understanding rhythm strips
TRANSCRIPT
Understanding Rhythm Strips
Waveforms and Components of The ECG Pattern
• A waveform – A positive or a negative defection that begins and ends at the baseline– It is an electrical representation of depolarization and repolarization
occurring in the heart• When there is NO electrical activity is detected, a straight line
(isoelectric or base line) is recorded• The waveforms produced by the heart’s electrical conduction
system are called– P– QRS– T– May or may not be a U Wave
ECG Waveforms
• P wave– Occurs when the right and left atria are stimulated
• QRS complex– Occurs when the right and left ventricles are stimulated
• T wave– Represents electrical recovery or return to a resting state
for the ventricles• U wave– If see, is thought to represent the repolarization of the
Purkinje fibers
ECG Waveforms
• P wave– Normally an upright and rounded waveform
• QRS complex– Usually the largest of all the waveforms and is
spike shaped and narrow in appearance• T wave– Appears as a slightly asymmetric upright waveform– It is usually larger than the P wave and smaller
than the QRS
ECG Waveform
EGC Waveform
ECG Segments
• Segment– Length of baseline between two waves• PR segment
– Represents the delay of the impulse in the AV node
• ST segment– Represents the early part of repolarization of the right and left
ventricles
ECG Intervals
• Interval is defined as the combination of a wave or several waves and a segment
• By measuring time intervals on the ECG, it can be determined how long the electrical wave takes to pass through the heart
ECG Intervals
• PR interval– P wave & PR segment– Corresponds to the spread of the electrical impulse
through the atria and the delay of the impulse in the AV node before it travels to the ventricular muscle tissue
• QT interval– QRS complex & ST segment & T wave– Represents electrical stimulation and recovery of the
ventricles
ECG Segments & Intervals
ECG Paper and Measurements
• ECG paper– Graph paper used to measure rates of impulse
formation and the duration of the electrical events that occur in the heart
– Vertical and horizontal lines, which from large and small boxes
– Vertical lines• Measure voltage in millivolts
– Horizontal lines• Measure time in seconds
ECG Paper and Measurements
• By counting the small or large boxes from the beginning to the end of the ECG waveforms and intervals, we can calculate the time it takes for the electricity to travel through certain parts of the heart and the rate at which impulses occur
ECG Paper and Measurements
Time Equivalents of Small Boxes
• 1 small box = 0.04 second
• 2 small boxes = 0.08 second• 3 small boxes = 0.12 second• 4 small boxes = 0.16 second• 5 small boxes = 0.20 second
Time Equivalents of Large Boxes
• 1 large box = 0.20 second• 5 large boxes = 1 second• 15 large boxes = 3 seconds• 30 large boxes = 6 seconds
Normal ECG Pattern and Measurements
• P Wave: Upright, smooth and rounded, and no more than 2.5 mm in height
Normal ECG Pattern and Measurements
• PR Interval: Measure 0.12 to 0.20 second wide or 3 to 5 small boxes
Normal ECG Pattern and Measurements
• QRS: Narrow in appearance, upright in Leads I, II, and III. Measures 0.04 to 0.11 second wide or 1 to 2 ½ small boxes
Normal ECG Pattern and Measurements
• ST Segment: Isoelectric
Normal ECG Pattern and Measurements
• T Wave: Slightly asymmetric, upright, and less than half the height of the QRS complex or 5 mm in height or less
Normal ECG Pattern and Measurements
• QT interval: QT interval is less than half the R-R interval or 0.36 to 0.44 seconds or 9 to 11 small boxes– The duration of the QT interval varies according to
age, gender, and heart rate• As the heart rate increases
– QT interval decreases
• As the heart rate decreases– QT interval increases
Normal ECG Pattern and Measurements
• QT Interval– Fast heart rate• Small QT interval
– Slow heart rate• Large QT interval
Normal ECG Pattern and Measurements
• U Wave: Upright and rounded. Usually less than 2 mm in height and smaller than that of the preceding T wave
Abnormal Characteristics of the ECG Pattern
• Abnormal P wave– Wide or notched-Left atrial enlargement or
ectopic impulse from atria– Tall and pointed (peaked) – Right atrial
enlargement or ectopic impulse from atria– Negative (Inverted) - ectopic pacemaker in the AV
junction
Abnormal Characteristics of the ECG Pattern
• Wide or notched
• Tall and pointed (peaked)
• Negative (inverted)
Abnormal Characteristics of the ECG Pattern
• Abnormal PR Interval– A PR interval greater than 0.20 second wide is
