Rate and Axis Flashcards
A “small box” on the ecg strip typically has a duration of:
40ms (.04s)
A “large box” on the ecg strip typically has a duration of:
200ms (.2s)
The full length of an ecg strip represents a duration of:
10s
Describe 2 methods for estimating rate from an ecg strip:
- The “300” method: count the number of large boxes between two successive R-waves. Divide 300 by this number to obtain the rate. Fast and easy, but imprecise and not effective for irregular rhythms
- The 10 second method: count the number of complexes in a single strip and multiply by 6. More time consuming but more precise and useful for irregualr rhythms
Assessment of the QRS axis usually only concerns its projection onto the ______ plane
frontal
assessment of the projection of the QRS axis onto the transverse plane is described as assessing the R-wave progression or transition
A QRS axis that is more negative than normal is referred to as:
Left Axis Deviation (LAD)
A QRS axis that is more positive than normal is referred to as:
Right Axis Deviation (RAD)
A QRS axis from +180° to +270° is referred to as:
“extreme axis” “superior axis” or “indeterminate axis”
Although not rigorously defined, a common guideline for normal range of QRS axis is:
-30° to +90°
What range of QRS axis is sometimes considered “physiologic LAD”?
0° to -30°
List and describe two non-pathologic factors which affect cardiac axis
Age: Generally rightwards axis at birth which drifts progressively leftwards with age
Body type: Tall and thin tends to have a vertical axis, short and obese more of a leftwards axis
Describe the “quadrant” approach to qualitative QRS axis determination.
- Compare the predominant deflections of leads I and aVF.
- Use the following table to estimate the QRS axis:
- In the case of potential LAD, compare to lead II. If lead II is predominantly positive, then the LAD is physiologic and can be considered a normal axis. If II is negative, then pathologic LAD is present.
Use the quadrant method to qualitatively assess the QRS axis in the following scenarios:
A. LAD (pathologic)
B. RAD
C. Normal Axis
D. Extreme Axis
E. Normal Axis (Physiologic LAD)
Describe the Equiphasic approach to QRS axis determination
- Find the most equiphasic (AKA most isoelectric) of the limb leads. The QRS axis will be 90° to this lead.
- Choose a lead that is 90° to the most equiphasic lead.
- If the QRS of this lead is predominantly positive, then this lead approximates the QRS axis.
- If the QRS of this lead is predominantly negative, then this lead is 180° to the QRS axis
Use the quadrant method and equiphasic method to qualitatively and quantitatively estimate the QRS axis of this ECG
- By quadrant: I is -ve, aVF is positive, therefore RAD
- By equiphasic: Most equiphasic is I, 90° to I is aVF, aVF is positive. Therefore the QRS axis is approximately +90° (likely slightly more)
Use the quadrant method and equiphasic method to qualitatively and quantitatively estimate the QRS axis of this ECG
By quadrant: I is +ve, aVF is -ve or equiphasic, II is positive. Therefore normal or physiologic LAD.
By equiphasic: Most equiphasic is aVF, 90° to aVF is I, I is positive. Therefore the QRS axis is approximately 0° (likely slightly negative)
Use the quadrant method and equiphasic method to qualitatively and quantitatively estimate the QRS axis of this ECG
By quadrant: I is -ve, aVF is +ve. Therefore RAD
By equiphasic: Most equiphasic is II, 90° to II is III, III is positive. Therefore the QRS axis is approximately 150°.
Use the quadrant method and equiphasic method to qualitatively and quantitatively estimate the QRS axis of this ECG
By quadrant: I is -ve, aVF is -ve. Therefore Extreme (Superior) AD
By equiphasic: Most equiphasic is aVL, 90° to aVL is II, II is negative. Therefore the QRS axis is approximately -120° (240°).
