25. MI Flashcards
sx indicating MI
- chest discomfort: heavy, crushing, pressure in the left retrosternal area across the chest; radiating in neck, jaw, L arm/shoulder, epigastrium, or between shoulder blades
- associated sx: nausea, emesis, diaphoresis, dyspnea
which populations are of particular concern for a silent or atypical MI
diabetics, elderly women
pathophysiology of an MI
narrowing of coronary arteries d/t erosion, fissuring, or rupture of plaque causing thrombus formation
what can a partial occlusion of coronary arteries cause
unstable angina (new and worsening CP) or NSTEMI
describe the progression of CAD/ACS
normal heart –> stable angina –> unatable angina –> NSTEMI –> STEMI
what would an ECG indicating subendocardial injury show?
epicardial ischemia/ infarction?
R waves normal, ST segment elevated, T wave peaked
diminishing amplitude of R wave, marked ST elevation
what is ischemia and how does it show up on ECG
- deficient blood supply, impairing repolarization
- inverted T wave
what is cardiac injury and how does it show up on ECG
- deficient blood supply, impairing ability to fully polarize
- ST segment shift
what is infarction and how does it show up on ECG
- dead tissue, unable to depolarize
- widened Q waves
when are troponin levels detectable, when do they peak and for how long can levels be elevated in relation to cardiac necrosis
- detectable 1-4 hours after onset of AMI
- peak 10-24 hours
- persist 5-14 days
*renal failure can also cause false positive
how can a NSTEMI be diagnosed
- elevated troponin, CK, CK/MB
- ST depression of T wave inversion in contigious leads
a subendocardial infaction is basically the same thing as ___
NSTEMI
how much is the ST segment elevated in STEMI (men vs women)
elevated 2+ mm in men (1.5+ mm in women) in absence of LVH
or 1+ mm in more than 2 contigious leads
what other cardiac issue may obscure ST elevation analysis
new LBBB, may need serial tracings to determine
ischemia causes ___ d/t ___
inverted T waves d/t altered repolarization
muscle injury causes ___
ST elevation
infarction causes ___ d/t ___
Q waves d/t absence of depolarization current from dead tissue and opposite currents from other parts of the heart
during recovery, which part of the ECG is the first to return to normals
ST segment, followed by T wave
anterior wall infarction is caused by occlusion of what artery?
in what leads is this seen?
anterior interventricular a
V2-V4 (Q waves and ST elevation)
technically V1-V7; V1 and V2 are septal leads
inferior wall infarction (RV infarction) is caused by occlusion of what artery?
in what leads is this seen?
right coronary artery
2, 3, AVF (Q waves and ST elevation)
lateral wall infarction is caused by occlusion of what artery?
in what leads is this seen?
circumflex artery
1, AVL (Q waves and ST elevation)
also V5, V6
posterior wall infarction is caused by occlusion of what artery?
in what leads is this seen?
posterior interventricular artery
V1-V3
how do you determine if a Q wave is significant
- Q wave is = 1/3 amplitude of entire QRS complex
- 1+ mm wide, lasting 0.4 s or more (more than 1 box wide)
large Q waves in the absence of ST changes indicates what?
old MI
what ECG findings indicate a posterior MI
large R waves and ST depression in V1-V3
