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EDITORIAL COMMENT

Sick Sinus SyndromeSynopsis*

Gordon A. Ewy, MD

SEE PAGE 531

S ick sinus syndrome (SSS) is a term used for avariety of cardiac arrhythmias, occurring pre-dominantly in the elderly, that result from a

senescent sinus node. Because the sinus node is thenormal pacemaker of the heart, its dysfunction is acause for concern. Although the major problem isfailure of the sinoatrial node, the symptoms wouldbe uncommon were it not for the diffuse nature ofthe dysfunction, accounting for the frequent failureof escape or rescue rhythms. Accordingly, SSS is char-acterized, not only by sinus node malfunction, result-ing in intermittent sinus pauses and rare sinus arrest,but also by inappropriate and often intermittentbradycardia, tachycardia, and the frequent alterna-tion between the 2 conditions (tachycardia-brady-cardia syndrome) (1,2).

When sinus node dysfunction is associated withsymptoms, or prolonged periods of asystole, it isreferred to as the sick sinus syndrome. Although Dr.Short (3) had previously published on “The Syndromeof Alternating Bradycardia and Tachycardia,” Dr.Ferrer (4) was evidently the first, in 1968, to use theterm sick sinus syndrome to describe the sluggish re-turn of sinoatrial nodal function in patients followingelectrical cardioversion.

Sick sinus syndrome is generally a disease of aging.It is uncommon in children. If present in children, itwas usually acquired post-operatively as a result oftrauma to the atrium during cardiac surgery to correctcongenital heart defects.

A characteristic feature of SSS is that the heart doesnot respond normally to stimuli that should produceincreased heart rates, such as exercise. Because SSS

*Editorials published in the Journal of the American College of Cardiology

reflect the views of the authors and do not necessarily represent the

views of JACC or the American College of Cardiology.

From the University of Arizona Sarver Heart Center, Tucson, Arizona.

Dr. Ewy has reported that he has no relationships relevant to the

contents of this paper to disclose.

is most common in the elderly, its symptoms may beattributed to the aging process rather than to a dis-ease. One of the hallmarks of aging is the progressiveloss of cells, and this loss of cells in the sinus node isa commonly reported pathological finding in patientswith SSS. The frequent lack of an effective escaperhythm emphasizes the diffuse nature of the con-duction system disease. Because the sinus node getsits blood supply from a branch of a coronary artery,SSS also can be caused by atherosclerosis and maybe associated with angina. The syndrome can beaccompanied by a variety of other supraventriculararrhythmias. Although the rescue rhythms are usu-ally atrial, the association of atrioventricular nodaldisease is not uncommon.

Clinically significant SSS often requires pacemakerimplantation. Ferrer (5) pointed out in 1982 that one-half of the 60,000 pacemakers implanted were forSSS. By 2006, SSS was one of the most common rea-sons for the escalating number of pacemaker im-plants (6).

In describing the epidemiology of SSS, Jensen etal. (7) in this issue of the Journal confirmed that SSSwas associated with the increasing age of the popu-lation, predicted to produce a steady increase in theincidence of SSS and, thus, in the need for permanentpacemaker implantation, estimating that by 2060,there will be more than 170,000 new cases of SSSper year.

The investigators of this study identified SSSby the International Classification of Disease-revision9-Clinical Modification (ICD-9-CM) code 427.81,which incorporates SSS, sinoatrial node dysfunction,tachycardia-bradycardia syndrome, and persistentsinus bradycardia. They considered SSS to be pre-sent if the medical record included a diagnosis ofSSS and symptoms or signs consistent with SSS

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(e.g., syncope, dizziness, bradycardia, sinus pauses),with no evidence of other conditions responsible forthe episode, such as atrioventricular block or medi-cation use (7). These investigators confirmed that theincidence of SSS increased with age, but found thatblacks had a lower risk than whites. They reportedthat the incidence of SSS was associated with greaterbody mass index, greater height, longer QRS interval,lower heart rate, and prevalent hypertension, rightbundle branch block, and cardiovascular disease (7).

The SSS may be difficult to diagnosis, becauseinitially, the symptoms may be mild and very inter-mittent. When the patient presents with symptomsconsistent with SSS, a detailed history of medica-tions, including alternative medications, is essential.In addition, it is rare, but the patient may be takingthe same medication prescribed by 2 different phy-sicians: one by a generic name and the other by atrade name, such as metoprolol and Toprol-XL, ordigoxin and Lanoxin, where known side effects ofoverdose are arrhythmias consistent with SSS.

The physical examination and the electrocardio-gram are important, including performing carotid si-nus pressure, while observing the electrocardiogram.

An asystole response of 3 or more seconds to carotidsinus pressure is strongly suggestive of SSS and anindication for a permanent pacemaker if the patienthas a history of syncope (8).

The definitive diagnosis is often made by ambu-latory monitoring or by electrophysiological studies.Modern ambulatory monitoring alternatives are oftenessential to this diagnosis. The increasing sophisti-cation, diagnostic ability, and surgical skills of themodern electrophysiologists make the diagnosis easyand therapy of patients with SSS effective. Jensenet al. (7) predict that with the aging of our population,SSS will be a major factor in increasing the need forpermanent pacemakers. This fact will drive researchinto more effective approaches to the diagnosis ofthe SSS and into decreasing the size and type ofpermanent pacemakers, as well as increasing thesophistication of future permanent pacemakers.

REPRINT REQUESTS AND CORRESPONDENCE: Dr.Gordon A. Ewy, Department of Medicine, Universityof Arizona Sarver Heart Center, 932 West San MartinDrive, Tucson, Arizona 85704. E-mail: gaewy1933@gmail.com.

RE F E RENCE S

1. Ewy GA. Management of bradydysrhythmiasand conduction disturbances. In: Ewy GA,Bressler R, editors. Cardiovascular Drugs and theManagement of Heart Disease. New York, NY:Raven Press, 1982:441–62.

2. Gregoratos G. Sick sinus syndrome. Circulation2003;108:e143–4.

3. Short DS. The syndrome of alternatingbradycardia and tachycardia. Brit Heart J 1954;16:208–14.

4. Ferrer MI. The sick sinus syndrome in atrialdisease. JAMA 1967;206:625–46.

5. Ferrer MI. The etiology and natural history ofsinus node disorders. Arch Intern Med 1982;142:371–2.

6. Birnie D, Williams K, Guo A, et al. Reasons forescalating pacemaker implants. J Am Coll Cardiol2006;98:93–7.

7. Jensen PN, Gronroos NN, Chen LY, et al. Inci-dence of and risk factors for sick sinus syndromein the general population. J Am Coll Cardiol 2014;64:531–8.

8. Epstein AE, DiMarco JP, Ellenbogen KA, et al.ACC/AHA/HRS 2008 guidelines for device-based

therapy of cardiac rhythm abnormalities: areport of the American College of Cardiology/American Heart Association Task Force on Prac-tice Guidelines (Writing Committee to Revise theACC/AHA/NASPE 2002 Guideline Update forImplantation of Cardiac Pacemakers and Anti-arrhythmia Devices). J Am Coll Cardiol 2008;51:e1–62.

KEY WORDS cardiac arrest, passiveventilation, prevention, ventricular fibrillation