EKG: Atrial/AV Nodal and Junctional Dysrhythmias

Focus topic: Atrial/AV Nodal and Junctional Dysrhythmias

In this chapter atrial/AV nodal and junctional rhythms will be discussed. Atrial/AV nodal rhythms are also known as supra ventricular because they occur above the ventricles. Atrial rhythms arise from an area within the atria that is different than the SA node. AV nodal rhythms occur due to problems in conduction through the AV node. Junctional rhythms stem from the tissue surrounding the AV node and the bundle of His known as the AV junction. These abnormal electrical impulses generate altered complexes and cardiac contractions that may not be able to provide for the best cardiac output. Atrial kick, that provides a boost in blood volume of 10% to 30% during the last part of the atrial contraction is usually diminished in these dysrhythmias and therefore, impacts the end cardiac output for the patient. Atrial dysrhythmias are thought to occur from one of three separate disturbances. These were reviewed below for the reader’s convenience.

  • Enhanced automaticity occurs in atrial tissue that does not normally function as an impulse generator. If the SA node is weakened and is not firing in a normal fashion, these foci will take over and create a new rhythm. Some of the causes of this reason for atrial dysrhythmias are hypocalcemia, hypokalemia, drug toxicity such as with digitalis compounds, hypoxia, acidosis, or something that might cause increased vagal tone. Remember that when the vagus nerve is stimulated, heart rate is decreased. Therefore, if the SA node has been given a command to decrease its automaticity, another site may choose to take over and cause new and varied rhythms to be produced.
  • Reentry rhythms occur when an impulse is able to return through the circuit and restimulate tissue during the repolarization phase of the myocardium. This can happen due to a potential circuit in an accessory AV pathway, a blocked circuit (so it finds a different way to get around the block), or a delay in the conduction circuit. Disease processes such as an acute myocardial infarction, cardiomyopathy, hyperkalemia, ischemic cardiac tissue, coronary arterial disease, or some types of medications may be etiologies.
  • Another name for triggered activity is “afterdepolarizations” and occurs during repolarization when cardiac cells are supposed to be silent or resting. A single impulse is created and it then stimulates tissue again or an escape type of pacemaker is triggered. This can create both atrial and ventricular dysrhythmias. This may produce one extra beat, extra beats that occur in “pairs,” or three or more beats in a row called a run. A sustained rhythm developed from this triggered activity can also be generated. This may occur from such things as hypoxia, increase in release of epinephrine and norepinephrine in the body, injury to myocardial cells, ischemia to cardiac tissue, medications that might prolong the repolarization process (some antibiotics, antidepressants, heart medications, antipsychotics, etc.), and hypomagnesemia.

Contents

Atrial/AV Nodal and Junctional Dysrhythmias: Atrial/AV Nodal Dysrhythmias

Focus topic: Atrial/AV Nodal and Junctional Dysrhythmias

Atrial/AV Nodal and Junctional Dysrhythmias: Premature Atrial Contraction

Focus topic: Atrial/AV Nodal and Junctional Dysrhythmias

Any beat that appears out of the normal pattern and is “early,” is considered to be a premature contraction or beat. It is easy to determine “prematurity” by using either calipers or a piece of paper to mark the QRS complexes. Find a point in the rhythm strip where there are two normal appearing sinus beats in a row. Make a mark on the piece of paper for each of these two QRS complexes. Move the piece of paper (or the calipers) so that the first mark on the piece of paper is on the second beat that was marked and note that the next beat falls exactly on the second mark on the piece of paper. Walk the piece of paper across the rhythm strip. The premature beat will fall out of the normal cadence of the regular sinus beats, that is, it will take place before the second mark on the piece of paper where a normal beat would be expected. If calipers are used, march the calipers across the rhythm strip in the same way and the premature beat will again be seen to fall short of the expected pace.

Premature beats occur from any tissue: atrial, AV junction, or ventricular. Premature atrial contractions or PACs, an atrial dysrhythmia, will be considered here. These may also be termed “premature atrial (or other location) complex” since many of them do not actually produce a contraction. These premature beats originating in the atrium are thought to occur as a consequence of altered automaticity or reentry problems.

Patients who have cardiac disease are at risk when PACs arise because they can be the forerunner of other atrial rhythms such as atrial fibrillation or atrial flutter. When associated with an acute myocardial infarction, they may indicate an impending episode of heart failure. Other causes of PACs include atrial enlargement, valvular disease, medication toxicities such as digitalis, electrolyte imbalances, or increased levels of thyroid hormone (hyperthyroidism).

