EKG BASICS Flashcards
definition: cardiac cells; electrically polarized at rest
myocytes
what charge do inside of myocytes have?
electro-negatively charged compared to outside
how is polarity maintained in myocytes?
sodium-potassium membrane pumps
how is relative electro-positive extracellular state maintained?
3 Na pumped out for every 2 K pumped in (requires ATP)
definition: electrical power source of the heart; depolarize spontaneously
pacemaker cells
definition: hard-wiring of the heart
electrical conducting cells
definition: the contractile machinery of the heart
myocardial cells
how is rate of depolarization of pacemaker cells determined?
determined by the innate electrical characteristics of that cell and the external neurohormonal input
what is the normal intrinsic pacing rate of the SA node?
60-100bpm, but can vary with ANS stimulation
definition: all heart cells possess ability to behave as a pacemaker. suppressed unless SA node fails
automaticity
what is the normal intrinsic pacing rate of the atrial foci?
60-75bpm
what is the normal intrinsic pacing rate of the junctional foci (AV node)?
40-60bpm
what is the normal intrinsic pacing rate of the ventricular foci?
25-40bpm
definition: ventricular conducting cells
purkinje fibers
definition: atrial conducting pathways that travel through the intra-atrial septum; allows for rapid activation of the LA from the RA
bachman’s bundle
definition: when a wave of depolarization reaches a myocardial cell, calcium is released within the cell allowing actin and myosin to interact, causing the cell to contract
excitation-contraction coupling
how is the duration of a wave measured?
fractions of a second
how is the amplitude of a wave measured?
millivolts
definition: shape and appearance of a wave
configuration
horizontal axis of EKG measures what?
time
vertical axis of EKG measures what?
voltage
small/large square horizontal distance =
0.04/0.2sec
small/large square vertical distance =
0.1/0.5mV
the P wave is a recording of what?
atrial depolarization
define what the 1st and 2nd part of the P wave represent
1st part: RA depolarization
2nd part: LA depolarization
definition: AV node delays conduction from the atria to the ventricles to allow atria to finish contracting/emptying their volume completely into the ventricles before the ventricles contract
AV nodal delay
name the three components of ventricular conduction
- bundle of his
- bundle branches
- terminal purkinje fibers
definition: marks the beginning of ventricular depolarization and contraction
QRS complex
definition: restoration of electronegative state so that myocardial cells can be restimulated
repolarization
represents the wave of ventricular repolarization
t wave
why do we not see the wave of atrial repolarization?
it is obscured by the QRS complex
definition: measures time from start of atrial depolarization to start of ventricular depolarization
PR interval
definition: measures time from end of ventricular depolarization to the start of ventricular repolarization
ST segment
definition: measures time from beginning of ventricular depolarization to the end of ventricular repolarization
QT interval
definition: a wave of depolarization towards a positive electrode
positive deflection
definition: a wave of depolarization away from a positive electrode
negative deflection
definition: a depolarizing wave moving perpendicular to a positive electrode
biphasic wave
a wave of repolarization moving toward a positive electrode gives a ________ ___________ and vice versa
negative deflection
a 12-lead EKG includes what leads?
six limb leads (2 electrodes on arms, 2 on legs = 3 standard leads + 3 augmented leads
six precordial leads (six electrodes placed across the chest)
position of V1 lead
4th intercostal (right)
position of v2 lead
4th intercostal (left)
position of v3 lead
between v2 and v4
position of v4 lead
5th intercostal space midclavicular
position of v5 lead
5th intercostal space anterior axillary line
position of v6 lead
5th intercostal space midaxillary line
describe where the positive and negative terminals of the precordial leads are
all electrodes are +
central - terminal is created by connecting all 3 extremity leads
which leads make up the anterior view of the heart?
v2, v3, v4
which leads make up the left lateral view of the heart?
I, aVL, v5, v6
which leads make up the inferior view of the heart?
II, III, aVF
which leads make up the right ventricular view of the heart?
aVR, v1
how long does the PR interval last on EKG?
0.12-0.2sec
what is the normal amplitude of the Q wave?
-0.1mV
a large negative deflection of the Q wave in leads II, III, and aVF denote what pathology?
inferior MI
the R wave is smallest/largest in which leads?
v1/v5
how long does a normal QRS complex last?
0.06-0.1sec
the QT interval composes ___% of the normal cardiac cycle (R-R)
40%
