16. Physiological Basis of the ECG Flashcards
how many electrodes are used in an ECG & how many readings does it produce
9 electrodes
12 readings
what does the ECG record
each electrode records a voltage difference btn itself and another
difference shown as a deflections (shows depol and repol)
when is a deflection produced in an ECG
part of the cardiac excitable tissue is at a different mem potential than the rest of the heart
-current flow can occur btn those regions
phase 0 & 3
electrodes report voltage differences in regions of —-
either the ventricles or atria
NOT btn the two
what are the steps of ECG deflection
- depol starts - there is diff btn diff parts –> deflection +
- once all cells are depol –> no diff
- repol starts - difference again – > - deflection
- once all repol –> no diff
*rmr measuring extracell potential*
where does current flow -negatively & -positively in the heart
average current flow occurs w/ negativity toward the base
& positivity towards the apex
what is the path of depolarization
start at SA node –> depol transmit to next contractile myocyte –> spread R to L thru atria = P wave
-at same time send signal to AV node –> then bundle of His –> bundle brances –> purkinje –> ventricles = beginning of QRS
which phase is represented by baseline on the ECG
phase 2
what is the PR interval
AV node delay
what direction does ventricular depolarization occur
R –> L
base–> apex
interior –> exterior
=QRS complex
what is represented at the ST segment
AP phase 2 delaying repol of ventricles
what direction does ventricular repol occur
L –> R
apex –> base
= T wave
What is Ca permeability btn the end of P wave & beginning of QRS in the atria
high Ca permeability
what is the state of all cells at the end of a P wave
all atrial cells depolarized
what is the state of the cells in the ST segment
all ventricular cells depolarized
-no deflection bc no difference
