SINUS NODE ARRHYTHMIAS

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When matters get even worse

Assess for a progression of the arrhythmia. Notify the practitioner immediately if the patient becomes unstable. Lower the head of the bed and administer atropine or epinephrine, as ordered or

as your facility’s policy directs. Withhold medications that may contribute to sinus pauses and check with the practitioner about whether those drugs should be continued.

If appropriate, be alert for signs of digoxin, quinidine, or procainamide toxicity. Obtain a serum digoxin level and a serum electrolyte level. If a pacemaker is implanted, give the patient discharge instructions about pacemaker care.

Sick sinus syndrome

Also called sinus nodal dysfunction, sick sinus syndrome refers to a wide spectrum of SA node abnormalities. The syndrome is caused by disturbances in the way impulses are generated or the inability to conduct impulses to the atrium.

Sick sinus syndrome usually shows up as bradycardia, with episodes of sinus arrest and SA block interspersed

with sudden, brief periods of rapid atrial fibrillation. Patients are also prone to paroxysms of other atrial tachyarrhythmias, such as atrial flutter and ectopic atrial tachycardia, a condition sometimes referred to as bradycardia-tachycardia (or brady-tachy) syndrome. Most patients with sick sinus syndrome are older than age 60,

but anyone can develop the arrhythmia. It’s rare in children except after open-heart surgery that results in SA node damage. The arrhythmia affects men and women equally. The onset is progressive, insidious, and chronic.

How it happens

Sick sinus syndrome results from a dysfunction of the sinus node’s automaticity or abnormal conduction or blockages of impulses coming out of the nodal region. (See Causes of sick sinus syndrome.) These conditions, in turn, stem from a degeneration of the area’s autonomic nervous system and partial destruction of the sinus node, as may occur with an interrupted blood supply after an inferior wall MI.

Blocked exits

In addition, certain conditions can affect the atrial wall surrounding the SA node and cause exit blocks. Conditions that cause inflammation or degeneration of atrial tissue can also lead to sick

Causes of sick sinus syndrome

Sick sinus syndrome may result from:

•conditions leading to fibrosis of the sino-

atrial (SA) node, such as increased age, atherosclerotic heart disease, hypertension, and cardiomyopathy

•trauma to the SA node caused by open heart surgery (especially valvular surgery), pericarditis, or rheumatic heart disease

•autonomic disturbances affecting autonomic innervation, such as hypervagatonia and degeneration of the autonomic nervous system

•cardioactive medications, such as digoxin (Lanoxin), beta-adren- ergic blockers, and calcium channel blockers.

sinus syndrome. In many patients, though, the exact cause of this syndrome is never identified.

Prognosis of the diagnosis

The significance of sick sinus syndrome depends on the patient’s age, the presence of other diseases, and the type and duration of the specific arrhythmias that occur. If atrial fibrillation is involved, the prognosis is worse, most likely because of the risk of thromboembolic complications.

If prolonged pauses are involved with sick sinus syndrome, syncope may occur. The length of a pause significant enough to cause syncope varies with the patient’s age, posture at the time, and cerebrovascular status. Consider significant any pause that lasts at least 2 to 3 seconds.

Long-term problems

A significant part of the diagnosis is whether the patient experiences symptoms while the disturbance occurs. Because the syndrome is progressive and chronic, a symptomatic patient needs lifelong treatment. In addition, thromboembolism may develop as a complication of sick sinus syndrome, possibly resulting in stroke or peripheral embolization.

What to look for

Sick sinus syndrome encompasses several potential rhythm disturbances that may be intermittent or chronic. (See Identifying sick sinus syndrome, page 80.) Those rhythm disturbances include one or a combination of:

•sinus bradycardia

•SA block

•sinus arrest

•sinus bradycardia alternating with sinus tachycardia

•episodes of atrial tachyarrhythmias, such as atrial fibrillation and atrial flutter

•failure of the sinus node to increase heart rate with exercise.

Check for speed bumps

Also look for an irregular rhythm with sinus pauses and abrupt rate changes. Atrial and ventricular rates may be fast, slow, or alternating periods of fast rates and slow rates interrupted by pauses.

The P wave varies with the rhythm and usually precedes each QRS complex. The PR interval is usually within normal limits but varies with changes in the rhythm. The QRS complex and T wave are usually normal, as is the QT interval, which may vary with rhythm changes.

