Lecture 7 Flashcards
______ deliver blood to myocardial cells
Coronary Arteries
______ return deoxygenated blood to RA via coronary sinus
Coronary Veins
Q wave
- First part of QRS
- First downward deflection from baseline
- Amp of Q wave is less than 25% of the R wave
- Duration
ST segment
- Flat line that follows the QRS complex and connects it to T wave
T wave
- Slightly asym and oriented in same direction as preceding QRS complex
- Max ht 5mm in limb leads; 10mm in precordial leads
Myocardial ischemia
- Can be reversed if supply of oxygen and nutrients is restored
- T wave and ST segment changes
- NO permanent damage
Where are the coronary arteries?
Epicardial surface of the heart
Where does myocardial ischemia generally appear first?
Sub-endocardial region
Causes of Myocardial Ischemia
- Atherosclerosis
- Vasospasm
- Thrombosis/embolism
- Decreased ventricular filling time (tachycardia)
- Decreased filling pressure in coronary arteries (severe hypotension or aortic valve dz)
Examples findings that are Not MIs (6)
- Subendocardial ischemia
- Transient ST depression
- New onset angina
- Transmural ischemia
- Transient ST elevation
- Variant angina
No Q MI (2)
- Non-ST elevation MI
- ST depression or T wave changes or normal ECG
Q wave MI (2)
- ST elevation MI
- Typical evolution of ST-T changes
Myocardial injury
- Occurs if ischemia progresses unresolved or untreated
- INJURY is a great degree of cell damage than ischemia, but without actual cell death
- ST changes
Mycardial infarction
- Death of myocardial cells
- Release of enzymatic breakdown products (Troponin, CK-MB, Myoglobin)
- If the pt survives, the infarcted tissue is replaced with scar tissue (EKG may show Q waves)
Direction of Depolarization
- Normally proceeds in an endocardial to epicardial direction
Where is the conduction system?
Subendocardial tissue
Direction of Repolarization
- Repolarization usually proceeds from an epicardial to endocardial direction
Where is the coronary circulation system?
Epicardial surface
Characteristics of Myocardial Ischemia
- Inverted T waves
- Tall, peaked T wave
- Depressed ST segement
Transmural Ischemia
- More significant ischemia involving the full myocardial wall, from endo to epicardium
- Repolarization reverses direction (endo to epicardial)
- T wave inversion in leads in ischemic regions
- T WAVES ARE SYMMETRICAL
T wave inversion
- Occurs because ischemic tissue DOES NOT REPOLARIZE NORMALLY
- Ischemic T wave is more SYMMETRICAL than a normal T wave (rt and lt sides are mirror images)
Peaked T waves (when is it seen, where is it seen)
- May be seen in early stages of acute MI
- > 6mm in limb leads
- > 12 mm in precord
ST Segment depression
- Significant ST segment > 1 mm below baseline measured 0.04 s to right of J pt, in 2 or more leads
Subendocardial Ischemia
- Inner layer of the heart and does not extend through entire ventricular wall
What is the last place to receive oxygen and nutrients
Endocardium
Progressive subendocardial ischemia and injury may progress to a subendocardial myoinfarct called what?
Non-Q wave infarction
Flat ST segment depression results from _____
Subendocardial infarct or injury
What does ST elevation indicate?
Myocardial injury or infarct in progress
ST segment elevation also seen in:
- Ventricular hypertrophy
- Conductiion abn
- PE
- Spont pneump
- Intracranial hemorrhage
- HyperK
- Pericarditis (seen in many leads)
What indicates the presence of irreversible myocardial damage or myocardial infarction?
Pathological Q waves
What are pathologic Q waves
> 0.04s
- At least 1/3 the ht of R wave in same QRS
- Present in 2 + leads
Why do pathologic Q waves dev?
- Infarcted areas of heart become electrically SILENT
- Take hrs or days to dev
- May persist for life
MI will less damage vs more damage
Q wave –> more extensive damage
Will you always have Q waves with MI?
No, you can only have ST-T changes, but no q waves
Rt coronary artery perfuses what?
- Rt atrium
- Rt ventricle
- Inferior and posterior walls of Lt ventricle
Left main coronary artery divides into what
Lt anterior descending and Lt circumflex
LAD perfuses
- anterior and lateral left ventricle
- anterior 2/3 of ventricular septum
- R and L bundle branches
LCX perfuses
- L atrium, anterolateral, posterolateral and posterior LV
Anterior MI
- changes is percordial (V1-4) with reciprocal changes in inferior leads
Lateral MI
- changes in lead I, aVL, V5 & 6, reciprocal changes in inferior leads
Inferior MI
Changes in leads II, III, and aVF, reciprocal changes in anterolateral leads
Posterior MI
- Reciprocal changes in V1 and 2
- Tall R waves with ST depression in theses leads
EKG Evolution in Q wave MI
- Normal
- Hyperacute T wave changes with ST elevation
- Marked ST elevation with hyperacute T wave changes
- Pathologic Q waves, less ST elevation, terminal T wave inversion
- Pathologic Q waves, T wave inversion
- Pathologic Q waves, upright T waves
Septal MI
V1-2
Anteroseptal MI
V1-3
Anterolateral MI
V1 or 2 to V5 or 6
How do you tell a new vs old MI?
Q wave in the absence of ST segment and T wave abn indicates healed or old infarct
What is the criteria for an abn R wave in posterior MI?
- Duration >/= 0.04s
- R >/= S
- Pt > 30 yo
- No signs of RVH
