Sinus bradycardia

Associate Editor-In-Chief:

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 not unexpected in highly trained athletes. It only requires treatment if the patient is symptomatic.

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

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

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.

Differential Diagnosis of Causes of Sinus Bradycardia
In alphabetical order.


 * Ambenonium
 * Acetylcholine
 * Alfentanil
 * Amiodarone
 * Amyloidosis
 * Anorexia nervosa
 * Atenolol
 * Babesiosis
 * Beta blocker
 * Bethanechol
 * Brucellosis
 * Bupivacaine
 * Calcium channel blocker
 * Carotid sinus hypersensitivity
 * Cardiac catheterization
 * Cardiac transplant
 * Cerebral edema
 * Cervical spine injury
 * Chagas disease
 * Cilobradine
 * Clonidine
 * Congenital Heart Disease correction
 * Corgard
 * Coughing
 * Cretinism
 * Decompression sickness
 * Defacation
 * Dengue fever
 * Deserpidine
 * Diabetic autonomic neuropathy
 * Digitalis
 * Diltiazem
 * Dimethyl sulfoxide (DMSO)
 * Diptheria
 * Distigmine
 * Drugs
 * Dysautonomia
 * Electrocution
 * Endocarditis
 * Fentanyl
 * Fetal distress
 * Glaucoma
 * Glioblastoma
 * Heart transplant
 * Hemochromatosis
 * High altitude sickness
 * Hypercalcemia
 * Hypercapnia
 * Hyperkalemia
 * Hypermagnesemia
 * Hypoglycemia
 * Hypokalemia
 * Hypothermia
 * Hypothyroidism
 * Hypoxia
 * Increased intracranial pressure
 * Ivabradine
 * Kwashiorkor
 * Legionella
 * Leptospirosis
 * Lidocaine
 * Lilly of the valley
 * Lithium
 * Lofexidine
 * Lyme disease
 * Malaria
 * Malnutrition
 * Meningitis
 * Micturition syncope
 * Miller-Dieker syndrome
 * Myocardial Infarction, particularly inferior MI
 * Myocarditis
 * Myotonic muscular dystrophy
 * Nausea
 * Nadolol
 * Neostigmine
 * Nerve gas
 * Neurocardiogenic syncope
 * Organophosphates
 * Paclitaxel
 * Physical training, elite athlete status
 * Physostigmine (Eserine / Antrilirium)
 * Post-tussive syncope
 * Procainamide (Procan-SR / Pronestyl)
 * Propranolol
 * Psittacosis
 * Q fever
 * Quinidine
 * Reserpine
 * Rheumatoid arthritis
 * Rheumatic fever
 * Rocky Mountain Spotted Fever
 * Sarcoidosis
 * Scleroderma
 * Sedatives
 * Sepsis
 * Sick Sinus Syndrome (SSS)
 * Sleep apnea
 * Sotalol (Betapace)
 * Spinal cord injury
 * Standing for a prolonged period of time may trigger the Bezold-Jarisch reflex
 * Starvation
 * Subarachnoid hemorrhage
 * Sufentanil
 * Suxamethonium
 * Systemic lupus erythematosus
 * Tight fitting neckwear
 * Toluene
 * TAVI (Transaortic Valve Intervention)
 * Trichinosis
 * Tumors of the neck
 * Tumor lysis syndrome
 * Typhoid Fever
 * Typhus
 * Vagal nerve stimulation
 * Vagotonia
 * Valsalva maneuver
 * Valve replacement
 * Vasovagal syncope
 * Verapamil
 * Viral hemorrhagic fever
 * Vomiting
 * Yellow fever
 * Zatebradine

Symptoms
The decreased heart rate can cause a decreased cardiac output resulting in symptoms such as lightheadedness, dizziness, hypotension, vertigo, and syncope.

Sinus bradycardia may lead to no symptoms in a young athlete.

Signs
There may be a wide pulse pressure. If cardiac output is reduced, there may be signs of end organ hypoperfusion.

Laboratory Studies
TFTs should be checked Check electrolytes, Ca, Mg Hypoglycemia should be excluded Consider a toxicologic screen

ECG Characteristics

 * 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

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)

Additional resources

 * ECGpedia: Course for interpretation of ECG
 * The whole ECG - A basic ECG primer
 * 12-lead ECG library
 * Simulation tool to demonstrate and study the relation between the electric activity of the heart and the ECG
 * ECG information from Children's Hospital Heart Center, Seattle
 * ECG Challenge from the ACC D2B Initiative
 * National Heart, Lung, and Blood Institute, Diseases and Conditions Index
 * A history of electrocardiography
 * EKG Interpretations in infants and children

Rzadkokurcz Sinusbradykardi Sinuzal bradikardi