L6: Myocardial Ischemia and Infarction Flashcards
Normal q Wave
Amplitude <25% of R wave
Duration
Max T wave heights
Limb leads→ 5 mm
Precordial leads→ 10 mm
ECG changes seen with ischemia
T wave inversion (delayed repolarization)
Symmetrical, peaked T waves
ST segment depression
ECG changes seen with injury
ST elevation in leads facing injury (incomplete depolarization)
ECG changes seen with infarct
Enlarging or new Q waves (electrically silent infarcted tissue)
Ischemia appears in the ______ first
Sub-endocardial region
Deeper myocardial layers are farthest from
the blood supply
Exposed to greater wall tension
Q waves on ECG without other changes
Old MI
Symmetrical T wave inversion =
Transmural ischemia
Asymmetrical T wave inversion=
RVH with strain
also has RAD
T waves are initially _______ and take two hours to _____
Initially: hyperacute (peaked)
2 hours after onset: inversion
Criteria for ST segment depression
ST segment > 1 mm below baseline measured .04 s (40 ms) to right of J point in 2 or more contiguous leads
Criteria for flat ST segment depression
Flat ST segment with slight T wave inversion
ST segment depression occurs during
Ischemia
ST segment elevation occurs during
Injury or infarction
Flat ST segment depression is seen with
Sub-endocardial ischemia and injury
Criteria for ST segment elevation
> 1 mm above baseline measured
0.04 s (40 ms) to right of J-point, in
2 or more contiguous leads
Other non-MI causes of ST segment elevation
Ventricular hypertrophy Conduction abnormalities Pulmonary embolism Spontaneous pneumothorax Intracranial hemorrhage Hyperkalemia ***Pericarditis***
ECG of Pericarditis
Diffuse ST segment elevation
Segment is flat or concave
ST/T waves gradually angle back down to next QRS complex
Pathologic Q waves take _____ to develop
Hours or days to develop +/- persist for life
What makes a Q wave pathologic?
> 0.04 s (40 ms) duration
At least 1/3 the height of R wave in same QRS
complex
AND
Present in 2 or more
contiguous leads
The initial >04 s QRS vector points away from the site of infarct
A Q wave infarct is
Transmural (more extensive)
STEMI
A Non-Q wave infarct is
Subendocardial (less extensvie)
NSTEMI
Right coronary artery perfuses…
right atrium
right ventricle
inferior and posterior walls of left ventricle
Left anterior descending (LAD) perfuses
Anterior + lateral left ventricle
Anterior ⅔ of ventricular septum
Right + Left bundle branches
