Sinus Bradycardia


Article Author:
Yamama Hafeez


Article Editor:
Shamai Grossman


Editors In Chief:
Susan Johnson
Alexandra Caley


Managing Editors:
Avais Raja
Orawan Chaigasame
Carrie Smith
Abdul Waheed
Khalid Alsayouri
Kyle Blair
Trevor Nezwek
Radia Jamil
Erin Hughes
Patrick Le
Anoosh Zafar Gondal
Saad Nazir
William Gossman
Hassam Zulfiqar
Navid Mahabadi
Hussain Sajjad
Steve Bhimji
Muhammad Hashmi
John Shell
Matthew Varacallo
Heba Mahdy
Ahmad Malik
Abbey Smiley
Sarosh Vaqar
Mark Pellegrini
James Hughes
Beata Beatty
Daniyal Ameen
Altif Muneeb
Beenish Sohail
Nazia Sadiq
Hajira Basit
Phillip Hynes
Komal Shaheen
Sandeep Sekhon


Updated:
5/14/2019 12:29:47 PM

Introduction

The sinoatrial node (SA) is the default pacemaker and therefore a crucial component of the hearts conduction system. It is located subepicardially and is crescent in shape. In an average adult, a sinoatrial node is 13.5 millimeters in length and is innervated by vagus and sympathetic nerves. The sinoatrial nodal artery supplies blood to the sinoatrial node, it branches off the right coronary artery in 60% of cases, whereas in 40% of cases it comes off the left circumflex coronary artery.[1][2] Sinus bradycardia is a cardiac rhythm with appropriate cardiac muscular depolarization initiating from the sinus node generating less than 60 beats per minute (bpm). Diagnosis of sinus bradycardia requires visualization of an electrocardiogram showing a normal sinus rhythm at a rate lower than 60 bpm. Where a normal sinus rhythm has the following criteria[3][4]:

  • Regular rhythm, with a P wave before every QRS.
  • P wave is upright in leads 1 and 2, P wave is biphasic in V1.
  • The maximum height of a P wave is less than or equal to 2.5 mm in leads 2 and 3.
  • The rate of the rhythm is between 60 bpm and 100 bpm.

Etiology

Sinus bradycardia has many intrinsic and extrinsic etiologies[5]][6][7][8][9][10].

Inherent Etiologies 

  • Chest trauma                                                            
  • Ischemic heart disease
  • Acute myocardial infarction
  • Acute and chronic coronary artery disease
  • Repair of congenital heart disease
  • Sick sinus syndrome
  • Radiation therapy
  • Amyloidosis
  • Pericarditis
  • Lyme disease
  • Rheumatic fever
  • Collagen vascular disease
  • Myocarditis
  • Neuromuscular disorder
  • X-linked muscular dystrophy
  • Familial disorder
  • Inherited channelopathy

Extrinsic Etiologies

  • Vasovagal simulation (endotracheal suctioning)
  • Carotid sinus hypersensitivity
  • Beta-blockers
  • Calcium channel blockers
  • Digoxin
  • Ivabradine
  • Clonidine
  • Reserpine
  • Adenosine
  • Cimetidine
  • Antiarrhythmic Class I to IV
  • Lithium
  • Amitriptyline
  • Narcotics
  • Cannabinoids
  • Hypothyroidism
  • Sleep apnea
  • Hypoxia
  • Intracranial hypertension
  • Hyperkalemia
  • Anorexia nervosa

Epidemiology

In clinical practice, adults over the age of 65 and young athletes of both sexes are commonly known to present with sinus bradycardia. One in 600 adults over the age of 65 has sinus node dysfunction, but more research needs to be done to collect epidemiologic data within the United States and globally for patients with sinus bradycardia.[11]

Pathophysiology

Sinus bradycardia as any of the other bradyarrhythmias is caused by a multitude of intrinsic and extrinsic factors which may compromise the integrity of the sinus node. These factors can cause failure of the impulse formation at the sinus node, impulse conduction at the atrioventricular node or bundle of His-Purkinje fibers.[9]

Histopathology

A specific group of patients with sinus bradycardia may show no nodal histopathology, yet associated findings are as follows[9][12]:

  • Nodal cell reduction and fibrosis
  • Nodal region amyloidosis
  • Sinus node hypoplasia or atrophy

