Unit 1: CV System Part E Flashcards
How can electrical activity in the heart be measured?
t can be measured using electrodes placed on the surface of the skin
At least ___ electrodes are required, placed in a triangular formation (___________) on the arms and legs (6-12 electrodes are typically used in clinical practice).
3
Einthoven’s triangle
What does an electrocardiogram show?
the summed electrical activity generated by ALL of the cells in the heart during the cardiac cycle
Electrocardiogram (ECG) is NOT the same as what? Explain why
an action potential
ECG is an EXTRAcellular recording that represents the SUM of MULTIPLE APs taking place in MANY heart muscle cells
AP is 1 electrical event in a SINGLE cell, recorded using an INTRAcellular electrode
The ECG tracing consists of _____ and ______ that correspond to electrical activity in the heart
WAVES
SEGMENTS
Waves
go ABOVE or BELOW the baseline (reflect depol. or repol. of the atria & ventricles)
Segments
sections of baseline b/t 2 waves
What are the 6 waves/segments called in an ECG?
- P wave
- PR Segment
- QRS Wave (Complex)
- ST segment
- T wave
- TP segment
P wave
atrial depolarization, quickly followed by atrial contraction
PR Segment
– AV node delay.
- Atria finish contracting and emptying (pushing last 20% of blood into ventricles = active filling of ventricles).
QRS Wave (Complex)
– Ventricular depolarization
- atrial repolarization also occurring, but it is hidden/covered up by the larger ventricular depolarization event).
- ventricular contraction begins
ST segment
– All fibers in the ventricles are contracted, emptying continues until half-way through T wave
T wave
Ventricular repolarization
TP segment
atria and ventricles relaxed and passively filling (80% of blood enters ventricles through passive filling)
tachycardia
Higher than 100 bpm at rest
bradycardia
Lower than 60 bpm at rest
What do ECG abnormalities result in?
result in arrythmias
What are the different types of ECG abnormalities?
- Heart Block
- Ventricular fibrillation
Heart Block
conduction through AV node is slowed
(AV node damage) and length of PR segment increases.
a. 1st Degree – all waves present, but PR segment (AV node delay) longer than normal.
b. 3rd Degree - complete blockage of signal from atria to ventricles, ventricles contract at AV bundle action potential rate of 30 APs/min. Results in asynchronous contraction and relaxation of atria and ventricles. Many P waves, fewer QRS waves. P waves not followed by QRS wave
Ventricular fibrillation
heart muscle no longer depolarizing
synchronously, making coordinated pumping action impossible
