INTERPRETING A RHYTHM STRIP
56
Recognizing normal sinus rhythm
Before you can recognize an arrhythmia, you must first be able to recognize normal sinus rhythm. Normal sinus rhythm records an impulse that starts in the sinus node and progresses to the ventricles through a normal conduction pathway—from the sinus node to the atria and AV node, through the bundle of His, to the bundle branches, and on to the Purkinje fibers. Normal sinus rhythm is the standard against which all other rhythms are compared. (See
Normal sinus rhythm.)
What makes for normal?
Using the 8-step method previously described, these are the characteristics of normal sinus rhythm:
•Atrial and ventricular rhythms are regular.
•Atrial and ventricular rates fall between 60 and 100 beats/minute, the SA node’s normal firing rate, and all impulses are conducted to the ventricles.
Normal sinus rhythm
Normal sinus rhythm, shown below, represents normal impulse conduction through the heart.
Each component of the
The atrial and ventricular |
A P wave precedes each QRS complex. |
ECG complex is present. |
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rhythms are regular. |
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Characteristics of normal sinus rhythm:
•Regular rhythm
•Normal rate
•A P wave for every QRS complex; all P waves similar in size and shape
•All QRS complexes similar in size and shape
•Normal PR and QT intervals
•Normal (upright and round) T waves
RECOGNIZING NORMAL SINUS RHYTHM |
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•P waves are rounded, smooth, and upright in lead II, signaling that a sinus impulse has reached the atria.
•The PR interval is normal (0.12 to 0.20 second), indicating that the impulse is following normal conduction pathways.
•The QRS complex is of normal duration (less than 0.12 second), representing normal ventricular impulse conduction and recovery.
•The T wave is upright in lead II, confirming that normal repolarization has taken place.
•The QT interval is within normal limits (0.36 to 0.44 second).
•No ectopic or aberrant beats occur.
That’s a wrap!
Rhythm strip interpretation review
Normal P wave
•Location—before the QRS complex
•Amplitude—2 to 3 mm high
•Duration—0.06 to 0.12 second
•Configuration—usually rounded and upright
•Deflection—positive or upright in leads
I, II, aVF, and V2 to V6; usually positive but may vary in leads III and aVL; negative or inverted in lead aVR; biphasic or variable in lead V1
Normal PR interval
•Location—from the beginning of the P wave to the beginning of the QRS complex
•Duration—0.12 to 0.20 second
Normal QRS complex
•Location—follows the PR interval
•Amplitude—5 to 30 mm high but differs for each lead used
•Duration—0.06 to 0.10 second, or half the PR interval
•Configuration—consists of the Q wave, the R wave, and the S wave
• Deflection—positive in leads I, II, III, aVL, aVF, and V4 to V6 and negative in leads aVR and V1 to V3
Normal ST segment
•Location—from the S wave to the beginning of the T wave
•Deflection—usually isoelectric; may vary from – 0.5 to + 1 mm in some precordial leads
Normal T wave
•Location—after the S wave
•Amplitude—0.5 mm in leads I, II, and III and up to 10 mm in the precordial leads
•Configuration—typically round and smooth
•Deflection—usually upright in leads I,
II, and V3 to V6; inverted in lead aVR; variable in all other leads
Normal QT interval
•Location—from the beginning of the QRS complex to the end of the T wave
•Duration—varies; usually lasts from 0.36 to 0.44 second
(continued)
INTERPRETING A RHYTHM STRIP
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Rhythm strip interpretation review (continued)
Normal U wave
•Location—after T wave
•Configuration—typically upright and rounded
•Deflection—upright
Interpreting a rhythm strip: 8-step method
•Step 1: Determine the rhythm
•Step 2: Determine the rate
•Step 3: Evaluate the P wave
•Step 4: Measure the PR interval
•Step 5: Determine the QRS complex duration
•Step 6: Examine the T waves
•Step 7: Measure the QT interval duration
• Step 8: Check for ectopic beats and other abnormalities
Normal sinus rhythm
Normal sinus rhythm is the standard against which all other rhythms are compared.
