CV III Flashcards
What is the conducting system of the heart
SA node - internodal pathways - AV node - AV bundle - left and right bundle branches - purkunje fibers
What is the bundle of His
AV bundle
What part of the conducting system passes into the ventricles
AV bundle/bundle of His
What are the 4 special conducting bundles
Backman’s bundle
Anterior, middle, posterior internodal pathways
What does the backman’s bundle do
Conducts APs front the SA pacemaker into the LA causing contraction
What do the anterior, middle, and posterior internodal pathways do
Conduct AP from SA node to AV node, depolarizing right atrial muscle along way
What is speed of atrial conduction
Relatively Slow
80-100ms
What prevents conduction directly from atria to ventricle
Layer of connective tissue
Why does conduction slow through AV node
Allows blood from atria to empty into ventricles, allows atrial contraction to pump little more blood in
What way does depolarization spread through heart
Through septum to apex then up the walls of ventricles from apex to base
What is speed of ventricular contraction
More rapid
60–100ms
How are ventricular muscles arranged and what does it ensure
Spiral arrangement
Ensures blood is squeezed upward from apex of heart
What is ventricular muscle attached to
Insertion and origin on AV ring
Start and come around to attach to AV ring on other side
What happens if electrical activity cannot be transferred from atria to ventricles (damage to AV bundle)
Complete conduction block
SA node continues as pacemaker for atria
Purkinje fibers must take over as pacemaker for ventricles but much slower
Requires artificial pacemaker
What does electrocardiography (ECG, EKG) measure
Records summed electrical activity generated by all cells of the heart
How is electrocardiogram work
Salt solutions lie NaCl based ECF are good conductors of electricity
What is Einthoven’s triangle
Triangle created around heart
Electrodes pairs attached to both arms and one leg
What are leads
Pairs of electrodes
How is ECG recorded using triangle
One electrode acts as positive and one negative
How many leads in modern ECG
12
Electrical activity of heart moving towards positive electrode
Upward deflection is recorded
Electrical activity moving away from positive electrode
Recorded as downward deflection
A vector moving perpendicular to axis of electrodes
Causes no deflection
What are ECGs a combination of
Waves and segments
Waves
Appear as deflections above or below the baseline
Waves of depolarization or repolarizations
Segments
Sections of baseline between two waves
Intervals
Combination of waves and segments
P wave
Atrial depolarization
P-R or P-Q segment
Conduction through AV node and AV bundle
Atria contract
QRS complex
Ventricular depolarization
T wave
Ventricular repolarization (K+ leaving)
What is hidden by ventricular depolarization
Atrial repolarization
What is QT interval
Time it takes for heart to depolarize and repolarize
What is the order of electrical events
P wave, P-R or P-Q segment, Q wave, R wave, S wave, S-T segment, T wave
What is S-T segment
Ventricles contract
What is heart rate
P wave to P wave or R-R
Tachycardia more than 70 r waves
Bradycardia less than 70 r waves
What do ECGs provide info on
HR and rhythm, conduction velocity, condition of tissues
How do arrhythmias appear on ECGs
Elongated segments or intervals, altered, missing or additional waves
Premature ventricular contractions
Purkinge fibres randomly kick in as pacemaker
Due to low O2, excessive Ca, hypokalemia, medications, exercise, adrenaline
Skipped beat or palpitation
Long QT syndrome
Delayed repolarization of ventricles
Palpitaitons, fainting, sudden death due to repeated ventricular contractions
Cardiac cycle
One complete contraction and relaxation
Phases of cardiac cycle (ventricles)
Diastole and systole
Diastole
Time during which cardiac muscle relaxes
Systole
Time during which cardiac muscle contracts
5 phases of a single cardiac cycle
- Heart at rest (atrial and ventricular diastole, late diastole)
- Completion of ventricular filling (atrial systole)
- Early ventricular filling (isovolumetric ventricular contraction)
- Heart pumps (ventricular ejection)
- Ventricular relaxation (isovolumetric ventricular relaxation, early diastole)
