Basic Dysrhythmia

Question 1

Cardiac Cell and Their Characteristics

Answer 1

Pacemaker cells are specialized cardiomyocytes whose primary role is generating their own electrical impulses. The pacemaker cells are found in four clusters throughout the heart.
1. SA node
2. AV node
3. Bundle of his
4. Purkinje fibers
Also, excitatory and conductive properties.

Myocardial cells are the work horses of the cardiac system. These cells exhibit both excitatory and conductive properties but what sets them apart is their ability to contract. Through controlled and organized contractions, the heart muscles push the blood throughout the chambers and out to the body for use.

Question 2

Introduction

Answer 2

1. We introduce
2. Have students introduce themselves including their home units and how long they have been a nurse.
3. Ask some basic dysrhythmia questions”
   - What is a dysthymia?
   - Can anyone name a cardiac dysrhythmia?

Question 3

Cardiac Conduction Review

Answer 3

1. SA or sinoatrial node is the primary pacemaker of the heart. It is located in the back upper right-hand corner of the right atrium. An impulse generated here then…
2. Travels via the internodal pathways to the AV junction.
3. The AV junction is made of two clusters of pacemaker cells.
4. The AV node is located in the bottom left-hand corner of the right atrium.
5. From the AV node the impulse then travels to the bundle of his which is located in the septal wall.
6. It then travels down the left and right bundle branches to reach the purkinjie fibers.

Question 4

Sinoatrial node

Answer 4

New information - Generates impulses at a rate of 60-100 bpm.

Question 5

AV node

Answer 5

The AV node slows electrical impulses from the SA node down to allow time for atrial kick.
- Who knows what the atrial kick is? In what common dysrhythmia is the atrial kick lost?
- The atrial kick is the atria’s contraction at the end of the cardiac cycle to push the last little amounts of blood into the ventricles to prepare for the next contraction. The atrial kick is lost in AFIB.

The AV node also polices rapid impulses from reaching the ventricles.
- Why might this be an issue? Too rapid of ventricular contraction leaves less time for adequate blood filling. This results in decreased CO due to inadequate blood being sent out.
The AV node maxes its transmission potentials out at 220 bpm.

The AV node can also take over in situations where the SA node is dysfunctional. However, the AV node only fires at a rate of 40-60bpm.

Question 6

Purkinje Fibers

Answer 6

Located in the endocardium at the apex of the heart. Are able to conduct precise impulses which allow the ventricles to have synchronized contractions.

Question 7

EKG leads

Answer 7

Smoke over fire
Clouds over grass
Earth in the middle

These are the ideal locations to place the leads. Every patient’s anatomy is not going to be the same, just get the leads as close to the preferred location as you can.

Question 8

P Wave

Answer 8

Tall, peaked P waves - seen with an enlarged R atrium. These can be seen with patients who have
- Tricuspid stenosis - great strain placed on R atrium having to deal with extra blood flow. Overtime dilates.
- A second example of a condition that can lead to tall, peaked T waves is cor pulmonal. Also known as pulmonary heart disease.

Wide, notched, M-shaped p waves - enlarged L atrium. This is a more common condition than R atrium enlargement. Some common causes of this are
- HTN - chronic HTN forces the hearts muscles to pump against greater resistance. This can result in thickening and enlargement of the atrium.

Ectopic P wave and wandering atrial pacemaker can present due to an ectopic location of the origin of the p wave. Most commonly they present with a negative deflection on the EKG.

Biphasic P wave - the P wave has two ways of deflection. Seen most often with L atrial enlargement.

Question 9

Saw tooth P waves

Answer 9

Saw tooth P waves or what look like P waves is most commonly associated with Atrial flutter. This is a type of atrial dysthymia that we will discuss in a bit. But these P waves are actually known as F waves and are caused by re-entry impulses.

Question 10

Inverted P wave

Answer 10

Ectopic P wave. Transposition of the R and L arm leads.

Question 11

No visible P wave

Answer 11

Lack of visible P waves can be seen in many dysthymias.
- A FIB
- A flutter
- Junctional - the atriums and the ventricles are contracting at the same time. Because the ventricles contraction is so much more powerful than the atrias, the EKG only picks up the ventricle contraction.

