Cardiac Cycle/Heart Sounds and Murmurs Flashcards
Describe the process of a pacemaker potential.
Phase 4 = funny current where there is hyperpolarisation activated by Na channel. Phase 0 = depolarisation via activation of VGCC. Phase 3 = repolarisation via activation of VGKC - K+ efflux.
Describe the process of atria/ventricular APs.
Phase 4 = resting phase - Na/K pump - Na out and K in - impermeable to Na but permeable to K. Phase 0 = rapid depolarisation - VGNaCs open then VGCCs open. Phase 1 = VGNaCs close. Phase 2 = plateau phase where VGCCs fully open so Ca enters and VGKCs start to open. The plateau phase is important as there is CICR and a refractory period so there is no more firing - allows proper emptying and filling of blood. Phase 3 = VGCCs close and VGKCs open fully - K efflux.
Describe the process of electrical conduction through the heart.
(1) Electrical activity generated in SAN spreads out via gap junctions into atria (2) At AVN, conduction is delayed to allow correct filling of ventricles (3) Conduction occurs rapidly through Bundle of His into ventricles (4) Conduction through Purkinje fibres spreads quickly throughout the ventricles. Ventricular contraction begins at the apex.
In a typical ECG trace what should times be systole and diastole?
Systole = 0.34s Diastole = 0.66s
Describe a typical ECG trace.
P wave = atrial depolarisation. PR segment = AV nodal delay. QRS segment = ventricular depolarisation and atria repolarisation. ST segement = ventricular contraction and emptying. T wave = ventricular repolarisation. TP segment = ventricles are relaxing and filling.
Give an overview of the cardiac cycle.
1) Blood enters atria and move into ventricles. Pressure in atria>ventricles so the tricuspid and mitral valves open and blood flows in aided by atria contraction.
2) . Pressure in full ventricles > atria, tricuspid and mitral valves close, contraction on closed ventricle, pressure increases in chamber. Contraction at the same volume but change in pressure. 3). Pressure in ventricles > aorta/pulmonary artery, pulmonary and aortic valves open, ejection of blood, blood enters atria. 4). Pressure in aorta/pulmonary artery > ventricles, aortic and pulmonary valves close, closed ventricle relaxes ready to receive blood. No change in volume.
How do you calculate stroke volume?
What is ejection fraction?
What are normal values for ejection fraction?
SV = EDV-ESV - usually 120ml - 40ml = 80ml
Ejection fraction = SV/EDV
2/3rd or more - lower values in heart value
What is the right atrial cycle and how does this affect jugular venous pressure?
Phase 1 = A wave - atrium contracting tricuspid valve open - increases pressure. Phase 2 - X descent - atrium relaxing then filling, tricuspid closed - pressure drops a lot. Phase 3 = V wave - atrium tense, full, tricuspid closed - pressure rises slightly. Phase 4 - Y descent - atrium emptying, tricuspid open - pressure drops.
What does a ventricular pressure-volume loop tell us?
The area inside the loop is equal to the amount of stroke work done. It relates to the amount of energy consumption during the cardiac cycle.
Work = change in ventricle pressure x change in volume.
What creates the ‘Lubb’ sound?
Closure of tricuspid/mitral valves at beginning of ventricular systole.
What creates the ‘Dupp’ sound?
Closure of aortic/pulmonary valves at beginning of ventricular diastole.
What are the other 2 smaller heart sounds.
One is due to turbulent blood flow into ventricles detected near end of first 1/3 diastole and is occasional. The other is forceful atrial contraction against a stiff ventricle and is pathological in adults.
