Cardio Phys Flashcards
What is the p-wave
Produced by atrial depolarisation
What is the PR interval
the time taken for excitation to spread through the atria, AV node and bundle of His.
Lasts 0.12 - 0.2s
What is the QRS interval
The time taken for excitation to spread through the ventricles (0.06-0.12s)
What is the QT interval?
duration of ventricular depolarisation. duration 0.3-0.4s. Varies inversely with HR.
What is einthoven’s triangle?
an equilateral triangle formed by the shoulders and pubic symphesis.
If current is travelling toward an electrode, is it positive or negative?
positive
Where does lead I go on the ECG
left to right arm
Where does lead II go on the ECG?
between left foot and right arm
Where dose lead 3 go on the ECG?
between L foot and L arm
What are the two phases of the cardiac cycle?
systole and diastole
What are the phases of systole?
isovolumetric contraction and ejection.
Ventricles contract, AV valves close, Intraventricular pressure rises until > aortic/pulmonary presure, then blood is ejected from the ventricle (stroke volume)
What is the sequence of events in the cardiac cycle?
Mid-diastole, end-diastole, isovolumetric contraction, ejection, isovolumetric relaxation, rapid ventricular filling
What are the events for diastole?
Ventricles relax, pressure in the aorta and pulmonary circuits are > ventricles, semi-lunar valves close. Isovolumetric ventricular relaxation. Mitral and tricuspid valves open, rapid ventricular filling occurs. Atria then contract to complete ventricular filling.
Events of mid-diastole:
Atrial pressure > ventricular pressure so blood flows into ventricles.
Ventricular pressures rise as blood flows into them
Events of late diastole:
SA node fires (p-wave). Atrial contraction pushes some blood back up the SVC, causing ‘a’ wave of CVP waveform.
Atrial contraction contributes 20% to LVEDV
Atrial contraction is more important during higher HRs, as there is less time for passive filling.
