Arrhythmias, Sick Sinus Syndrome

Basics

Description

The term sick sinus syndrome (SSS) incorporates a number of disorders involving impulse generation in the atria.
Included are sinus bradycardia, sinus pauses or arrest, sinoatrial exit block, and the bradycardia-tachycardia syndrome (bradycardia alternating with atrial tachycardias, usually atrial fibrillation, but also atrial flutter and ectopic atrial tachycardia).
Sinus pauses or arrest implies failure of normal intrinsic cardiac pacemaker function.
Asymptomatic pauses of >2 sec have been reported in >10% of patients undergoing ambulatory monitoring.
Pauses of >3 sec are uncommon, but frequent enough and asymptomatic such that pauses alone do not constitute evidence for pacemaker implantation.
Patients may be symptomatic from paroxysmal tachycardia or bradycardia or both.
Synonym(s): Bradycardia-tachycardia syndrome; Brady-tachy syndrome; Sinus node dysfunction

SSS is typically a disease of the elderly.
The incidence of AV block is increased, suggesting a global disease of the specialized conduction system.
The elderly are especially susceptible to drug-induced sinus node dysfunction.

No specific contraindication to pregnancy
Extremely slow heart rates may compromise uterine blood flow, and atrial arrhythmias are more frequent during pregnancy.

Epidemiology

Incidence
Incidence increases with age.

Risk Factors

Structural heart disease
Increasing age

Pathophysiology

Sinus bradycardia and sinus pauses are common during sleep and do not constitute a pacing indication per se.

Etiology

Any structural heart disease
Aging process
MI leading to damage to the sinoatrial node or atria

Associated Conditions

Structural heart disease

Diagnosis

Signs and symptoms:

None
Lightheadedness
Syncope
Dyspnea, CHF
Stroke if atrial fibrillation
Fatigue
In older persons, personality and memory changes, nausea, and nonspecific complaints
Symptoms may be due to bradycardia itself, or to ventricular arrhythmias precipitated by bradycardia (eg, torsade de pointes ventricular tachycardia).

Tests

EKG
Ambulatory monitor/event recorder
Holter monitor/telemetry
Rarely, invasive electrophysiologic study is needed to assess sinus node dysfunction.
These studies are associated with a significant number of both false-positive and -negative test results.

Lab

No laboratory test is needed to diagnose SSS.
Thyroid function should be assessed because hypothyroidism may cause bradycardia.

Differential Diagnosis

Symptoms alone are not sufficient to assign a diagnosis of SSS. Symptoms must be correlated with the rhythm. This correlation is especially important when assessing the need and justification for permanent pacing. The differential diagnosis includes:

Normal sinus arrhythmia
Reversible causes of sinus node dysfunction such as drug toxicity
Hypothyroidism

Treatment

Medication

There are no drugs to treat intrinsic sinus node dysfunction. Permanent pacing is usually required and is very effective to relieve symptoms of sinus node dysfunction.

Additional Treatment

General Measures

If the SSS is due to nonessential drug therapy, those drugs should be stopped.
When there is not a reversible cause of SSS, pacing is indicated to manage bradycardia and to allow drug therapy of tachycardia when it is present.
Patients with SSS associated with atrial fibrillation (bradycardia-tachycardia syndrome) may need to be anticoagulated (based on CHADS score).
There is no known way to prevent the development of intrinsic sinus node dysfunction.

Surgery

The indications for pacemaker implantation are outlined in the American College of Cardiology/American Heart Association Guidelines referenced below and include:
Sinus node dysfunction correlated with symptomatic bradycardia, including frequent sinus pauses that produce symptoms. In some patients, bradycardia is iatrogenic and will occur as a consequence of essential long-term drug therapy of a type and dose for which there are no acceptable alternatives. (Class I indication)
Symptomatic chronotropic incompetence (Class I indication)
Sinus node dysfunction occurring spontaneously or as a result of necessary drug therapy, with heart rate <40 bpm when a clear association between significant symptoms consistent with bradycardia and the actual presence of bradycardia has not been documented. (Class IIa indication)
Syncope of unexplained origin when major abnormalities of sinus node function are discovered or provoked in electrophysiologic studies (Class IIa indication)
In minimally symptomatic patients, chronic heart rate <40 bpm while awake (Class IIb indication)

In-Patient Considerations

Admission Criteria

When patients have extremely slow heart rates, severe symptoms, or ventricular arrhythmias as a result of bradycardia (torsade de pointes ventricular tachycardia), admission is warranted.
Drug toxicity may be another indication for admission. Patients may be discharged after the arrhythmias have been treated.

Ongoing Care

Follow-Up Recommendations

Patient Monitoring

Pacemaker follow-up for those with permanent pacemakers
For patients without pacemakers, systematic EKG and ambulatory monitoring are used to identify disease progression (eg, longer pauses). This is especially true when new negatively chronotropic drugs are prescribed.

Diet

No specific diet.

Patient Education

Mostly related to pacemaker follow-up in those with pacemakers
If drug toxicity is the cause, counsel to take measures to avoid further toxicity.
Recommendations regarding activity depend on hemodynamic consequences of bradycardias and tachycardias.

Prognosis

Prognosis is governed by underlying heart disease and competing mortality. If SSS is associated with AV block, prognosis is worse than if AV block were absent.

Additional Reading

1 ACC/AHA/NASPE 2002 Guideline update for implantation of cardiac pacemakers and antiarrhythmia devices. Circulation. 2002;106: 2145-2161.

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