avalon medical educator’s 1. · characteristics of cardiac cells automaticity: refers to the...

Avalon Medical Educator’s 1.

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Thank you for your interest in Avalon Medical Educator’s IV Certification Course. It is our goal to make this course a stress free and even fun experience for you. The program is made up of two components: a 6 hour home study component and a 6 hour classroom section, for a total of 12 contact hours at the completion of the program. This program is recommended for those who have EKG “anxiety” or as a refresher for RN’s, LPN’s or any medical professionals who will be taking ACLS. Again, thank you for choosing Avalon Medical Educator’s for your educational needs. Before you leave, take a look at the additional training programs we offer. We offer many different training locations and are always willing to bring the training to you. *Refer a friend to the course and receive 10% off your next class with Avalon Medical Educator’s.


Basic EKG Course

Day 1 Agenda

9:00 – 9:15 Welcome and Introductions 9:15 – 10:00 Heart anatomy, conduction system 10:40 – 10:50 Break 10:50 – 12:30 Rhythm identification, rhythm breakdown, components of a complex. 12:30 – 1:20 Lunch 1:20 – 2:30 Rhythm review 2:30 – 2:40 Break 2:40 – 3:45 Practice reading EKG strips, group identification review 3:45 – 5:00 12-lead placement and written examination


Anatomy of the Heart

The human heart is the hollow, muscular organ in the thoracic cavity that maintains the circulation of blood throughout the body. It is surrounded by a membrane called the pericardium. The pericardium consists of a layer of fibrous connective tissue and a layer of thin, serous tissue and is attached to the vena cava, the aorta, the diaphragm, and the sternum. The pericardial cavity, the potential space between the pericardium and the heart, contains the watery pericardial fluid. This fluid prevents friction between the pericardium and the heart.

The heart wall consists of the epicardium (inner layer), the myocardium (middle layer comprised of cardiac muscle tissue), and the endocardium (lining of the myocardium that covers the heart valves). The heart has a right side and a left side. Each side has a relatively thin-walled chamber that receives blood returning to the heart (atrium) and a muscular chamber that pumps blood out of the heart (ventricle).

Blood Flow

The flow of blood through the heart is controlled by the opening and closing of valves and the contraction and relaxation of the myocardium. Heart valves are controlled by pressure changes within each chamber and contraction and relaxation are controlled by the heart's conduction system.

Blood that has traveled through the body returns to the heart and enters the right atrium. This blood flows through the tricuspid valve into the right ventricle. The right ventricle pumps the blood to the lungs, where it absorbs oxygen. Oxygen-rich blood returns from the lungs and enters the heart through the left atrium. Blood passes from the left atrium through the mitral valve and into the left ventricle.

The left ventricle, the largest and most muscular of the four chambers, is the main pumping chamber of the heart. When the left ventricle contracts the blood is pumped through the aortic valve into the main artery of the body (aorta). The aorta supplies blood to smaller arteries that travel to the head, arms, abdomen, and legs. These arteries supply oxygen-rich blood to the organs and tissues of the body, which require oxygen to function. The coronary arteries supply oxygen-rich blood to the tissues of the heart.

Oxygen-poor blood travels from organs and tissues to the heart through veins. The vena cava is the major vein that returns blood to the right atrium of the heart. The vena cava superior returns blood from the head, neck, upper extremities, and chest. The vena cava inferior returns blood from the lower extremities, the pelvis, and the abdomen. The coronary sinus drains blood from the coronary arteries into the right atrium.


Conduction System

An electrical impulse travels through the heart and initiates contractions of the chambers. The heart's "spark plug" is an area of specialized heart tissue called the sinoatrial node (SA node), which is located in the right atrium. Each time the SA node "fires," an electrical impulse is generated that travels through the right and left atria, signaling these chambers to contract and pump blood into the ventricles.

