2 Basics: Waves, Complexes, Intervals, and HR Flashcards
The vertical axis of the ECG paper represents ______ and the horizontal axis represents ______
Voltage
Time
One large box on the ECG paper represent…
- 2 seconds of time
0. 5 mV
One small box on the ECG paper represents …
- 04 seconds
0. 1 mV
What is the isoelectric line?
Flat line that occurs when no electrical activity is occurring or impulses are too weak to be detected
Used as a baseline to identify changing electrical movement
The P wave is produced by…
Initiation of impulse in SA node
Depolarization of RA and LA
Impulse passing through AV junction
Normal P waves are…
Upright and round
- 06-0.10 s (60-100 ms)
- 5-2.5 mm high
The PR interval begins at _________ and ends at _________
The start of the P wave
The beginning of the QRS complex
Normal PR interval
0.12 - 0.20 s (120-200 ms)
The beginning of the P wave to the beginning of the QRS complex
PR interval
What is the PR segment?
Flat (isoelectric) line between the end of the P wave and the start of the QRS complex
What are the components of the QRS complex?
Q wave - first negative deflection following PR segment
R wave - any positive deflection following Q wave or PR segment
S wave - any negative deflection that extends below the baseline following the R wave
Normal QRS duration is…
0.06 to 0.12 s (60-120 ms)
Flat line that follows QRS complex
ST segment
Larger, slightly asymmetrical waveform that follows ST segment
T wave
Point were the QRS complex meets the ST segment
J-point
What is the QT interval?
Beginning of the QRS complex to the end of the T wave
Represents time of ventricular depolarization and repolarization
Normal duration of QT interval
0.36 - 0.44 s (360-440 ms)
Varies depending on the HR - as HR slows, the QT increases
What does a normal ECG rhythm look like (Limb Lead II)?
Upright, round P waves occurring at regular intervals at ~60-100 bpm
PR interval of normal duration (0.12-0.20 s) followed by a QRS complex of normal upright contour and duration (0.06-0.12s)
Flat ST segment followed by an upright, slightly asymmetrical T wave
What is the calibration mark and why is it there?
Helps ensure ECG machine is properly calibrated
Serves as reference point on ECG tracing
Standard signal is 1.0 mV in amplitude (2 large boxes)
Markings on ECG tracing that are not a product of heart’s electrical activity
Artifact
Many causes (ie patient movement)
Can mimic life-threatening dysrhythmias
These leads record difference in electrical potential between a positive and negative electrode using a third electrode called a ground
Bipolar leads (limb leads I, II, III)
What are the poles for Lead I?
Right arm is negative
Left arm is positive
What are the poles for Lead II?
Right area is negative
Left leg is positive
What are the poles for Lead III?
Left arm is negative
Left leg is positive
Which leads are bipolar?
Leads I, II, III
All the rest are unipolar
______ use one positive electrode and a reference point calculated by the ECG machine (center of the heart)
Unipolar leads
Which leads are unipolar?
Augmented Limb Leads
• aVr - augmented vector Right
• aVl - augmented vector Left
• aVf - augmented vector foot
Precordial leads (“chest” or “V” leads) • V1-6
What are the three augmented limb leads?
aVr, aVL, aVf
All unipolar
Enhanced by ECG machine b/c waveforms produced by these leads are normally small
Augmented limb leads use the same electrodes as limb leads but …
One is positive, the other two have no charge and serve as a common ground
Which direction is positive for aVr?
Right arm - views base of the heart (atria and great vessels)
Which direction is positive for aVL?
Left arm - views lateral wall of left ventricle
Which direction is positive for aVf?
Left leg - view inferior wall of left ventricle
The precordial leads are all…
Positive electrodes
Lead placement:
V1
4th ICS on the right side of the sternum
Lead placement:
V2
4th ICS on the left side of the sternum
Lead placement:
V3
Halfway between V2 and V4 🙄
Lead placement:
V4
5th ICS in MCL (Septum)
Lead placement:
V5
Anterior auxiliary line, same horizontal plane as V4
Lead placement:
V6
Midaxillary line, same horizontal plane as V4
Leads _________ should be on the same horizontal plane
V4-V6
What views are provided by the precordial leads?
Anterior and lateral views of the heart in a horizontal plane
When are Modified Chest Leads (MCL) used?
For patient monitoring in ED, telemetry, and ICU
MCL1 and MCL6 provide continuous cardiac monitoring
When using Modified Chest Leads, where do you place the positive electrode?
