Ischemia and MI: Signs, Symptoms and Treatment Flashcards
What three factors put the heart at a distinct disadvantage for ischemia?
- the heart has a poor ability to function anaerobically - cardiac muscle has high o2 demand
- the heart receives blood during diastole (if ischemic receive less)- diastolic pressure is the driving force of coronary artery perfusion
- coronary arteries are surface arteries- blood must pass through an extensive network of capillaries to endocardial areas
What is the definition of ischemia?
inadequate perfusion of myocardial blood to endocardial tissue
What three things commonly decrease lumen size?
atheroscolerosis, clot formation or rupture (non-stenotic), coronary artery spasm (rare)
When does endocardial ischemia begin?
as myocardial oxygen demand increases which increased HR and SBP
Why does the ischemia cascade continue?
- decreased relaxation of the ischemic tissue
- decreased compliance of left ventricle
- increased diastolic pressure in LV
all leads to less diastolic filling time
What are signs and symptoms of ischemia?
angina, anginal equivalent, ECG changes, inappropriate hemodynamic response to activity, diagnostic testing
What is angina?
ischemia in myocardium is sensed by CNS
this sensation is referred to as noxious stimuli to anterior chest and arms
substernal chest pressure or pain, anything belly button up worse with exercise and better with rest
What is stable angina?
reproducible with the same stress or effort- correlates closely with myocardial oxygen demand
rate pressure product- RPP = HR X SBP (myocardial workload)
What is unstable angina?
this is worse because it occurs with or without effort
often progressive into MI
What are two other types of angina?
- varient/ prizmetal- typically at rest due to spasm
2. asymptomatic/ silent- common with DM/ and neuropathy, may present as DOE, in more females
What medication can help relieve angina?
nitroglycerine
What is angina equivalent?
occurs with silent ischemia, most commonly felt as SOB, more common with DM and females
However same rules apply as angina…rely on vitals and gut instinct
What does ischemia look like on an EKG?
ST segment depression
MI is ST elevation
What two chemicals can be given to simulate a maximal exercise test?
Adenosine or Dobutaimne
What is a cardiac catherization?
cath snaked up through femoral artery up through the aorta and into coronary arteries, dye is used to find presence of stenosis
PT- bed rest immediately after, time until moving is determined by facility 1/2 hr to 2 hours
What does ischemia turn into a MI?
complete interruption of myocardial blood supply, typically more common in left ventricle
cell death may occur as early as 15 minutes….time is muscle
What are mechanisms of a MI?
- atherosclorosis to complete occlusion
- near total obstruction coupled with thrombosis
- near total obstruction with spasm
- near coupled occlusion with increased myocardial demand
- plaque rupture
What is a demand MI?
hypovolemia (decrease in circulating blood in body) or increased metabolic stress on an already compromised coronary artery
What factors influence the site and extent of tissue necrosis?
- anatomic distribution of the artery
- adequacy of collateral circulation
- presence of prior infarction
- factors affecting myocardial demand
What three things affect myocardial demand?
HR and SBP, LV end diastolic pressure and volume, ANS activity (catecholamines)
What are the three components of the injury zone?
- zone of infarction
- zone of hypoxic injury
- zone of ischemia
What is the zone of infarction?
after an MI it is the necrotic area of tissue death
What happens 18-24 hours after an MI to the infarction zone?
inflammatory process begins and a connective tissue scar begins to form
What happens 4-10 days after an MI to the infarction zone?
necrotic debris is cleared and collagen matrix is laid down