The impulse then travels into another area of specialized heart tissue called the atrioventricular node (AV node), which is located between the atria and the ventricles. The electrical impulse is conducted through the AV node and wire-like pathways (Purkinje fibers) to the ventricles, signaling the ventricles to contract and pump blood into the lungs and throughout the body.

The normal sequence of electrical activation of the chambers of the heart is called sinus rhythm. It occurs each time the heart beats, usually about 60 to 80 times every minute. In a normal heartbeat, the atria contract simultaneously while the ventricles relax. Then, the ventricles relax and the atria contract. The term systole refers to contraction and the term diastole refers to relaxation. A heartbeat consists of the systole and diastole of the atria and the systole and diastole of the ventricles.


Normal Conduction of the heart:

SA node --> atrial muscle --> AV node --> bundle of His --> Left and Right Bundle Branches --> ventricular muscle


It all starts at the cellular level

Myocardial cells are the working cells of the myocardium; they contain contractile filaments and form the muscular layer of the walls of the atria and ventricles. The primary responsibility is contractility.

Pacemaker calls are specialized cells of the conduction system that are capable of spontaneously generating and conducting electrical impulses. The primary property is that of automaticity, conductivity and excitability.

Characteristics of Cardiac Cells

Automaticity: Refers to the cells ability to spontaneously initiate an impulse. (Pacemaker cells posses this ability).

Excitability: The ability of the cardiac muscle to respond to an outside stimulus. (Chemical, mechanical or electrical).

Conductivity: The ability of a cell to transmit an impulse to another cell.

Contractility: How well the cell contracts after receiving the impulse.

The Sodium Potassium Pump

A mechanism of active transport that moves potassium ions into and sodium ions out of a cell along a protein (or enzyme) channel. It is found in all human cells, but is especially important in nerve and muscle cells. The sodium-potassium pump uses active transport, with energy supplied by ATP (adenosine triphosphate) molecules, to move 3 sodium ions to the outside of the cell for each 2 potassium ions that it moves in. One third of the body's energy expenditure is used in this process.

Depolarization and Repolarization Action Potential Curve

Some of the cells (called excitable cells) are capable to rapidly reverse their resting membrane potential from negative resting values to slightly positive values. This rapid change in membrane potential is called an action potential. An action potential is brought on by a rapid change in membrane permeability to certain ions. Excitable cells include neurons (nerve cells) and muscle cells.

Let's consider an action potential generated by a nerve cell, a considerably simpler event than a cardiac action potential. Inside all cells there is a high concentration of potassium ions and low concentration of sodium ions. The extracellular space contains the opposite: a high concentration of sodium ions and a low concentration of potassium ions. The imbalance between ions inside and outside the cells creates a resting


membrane potential which is about -60 mV. Upon activation of certain ion channels potassium ions diffuse out of the cell and sodium ions move into the cell, moving from high concentrations of ions to low concentrations. As more positively charged sodium ions get into the cell, the membrane potential becomes less negative and reaches a threshold at -45 mV. Once this occurs, many more sodium channels are open and the membrane potential begins rising more rapidly (rising phase) until it reaches the peak of the action potential. By that time the sodium channels are closed and cell begins to repolarize, returning the membrane potential to its original resting state. A brief period of overcompensation, called hyperpolarization, occurs when the membrane potential becomes more negative then its original resting state. Thus, the action potential of the cell is the change in voltage of the membrane potential that causes it to go from its negative resting state to a positive value for a very brief time.

What if things just don’t work together perfectly?

If the site speeds up and takes over as the Pacemaker, irritability or an early beat can occur. Actually a safety feature to protect the heart is known as an escape beat. All cardiac tissue has the ability to function as the potential pacemaker of the heart. When the SA node fails or slows down, the next highest inherent rate will usually take over the SA node.

The Graph Paper

As you can see on the graph paper above, each small square is 1 mm in length and represents 0.04 seconds and each larger square is 5 mm in length and represents 0.2 seconds.