Clinical Alert

PACs can be considered to be a normal phenomenon and many “healthy” people can experience these. These extra beats can be prompted by the intake of certain items such as caffeine, nicotine, or alcohol and can also be generated during periods of fatigue or anxiety producing situations as well as disease processes such as infections or generalized fever. People who have these PACs may complain of “palpitations” or the feeling of a “skipped beat.” PACs in patients who have non-diseased hearts are ordinarily not harmful.

A premature atrial contraction can be identified by a P wave that is both early in the cycle and has a different appearance than the other P waves in the rhythm strip. This P wave may have a notched formation, may be biphasic, or may look flat or pointed. The QRS that follows the premature P wave has the same configuration as the other QRS complexes that are present. There is also an incomplete or noncompensatory pause after the premature beat. A noncompensatory pause means that the distance between three normal beats compared to three beats that includes the premature beat is longer, that is, the three beats that include the premature beat is shorter. Noncompensatory pause with PACs demonstrates the noncompensatory pause found with premature atrial contractions.

Characteristics of a PAC are given as follows (Underlying normal sinus rhythm with PACs):

  • Regularity: Irregular rhythm (underlying rhythm is regular)
  • Rate: Can be normal, bradycardic, or tachycardic—more often is normal between 60 to 100 beats per minute

Atrial/AV Nodal and Junctional Dysrhythmias: Noncompensatory pause with PACs

Focus topic: Atrial/AV Nodal and Junctional Dysrhythmias

Atrial/AV Nodal and Junctional Dysrhythmias

Atrial/AV Nodal and Junctional Dysrhythmias: Underlying normal sinus rhythm with PACs

Focus topic: Atrial/AV Nodal and Junctional Dysrhythmias

Atrial/AV Nodal and Junctional Dysrhythmias

  • P wave: Present for each QRS complex but is premature and can be of different configuration
  • PR interval: May be normal—0.12 to 0.20 seconds or can be prolonged
  • QRS complex: Less than 0.10 seconds in width—depends on the underlying rhythm
  • QT interval: Normal
  • T wave: Normal configuration and size
  • ST segment: Normal configuration and size

Underlying normal sinus rhythm with PACs demonstrates PACs that are occurring with an underlying normal sinus rhythm. Note that the PACs are arising after each normal beat. This is known as bigeminy. When these or other premature beats develop after every second beat, so that every third beat is premature, it is called trigeminy. Every fourth beat as a premature complex is quadrigeminy. When they occur otherwise, they are noted to be occasional. When premature beats occur together, they are said to “coupled” or “couplets”. Three premature beats together would be called tripling.

Two other abnormalities that can occur with PACs are aberrantly conducted PACs and nonconducted PACs. If the PAC comes about very early in the cardiac cycle, it can be carried through the right bundle branch very slowly. This will cause a widened QRS complex which will not mimic the underlying rhythm. A nonconducted PAC means that the P wave occurred so early that it is actually buried within the T wave of the preceding complex and therefore was unable to complete conduction. The AV junction could not carry through another contraction or complex at that time.

Atrial/AV Nodal and Junctional Dysrhythmias: Wandering Atrial Pacemaker

Focus topic: Atrial/AV Nodal and Junctional Dysrhythmias

Wandering atrial pacemaker is also known by its abbreviation, WAP. A newer term is multiform atrial rhythm. When WAP occurs, the origination of the impulse changes from the SA node to another location or locations in the atria, or in the AV junction. This can also be known as a supra-ventricular rhythm because it occurs above the ventricles. Each impulse is conducted in a normal fashion through the ventricles; consequently, the duration of the QRS is the same. The P waves change their morphology each time the focus or origination of the impulse changes. In order to label a rhythm strip as wandering atrial pacemaker (multiform atrial rhythm) three or more distinct P waves are identified. P waves may be the same for at least two to three beats before the site travels to another location in the atria. The rate is usually normal or slow and may be a routine variant in normal, healthy young people, in athletic individuals, or in some patients during the sleep cycle. If the rate is higher than 100, this takes on a new classification called multi-focal atrial tachycardia.

