25. MI

Question 1

sx indicating MI

Answer 1

• 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

Question 2

which populations are of particular concern for a silent or atypical MI

Answer 2

diabetics, elderly women

Question 3

pathophysiology of an MI

Answer 3

narrowing of coronary arteries d/t erosion, fissuring, or rupture of plaque causing thrombus formation

Question 4

what can a partial occlusion of coronary arteries cause

Answer 4

unstable angina (new and worsening CP) or NSTEMI

Question 5

describe the progression of CAD/ACS

Answer 5

normal heart –> stable angina –> unatable angina –> NSTEMI –> STEMI

Question 6

what would an ECG indicating subendocardial injury show?

epicardial ischemia/ infarction?

Answer 6

R waves normal, ST segment elevated, T wave peaked

diminishing amplitude of R wave, marked ST elevation

Question 7

what is ischemia and how does it show up on ECG

Answer 7

• deficient blood supply, impairing repolarization

- inverted T wave

Question 8

what is cardiac injury and how does it show up on ECG

Answer 8

• deficient blood supply, impairing ability to fully polarize
• ST segment shift

Question 9

what is infarction and how does it show up on ECG

Answer 9

• dead tissue, unable to depolarize

- widened Q waves

Question 10

when are troponin levels detectable, when do they peak and for how long can levels be elevated in relation to cardiac necrosis

Answer 10

• detectable 1-4 hours after onset of AMI
• peak 10-24 hours
• persist 5-14 days

*renal failure can also cause false positive

Question 11

how can a NSTEMI be diagnosed

Answer 11

• elevated troponin, CK, CK/MB

- ST depression of T wave inversion in contigious leads

Question 12

a subendocardial infaction is basically the same thing as ___

Answer 12

NSTEMI

Question 13

how much is the ST segment elevated in STEMI (men vs women)

Answer 13

elevated 2+ mm in men (1.5+ mm in women) in absence of LVH

or 1+ mm in more than 2 contigious leads

Question 14

what other cardiac issue may obscure ST elevation analysis

Answer 14

new LBBB, may need serial tracings to determine

Question 15

ischemia causes ___ d/t ___

Answer 15

inverted T waves d/t altered repolarization

Question 16

muscle injury causes ___

Answer 16

ST elevation

Question 17

infarction causes ___ d/t ___

Answer 17

Q waves d/t absence of depolarization current from dead tissue and opposite currents from other parts of the heart

Question 18

during recovery, which part of the ECG is the first to return to normals

Answer 18

ST segment, followed by T wave

Question 19

anterior wall infarction is caused by occlusion of what artery?

in what leads is this seen?

Answer 19

anterior interventricular a

V2-V4 (Q waves and ST elevation)
technically V1-V7; V1 and V2 are septal leads

Question 20

inferior wall infarction (RV infarction) is caused by occlusion of what artery?

in what leads is this seen?

Answer 20

right coronary artery

2, 3, AVF (Q waves and ST elevation)

Question 21

lateral wall infarction is caused by occlusion of what artery?

in what leads is this seen?

Answer 21

circumflex artery

1, AVL (Q waves and ST elevation)
also V5, V6

Question 22

posterior wall infarction is caused by occlusion of what artery?

in what leads is this seen?

Answer 22

posterior interventricular artery

V1-V3

Question 23

how do you determine if a Q wave is significant

Answer 23

• Q wave is = 1/3 amplitude of entire QRS complex

- 1+ mm wide, lasting 0.4 s or more (more than 1 box wide)

Question 24

large Q waves in the absence of ST changes indicates what?

Answer 24

old MI

Question 25

what ECG findings indicate a posterior MI

Answer 25

large R waves and ST depression in V1-V3