History and Physical

Majority of patients with sinus bradycardia do not have symptoms. Healthy young adults and athletes tend to have an increased vagal tone which keeps them in sinus bradycardia at rest. Also, patients above the age of 65 tend to have sinus bradycardia during sleep secondary to the aging of the sino-atrial node. Using history to relate to the symptoms of a patient with sinus bradycardia on an electrocardiogram is essential to come to the correct diagnosis. Those who present with symptoms may present with fatigue, exercise intolerance, lightheadedness, dizziness, syncope or presyncope, worsening of anginal symptoms, worsening of heart failure or cognitive slowing. When taking a history a health care provider must include relevant questions which help narrow down the differential. Such as any recent medication changes, medication overdoses, chest pain, shortness of breath, history of prior myocardial infarction, symptoms of intermittent palpitations, history of chest trauma, rash or recent tick bite, current or past diagnosis of streptococcus pharyngitis, family history of sinus bradycardia, family history of muscular dystrophy. Moreover, physical exam findings should be correlated with the history given by the patient to help narrow the differential diagnosis, such as any murmur heard during the physical exam or any skin exam findings of a developing rash.[13][14]

Evaluation

The most significant component of evaluation for a patient who presents with signs and symptoms of sinus bradycardia is history and physical exam. These should include vital signs (respiratory rate, blood pressure, temperature, and heart rate) and an electrocardiogram. During evaluation it should be established whether the patient is hemodynamically unstable, evaluation for this includes high blood pressure, altered mental status or difficulty breathing. If the patient is healthy, athletic and has no symptoms than no further medical intervention is required. On the contrary, in older individuals, sinus bradycardia may point towards an unhealthy sinus node. Patients with congestive heart failure often have sinus bradycardia. These patients may have compromised blood supply from the right coronary artery or left circumflex artery to the sinus node secondary to some underlying ischemic heart disease.[15]

Treatment / Management

A patient in sinus bradycardia should be evaluated for hemodynamic instability. If found to be hemodynamically unstable patient can be treated with intravenous (IV) atropine 0.5 mg push every 3 to 5 minutes up to 3 mg total. If the patient's symptoms and heart rate do not improve, the patient is a candidate for a temporary pacemaker. If the patient on arrival is hemodynamically stable but has signs and symptoms of acute myocardial infarction, they should be treated for an acute myocardial infarction appropriately. If there are no signs or symptoms of acute myocardial infarction in a hemodynamically stable patient, then workup should be initiated for an infectious etiology (including chest x-ray, blood cultures, urinary analysis, viral panel) together with thyroid function tests. If a patient is found to have an infectious etiology or a thyroid abnormality, the patient should be appropriately treated for these underlying etiologies and re-evaluated. Upon re-evaluation, if this patient is no longer symptomatic and his heart rate returns to within normal limits patient could be evaluated for a possible sick sinus syndrome or a long-term implantable loop recorder. While management decisions are being made for a patient with sinus bradycardia patient's medication list should also be reviewed for possible causes of bradycardia, and those medications should be withdrawn if possible. If a patient has comorbid conditions that require him to be on certain medications which may be causing his sinus bradycardia than in that case-patient may be a candidate for a permanent pacemaker. In cases where medication can be withdrawn than medication, withdrawal is made and if symptoms and heart rate still do not improve than the patient may be evaluated for a permanent pacemaker.[16]

Differential Diagnosis

Differentiation of sinus bradycardia from other bradyarrhythmias is done by establishing a relationship between P waves and QRS complexes on an electrocardiogram. Nondiscernible P waves are associated with junctional or ventricular escape rhythms. Whereas, second or third degree AV blocks will have more than 1-to-1 relationship between P waves and QRS complexes[11][12]

Rhythms on the differentials are:

  • Sick sinus rhythm
  • Wandering atrial pacemaker
  • Junctional escape rhythm
  • Ventricular escape rhythm

Prognosis

Prognosis is good when the rhythm is promptly identified by a healthcare provider. 

Complications

If not identified promptly symptomatic complications such as syncope, fatigue or dizziness can occur. 

Deterrence and Patient Education

Multiple resources are available for providers to help educate patients about this rhythm and its potential symptomatic complications. A patient who comes to the hospital or a clinic and has this rhythm identified should be provided with educational pamphlets if they are available at the facility.

 

 

Pearls and Other Issues

There is a growing clinical consensus to lower the diagnosis threshold of sinus bradycardia to less than 50 bpm as there is a significant population size with a resting heart rate between 50 to 60 bpm. At present, the diagnostic consensus remains at a rate lower than 60 bpm with only the American College of Cardiology/American Heart Association/American College of Physicians–American Society of Internal Medicine (ACC/AHA/ACP–ASIM) Task Force recommending that it be diagnosed at 50 bpm.[4]

Enhancing Healthcare Team Outcomes

Educating patients at risk for this rhythm and making a closed loop communication between them and their providers can help further improve the management of these rhythms.


Interested in Participating?

