Atrial Rhythms | Premature Atrial Complex

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Authors and Reviewers

Authored by Thomas O'Brien.
Medically reviewed by Dr. Jonathan Keroes, MD, Cardiology.
Last Update: 2/4/2022

Introduction

• The five-steps of rhythm analysis must be followed regardless of how simple of complex the tracing is you are reviewing.
• The information gathered in these steps are telling a story.
• The title of that story is the interpretation.

Atrial Dysrhythmias Types

The dysrhythmias in this category occur as a result of problems in the atria. These atrial dysrhythmias primarily affect the P wave. We will be discussing the following complexes and rhythms:

• Premature Atrial Complexes (PAC’s)
• Wandering Atrial Pacemaker
• Multifocal Atrial Tachycardia
• Atrial Flutter
• Atrial Fibrillation

Intro to PAC

• PAC's can occur for a number of different reasons i.e., diet, fatigue, stress, disease, ischemia to name a few.
• Premature complexes frequently occur in bradycardic rhythms, but may occur almost any time.
• PAC's occur when an early electrical impulse occurs from a location in the atria other than the SA node.

Intro to PAC 2

• This early impulse causes an early cardiac complex which disrupts the underlying rhythm.
• The locus of stimulation being different, results in a change in the morphology of the P wave.
• PAC's can occur occasionally or frequently.
• PAC's can be observed with or without a pattern
• The P wave with PAC's will always be upright

EKG Analysis

Notice the following: the R to R interval is irregular, the fifth complex is early and the P wave on the early complex is a different shape.

EKG Practice Strip

Analyze this tracing using the five steps of rhythm analysis.

Description

• Rhythms are often named according to the origin of the electrical activity in the heart or the structure where the problem is occurring.
• Wandering Atrial Pacemaker is aptly named due to the electrical impulses causing the atrial activity are moving or wandering.
• These changes in the locus of stimulation affect the morphology of the P waves.

Analysis

• In Wandering Atrial Pacemaker, you must observe at least three different shaped P waves. No other changes in the tracing may be observed. The rhythm may or may not be regular.
• The PR interval is often affected, but does not have to be.
• The bottom line, is you must observe at least three different shaped P waves.

Practice Strip

Analyze this tracing using the five steps of rhythm analysis.

Multifocal Atrial Tachycardia

• Multifocal Atrial Tachycardia is just a faster version of Wandering Atrial Pacemaker. The criteria is the same as Wandering Atrial Pacemaker with the only difference being the heart rate exceeds 100 bpm.
• These changes in the locus of stimulation within the atria affect the morphology of the P waves.
• Remember, you must observe at least three different shaped P waves.
• Due to the presence of irregular R to R intervals coupled with the changing P wave morphology, some people have confused this rhythm with Atrial Fibrillation.

Description

• Atrial Flutter occurs when there is an obstruction within the atrial electrical conduction system.
• Due to this impediment a series of rapid depolarizations occur.
• These depolarizations may occur two, three, four or more times per QRS complex.
• The AV node functions like a “gatekeeper” blocking the extra impulses until the ventricular conduction system is able to accept the impulse.
• The impulse that is accepted will cause the QRS complex to occur.

Analysis

• Each flutter wave represents atrial depolarization. This will be noted next to the P wave step in rhythm analysis. Instead of P waves, this tracing has “F” waves. No P waves mean there is no PR interval measurement.
• When the tracing is interpreted, the ratio of F waves to each QRS complex will be documented along with the rhythm i.e. Atrial Flutter 4:1 (indicates 4 “F” waves to each QRS complex). Not all Atrial Flutter will have a regular rhythm. In that case just document and report your observations.

Practice Strip

• Analyze this tracing using the five steps of rhythm analysis.
• Compare your answers with the answers on the next slide.

Practice Strip Answers

• Rhythm: Regular
• Rate: Ventricles - 80, Atria - 320
• P wave: "F" waves
• PR interval: absent
• QRS: 0.08
• Interpretation: Atrial Flutter 4:1

Description

• Atrial Fibrillation occurs when multiple electrical impulses occur within the atria. This chaotic electrical activity results in a chaotic wave form between the QRS complexes. P waves are absent. They are replaced by lower case "f" waves. No P waves means there is no PR interval measurement.
• This rapid electrical activity overwhelms the AV node causing impulses to enter the ventricular conduction system at irregular points. This results in irregular R to R intervals.

Analysis

• Not all fibrillatory waves are created equal. The "f" waves can be coarse (majority measure 3 mm or more) or can be fine (majority of waveforms measure less than 3 mm) to almost absent. Regardless always report your observations. Many times when a patient has "new onset" Atrial Fibrillation the patient will report with a heart rate of 160 bpm or more.

Mechanisms

Practice Strip

Analyze this tracing using the five steps of rhythm analysis.