Myocardial Ischemia Flashcards
What is the major component of Ischemic heart disease?
- Ischemic heart disease is characterized by an imbalance between metabolic oxygen demand and myocardial oxygen supply
- demand exceeds supply
What can myocardial ischemia be caused by?
- Narrowing of coronaries (atherosclerosis)- most common cause
- severe hypertension, tachycardia, or hypotension
- coronary artery vasospasm
- hypoxia
- anemia
- severe aortic insufficiency or aortic stenosis
What is the incidence of Ischemic heart disease?
- Present in 10 million american adults
- 1.5 million suffer from MI with 1/3 mortality
- It is a major cause of peri-op morbidity and mortality
- estimated to be 30% of surgical patients
What are major risk factors for myocardial ischemia?
- Increasing age
- male gender
- Hypercholestremia (high LDL)
- Diabetes
- hypertension (increased demand)
- Cigarette smoking
- genetic predisposition
- obesity
- Peripheral and cerebrovascular disease
- CAD
- menopause
- Older birth controls with ligh levels of estrogen
- sedentary lifestyle
- psychosocial characteristics (high stress)
What is one of the biggest signs of ischemic heart disease?
What will we do if this is a new symptom?
(chart)
- Angina
- New or changed angina = acute coronary syndrome
- will check 12 leak EKG
- No ST-segment elevation and Troponin - = unstable angina
- No ST-segment elevation and Troponin + = MI
- ST-segment elevation and Troponin + = MI
Why is unstable angina not good?
What is an unstable plaque?
- because at any moment that person can have an MI; very high risk
- An atherosclerotic plaque with lipids inside and a thin fibrous cap
- This plaque can rupture
- Thrombus will form over lesion and vessel will constrict, causing acute decrease in coronary blood flow–>unstable angina or MI
Why do you want to avoid phenylephrine in pts with a history of MI?
It can cause coronary artery vasospasm
What is the role of stress in acute cardiac events?
- Central and Autonomic nervous system is activated, causing physiologic response:
- Catecholamine release, increasing HR, BP, coronary constriction
- decreased plasma volume and increased platelet activity
- Physiologic effects cause cardiac effects
- Electrical instability
- increased demand, decreased supply
What is stable angina?
What is Unstable angina?
- Stable angina- no change in what precipitates the pain for at least 60 days
- frequency and duration of pain the same
- fixed narrowing (usually 75% or >)
- pain relieved by rest, reducing demand, or vasodilator like nitroglycerine
- Unstable angina- caused by less than normal activity
- Crescendo
- lasts longer
- occurs more frequently
- signals impending myocardial infarction
- If pt describes symptoms of unstable angina, cancel the case!
What is Prinzmetal Angina?
- Angina that occurs at rest
- Usually caused by coronary spasm instead of atherosclerosis
- may happen in a plaque area or a normal area
- Sometimes association with other vasospastic diseases like Raynaud’s
What is Myocardial Infarction?
Where does it typically begin?
What does the size depend on?
- Necrosis caused by ischemia
- w/in 20-30 minutes of ischemia
- Typically begins in the subendocardial regions
- usually reaches full size in 3-6 hours
- Size depends on:
- proximity of lesion
- collateral circulation
What are some complications of Myocardial Infarction?
- Papillary muscle dysfunction leads to valvular disease
- External rupture of the infarct can cause cardiac tamponade and death (day 4-7 post MI)
- Thrombi can cause stroke
- Acute pericarditis (infection of the necrosed area)- usually day 2-4
- Ventricular aneurysm- usually at the anteroapical region
- Arrhythmias
- decreased LVF, may have pulmonary edema
- Cardiogenic shock (rare)
- rupture of wall, septum, papillary muscle
What is the gold standard for knowing if there has been a myocardial ischemic event?
- Troponin level is gold standard
- can determine presence and extent of injury
Where would the MI be if the RCA is occluded?
Where would the MI be if the LCA is occluded?
Where would the MI be if the LAD is occluded?
Where would the MI be if the LCX is occluded?
- RCA = posterior, inferior MI
- LCA = massive anterolateral MI
- LAD = Anteroseptal MI
- LCX = Lateral MI
Which lead do you want to be in for someone who has had ischemic disease?
2 and V5
Because you want to look at the inferior and anterior portion of the heart which is where the left ventricle sits because it is most likely to become ischemic (d/t higher O2 needs)
How is myocardial ischemic disease managed pharmacologically?
(5)
-
Beta blockers- reduce contractility and HR
- helps reduce demand and increase supply
- Calcium channel blockers- dilate the coronary arteries, reduce contractility, reduce afterload
- Ace inhibitors- may improve contractility by afterload reduction
- Nitrates- dilate coronary arteries and collateral blood vessels, decrease peripheral vascular resistance (afterload), venodilation (preload)
- Antiplatelet drugs- reduce potential for thrombosis
The risk of perioperative death due to cardiac causes is ____ in the general population.
When do most perioperative MIs occur?
<1%
24-48 hours after surgery
What are the elective surgery recommendations after having a procedure for myocardial ischemic disease?
(chart)
What causes decreased Oxygen supply?
- tachycardia
- hypotension
- vasoconstriction
- O2 carrying capacity
- Acid/base, anemia, hypoxia
- increased viscosity
- arterial patency
- coronary spasm
What causes increased O2 demand?
- Tachycardia
- increased contractility, preload, afterload
- shivering
- hyperglycemia
- hypertension
- **It is easier for us to control the demand than the supply
How do you determine what kind of work up required or if you can proceed with surgery in a patient who has been previously revascularized?
(chart)
How do you determine what kind of work up is required or if the surgery can proceed in a patient with myocardial ischemic disease who has NOT been previously revascularized?
(chart)
What are important considerations for the anesthesia of a patient with myocardial ischemic disease?
Regional
General
- Regional- good option if available
- pre-emptively treat hypotension with fluids and phenylephrine
- if bradycardic, use ephedrine
- General
- maintain balance between O2 supply and demand
- do not allow for long periods of hypotension as it causes decreased BF to coronaries
- important to maintain BP within 20% of patient’s baseline
Monitoring for ischemia:
RCA: leads used, area of myocardium involved
Circumflex: leads used, area of myocardium involved
LAD: leads used, area of myocardium involved
(chart)
Induction of a pt with myocardial ischemic disease:
goals
drugs to use
- Goal to have minimal hemodynamic effect during laryngoscopy
- try to minimize response- opioids, lidocaine
- If severe cardiac dysfunction, use Etomidate or High opioid technique
What should be your goals for maintenance of anesthesia for pts with myocardial ischemic disease?
- Avoid tachycardias
- maintain normal preload and afterload
- decrease contractility if LVF is normal (EF normal)
- ok to use high gas technique
- high opioid technique to maintain contractility if pt has LV dysfunction
- normal sinus rhythm
- Control demand- metabolic O2 need
What are the intra-op considerations for a patient with myocardial ischemic disease?
(chart)
- Surgery will set off inflammatory response that will ultimately cause decreased oxygen delivery
- Surgery will set off neuroendocrine stress response that will ultimately increase oxygen demand
