Electrocardiogram Electrocardiogram Rhythm InterpretationRhythm Interpretation

by

Evan M. Hodell 12/00

What is an EKG?

• An EKG is a method of measuring, displaying and recording the electrical activity of a heart

• Electrical stimuli is amplified to create a “rhythm strip” by a machine that consistently produces representations of the heart’s electrical activity

BASIC TERMINOLOGY

• Arrhythm ia: Abnormal rhythm• Base line : Flat, straight, isoelectric line• Wave form : Movement away from the

baseline, up or down• S e gm e nt: A line between waveforms• Inte rval: A waveform plus a segment• C om ple x: Combination of several

waveforms

Electrical System of Heart

Components of a NSR

Components of a NSR

Point of OriginPoint of Origin NameName

• SA Node- Sinus rhythm– Causes regular, rounded P waves, and normal,

narrow QRS complexes

• Atria- Atrial rhythm– Causes irregularly shaped P waves, but still normal,

narrow QRS complexes

• AV Node- Junctional rhythm– Normal, narrow QRS complexes with no P waves

• Perkinjie Fibers- Ventricular rhythm – No P waves, and irregular, wide QRS complexes

Beginning to Beginning to Recognize RhythmsRecognize Rhythms

• Step 1: Are there P waves?

• Step 2: Are there QRS complexes?

• Step 3: Are the P waves and QRS complexes related?

Example 1

• STEP 1.–Are there P waves?

Example 1 Continued

• Are there P waves?– Yes, P waves are easily identifiable

and regular in rate.

Example 1 Continued

• STEP 2.– Are there QRS complexes?

Example 1 Continued

• STEP 2.– Yes there are normal, narrow, QRS

complexes.

Example 1 Continued

• STEP 3– Are they related, 1:1?

Example 1 Continued

• STEP 3– Are they related, 1:1?

• Yes, there is one P wave for every QRS.

• This is called a sinus rhythm

Example 2

• Follow steps 1-3 as demonstrated in Ex. 1.• This is also a sinus rhythm.

• Note: The P waves are smaller, yet their regularity in relation to the QRS complexes gives them away.

Example Three

• Following the same steps, this one doesn’t match up!?!?

Example 3 continuedExample 3 continued• Step 1

– Are there P waves?• Yes,

– Note: notice the dotted arrows indicate the location of P waves buried in the stronger electrical activity of the QRS complexes.

Example 3 ContinuedExample 3 Continued

• STEP 2–Are there QRS complexes?

•Yes, there are normal, narrow QRS complexes.

Example 3 Continued• STEP 3.

– Are they related?• NO, they are both regular in shape and rate, but

there is no relation between them.

– This shows a Complete Heart Block, also called a 3rd degree block.

– Can the Heart effectively pump blood if the Atria and Ventricles are not working together?

Case Study of Beau

• Beau is an 11 y/o 45 lb. Male Australian Shepard.

• Physical exam: see overhead • Beau presents with a moderate, chronic, nocturnal

cough with mild dyspnea. Secondary exam also reveals a pounding irregular heartbeat and Grade 4 murmur.

• Electrocardiogram was ordered in addition to other tests. Result:

Case Study of Beau• EKG reveals a Sinus Arrhythmia,

– Beaus heart is “firing off” Premature Atrial Contractions, “PAC’s.

• Potentially indicative of atrial enlargement, or other heart irritability, which may or may not be related to Beau’s cough and current presentation.

4. Normal Intervals for the Human, Dog and Cat

• Human- HR- 60-100 bpm» PR interval- 0.12-0.20 sec» QRS width max= 0.11 sec » QT interval= 0.36-0.44 sec

• Dog- HR- 60-220 bpm» PR interval= 0.06-0.13 sec» QRS width max= 0.06 sec for large

0.05 sec for small» QT interval= 0.15-0.25 sec

• Cat- HR = 120-240 bpm» PR interval= 0.05-0.09 sec» QRS width max= 0.04 sec» QT interval= 0.12-0.18 sec

» -Tilley L.P. et al 1995

References

• Aehlert RN Ph. ECG’s Made Easy, Mosby Year Book 1995

• Bledsoe, B. Brady Paramedic Emergency Care, Prentice Hall New Jersey, 1988

• Foster, Bruce D.O. Twelve-Lead Electrocardiography for the ACLS Provide, Waynesboro PA, W.B. Saunders Co., 1996

• Fox. P.R. and Kaplan P. Contemporary Cardiology Issues in Small Animal Practice, Churchill Livingston, New York 1987

• Smith F.W.K, D.J. Hallock, Manual of Canine and Feline Cardiology W.B. Saunders, Philadelphia 1995

• Tilley, L.P. Essentials of Canine and Feline Electrocardiography, 3rd edition Williams and Wilkins, Baltimore 1995