The Electrocardiogram Flashcards
Name the complexes in an ECG
P, QRS, T
What do the complexes in ECG represent
P- atrial depolarization
QRS- ventricular depolarization
T- ventricular repolarization
When does the atria repolarize on an ECG
During the QRS complex but cannot see
Why does the QRS complex have a faster increasing/decreasing slope than the other complexes?
QRS complex associated with impulses from purkinje fibres. Note that electrical impulses from purkinje are spread faster than all other conduction pathways
What does ECG stand for
Electrocardiogram
What does ECG measure
Movement of positive charge
What does an upward deflection vs a downward deflection mean?
Upward- positive charge is moving towards the electrode
Downward- positive charge is moving away from the electrode
What symbol represents the recording electrode?
+
Why is ventricular repolarization a positive deflection? Start by listing the layers of ventricular myocyte cells
Inner to outer: endocardium -> myocardium -> epicardium
During repolarization, the epicardium is repolarized first, therefore it has a more negative voltage than the endocardium and myocardium. Since the endocardium is still waiting to be repolarized, the flow of net positive charge will be towards the epicardium (flow from more positive area to more negative area). The positive charge is moving towards the recording electrode therefore an upward deflection
Why is the T wave positive?
Because ventricular repolarization is a positive deflection of the recording electrode
What are some advantages of ECG
- simple
- cheap
- info about: orientation, chamber size, arrhythmia, conduction block, ischemia, congenital defects
What is Wolff-Parkinson-White syndrome
heart beats abnormally fast for periods of time. Caused by extra electrical connections in heart
Name the types of ECG leads. how many ECG leads and electrodes are there?
12 lead ECG
10 electrodes
———
3 bipolar limb leads
3 augmented voltage limb leads (derived from bipolar)
6 precordial or ‘chest’ leads
1 reference electrode
augmented and precordial are unipolar leads
What are the positions of the three standard bipolar leads?
note: + means recording electrode
Lead 1: RA- to LA+
Lead II: RA- to LL+
Lead III: LA- to LL+
Lead II looks through septum (best view of conduction system)
What is Einthoven’s law and triangle
Law I + III = II
Triangle- all leads measure the same thing from different angles
What are the three augmented voltage leads called?
aVR- right arm
aVL- left arm
aVF- left leg (foot)
How are the 6 precordial leads organized
V1 and V2- septal
V3 and V4- anterior
V5 and V6- lateral
What electrical conduction blocks effect which complex in ECG
AV node block- long PR
Pre-excitation (WPW)- short PQ
Bundle branch block- effects QRS complex
Long QT syndrome- delayed ventricular repolarization
Short QT syndrome- repolarize too early
Mean electrical axis: what is the normal axis
0 to +90
Mean electrical axis: right axis deviation
-Right ventricle hypertrophy- blockage in pulmonary circulation
-Infants
-Tall and thin
Mean electrical axis: left axis deviation
- Left ventricle hypertrophy
- obesity and pregnancy- abdomen pressure on heart
Mean electrical axis: extreme axis
Dextrocardia- heart on right side of chest
Cardiac pacemaker- implant
What lead produces the most biphasic QRS complex
Perpendicular electrode
What is sinus bradycardia
Heart beats slower than expected
Draw the mean electrical axis- label leads, values
