Bradyarrhythmias
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Article at a Glance
- Bradycardia is defined as a heart rate below 60 beats per minute; however, symptoms do not usually occur unless the heart rate is below 50 beats per minute.
- Hypoxemia is often associated with bradyarrhythmias, and oxygen supplementation may improve the patient’s condition.
- It is important to determine whether symptoms are related to the slow heart rate or to another clinical condition.
- While first-degree atrioventricular (AV) block is rarely symptomatic and usually benign, second- and third-degree AV blocks can be associated with severe signs and symptoms, such as shock and pulmonary edema.
Adult Bradycardia with a Pulse Algorithm
A bradyarrhythmia is a medical condition in which a patient presents with a heart rate of less than 60 beats per minute.1 Symptoms do not usually present until the heart rate is less than 50 beats per minute. Refer to Box 1 of the Adult Bradycardia With a Pulse Algorithm.What is Bradyarrhythmia?
Bradycardia is defined as a heart rate of fewer than 60 beats per minute.
Due to significant loss of cardiac output in bradycardia, patients will show signs and symptoms of hypoxemia. To compensate, they will show an increase in respiratory effort (i.e., tachypnea). Patients’ vital signs must be monitored with special attention to oxygenation and ventilation. A pulse oximeter is recommended to monitor arterial oxygen saturation. When a patient shows signs of hypoxemia (low oxygen saturation < 94%), provide oxygen supplementation at 100% fraction inspired oxygen (FiO2).2 Close monitoring is recommended at this point with a cardiac monitor. A 12-lead electrocardiogram (ECG) must be performed as well. Intravenous access is likewise recommended in case emergency medications are required. With all of this information, the clinician attempts a possible diagnosis of the patient’s medical condition. Refer to Box 2 of the Adult Bradycardia With a Pulse Algorithm. The next questions to answer are: The answers to these questions lead the clinician to potential interventions and treatments for the patient.Hypoxemia in Bradycardia
Related Video – Bradyarrhythmia Treatment
If, after providing oxygen and the patient’s symptoms improve, then the clinician may opt to monitor and observe the patient, either in the emergency department or on a cardiac ward. If the bradyarrhythmia is persistent and the patient remains symptomatic or becomes unstable, the clinician then determines if the patient is hypotensive, has an altered mental status, shows signs of shock, has ischemic chest discomfort, or is in acute heart failure. These are severe conditions resulting from the bradyarrhythmia. Refer to Box 3 of the Adult Bradycardia With a Pulse Algorithm.Stable versus Unstable
Hypotension is one of the symptomatic conditions that may result from bradyarrhythmia.
For example, a second-degree atrioventricular block (or Mobitz type II) can cause severely decreased cardiac output, which can compromise coronary blood flow and lead to acute myocardial infarction. That example highlights a symptomatic bradycardia that is directly related to the slow heart rate.
Read: Bradyarrhythmia Treatment
Atrioventricular (AV) blocks can be caused by acute myocardial infarction, medications, or electrolyte imbalances.3 First-degree AV blocks are often benign, and ECG findings will show an increased PR interval of more than 0.20 seconds.AV Blocks
In a first-degree AV block, the PR interval is longer than 0.20 seconds.
Second-degree AV block, Mobitz type I, is often referred to as Wenckebach. It is characterized by a lengthening PR interval until a QRS complex is dropped.
In a second-degree AV block, impulses are blocked below the AV node. The arrow indicates a “dropped”
Second-degree AV block, Mobitz type II, blocks impulses below the AV node within the His-Purkinje system.4 This type of AV block almost always causes symptoms. It is commonly associated with acute myocardial infarction and may transform into a third-degree AV block.
In the ECG tracing for second-degree AV block, Mobitz type II, the first and second prolonged PR intervals have a fixed duration followed by a QRS complex, and the third QRS complex is dropped.
Second-degree AV block, Mobitz type II
Third-degree AV block occurs at the atrioventricular node. The atria beat at their own rate while the ventricular rate is determined by a junctional or ventricular pacemaker. The P waves march through and are unrelated to the QRS complex. The third-degree AV block may be permanent or transient.
A third-degree AV-block occurs at the AV node.
Related Video – ECG Rhythm Review – Third-Degree Heart Block
This article summarizes what the clinician needs to look for in a patient with bradycardia and how to recognize and evaluate first-, second-, and third-degree AV blocks.
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Editorial Sources
ACLS Certification Association (ACA) uses only high-quality medical resources and peer-reviewed studies to support the facts within our articles. Explore our editorial process to learn how our content reflects clinical accuracy and the latest best practices in medicine. As an ACA Authorized Training Center, all content is reviewed for medical accuracy by the ACA Medical Review Board.
1. Kevin McLendon; Charles V. Preuss. Atropine. National Library of Medicine. 2022.
2. American Heart Association. Management of Symptomatic Bradycardia and Tachycardia. 2005.
3. San Mateo County Emergency Medical Services. Symptomatic Bradycardia. 2019.
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