Cardiovascular 3 Flashcards
What is the primary function of the SA node?
It serves as the pacemaker of the heart.
What are the four special conducting bundles in atrial conduction?
SA node, AV node, Bachmann’s bundle, and internodal pathways.
What does Bachmann’s bundle do?
Conducts action potentials from the SA pacemaker into the left atrium.
What are the three types of internodal pathways?
Anterior, middle, and posterior internodal pathways.
What is the role of the internodal pathways?
Conduct the action potential from the SA node to the AV node.
How does atrial conduction compare to ventricular conduction?
Atrial conduction is relatively slow.
What is the typical time for atrial conduction?
80-100 ms.
Fill in the blank: The action potentials from the SA node depolarize the _______ muscle.
right atrial
True or False: Atrial conduction is faster than ventricular conduction.
False
Ventricular Ring
a layer of connective tissue that prevents conduction directly from atria to ventricle
-conduction slow down through the AV node to allow blood from atria to empty into ventricles
Ventricular conduction Depolarization
-process through the septum to the apex (bundle of his followed by bundle branches)
-then spreads up the walls of the ventricles from apex to Purkinje fibers, or the base
Ventricular conduction occurs
More rapidly, about 60-100ms
Pathway of ventricular conduction
SA node, AV node, Bundle of His, Bundle branches, Purkinje fibres
Ventricular muscles have what arrangement that does what?
They have spiral arrangement that ensures blood is squeezed UP from the apex (bottom left) of the heart
What happens if electrical activity cannot be transferred from the atria into the ventricles?
A complete conduction block is caused by damage in conduction pathway
-block at bundle of his fresults in complete dissasociation between the atria and ventricles
What happens during a complete conduction block?
The SA node continues to be the pacemaker, but the electrical activity doesn’t make it to the ventricles
-Purkinje fibres take over as pacemaker for the ventricles
-requires an artificial pacemaker
ECG
Electrocardiogram
-place electrodes on the skins surface and record the electrical activity of all the cells of the heart
Einthovens triangle for ECG
Right arm negative, left arm positive on top negative on bottom, legs are both positive
-creates a triangle of positive to negative attachments
If the electrical activity of the heart is moving towards the positive electrode of the lead, what kind of deflection happens
An upward direction comes from electrical activity moving upwards
-current flow vector is pointed towards the positive electrode
Electrical activity moving AWAY from a positive electrode is
A downward reflection
-current flow vector is pointed towards the negative electrode
Electrical activity moving perpendicular to the axis of the electrodes causes
No deflection
-across the lead
-vector that is pointed perpendicular to the axis of the electrode
ECG waves
Appear as deflections above or below the baseline
ECG Segments
Are the sections of baseline between 2 waves
ECG Intervals
Are the combination of waves and segments
P wave
Atrial depolarization
P-R segment
conduction through AV node and AV bundle
-atria contract
QRS complex
The rise, where R is the top
-ventricular depolarization (contraction)
-hides atrial repolarization
T wave
The end after the QRS
-ventricular repolarization (relaxing)
Q wave
Depolarization (contraction) of ventricular septum
R wave
Ventricle walls depolarizing (contracting)
ST Segment
Plateau phase
-calcium and potassium come in
T wave
Ventricular repolarization
Ca channels close, potassium out
Heart rate in ECG
Is the P-wave to P-wave or R to R
Tachycardia
Faster heart rate
Bradycardia
Slower HR
Arrhythmia
Abnormal heart beat
-can be the result of many issues
How to tell issues with the heart through ECG
-is each P, Q, R, S, T wave present?
-is there one QRS complex for every P wave?
-is the PR segment constant?
-elongated segments indicate some sort of damage
Arrthymias can appear as
Elongated segments or intervals
-altered, missing, or additional waves
Premature ventricular contractions
Purkinje fibers randomly kick in as pacemakers
-due to; insufficient O2 to myocardium, excessive Ca2+, hypokalemia, meds, exercise, high adrenaline
Is perceived as a skipped beat or palpation
Long QT syndrome
Usually due to K+
-delayed repolarization of the ventricles
-can be drug induced
Cardiac Cycle
One complete contraction and relaxation
Diastole vs Systole
Diastole is the time which cardiac muscle relaxes
Systole is the time which cardiac muscle contracts
5 Phases of a single cardiac cycle:
- The heart at rest: atrial and ventricular diastole, late diastole
- Completion of ventricular filling (atrial systole)
- Early ventricular contraction (isovolumetric ventricular contraction)
- The heart pumps (ventricular ejection)
- Ventricular relaxation (isovolumetric ventricular relaxation, early diastole)
The Lub and Dub sounds of the heart are
LUB: AV valves snapping shut during early ventricular contraction
DUB: semi lunar valves snapping shut during ventricular relaxation
Step 1: The heart at rest
Atrial and Ventricular Diastole (late diastole)
-cycle starts with atria relaxes and filling with blood from veins
-ventricles begin to relax, when ventricles are relaxed enough and pressure in atria exceeds ventricles, AV valve opens and ventricles fill passively with blood from atria
Step 2: Completion of ventricular filling
Atrial Systole
-most blood enters ventricles passively but under normal resting conditions, the last 20% enters when the atria contract
Step 3: Early ventricular contraction
Isovolumetric Ventricular Contraction
-ventricles begin to contract, builds up pressure in ventricles ands causes AV valves to snap shut
-this snapping shut is the LUB
-both valves are now closed and then the ventricle continues to contract building up pressure
Step 4: The Heart Pumps
Ventricular Ejection
-as the ventricles contract pressure in the ventricle exceeds pressure in the outflow arteries (aorta or pulmonary arteries), causing the semi lunar valves to open and blood to flow out
Step 5: Ventricular Relaxation
Isovolumetric Ventricular Relaxation
-ventricles begin to relax, pressure in the outflow artieries begin to exceed the ventricles, causing blood to attempt to flow backward into the ventricles
-causes the semi lunar valves to snap shut, causing the DUB
Step 5: Ventricular Relaxation
Isovolumetric Ventricular Relaxation
-ventricles begin to relax, pressure in the outflow artieries begin to exceed the ventricles, causing blood to attempt to flow backward into the ventricles
-causes the semi lunar valves to snap shut, causing the DUB
