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The following is an overview of the rhythms used regularly in ACLS and examples of EKG strips.

Pulseless Electrical Activity (PEA) Rhythm

PEA rhythm occurs when any heart rhythm that is observed on the electrocardiogram (ECG) does not produce a pulse. PEA can come in many different forms. Sinus Rhythm, tachycardia, and bradycardia can all be seen with PEA.

Performing a pulse check after a rhythm/monitor check will ensure that you identify PEA in every situation.

Pulseless electrical activity usually has an underlying treatable cause. The most common cause in emergency situations is hypovolemia.

PEA is treated by assessing and correcting the underlying cause. These causes can be summed up in the 6 H’s and 6 T’s of ACLS.

When an underlying cause for pulseless electrical activity cannot be determined, PEA should be treated in the same fashion as asystole

Pulseless electrical activity is treated using the right branch of the puslesless arrest arrest algorithm.

Asystole or “flatline”

Asystole is not actually a true rhythm but rather is a state of no cardiac electrical activity. The main treatment of choice for asystole is the use of epinephrine and CPR.

Asystole is treated using the right branch of the puslesless arrest arrest algorithm. Click below to view the pulseless arrest algorithm diagram. When done click again to close the diagram.
Pulseless Arrest Algorithm Diagram.»

During asystole, there is no blood flow to the brain and other vital organs. This results in very poor outcomes if resuscitation is successful.

If asystole is visualized on the monitor, you should ensure that all leads are connected properly. If all leads are properly connected, you should rapidly assess for any underlying causes for the asystole.

As with pulseless electrical activity (PEA), asystole can have possible underlying causes which can be remembered using the H’s and T’s mnemonic.

Pulseless Ventricular Tachycardia

The pulseless ventricular tachycardia rhythm is primarily identified by several criteria. First, the rate is usually greater than 180 beats per minute and the rhythm generally has a very wide QRS complex.

Second, the patient will be pulseless and third, the rhythm originates in the ventricles or AV node. This is in contrast to other types of tachycardias which have origination above the ventricular tissue (in the atria).

Not all ventricular tachycardias are pulseless and therefore, pulselessness must be established prior to beginning an algorithm. This is accomplished simply by checking a carotid or femoral pulse.

Pulselessness with a tachyarrhythmia occurs because the ventricles are not effectively moving blood out of the heart and there is therefor no cardiac output. Many tachyarrhythmias of a rate >150 will deteriorate into pulselessness if timely treatment is not given.

Pulseless ventricular tachycardia is treated using the left branch of the puslesless arrest arrest algorithm.

Ventricular Fibrillation

Ventricular fibrillation or VF occurs when there are uncoordinated contractions within the ventricles of the heart. The primary cause of VF is hypoxia (lack of oxygen) to the heart muscle which causes hyperirritability in the cardiac muscle tissue.

As a result, multiple muscles cells within the ventricles simultaneously fire as pacemakers causing a quivering or fibrillation that is ineffective for adequate cardiac output.

The two images above show what ventricular fibrillation will look like on a EKG rhythm strip.

VF can rapidly lead to heart muscle ischemia and there is a high likelihood that it will deteriorate into asystole.

Ventricular fibrillation is treated using the left branch of the puslesless arrest arrest algorithm.

First-Degree Heart Block

Also called first-degree AV block is a disease of the electrical conduction system of the heart in which the PR interval is lengthened beyond 0.20 seconds.

This lengthening of the PR interval is caused by a delay in the electrical impulse from the atria to the ventricles through the AV node

Normally and in the case of ACLS, first-degree heart block is of no consequence unless it involves myocardial infarction or an electrolyte imbalance.

Although first-degree heart block is not clinically significant for ACLS, recognition of the major AV blocks is important because treatment decisions are based on the type of block present

second-Degree Heart Block (Type 1)

Also called Mobitz 1 or Wenckebach is a disease of the electrical conduction system of the heart in which the PR interval» has progressive prolongation until finally the atrial impulse is completely blocked and does not produce a QRS electrical impulse.

