making regular cardiac monitoring important for affected individuals 1. The incidence of sudden death is extremely low, and SND does not appear to affect survival whether untreated or treated with pacemaker therapy 1. Physiological pacing (atrial or dual-chamber) has been definitely shown to be superior to VVI pacing, as it lowers the risk of developing atrial fibrillation and improves quality of life 1.
From the Research
Definition of Sick Sinus Syndrome
- Sick sinus syndrome refers to a collection of disorders marked by the heart's inability to perform its pacemaking function 2.
- It is a set of diseases with abnormal cardiac pacing, which manifests as diverse cardiac arrhythmias, especially bradycardia 3.
- The term sick sinus syndrome should be reserved for patients with symptomatic sinus-node dysfunction 4.
Causes and Pathophysiology
- Intrinsic causes of sick sinus syndrome include degenerative fibrosis, ion channel dysfunction, and remodeling of the sinoatrial node 2.
- Extrinsic factors can be pharmacologic, metabolic, or autonomic, and can exacerbate or mimic the condition 2.
- Age-related interstitial fibrosis is considered to be the common pathophysiological mechanism between sick sinus syndrome and atrial fibrillation 3.
Symptoms and Diagnosis
- Symptoms of sick sinus syndrome are often subtle early on and become more obvious as the disease progresses, and are commonly related to end-organ hypoperfusion 2.
- Cerebral hypoperfusion is most common, with syncope or near-fainting occurring in about one-half of patients 2.
- Diagnosis is ultimately made by electrocardiographic identification of the arrhythmia in conjunction with the presence of symptoms 2.
- If electrocardiography does not yield a diagnosis, inpatient telemetry monitoring, outpatient Holter monitoring, event monitoring, or loop monitoring may be used 2.
Treatment
- Treatment of sick sinus syndrome includes removing extrinsic factors, when possible, and pacemaker placement 2.
- Pacemakers do not reduce mortality, but they can decrease symptoms and improve quality of life 2.
- Pacemaker implantation is the first-line treatment for symptomatic patients with sick sinus syndrome and documented bradycardia history 3.
- Catheter ablation may also be used as an alternative second-line therapy for some patients with sick sinus syndrome and atrial fibrillation 3.