Each large square has 5 small squares each at 0.04X5 = 0.2 seconds.

The Voltage is measured by comparing the height of the spike to the horizontal lines on the graph paper. Time is measured by comparing the markings to the vertical lines on the graph paper.


EKG’s are graphic representations of the electrical activity within the heart. It can provide information on conduction disturbances, electrical effects of medications and electrolytes, and the mass of the cardiac muscle. It is important to note that: It does not provide information about mechanical activity, Structural disorders or perfusion disorders such as PEA.

Electrodes are sensing devices that pick up the electrical activity below them. The ECG machine can then convert them into waves. The leads provide a view of the heart’s electrical activity between two electrodes. So therefore, basic dysrhythmia interpretation requires the monitoring of only one lead. A standard ECG tracing usually looks at 12 leads.

Modern ECG's utilize 12 leads which are composed of 6 limb leads and 6 precordial leads.

• Limb leads are: I, II, III, aVR, aVL, and aVF.

(The lower case "a" in this notation refers to "augmented" in the sense that the person who developed the augmented leads discovered that he had to augment or amplify the voltage in the EKG machine to get a tracing that would be of similar magnitude as leads I, II, and III.)

Furthermore each of the leads are bipolar in the sense that it requires two sensors which are on the skin to make a lead. If one connects a line between two sensors, one has a vector with the positive end being at one electrode and negative at the other.


The augmented leads utilize two electrodes for a negative pole and one electrode to form the positive pole. The positioning for leads I, II, and III were first given by Einthoven as shown by this equilateral triangle called Einthoven's Triangle.

Basic Components include:

The wave is a deflection from baseline that represents a cardiac event. A segment is a specific portion of the complex as represented on a ECG. The interval is a distance measured as time between two cardiac events. The baseline is a line from the end of the T wave to the beginning of the P wave, also called the isoelectric line.

The PR Segment

The PR segment is part of the PR interval and is that area noted from the end of the P wave to the beginning of the QRS complex. Once the electrical impulse reaches it, there is a delay in conduction through the AV node, allowing time for the contents of the atria to empty into the ventricles before ventricular contraction begins. The impulse then spreads to the bundle of His, bundle breaches, and Purkinje fibers. The PR segment is normally an isoelectric (flat) line because these structures are so small that electrical activity generated within them is not usually detected on the ECG.

The PR Interval

The P wave is followed by a line which is known as the PR segment. The P wave + the PR segment = the PR interval (PRI). The PR interval reflects depolarization of the right and left atria (P wave) and the spread of the impulse through the AV node, bundle of His, right and left bundle branches, and the Purkinje fibers.

Normal Characteristics of the PR Interval

- Begins with the onset of the P wave and ends with the onset of the QRS complex

- Normally measures 0.12 to 0.20 second

Abnormal PR Intervals

- A long interval (greater than 0.20 second) indicates the impulse was delayed as it passed through the AV node (as seen in first-degree AV block and digitalis toxicity) (digitalis prolongs conduction through the AV node). The P wave associated with a prolonged PR interval may be normal or abnormal.

- A PR interval of less than 0.12 second may be seen when the impulse originates in an ectopic pacemaker in the atria close to the AV node or in the AV junction.


- A shortened PR interval may also occur if the electrical impulse progresses from the atria to the ventricles through an abnormal conduction pathway which bypasses the AV node and depolarizes the ventricles earlier than usual. Wolff-Parkinson-White and Lown-Ganong-Levine syndrome are examples of conditions in which this may be seen.

- The QRS Complex

Ventricular depolarization produces the Q wave, the R wave, and the S wave. Atrial repolarization usually takes place during this time, but the QRS complex overshadows it on the ECG.

The Q wave is the first negative, or downward, deflection following the P wave. It represents depolarization of the interventricular septum. The R wave is the first positive, or upward, deflection following the P wave. The negative wave following the R wave is known as the S wave. The R and S waves represent depolarization of the right and left ventricles.

