ACLS Case: Symptomatic Bradycardia
ACLS Case: Symptomatic Bradycardia
Introduction
There is one key point that rescuers must remember when managing a patient with bradycardia. First, bradycardia is not always harmful. Some people, such as athletes, may have a low resting heart rate because they are in excellent physical condition and the heart muscle is working efficiently. Individuals taking certain medications such as beta-blockers may also have low heart rates related to the effects of treatment.
The critical distinction to make when determining that a patient has an abnormally slow rate is whether it is causing any symptoms that may indicate a problem.
For this case, students must be able to recognize and differentiate between several bradyarrhythmias:
- Sinus bradycardia
- First-degree AV block
- Second-degree AV block: Type l (Wenckebach/Mobitz l)
- Second-degree AV block: Type II (Mobitz II)
- Third-degree AV block
Bradycardia is said to be symptomatic when the heart rate is slow, the patient has symptoms, and the symptoms are related to the slow heart rate.
Bradycardia Signs and Symptoms
Short Description
This algorithm outlines the steps to guide the responder to efficiently assess the patient and manage bradycardia.
Algorithm at a Glance
- The responder quickly identifies bradycardia with a pulse.
- The goal is to identify and treat the underlying cause of bradycardia.
- If the patient is symptomatic, treatment begins immediately to prevent deterioration.
- If the patient is not symptomatic, the patient is closely monitored.
Goals for the Management of Adult Patients with Bradycardia
The team must succeed in the following goals to successfully manage bradycardia:
- Recognize and differentiate among several bradyarrhythmias:
- Sinus bradycardia
- First-degree AV block
- Second-degree AV block: Type l (Wenckebach/Mobitz l)
- Second-degree AV block: Type II (Mobitz II)
- Third-degree AV block
- Recognize the signs and symptoms of symptomatic bradycardia.
Related Video: Understanding the Adult Bradycardia with a Pulse Algorithm
The Adult Bradycardia with Pulse Algorithm
This algorithm was created to present the steps for assessing and managing bradycardia with a pulse.
Adult Bradycardia With Pulse Algorithm
Box 1: Identification of Bradycardia
Bradycardias are heart rates < 60 bpm. When symptoms arise, the rate has usually fallen to < 50 bpm, and this is the working definition of bradycardia in the AHA algorithm.
Box 2: Identifying and Treating the Underlying Cause
Bradycardia causes a significant decrease in cardiac output, which leads to the signs and symptoms associated with bradyarrhythmias. It is vital to identify symptomatic bradycardia and begin treatment.
The responder must ensure that the patient’s airway is patent and administer oxygen if hypoxemic. The team monitors oxygen saturation continuously.
Cardiac monitoring should be initiated to identify the rhythm. It is essential to obtain IV or IO access for fluid and medication therapy. The team monitors the patient’s blood pressure and obtains a 12-lead ECG if that does not delay therapy.
Box 3: Bradycardia With Symptoms?
Untreated symptomatic bradycardia can lead to cardiac arrest. The team assesses for signs and symptoms of hemodynamic instability, including:
- Altered mentation
- Hypotension
- Signs of shock
- Chest discomfort
- Heart failure
If the patient is hemodynamically stable, the team proceeds to Box 4; if hemodynamically unstable, they proceed to Box 5.
Hypotension, or low blood pressure, is one of the symptoms of bradycardia.
Box 4: Treatment of Asymptomatic Bradycardia
If the patient has no severe signs and symptoms associated with bradycardia, the team continues to monitor and observe. Continuous reassessment is essential, as the patient’s condition may deteriorate.
Box 5: Treatment of Symptomatic Bradycardia
Medication, electrolyte imbalance, or myocardial disease secondary to acute MI can cause AV blocks. It is critical for the team to determine if the symptoms are caused by the bradycardia. If not, they treat the underlying cause.
Key Takeaway:
The most important question before treating bradycardia is whether the patient’s symptoms are caused by the bradycardia or some other issue.
Treatment
Atropine, an anticholinergic drug, is the first-line drug for the treatment of symptomatic bradycardia. Atropine increases AV nodal conduction and thus improves the symptoms of bradycardia. This drug may be used to temporarily improve bradycardia until the team discovers a more permanent solution, such as pacing.
For this indication, atropine is given at a dose of 1.0 mg IV every 3 to 5 minutes up to a maximum of 3 mg. It should be noted that atropine can cause further bradycardia if the clinician administers a dose < 0.5 mg.
The first line of treatment for symptomatic bradycardia is atropine.