Question 12

Wolff-Parkinson White

Answer 12

WPW is a congenital condition where there is an extra pathway available between the atria’s and the ventricles. This pathway bypasses the AV node, meaning it doesn’t get slowed down. This results in the potential for rapid signal transmission which can result in a shortened PR interval among other things.

Question 13

QRS

Answer 13

The QRS complex represents ventricular depolarization. It can present in a wide range of ways.

Question 14

Refractory periods

Answer 14

The refractory periods are periods of time after ventricular depolarization where the myocytes are unable (in the case of absolute refractory) or less apt (in the case of relative refectory period) to respond to electrical stimulation.

The refractory periods allow the cardiac myocytes time to reset and prevents the occurrence of too rapid of impulse response. If an additional impulse is able to be propagated during the refractory periods this can lead to ventricular tachycardia a potentially lethal arrythmia.

Question 15

ST segement

Answer 15

STEMI/NSTEMI
ST elevation myocardial infarction and non

These both get their name dealing with the ST segment, which is the early part of ventricular repolarization.

The ST elevation seen on STEMI is actually caused by the ischemic areas decreased ability to make ATP. This drop in energy production leads to transport channels remaining open, allowing potassium to leave the myocardial cells that are infarcted. This creates a current difference between the infarcted cells and the healthy ones.

Question 16

Flat T waves and U waves

Answer 16

Flat T waves and prominent U waves (which are normally not seen) are indicative of hypokalemia.

Question 17

Qt VS Qtc

Answer 17

The QTc is the QT adjusted for the heart rate. This allows a value to be designated which allows classification of normal or prolonged.

Prolonged QT intervals are associated with short-term mortality, especially in hospitalized patients. Dizziness, fainting, and sudden cardiac death can occur due to Torsade’s de Ponte. The longer the QT interval the greater chance of going into this dysrhythmia.

Question 18

How to assess rhythm regularity

Answer 18

The index card method - use an index card to mark the top of three R waves. You can slide the index card over and see if each R wave matches up. This is a quick and easy but not perfect way.

A more involved way is to mark the R waves on the index card and then count the number of small boxes between each R wave.

A regular rhythm will have less than .12 variance between R-to-R intervals.

Question 19

Determining the heart rate

Answer 19

There is a couple different methods used to determine the heart rate on an EKG of a regular rhythm:

1. Large square method - divide 300 by the number of large squares between R-to-R intervals. 300 because that is how many large boxes there are in a minute. This method works great for regular, not too fast of heart rates.
2. The small square method - divide 1500 by the number of small squares within the R-to-R interval (1500 because that is how many small squares are in a minute). This method is better used for determining the rate of faster rhythms where the R waves are closer together.
3. The previous two methods are useful in determining the rate for regular rhythms. The R wave method can be used to determine the rate in irregular rhythms. This is done by simply counting the number of R waves in a period of 10 seconds and then multiplying this answer by 6. This method can also be used to assess regular rhythms.

Alternatively, if you are unsure of the time duration of the strip, you can count 30 large squares and determine the number of R waves within, 30 large squares is 6 seconds. Then multiply that answer by 10.

Question 20

Premature beats

Answer 20

Premature beats such as PVCs and PACs are not counted because they originate from somewhere other than the pacemaker sites.

Question 21

P waves

Answer 21

Is there one P wave for each QRS - this can be different in conditions involving AV blocks. A sinus rhythm or regular rhythm will have one P wave per QRS complex.

We talked about P wave abnormalities earlier in the lecture. Tall peaked, M shaped, inverted, etc.

Question 22

PR interval

Answer 22

Time between atrial depolarization and ventricular depolarization

Question 23

Causes of Sinus Tach

Answer 23

Sinus Tach: The majority of sinus tach presentation can be explained by increased oxygen demand from the body. The body responds by increasing the HR to supply more oxygen.
- Exercise and exertion - the cells are using energy at increased rates. To replenish this energy, they need more oxygen to increase ATP production. This can be accomplished via a higher HR.
- Anxiety, excitement, pain, stress - these are all stress type responses which trigger the sympathetic nervous system to release catecholamines to prepare for “fight or flight” situations. This includes increasing the HR.
- Hypoxia, hypotension, HF, anemia - these are issues of reduced blood volume or flow or both throughout the body. Since the blood is what transports oxygen the heart attempts to compensate for this reduced flow by increasing the rate of flow of the volume that it does have.
- Dopamine and epinephrine - examples of catecholamines that were discussed earlier.