7f: Symptomatic Bradycardia (2024)

This is the sixth lesson in chapter 7. This lesson contains information pertaining to bradycardia, its symptoms and the types of bradycardia. Bradycardia is defined and how it should be treated is explained, according to the ACLS Survey.

Bradycardia is defined as a heart rate of less than 60 beats per minute. While any heart rate less than 60 beats per minute is considered bradycardia, not every individual with bradycardia is symptomatic or having a pathological event. Individuals in excellent physical shape often have sinus bradycardia.

Symptomatic bradycardia may cause a number of signs and symptoms including low blood pressure, pulmonary edema and congestion, abnormal rhythm, chest discomfort, shortness of breath, lightheadedness, and/or confusion. Symptomatic bradycardia should be treated with the ACLS Survey.

If bradycardia is asymptomatic but occurs with an arrhythmia listed below, obtain a consultation from a cardiologist experienced in treating rhythm disorders.

Symptoms of bradycardia include shortness of breath, altered mental status, hypotension, pulmonary edema or congestion, and weakness, dizziness, or lightheadedness.

Sinus bradycardia rules include R-R intervals to be regular and overall rhythm to be regular. The rate is less than 60 beats per minute, but usually more than 40 beats per minute. There is one P wave in front of every QRS, and they appear uniform. The PR interval measures between 0.12 and 0.20 seconds in duration and is consistent. The QRS complex measures less than 0.12 seconds.

First degree AV block rules include R-R intervals to be regular and overall rhythm to be regular. The rate depends on the underlying rhythm. There is one P wave in front of every QRS, and they appear uniform. The PR interval measures more than 0.20 seconds in duration and is consistent. The QRS complex measures less than 0.12 seconds.

Second-degree type I AV block, or Wenkebach, rules include R-R interval to be irregular, but there is usually a pattern to it. The R-R interval gets longer as the PR interval gets longer. The ventricular rate is usually slightly lower than the atrial rate due to some atrial beats not being conducted. The atrial rate is usually normal. P waves are upright and uniform. Most complexes will have a P wave in front of them; however, there will be some P waves that do not have a QRS complex. The PR interval gets progressively longer until there is a dropped QRS complex. The QRS complex measures less than 0.12 seconds.

Second-degree type II AV block, or Mobitz II, rules include the R-R interval to be regular if there is a consistent conduction ratio. If the conduction ratio is not constant, the R-R interval will be irregular. The atrial rate is normal. The ventricular rate is slower, usually half to one third slower than the atrial rate. P waves are upright and uniform. There is not a QRS following every P wave. The PR interval can only be measured on conducted beats, and it is usually constant across the strip. It may or may not be longer than a normal PR interval (which is 0.12 seconds). The QRS complex measures less than 0.12 seconds.

Third-degree AV block, or complete heart block, rules include R-R interval to be regular, and P-P interval to also be regular. The atrial rate is regular and normally 60 to 100. The rate of QRS complexes is dependent on the focus. If the focus is ventricular, the rate will be 20 to 40. If the focus is junctional, the rate will be 40 to 60. P waves are upright and uniform. There is not a QRS following every P wave. The PR interval can only be measured on conducted beats, and it is usually constant across the strip. It may or may not be longer than a normal PR interval (which is 0.12 seconds). The QRS complex interval may be normal but is more likely to be prolonged.

Here’s a quick summary of all the symptomatic bradycardia.

Sinus bradycardia is a normal rhythm with a slow rate.
First degree AV block has PR interval longer than 0.20 seconds.
Second-degree type I AV block has PR interval increase in length until QRS complex is dropped.
Second-degree type II AV block has PR interval same length with intermittently dropped QRS.
Third-degree AV block has a P wave and QRS complex that are not coordinated with each other.

For Adult Bradycardia with Pulse Algorithm, refer to Figure 36 in your corresponding ACLS manual.

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