We are looking for contributors to author, edit, and peer review our vast library of review articles and multiple choice questions. In as little as 2-3 hours you can make a significant contribution to your specialty. In return for a small amount of your time, you will receive free access to all content and you will be published as an author or editor in eBooks, apps, online CME/CE activities, and an online Learning Management System for students, teachers, and program directors that allows access to review materials in over 500 specialties.

Improve Content - Become an Author or Editor

This is an academic project designed to provide inexpensive peer-reviewed Apps, eBooks, and very soon an online CME/CE system to help students identify weaknesses and improve knowledge. We would like you to consider being an author or editor. Please click here to learn more. Thank you for you for your interest, the StatPearls Publishing Editorial Team.

Sinus Bradycardia - Questions

Take a quiz of the questions on this article.

Take Quiz
A 34-year-old is about to undergo an elective surgery. The anesthesiologist notes that the heart rate is 38 beats per minute. Which of the following is an appropriate decision in the management of this patient?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
A patient is complaining of chest pain. An electrocardiogram (EKG) shows sinus bradycardia at 38 beats per minute with occasional premature ventricular contractions. Which of the following are most appropriate for treatment?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
Which of the following conditions is treated with atropine?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
A 38-year-old male with a past medical history of hypertension and coronary artery disease presents to an outpatient clinic. He states that he has been experiencing dizziness after sitting up from his recliner at night for the last 2 months. AN ECG shows sinus rhythm at a rate of 52 beats/min. An adult patient with sinus bradycardia will have a heart rate less than what threshold?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
Select the diagnosis not associated with sinus bradycardia.



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
What is the treatment of choice for symptomatic bradycardias if atropine cannot be given?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
In an athlete, which arrhythmia is considered normal?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
A patient has a resting heart rate of 50 bpm that is regular. What is the correct term for this?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
A 53-year-old male has a past medical history of uncontrolled type 2 diabetes mellitus (hemoglobin A1C of 10), coronary artery disease, and hyperlipidemia. He is exercising on a stationary bicycle. Which of the following is an abnormal response to exercise?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
What is the best agent to increase heart rate for a bradycardic transplanted heart?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
A 58-year-old female who resides in California and has a past medical history of type II diabetes mellitus, rheumatoid arthritis, and osteoarthritis presents with symptoms of fatigue and weakness, which started 3 weeks ago. Her vitals upon triage at the clinic are a blood pressure of 120/87 mmHg, temperature 98.0 F, pulse oximetry 97% on room air, and heart rate 50 beats/min. An electrocardiogram is done which shows sinus rhythm with a heart rate of 57 beats/min. She denies any chest pain, fevers, chills, cough, shortness of breath, or recent travel. Which of the following is the best next test to order?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
A 43-year-old female with past medical history of hypertension, type 2 diabetes mellitus, coronary artery disease, and hyperlipidemia presents to her primary care physician’s clinic for follow up. Her vitals during this visit are blood pressure 126/75 mmHg, heart rate of 53 beats per minute, respiratory rate of 17/minute and oxygen saturation of 97% on room air. EKG shows sinus bradycardia. Her home medications include amlodipine 5 mg daily, hydrochlorothiazide 12.5 mg daily, lisinopril 10 mg daily, and metoprolol succinate 12.5 mg daily. Which of the following is the next step in management for this patient?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up