The rhythm strip will have the following features (Wandering atrial pacemaker/multiform atrial rhythm):

  • Regularity: May be slightly irregular due to different foci
  • Rate: Usually normal or bradycardic
  • P wave: Present for each QRS complex but at least three distinct P waves are seen per rhythm strip
  • PR interval: Variable but usually remains below 0.20 seconds
  • QRS complex: Less than 0.10 seconds in width
  • QT interval: Normal or can vary
  • T wave: Normal configuration and size
  • ST segment: Normal configuration and size

Atrial/AV Nodal and Junctional Dysrhythmias: Wandering atrial pacemaker/multiform atrial rhythm

Focus topic: Atrial/AV Nodal and Junctional Dysrhythmias

Atrial/AV Nodal and Junctional Dysrhythmias

Clinical Alert

This is a dysrhythmia that is usually temporary. Because of this, the health care provider may see it on the cardiac monitor, but it may not manifest itself during the time the EKG tracing is taken. Be sure to print out rhythm strips that demonstrate this fleeting rhythm. Although it is not usually serious, in those patients who have cardiac disease, it bears watching and notification of the patient’s medical provider. Patients may experience this if they have an increase in vagal or parasympathetic tone, some types of heart disease, or if they have developed digitalis toxicity.

Patients are usually unaware that this rhythm abnormality is taking place and no treatment is usually necessary. This dysrhythmia will usually assume a normal rhythm when the SA node is able to generate impulses at its normal firing rate again. Existing underlying disease processes or toxicity problems should be addressed as treatment.

Atrial/AV Nodal and Junctional Dysrhythmias: Multifocal Atrial Tachycardia

Focus topic: Atrial/AV Nodal and Junctional Dysrhythmias

Wandering atrial pacemaker that presents with a rate greater than 100 beats per minute is labeled as multi-focal atrial tachycardia (MAT), another supra-ventricular rhythm. Another name that might be used interchangeably with this is chaotic atrial tachycardia. As in wandering atrial pacemaker, the site that is generating the impulse for conduction is changing and therefore the P waves will have different configurations throughout the rhythm strip. One of the greatest identifying characteristics for this dysrhythmia is that although the rhythm is irregular and fast, there is a distinct P wave for each QRS complex.

The most common reason for this dysrhythmia is chronic obstructive pulmonary disease. Other causes include acute myocardial infarctions, hypoxia, sepsis, toxicities such as digitalis or theophylline, respiratory failure, electrolyte imbalances, and rheumatic heart diseases.

This is another dysrhythmia that usually will resolve once the underlying condition is diagnosed and treated appropriately. Therefore, the focus of treatment will include the overall picture of the patient and does not center on the dysrhythmia that the primary disorder has created. Medications may be ordered to control the rate.

Characteristics of multi-focal atrial tachycardia include (Multi-focal atrial tachycardia):

  • Regularity: Irregular
  • Rate: Greater than 100 beats per minute (usually 100-200 beats per minute)
  • P wave: Present for each QRS complex but at least three distinct P waves are seen per rhythm strip
  • PR interval: Variable
  • QRS complex: Less than 0.10 seconds in width
  • QT interval: Can be difficult to determine
  • T wave: Usually distorted
  • ST segment: Usually distorted

Atrial/AV Nodal and Junctional Dysrhythmias: Multi-focal atrial tachycardia

Focus topic: Atrial/AV Nodal and Junctional Dysrhythmias

Atrial/AV Nodal and Junctional Dysrhythmias

Clinical Alert

This dysrhythmia can sometimes be confused with atrial fibrillation. If the health care provider looks closely at the EKG tracing, multifocal atrial tachycardia will have visible P waves present for each QRS, which atrial fibrillation will not have.

Atrial/AV Nodal and Junctional Dysrhythmias: Atrial Tachycardia

Focus topic: Atrial/AV Nodal and Junctional Dysrhythmias

Both altered automaticity and triggered activity can cause atrial tachycardia, a form of a supra-ventricular tachycardia. When irritable tissue in the atria supersedes the SA node and fires at a high rate of speed—150 to 250 beats per minute—this action can shorten diastole reducing the atrial kick, ultimately shrinking cardiac output. This loss of cardiac output also places stress on heart tissue since coronary perfusion is decreased at the same time.

In generic atrial tachycardia each QRS complex is preceded by a P wave and the QRS complex is usually normal, however, the P wave will usually have a different type of configuration than if the SA node were the firing tissue. Short bursts of atrial tachycardia can be exhibited if three or more complexes are noted to represent a rate of 150 to 250 beats per minute. A sustained rhythm (lasting more than 30 seconds) may or may not arise (Atrial tachycardia).

