Sinus bradycardia

Defined as a sinus rhythm with a resting heart rate of 60 beats per minute or less.

Rhythm arises from the sinus node and causes a P wave on the ECG that is normal in amplitude and vector and are typically followed by a normal QRS complex and T wave.

Commonly, an incidental finding in otherwise healthy individuals.

Commonly noted in young adults or sleeping patients.

May be related to increased vagal tone, as may be seen in athletes.

Associated with pathologic conditions to include: inferior wall myocardial infarction, electrolyte disorders, infection, sleep apnea, drug effects, hypoglycemia, hypothyroidism, and increased intracranial pressure, sinus atrial block, and sick sinus syndrome.

Frequency is unknown, but it is estimated to be 3 in 5000.

Medications responsible include digitalis, beta-blockers, and calcium channel-blocking agents, class I antiarrhythmic agents and amiodarone.

Rarely associated with lithium, paclitaxel, toluene, dimethyl sulfoxide (DMSO), topical ophthalmic acetylcholine, fentanyl, clonidine, hypothermia, hypoglycemia, and sleep apnea.

May be associated with infections of diphtheria, rheumatic fever, or viral myocarditis.

Most often asymptomatic.

In apparently healthy, non-athletic individuals older than 40 years there is no association with cardiovascular mortality.

Some studies suggest that asymptomatic bradycardia may be associated with modestly reduced cardiovascular mortality.

Symptoms may include: Syncope,dizziness,lightheadedness, chest pain, shortness of breath, exercise intolerance.

Examination reveals a slow, regular heart rate.

Prognosis is dependent on the etiology.

SB associated with a sick sinus syndrome have a relatively poor prognosis, with 5-year survival rates in the range of 47-69%.

Laboratory studies may be helpful if the cause of the bradycardia is thought to be related to electrolytes, drug, or toxins.

In cases of sick sinus syndrome, routine laboratory studies are rarely of specific value.

SB secondary to sick sinus syndrome usually requires placement of a pacemaker.

Sinus bradycardia secondary to therapeutic use of drugs requires discontinuation of the drug.

Management occasionally requires intravenous atropine and temporary pacing.

Postinfectious sinus bradycardia usually requires permanent pacing.

Treatment of sinus bradycardia is usually not indicated for asymptomatic patients.

Temporary pacing is recommended in symptomatic patients unresponsive or only temporarily responsive to atropine.

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