Cardiac revision (Wk: 3) Flashcards
Define systole and at what point in a ECG does it start and end?
= ventricular contraction
- starts at R and ends at end of T wave.
Define diastole
From end of T wave though P and Q to R.
What are the basic principles of the heart and flow?
- blood flows from higher pressure to lower pressure.
- Contraction creates higher pressure while relaxation creates lower pressure.
- AV vales open when atrial pressures are higher than ventricular pressures. and close when pressure gradient is reversed.
- semi luna valves close when ventricular pressure exceeds aortic/pulmonary pressure and close when the reverse is true.
Explain the cardiac cycle steps
Phase 1: atrial depolarisation
- commences at stilulation of SA node
- causing atrial depolarisation and thus contraction.
- shown as the p wave. Atrial contraction commences shortly after the p wave commences= atrial pressure increases forcing blood into the ventricles.
- atrial contraction occurs, however, note that contraction accounts for not much of ventricle filling as pressure mismatch between the atrium and the ventricle causes most to occur via passive blood flow before this point.
- pressure in atrium begins to fall and thus AV valves close= producing the first health sound S1. + systoly begins.
Phase 2: isovolumentric contraction
- Ventricular depolarisation (QRS complex) causing ventricular contraction.
- for a short time the semi luna valves stay closed during ventricular contraction called isovolumetric contraction.
Phase 3: rapid ejection
- when pressures in the ventricles exceed the pressures in the aorta and pulmonary artery.
- semi luna valves open and blood is ejected out of the ventricles.
Phase 4: reduced ejection
- ventricular pressure decreases.
- when ventricular pressures fall below aortic and pulmonary artery the semi luna valves close= causing S2 sound
Phase 5: isovolumetric relaxation
- ventricles relax with all valves closed
Phase 6: ventricular filling
- when Atrial pressure exceeds ventricular pressure blood begins to passively fill the ventricules.
- atria contract to finish this phase and the cycle repeats.
What is the P wave on an ECG representing?
= atrial depolarisation from SA node stimulation.
Explain the key landmarks of the progression of conduction thought the heart.
- Sino atrial node (SA)
- Atrio ventricular node (AV)
- AV bundle (bundle of his)
- R and L bundle branhes
- perkinje fibres
Explain the progression of conduction through the heart.
Sino atrial node (SA)
- located in the RA near the SVA
- natural pacemaker
- initiates heartbeat
- determines heart rate
- innovates atrial contraction
Atrio ventricular node (AV)
- located on the low side of the atrium near the AV valve
- acts as electrical gateway to the valves.
- delays passive of electrical impulses to the ventricles to ensure atrium eject all blood to ventricles before they contact
- receives impulses form the SA node and passes them on to the AV bundle
AV bundle (bundle of his)
- conduct impulses to the apex’s of the heart.
Purkinje fibres
- take innovation up the sides of the heart
What is an ECG a recording of?
= the action potential of each node and cels of the myocardium.
What does the P wave represent on an ECG?
= SA node firing to cause atrial depolarisation contraction
What does the P-Q segment represent on an ECG?
= the time taken for signal to travel from AV node ot SA node.
= ventricular deploarisation
What does the Q wave represent on an ECG?
= depolarisation of in the intraventricular septum.
What does the R wave represent on an ECG?
= depolarisation of the main mass of the ventrciles
What does the S wave represent on an ECG?
= last phase of ventricule depolarisation at the base of the heart.
*atrial repolarisation also occurs at this time but the signal is obscured by the large QRS complex
What does the S-T segment represent on an ECG?
= the plateau in the myocardial action potential.
- this is when ventricles contract and pump blood.
What does the T wave represent on an ECG?
= ventricular repolarisation immediately before ventricular diastole.