Characteristics
•Regular rhythm
•Normal rate
•P wave for every QRS complex; all P waves similar in size and shape
•All QRS complexes similar in size and shape
•Normal PR and QT intervals
•Normal T waves
Quick quiz
1.The P wave represents:
A.atrial repolarization.
B.atrial depolarization.
C.ventricular depolarization.
D.ventricular repolarization.
Answer: B. The impulse spreading across the atria, or atrial depolarization, generates a P wave.
2.The normal duration of a QRS complex is:
A.0.06 to 0.10 second.
B.0.12 to 0.20 second.
C.0.24 to 0.28 second.
D.0.36 to 0.44 second.
Answer: A. Normal duration of a QRS complex, which represents ventricular depolarization, is 0.06 to 0.10 second.
QUICK QUIZ |
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3. To gather information about impulse conduction from the atria to the ventricles, study the:
A.P wave.
B.PR interval.
C.ST segment.
D.T wave.
Answer: B. The PR interval measures the interval between atrial depolarization and ventricular depolarization. A normal PR interval is 0.12 to 0.20 second.
4. The period when myocardial cells are vulnerable to extra stimuli begins with the:
A.end of the P wave.
B.start of the R wave.
C.start of the Q wave.
D.peak of the T wave.
Answer: D. The peak of the T wave represents the beginning of the relative, although not the absolute, refractory period, when the cells are vulnerable to stimuli.
5. Atrial and ventricular rates can be determined by counting the number of small boxes between:
A.the end of one P wave and the beginning of another.
B.two consecutive P or R waves.
C.the middle of two consecutive T waves.
D.the beginning of the P wave to the end of the T wave.
Answer: B. Atrial and ventricular rates can be determined by counting the number of small boxes between two consecutive P or R waves and then dividing that number into 1,500.
Test strips
Now try these test strips. Fill in the blanks below with the particular characteristics of the strip.
Strip 1
Atrial rhythm: ________________ |
QRS complex: ________________ |
Ventricular rhythm: ___________ |
T wave:______________________ |
Atrial rate: ___________________ |
QT interval: __________________ |
Ventricular rate: ______________ |
Other: _______________________ |
P wave:______________________ |
Interpretation: ______________ |
PR interval: __________________ |
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INTERPRETING A RHYTHM STRIP
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Strip 2
Atrial rhythm: ________________ |
QRS complex: ________________ |
Ventricular rhythm: ___________ |
T wave:______________________ |
Atrial rate: ___________________ |
QT interval: __________________ |
Ventricular rate: ______________ |
Other: _______________________ |
P wave:______________________ |
Interpretation: ______________ |
PR interval: __________________ |
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Answers to test strips
1.Rhythm: Atrial and ventricular rhythms are regular Rate: Atrial and ventricular rates are each 79 beats/minute P wave: Normal size and configuration
PR interval: 0.12 second
QRS complex: 0.08 second; normal size and configuration T wave: Normal configuration
QT interval: 0.44 second Other: None
Interpretation: Normal sinus rhythm
2.Rhythm: Atrial and ventricular rhythms are regular Rate: Atrial and ventricular rates are each 72 beats/minute P wave: Normal size and configuration
PR interval: 0.20 second
QRS complex: 0.10 second; normal size and configuration T wave: Normal configuration
QT interval: 0.42 second Other: None
Interpretation: Normal sinus rhythm
Scoring
If you answered all five questions correctly and filled in all the blanks pretty much as we did, hooray! You can read our rhythm strips anytime.
If you answered four questions correctly and filled in most of the blanks the way we did, excellent! You deserve a shiny new pair of calipers.
If you answered fewer than four questions correctly and missed most of the blanks, chin up! You’re still tops with us.
Part II Recognizing arrhythmias
4 |
Sinus node arrhythmias |
63 |
5 |
Atrial arrhythmias |
87 |
6 |
Junctional arrhythmias |
111 |
7 |
Ventricular arrhythmias |
127 |
8 |
Atrioventricular blocks |
153 |