Prolonged pauses with sick sinus syndrome cause syncope. Consider significant any pause lasting

2 to 3 seconds.

No set pattern

The patient’s pulse rate may be fast, slow, or normal, and the rhythm may be regular or irregular. You can usually detect an irregularity on the monitor or when palpating the pulse, which may feel inappropriately slow, then rapid.

If you monitor the patient’s heart rate during exercise or exertion, you may observe an inappropriate response to exercise such as a failure of the heart rate to increase. You may also detect episodes of brady-tachy syndrome, atrial flutter, atrial fibrillation, SA block, or sinus arrest on the monitor.

Extra sounds

Other assessment findings depend on the patient’s condition. For example, he may have crackles in the lungs, an S3 heart sound, or a dilated and displaced left ventricular apical impulse if he has underlying cardiomyopathy.

The patient may show signs and symptoms of decreased cardiac output, such as hypotension, blurred vision, and syncope, a common experience with this arrhythmia. (See Check mental status.)

Monitoring heart rate during exercise may show an inappropriate response. Can I stop now?!

How you intervene

As with other sinus node arrhythmias, no treatment is necessary if the patient is asymptomatic. If the patient is symptomatic, however, treatment aims to alleviate signs and symptoms and correct the underlying cause of the arrhythmia.

Atropine or epinephrine may be given initially for symptomatic bradycardia. A temporary or permanent pacemaker may be used. Tachyarrhythmias may be treated with antiarrhythmic medications, such as metoprolol and digoxin.

Drugs don’t always help

Unfortunately, medications used to suppress tachyarrhythmias may worsen underlying SA node disease and bradyarrhythmias. The patient may need anticoagulants if he develops sudden bursts, or paroxysms, of atrial fibrillation. The anticoagulants help prevent thromboembolism and stroke, a complication of the condition. (See Recognizing an embolism.)

Ages

and stages

Check mental status

Because the older adult with sick sinus syndrome may have mental status changes, be sure to perform a thorough assessment to rule out such disorders as stroke, delirium, or dementia.

SA node

•Acts as primary pacemaker

•Inherent firing rate of 60 to 100 times/ minute in a resting adult

•Supplied by blood from the right coronary artery and left circumflex artery

Sinus arrhythmia

Characteristics

•Rhythms: Irregular, corresponding to the respiratory cycle

•Rates: Within normal limits; vary with respiration

•Other parameters: QT interval variations

Treatment

•No treatment if asymptomatic

•Correction of the underlying cause

Sinus bradycardia

Characteristics

•Rhythms: Regular

•Rates: Less than 60 beats/minute

•Other parameters: Normal

Treatment

•No treatment if asymptomatic

•Correction of the underlying cause

•Temporary pacing to increase heart rate

•Atropine or epinephrine to maintain heart rate

•Dopamine for hypotension

•Permanent pacing if necessary

Sinus tachycardia

Characteristics

•Rhythms: Regular

•Rates: Both equal, generally 100 to 160 beats/minute

•PR interval: Normal

•QRS complex: Normal

•T wave: Normal

•QT interval: Shortened

Treatment

•No treatment if asymptomatic

•Correction of the underlying cause

•Beta-adrenergic blockers or calcium channel blockers if symptomatic

Sinus arrest

Characteristics

•Rhythms: Regular, except for missing PQRST complex

•Rates: Equal and usually within normal limits; may vary as a result of pauses

•P wave: Normal and constant when P wave is present; not measurable when P wave is absent

•QRS complex: Normal when present; absent during pause

•T wave: Normal when present; absent during pause

•QT interval: Normal when present; absent during pause

Treatment

•No treatment if asymptomatic

•Correction of the underlying cause

•Atropine or epinephrine to maintain heart rate

•Temporary pacemaker to maintain adequate cardiac output and perfusion

•Permanent pacemaker if necessary

Sick sinus syndrome

Characteristics

•Rhythms: Irregular with sinus pauses and abrupt rate changes

•Rates: Fast, slow, or combination of both

•P wave: Variations with rhythm and usually before QRS complex

•QRS complex: Normal

•T wave: Normal

•QT interval: Normal; variations with rhythm changes

Treatment

•No treatment if asymptomatic

•Correction of the underlying cause

•Atropine or epinephrine for symptomatic bradycardia

•Temporary or permanent pacemaker if necessary

•Antiarrhythmics, such as metoprolol and digoxin, for tachyarrhythmias

•Anticoagulants if atrial fibrillation develops