Questions and Answers
What is the formula to calculate a regular heart rate from an ECG?
What is the significance of a PR interval less than 120 ms?
Which of the following would indicate Left Axis Deviation (LAD) on an ECG?
What is the significance of different P wave morphologies in an ECG?
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What is the range of the normal axis on an ECG?
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Which of the following conditions is associated with a prolonged PR interval (>200ms or 0.2 sec)?
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What is the degree of lead I in the Hexaxial Reference System?
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What is the significance of a depressed TP segment in an ECG?
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Study Notes
ECG Analysis
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Rate Calculation
- Regular rate: divide 300 by the number of big boxes or 1500 by the number of small boxes
- Irregular rate: multiply the number of QRS complexes in the rhythm strip by 6
- Ventricular heart rate: measure the number of boxes between adjacent QRS complexes
- Atrial heart rate: measure the number of boxes between adjacent P waves
Rhythm/Regularity
- No specific details mentioned in the text
P Waves
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Three Key Questions
- Are P waves upright in leads I, II, and aVF?
- Are P wave morphologies the same or different?
- Is there any evidence of atrial enlargement?
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Different P Wave Morphologies
- May indicate abnormalities in rhythms like premature atrial contractions (PACs) or multifocal atrial tachycardia (MAT)
PR Intervals
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PR Interval Interpretation
- Less than 120 ms: possible Wolff-Parkinson-White (WPW) syndrome
- Prolonged (>200 ms or 0.2 sec): possible 1st degree AV Block
- Elevated TP segment: atrial infarction
- Depressed TP segment: pericarditis
Axis
-
Hexaxial Reference System
- Lead I: 0 degrees
- Lead II: +60 degrees
- Lead III: +120 degrees
- Lead aVF: +90 degrees
- Lead aVR: -150 degrees
- Lead aVL: -30 degrees
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Normal Axis
- Range: -30 degrees to +90 degrees
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Left Axis Deviation (LAD)
- Range: -30 degrees to -90 degrees
- Indicates inferior MI, left bundle branch block (LBBB), or left ventricular hypertrophy (LVH)
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Right Axis Deviation (RAD)
- Range: +90 degrees to +180 degrees
- Indicates lateral MI, right ventricular hypertrophy, or pulmonary embolism
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Northwest/Extreme Axis (NW)
- Range: +/-180 degrees to -90 degrees
- Indicates apical MI, right ventricular hypertrophy (RVH), hyperkalemia, or ventricular tachycardia (VT)
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Determining Axis
- The lead with the greatest deflection of electrical current determines the axis
- The lead perpendicular to this lead should have a depolarization that is either flat-lined or balanced in terms of negative and positive current
QRS Complex
-
QRS Complex Analysis
- Examine QRS complex duration
- If duration is wide, examine morphology, especially in V1-V6
- Assess voltage (increased or low)
-
QRS Complex Duration
- Normal: 0.12 seconds (indicates RBBB or LBBB)
- Measured from the beginning of QRS to the end
- Narrow QRS indicates intact conduction through the His/Purkinje system
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Description
Analyze and interpret an electrocardiogram (ECG) incorporating various features including rate, rhythm, axis, P waves, PR interval, and QRS complex. Learn how to calculate regular and irregular heart rates, and understand the significance of each component.