The beginning of the QRS is measured from the point where the first wave of the complex begins to deviate from the baseline.; The point at which the last wave fo the complex begins to level out at above, or below the baseline marks the end of the QRS complex.

Normal Characteristics of the QRS Complex

- The amplitude if the R or S wave in the QRS complex in Lead II may vary from 1 to 2 mm to 15mm or more.

- The normal Q wave is less than 25% of the amplitude if the R wave. - The duration of the QRS complex is 0.10 second or less. - The duration of the Q wave does not normally exceed 0.04 second - The direction of the QRS complex may be predominantly positive,

predominantly negative, or biphasic (partly positive, partly negative).

Abnormal QRS Complexes

- The duration of an abnormal QRS complex is greater than 0.10 second. - The duration of a QRS caused by an electrical impulse originating in an

ectopic pacemaker in the Purkinje network or ventricular myocardium is usually greater than 0.12 second and often 0.16 second greater.

- If the electrical impulse originates in a bundle branch, the duration of the QRS may be only slightly greater than 0.10 second.

- The amplitude of the waves in an abnormal QRS complex may vary from 1 to 2 mm to 20 mm or more.


The ST Segment

The portion of the ECG tracing between the QRS complex and the T wave is called the ST segment. The ST segment represents the early part of repolarization of the right and left ventricles. ST segment elevation or depression is determined by measuring at a point 0.04 second (one small box) after the end of the QRS complex (J point).

Normal Characteristics of the ST Segment

- Begins with the end of the QRS complex and ends with the onset of the T wave.

- The point where the QRS complex and the ST segment meet is called the “junction” or “J” point.

- The ST segment is typically isoelectric (flat), however, it may normally be elevated 1-2 mm in leads I, II, or III.

- The normal ST segment begins at the isoelectric line, extending from the end of the S wave and curving gradually upwards to the beginning of the T wave.

Abnormal ST Segments

- A horizontal ST segment (forms a sharp angle with the T wave) is suggestive of ischemia.

- ST segment depression is suggestive of myocardial ischemia - More than 1-2 mm ST segment elevation in two contiguous leads is

suggestive of acute myocardial infarction. - Digitalis causes a depression (scoop) of the ST segment sometimes referred

to as a “dig dip.” The T Wave

Ventricular repolarization is represented on the ECG by the T wave. The absolute refractory period is still present during the beginning of the T wave. At the peak of the T wave, the relative refractory period has begun. It is during the relative refractory period that a stimulus may produce ventricular dysrhythmias.

The beginning of the T wave is identified as the point where the slope of the ST segment appears to become abruptly or gradually steeper. The T wave ends when it returns to the baseline. It may be difficult to clearly determine the onset and end of the T wave.


Normal Characteristics of the T Wave

- Slightly asymmetrical - In Leads I, II, and III, is not greater then 5 mm amplitude.

Abnormal T Waves

- The T wave following an abnormal QRS complex is usually opposite in direction of the QRS.

- Inverted T waves are suggestive of myocardial ischemia. - Peaked T waves are commonly seen in patients with hyperkalemia.

The QT Interval

The QT interval represents total ventricular activity—the time from ventricular depolarization to repolarization of the ventricles. It is measured from the beginning of the QRS complex to the end of the T wave. It normally lasts 0.36 to 0.44 second, but varies with the patient’s heart rate (it is longer with slower heart rates and shorter with faster ones), age, and sex.

A prolonged QT interval indicates a lengthened relative refractory period (vulnerable period) which puts the ventricles at risk for life-threatening dysrhythmias such as Torsades de Pointes.

A prolonged QT interval may be congenital, of familial origin, or caused by medications such as certain antidysrhythmic agents (quinidine, procainamide, disopyramide), some cyclic antidepressants, electrolyte imbalance (hypokalemia), cerebrovascular disease, hypothermia, or bradycardia.

