Acute Coronary Syndromes

Acute Coronary SyndromeDefinition: a constellation of symptoms related to obstruction of coronary arteries with chest pain being the most common symptom in addition to nausea, vomiting, diaphoresis etc.

Chest pain concerned for ACS is often radiating to the left arm or angle of the jaw, pressure-like in character, and associated with nausea and sweating. Chest pain is often categorized into typical and atypical angina.

• Typical anginal pain —All three of the following

• Substernal chest discomfort• Onset with exertion or emotional stress• Relief with rest or nitroglycerin

• Atypical anginal pain• 2 of the above criteria

• Noncardiac chest pain• 1 of the above

Acute coronary syndrome

• Based on ECG and cardiac enzymes, ACS is classified into:– STEMI: ST elevation, elevated cardiac enzymes– NSTEMI: ST depression, T-wave inversion, elevated

cardiac enzymes– Unstable Angina: Non specific EKG changes, normal

cardiac enzymes

Unstable Angina

• Occurs at rest and prolonged, usually lasting >20 minutes

• New onset angina that limits activity• Increasing angina: Pain that occurs more

frequently, lasts longer periods or is increasingly limiting the patients activity

EKGSTEMI:

Q waves , ST elevations, hyper acute T waves; followed by T wave inversions.

Clinically significant ST segment elevations: > than 1 mm (0.1 mV) in at least two anatomical contiguous leads or 2 mm (0.2 mV) in two contiguous precordial leads (V2 and V3)

EKG

• NSTEMI:– ST depressions (0.5 mm at least) or T wave

inversions ( 1.0 mm at least) without Q waves in 2 contiguous leads with prominent R wave or R/S ratio >1.

– Isolated T wave inversions:• can correlate with increased risk for MI • may represent Wellen’s syndrome:

– critical LAD stenosis– >2mm inversions in anterior precordial leads

Cardiac Enzymes• Troponin is primarily used for diagnosing MI because it

has good sensitivity and specificity.– CK-MB is more useful in certain situations such as post

reperfusion MI or if troponin test is not available

• Other conditions can cause elevation in troponin such as renal failure or heart failure

• The increasing troponin trend is the important thing to look for in diagnosing MI. Order Troponin together with ECG when doing serial testing to rule out ACS.

Pathophysiology

• ACSs result from myocardial ischemia due to imbalance between myocardial O2 demand & supply – usually due to occluded coronary artery thrombus

• STEMI, NSTEMI, & unstable angina fall under this heading– unstable angina does not produce detectable

biochemical marker levels

9

Plaque Rupture & Clot Formation• > 90% of ACSs caused by rupture or erosion of an

atherosclerotic plaque• Plaques likely to rupture

– those that occlude < 50% of the lumen– eccentric shape – thin fibrous cap with large fatty core

• Clots form on top of ruptured plaques & partially or fully occlude the artery lumen

• Exposure of collagen & tissue factor from the plaque induces platelet adhesion & activation – promotes release of vasoactive substances

10

11

Atheroma Production

A: normal muscular artery. The adventitia, or outermost layer of the artery, consists principally of recognizable fibroblasts intermixed with smooth muscle cells loosely arranged between bundles of collagen and surrounded by proteoglycans. It is

usually separated from the media by a discontinuous sheet of elastic tissue, the external elastic lamina .B: platelet aggregates, or microthrombi, form as a result of adherence of the platelets to the exposed subendothelial

connective tissue. Platelets that adhere to the connective tissue release granules whose constituents may gain entry into the arterial wall. Platelet factors thus interact with plasma constituents in the artery wall and may stimulate events shown in the

next illustrationC: smooth muscle cells migrate from the media into the intima and actively multiply within the intima. Endothelial cells

regenerate in an attempt to re-cover the exposed intima, which thickens rapidly owing to smooth muscle proliferation and formation of new connective tissue.

Plaque Rupture & Clot Formation

• Platelet activation: changes on platelet GP IIb/IIIa receptors lead to formation of fibrin bridges– inclusion of many platelets creates “white” clots– more common in NTSE ACS – incomplete artery occlusion

• Coagulation cascade activated: fibrin traps RBCs– clots have red appearance– more common in STEMI ACS – more likely to completely occlude vessels

• Myocardial ischemia can result from microthrombi embolization & lead to necrosis

12

Electrocardiogram

• 12-lead ECG should be done within 10 min of ED arrival

• Key findings indicating myocardial damage– ST-segment elevation– ST-segment depression– T-wave inversion

13

Biochemical Markers

• Evaluate troponin & CK MB to confirm MI– released in response to myocardial necrosis

• 3 measurements taken over the 1st 12 to 24 hrs• MI diagnosis:– > 1 one troponin value greater than MI decision limit

set by labor – 2 CK MB values greater than MI decision limit set by

lab14

The Three I’s

• Ischemia= ST depression or T-wave inversion

Represents lack of oxygen to myocardial tissue

The Three I’s

• Injury = ST elevation -- represents prolonged ischemia; significant when > 1 mm above the baseline of the segment in two or more leads

The Three I’s

• Infarct = Q wave — represented by first negative deflection after P wave; must be pathological to indicate MI

What part of the heart is affected?

II, III, aVF =

Inferior Wall

I

II

III

aVR

aVL

aVF

V1

V2

V3

V4

V5

V6

Inferior Wall MI

Based on the EKG, which vessel in the heart is blocked?

• II, III & aVF = Inferior Wall MI = Right Coronary Artery blockage

Which part of the heart is affected?

I

II

III

aVR

aVL

aVF

V1

V2

V3

V4

V5

V6

• Leads V1, V2, V3, and V4 =

Anterior Wall MI

Anterior Wall MI

Based on the EKG, which vessel in the heart is blocked?

• V1 - V4 = Anterior Wall (Left Ventricle) = Left Anterior Descending Artery Blockage

What part of the heart is affected?

I, aVL, V5 and V6 Lateral wall of left

ventricle

I

II

III

aVR

aVL

aVF

V1

V2

V3

V4

V5

V6

Lateral Wall MI

Based on the EKG, which vessel in the heart is blocked?

• I, aVL, V5 + V6 = Lateral Wall = Circumflex Artery Blockage

THANK YOU

27