In the same position as precordial leads V1 or V6
Different combinations of leads will tell you about…
Different surfaces of the heart
Which are considered the Anterior Leads?
V1-4
Which are considered the Lateral Leads?
Lead I, aVL, and V5-6
Which are considered the Inferior Leads
II, III, aVf
Why do we use so many god damn leads?
Help to distinguish focal problems from more widespread problems (Ischemia/infarct vs drug/electrolyte effects)
What are the five steps in analyzing an ECG?
Determine regularity
Calculate rate
Evaluate P waves
Evaluate QRS complexes
Evaluate PR intervals
Characteristics of Normal Sinus Rhythm
Rhythm: Regular
Rate: 60-100 bpm
P waves: Upright and rounded (in most leads), one preceding each QRS complex
QRS complexes: Narrow, 0.06 - 0.12 seconds
PR interval: 0.12 - 0.20 seconds
T waves: Upright and slightly asymmetrical
How do you describe a regular rhythm?
The distance of the R-R intervals and P-P intervals is the same
How do you describe an irregular rhythm?
The distance of the R-R intervals and P-P intervals differs
Irregular rhythms are considered ABNORMAL
What are the three methods of determining rhythm regularity?
Caliper Method
Pen and Paper Method
Counting the Small Squares Method
What are the different types of rhythm irregularity?
Occasional or very
Slightly
Sudden acceleration in HR (or slowing)
Patterned
Totally
Variable Conduction Ratio
What type of rhythm is this:
Pacemaker changes location from site to site
Slightly irregular
Referred to as “wandering atrial pacemaker”
Sudden HR acceleration is also referred to as…
Paroxysmal tachycardia
A normal rate that suddenly accelerates to a rapid rate producing an irregularity in the rhythm
Irregularity repeating itself in a cyclic fashion is referred to as…
Patterned irregularity
Examples:
Sinus Dysrhythmia (ie - respiration)
2nd-degree AV heart block
Type I
Totally Irregular (or Irregularly Irregular) rhythms are typically seen in ….
Atrial fibrillation
Ectopic sites in the atria fire at a rate of more than 350 bpm
Only some of the atrial impulses are conducted through the AV node
What are the different methods for calculating HR?
6-second interval x 10 method
Large-Box Estimate (count-down method)
1500 method
Rate Calculator
How does the 6-second interval x 10 method work?
Count the number of QRS complexes found in a 6-second portion of the ECG and multiply by 10
Quick and easy (no tools) but not as accurate as other methods
How does the Large-Box countdown method work?
Find an R wave located on or near a bold line
Count down along each bold line until the next consecutive R wave (300, 150, 100, 75, 60, 50, 43)
The bold line it falls on or is closest to represents the HR
What is the downside of the countdown method?
Less accurate with irregular rhythms
What’s the best way to interpolate the rate when use the countdown method and the R-R interval falls between the large boxes?
If rate is between 100-75, there are 25 numbers between them, so each small box can represent 5 bpm (25/5) - so 95, 90, 85, 80
Most accurate method for calculating HR
1500 method - count the number of small squares between two consecutive R waves and divide 1500 by that number
Requires no special tools but math is required (boo)
CANNOT be used with irregular rhythms
What is a normal HR in adults?
60-100 bpm
Heart rate < 60
Bradycardia
Heart rate > 100
Tachycardia
First deflection from baseline at the beginning of cardiac cycle
Sinus P wave
How does a normal p wave appear on lead II?
Upright and rounded
Precedes each QRS complex
Duration 0.06 - 0.10 seconds
Amplitude 0.5 - 2.5 mm
Tall, rounded or peaked, P waves may be seen with …
Increased right atrial pressure and right atrial dilation
Amplitude > 2.5 mm suggests RAE
Aka P pulmonale
Wide (enlarged), notched or biphasic P waves may be seen in …
Increased left atrial pressure and left atrial dilation
Width > 10.s (2.5 small boxes) suggests LAE
Aka P mitrale
What is P pulmonale?
Right Atrial Enlargement (RAE)
P wave > 2.5 mm TALL
What is P mitrale?
Left Atrial Enlargement (LAE)
P wave > 0.10s (2.5 small boxes)
What can cause different looking P waves?
Impulses arising from the atria but NOT the SA node
Seen with:
• Premature atrial complexes (PACs)
• Wandering atrial pacemaker
• Atrial tachycardia
P wave of early beat that differs in appearance from underlying rhythm
Premature atrial complex (PAC)
What happens to the P wave during atrial tachycardia?
