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
