Electrophysiology of the Heart Flashcards
What is preload?
ventricular filling (diastole).
What is the directional orientation of the electrical conduction of the heart?
begins in posterior wall of right atrium, it starts to come forward, then turns backward toward your left heel. This is the normal vector.
When a wave of energy is going toward a positive electrode, what does it show?
a positive deflection (upward)
When a wave of energy is going away from a positive electrode, what does it show?
a negative deflection (downward)
What node forms the P wave on the EKG?
the SA node
What if there is greater than 3 boxes between QRS?
there is an interventricular conduction delay
Should the ST segment be flat?
YES.
Between what degrees should we see positive deflections?
down toward the belly button (0-110 degrees)
If the heart is hypertrophied, will the EKG show a larger or smaller signal?
larger
What would a pericardial effusion do to the EKG signal?
decrease it, because the fluid around the heart is blocking it.
Should T waves normally be upright on an EKG on all leads?
YES (except avR).
Does the Q wave have to be of significant dimensions to be indicative of an MI?
YES
What can accessory pathways do to the conduction system?
shorten the PR interval or alter the QRS interval.
If there is a right axis shift (due to right ventricular hypertrophy), what will happen to avL and lead I?
They will both be inverted.
What is a dipole?
a separation of a positive and negative charge, and is led by the positive end. This positive end is going to go towards a positive electrode to form a positive (upward) deflection on the EKG.
So, what does it mean if we see a positive deflection on an EKG?
There was positive current coming TOWARD a positive electrode.
So, what does it mean if we see a negative deflection on an EKG?
There was a positive current going AWAY from a positive electrode.
Why are the deflections in leads I, II, and III all positive in a normal EKG?
because the electrodes a placed such that when the depolarization travels from the SA node throughout the heart, it follows the direction of the + electrodes of Einthoven’s triangle. So any impulse traveling down and to the left on the body will show up as a positive deflection.
What are the normal axial degrees for depolarization in a healthy heart?
-30 to 90.
At what axis would the heart most likely be if there were huge QRS complexes in lead II?
60 degrees, because this almost matches the vector of lead II.
At what axis would the heart most likely be if there were huge QRS complexes in lead III?
120 degrees, because this angle matches more closely with lead III.
What does it mean if we see huge deflections in avR?
there is right axis deviation.
What do the augmented leads each reflect?
Each corresponding corner of einthoven’s triangle as if everything else were negative and each of these were +. So, the deflection for aVR will be downward, the deflection for aVL will be a little of both (more downward though), and the deflection for aVF will be upward). Think if I follow the depolarization of the heart starting at the SA node, what would each of these corners pick up (designating each as positive).
What will hyperkalemia (ex. giving a patient K+) do to the QRS complex?
Spread it out, and peak the T wave.
What will hypokalemia (ex. from vomiting excessively) do?
Tighten the QRS complex (and lengthen QT interval) and you’ll see a “u” wave.
What will hypercalcemia do to the EKG?
Pull everything together (shorten PR interval)
What will hypocalcemia (ex. blocking Ca++ channels) do to the EKG?
prolonged PR interval.
What is a sinus rhythm?
any cardiac rhythm where depolarization of the cardiac muscle begins at the SA node.
What would you see in absence of the SA node?
just QRST; no P wave.
What does a flat line on an EKG mean?
could be that the lead is perpendicular and the impulse is in the middle
How do we remember colors for electrode placements?
Think cowboy hats: white= good guys on RIGHT arm, and black= bad guys on the LEFT arm.
Think traffic light for feet: green light= gas pedal, which you push with your RIGHT foot, and red light= clutch, which you push with your LEFT foot to stop.
What do inverted T waves indicate?
ischemia
What is a STEMI?
ST elevation
