Cardio 5 Flashcards
T or F
All deoxygenated blood passes through either the SVC or the IVC on its way to the right atria. Why?
F
the coronary circulation has its own opening directly into the right atria
T or F
The Purkinje fibres can fire independently if the sinus node doesn’t generate an impulse. Why?
T
all cells in the conduction of the heart can fire their action potential to beat on their own, however, the sinus node is usually faster and “controls” the electric activity
T or F
The Purkinje fibres form synapses with the myocardium in ventricles, allowing ventricles to fire in synchrony
F
The whole statement is true EXCEPT CARDIAC CELLS DON’T HAVE SYNAPSES
T or F
Na+ ions passes through gap junctions of cells where one is active and the other is resting
T
It is a very small amount but Na+ does travel through the gap junction (most in the interstitial fluid)
What is a ECG/EKG
a recording of the electrical activity of the heart
What is the difference between ECG and EKG
ElectrocardioGRAPH: the device
electrocardioGRAM: the recording
What is the order of “waves” on the ECG reading
P QRS T
What happens during the P-wave? What is visible on the ECG reading, and why?
- Sinus node fibres: invisible
- Atrial activation: visible
- AV node activation: invisible
Anything that is a small activity will not appear on a reading
What happens during the Q-wave? What is visible on the ECG reading?
- His bundle activation: invisible
- Left bundle activation: invisible
- Septum activation: visible, Negative deflection
What happens during the R-wave? What is visible on the ECG reading?
- Purkinje fibres activation: invisible
- Ventricle activation
What happens during the S-wave? What is visible on the ECG reading?
- late activation of the ventricle: visible
Everything is activated at the end of this wave
How can the QRS complex be identified?
It’s the first negative deflection from the baseline
What happens during the T-wave? What is visible on the ECG reading?
- Ventricle repolarization: visible
What is a segment?
the baseline interval between two defelctions
What is an interval?
a range including deflections
Where is the P-R segment? What does it indicate?
From the end of the P to the start of the Q
It is the delay between atrial and ventricular activation
(there is no baseline between R and Q and a segment is the baseline interval so even if it is called the P-R segment it stops at Q)
Where is the P-R interval?
What does it indicate?
It starts at the beginning of P and ends at the beginning of Q
It is the Atrioventricular transit time
Where is the S-T segment? What does it indicate?
It starts at the end of the S wave and ends at the beginning of the T wave
It shows the time between depolarisation and repolarisation
Where is the Q-T interval? What does it indicate?
It starts at the beginning of the Q wave and ends at the end of the T wave.
It is proportional to the Action Potential time
Where is the QRS interval? What does it indicate?
From the start of Q to the end of S
it should be fast to show the activation of the heart ish
What does a long P-R interval indicate?
it may indicate a AV block
What does a long S-T segment indicate?
some tissues have abnormal AP (typical of an MI)
What does a long Q-T interval indicate?
there is a problem with repolarization
Why is an ECG useful in the medical context?
It allows people to identify cardiac problems in a non-intrusive way
How can a local circuit current be measured?
With extracellular electrodes where they feel the voltage difference between a depolarised cell and its neighbour
What is the formula to know a voltage difference between two electrodes?
V = +ve - -ve
If depolarizing propagation is going left to right
Will the voltage be positive or negative?
(-ve electrode on the left, +ve on the right)
The -ve electrode will sense a -ve charge, whereas the +ve electrode will sense a +ve charge
Since V = (+ve) - (-ve)
V = (+) - (-) = + voltage
If depolarising propagation is going right to left
Will the voltage be positive or negative?
(-ve electrode on the left, +ve on the right)
The -ve electrode will sense a +ve charge, whereas the +ve electrode will sense a -ve charge
Since V = (+ve) - (-ve)
V = (-) - (+) = - voltage
If repolarising propagation is going left to right
Will the voltage be positive or negative?
(-ve electrode on the left, +ve on the right)
The -ve electrode will sense a +ve charge, whereas the +ve electrode will sense a -ve charge
Since V = (+ve) - (-ve)
V = (-) - (+) = - voltage
What are the four general rules to know the sign of a voltage when only knowing the direction of propagation?
DEPOLARISATION going towards the +ve electrode, +V
DEPOLARISATION going towards the -ve electrode, -V
REPOLARISATION going towards the +ve electrode, -V
REPOLARISATION going towards the -ve electrode, +V
Why is the T wave positive (repolarisation of the ventricle) as well as the R wave (ventricular excitation) when they are opposite events (depol. repol)?
Because the repolarisation wave moves in the opposite direction as the depolarisation wave. (in to out then out to in due to different AP speeds)
What is bipolar lead ECG?
Three physical limb electrodes measure the electrical potential between two electrodes (triangle thingy). Each lead acts as a reference for another, creating three frontal plane measurements
What is unipolar lead ECG?
Measures electrical activity at a single electrode relative to a computed reference. They measure in the frontal and horizontal planes.
How does the unipolar system measure in both planes?
The limb leads measure in the frontal plane (Left to right differences and top to bottom), while the chest leads measure the horizontal plane (front to back)
Since many planes are measured, how is that going to affect the ECG reading?
The different points of view and the orientation of the leads will change the direction of the peaks in the reading
(to or from a lead will change sign +/-)
