Electrical Consequences of MI

Question 1

4 Phases of MI Problems

Answer 1

Acute Ischemia - 0-12 hrs
Evolution of Infarcation - 12-48 hrs
Convalescent Phase - 72 hrs-6 weeks
Chronic Phase

Question 2

2 Effects on Border Zone and 1 in Ischemic Zone in Acute Ischemia

Answer 2

Partial Depol
AP shortens, Voltage-dep refractory period shorter
Ischemic Zone: Very slow conduction if at all

Question 3

Voltage Gradient

Answer 3

Normal Tissue will have stronger depol on AP and be more repol’d at rest compared to its neighboring ischemic tissue, so current will flow when it shouldn’t

Question 4

Acute Ischemic Re-Entry

Answer 4

Might come into ischemic zones from both sides, but often will just block at refractory period when they meet. However it might travel outside ischemic zone and circle back around to cause either a PVC -> nonsustained (polymorphic) VT (maybe) -> Vent Fib

Question 5

Important Point about Acute Arrhythmias

Answer 5

Aren’t expected to last bc tissue properties will change so not too worrisome (manage so they don’t die though)

Question 6

Coronary Spasm

Answer 6

Causes temporary ischemic phase that usually reverses on its own. However if ischemia b/w 5-30 min, when reperfusion happens can get SUPER long depol putting at risk of triggered activity

Question 7

TA

Answer 7

Delayed repol means time dependent Ca channels might refract while still depol’d, so can get TA -> VT -> (maybe Vfib)

Question 8

Enhanced Automaticity

Answer 8

Usually benign in evolution phase. AV junction takes over pacemaker function w/ inf. wall MI -> also leads to parasymp stimulation to lower SA node. Don’t interfere with it

Question 9

Infarct Evolution Vtach

Answer 9

Usually more stable and less likely to progress to Vfib. (but might be prolonged and dangerous in itself, unlike acute phase)

Question 10

Convalescent Phase Arrhythmias

Answer 10

Frequent PVCs and VT indicate long-term risk (unlike acute phase) when accompanied by large infarct and low EF

Question 11

Remodeling in Chronic Phase

Answer 11

Hypertrophy and dilation

Question 12

Chronic Phase Arrhythmias

Answer 12

Stable monomorphic VTs have variable risk - can be life threatening if very rapid

Question 13

Risk Enhancer in Chronic Phase

Answer 13

LV dysfunction and coronary artery disease - future ischemic events can really fuck your whole world up if you’ve already had electrical problems from previous MI