cardiorespiratory Flashcards
why is an ECG clinically relevant?
identify and evaluate conduction abnormalities
identify structural abnormalities
identify perfusion abnormalities
how may conduction abnormalities affect heart function?
usually the conduction system produces a cascade of electrical activity that can orchestrate/stimulate mechanical events to result in cardiac output
disruption in conduction system prevents mechanical processes from taking place
how may structural abnormalities affect heart function?
size of myocardium - if enlarged, available volume for the ventricles to take in blood for ejection reduces
how may perfusion abnormalities affect heart function?
interruption of blood flow may cause abnormal behaviour of deprived tissue
what are the practical advantages of an ECG?
relatively cheap and easy to undertake
reproducible results between people and centres
quick turnaround on results/report
is the pain retrosternal?
brought on by exertion?
relieved by rest or GTN?
all yes - typical
2 yes, 1 no - atypical
1 yes, 2 no - non-cardiac
what is a vector?
quantity that has both magnitude and direction
how is a vector represented?
arrow in net direction of movement
size reflects magnitude
what does the isoelectric line on an ECG represent?
no net change in voltage
i.e. vectors are perpendicular to the lead.
what does the width of a deflection on an ECG represent?
‘duration’ of the event
what does an upward deflection on an ECG represent?
towards cathode (+)
wave of excitation travelling towards positive electrode
what does an downward deflection on an ECG represent?
towards anode (-)
wave of excitation travelling towards negative electrode
what is a ‘wave’ on an ECG?
upwards and downwards deflection until return to isoelectric line
what does the steepness of line on an ECG represent?
velocity of action potential (steeper = faster)
what does the P wave show?
atrial excitation phase
what does the P wave stimulate?
atrial systole
what does the QRS complex show?
ventricular excitation phase
what does the QRS complex stimulate?
ventricular systole
what does the T wave show?
relaxation of ventricles
how do the P wave and QRS complex correspond to pressure in the aorta?
slight decrease (85mmHg to 75mmHg)
how does the T wave correspond to pressure in the aorta?
pressure increases between end of S and beginning of T (75mmHg to 115mmHg)
slight decrease over course of T wave (115mmHg to 100mmHg)
how does the relaxation phase (after repolarisation of ventricles, i.e. T wave) correspond to pressure in the aorta?
slight increase (~5mmHg)
steady decrease back to baseline (85mmHg)
how do the P wave and QRS complex correspond to pressure in the atrium?
slight increase from baseline (10mmHg to 15mmHg), decreases to baseline at R/S - a wave
slight increase from S (10mmHg to 15mmHg), decreases to baseline before T - c wave
how does the T wave correspond to pressure in the atrium?
slight increase from start of T to after end of T (10mmHg to 15mmHg) - v wave