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Signs and symptoms

Often sick sinus syndrome produces no symptoms, especially early in the disease course. Signs and symptoms usually appear in more advanced disease and more than 50% of patients will present with syncope or transient near-fainting spells.^[1] Other presenting signs or symptoms can include confusion, fatigue, palpitations, chest pain, shortness of breath, headache, and nausea. Patients can also present with symptoms of congestive heart failure, stroke or transient ischemic attacks due to the abnormal rhythm.^[1]

Complications

The most common complication of sick sinus syndrome is developing tachycardia-bradycardia syndrome with abnormal atrial rhythms such as atrial tachycardia, atrial fibrillation, and flutter.^[1] These rhythms increases the risk of clot formation in the atrium, embolization, and stroke.^[1]

Developing sinus arrest, sinus node exit block, sinus bradycardia, atrioventricular block, and other types of abnormal rhythms are also common complications.^[1][2] Sick sinus syndrome shares a close association with the presence of atrial fibrillation due to their shared etiology of remodeling.^[2]

Causes

Sick sinus syndrome can be caused by intrinsic and extrinsic factors that effect the normal functioning of the sinus node. Intrinsic causes can include degeneration, dysfunction, or remodeling of the sinus node while extrinsic causes can create or worsen underly atrial arrhythmias.^[1] Intrinsic causes tend to be responsible for permanent sick sinus syndrome while extrinsic causes are more commonly temporary.^[2]

Intrinsic Causes

Age-related degenerative fibrosis of the sinus node is often identified as the most common intrinsic cause.^[1][2] Other intrinsic causes include inherited ion channel dysfunctions, remodeling diseases such as heart failure and atrial fibrillation, infiltrative diseases such as sarcoidosis, amyloidosis, hemochromatosis, and connective tissue diseases, inflammatory etiology such as rheumatic fever, Chagas disease, and Lyme disease, as well as atherosclerotic and ischemic changes to the sinus node artery.^[1][2]

Inherited sick sinus syndrome have been associated with mutations of the gene responsible for formation of Alpha subunit of sodium channel (SCN5A).^[2]

Extrinsic Causes

Common cardiac pharmacology such as beta-blockers, calcium channel blockers, digoxin, sympatholytic medication, and other antiarrhythmics can alter sinus node function to create an arrhythmia such as sick sinus syndrome. Electrolyte abnormalities such as hyperkalemia, hypokalemia, and hypocalcemia can also alter normal sinus node functioning. Hypothyroidism, hypoxia, hypothermia, and various toxins have also been associated with sinus node dysfunctions.^[1][2]

Diagnosis

Electrocardiogram

The primary 12-lead electrocardiogram (ECG) finding in sick sinus syndrome is inappropriate sinus bradycardia.^[3] Sick sinus syndrome can also present with sudden sinus arrest with or without junctional escape, sinoatrial block, prolonged asystolic period followed by tachycardias, or bradycardia-tachycardia syndrome presenting as various atrial arrhythmias such as atrial fibrillation, flutter, tachycardia, or paroxysmal supraventricular tachycardia.^[3][1]

Clinical Diagnosis

Diagnosing sick sinus syndrome requires clinical symptoms as well as ECG abnormalities. If ECG findings cannot be identified, prolonged cardiac monitoring should be pursued either with a Holter monitor in an outpatient setting or telemetry while inpatient, due to the transient nature of abnormal ECG findings.^[1] If Holter or telemetry monitoring fails to identify ECG changes and suspicion of sick sinus syndrome remains high due to severe symptoms or episodes of syncope, implantable loop recorders should be considered for extended monitoring up to 24 months.^[3]

Exercise stress test can be utilized to identify intrinsic causes of sick sinus syndrome. Head-up tilt test can be used to discriminate bradycardia caused by dysfunction of the autonomic nervous system.^[1][3]

Treatment

Pacemaker implantation is the primary treatment modality of symptomatic sick sinus syndrome.^[1][3][4] The goal of this treatment modality is to relive symptoms associated with sick sinus syndrome and improve quality of life.^[1] Dual chamber pacemakers are preferred due to the possibility of developing atrioventricular block^[1] as well as long term cost-effectiveness relative to single-chamber atrial pacemakers^[5].

In tachycardia-bradycardia syndrome, medication based management can treat atrial tachyarrhythmias. However, these medication may exacerbate underlying bradyarrhythmia. Therefore, specialized dual chamber pacemaker capable of managing atrial tachyarrhythmias as well as bradyarrhythmias is implanted before drug therapy is begun.^[3]

Epidemiology

Overall incidence of sick sinus syndrome increases with age^[6] with 1 in 1000 in adults over 45 years old^[2] and 1 in 600 cardiac patients over 65 years old^[1]. Sick sinus syndrome is the primary indication for approximately 30%-50% of all pacemaker implantation in the United States^[6]. Sick sinus syndrome is a relatively uncommon syndrome in the young and middle-aged population.

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1. Semelka, M; Gera, J; Usman, S (May 2013). "Sick sinus syndrome: a review". American Family Physician (Review). 87 (10): 691–6. PMID 23939447.
2. John Roy M.; Kumar Saurabh (2016-05-10). "Sinus Node and Atrial Arrhythmias". Circulation. 133 (19): 1892–1900. doi:10.1161/CIRCULATIONAHA.116.018011.
3. De Ponti, Roberto; Marazzato, Jacopo; Bagliani, Giuseppe; Leonelli, Fabio M.; Padeletti, Luigi (2018-06). "Sick Sinus Syndrome". Cardiac Electrophysiology Clinics. 10 (2): 183–195. doi:10.1016/j.ccep.2018.02.002. ISSN 1877-9182. {{cite journal}}: Check date values in: |date= (help)
4. Drago F, Silvetti MS, Grutter G, De Santis A (July 2006). "Long term management of atrial arrhythmias in young patients with sick sinus syndrome undergoing early operation to correct congenital heart disease". Europace. 8 (7): 488–94. doi:10.1093/europace/eul069. PMID 16798761.
5. Sj, Edwards; C, Karner; N, Trevor; V, Wakefield; F, Salih (2015-08-24). "Dual-chamber pacemakers for treating symptomatic bradycardia due to sick sinus syndrome without atrioventricular block: a systematic review and economic evaluation". Health Technology Assessment. 19 (65). doi:10.3310/hta19650. ISSN 2046-4924. PMC 4781212. PMID 26293406.
6. Jensen, Paul N.; Gronroos, Noelle N.; Chen, Lin Y.; Folsom, Aaron R.; deFilippi, Chris; Heckbert, Susan R.; Alonso, Alvaro (2014-08). "Incidence of and Risk Factors for Sick Sinus Syndrome in the General Population". Journal of the American College of Cardiology. 64 (6): 531–538. doi:10.1016/j.jacc.2014.03.056. PMC 4139053. PMID 25104519. {{cite journal}}: Check date values in: |date= (help)