CPR 20 - ECG Basics 1 - Dipole Waves, Intervals, and Segments Flashcards
What is an ECG actually measuring?
On the outside of a resting cell the overall charge is positive. When that cell depolarizes the overall outside charge becomes negative. When an AP travels through the heart it causes a wave of charge change outside of the cells (from positive to negative). An ECG uses electrodes to detect this wave. If the wave moves towards the positive electrode it is recordes as an uptick. If the wave moves away from the positive electrode it is recorded as downtick. An uptick can also occur if the flow is away from the positive electrode but the charge change if from negative to positive (as with repolarization).
What causes the Q wave on an ECG?
What causes the R wave on an ECG?
What causes the S wave on a ECG?
Why does the S wave dip back below the base line?
Not really known and is of not much clinical significance
What cause the T wave on an ECG?
The repolarization of the heart
What can an ECG be used to assess?
What does the amplitude of deflection on a segment of an ECG refer to?
The mass of tissue that is being depolarized/repolarized. The larger the amplitude the larger the mass of tissue.
Which heart layers depolarize and repolarize first?
Define ECG Segment and Interval.
List the clinically relevant ECG Intervals and Segments, from what points they are measured, and how they’re affected by heart rate.
PR interval - beginning of P to beginning of QRS; shortens with increased HR
ST segment - end of QRS to beginning of T; not affected by HR
QT interval - beginning of Q to the end of T; shortens with increased HR
TP segment - end of T to beginning of P; shortens with increased HR
RR interval - peak of QRS to peak of PRS; shortens with increased HR
What does the PR interval assess and how will an increased HR change it? What is occuring with the atria/ventricles at this point?
What does the ST segment assess? What is occuring with the atria/ventricles at this point?
What does the QT interval assess? What is occuring with the atria/ventricles at this point? How does HR affect this interval?
What does the TP segment assess? What is occurring with the atira/ventricles at this point?
What does the RR interval assess?
Where does each segment of the ECG correlate to the cardiac action potential?
