- •Contents
- •Contributors and consultants
- •Not another boring foreword
- •A look at cardiac anatomy
- •A look at cardiac physiology
- •A look at ECG recordings
- •All about leads
- •Observing the cardiac rhythm
- •Monitor problems
- •A look at an ECG complex
- •8-step method
- •Recognizing normal sinus rhythm
- •A look at sinus node arrhythmias
- •Sinus arrhythmia
- •Sinus bradycardia
- •Sinus tachycardia
- •Sinus arrest
- •Sick sinus syndrome
- •A look at atrial arrhythmias
- •Premature atrial contractions
- •Atrial tachycardia
- •Atrial flutter
- •Atrial fibrillation
- •Wandering pacemaker
- •A look at junctional arrhythmias
- •Premature junctional contraction
- •Junctional escape rhythm
- •Accelerated junctional rhythm
- •Junctional tachycardia
- •A look at ventricular arrhythmias
- •Premature ventricular contraction
- •Idioventricular rhythms
- •Ventricular tachycardia
- •Ventricular fibrillation
- •Asystole
- •A look at AV block
- •First-degree AV block
- •Type I second-degree AV block
- •Type II second-degree AV block
- •Third-degree AV block
- •A look at pacemakers
- •Working with pacemakers
- •Evaluating pacemakers
- •A look at biventricular pacemakers
- •A look at radiofrequency ablation
- •A look at ICDs
- •A look at antiarrhythmics
- •Antiarrhythmics by class
- •Teaching about antiarrhythmics
- •A look at the 12-lead ECG
- •Signal-averaged ECG
- •A look at 12-lead ECG interpretation
- •Disorders affecting a 12-lead ECG
- •Identifying types of MI
- •Appendices and index
- •Practice makes perfect
- •ACLS algorithms
- •Brushing up on interpretation skills
- •Look-alike ECG challenge
- •Quick guide to arrhythmias
- •Glossary
- •Selected references
- •Index
- •Notes
5
Atrial arrhythmias
Just the facts
In this chapter, you’ll learn:
the proper way to identify the various atrial arrhythmias
the causes, significance, treatment, and nursing implications of each arrhythmia
assessment findings associated with each arrhythmia
interpretation of atrial arrhythmias on an ECG.
A look at atrial arrhythmias
Atrial arrhythmias, the most common cardiac rhythm disturbances, result from impulses originating in areas outside the sinoatrial (SA) node. These arrhythmias can affect ventricular filling time and diminish the strength of the atrial kick, a contraction that normally provides the ventricles with about 15% to 25% of their blood.
Triple play
Atrial arrhythmias are thought to result from three mechanisms— enhanced automaticity, circus reentry, and afterdepolarization. Let’s take a look at each cause and review specific atrial arrhythmias:
• Enhanced automaticity—An increase in the automaticity (the ability of cardiac cells to initiate impulses on their own) of the atrial fibers can trigger abnormal impulses. Causes of increased automaticity include extracellular factors, such as hypoxia, acidosis, hypocalcemia, and digoxin toxicity, and conditions in which the function of the heart’s normal pacemaker, the SA node, is diminished. For example, increased vagal tone or hypokalemia can increase the refractory period of the SA node and allow atrial fibers to fire impulses.
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•Reentry—In reentry, an impulse is delayed along a slow conduction pathway. Despite the delay, the impulse remains active enough to produce another impulse during myocardial repolarization. Reentry may occur with coronary artery disease, cardiomyopathy, or myocardial infarction (MI).
•Triggered activity—An injured cell sometimes only partly repolarizes. Partial repolarization can lead to a repetitive ectopic firing called triggered activity. The depolarization produced by triggered activity is known as afterdepolarization and can lead to atrial or ventricular tachycardia. Afterdepolarization can occur with cell injury, digoxin toxicity, and other conditions. Now let’s examine each atrial arrhythmia in detail.
Premature atrial contractions
Premature atrial contractions (PACs) originate outside the SA node and usually result from an irritable spot, or focus, in the atria that takes over as pacemaker for one or more beats. The SA node fires an impulse, but then an irritable focus jumps in, firing its own impulse before the SA node can fire again.
PACs may be conducted through the atrioventricular (AV) node and the rest of the heart, depending on their prematurity and the status of the AV and intraventricular conduction system. Nonconducted or blocked PACs don’t trigger a QRS complex.