The U Wave

The significance of the U wave is not definitely known but is thought to represent the repolarization of the Purkinje fibers. U waves are not easily identified due to their low amplitude. U waves, when seen, will follow the T wave and will be in the same direction as the T wave. A U wave taller than 2 mm is considered abnormal and may suggest hypokalemia or the effects of digoxin or quindine on the conduction system. A U wave that is seen in a direction opposite that of the T wave, preceding it may be indicative of cardiac disease.


Interpretation of Arrhythmias from Electrocardiogram: There are five basic steps which assist in the identification of arrhythmias. The electrocardiogram should be studied in an orderly fashion in the following manner:

Step 1… Calculate the heart rate. The two simplest methods for obtaining the rate are:

a. Count the number of “R” waves in a 6-inch strip of the electrocardiographic tracing (which equals to 6 seconds). Multiply this sum by 10 to get the rate per minute. Since the electrocardiographic paper is marked into 3-inch intervals (at the top margin), the approximate heart rate can be rapidly calculated.

b. Commercially available rate calculators, which measure the distance between “R” waves, may be placed on the electrocardiogram and the heart rate read directly from the scale.

On the basis of heart rate alone arrhythmias can be divided into:

a. Slow rate (bradycardia), where there are less than 60 beats per minute; b. Normal rate, where the rate is between 60-100 per minute; c. Fast rate (tachycardia), where there are more than 100 beats per minute.

Since several arrhythmias are characterized only by rate changes, rate calculation is essential in interpreting any electrocardiogram.

Step 2… Measures the regularity (rhythm) of the “R” waves. This can be done by gross observation or actual measurement of the intervals. If the “R” waves occur at regular intervals (with a variance of less than 0.12 seconds between beats), the ventricular rhythm is normal. When there are differences in “R” – “R” intervals (greater than 0.12 seconds, the ventricular rhythm is said to be irregular. This division of ventricular rhythm into regular and irregular categories assists in identifying the mechanism of many arrhythmias.

Step 3… Examine the “P” waves. If “P” waves are present and precede each QRS complex, the heart beat originates in the sinus node and a sinus rhythm exists.


The absence of “P” wave or an abnormality in their position with respect to the QRS complex indicated that the impulse started outside the SA node and than an ectopic pacemaker is in command.

Step 4… Measure the “PR” interval. Normally, this interval should be between 0.10 and 0.20 seconds. Prolongation or reduction of this interval beyond these limits indicates a defect in the conduction system between the atria and the ventricles.

Step 5… Measure the duration of the QRS complex. If the width between the onset of the “Q” wave and the completion of the “S” wave is more than 0.12 seconds an interventricular conduction delay exists. Normal is 0.06 to 0.12 seconds.

When interpreting the following rhythms assume that all strips are 6 seconds.

Each rhythm strip must be analyzed in a systematic fashion. It is helpful to consider the following questions:

1. Is the rate fast or slow? Are the atrial and ventricular rates the same? 2. Are the P wave to P wave and R wave to R wave intervals regular or

irregular? If the rhythm is irregular, is it consistent, or is it an irregular irregularity?

3. Is there a P wave before each ventricular complex? Does a P wave follow the QRS complex? Are the P and the QRS complexes identical and normal in configuration?

4. Are the PR and QRS intervals within normal limits? 5. When correlated with clinical observation of the patient, what is the

significance of the dysrhythmia?

ECG Troubleshooting

Artifacts are distortions that obscure the cardiac impulse on the ECG tracing. Artifacts may be caused by electrical, mechanical or patient interference. This often makes accurate interpretation difficult. They may be similar to a life threatening dysrhythmia; so remember to check the patient.


NormalSinusRhythm

Normal Sinus Rhythm (NSR). Here the pacemaker site is in the sinus node. This is verified by the normal P wave configuration.

Rate: 60 to 100 per minute (atrial and ventricular rates are equal).

