EKG Page
EKG Mean Axis and Supraventricular Rhythm Review

Mean Axis Review
What does the EKG axis mean?
It means the net direction of electrical activity

Do we examine the P wave or T wave electrical axis?
The P wave axis is rarely determined. However, the T wave axis is determined in instances such as an infarcted heart myocardium or ischemia.

So what is the most important axis?
QRS or ventricular depolarization

What are the steps to determine the mean QRS axis?
Step 1) Determine the deflection (positive or negative) of Lead I
Step 2) Determine the deflection (positive or negative) of Lead AVF
These steps specify the quadrant in which the vector will go through.
Step 3) Determine the most biphasic lead.
Note, since a vector is perpendicular to the biphasic lead, you now know that the mean QRS is running (perpendicular) through the biphasic lead.
Also, Steps 1 and 2 have established where the vector will be; so you now have a specific direction and area in which the mean QRS axis exists.

In degrees, what is the normal QRS axis range?
+105 degrees to –30 degrees

In degrees, what is the area for left axis deviation?
-30 degrees to –90 degrees

In degrees, what is the area for right axis deviation?
+105 degrees to ±180 degrees

In degrees, what is the area for extreme right axis deviation?
±180 degrees to –90 degrees

Draw and label the hexaxial system. Be able to identify all leads that are perpendicular to each other.

Supraventricular Rhythm Review
What does the term supraventricular mean?
That the atrial foci and junctional foci are above the ventricles.

In what leads is the P wave upright?
I, II, AVF, AVL, V5-V6

In what lead is the P wave normally inverted?
AVR

In what leads may the P wave be biphasic?
V1 and sometimes III

In what leads is the P wave variable?
V2-V4

What is the duration (seconds) of the P wave?
< 11 seconds

What is a normal and borderline duration of the QRS complex?
Normal less than or equal to 0.10 seconds, borderline is 0.11- 0.12 sec

What is the normal duration of the PR Interval
0.12-0.20 sec

What is the main difference in the multifocal atrial tachycardia (MAT) and the wandering atrial pacemaker?
The differentiation from wandering atrial pacemaker MAT is solely rate. The is usually > 100 b/min in the MAT.

What does paroxysmal mean?
Sudden

What is the rate of paroxysmal atrial tachycardia (PAT)?
Usually around 160 to 220 b/min (may be up to 250 b/min)
Note, this arrythmia arises SUDDENLY. Also, because the origin of this tachyarrhythmia is a very irritable atrial focus, the atrial depolarizations of PAT do not look like sinus-generated P waves.

What is the rate of atrial flutter?
220 to 300 b/min
It is characterized by a series of flutter waves that have the "saw tooth" baseline.
With atrial flutter the baseline is never isoelectric.

What is the medical term for rapid heart beat?
Tachycardia

What is atrial fibrillation?
This results from random chaotic depolarizatin of the atria.
There is no organied electrical activity and thus no pumping action of the atria.
No single impluse depolarizes the atria completely.

For clarity, what is the physical relationship of the AV node to the AV junction?
The AV junction is part of the AV node which transmits the impulse to the ventricles.

What is a junctional rhythm?
If the QRS complexes are regular and narrow, denoting a supraventricular rhythm, and P waves are NOT possible to discern, a junctional or nodal rhythm is likely.
Cells at the AV note are capable of depolarizing spontaneously.
The intrinsic rate of junctional cells is normally 40 to 55 beats/min
Impulses that originate in the AV node are transmitted in RETROGRADE (backward) direction to the atrium and thus produce P waves that may well be inverted. The same impulses are transmitted ANTEGRADE (forward) to the ventricles. In some cased the P wave precedes the QRS, depolarizing the atrium before the ventricles.
If the P impulse reaches the atrium and ventricles at the same time, the P wave is often buried in the QRS complex. If the junctional impulse reaches the ventricles slightly before the retrograde transmission to the atrial, the QRS may actually precede the P wave.

Note, when a junctional rhythm occurs, and is unrelated to drugs, this is referred to as an escape rhythm due to a poor functioning SA node.

What is an escape rhythm?
This is an alternative pacemaker (other than the SA node).

Is there such an arrhythmia as junctional tachycardia?
Yes, junctional tachycardia usually is a rate of 80 to 120 b/min

What does "irregularly irregular" describe?
This is an irregular and chaotic rhythm that has no predictable recurring pattern.
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