abnormal– This may be seen in • AV blocks• Hypothyroidism• Digitalis toxicity
Abnormal Characteristics of the ECG Pattern
• Abnormal QRS complex:– A wide QRS (greater than 0.12 second wide)• may be seen when an impulse originates from an
ectopic site in the ventricular myocardium• If there is a delay or block of the impulse in the bundle
branches
Abnormal Characteristics of the ECG Pattern
• Abnormal ST segment– Elevated ST segment• Elevated more than 1 mm in the limb leads or 2 mm in
the precordial leads – Suggestive of myocardial injury
» infarction
Abnormal Characteristics of the ECG Pattern
• Abnormal ST segment– Scoop ST depression• May be caused by digitalis toxicity
– Depressed ST segment• More than 1 mm
– Suggestive of myocardial ischemia
Abnormal Characteristics of the ECG Pattern
• Abnormal T wave– Negative (inverted) • Suggest myocardial ischemia or infarction
Abnormal Characteristics of the ECG Pattern
• Abnormal T wave– Low, flattened T waves• Can be seen with hypokalemia (low potassium)
Abnormal Characteristics of the ECG Pattern
• Abnormal T Wave– Tall Tented T waves• Suggestive of hyperkalemia (high potassium)
Abnormal Characteristics of the ECG Pattern
• Abnormal QT interval– Prolonged (greater than 0.44 seconds)• May be congenital or acquired
– i.e. medications, electrolyte abnormalities
Abnormal Characteristics of the ECG Pattern
• Abnormal U Wave– A U wave taller than 2 mm• Electrolyte imbalance • Medications• Hyperthyroidism• Central nervous system disease
Steps for Analyzing a Rhythm Strip
• A quick method for analyzing a rhythm strip– There are several steps in analyzing a rhythm strip– When analyzing a rhythm strip, don’t forget to
check the patient
Steps for Analyzing a Rhythm Strip
• Step 1:– Evaluate the P waves• Look for the presence of P waves and compare the
shape and size of all P waves• All the P waves should be upright and rounded and
uniform in appearance• P wave should be present before each QRS
Steps for Analyzing a Rhythm Strip
• Step 2:– Evaluate QRS Complexes• All of the QRS’s should be uniform and narrow in
appearance
Steps for Analyzing a Rhythm Strip
• Step 2: continued– Measuring the QRS less than 0.12• Begin from the point where the first wave of the
complex begins to deviate from the baseline and end where the complex returns to the baseline• Count the number of small boxes and multiply by o.o4
seconds
Steps for Analyzing a Rhythm Strip
• Step 3:– Calculate the Atrial and Ventricular Heart Rates• There are a couple of methods to discuss• One will only be used by an MST
– Six-Second Method
Steps for Analyzing a Rhythm Strip
• Step 3: continued– A normal heart rate in the resting adult is between
60 and 100– A rate below 60• bradycardia
– A rate above 100• tachycardia
– The atrial rate should be the same as the ventricular rate
Steps for Analyzing a Rhythm Strip
• Step 3: continued– Six-Second Method (can be used for regular or
irregular rhythm patterns)• Print off six seconds of ECG paper (use markers at the
top or bottom of the paper– Atrial Rate
» Count the number of P waves within a period of six seconds and multiply that number by 10
– Ventricular Rate» Count the number of QRS complexes within six seconds
and multiply by 10
Steps for Analyzing a Rhythm Strip
• Step 3: continued– Small Box Method (best used if the rhythm is
regular, but may be used if the rhythm is irregular and a rate range is given)• Atrial rate
– Count the number of small boxes between two P waves, and find the corresponding rate on the small box calculation chart
• Ventricular rate– Count the number of small boxes between two QRS
complexes and find the corresponding rate on the small box calculation chart
Steps for Analyzing a Rhythm Strip
• Step 4:– Determine the regularity of the rhythm (pattern)• Measure the distance between two consecutive QRS’s
and compare that distance with the other R-R intervals• If the rhythm is regular, the R-R intervals will be the
same
Steps for Analyzing a Rhythm Strip
• Step 5: – Measure the PR intervals• Count the number of small boxes from the beginning of
the P wave to the beginning of the QRS• Multiply this number by 0.04 seconds• The PR intervals should all be the same and measure
0.12 to 0.20 seconds
Steps for Analyzing a Rhythm Strip
• Step 6: – Measure the QT interval• Count the number of small boxes from the beginning of
the Q wave to the end of the T wave• Multiply this number by 0.04 seconds• 0.36 to 0.44 seconds or 9 to 11 small boxes for normal
range
Steps for Analyzing a Rhythm Strip
• Step 7: – Compare your findings to what is normal for the
patient