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Introduction

Electrocardiography is an electronic tracing of the conduction system of the heart.  An ECG gives us a picture of the neuro/electrical impulses as they travel from the sinoatrial node through the atrium and the atrioventricular node to the Bundle of His, Purkinje fibres and into the myocardial cells.  This is the “freeway system” of the heart and it carries the electrical impulses that stimulate the heart to contract.

These neuro/electrical impulses can be detected at the body surface using electrodes.  The tracings can be used to determine the action of the heart muscle.  Changes in rate and rhythm of the heart can be determined.  Decreased circulation of blood and oxygen to the heart muscle can cause loss of function or altered function of the conduction system, thereby, changing the path of the impulses and generating dysrrhythmias (altered rhythms) or arrhythmias (no rhythm)

1. EKG Vocabulary

Review this list of terms: aortic arch, asystole, atrioventricular, "AV") node, atrium, bradycardia, carotid sinus, congestive heart failure (CHF), contractility, coronary insufficiency, diastole, ectopic, edema, electrocardiogram (ECG, EKG), fibrillation, flutter, infarction, ischemia, sinoatrial (SA) node, sinus rhythm, systole, tachycardia, ventricle, etc. Use  ww.medical-dictionary.com

Additional vocabulary:  Bundle of His, Purkinje fibres, electrodes, dysrrhythmia, arrhythmia, myocardial, pacemaker, depolarization, and repolarization.

2. EKG Waveform

In the following graphic, Q is the bottom starting point, R the top point, and S the bottom end point of the QRS Complex.

Each wave in this schematic drawing of a PQRSTcomplex represents an electrical event in the heart. 

The P wave represents depolarization of the atrium which causes atrial contraction and the pumping of blood from the atrium into the ventricle.  Normally the P wave should be an upright (positive) deflection.  The P – R Interval is a reflection of the length of time the atrium takes to pump blood from the atrium to the ventircle.  The P – R interval starts with the beginning of the P wave and ends with the beginning of the QRS complex.  Its length varies based on the heart rate and the function of the AV node.  Atrial contraction begins at the peak of the P wave and continues to the beginning of the QRS complex.  At this point the atrioventricular valves (mitral and tricuspid) close.  Blood is trapped in the ventricle with all valves closed. The pressure rises.

The QRS complex represents depolarization of the ventricle.  Ventricular contraction corresponds to the peak of this complex and continues through the ST segment and the T wave.  Pressure builds in the ventricle until the semilunar valves (aortic and pulmonic) open.  Blood rushes out with the ventricular contraction and the pressure in the ventricle drops. The aortic and pulmonic valves close.  The semilunar valves open at the onset of the ST segment.  The semilunar valves slam shut at the conclusion of the T wave.

See Wiggers Diagram at  http://sprojects.mmip.mcgill.ca/cardiophysio/EKGwiggers.htm 

3. Normal Sinus Rhythm

Normal Sinus Rhythm: “NSR” is the term used to describe a rhythm generated in the sinoatrial (SA) node with a rate between 60 and 100 beats per minute.  We determine sinus rhythm by several criteria.

1.      A P wave precedes each QRS complex. 

2.      The P wave is not taller than 3 mm, it is not wider than 0.11 seconds, it is not peaked or notched. 

3.      The P-R interval, which is from the beginning of the P wave to the beginning of the QRS complex, represents the depolarization of the atrium.  Its length should be 3 – 5 small squares.  One small square is equal to 0.04 seconds.  Five small squares makes up one large square which is equal to 0.20 seconds (5 x 0.04 = 0.20).  The normal P-R interval is 0.12 (3 small squares) to 0.20 (5 small squares) seconds in length.  Again, this can vary with heart rate and AV node function.  A malfunction in the AV node will cause the P-R interval to be greater than 0.20 seconds. 

4.      Each P wave is followed by a QRS complex.  The QRS complex represents depolarization of the ventricle. 

5.      Three waves compose the QRS complex.  The first downward (negative) deflection from the baseline is the Q wave.  It should be less than ¼ as tall as its succeeding R wave.  The R wave is an upward (positive) deflection. As the R wave descends below the baseline, it comes the S wave. 

