Sinus bradycardia originates in the sinoatrial (SA) node of the heart (also known as the pacemaker) and occurs when an individual’s heart rate is 60 beats per minute or less and otherwise presents as a sinus rhythm on an electrocardiogram (ECG). During sinus bradycardia, the function of the SA node can become compromised due to numerous potential causes, resulting in electrical charges being produced at a reduced rate, thus resulting in a decreased heart rate. Many cases of sinus bradycardia are considered a normal variant. It is not uncommon for this cardiac rhythm to be found incidentally in healthy individuals, particularly when they are sleeping or if they are young adults or athletes (often due to increased vagal tone). Individuals with this cardiac rhythm generally do not become symptomatic until their heart rate is less than 50 beats per minute. However, patients may exhibit functional or relative bradycardia, where their heart rate lies within a normal range of 60-100 beats per minute, but this rate may be insufficient for their needs due to the demand placed upon their body. An example of functional or relative bradycardia is a patient experiencing septic shock, yet presenting a heart rate of 77 beats per minute.
An individual may develop symptoms with sinus bradycardia because, at a slower rate, the heart is unable to pump enough oxygenated blood to the body. This can result in symptoms such as shortness of breath, fatigue, dizziness, or syncope. If a patient is hemodynamically stable, treatment for sinus bradycardia is dependent on the respective cause of this cardiac rhythm and can vary from medication management to the placement of a permanent pacemaker (as examples).
Sinus bradycardia can occur in both adult and pediatric patients. However, this article will focus on this cardiac rhythm in adult patients, utilizing Advanced Cardiovascular Life Support (ACLS) guidelines to navigate care of the patient. Pediatric Advanced Life Support (PALS) algorithms can guide care of a pediatric patient experiencing sinus bradycardia.
Signs or symptoms the patient may experience with sinus bradycardia include:
There are numerous potential causes for the development of sinus bradycardia. Examples include:
Patients with sinus bradycardia may be asymptomatic. However, if the adult patient with sinus bradycardia is symptomatic, has a heart rate of less than 50 beats per minute, and the patient’s symptoms result from poor perfusion due to the decreased heart rate, this patient is presenting with unstable bradycardia. Signs and symptoms of unstable bradycardia may include chest pain, hypotension, an altered mental status, acute heart failure, or shock. If it is determined that an adult patient with bradycardia has a pulse, is symptomatic, and is hemodynamically unstable, the ACLS Adult Bradycardia Algorithm should be utilized to facilitate evaluation and treatment of the patient.
Within the ACLS Adult Bradycardia Algorithm, an initial step is for the medical professional to identify and treat any potential underlying causes of the patient’s condition. This includes identifying the patient’s cardiac rhythm, monitoring their vital signs, managing their airway, and providing supplemental oxygen if needed. Additionally, intravenous (IV) access should be established and a 12-lead ECG should be completed, if available. The medical professional should also evaluate any possible hypoxic and toxicological (H’s & T’s) causes for the patient’s clinical condition. If the patient is not showing any signs or symptoms of poor perfusion due to unstable bradycardia, the patient can be observed and monitored for any potential change in their clinical condition. The patient’s clinical condition and response to treatment may necessitate the medical professional to utilize multiple interventions concurrently while also monitoring for changes to prevent the patient’s clinical condition from deteriorating.
If the patient has no immediately reversible causes and is demonstrating signs or symptoms of poor perfusion as a result of a bradyarrhythmia, the ACLS Adult Bradycardia Algorithm indicates that atropine be administered. Atropine is considered a first-line treatment at a dose of 1 mg intravenously, eligible to be repeated every 3-5 minutes until a cumulative total of 3 mg has been administered. For patients experiencing myocardial infarction or acute coronary ischemia, atropine should be used cautiously, as it may potentially increase the size of the infarct or worsen ischemia. Atropine should not be used in patients who have had a heart transplant, as it can increase the risk of ventricular fibrillation. These patients should be treated with dopamine, epinephrine, or pacing. In general, dopamine or epinephrine infusions may be utilized as second-line options for managing symptomatic bradycardia when this cardiac rhythm does not respond to atropine.
If the patient with bradycardia continues to demonstrate signs and symptoms of unstable bradycardia after the use of medications, transcutaneous pacing (TCP) can be initiated. Transcutaneous pacing transmits an electrical stimulus from an external power source (such as a defibrillator with a pacing function) through electrodes applied to the surface of the patient’s skin. TCP can be performed by ACLS providers, and it is considered noninvasive. It is important to note that TCP can be painful; the patient should be sedated before implementing this intervention if they are conscious (whenever possible). TCP is an intervention to bridge treatment until the patient can receive expert consultation at a higher level of care.
Patients with bradycardia who are hypothermic should be rewarmed to a normothermic state before treatment decisions are made, to avoid the risk of myocardial irritation. Note that TCP is not recommended for patients experiencing hypothermia. However, in patients being treated with therapeutic hypothermia, bradycardia may occur, and the course of treatment will be dependent on the patient’s perfusion status.
While the ACLS Adult Bradycardia Algorithm guides urgent and emergent care of the patient with bradycardia, treatment of bradycardia is focused on the underlying cause of this cardiac rhythm once a patient is hemodynamically stable. For example, it is essential to evaluate the medications a patient is taking, as they may be a potential cause of this cardiac rhythm and should be reviewed and managed under expert care. In some patients (such as those with postinfectious bradycardia), a permanent pacemaker may need to be placed to manage this cardiac rhythm. Generally speaking, continued or long-term monitoring of a patient under expert care in an outpatient setting may be required depending on the cause of the bradycardia.
The medical professional utilizing ACLS or PALS guidelines to care for patients must be able to identify cardiac rhythms in order to provide appropriate, safe, and effective care. An index of cardiac rhythms that the medical professional must be knowledgeable of is available as a resource. Detailed information regarding each cardiac rhythm is presented to help assist in rhythm identification, potential signs or symptoms associated with a cardiac rhythm, possible etiologies, and emergent treatment recommendations. An example of a case study specific to bradycardia can be found here.
American Medical Resource Institute (AMRI) offers multiple resources to prepare you for your Basic Life Support (BLS), ACLS, or PALS certification course. If you prefer to reinforce your learning through questions in a question-bank format to evaluate or strengthen your understanding of BLS, ACLS, or PALS guidelines or principles, we offer practice questions and quiz questions. A library of case studies is also available to assess and reinforce your understanding using scenario-based learning.
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