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ACUTE CORONARY SYNDROMES: Acute MI and Unstable Angina


Main symptom of ischemic heart disease is chest pain ... acute coronary ischemia. inflammatory heart disease. cardiomyopathies. circulatory failure & shock ... – PowerPoint PPT presentation

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Title: ACUTE CORONARY SYNDROMES: Acute MI and Unstable Angina

  • Tintinalli Chapter 50
  • September 20, 2005

Acute Coronary Syndrome (ACS)
  • Ischemic heart disease accounts for 500,000
    deaths annually in the U.S.
  • CAD and myocardial ischemia contribute to 5
    million ER visits yearly for chest pain
  • 15 of pts with chest pain will have acute MI and
    25-30 will have unstable angina

  • a term used to describe pts with acute CP and
    other symptoms of myocardial ischemia
  • During the initial exam, often not possible to
    determine whether permanent damage to the
    myocardium has occurred
  • Only in retrospect after serial ECGs or cardiac
    markers can the distinction b/w AMI or UA be made

  • ACS is caused by secondary reduction in
    myocardial blood flow due to
  • coronary arterial spasm
  • disruption of atherosclerotic plaques
  • platelet aggregation or thrombus formation at
    site of atherosclerotic lesion

Thrombus formation
  • Atherosclerotic plaque formation occurs through
    repetitive injury to vessel wall
  • When plaque ruptures, potent thrombogenic
    substances are exposed to platelets
  • These platelets respond by adhesion, activation,
    and aggregation thus initiating thrombus
    formation in the coronary vessels

  • The extent of O2 deprivation and thus clinical
    presentation of ACS depend on the limitation of
    O2 delivery by thrombus adhering to fixed,
    fissured, or eroded plaques

Stable Angina
  • Ischemia occurs only when activity induces O2
    demands beyond the supply restrictions imposed by
    a partially occluded coronary vessel
  • occurs at a relatively fixed and predictable
    point and changes slowly over time
  • atherosclerotic plaque has not ruptured thus
    there is little superimposed thrombus

  • Atherosclerotic plaque rupture and platelet-rich
    thrombus develop
  • Degree and duration of O2 supply-demand mismatch
    determines whether reversible myocardial ischemia
    w/o necrosis (unstable angina) or myocardial
    ischemia w/ necrosis (myocardial infarction)

Clinical Features
  • Main symptom of ischemic heart disease is chest
  • need to characterize its severity, location,
    radiation, duration, and quality
  • ask about associated symptoms N/V, diaphoresis,
    dyspnea, lightheadedness, syncope, palpitations

  • Reproducible chest wall tenderness is not
  • Patients with ACS may complain of easy
  • Usually an AMI is accompanied by more prolonged
    and severe chest discomfort and more prominent
    associated symptoms

Angina Pectoris
  • Exercise, stress, or cold environment classically
    precipitates angina
  • duration of symptoms typically occasionally lasting up to 20 minutes
  • usually improves within 2-5 minutes after rest or

  • Up to 30 of patients with AMI are clinically
  • Some of these patients have had atypical symptoms
    for which they didnt pursue medical advice
  • Worse prognosis for pts who have atypical
    symptoms at the time of their infarction
  • women and elderly most likely to have atypical

Cardiac Risk Factors
  • Age over 40
  • male
  • postmenopausal females
  • family history
  • cigarette smoking
  • hypertension
  • High cholesterol
  • truncal obesity
  • sedentary lifestyle
  • diabetes
  • previous cardiac hx

Cardiac Risk Factors
  • Risk factors are modestly predictive of CAD is
    asymptomatic patients
  • In the ER, risk factors are poor predictors of
    cardiac risk for MI or other ACS
  • In males, only DM and family history are weakly
  • Cardiac risk factors are not predictive of ACS in
    female ER chest pain pts

Physical Examination
  • Not helpful in distinguishing pts with ACS from
    those with non cardiac etiologies
  • Pts may appear deceptively will without distress
    or be uncomfortable, pale, cyanotic, and in
    respiratory distress.

Vital Signs
  • Bradycardic rhythms are more common with inferior
    wall MI
  • in the setting of anterior wall MI, bradycardia
    or heart block is very poor prognostic sign
  • Extremes of blood pressures are associated with
    worse prognosis

Heart Sounds
  • S1 and S2 are often diminished due to poor
    myocardial contractility
  • S3 is present in 15-20 of pts with AMI
  • implies a failing myocardium
  • S4 is common in pts with long standing HTN or
    myocardial dysfunction
  • Presence of new systolic murmur is an ominous
  • signifies papillary m. dysfunction, flail leaflet
    of mitral valve, or VSD