Sinus Bradycardia - References

References

Normal sinus heart rate: sinus tachycardia and sinus bradycardia redefined., Spodick DH,, American heart journal, 1992 Oct     [PubMed]
ACC/AHA clinical competence statement on electrocardiography and ambulatory electrocardiography. A report of the ACC/AHA/ACP-ASIM Task Force on Clinical Competence (ACC/AHA Committee to Develop a Clinical Competence Statement on Electrocardiography and Ambulatory Electrocardiography)., Kadish AH,Buxton AE,Kennedy HL,Knight BP,Mason JW,Schuger CD,Tracy CM,Boone AW,Elnicki M,Hirshfeld JW Jr,Lorell BH,Rodgers GP,Tracy CM,Weitz HH,, Journal of the American College of Cardiology, 2001 Dec     [PubMed]
Arrhythmias documented by 24 hour continuous electrocardiographic monitoring in 50 male medical students without apparent heart disease., Brodsky M,Wu D,Denes P,Kanakis C,Rosen KM,, The American journal of cardiology, 1977 Mar     [PubMed]
Point mutation in the HCN4 cardiac ion channel pore affecting synthesis, trafficking, and functional expression is associated with familial asymptomatic sinus bradycardia., Nof E,Luria D,Brass D,Marek D,Lahat H,Reznik-Wolf H,Pras E,Dascal N,Eldar M,Glikson M,, Circulation, 2007 Jul 31     [PubMed]
Familial sinus bradycardia associated with a mutation in the cardiac pacemaker channel., Milanesi R,Baruscotti M,Gnecchi-Ruscone T,DiFrancesco D,, The New England journal of medicine, 2006 Jan 12     [PubMed]
Cannabinoids and Symptomatic Bradycardia., Heckle MR,Nayyar M,Sinclair SE,Weber KT,, The American journal of the medical sciences, 2018 Jan     [PubMed]
Friedreich's ataxia (FA) associated with diabetes mellitus type 1 and hypertrophic cardiomyopathy: analysis of a FA family., Gucev Z,Tasic V,Jancevska A,Jordanova NP,Koceva S,Kuturec M,Sabolic V,, Medicinski arhiv, 2009     [PubMed]
Cardiac involvement in the muscular dystrophies., Silvestri NJ,Ismail H,Zimetbaum P,Raynor EM,, Muscle & nerve, 2017 Nov 11     [PubMed]
Cardiac involvement in myotonic dystrophy: The role of troponins and N-terminal pro B-type natriuretic peptide., Valaperta R,De Siena C,Cardani R,Lombardia F,Cenko E,Rampoldi B,Fossati B,Brigonzi E,Rigolini R,Gaia P,Meola G,Costa E,Bugiardini R,, Atherosclerosis, 2017 Dec     [PubMed]
Pathology of sinoatrial node. Correlations with electrocardiographic findings in 111 patients., Thery C,Gosselin B,Lekieffre J,Warembourg H,, American heart journal, 1977 Jun     [PubMed]
New insights into pacemaker activity: promoting understanding of sick sinus syndrome., Dobrzynski H,Boyett MR,Anderson RH,, Circulation, 2007 Apr 10     [PubMed]
Remodeling of sinus node function in patients with congestive heart failure: reduction in sinus node reserve., Sanders P,Kistler PM,Morton JB,Spence SJ,Kalman JM,, Circulation, 2004 Aug 24     [PubMed]
Reconstruction of the human sinoatrial node., Truex RC,Smythe MQ,Taylor MJ,, The Anatomical record, 1967 Dec     [PubMed]
Structure, function and clinical relevance of the cardiac conduction system, including the atrioventricular ring and outflow tract tissues., Dobrzynski H,Anderson RH,Atkinson A,Borbas Z,D'Souza A,Fraser JF,Inada S,Logantha SJ,Monfredi O,Morris GM,Moorman AF,Nikolaidou T,Schneider H,Szuts V,Temple IP,Yanni J,Boyett MR,, Pharmacology & therapeutics, 2013 Aug     [PubMed]
Part 8: adult advanced cardiovascular life support: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care., Neumar RW,Otto CW,Link MS,Kronick SL,Shuster M,Callaway CW,Kudenchuk PJ,Ornato JP,McNally B,Silvers SM,Passman RS,White RD,Hess EP,Tang W,Davis D,Sinz E,Morrison LJ,, Circulation, 2010 Nov 2     [PubMed]
Survey of cardiac pacing in the United States in 1989., Bernstein AD,Parsonnet V,, The American journal of cardiology, 1992 Feb 1     [PubMed]

Disclaimer

The intent of StatPearls is to provide practice questions and explanations to assist you in identifying and resolving knowledge deficits. These questions and explanations are not intended to be a source of the knowledge base of all of medicine, nor is it intended to be a board or certification review of CNS-Adult-Gerontology. The authors or editors do not warrant the information is complete or accurate. The reader is encouraged to verify each answer and explanation in several references. All drug indications and dosages should be verified before administration.

StatPearls offers the most comprehensive database of free multiple-choice questions with explanations and short review chapters ever developed. This system helps physicians, medical students, dentists, nurses, pharmacists, and allied health professionals identify education deficits and learn new concepts. StatPearls is not a board or certification review system for CNS-Adult-Gerontology, it is a learning system that you can use to help improve your knowledge base of medicine for life-long learning. StatPearls will help you identify your weaknesses so that when you are ready to study for a board or certification exam in CNS-Adult-Gerontology, you will already be prepared.

Our content is updated continuously through a multi-step peer review process that will help you be prepared and review for a thorough knowledge of CNS-Adult-Gerontology. When it is time for the CNS-Adult-Gerontology board and certification exam, you will already be ready. Besides online study quizzes, we also publish our peer-reviewed content in eBooks and mobile Apps. We also offer inexpensive CME/CE, so our content can be used to attain education credits while you study CNS-Adult-Gerontology.