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Sinus Node Dysfunction

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    Disclaimer: These citations have been automatically generated based on the information we have and it may not be 100% accurate. Please consult the latest official manual style if you have any questions regarding the format accuracy.

    AMA Citation
    Sinus Node Dysfunction. In: Crawford MH, Aras M, Sanchez JM. Crawford M.H., & Aras M, & Sanchez J.M.(Eds.),Eds. Michael H. Crawford, et al.eds. Quick Dx & Rx: Cardiology. McGraw-Hill; Accessed July 13, 2020. https://accesscardiology.mhmedical.com/content.aspx?bookid=2470&sectionid=196388904
    APA Citation
    Sinus node dysfunction. Crawford MH, Aras M, Sanchez JM. Crawford M.H., & Aras M, & Sanchez J.M.(Eds.),Eds. Michael H. Crawford, et al. (2018). Quick Dx & Rx: Cardiology. McGraw-Hill. https://accesscardiology.mhmedical.com/content.aspx?bookid=2470&sectionid=196388904
    MLA Citation
    "Sinus Node Dysfunction." Quick Dx & Rx: Cardiology Crawford MH, Aras M, Sanchez JM. Crawford M.H., & Aras M, & Sanchez J.M.(Eds.),Eds. Michael H. Crawford, et al. McGraw-Hill, 2018, https://accesscardiology.mhmedical.com/content.aspx?bookid=2470&sectionid=196388904.

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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

  • Stabilization of precipitating cause

FOLLOW-UP

  • Two weeks after discharge from the hospital

  • Depends on comorbid ...

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