Diagnostic Features of ECGs Flashcards
1
Q
Steps of cardiac conduction/depolarization
A
- sinoatrial (SA) node = pacemaker
- Electrical impulses initiated @ SA node –> internodal tracts –> wave of depolarization in the atrium –> atrioventricular (AV) node.
- @ AV node: brief delay –> impulses to Bundle of His and activate the ventricles through the right and left bundles
- bundles –> Purkinje fibers –> activate ventricular myocardial cell depolarization and contraction.
2
Q
Main clinically relevant components of EKG (6)
A
- P wave
- PR interval
- QRS complex
- QT interval
- T wave
- U wave
3
Q
P wave fxnl action
A
atrial depolarization
4
Q
PR interval fxnl significance
A
- measure of AV node conduction time
- normal = 0.12 - 0.20 secs
5
Q
QRS fxnl significance
A
- ventricular depolarization
- normal duration = 0.06 - 0.10 secs
- Q: negative
- R: positive
- S: late negative deflection
6
Q
QT interval fxnl significance
A
- lasts from begin of Q to end of T
- total duration of depolarization and repolarization
7
Q
T wave fxnl significance
A
ventricular repolarization
8
Q
U wave fxnl significance
A
- not always seen
- follows T wave
- possibly repolarization of purkinje fibers or papillary muscles
9
Q
Line measurements/speed of EKG paper
A
- paper speed = 25mm/sec
- vertical lines = 0.04 sec
- thick vertical lines = 0.2 sec
10
Q
Calculation of heart rate from EKG
A
HR=300/# of heavy lines between P waves
11
Q
EKG changes produced by ventricular hypertropy
A
- both left and right ventricular hypertrophy result in greater muscle mass –> greater voltage associated with depolarization and repolarization of the myocardium.
- ecg ventricular hypertrophy is seen as a R wave with greater amplitude.
- Left ventricular hypertrophy: large positive deflections (R waves) in V5 and V6 and large n_egative deflections (S waves) in V1._
- Right ventricular hypertrophy: high voltage in V1 and V2.
12
Q
EKG changes caused by myocardial ischemia
A
- Ischemic changes alter ventricular repolarization and affect the ST segment and the T wave.
- Ischemia due to sudden high oxygen demand in the presence of a fixed coronary obstruction causes depression of the ST segment.
- In some patients a resting ekg is normal, but ST depression is only visible during exercise due to transient ischemia.
- Ischemia due to acute coronary artery obstruction during low oxygen demand can cause T wave inversion.
- Normally, T waves are in the same direction of the QRS complex.
Inversion of a T wave→myocardial ischemia
13
Q
EKG changes in acute myocardial infarction
A
- ST elevation is a sign of transmural injury in an acute coronary syndrome, usually with a clot due to platelet aggregation obstructing a coronary artery.
- Sizeable (>0.04 s) Q waves can be a sign of transmural necrosis. Infarcts usually involve only the left ventricle.
- Inferior leads (II, III, aVF): inferior infarcts
- V1-V4: anterior wall infarct
- I, aVL and V5, V6: lateral wall infarcts.
14
Q
Evolution of transmural acute myocardial infarct
A
- Giant upright “hyperacute” T wave
- T wave inverts and ST segment rises.
- Sometimes, ST elevation precedes of occurs simultaneously with T inversion.
- Q waves are usually the last to develop.
15
Q
Transmural vs. subendocardial acute myocardial infarction
A
- Transmural—involves the entire thickness of the LV
- Subendocardial—localized to the inner layer of the LV wall.
- Subendocardial infarcts do not have Q waves or ST elevation.
- They do have persistent ST depression.
