Electrophysiology Conduction Pathway Flashcards
Dominant pacemaker
Sinoatrial (SA) Node
Location of SA Node
Right atrium, near the inlet of superior vena cava
Function of the SA node
Receives blood from the right coronary artery
Intrinsic rate of SA node
60-100 bpm
Intrinsic rate if AV junction
40-60bpm
Location of Atrioventricular (AV) node
Posterior septal wall, right atrium
Function of the AV valve
- Delays impulse conduction
- Allows time for atria to empty blood into ventricles
Location of Bundle branches- Ventricles
Interventricular septum
Function of Bundle Branches- Ventricles
Relays impulses to purkinje fibres
Intrinsic rate of Bundle Branches- Ventricles
20-40 bpm
Location of Purkinje Fibres- Ventricles
Ventricular myocardium
Functions of Purkinje Fibres- Ventricles
Relays impulses to myocardium
Intrinsic rate of Purkinje Fibres- Ventricles
20-40 bpm
An abnormal condition in which either cardiac cells are not normally associated with a pacemaker function, begin to depolarize spontaneously OR pacemaker site other than SA node increases its firing rate beyond that which is considered normal
Enhanced Automaticity
Occur during repolarization (after depolarizations) when cells are normally quiet
Abnormal Electrical Impulses
- Slowed: all impulses are conducted, but it takes longer than normal
- Intermittent- Some impulses are conducted
Partial Conduction block
No impulses are. conducted through the affected area
Complete Conduction Block
An impulse returns to stimulate tissue that was previously depolarized
Reentry
Precordial Lead
12 Lead ECG
Wave of depolarization moving across myocardium
Positive Lead
Towards positive electrode at left leg
Positive Deflection
Away from negative electrode at left leg
Negative Deflection
What is an artifact caused by?
- Muscle tremors
- Patient movement
- Loose electrodes/Poor contact
- Pacemaker activity
- Ambulance moving
- 60 cycle interference
Views the inferior surface of the left ventricle
Lead II and Einthoven’s Triangle
Vertical Axis is a measurement of
Voltage/amplitude (strength) of impulse
- 1mm = 0.1 millivolt (mV)
- 1 mV = 10 mm or 2 large boxes
Horizontal axis is measurement of
Time
- 5 large boxes = 1 second
- 15 large boxes = 3 seconds
- 30 large boxes = 6 seconds
A straight line recorded when electrical activity is not detected. Defines positive or negative deflections. measures deviations above and below.
Baseline (isoelectric line)
What does ST elevation indicate?
Cardiac event
Movement away from baseline in either positive or negative direction
Waveform
A line between waveforms; named by waveform that follows it
Segment
Several waveforms
Complex
First waveform preceding QRS complex. Normally upright, rounded in lead II
P Wave
What does P wave indicate?
Atrial depolarization
Times for PR interval
0.12-0.20 seconds
- 3-5 small boxes
- Start of P wave to the first deflection or Q wave
Where is the PR segmant?
Part of the PR interval
- Horizontal line between end of P wave and beginning of QRS complex
- Normally isoelectric (flat)
What does a Long PR interval indicate?
Impulse was delayed as it passed through atria, AV node or AV bundle
What does a short PR Interval indicate?
This may be seen when impulse originates in atria close to AV node or AV bundle
QRS Complex
- Q Wave
- R Wave
- S Wave
- J point
First downward deflection after P wave (often not present)
Q Wave
First upward deflection after Q or P wave (always positive)
R Wave
First downward deflection after R wave (always negative)
S Wave
Small notch at the start of ST segmant
J Point
- Normally narrow <0.12 sec (3 boxes)
- Measured from beginning of Q or R wave to end of S wave
QRS Complex
What does the QRS complex indicate?
- Ventricular depolarization
- Atrial repolarization
Normal Q Waves
Less than 0.03 seconds
More than 0.03 seconds in duration or more that 30% of the following R wave height in that lead or both
Abnormal (pathologic) Q Wave
- Measured from end of QRS complex to beginning of T wave
- Normally flat
ST Segmant
What does the ST segment indicate?
Early part repolarization of right and left ventricles
First waveform following QRS complex, normally upright and slightly rounded in lead II
T Wave
What does the T wave indicate?
Ventricular repolarization
Portion of ECG tracing from beginning of the QRS complex to the end to T wave. Represents total ventricular activity
QT Interval
Used to determine ventricular rate and regularity
R-R interval
Main points from cardiac cycle
- Venous blood fills both atria
- Blood is ejected from the atria to ventricles
- Blood is ejected from ventricles to pulmonary and systemic arteries
What does ST elevation or depression Indicate?
Myocardial ischemia or injury
