An atrioventricular (AV) block is also called a heart block. A first-degree AV block occurs when electrical conduction through the AV node of the heart is delayed and the impulse between the atria and ventricles is slowed. However, there is no interruption in the conduction between the atria and the ventricles.
With a first-degree AV block, this delay in conduction often presents due to a minor defect in AV conduction that occurs either at or below the AV node. Typically, if the patient’s PR interval remains less than 0.30 seconds, this rhythm is not disruptive to patients. However, if the PR interval is greater than 0.30 seconds, increased symptom development can occur due to reduced ventricular filling within the heart.
In younger patients, the cause of this rhythm tends to result from increased vagal tone, whereas in older patients, this rhythm is frequently due to fibrosis within the cardiac conduction system. This rhythm is often initially identified on an electrocardiogram (ECG), as patients typically have no symptoms.
In general, most patients with a first-degree AV block have no symptoms. However, patients with increased PR intervals that extend beyond 0.30 seconds may experience symptoms such as lightheadedness, dyspnea, chest pain, general malaise, or syncope.
This rhythm can be a normal variant for an individual.
Risk factors for the development of a first-degree AV block include:
Patients with a first-degree AV block are almost always asymptomatic. Often, this rhythm is found incidentally on an ECG, as patients may be unaware of this rhythm disturbance. For most patients with a first-degree AV block, this rhythm does not require treatment.
However, should the adult patient with a bradyarrhythmia such as a first-degree AV block be symptomatic and have a heart rate that is generally less than 50 beats per minute, the Advanced Cardiovascular Life Support (ACLS) Adult Bradycardia Algorithm should be utilized to facilitate evaluation and treatment of the patient. If the patient with bradycardia has a first-degree AV block (or other bradyarrhythmia) and is symptomatic, it is important to determine if their signs or symptoms are due to the reduced heart rate. If so, this would then be considered unstable bradycardia.
Signs and symptoms of unstable bradycardia may include:
If the patient is not demonstrating signs or symptoms of poor perfusion (as described above), the patient can be observed and monitored for any potential change in their clinical condition. However, if it is determined that the adult patient with a bradyarrhythmia is symptomatic, unstable (showing signs or symptoms of poor perfusion), and has a pulse, the ACLS Adult Bradycardia Algorithm should be followed by the healthcare provider to guide further evaluation and treatment.
The ACLS Adult Bradycardia Algorithm recommends that the ACLS Primary Assessment be completed by the healthcare provider as an initial step to identify and treat potential underlying causes for the patient’s condition. Examples of necessary elements included within the ACLS Primary Assessment are managing the patient’s airway, providing supplemental oxygen if needed, determining the patient’s cardiac rhythm, and monitoring their vital signs.
In addition, intravenous (IV) access should be established, a 12-lead ECG should be obtained if possible, and the healthcare provider should assess and consider possible hypoxic and toxicological (H’s & T’s) causes for the patient’s clinical condition. The patient’s clinical condition and their response to treatment may require the healthcare provider to utilize multiple interventions simultaneously while continuing to monitor for any changes to prevent the patient’s condition from deteriorating.
If the patient is symptomatic and does not have any immediately reversible causes and is demonstrating signs or symptoms of poor perfusion as a result of a bradyarrhythmia, the ACLS Adult Bradycardia Algorithm recommends that atropine be administered. Atropine is considered a first line treatment at a dose of 1 mg intravenously, and is eligible to be repeated every 3-5 minutes until a total dose of 3 mg has been administered. Dopamine or epinephrine infusions may be utilized as second line options for the management of a symptomatic bradyarrhythmia.
If the patient experiencing bradyarrhythmia continues to display signs and symptoms of unstable bradycardia after the use of medications, transcutaneous pacing (TCP) can be utilized. 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 in strategic locations near the heart.
ACLS providers are able to perform TCP, but this treatment can be painful for the patient. If the patient is conscious, they should be sedated prior to implementing this intervention, if possible. TCP is considered an intervention to bridge treatment until the patient can be transferred to a higher level of care for expert consultation. Such a situation is highly uncommon.
Most often, patients with a first-degree AV block do not experience hemodynamic instability and do not require treatment. This rhythm is largely considered benign. If medications contribute to the development of this rhythm, they can be modified or removed from the patient’s medication regimen under expert care and monitoring. As patients with a first-degree AV block advance in age, the likelihood of developing atrial fibrillation or more progressive AV blocks increases. Continued and regular monitoring under the care of an expert can help patients with a first-degree AV block identify potential worsening cardiac changes or complications throughout their lifespan.
Healthcare providers utilizing ACLS or PALS to care for patients need to be able to quickly identify cardiac rhythms. A detailed index of common cardiac rhythms that healthcare providers must know is available as a reference with information about each pattern.
Beyond that, multiple other resources are available on the American Medical Resource Institute (AMRI) website to prepare you for your ACLS certification course. Are you searching for additional opportunities to evaluate or strengthen your knowledge and skills? Practice questions and a library of case studies are available to determine and reinforce your understanding of ACLS, Pediatric Advanced Life Support (PALS), and Basic Life Support (BLS) principles and protocols.
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