205 L10 Flashcards
Electrocardiogram
The electrocardiogram (ECG) visualizes the ——– activity spreading through the ——. It’s the sum of the ——— activity of the heart = VOLTAGE / TIME recording. It is recorded by ——— at different sites on the body that are connected to the —–, and are able to measure a ——– difference between different sites on the body caused by the electrical activity of the heart. This electrical activity can be recorded at a site distant from the heart because the body tissues act as ———. The heart is not the only source of electrical activity in the body, e.g. skeletal muscle
The electrocardiogram (ECG) visualizes the electrical activity spreading through the heart.. It’s the sum of the electrical activity of the heart = VOLTAGE / TIME recording. It is recorded by electrodes at different sites on the body that are connected to the skin, and are able to measure a potential difference between different sites on the body caused by the electrical activity of the heart. This electrical activity can be recorded at a site distant from the heart because the body tissues act as conductors. The heart is not the only source of electrical activity in the body, e.g. skeletal muscle
Because of the ——– conducting network the different groups of cells along the ——– are ———– very close together and the depolerisation stacks up to give the ——- complex
Because of the purkinje/fast conducting network the different groups of cells along the ventricle are depolerising very close together and the depolerisation stacks up to give the QRS complex
Because of the ——– conducting network the different groups of cells along the ——– are ———– very close together and the depolerisation stacks up to give the ——- complex
Because of the purkinje/fast conducting network the different groups of cells along the ventricle are depolerising very close together and the depolerisation stacks up to give the QRS complex
What is a dipole?
A pair of equal but opposite charges separated by a small distance
The voltage measured in the ECG depends on the positioning of the ——-.
Electrodes
If there is a bigger potential difference between the 2 electrodes, there will be more —– and change in ——- measured.
If there is a bigger potential difference between the 2 electrodes, there will be more current and change in voltage measured.
When electrodes are placed at ——- distances the fields become ———, changing the size of the —- and measured ——–.
When electrodes are placed at greater distances the fields become weaker, changing the size of the dipole and measured voltage.
What factors does the measured potential depend on?
Magnitude of charges (dipole)
Orientation of dipole & electrodes
Distance between dipole ad electrodes
What factors does the measured potential depend on?
Magnitude of charges (dipole)
Orientation of dipole & electrodes
Distance between dipole ad electrodes
Wave front dipole - propagating wave
The resting potential of non active tissue inside is ——-, in cardiac tissue about —– and outside is ——–.
As the wave of activation spreads, the cells ——- and you get ——– rushing into the cells making the membrane potential ——–, therefore the extracellular space becomes relatively more ———-.
ECG is measuring from the —– of the body, so what we see is measured from the —– fluid
ECG recording is designed so that we get a +ve deflection when +ve pole faces the +ve electrode.
The resting potential of non active tissue inside is negative, in cardiac tissue about -80 and outside is positive.
As the wave of activation spreads, the cells depolerize and you get sodium rushing into the cells making the membrane potential positive, therefore the extracellular space becomes relatively more negative.
ECG is measuring from the outside of the body, so what we see is measured from the extracellular fluid
ECG recording is designed so that we get a +ve deflection when +ve pole faces the +ve electrode.
A bipolar system measures the difference in potential between —- electrodes. Potentials are recorded between combinations of –,– and –.
A bipolar system measures the difference in potential between 2 electrodes. Potentials are recorded between combinations of RA, LA and LL.
What are the 3 standard bipolar limb leads?
Lead l = LA-RA
Lead ll = LL-RA
Lead lll = LL-LA
At any instant during the cardiac cycle: Lead – + Lead—– = Lead —-
Lead l + Lead lll = Lead ll
A unipolar system measures potential of —– electrode relative to some constant reference.
To use unipolar leads we need to form a —— lead.
All —– electrodes are connected together into one end of the ——– called the wilson’s central terminal. This can be the ——- lead. The combination of the —- electrodes during the cardiac cycle gives a constant voltage of —V as the volts —– each other out.
We have another electrode which is the ——– electrode. If the ——- is facing the —— electrode a ——– deflection is recorded.
One end of the electrode (negative) is in the centre of the chest and can be paired up with VR, VL or VF
A unipolar system measures potential of 1 electrode relative to some constant reference.
To use unipolar leads we need to form a reference lead.
All 3 electrodes are connected together into one end of the voltmeter called the wilson’s central terminal. This can be the reference lead. The combination of the 3 electrodes during the cardiac cycle gives a constant voltage of 0V as the volts cancel each other out.
We have another electrode which is the exploring electrode. If the dipole is facing the exploring electrode a positive deflection is recorded.
One end of the electrode (negative) is in the centre of the chest and can be paired up with VR, VL or VF
What set of leads are used to measure the electrical activity in the horizontal plane?
Unipolar chest leads V1-V6
