Sinus bradycardia

Sinus bradycardia
Sinus bradycardia.
ICD-9	427.81
MeSH	D001146

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor-In-Chief: Cafer Zorkun, M.D., Ph.D. [2]

Overview

Sinus bradycardia is a heart rhythm that originates from the sinus node and has a rate of under 60 beats per minute. Common causes include sick sinus syndrome and pharmacotherapy such as beta-blockers. Sinus bradycardia is fairly common in highly trained athletes. It only requires treatment if the patient is symptomatic.

Pathophysiology

This rhythm may be caused by one of the following:

• Increased vagal tone
• Intrinsic disease of the SA node
• An effect of drugs, such as the use of digitalis or beta-blockers
• Sleep
• Sinus bradycardia is a normal finding in a healthy, well-conditioned athlete

Genetics

The HCN4 genetic variant is associated with sinus bradycardia. Certain sodium channelopathies are associated with sinus bradycardia.

Overview

Causes by Organ System

Cardiovascular	No underlying causes
Chemical/Poisoning	No underlying causes
Dental	No underlying causes
Dermatologic	No underlying causes
Drug Side Effect	No underlying causes
Ear Nose Throat	No underlying causes
Endocrine	No underlying causes
Environmental	No underlying causes
Gastroenterologic	No underlying causes
Genetic	No underlying causes
Hematologic	No underlying causes
Iatrogenic	No underlying causes
Infectious Disease	No underlying causes
Musculoskeletal/Orthopedic	No underlying causes
Neurologic	No underlying causes
Nutritional/Metabolic	No underlying causes
Obstetric/Gynecologic	No underlying causes
Oncologic	No underlying causes
Ophthalmologic	No underlying causes
Overdose/Toxicity	No underlying causes
Psychiatric	No underlying causes
Pulmonary	No underlying causes
Renal/Electrolyte	No underlying causes
Rheumatology/Immunology/Allergy	No underlying causes
Sexual	No underlying causes
Trauma	No underlying causes
Urologic	No underlying causes
Miscellaneous	No underlying causes

Epidemiology and Demographics

Among people under 25 years of age, approximately 30% have sinus bradycardia. During sleep, heart rates may decline by 25 beats per minute in young patients, and 15 beats per minutes in the elderly. Heart rates of 30 beats/minute and pauses of up to 2 seconds are not uncommon in healthy people

Diagnosis

Symptoms

The decreased heart rate can cause a decreased cardiac output resulting in symptoms such as:

• Dizziness
• Lightheadedness
• Presyncope
• Syncope
• Vertigo

Sinus bradycardia may be associated with no symptoms in a young athlete.

Physical Examination

Vitals

• There may be a wide pulse pressure

Skin

If cardiac output is reduced, there may be signs of end organ hypoperfusion such as cold clammy skin

Laboratory Studies

Based upon the patient's history and demographics, the following laboratory studies should be considered:

• Serum electrolytes including Ca, Mg
• TFTs should be checked
• Hypoglycemia should be excluded
• Consider a toxicologic screen

Electrocardiogram

• Rate: Less than 60
• Rhythm: Regular
• P waves: Upright, consistent, and normal in morphology and duration
• PR Interval: Between 0.12-0.21 seconds in duration
• QRS complex: Less than 0.12 seconds in width, and consistent in morphology
• Early repolarization is accentuated in the setting of sinus bradycardia
• Sinus arrhythmia often accompanies sinus brdycardia

EKG Examples

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Shown below is an EKG depicting sinus bradycardia. The heart rate is around 40 bpm. It also shows PR prolongation and decrease in QRS complex.

Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/File:Rhythm_sinusbradycardia.png

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Shown below is an EKG example of sinus bradycardia. The heart rate is around 45 bpm. It also shows PR prolongation and a shortening of the QRS complexes.

Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/File:Sinusbradycardia.png

---

Shown below is an EKG example of sinus bradycardia. The heart rate is around 45 bpm.

Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/Main_Page

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Treatment

Acute Management

• If a patient is symptomatic, intravenous access should be established.
• Atropine can be administered down an endotracheal tube or can be administered intravenously. The dose is 0.5-1 mg IV or ET q 3-5 min up to 3 mg total (0.04 mg/kg). The pediatric dosing is 0.02 mg/kg/dose IV, minimum of 0.1 mg. Isoproteronol (Isoprel) has been used in the past, but carries risks.
• Transcutaneous pacing can be undertaken while a temporary wire is being placed.
• Offending or exacerbating agents such as beta-blockers, calcium channel blockers or digitalis should be discontinued and underlying causes treated.
• Sleep apnea is a common cause and should be treated with weight loss and BiPAP.
• Continuous monitoring in the hospital is recommended.

Chronic Management

Asymptomatic sinus bradycardia requires no treatment. Patients with sick sinus syndrome generally require a pacemaker.

ACC/AHA/HRS Guideline Recommendations for Pacemaker Implantation (DO NOT EDIT)

Recommendations for Permanent Pacing in Sinus Node Dysfunction (SND)

“

Class I 1. Permanent pacemaker implantation is indicated for SND with documented symptomatic bradycardia, including frequent sinus pauses that produce symptoms.(Level of Evidence: C) 2. Permanent pacemaker implantation is indicated for symptomatic chronotropic incompetence. (Level of Evidence: C) 3. Permanent pacemaker implantation is indicated for symptomatic sinus bradycardia that results from required drug therapy for medical conditions. (Level of Evidence: C) Class IIa 1. Permanent pacemaker implantation is reasonable for SND with heart rate less than 40 bpm when a clear association between significant symptoms consistent with bradycardia and the actual presence of bradycardia has not been documented. (Level of Evidence:C) 2. Permanent pacemaker implantation is reasonable for syncope of unexplained origin when clinically significant abnormalities of sinus node function are discovered or provoked in electrophysiological studies. (Level of Evidence: C) Class IIb 1. Permanent pacemaker implantation may be considered in minimally symptomatic patients with chronic heart rate less than 40 bpm while awake. (Level of Evidence: C) Class III 1. Permanent pacemaker implantation is not indicated for SND in asymptomatic patients. (Level of Evidence:C) 2. Permanent pacemaker implantation is not indicated for SND in patients for whom the symptoms suggestive of bradycardia have been clearly documented to occur in the absence of bradycardia. (Level of Evidence:C) 3. Permanent pacemaker implantation is not indicated for SND with symptomatic bradycardia due to nonessential drug therapy. (Level of Evidence: C)

”

References

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