Sinus Node Dysfunction

KEY FEATURES

ESSENTIALS OF DIAGNOSIS

• Sinus bradycardia with rate < 50 bpm

• Sinoatrial exit block second-degree type I: progressively shorter P-P intervals followed by failure of occurrence of a P wave

• Sinoatrial exit block second-degree type II: pauses in sinus rhythm that are multiples of basic sinus rate

• First-degree and third-degree sinoatrial exit blocks are difficult to diagnose

• Sinus arrest or pause: failure of occurrence of P waves at expected times

GENERAL CONSIDERATIONS

• Also referred to as sick sinus syndrome

• Usually caused by a degenerative process associated with aging

• Negative chronotropic drugs may cause a similar problem

• Tachycardia–bradycardia syndrome (bradycardia secondary to sinus node dysfunction coupled with supraventricular arrhythmia such as atrial fibrillation)

• Differentiation between sinus arrest and high-grade exit block is not possible without direct recordings of sinus node discharge

• Myocardial infarction (MI), digitalis toxicity, stroke, and excessive vagal tone all may cause this problem

CLINICAL PRESENTATION

SYMPTOMS AND SIGNS

• Syncope

• Lightheadedness

• Dizziness

• Symptoms of concomitant illness such as MI

PHYSICAL EXAM FINDINGS

• Bradycardia

• Irregular heart sounds

• Other findings depend on precipitating cause

DIFFERENTIAL DIAGNOSIS

• Blocked premature atrial contraction may resemble sinoatrial exit block

• Marked sinus arrhythmia

• Conditions with high vagal tone (eg, young athletic individual, cough, micturition)

DIAGNOSTIC EVALUATION

LABORATORY TESTS

• Depends on suspected concomitant illness or precipitating causes

• CBC, basic metabolic panel, thyroid-stimulating hormone

ELECTROCARDIOGRAPHY

• ECG to document rhythm disturbance

IMAGING STUDIES

• None required for the rhythm alone

• Echocardiogram may be done if the precipitating cause is MI or myocarditis

DIAGNOSTIC PROCEDURES

• Electrophysiologic study rarely indicated

TREATMENT

CARDIOLOGY REFERRAL

• If associated with syncope or symptoms of cerebral hypoperfusion, then referral to an electrophysiologist is required

HOSPITALIZATION CRITERIA

• Syncope

• Usually hospitalized for precipitating cause

MEDICATIONS

• Avoid or eliminate negative chronotropic drugs

THERAPEUTIC PROCEDURES

• Symptomatic patients without reversible cause need a pacemaker

• Although atrial pacing may be sufficient because most patients subsequently develop atrioventricular nodal disease, dual-chamber pacemakers are recommended

SURGERY

• None required

MONITORING

• ECG monitoring for hospitalized patients

DIET AND ACTIVITY

• General healthy lifestyle

• Depends on underlying medical illness

ONGOING MANAGEMENT

HOSPITAL DISCHARGE CRITERIA

• After pacemaker implantation

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