DSA #1: Origin of Heartbeat/ECG Flashcards
The first set of leads developed were the?
Standard limb leads, also knows as the bipolar leads
What is the charge of the bipolar lead of the right arm?
Always negative (-)
What is the charge of the bipolar lead of the left leg?
Always positive (+)
What is the charge of the bipolar lead of the left arm?
Whatever’s left
What are the bipolar lead I connections?
1 “L”: Left arm to right arm
What are the bipolar lead II connections?
2 “L’s”: Left Leg to right arm
What are the bipolar lead III connections?
3 “L’s”: Left Leg to Left arm
What were augmented unipolar leads designed for?
To increase the size of the signals (heart’s electrical activity) and giving s new views of that activity
How do augmented unipolar leads compare to standard limb leads?
Use the same electrodes as you used for the standard limb leads. The only thing that changes is how these electrodes are connected.
How are the three electrodes utilized in augmented unipolar leads?
Two of the three electrodes we had used are tied together and brought to the ground. The remaining electrode become the exploring or active lead.
What is one of the limitations of either the augmented unipolar leads or the standard limb leads?
They all look at the heart from the same plane (the coronal)
What came into use so that we could view the heart from the transverse or horizontal plane?
The six chest leads
How does current flow in unipolar leads?
Current moving towards an active electrode produces a positive deflection, away a negative deflection.
What is the P wave?
SA nodal depolarization; atrial depolarization
What is the PR interval?
Depolarization travels from SA node through AV node via internodal pathway (getting to the AV node is quick!)
What is the QRS complex?
Ventricular depolarization (includes bundle branches and purkinje fibers)
What is the T wave?
Ventricular repolarization
What is the QT interval?
Total time the ventricles spend depolarized. Measured from beginning of QRS complex to end of T wave
What is the ST segment?
The tme between the end of the QRS complex and the beginning of the T wave. Along with the QRS complex, during this time the ventricle is in the absolute refractory period.
What does the x-axis and y-axis indicate on an ECG?
x-axis: time
y-axis: voltage
Why does the T-wave appear to moving in the same direction as the QRS complex did (upwards), despite the fact it represents the opposite electrical event?
Repolarization is heading the opposite direction (“two” negatives) and electronics perceive two negatives as a positive (+).
What is the normal range for the PR interval (secs)?
0.12 - 0.20 seconds
What is the normal range fro QRS duration?
up to 0.10 sec
What is the normal range for the QT interval; and what must it be corrected for?
up to 0.43 sec (must be corrected for heart rate)
What is the normal range for R-R interval (heart rate); what does it represent?
- Time between beats, used to calculate heart rate
- 0.6 - 1.0 sec
(heart rate: 60 - 100 bpm)
What is the normal range for mean electrical axis?
-30 to +110 degrees is the widest normal range
(0 to +90 is considered normal by most)
How much time does each square represent on the x-axis of the ECG?
25 mm/sec, 1 sq = 1mm so 1 sq = 1/25 = 0.04 sec
How are calculations made on a ECG?
- Figure out which seqment you are looking for
- Count the number of squares in the segment
- (# squares) x (0.04 sec/square)
What would be calculated between the blue lines?
The PR interval
What would be calculated between the blue lines?
The QRS duration
What would be calculated between the blue lines?
The QT interval
What would be calculated between the blue lines?
The R-R interval
*The time between two QRS complexes = instataneous heart rate
What does the mean electrical axis tell us?
The net direction the depolarization or repolarization is heading, typically used for the ventricles.
To calculate the mean electrical axis of the ventricles, what is used?
The QRS complex; indicating net direcion of the depolarization of the ventricles
*Normal: 0 to 90 degrees
In a patient with left ventricular hypertrophy but a normal conduction pathway, what would you expect to see on an ECG?
Increase the amplitude (height) of the QRS complex
*Remember hypertrophy refers to having more muscle cells (or bigger ones), leading to more current flow during depolarization.
What event on an ECG represents phase 0 of the ventricular action potential?
QRS complex
During what part of the ECG is the ventricular condunctance for calcium the highest?
ST segment