In cases of AMI, atropine should be used with caution because an increase in heart rate may step up myocardial oxygen demand and worsen the area of ischemia or infarction. Atropine is ineffective in heart transplant patients because they lack vagal innervation.
Bradyarrhythmias unlikely to respond to atropine are second-degree AV block, Mobitz type II, and third-degree AV block with a wide QRS complex that represents the block to be non-nodal. These blocks are likely to need transcutaneous pacing.
Related Video: Atropine – ACLS Drugs
When treating bradycardia, it is important for the team to quickly recognize the bradycardia rhythms.
Related Video: ECG Rhythm Review – Sinus Bradycardia
Sinus Bradycardia
Severe bradycardia, which brings an increased risk for cardiac arrest, will be accompanied by clinical signs such as hypotension, altered mental status, shock, chest discomfort, and acute heart failure.
Medications, electrolyte imbalances, or myocardial diseases secondary to AMI can cause AV blocks.
An ECG strip displays sinus bradycardia.
Related Video: One Quick Question What are the First-Degree Heart Block Criteria?
First-Degree AV block
First-degree heart blocks are often benign, and their ECG findings show an increased PR interval of more than 0.20 seconds.
The AV node maintains the sinus impulse longer than usual before it is conducted through the ventricles, but each impulse is conducted. Once into the ventricles, conduction proceeds normally.
Related Video: One Quick Question: What are the Second Degree Heart Block Criteria?
Second-Degree AV Block Type I
In second-degree heart block (Wenckebach type I), the sinus node initiates impulses, and each one remains in the AV node a little longer than that preceding it until one is blocked completely. The conducted impulses travel through the ventricles normally.
Related Video: ECG Rhythm Review – Second-Degree Heart Block (Type 2)
Second-Degree AV Block Type II
Second-degree AV block (Mobitz Type II) is frequently associated with AMI and may transform into third-degree AV block, causing severe bradycardia. Immediate treatment in these cases is necessary. Impulses are blocked below the AV node within the His-Purkinje system, and this causes symptoms.
Characteristic in this ECG tracing is that the PR intervals have a fixed duration and the P waves have a constant rate. Conducted beats are followed by a QRS complex, and intermittently there are non-conducted P waves, after which the QRS is dropped.
This may or may not follow a pattern, but when there are a predictable number of P waves relative to QRS complexes, the rhythm will be described as a ratio, e.g., 2:1 Mobitz II block.
Related Video: ECG Rhythm Review – Third-Degree Heart Block
Third-Degree AV Block
The heart block occurs at the AV node in third-degree AV block. The atria beat at their own rate while a junctional or ventricular pacemaker determines the ventricular rate. The P waves march through and are unrelated to the QRS complexes, which occur at a slower rate, and this generally causes symptoms. Third-degree AV block may be permanent or transient.
Box 6: Further Considerations
The team considers expert consultations and transvenous pacing if symptomatic bradycardia persists.
Alternative Drugs to Consider
Alternative drugs for symptomatic bradycardia are vasoactive medications such as dopamine and epinephrine that are used if atropine fails to achieve its therapeutic effect. If a β-blocker or calcium channel blocker is causing the bradycardia, the following alternative drugs should be considered.
Dopamine
If bradycardia is associated with hypotension, dopamine can be administered as an alternative to atropine. It is given via IV infusion at a rate of 5–20 mcg/kg/min and titrated until the patient responds.
Dopamine is a catecholamine with α- and β-adrenergic effects. It can increase the heart rate at low doses, whereas it is more likely to cause vasoconstriction at higher doses.
Related Video: Dopamine – ACLS Drugs
Epinephrine
Like dopamine, epinephrine is also a catecholamine with α- and β-adrenergic effects, and the clinician may consider using it as a substitute for atropine. Epinephrine is administered via IV infusion at a rate of 2–10 mcg/min and titrated until the patient responds.
Related Video: Epinephrine – ACLS Drugs
Key Takeaway
Atropine is the initial treatment for bradycardia.
In summary, AHA guidelines for CPR and ECC recommend that if bradycardia produces unstable signs and symptoms for the patient, then the initial treatment is atropine.
These signs and symptoms include acutely altered mental status, chest discomfort, acute heart failure, hypotension, or signs of shock that persist despite adequate airway and breathing.
If atropine is ineffective, β-adrenergic agonists can be used to improve the rate (dopamine or epinephrine), or transcutaneous pacing may be utilized temporarily as a bridge until the patient is ready for emergency transvenous pacing if necessary.