Download Physio ch11 book notes [5-29

Physiology
Ch 11 The Normal Electrocardiogram
Notes
Normal ECG-P wave- caused atrial depol, just before contraction= depolarization wave
-atrial repol happens during QRS complex and is not seen on ECG
-(0.15-0.20sec after end of p wave)
-QRS complex- technically, 3 separate waves (Q, R and S)- vent depol, before
contraction= depolarization wave
-T wave- vent repol, approx 0.25-0.35 sec after depol= repolarization wave
- vents remain contracted from end of QRS, until end of T wave
When muscle is in complete depol or in complete repol, the ECG is at baseline, the spikes
and waves away from baseline show that there is movement of the impulse.
Voltage and Time Calibration of ECG
Standard Calib:
-Horizontal lines- 10 small line divs up(+) or down(-) = 1 millivolt
-Vertical lines- time; paper speed of 25mm/sec
25mm=1sec
5mm segments=0.20 sec (dark lines)
further split into 5 more boxes=0.04sec
-Normal Voltage-When recorded on the arms or leg:
-QRS complex= 1.0-1.5mv from top of R to bottom of S
-P wave= 0.1-0.3mv
-T wave=0.2-0.3mv
P-Q or P-R interval- the time btwn the start of the P wave and the start of the QRS complex.
Btwn atrial and vent. excitation
Q-T interval- period of vent contraction
HR as determined by ECG- the reciprocal of the time interval btwn two successive heart
beats.
Methods for recording ECGs
Recorders: these days, computer based systems; used to be moving paper with pen
Different pen types: those connected to an inkwell on one side; those that are
made hot and write on paper that turns dark when heated; others turn dark when exposed
to electric current and the “pen” emits current to an electrode on the back. Seriously why
do we need to waste time reading that? [/Pointless info]
Flow of Current around the Heart during the cardiac cycle
(+)charge on exterior, (-) charge on interior
upon depol, (-) charge leaks out of cell, making exterior surface (-)
-meter with (-) end in depol’d area (also –) and (+) end in non-stimulated
area= reads =(+)
-meter with (+)end in depol’d area(-) and (+)end in non-stim=reads (-)
-meter with (-) and (+) ends in non-stim area = reads 0 (zero)
Flow of Electrical Currents in the chest around the heart
Heart suspended in conductive medium. The average current flow occurs with (-)
toward the base of the heart and (+) toward the apex
Just before depol ends, the average direction of the current flow reverses for 0.01sec
-In normal, healthy heart, current flow from (-) to (+) mostly from base to apex
during all of depol, expect the very end
ECG leads
3 bipolar leads:
“bipolar”: means from two diff sides of the heart
“lead”: not a single wire, but a combination of two wires and their electodes
to make a complete circuit btwn the body and the electrocardiograph.
Lead I= (-) on R arm, (+) on L arm
Lead II= (-) on R arm, (+) on L leg
Lead III= (-) on L arm, (+) on L leg
Einthoven’s Triangle- drawn around the heart… points downward
Einthoven’s Law- if the electrical potentials of any 2 of the 3 bipolar leads in known, the 3rd
can be figured out mathematically by summing the first 2.
When diagnosing arrhythmias, it does not matter which lead is used
When diagnosing damage in the vent of atrial muscle, or perkinje system- it does
matter bc abnormalities change the patterns in some leads, but not others.
Chest Leads (precordial leads)
V1-V6
(+) electrodes at 6 places on the chest, near the heart
(-) electrods connected at equal resistances in the RA, LA, and LL at the same
time. Called the “indifferent electrode”
Leads V1-2= mostly (-), closer to base of heart
Leads V4-6= mostly (+), closer to apex of heart
Augmented Unipolar Limb Leads
Another system of leads, two of the limbs are connected to the (-) terminal,
rd
and the 3 limb is connected to the (+) terminal.
When (+) on RA= aVR- this reading is inverted
When (+) on LA= aVL
When (+) on LL= aVF