Rhythm: Regular (R-R intervals and P-P intervals are constant).

P Waves: Upright and uniform, precede each QRS complex.

P-P intervals: Within normal limits (0.12-0.20 seconds in duration) and constant.

QRS intervals: Within normal limits (less than or e equal to 0.12 seconds in duration).

SinusTachycardia

Sinus Tachycardia. Pacemaker is again present in the sinus node.

Rate: Between 100 and 150 beats per minute.



P-R intervals: Within normal limits (0.12-0.20 seconds) and constant.

QRS intervals: Within normal limits (less than or equal 0.12 seconds).

Sinus Bradycardia

Sinus Bradycardia. The pacemaker site is the sinus node.

Rate: Less than 60 beats per minute.




P-R intervals: Within normal limits (0.12- 0.20 seconds) and constant.

QRS intervals: Within normal limits (less than or equal to 0.12 seconds).

Premature Atrial Contractions (PAC’s)

Premature Artial Contractions. These may result from an ectopic site or focus located ion either the right or the left atrium. This discharges the atria before the arrival of the next sinus impulse, and an ectopic atrial contraction may result. The QRS is usually normal but may be aberrant. There is often an incomplete compensatory pause following a PAC.

Rate: Is dependent on the rate of the underlying rhythm.

Rhythm: Irregular (underlying rhythm is disrupted by presence of early beat.

P Waves: Present with the underlying rhythm and premature beats.

P-R Intervals: Present with the underlying rhythm and premature beats, is within normal limits.

QRS Intervals: Premature beats are narrow (less than or equal to 0.12 seconds) and look the same as QRS complexes of the underlying rhythm. T waves of the premature beats are of the same direction as the R waves. PACs are not usually followed by a compensatory pause.

AtrialFlutter

Atrial Flutter. This dysrhythmia results from a rapid, irritable atrial focus. Atrial activity is seen as flutter of F waves (about 300 per minute) showing a “sawtooth” configuration. Most often the ventricular rate is about 150 beats per minute. The ventricles cannot respond as rapidly as the atrial stimulation, so there is a degree of block (2:1, 3:1, 4:1, etc.) of atrial rate to ventricular response.

Rate: Depends on ventricular response, may be normal, slow or fast.

Rhythm: Atrial rhythm is regular; depending on conduction ratio, ventricular rhythm may be regular or irregular.

P Waves: There are no discernible P waves. The atrial activity is represented by “flutter waves” which produce a characteristic “sawtooth appearance”


P-R Intervals: Absent

QRS Intervals: Within normal limits (less than or equal to 0.12 seconds).

Atrial Fibrillation

Atrial Fibrillation. Multiple irritable atrial foci produces minimal areas of depolarization, none of which is enough to depolarize the whole atrium. Subsequently, standard P waves are missing and instead there is multiple disorganized minimal electrical activity (no definite P waves). The ventricular response is totally irregular and this is usually referred to as an “Irregular Irregularity”.

Rate: Depends on ventricular response, may be normal, slow, or fast.

Rhythm: Totally (grossly) irregular. Also referred to as irregularly irregular.

P Waves: There are no discernible P waves. The baseline is chaotic as the atrial activity is represented by “fibrillatory waves”.

P-R Intervals: Absent

QRS Intervals: Within normal limits (less than or equal 0.12 seconds).


Premature Junctional Contractions

Premature Junctional Contractions. Premature junctional contractions may occur from a discharge in the AV junctional region. Characteristically, negative (inverted) P waves are seen. Junctional dysrhythmias themselves are similar to those described as atrial rhythms, as both are “supraventricular” and have the same significance. Note: Always study P waves in Lead II.

Rate: Is dependant on the rate of the underlying rhythm.

Rhythm: Irregular (underlying rhythm is disrupted by presence of early beats).

P Waves: Typically present with the underlying rhythm. If present they will be abnormal, differing in size, shape, and direction from normal P waves. If present, the P waves are usually inverted.