With the rapid rate, the P wave is likely buried in the T wave of the preceding beat
When this occurs, the T waves are often peaked, notched, or larger than normal
What are “F” waves?
Flutter waves - produced when an ectopic site in the atria fires rapidly at a rate of 250-350 bpm
Often described as a “saw-toothed” pattern - more P waves than QRS complexes
What are ”f” waves?
Fibrillatory waves - Produced when the atria fire rapidly from many sites at a rate >350pm
Absence of discernible P waves, instead there is a chaotic looking baseline preceding the QRS complexes
What produces inverted P waves?
Retrograde depolarization of the atria
Associated with dysrhythmias that originate from the AV junction
Inverted P waves occur when…
Depolarization arises from the:
• Lower right atrium near the AV node
• Left atrium
• AV junction
May immediately precede, occur during, or follow the QRS complex
What does more P waves than QRS complexes indicate?
The impulse was initiated in the SA node or atria but was blocked and did not reach the ventricles
What are the different components of the QRS complex?
Q wave - first negative deflection following he PR segment
R wave - any positive deflection following Q wave or PR segment
S wave - any negative deflection that extends below the baseline following the R wave
Normal QRS duration is ….
0.06 to 0.12s
When looking at the QRS complex, there is only one _______ but there can be more than ________
Q wave
R or S wave
In that case, the second R or S wave is called R’ or S’
If the R or S wave is small, use the lower case “r” or “s”
How to measure the QRS complex
Starting point is where the first wave of complex starts to move away from baseline
Ending point is where the last wave of the complex begins to level out (flatten) at, above, or below the baseline
Measurement of the QRS complex should include _______ but it shouldn’t __________
Entire S wave
Overlap into the ST segment or the T wave
QRS complexes should appear normal (upright and narrow) if…
Rhythm is initiated from a site above the ventricles (SA node, atria, AV junction)
Conduction has progressed normally from the bundle of His, through the right and left bundle branches, and through the purkinje fibers
Normal depolarization of the ventricles has occurred
Normal QRS can be seen in dysrhythmias that…
Arise from above the ventricles, unless there is a conduction delay through the ventricles or other type of abnormality
When do you see abnormal QRS complexes?
When there is abnormal depolarization of the ventricles
Pacemaker site in these abnormal QRS complexes can be…
• SA node
• Ectopic pacemaker in the atria, AV junction, bundle branches, purkinje network, or ventricular myocardium
What are some examples of causes for abnormal QRS complexes?
Ventricular hypertrophy Intraventricular conduction disturbance Aberrant ventricular conduction Ventricular pre-excitation Ventricular ectopic or escape pacemaker Ventricular pacing by cardiac pacemaker
TALL QRS complexes are usually caused by…
Hypertrophy of one or both ventricles
An abnormal pacemaker
Aberrantly conducted beat
Low-voltage QRS complexes are more commonly seen in…
Obese patients
Pericardial effusion
Hypothyroidism
Wide-Bizarre QRS complexes are often the result of…
Intraventricular conduction defect - right or left bundle branch block
They are of supraventricular origin
Aberrant conduction occurs when …
Electrical impulses reach the bundle branch while it is still refractory after conducting a previous electrical impulse
The impulse travels down the unaffected bundle branch first, followed by the other —> wider than normal QRS complex
_______ denotes depolarization of the heart from the SA node through the atria, AV node, and His-Purkinje system
PR interval
Measured from the beginning of the P wave to the beginning of the Q wave (or R wave if Q is absent)
PR intervals are considered abnormal if they are…
Shorter than 0.12 s
Longer than 0.20 s
Absent
Vary in duration
Shorter PR intervals (< 0.12 s) occur when…
The impulse originates in the atria close to the AV junction or in the AV junction
An impulse arises from a supraventricular site but travels through abnormal accessory pathways to the ventricles
Shorter PR intervals lead to …
Premature ventricular depolarization (PRE-EXCITATION)
Longer PR intervals occur when…
There is a delay in impulse conduction through the AV node
Ex: 1st-degree AV heart block
In __________, the pacemaker site moves from beat to beat causing the P waves to appear different and the PR intervals to vary
Wandering atrial pacemaker
2nd degree AV heart block Type I has PR intervals that are…
Progressively longer until a QRS complex is dropped, then the cycle repeats
Absent PR intervals occur in…
Atrial flutter and fibrillation and in ventricular dysrhythmias
In 3rd degree AV heart blocks, what happens to the PR interval
It is not measurable
All of the impulses are blocked as they travel through the AV node
Essentially, the atria and ventricles are beating independently of each other