Atrial/AV Nodal and Junctional Dysrhythmias: Atrial tachycardia

Focus topic: Atrial/AV Nodal and Junctional Dysrhythmias

Atrial/AV Nodal and Junctional Dysrhythmias

Characteristics of atrial tachycardia include:

  • Regularity: Regular
  • Rate: 150 to 250 beats per minute
  • P wave: Present but the rate is so fast that they can be buried in the T wave of the previous beat—will have different configuration than normal SA node P wave
  • PR interval: May vary
  • QRS complex: Less than 0.10 seconds in width—may be aberrant
  • QT interval: May be difficult to discern
  • T wave: Usually distorted due to presence of P wave
  • ST segment: Usually distorted

One form of atrial tachycardia is known as paroxysmal atrial tachycardia (PAT). This variety has a sudden beginning and ending and can be initiated by PACs. This can look closely like paroxysmal supra-ventricular tachycardia (PSVT), but may not respond to carotid massage as well as PSVT. A buildup to the increased rate and a slowdown period may be seen with the rhythm, PAT. In this type, a re-entrant circuit may be present (Paroxysmal atrial tachycardia).

Characteristics of paroxysmal atrial tachycardia include:

  • Regularity: Regular
  • Rate: 150 to 250 beats per minute for period of atrial tachycardia
  • P Wave: Present abnormal may be buried in previous T wave
  • PR interval: May vary
  • QRS complex: Less than 0.10 seconds in width, but may be aberrant
  • QT interval: May be difficult to determine
  • T wave: Usually distorted due to presence of P wave
  • ST segment: Usually distorted

Atrial/AV Nodal and Junctional Dysrhythmias: Paroxysmal atrial tachycardia

Focus topic: Atrial/AV Nodal and Junctional Dysrhythmias

Atrial/AV Nodal and Junctional Dysrhythmias

Another form of atrial tachycardia is atrial tachycardia with block. In this form the atria are firing at an increased rate of 150 to 250 beats per minute; however, the AV node protects the heart by not allowing each of these impulses to be conducted. The ventricular rate is slower and the block within the AV node can be constant or variable. Therefore, all three components  the atrial rate, the ventricular rate, and the block can be regular, but separate. When regular blocks are present, the terms 2:1, 3:1, etc. may be used which denote that there are two atrial beats for each ventricular beat or three atrial beats for each ventricular beat that occurs. If the block is variable, that is, at times there are two atrial beats prior to a ventricular response and then three atrial beats with a ventricular response (this is only one example, any variety of variability can occur), then the rhythm is stated as atrial tachycardia with variable block. Multi-focal atrial tachycardia (MAT) is also considered to be a form of atrial tachycardia (Atrial tachycardia with 2:1 block, Atrial tachycardia with 2:1 block, and Atrial tachycardia with variable block).

Atrial/AV Nodal and Junctional Dysrhythmias: Atrial tachycardia with 2:1 block

Focus topic: Atrial/AV Nodal and Junctional Dysrhythmias

Atrial/AV Nodal and Junctional Dysrhythmias

Atrial/AV Nodal and Junctional Dysrhythmias: Atrial tachycardia with 2:1 block

Focus topic: Atrial/AV Nodal and Junctional Dysrhythmias

Atrial/AV Nodal and Junctional Dysrhythmias

Characteristics of atrial tachycardia with block are:

  • Regularity: Regular or irregular depending on block
  • Rate: 150 to 250 beats per minute for period of atrial tachycardia
  • P wave: Present morphology may be abnormal  may be buried in previous T wave more P waves than QRS complexes
  • PR interval: 0.12 to 0.20 seconds
  • QRS complex: Less than 0.10 seconds
  • QT interval: May be difficult to determine
  • T wave: Can be distorted due to presence of P wave
  • ST segment: Usually distorted

Atrial/AV Nodal and Junctional Dysrhythmias: Atrial tachycardia with variable block

Focus topic: Atrial/AV Nodal and Junctional Dysrhythmias

Atrial/AV Nodal and Junctional Dysrhythmias

Clinical Alert

Interpreting EKGs can be a difficult process when attempting to determine rhythms that are fast. Health care providers will find throughout their practice that sometimes practitioners will not always agree with analyses of EKG tracings. The faster rhythms are difficult and do not always conform to “black and white” rules.

Patients with atrial tachycardias may present with no symptoms or may complain of the feeling of “fluttering” associated with palpitations. They may feel dyspneic, have generalized weakness, blurred vision, hypotension, dizziness or lightheadedness, chest pain or pressure, or have had a syncopal or near syncopal episode. If the tachycardic episode was short, they will most likely have no symptoms or state that they felt momentarily ill with any of the above symptoms. Etiologies of atrial tachycardias are listed in Etiologies of Atrial Tachycardias.