P-R Intervals: Typically present with the underlying rhythm. If the present with the premature beats, will be less than 0.12 seconds.

QRS Intervals: Premature beats are narrow (less than or equal to 0.12 seconds) and look the same as QRS complexes of the underlying rhythm. T waves of the premature beats are of the same direction as the R waves. PJCs are not usually followed by a compensatory pulse.


AV Block. When conduction is slowed through the AV node, it may present with three main types of impairment- first, second, or third degree AV block.

First Degree AV Block

First-Degree AV Block. First-degree AV block or prolonged AV conduction is simply a delay in passage of the impulse through the AV node so that the PR interval is prolonged greater than 0.21 second. All P waves are conducted. The delay may actually be in the atria, His bundle, or bundle branches as well. Note: the number of P waves is equal to the number of QRS complexes.

Rate: Regular

Rhythm: Regular Rhythm

P Waves: Precedes each QRS. Upright.

P-R Intervals: Greater than 0.20 second but at a constant rate.

QRS Intervals: Usually normal duration and configuration.

Second Degree AV Block Mobitz Type I (Wenckebach)


Second Degree AV Block. The degree of impairment is now advanced so that some impulses fail to pass through the ventricles, resulting in “dropped” beats. Second degree AV block is usually divided into two main types. In Mobitz Type 1 or Wenckebach phenomenon, the PR interval lengthens progressively to the point where an impulse fails to reach the ventricle and a beat is dropped.

Rate: Ventricular rate is slightly slower than normal.

Rhythm: Irregular, appears as a pattern (cycle seems to occur over and over again).

P Waves: Upright and uniform, there are more P waves than QRS complexes as some of the QRS complexes are blocked.

P-R Intervals: Get progressively longer until a QRS complex is “dropped”. After the blocked beat, the cycle starts all over again.

QRS Intervals: Within normal limits (less than or equal to 0.12 seconds).

Second Degree AV Block Mobitz Type II

Mobitz Type II AV Block. This is the more serious type. P waves will occur without a subsequent QRS complex, often in the ratio of atrial to ventricular responses such as 2:1, 3:1, etc. PR interval is constant.


Rate: The ventricular rate is slower than normal (less than 60 beats per minute) while the atrial rate is within normal range.

Rhythm: Typically regular. Is irregular if the conduction ratio (number of P waves to each QRS complex) varies.

P Waves: Upright and uniform. There are more P waves than QRS complexes.

P-R Intervals: Constant, can be normal or longer than normal (greater than 0.20 seconds).

QRS Interval: Within normal limits (less than or equal to 0.12 seconds).

Third Degree AV Block (Complete heart block)

Third-Degree (Complete) AV Block. This abnormality is present when no impulses from the atria reach the ventricles. The atria and ventricles beat independently, and the ventricular pacemaker may be in the region of the AV node, Bundle of His, or bundle branch Purkinje system. The lower pacemaker lies in the ventricle, the slower the ventricular rate. This is often referred to as idioventricular rhythm. There is no regular relationship between the P waves and QRS complexes.

Rate: The ventricular rate is slower than normal (less than 60 beats per minute) while the atrial rate is within normal range.

Rhythm: Regular


P Waves: There are more P waves than QRS complexes.

P-R Intervals: There is no relationship between the P waves and QRS complexes, “the P waves seem to march right through the QRS complexes.”

QRS Intervals: May be normal or wide, is dependent upon how in the conduction pathway the escape beats are.

Frequent Premature Ventricular Contractions

Multifocal Premature Ventricular Contractions

Premature Ventricular Contractions (PVCs). Premature ventricular contractions occur in both healthy and diseased hearts. These ectopic beats may occur singly or in clusters of two or more. They also occur in bigeminy. Complex PVCs can increase the risk of ventricular tachycardia and ventricular fibrillation.

Rate: Determined by the underlying ventricular rate and number of PVCs.