How it happens
PACs, which commonly occur in a normal heart, can be triggered by alcohol, nicotine, anxiety, fatigue, fever, and infectious diseases. A patient who eliminates or controls those factors can correct the arrhythmias.
PACs may also be associated with coronary or valvular heart disease, acute respiratory failure, hypoxia, pulmonary disease, digoxin toxicity, and certain electrolyte imbalances.
PACs are rarely dangerous in a patient who doesn’t have heart disease. In fact, they commonly cause no symptoms and can go unrecognized for years. The patient may perceive PACs as normal palpitations or skipped beats.
The nicotine in cigarattes can cause PACs. Yuk!
PREMATURE ATRIAL CONTRACTIONS |
89 |
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Early warning sign
However, in patients with heart disease, PACs may lead to more serious arrhythmias, such as atrial fibrillation and atrial flutter. In a patient with an acute MI, PACs can serve as an early sign of heart failure or an electrolyte imbalance. PACs can also result from the release of the neurohormone catecholamine during episodes of pain or anxiety.
What to look for
The hallmark ECG characteristic of a PAC is a premature P wave with an abnormal configuration when compared with a sinus P wave. (See Nonconducted PACs and second-degree AV block.)
When the PAC is conducted, the QRS complex appears similar to the underlying QRS complex. PACs are commonly followed by a pause.
The PAC depolarizes the SA node early, causing it to reset itself and disrupt the normal cycle. The next sinus beat occurs sooner than it normally would, causing the P-P interval between two normal beats that have been interrupted by a PAC to be shorter than three consecutive sinus beats, an occurrence referred to as noncompensatory. (See Identifying premature atrial contractions, page 90.)
Lost in the T
When examining a PAC on an ECG, look for irregular atrial and ventricular rates. The underlying rhythm is usually regular. An irregular rhythm results from the PAC and its corresponding pause. The P wave is premature and abnormally shaped and may be lost in the previous T wave, distorting that wave’s configuration. (The T wave might be bigger or have an extra bump.) Varying configurations of the P wave indicate more than one ectopic site.
The PR interval can be normal, shortened, or slightly prolonged, depending on the origin of the ectopic focus. If no QRS complex follows the premature P wave, a nonconducted PAC has occurred.
PACs may occur in bigeminy (every other beat is a PAC), trigeminy (every third beat is a PAC), or couplets (two PACs in a row).
The patient may have an irregular peripheral or apical pulse rhythm when the PACs occur. He may complain of palpitations, skipped beats, or a fluttering sensation. In a patient with heart
Mixed signals
Nonconducted PACs and second-degree AV block
Don’t confuse nonconducted premature atrial contractions (PACs) with type II second-degree atrioventricular (AV) block. In type II seconddegree AV block, the P-P interval is regular. A nonconducted PAC, however, is an atrial impulse that arrives early to the AV node, when the node isn’t yet repolarized.
As a result, the premature P wave fails to be conducted to the ventricle. The rhythm strip below shows a
P wave embedded in the preceding T wave.
P wave |
QRS |
|
complex |
||
|
Nonconducted PAC
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Identifying premature atrial contractions
This rhythm strip illustrates premature atrial contraction (PAC). Look for these distinguishing characteristics.
The rhythm is |
Premature and |
The baseline |
|
abnormally shaped P |
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irregular when a PAC |
|||
waves occur. |
rhythm is regular. |
||
occurs. |
|||
|
|
• Rhythm: Irregular |
• PR interval: 0.20 second |
• QT interval: 0.32 second |
• Rate: 90 beats/minute |
• QRS complex: 0.08 second |
• Other: Noncompensatory pause |
• P wave: Abnormal with PAC; |
• T wave: Abnormal with some em- |
(first PAC) |
some lost in previous T wave |
bedded P waves |
|
disease, signs and symptoms of decreased cardiac output—such as hypotension and syncope—may occur.
How you intervene
Most patients who are asymptomatic don’t need treatment. In symptomatic patients, however, treatment may focus on eliminating the cause, such as caffeine, alcohol, and nicotine.
When caring for a patient with PACs, assess him to help determine what’s triggering the ectopic beats. Tailor your patient teaching to help the patient correct or avoid the underlying cause. For example, if applicable, the patient should eliminate caffeine or nicotine or learn stress reduction techniques to lessen his anxiety.
If the patient has ischemic or valvular heart disease, monitor him for signs and symptoms of heart failure, electrolyte imbalances, and the development of more severe atrial arrhythmias.
PACs may be caused by too much caffeine or alcohol.