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Flashcards in lecture 5a Deck (48):
1

ischemia heart disease (IHD) definition

a condition in which there is an inadequate supply of blood & oxygen to a portion of the myocardium

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IHD typically occurs when

there is an imbalance between myocardial oxygen supply ad demand

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the most common cause of myocardial ischemia is

atherosclerotic disease of an epicardical coronary artery (90%) sufficient to cause a regional reduction in myocardial blood flow and inadequate perfusion of the myocardium supplied by the involved coronary artery

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what is the most common serious, chronic, life-threatening illness in the US?

IHD

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what are associated with IHD

genetic factors, high-fat & energy rich diet, smoking & a sedentary lifestyle

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powerful risk factors for IHD

obesity, insulin resistance, & T2DM

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MVO2 (myocardial oxygen demand)=

O2 delivery

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hypoxia

- lack of oxygen
-exacerbates effects of atherosclerosis
- anemia
-cyanotic heart disease
- advanced lung disease

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ischemia

mainly lack of oxygen, but also nutrients

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factors that effect MVO2 (myocardial oxygen demand)

HR
myocardial contractility
myocardial wall tension (stress)
BP
ionotropic status

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adequate oxygen-carrying capacity of blood is determined by

-inspired level of oxygen
- pulmonary function
- hemoglobin concentration & function

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blood flows through the coronary arteries in a phasic fashion, with majority occuring during

diastole

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75% of the total coronary resistance to flow occurs across 3 sets of arteries

1. Large epicardial arteries (R1)
2. prearteriolar vessels (R2)
3. arteriolar & intramyocardial capillary vessels (R3)

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in the absense of significant flow-limiting atherosclerotic obstructions, R1 is tirvial:

the major determinant of coronary resistance is found in R2 and R3

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coronary circulation is controlled by the heart's requirements for oxygen

metabolic regulation
auto regulation

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metabolic regulation

exercise, emotional stress (coronary vascular resistance)

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auto regulation

the coronary blood flow is maintained on the same level, independently on physiological alterations in BP

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large portion of the myocardium is effects if atheroscleosis occurs

in left coronary artery

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rupture

fibrous cap is broke
- tissue factor is released & initiates coagulation

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other causes of ischemia

- spasms: prinzmetal's angina
- thrombi
- emboli
- BP decrease
- ostial narrowing due to aortitis
- congenital abnormalities
- severe left ventricular hypetrophy due to aortic stenosis
- severe anemia or the presence of carboxyhemoglobin
- abnormal constriction or failure of normal dilation of the coronary resistance vessels

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where does atheroscleosis occur?

-sites of increased turbulence in coronary flow
- brand points in the epicardial arteries

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risk factors for atherosclerosis & IHD

high LDL
low HDL
smoking
HTN
DM

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severity of symptoms depends on

degree & location of stenosis & how fast it develops

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50% stenosis

limited ability to increase blood flow in the response to an increased demand

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80% stenosis

blood flow at rest may be reduced

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stenosis where are particularly hazardous?

of the left main coronary artery of the proximal left anterior descending coronary artery

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gradually developing stenosis causes formation of

collateral vessels
- these are good!

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stenosis of the epicardial artery leads to

the dilation of the distal resistance vessels

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effects of ischemia

- inadequate perfusion
- decreased myocardial O2 tension
- mechanical, biochemial & electrical disturbances
- regional disturbances of ventricular contractility
- segmental hypokinesia
- segmental akinesia
- segmental dyskinesia
- reduced myocardial pump function

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effects of acute ischemia

(failure of relaxation & contraction)
- transient left ventricular failure
- mitral regurgitation if the papillary muscle apparatus is involved

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left ventricular failure

- worst scenario!
- dramatic < BP
- hypoperfusion to the brain
- stroke

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mitral reguritation

-blood flowing back
- problems in the pulmonary circulation

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transient ischemia

angina pectoris

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prolonged ischemia

actute MI

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infarction=

tissue necrosis
- irreversible tissue damage

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ECG effects of ischemia

- nature of process (reversible vs irreversible
- duration (acute vs chronic)
- the extent (transmural vs subendocardial)
localization (anterior vs inferioposterior)
- presence of other underlying abnormalities (ventricular hypertrophy, conduction defects)

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ST depression

Partial thickness
possible ischemia

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ST elevation

total thickness
MI

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effects of ischemia: arrhythmias

- electrical instability, which may lead to isolated ventricular premature beats or even ventricular tachycardia or ventricular fibrillation
- most patients who die suddenly from IHD do so as a result of ischemia-induced ventricular tachyarrhythmias

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IHD can be classified as

chronic coronary artery disease or
acute coronary syndromes

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chronic coronary artery disease (CAD)

stable angina

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acute coronary syndromes (ACS)

- STEMI
- unstable angina
- NSTEMI
- sudden cardiac death
- prinzmental's variant angina

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CAD- stable angina pectoris clinical manifestations

- male >50 or women >60
- chest discomfort
- crescendo-decresendo
- can radiate down shoulder & to both arms
- can arise or radiate to the back, interscapular region, root of neck, teeth & epigrastric
- rarely localized below umilicus or above mandible
- episodes typically caused by exertion or emotion, heavy meal or cold
- symptoms releived by SL NTG***

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symptom of myocardial ischemia

-angina
- dyspnea
- nausea
- fatigue
- faintness

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may indicate UA

- angina occurring with less exertion than in the past, occurring at rest or awakening the patient from sleep

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patients should be questioned & examined for

claudication, stroke & transient ischemia attacks

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evidence of atherosclerotic disease at other sites

- abdominal aortic aneurysm
- carotid arterial bruits
- diminished arterial pulses on lower extremities

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laboratory exam

- check urine for evidence of DM & renal disease
- cholesterol, glucose, Creatinine, Hct, thyroid function
- X-ray- cardiac enlargement, aneurysms, signs of heart failure
- C-reactive protein
- ECG
- stress testing
- cardiac imaging
-coronary arteriography