Rhythm: Irregular during PVC; underlying rhythm may be regular.

P Waves: Typically present with the underlying rhythm but not the premature beats.

P-R Intervals: Typically present with the underlying rhythm but not the premature beats.

QRS Intervals: Occurs earlier than expected; duration exceeds 0.12 second with bizarre configuration. T waves of the premature beats take an opposite direction to the R waves. PVCs usually followed by a complete compensatory pause.

Ventricular Tachycardia

Ventricular Tachycardia. This dysrhythmia represents a grave, life threatening situation in certain circumstances. This diagnosis is suggested any time a series of three of more bizarre, premature ventricular beats is present.

Rate: Ventricular rate is between 150-250 beats per minute. If the rate is less than 150 it is referred to as slow VT. If the rate is greater than 250 it is referred to as ventricular flutter.

Rhythm: Typically regular.

P Waves: Typically absent (if seen, they are dissociated).

P-R Intervals: Absent.

QRS Intervals: Wide (greater than 0.12 seconds) and bizarre. T waves of the ventricular beats take an opposite direction to the R waves. Beats are usually followed by a compensatory pulse.


Ventricular Fibrillation (Coarse)

Ventricular Fibrillation. The ventricles discharge in a completely disorganized fashion with bizarre fibrillatory activity. There is no pattern of any sort and no definite QRS complexes. The ventricular muscle, if observed, is simply quivering. Two types are described: coarse ventricular fibrillation of fairly high amplitude, and fine ventricular fibrillation of low amplitude.

Rate: Cannot be determined as there are no discernible waves to measure.

Rhythm: Totally chaotic

P Waves: There are no discernible P waves.

P-R Intervals: There are no intervals

QRS Intervals: There are no discernible QRS complexes

Cardiac Standstill/ Asystole

Rate: Absent

Rhythm: Absent


P Waves: There is no electrical activity only a flat line.

P-R Intervals: There is no electrical activity only a flat line.

QRS Intervals: There is no electrical activity only a flat line.

Ventricular Asystole

Rate: Absent.

Rhythm: Absent

P Waves: Upright and uniform.

P-R Intervals: There is no electrical activity only a flat line.

QRS Intervals: There is no electrical activity only a flat line.

Agonal

Rate: Less than 20

Rhythm: Irregular

P Waves: There is no electrical activity only a flat line.

P-R Intervals: Not measurable.

QRS Intervals: Greater than 0.12 seconds and irregular.

Idioventricular

Rate: Between 20-40

Rhythm: Essentially regular.


P Waves: May be absent or with retrograde conduction to the atria. May appear after QRS complex.

P-R Intervals: Not measurable.

QRS Intervals: Greater than 0.12 seconds.

Pacer In Capture

Rate: Varies according to preset rate of [pacemaker.

Rhythm: Regular if pacing is constant, irregular if on demand.

P Waves: May be present or absent. Normal or abnormal.

P-R Intervals: Depends on underlying rhythm.

QRS Intervals: If pacemaker induced. QRS complex 0.10 or greater. Appearance is bizarre, resembling PVC’s.

Note: Pacemaker. Spikes only indicate that a pacemaker is discharging. If spikes do not elicit a QRS complex, the pacemaker is not capturing.


Bibliography Aehlert, Barbara. ECGs Made Easy. Maryland Heights, MO: Mosby Jems/Elsevier, 2011. Print. "Lesson VI - ECG Conduction Abnormalities." EHSL - Spencer S. Eccles Health Sciences Library Home Page. Web. 08 Oct. 2010. <http://library.med.utah.edu/kw/ecg/ecg_outline/Lesson6/index.html#First>. Potter, P., Perry, A. Fundamentals of Nursing, 6th ed. St. Louis: Mosby, 2006. "The Six Second ECG." Print. Rpt. in Vol. Version 1.2. Nursecom Educational Technologies, 2004. Print.

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