EKGs Flashcards
To learn how to read an EKG and how to recognize important features
How many seconds does one small horizontal box represent?
0.04 seconds (40 milliseconds)
How many seconds does one large horizontal box represent?
0.20 seconds (200 milliseconds)
How many small horizontal boxes make one large horizontal box?
5
How many millivolts does one small vertical box represent?
0.1 millivolts
What waves make up an EKG and what do they represent?
P Wave: Atrial Depolarization
QRS Wave: Ventricular Depolarization
T Wave: Ventricular Repolarization
U Wave: Purkinje Fiber Repolarization
How do you calculate the rate?
300-150-100-75-60-50 OR If the EKG is a 10 second strip, you can count the number of QRS complexes and multiply by 6 (only if rhythm is regular)
Describe where the leads should be placed on the patient.
V1: 4th intercostal space, right sternal border
V2: 4th intercostal space, left sternal border
V3: Between V2 and V4
V4: 5th intercostal space, left midclavicular line
V5: In line with V4, left anterior axillary line
V6: In line with V5, left midaxillary line
What leads should you look at to determine the axis?
Lead I and aVF. If aVF is equivocal, look at lead II
What degrees are each of the limb leads at (bipolar and unipolar)?
Bipolar limb leads include leads I, II, and III. Lead I is at 0 degrees. Lead II is at +60 degrees. and Lead III is at +120 degrees.
Unipolar limb leads include aVR, aVL, and aVF. aVR is at -150 degrees. aVF is at -30 degrees. And aVF is at +90 degrees.
What is a normal axis delineated by?
Positive QRS deflection in Lead I and aVF
What is a left axis deviation delineated by?
Positive QRS deflection in Lead I and negative QRS deflection in aVF
What is a right axis deviation delineated by?
Negative QRS deflection in Lead I and positive QRS deflection in aVF
True or False: Right axis deviation is normal for a pediatric patient.
True.
In what instances will you see an extreme axis deviation on EKG?
- Ventricular rhythms (i.e. ectopy)
- Hyperkalemia
- Severe right ventricular hypertrophy (i.e. pulmonary hypertension)
- Lead malposition
What is the difference between intervals and segments on an EKG?
Segments do NOT contain waves. Intervals do contain waves.
Describe the PR interval.
Start of the P wave to the start of the QRS wave.
Normal Length: 120-200 milliseconds (3 small boxes to 5 small boxes OR 3 small boxes to 1 large box)
What does a long and short PR interval indicate?
AV conduction abnormality.
Long: AV blocks
Short: Pre-excitation syndromes
Describe the QRS interval.
Normal Length: 70-100 milliseconds (some books say <120 milliseconds)
What does a wide and narrow QRS interval indicate?
Wide: Usually due to a bundle block
Narrow: Supraventricular origin
Describe the QT interval.
Start of the Q wave to the end of the T wave
Ventricular depolarization and repolarization.
What is a normal QT interval?
Men: 350-440 milliseconds
Women: 350-460 milliseconds
The T wave should fall at less than half of the R-R interval.
Women take longer to get ready
Why do we often reference the corrected QT (or QTc) to determine the QT Interval length?
Because the QT interval changes with heart rate and is often only accurate if the heart rate is between 60 and 100.
How do you calculate the QTc?
Bazett’s Formula: QT interval/ Square root of the R-R interval
Men: 350-440 milliseconds
Women: 350-460 milliseconds
Some research indicate that >480 milliseconds is concerning for prolonged/long QT
What are we worried about with a long QT interval?
Risk of Torsades
What is the normal morphology of a P wave?
Normal P Wave Axis: 0 to +75 degrees
P waves should be upright in Leads I and II and down in aVR
Amplitude: <2.5mm in limb leads and <1.5mm in precordial leads
First 1/3 of the P wave corresponds to right atrial activation. Final 1/3 of the P wave corresponds to left atrial activation. Middle 1/3 is a combination of the two.
How will the P wave look in right atrial hypertrophy and left atrial hypertrophy?
Right Atrial Hypertrophy: Taller (>2.5mm)
Left Atrial Hypertrophy: Wider (>120 milliseconds)
What is P. Mitrale?
A biphid P wave with >40 milliseconds (1 small box) between peaks.
Classic for mitral stenosis
Where are Q waves normally seen?
In left-sided leads (I, aVL, V5, and V6)
Deep, narrow Q waves (>2mm) in Lead III and aVR can be a normal variant.
Q waves indicate normal left to right depolarization of the septum
What are pathological Q waves?
Q waves that are >1mm wide, >2mm deep, and/or more than 25% of the QRS complex in leads V1-V3
Q waves should NOT be present in V1-V3
What do the presence of pathological Q waves indicate?
Current or Old MI
Hypertrophic Cardiomyopathy
Infiltrative Cardiac Diseases
What are 3 key abnormalities of R waves that should NOT be missed?
- Dominant R wave in V1
- Dominant R wave in aVR
- Poor R wave progression
True or False: A dominant R wave in V1 is normal in pediatric patients.
True
What EKG findings should cause you to obtain a posterior EKG?
Dominant R wave in V1 with accompanying ST depression in the anterior pre-cordial leads.
Obtain a posterior EKG to look for a posterior MI
What toxicity/overdose should you be thinking of when you see a dominant R wave in aVR?
Sodium Channel Blockade (i.e. TCA Overdose)
Describe R wave progression.
In Lead I, the R wave should be small. The R wave becomes larger throughout the precordial leads, to the point where the R wave is larger than the S wave in Lead V4.
What is the Sokolov-Lyon Criteria?
Helps determine if there is left ventricular hypertrophy.
LVH is present if:
- The R wave in aVL is > 11mm OR
- (S wave in V1 or V2) + (R wave in V5 or V6) > 35mm
True or False: Inverted T waves are a normal finding in children.
True.
Where is it normal to see inverted T waves on an EKG?
Leads III, aVR, and V1
Of note, while an inverted T wave in Lead III can be a normal variant, if it is changed from previous EKGs…it is considered abnormal
True or False: U waves enlarge as the heart rate slows.
True.
True or False: Inverted U waves are a normal variant.
False. Inverted U waves usually represent pathologic heart disease (i.e. CAD or MI, especially if in the presence of chest pain)
What is a Delta wave and what does it signify?
A Delta wave is a slurred upstroke to the QRS complex that is seen in WPW (pre-excitation syndrome)
What is an Epsilon wave and what does it signify?
An Epsilon wave is a small positive deflection at the end of the QRS complex that may indicate Arrythmogenic Right Ventricular Dysplasia.
ARVD leads to an increased risk of ventricular tachycardia and death