Electrocardiogram Flashcards
What are the 4 phases of the Fast AP?
Depolarization - Fast voltage gated Na channels open
Initial Repolarizing phase - Fast voltage gated Na channels close and fast voltage K channels open
Plateau phase - L-type voltage gated ca channels open, fast voltage gated k channels close and slow voltage gated K channels partially open
Final repolarizing phase - ltype voltage Ca channels close and slow voltage gated K channels fully open
What type of ion movement is occuring during the plateau pahse of the fast AP
Ca ions diffuse in while K diffuse out - thye cancel eachother out
Where do Fast AP occur?
Contractile muscle fiber
Where do slow AP occur?
Autorhythmic cardiac muscle fiber
What are the phases in the slow AP?
Pacemaker potential - Volatage gated K channels close and F(funny) type Na channels open. T-type voltage gated ca channels open
Depol pahse - L-type voltage gated ca channels open
Repol - L-type voltage gated Ca channels close, voltage gated K channels open
Is the intrinsic rate higher or lower than a typical resting heart rate? Why is this occurring?
Higher, the vagus nerve is influencing
The sympathetic nervous system ___ the slope of the pacemaker potetial
Increases
The parasympathetic nervous sysrem ___ the slope of the pacemaker potential
decreases
Skeletal muscle AP can summate to sustain contraction. Cardiac muscles will not pump if sustained contraction (tetany) occurs. Thus, muscle contraction happens much slower/faster?
slower
Summation and tetany can occur in
skeletal muscle
Summation and tetany cannot occur in cardiac muscle. Why is this the case?
cardiac muscle cannot be re-excited until its previous contraction is over. The refractory period is about 250msec, due to the prologned plateau phase
Excitation of the heart normally occurs in an ____ fashion which allows ____ pumping of blood
Ordered, effectve
Why are the AP of cardiac muscle sustained?
They are sustained so that the contraction is maintained until the entire myocardium has had time to depolarize and contract. This prevents premature relaxation. It also prevents tetany because after the heart contracts it must relac and fill again
What is the significance of the atrial to ventricular delay?
Allows the atria to completely empty into the ventricles.
What type of conduction velocity does the AV node have?
slow
What are the six requirements of effective pumping of blood?
Depolarization propagates through cardiac muscle very rapidly. Cells of the ventricles contract simultaneosly
The AP of cardiac muscle are sustained. Maintains contraction while the entire myocardium has time to depol and contract. Prevents premature relaxation and tetany
Absence of tetany
Temporary inactivation of certain ion channels allows the heart to relax and fill
Substantial atrial to ventricular delay
Atria drains completely - AV node has a slow conduction velocity and delays signal
Coordinated contraction of vent cells
Max systolic P by working together
Vent contraction begins at apex and progressses upwards to eject blood into arteries. More efficient than a simple squeeze from all directions
Augustus Waller
First human EKG (jimmy the bulldog)
William Einthoven
Invented the first practical EKG and received the nobel prize
ECG
Captures a picture of the electrical activity of the heart in various planes
How can electrical activation of the heart be detected?
Using skin electrodes placed on the body
Bipolar leads
Positive and negative leads
Draw Eithoven’s triangle
What ae the 6 things an ECG can tell us?
Anatomical orientation of the hear
Rel. size of chambers
Disturbances in rythm/conduction
Extent and localization of ischemia (low O levels)
Effect of altered electrolyteconc
Influence of certain drugs
What is the simple approach to interpret ECG?
Rate, rhythm, axis, intervals, ST segments, T waves
What does the rhythm on an ECG refer to?
What is driving the vent rate which is the SA node
What type of potential are we measuting in the ECG? (diff than neuro)
Extracellular potential
What is lead 2 good and bad at?
Good at - view from base to heart
bad - left to right
Where is lead 2 placed? What does it compare?
RA (neg) and LL (pos)
What does a depolarization wave toward the + electrode (LL)? Replol?
Depol - positive
Repol - neg
A wave of depol traveling toward a positive elctrode results in ___ deflection
positive
A wave of repol traveling towards a positive electrode results in
negative deflection
Vector
summation of the electrical acitivity that is occuring
Where does the electrical activity of the heart originate?
SA node
P-wave
depol of both atria
Q wave
activation of interven septum
R wave
The LandR ventricle are activated
S wve
small areas of the vent are activated
T wave
Vent repolarizes
Why can we not see any deflection on the ECg during the time that the SA node AV node and the His=purkinje system undergo deploar
because they do not produce a larfe enoug helectrical signal to be transmitte to the surface of the body
The P-wave (QRS complex) is ___ generated by contraction of the atria/vent, rather generated by
NOT, electrical acitivyt of the muscle
The SA node, AV node, Bundle of HIS bundle branches and purkinje fibers are not ))) but rather
nerve, specialized cardiac muscle cells
Can we see the depol or repol of the atria?
We can only see the depol. Repol is overshadowed by the QRS complex - depol of vent
Sinus Rhythm. 3 cond
cardiac ryhthm where depol of the cardiac muscle begins at SA node
P wave should be upright in lead 2
Each QRS complex is preceeded by normal P wave
PR interval remians constant
2nd degree heart block
2:1 ration of Pwaves to QRS
Premature atrial contraction
Premature atrial depol. Beat arising from an abnormal place or position
What is the most common type of irregular heartbeat?
AF
What is the most serios cardiac arrhythmia
Vent tachycardia and Fibrillation
