Flashcards in Cardiology Physiology Deck (70)
Action potential in the T tubules of cardiac myocytes triggers calcium entry in which 2 ways?
1) L type channels - voltage sensitive Ca2+ channels
2) Calcium induced calcium release - Calcium released from SR
What protein does calcium interact with to induce contraction?
What is the resting potential and threshold potential of pacemaker cells?
Resting = -60mV
Threshold = -40mV
What is the resting potential and threshold potential of cardiac myocytes?
Resting = -90mV
Threshold = -65mV
What is the TFR of a cardiac myocyte?
ARP (absolute refractory period) + RRP (relative refractory period)
In an ECG what direction does the depolarisation go in a +ve and -ve deflection?
Towards an electrode = +ve deflection
Away from an electrode = -ve deflection
What are Einthoven's 6 leads?
RA, LA, LA
Lead I - LA -RA
Lead II - LL-RA
Lead III - LL-LA
Augmented limb leads (recorded with respect to 0)
aVR = RA
aVL = LA
aVF = LL
What are Virchows leads?
Chest leads (V1-V6) Unipolar leads recorded with respect to 0
What leads is the electrical axis of the heart to do with?
What is the electrical axis of the heart?
Max current produced by an ECG - normally lead II (60 degrees) but can be anywhere between -30 and 90 degrees (einthoven's leads)
What would left deviation (-150 - -30) and right deviation (+90 - -150) tell you?
Left deviation - left ventricular hypertrophy
Right deviation - right ventricular hypertrophy
What is the left ventricular axis and which leads is it to do with?
To do with Virchows leads
Max current generated by ECG - towards V6
What are the 4 phases of the heart beat?
1) Diastolic ventricular filling (passive phase followed by active phase when atria contract)
2) Isovolumic contraction (semilunar valves closed by ventricles contracting)
3) Systolic ejection ( 2nd phase of ventricular systole - ventricles contracting and blood ejecting - during this phase atria relax and fill with blood)
4) Isovolumic relaxation (ventricles relax, semilunar valves close, atria continue to fill)
What is cardiac power and how is it calculated?
Rate of work done by the heart
Cardiac power = pressure x flow rate
What is EDV?
End diastolic volume
What is ESV?
End systolic volume
How is stroke volume calculated?
EDV - ESV
How is ejection fraction (LVEF) calculated?
What is the main source of ATP for the heart?
Free fatty acids
What does the difference between LV and aortic pressure tell us?
The extent of aortic stenosis
What is V (blood velocity)?
Distance travelled per particle per unit of time
What is the equation linking pressure, blood flow and resistance?
Pressure = blood flow x resistance
What is the difference between the action potential in cardiac and skeletal muscle and what is the purpose of this difference?
Presence of plateau caused by Ca2+ ions in the cardiac myocyte action potential
Maintains contractile period during depolarisation
What happens to the troponin tropmyosin complex during systole?
Calcium binds to troponin, troponin-tropomyosin complex moves and myosin can now dock onto the exposed binding sites
What happens to the longitudinal and horizontal and circumferential filaments during systole?
Longitudinal filament shortening
Horizontal and circumferential filament thickening
In which 2 ways can heart rate be increased?
1) Sympathetic innervation
2) Adrenaline - beta 1 agonism
In which 2 ways can stroke volume be increased?
1) Increase pre load
2) Sympathetic input - prolonged opening of Ca2+ channels, enhances calcium action in excitation/contraction coupling mechanisms
What happens to the LVEF of a failing heart?
What is the physiological LVEF and the LVEF in exercise?
Physiological LVEF - 50-75%
LVEF in exercise - can reach 90%