Caring for individuals with atrial tachycardias depends on the patient’s condition, the cause, and the type of tachycardia. Treating the cause is a vital intervention. It is important to know what medications the patient is taking, such as digitalis, as well as creating an environment in which the patient feels safe to acknowledge the intake of illicit drugs. Valsalva’s technique and carotid sinus massage (to be discussed later) can be attempted, but does not usually work as well with these dysrhythmias. A momentary slowing of the heart rate may be seen with a subsequent return to the rhythm. Medications such as Adenocard (adenosine), Amiodarone, calcium channel blockers, or beta-blockers may be attempted. Synchronized cardioversion, atrial overdrive pacemaker, or catheter ablation may also be used when medications are not successful.

Atrial/AV Nodal and Junctional Dysrhythmias: Etiologies of Atrial Tachycardias

Focus topic: Atrial/AV Nodal and Junctional Dysrhythmias

Atrial/AV Nodal and Junctional Dysrhythmias

Atrial/AV Nodal and Junctional Dysrhythmias: Paroxysmal Supraventricular Tachycardia

Focus topic: Atrial/AV Nodal and Junctional Dysrhythmias

The term supraventricular simply means that the impulse generator is above the ventricles. Many types of dysrhythmias are labeled “supraventricular” including the atrial tachycardias listed above and both atrial fibrillation and atrial flutter. When P waves are not present, the term PSVT or paroxysmal supraventricular tachycardia can be used. Two types of PSVT are usually discussed and are known by the causative factor that generates their impulse formation and subsequent conductions. These are known as AV nodal reentrant tachycardia (AVNRT) and AV reentrant tachycardia (AVRT). In AVNRT a reentry problem occurs at the AV node. Two pathways are actually present—one fast and one slow. Two factors are present which allows for the extremely fast heart rate. These factors are the rate at which the impulse can be conducted through the pathway and the recovery time, known as the refractory period. One pathway conducts impulses rapidly but has a slower refractory period which allows for an extended recovery period. The second pathway, the slower one, takes a longer time to process the impulse and conduct it through the tissue, but has a shorter refractory time which allows for a more rapid recovery phase. When these two are working together, impulses are going through both areas, and a loop is formed where one side is in its recovery or refractory interval and the other is generating an impulse that is able to pass through. An open ended circuit is created and rapid, regular rhythms are created. These are usually narrow complex tachycardias.

In AVRT the reentry occurs due to a pathway that is not in the AV node or the bundle of His. This pathway is still above the ventricles; however, since it travels through a different passageway, it has a special term, preexcitation, associated with it. Preexcitation means that the ventricle is triggered earlier than expected because of the special conduit that has been created. This pathway is an accessory pathway. Sometimes an accessory pathway will actually connect back to the normal route of the AV node. If this happens it is called a bypass tract.

One very good example of this type of reentry supraventricular tachycardia is Wolff-Parkinson-White (WPW) syndrome. In this disease process, the pathway is created during fetal development by extra filaments of cardiac tissue that constructed a special bridge connecting the atria and the ventricles. This bridge is called the bundle of Kent.

Clinical Alert

When the tachycardia, WPW is present, the identifying characteristics of this distinctive syndrome are not able to be recognized. These characteristics are noted on the normal EKG tracing prior to or after the tachydysrhythmia has terminated. See Distinguishing Traits for Wolff-Parkinson-White (WPW) Syndrome for the distinguishing traits of this disorder. Another important aspect of this unique disease process is that it usually occurs in infants, young children, and adults up to the age of 35 years.

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Atrial/AV Nodal and Junctional Dysrhythmias: Distinguishing Traits for Wolff-Parkinson-White (WPW) Syndrome

Focus topic: Atrial/AV Nodal and Junctional Dysrhythmias

Atrial/AV Nodal and Junctional Dysrhythmias

Atrial/AV Nodal and Junctional Dysrhythmias: Paroxysmal supraventricular tachycardia

Focus topic: Atrial/AV Nodal and Junctional Dysrhythmias

Atrial/AV Nodal and Junctional Dysrhythmias

When PSVT is present, the following characteristics will be present (Paroxysmal supraventricular tachycardia and Sustained paroxysmal supraventricular tachycardia):

  • Regularity: Regular
  • Rate: 150 to 250 beats per minute
  • P wave: Undetectable—may be hidden within the QRS complex
  • PR interval: Not measurable
  • QRS complex: Less than 0.10 seconds
  • QT interval: May be difficult to determine
  • T wave: Can be distorted due to presence of P wave
  • ST segment: May be depressed

Atrial/AV Nodal and Junctional Dysrhythmias: Sustained paroxysmal supraventricular tachycardia

Focus topic: Atrial/AV Nodal and Junctional Dysrhythmias

Atrial/AV Nodal and Junctional Dysrhythmias

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