6.      The ST segment begins when the S wave returns to the baseline. 

7.      The normal QRS complex is less than three small squares wide (0.12 seconds). 

See www.12leadECG.com.  This is the web site for 3 new books on 12 lead and rhythm interpretation. 

EKG Library

  EKG Rounds   EKG Fileroom

Self-test for practice, not to be submitted. Write out the right answers for yourself as AAAA AAAA AAAA.

1. On EKG paper, a small box stands for A-0.20, B-0.40, C-0.02, D-0.04 seconds. 
2. The depolarization of the atrial myocardia is the A-P Wave, B-QRS Complex, C-T-Wave, D-none of these. 
3. The depolarization of the ventricalar myocardia is the A-P Wave, B-QRS Complex, C-T-Wave, D-none of these.
4. The first hear sound is produced at A-Q, B-R, C-S, D-T-wave.
5. The semilunar valve opens at A-Q, B-R, C-S, D-J. 
6. A QRS complex of 0.14 seconds is normal. A-true, B-false.
7. A T-wave of 0.04 seconds is normal. A-true, B-false.
8. The atrium of the heart is the A-large, B-holding, C-exit, D-entrance chamber of the heart.
9. EKGs show the potential of the heart during A-rest, B-contraction, C-full operation, D-action.
10. The mitral value is between the left atrium and the A-left, B-right, C-upper, D-lower ventricle.
11. The mitral value has A-1, B-2, C-3, D-4 valve cusps.
12/ Sinus rhythm is the A- normal, B-regular, C-usual, D-all, 3 rhythm of a health heart.

 

Atrial Fibrillation (A-Fib)   Definition: In A-Fib there are many ectopic foci on the atria. The atria discharge impulses at rates greater than 400 beats per minute. This serious arrhythmia may be chronic or intermittent. A-Fib is labelled as controlled if there are less than 100 beats per minute, uncontrolled if there are more than 100 beats per minute. Possible causes are hypertension, ischemia, myocardial disease, pericardial disease, hyperthyroidism, chronic congestive heart failure, chronic obstructive pulmonary disease, edema associated with status post heart surgery, and the aging heart. EKG Characteristics: Rate: Controlled A-Fib less than 100 bests per minute, uncontrolled more than 100 beats per minute. Atrial rate is almost indiscernible. Rhythm: Atrial and ventricular both very irregular. P Wave: No P waves, baseline has fibrillatory waves. PR Interval: Indiscernible. QRS Complex: Normal configuration 0.08-0.12 seconds. ST Segment: Indiscernible. T Wave: indiscernible. Nursing Intervention: Notify MD and start oxygen administration. Drugs commonly used to treat A-Fib are  anticoagulants, beta blockers and calcium channel blockers. If drug treatment fails to treat this arrhythmia, cardioversion may be used. If the rhythm is more than 48 hours old, the physician may consider cardioversion to return the patient to a normal sinus rhythm.  Patients with chronic atrial fibrillation will require anti coagulation to prevent mural wall emboli from forming.

 

Atrial Flutter (A-Flutter)   Definition: A-Flutter is an atrial arrhythmia characterized by the "sawtooth" atrial baseline at a rapid rate that is greater than 250 beats per minute. Possible causes are enlarged atria, chronic obstructive pulmonary disease, valve disease and pericarditis. EKG Definitions: Rate: Atrial rate is rapid, greater than 250 beats per minute. Ventricular rate varies. Rythm: Atrial rhythm is regular. Ventricular rhythm could be regular or irregular. P Wave: A "sawtooth" baseline or flutter waves are present. PR Interval: Not measurable. QRS Complex: Usually normal configuration 0.08-0.12 seconds. ST Segment: Sometime indiscernible. T Wave: Sometimes indiscernible. Nursing Intervention: Notify MD if this a new rhythm. If dyspneic, give oxygen. Common drugs to treat A-Flutter are digoxin, quinidine, anticoagulants, beta blockers, and calcium channel blockers. Cardioversion may also be used if drug treatment is not successful. TEST Study this web-site for 3 hours for an approved (RN-CEP 11430, MFT- PCE 39) 3-hours Continuing Education Certificate (0.3 CEUs). Then take the AutoTest or eTest.  Test: 1) click her for the self-correcting test & online payment, and 2) receive your certificate immediately online. All is online, nothing by post-mail.