Lecture 8 - Heart Rhythmicity and Normal ECG Flashcards
What is duration of the PR interval and what is the significance of this timing?
(L8 S20)
-0.16 seconds; this is the delay of SA node AP conductance to the Purkinje fibers
What is a monophasic action potential?
- depolarization and repolarization of tissue
- in the ventricle it would be the QT interval
What is the duration of the QT interval?
-0.35 secs
What does the P wave and QRS complex represent in the atrial and ventricular APs respectively?
(L8 S16)
-phase 0
What are the connections of lead I?
How does it look at the heart?
What is the angle of its axis?
- negative on R arm
- positive on L arm
- look from R to L
- 0 degrees
What are the connections of lead II?
How does it look at the heart?
What is the angle of its axis?
(L8 S32)
- negative on R arm
- positive on L leg
- looks at heart from upper right to lower left
- 60 degrees
What are the connections of lead III?
How does it look at the heart?
What is the angle of its axis?
- negative on L arm
- positive on L leg
- looks at heart from upper left to lower left
- 120 degrees
What is the name of the triangle around the heart formed by the limb lead placements?
-Einthoven’s triangle
A __________ charge causes a __________ deflection on an EKG.
Negative; positive/upward
The length of an vector represents __________ and the direction represents __________.
Magnitude of voltage; direction of current flow
What leads make up a standard 12 lead EKG?
L8 S39
Bipolar limb leads:
-I, II, and III
Augmented limb leads:
-aVR, aVF, aVL
Precordial leads (standard leads): -V1-V6
What is the mean electrical axis of the heart and what is responsible for this?
- 59 degrees
- the apex of the heart remaining positive with respect to the the base of the heart during ventricular depolarization (QRS)
What conditions result in an abnormal QRS axis?
- change in heart position
- hypertrophy
- bundle branch blocks
- fluid in the pericardium
- pulmonary emphysema
What conditions result in increased or decreased QRS voltages?
Increased:
-hypertrophy
Decreased:
-cardiomyopathies
What is the normal QRS duration?
-0.06-0.08 seconds