Cardiac Cycle Flashcards
Does the pulmonary or systemic circulation have a higher pressure?
Systemic
Which structure is responsible for venous drainage of the heart?
Coronary sinus
What drains into the coronary sinus?
Left ventricle, most epicardial ventricular veins
Stages of heartbeat 1) 2) 3) 4) 5)
1) Late diastole 2) Arterial systole 3) Isometric ventricular contraction 4) Ventricular ejection 5) Isometric ventricular relaxation
What are the only part of venous and arterial vessels that run parallel in the same direction?
Coronary sinus, circumflex artery
When does left coronary flow mostly occur?
Diastole
Why does left coronary flow occur mostly during diastole?
Difference in pressure between aorta and left ventricle During systole there is no such difference
What is the rate of SA node pacemaker?
~70 beats/minute
What is the rate of AV node autorhythmicity?
~50 beats/minute
What is the rate of Purkinje fiber autorhythmicity?
25-40 betas/minute
How does the SA node communicate with the AV node?
Internodal pathways through the right atrium
Electrical conduction in heart
1) SA node 2) Internodal pathways 3) AV node 4) AV bundle 5) Bundle branches 6) Purkinje fibers
What does the ECG measure?
Whole heart average extracellular potential (from the body surface) Depolarisation either towards or away from electrodes
What are the ECG electrodes connected to in Einthoven’s triangle?
Left leg Right arm Left arm
What is isovolumetric contraction/relaxation?
1) Function of elastic wall of heart 2) Contraction of ventricles with no corresponding change in volume 3) When intraventricular pressure doesn’t exceed the pressure in aorta –> aortic valve doesn’t open
Is diastole passive?
No. ATP required to pump Ca from smooth muscle cytoplasm
How do the ventricles fill with blood?
25% from atrial contraction 75% passively during diastole
Stroke volume
Amount of blood injected each time the heart contracts
Does the nervous system regulate SA depolarisation?
Yes Regulated by the autonomic nervous system
Why do Purkinje fibers conduct AP to base of heart first?
So that the base of the heart contracts first This prevents blood being trapped in the heart
Do myocardial cells summate graded potentials?
No Long refractory period prevents this
What are the waves in an ECG?
1) P wave 2) QRS complex 3) T wave
What is the P wave?
Atrial depolarisation
What is the QRS complex?
Ventricular depolarisation
What do the different parts of the QRS complex represent?
1) Q - Depol of bundle of His, Purkinje fibers 2) R - Depol of bottom of ventricles 3) S - Depol of the upper part of ventricles
When do the ventricles contract on an ECG?
In the period directly after the S wave
When do the atria contract on an ECG?
In the period directly after the P wave
What is the T wave?
Repolarisation of the ventricles
What is the ST segment?
Depolarisation of the ventricles
What will an ECG look like it the leads are placed 180 degrees in the opposite direction?
A mirror image
Is there electrical activity elsewhere in the heart during the QRS complex?
Yes, but these deflections are overwhelmed by the left ventricle
What is the standard ECG today?
9 electrodes, 12 leads
How is a modern ECG represented?
4 lines: First 3 lines are the 12 leads (3 rows by 4 columns) Bottom line is the long arm of lead 2, which shows the rhythm of the heart
What results in a positive ECG reading?
Electrical activity towards the positive electrode
What are the three intervals of an ECG?
PR QRS QT
Atrial fibrillation
Erratic atrial activity Not linked to SA node pacemaking Normally 1 P wave per QRS complex. This is not the case in atrial fibrillation
Possible causes of atrial fibrillation
Idiopathic electrolyte imbalance Dilated atria Sympathetic hyperactivity
Ventricular fibrillation
Ventricles beat independently of the atria Less common than atrial fibrillation, much more serious No obvious pattern to ECG
Possible causes of ventricular fibrillation
Ischaemia in heart attack Electrocution
How to restore normal rhythm from ventricular fibrillation
Defibrillator (electric shock)
Does the diastolic pressure in the aorta fall more quickly or slowly than in the ventricles?
More slowly It feeds to into smaller vessels (capillaries)
When do valves close?
When the pressure in the current compartment exceeds that in the previous compartment
What can be heard and not heard from the heart?
Can hear turbulent flow Can’t hear laminar flow
Heart sounds 1) 2)
1) Atrioventricular valves closing 2) Semilunar valves closing
Which heart action corresponds with the sound of the atrioventricular valves closing?
Ventricular contraction
Which heart action corresponds with the sound of the semilunar valves closing?
Ventricular relaxation
What does a noise when the valves are open indicate?
A defect in the valves Non-laminar flow
Measurements depicted on a Wigger’s diagram
1) ECG 2) Heart pressure 3) Heart sounds 4) Left ventricular volume
Average time between P waves
~800msec
What does the dicrotic notch represent?
Closure of the aortic or pulmonary valve
When does artrial systole occur relative to ECG?
After P wave
When does ventricular ejection occur relative to ECG?
After QRS complex
When does the left ventricle fill relative to ECG?
QRS complex
