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 not unexpected 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.

Causes

Causes by Organ System

Cardiovascular	Carotid sinus hypersensitivity, Carotid sinus syndrome, Miller-Dieker syndrome, Myocardial infarction, Myocardial Infarction, particularly inferior MI, Myocarditis, Myotonic muscular dystrophy, Neurocardiogenic syncope, Sick sinus syndrome, Valsalva maneuver, Vasovagal syncope,Hemochromatosis, Endocarditis, Distichiasis-heart and vasculature anomalies-sinus bradycardia
Chemical / poisoning	Carbamates, Dimethyl sulfoxide, Grayanotoxin, Lily of the valley, Nerve gas, Organophosphates, Toluene
Dermatologic	No underlying causes
Drug Side Effect	Alfentanil, Ambenonium, Amiodarone, Atenolol, Beta blocker, Bethanechol, Bupivacaine, Calcium channel blocker, Cilobradine, Clonidine, Corgard, Diabetic autonomic neuropathy, Digitalis, Distigmine, Dronedarone, Fentanyl, Fingolimod, Ivabradine, Lidocaine, Lithium, Lofexidine, Muscarinic agonist, Nadolol, Neostigmine, Paclitaxel, Physostigmine, Procainamide , Propranolol, Quinidine, Reserpine, Sedatives, Sotalol, Sufentanil, Suxamethonium, Verapamil, Zatebradine, Diltiazem, Deserpidine
Ear Nose Throat	No underlying causes
Endocrine	Cretinism, Hypothyroidism, Hemochromatosis
Environmental	Decompression sickness, High altitude sickness
Gastroenterologic	Nausea, Hemochromatosis, Vomiting
Genetic	Hemochromatosis, Miller-Dieker syndrome
Hematologic	Hemochromatosis
Iatrogenic	Cardiac catheterization, Cardiac transplant, Congenital Heart Disease correction, Heart transplant, Transaortic Valve Intervention, Valve replacement, Hemochromatosis
Infectious Disease	Babesiosis, Brucellosis, Chagas disease, Dengue fever, Endocarditis, Legionella, Leptospirosis, Lyme disease, Malaria,Meningitis, Psittacosis, Q fever, Rheumatic fever, Rocky mountain spotted fever, Sepsis, Trichinosis, Typhoid Fever, Typhus, Viral hemorrhagic fever, Yellow fever, Diptheria
Musculoskeletal / Ortho	Hemochromatosis, Myotonic muscular dystrophy, Rheumatoid arthritis, Cervical spine injury
Neurologic	Cerebral edema, Dysautonomia, Increased intracranial pressure, Raised intracranial pressure, Seizure, Subarachnoid hemorrhage, Vagal stimulation, Miller-Dieker syndrome, Neurocardiogenic syncope, Vasovagal syncope, Deserpidine, Meningitis, Glioblastoma, Acute spinal cord injury
Nutritional / Metabolic	Kwashiorkor, Malnutrition, Hypercalcemia, Hyperkalemia, Hypermagnesemia, Hypoglycemia, Hypokalemia, Starvation
Obstetric/Gynecologic	Fetal distress
Oncologic	Glioblastoma, Tumor lysis syndrome, Tumors of the neck
Opthalmologic	Glaucoma, Distichiasis-heart and vasculature anomalies-sinus bradycardia,
Overdose / Toxicity	Alfentanil, Ambenonium, Amiodarone, Atenolol, Beta blocker, Bethanechol, Bupivacaine, Calcium channel blocker, Cilobradine, Clonidine, Corgard, Diabetic autonomic neuropathy, Digitalis, Distigmine, Dronedarone, Fentanyl, Fingolimod, Ivabradine, Lidocaine, Lithium, Lofexidine, Muscarinic agonist, Nadolol, Neostigmine, Paclitaxel, Physostigmine, Procainamide , Propranolol, Quinidine, Reserpine, Sedatives, Sotalol, Sufentanil, Suxamethonium, Verapamil, Zatebradine, Diltiazem, Deserpidine
Psychiatric	Anorexia nervosa
Pulmonary	Hypoxia, Sleep apnea, Hypercapnia
Renal / Electrolyte	No underlying causes
Rheum / Immune / Allergy	Rheumatoid arthritis, Sarcoidosis, Scleroderma, Systemic lupus erythematosus, Rheumatic fever, Amyloidosis
Sexual	No underlying causes
Trauma	Acute spinal cord injury, Cervical spine injury
Urologic	Micturition syncope
Dental	No underlying causes
Miscellaneous	Aging, Amyloidosis, Coughing, Decompression sickness, Defacation, Electrocution, Elite athlete, High altitude sickness, Hypercalcemia, Hypercapnia, Hyperkalemia,Hypermagnesemia, Hypoglycemia, Hypokalemia, Hypothermia, Physical training, Post-tussive syncope, Sleep, Standing for a prolonged period of time may trigger the Bezold-Jarisch reflex, Starvation, Tight fitting neckwear, Vomiting, Valsalva maneuver, Nausea

Causes in Alphabetical Order

Acute spinal cord injury Aging Alfentanil Ambenonium Amiodarone Amyloidosis Anorexia nervosa Atenolol Babesiosis Beta blocker Bethanechol Brucellosis Bupivacaine Calcium channel blocker Carbamates Cardiac catheterization Cardiac transplant Carotid sinus hypersensitivity Carotid sinus syndrome 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 Diptheria Distichiasis-heart and vasculature anomalies-sinus bradycardia Distigmine Dronedarone Dysautonomia Electrocution Elite athlete Endocarditis Fentanyl Fetal distress Fingolimod Glaucoma Glioblastoma Grayanotoxin Heart transplant Hemochromatosis High altitude sickness Hypercalcemia Hypercapnia Hyperkalemia Hypermagnesemia Hypoglycemia Hypokalemia Hypothermia Hypothyroidism Hypoxia Increased intracranial pressure Ivabradine Kwashiorkor Legionella Leptospirosis

Lidocaine Lily of the valley Lithium Lofexidine Lyme disease Malaria Malnutrition Meningitis Micturition syncope Miller-Dieker syndrome Muscarinic agonist Myocardial infarction Myocardial Infarction, particularly inferior MI Myocarditis Myotonic muscular dystrophy Nadolol Nausea Neostigmine Nerve gas Neurocardiogenic syncope Organophosphates Paclitaxel Physical training Physostigmine Post-tussive syncope Procainamide Propranolol Psittacosis Q fever Quinidine Raised intracranial pressure Reserpine Rheumatic fever Rheumatoid arthritis Rocky mountain spotted fever Sarcoidosis Scleroderma Sedatives Seizure Sepsis Sick sinus syndrome Sleep Sleep apnea Sotalol 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 Transaortic Valve Intervention Trichinosis Tumor lysis syndrome Tumors of the neck Typhoid Fever Typhus Vagal stimulation Valsalva maneuver Valve replacement Vasovagal syncope Verapamil Viral hemorrhagic fever Vomiting Yellow fever Zatebradine

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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Below ECG images show sinus bradycardia.

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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)

”

Sources

• Image courtesy of ECGpedia

See also

• Sinus arrest
• Junctional bradycardia

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