Once the p-wave is blocked and no QRS is generated, the cycle begins again with the prolongation of the PR interval.

One of the main identifying characteristics of second degree heart block type 1 is that the atrial rhythm will be regular.

In the above image, notice that the p-waves are regular, the PR-interval progressively gets longer until a QRS is dropped and only the p-wave is present.

Although second degree heart block type-1 is not clinically significant for ACLS, recognition of the major AV blocks is important because treatment decisions are based on the type of block present.

Second-Degree (AV) Heart Block (Type 2)

Also called Mobitz II or Hay is a disease of the electrical conduction system of the heart. Second-degree AV block (Type 2) is almost always a disease of the distal conduction system located in the ventricular portion of the myocardium.

This rhythm can be recognized by the following characteristics:

nonconducted p-waves (electrical impulse conducts through the AV node but complete conduction through the ventricles is blocked, thus no QRS)
P-waves are not preceded by PR prolongation as with second-degree AV block (Type 1)
fixed PR interval
The QRS complex will likely be wide click here to see why»

Second-degree AV block (Type 2) is clinically significant for ACLS because this rhythm can rapidly progress to complete heart block

Secocnd-degree AV block (Type 2) should be treated with immediate transcutaneous pacing or transvenous pacing because there is risk that electrical impulses will not be able to reach the ventricles and produce ventricular contraction.

Complete Heart Block

Third-degree AV block or complete heart block is the most clinically significant AV block associated with ACLS. Complete heart block occurs when the electrical impulse generated in the SA node in the atrium is not conducted to the ventricles.

When the atrial impulse is blocked, an accessory pacemaker in the ventricles will typically activate a ventricular contraction. This accessory pacemaker impulse is called an escape rhythm.

Because two independent electrical impulses occur (SA node impulse & accessory pacemaker impulse), there is no apparent relationship between the P waves and QRS complexes on an ECG.

Characteristics that can be seen on an ECG include:

P waves with a regular P to P interval
QRS complexes with a regular R to R interval
The PR interval will appear variable because there is no relationship between the P waves and the QRS Complexes

In the image above note that the p-waves are independent of the QRS complexes. Also note the 4th QRS complex (impulse) looks different from the others. This is because it is from a different accessory pacemaker in the ventricle than the other QRS complexes.
Common Causes

The most common cause of complete block is coronary ischemia and myocardial infarction. Reduced blood flow or complete loss of blood flow to the myocardium damages the conduction system of the heart, and this results in an inability to conduct impulses from the atrium to the ventricles.

Those with third-degree AV block typically experience bradycardia, hypotension, and in some cases hemodynamic instability.

Supraventricular Tachycardia (SVT)

SVT is a broad term for a number of tachyarrhythmias that originate above the ventricular electrical conduction system (purkinje fibers).

Classic Paroxysmal SVT has a narrow QRS complex & has a very regular rhythm. Inverted P waves are sometimes seen after the QRS complex. These are called retrograde p waves

The heart fills during diastole, and diastole is normally 2/3 the cardiac cycle. A rapid heart rate will significantly reduce the time which the ventricles have to fill. The reduced filling time results in a smaller amount of blood ejected from the heart during systole. The end result is a drop in cardiac output & hypotension.

With the drop in cardiac output, a patient may experience the following symptoms. These symptoms occur more frequently with a heart rate >150 beats per minute:

Shortness of air (S)
Palpitation feeling in chest (S)
Ongoing chest pain (U)
Dizziness (S)
Rapid breathing (S)
Loss of consciousness (U)
Numbness of body parts (S)

The pathway of choice for SVT in the tachycardia algorithm is based on whether the patient is stable or unstable. The symptoms listed above that would indicate the patient is unstable are noted with the letter (U). Stable but serious symptoms are indicated with the letter (S).

Unstable patients with SVT and a pulse are always treated with cardioversion

Stat Life Medical Training conducts ACLS courses at the following locations: Jacksonville and Orlando Florida

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