  • 12 lead is single best test to identify pts with
    AMI upon presentation to ER
  • Current guidelines state that the initial 12 lead
    ECG must be obtained and interpreted within 10
    minutes of patient presentation
  • Yet ECG has a relatively low sensitivity for
    detection of AMI

  • ST segment is elevated on the initial ECG in
    approximately 50 of pts with AMI
  • most other AMI pts will have ST depression and/or
    T wave inversions
  • Only 1-5 of pts with AMI have an entirely normal
    initial ECG

ECG criteria and AMI
  • Anteroseptal --
  • Anterior --
  • anterolateral --
  • QS deflections in V1-V3, possibly V4
  • rS defection in V1, Q waves V2-4 or decr in
    amplitude of initial R wave in V1-V4
  • Q waves in V4-6, I, aVL

ECG Criteria and AMI
  • Lateral --
  • inferior --
  • inferolateral --
  • true posterior --
  • right ventricular --
  • Q waves in I, aVL
  • Q waves II, III, aVF
  • Q waves II, III, aVF, and V5-V6
  • Initial R waves in V1-V2 0,04s and R/S ratio 1
  • Q waves II, III, aVF ST elevation rV4

  • In distributions previously described
  • ST elevation suggests acute transmural injury
  • ST depression suggests subendocardial ischemia
  • All inferior wall MI should have right sided ECG
  • ST elevation in rV4 indicates right ventricular

  • Reciprocal ST segment changes predict
  • a larger infarct distribution
  • an increased severity of underlying CAD
  • more severe pump failure
  • a higher likelihood of cardiovascular
  • increased mortality

Difficult ECG interpretations
  • ST elevation in absence of AMI
  • early repolarization
  • LVH
  • pericarditis/myocarditis
  • Left ventricular aneurysm
  • Hypertropic cardiomyopathy
  • hypothermia
  • ventricular paced rhythms
  • LBBB

Difficult ECG interpretations
  • ST depression in absence of ischemia
  • hypokalemia
  • digoxin effect
  • cor pulmonale and right heart strain
  • early repolarization
  • LVH
  • ventricular paced rhythms
  • LBBB

Difficult ECG interpretations
  • T wave inversions without ischemia
  • persistent juvenile pattern
  • seizures or Stokes Adams syncope
  • post-tachycardia T wave inversion
  • post-pacemaker T wave inversion
  • Intracranial pathology (CNS hemorrhage)
  • Mitral valve prolapse
  • pericarditis
  • primary or secondary myocardial disease

  • T wave inversion without ischemia
  • PE or cor pulmonale
  • spontaneous PTX
  • myocardial contusion
  • LVH
  • ventricular paced rhythms
  • RBBB
  • LBBB

  • In the setting of LBBB, the following are
    indicative of AMI
  • 1. ST elevation 1mm or greater and concordant
    with the QRS complex
  • 2. ST depression 1mm or more in leads V1, V2, or
  • 3. ST elevation 5mm or greater and discordant
    with the QRS complex

Cardiac Enzymes
  • Serial measurements are more sensitive and
    accurate than initial single measurement
  • serum markers have less utility in the diagnosis
    of UA, only about 50 will have elevated

  • Most commonly used marker in ACS
  • a serial rise to above 5 times baseline followed
    by fall back to baseline is considered diagnostic
    for AMI
  • peaks at 12-24 hours, with fall back to baseline
    in 2-3 days
  • useful in detecting recurrent infarction after
    the initial 24-48 hours by noting a repeat
    elevation in the level

Conditions Associated with Elevated CK-MB
  • Unstable angina
  • acute coronary ischemia
  • inflammatory heart disease
  • cardiomyopathies
  • circulatory failure shock
  • DTs
  • Rhabdomyolysis
  • Cardiac surgery
  • skeletal m. trauma
  • dermatomyositis, polymyositis
  • myopathic disorders
  • muscular dystrophy
  • vigorous exercise
  • malignant hyperthermia
  • Ethanol poisoning (chronic)

  • Main regulatory protein for the actin-myosin
  • 3 subunits
  • inhibitory subunit (Trop I)
  • tropomyosin binding subunit (Trop T)
  • calcium binding subunit (Trop C)
  • Trop I has not been identified in skeletal m.
    during any stage of develop therefore specific to

  • Peak level in 12 hours
  • prolonged elevation for 7 to 10 days before
    returning to baseline
  • thus making trop of no use in detecting recurrent
    infarctions during this time
  • Rise in serum Trop I or T is considered
    diagnostic for AMI
  • Low level elevations in Trop correlate with risk
    for CV complications in UA, CAD, and renal failure

  • Rises within 2-3 hours of symptoms onset
  • peaks within 4 to 24 hours
  • more sensitive than CK and CK-MB but not specific
    for cardiac muscle
  • there is a high false-positive rate due to its
    presence in all muscle tissue

Complications of MI
  • 1. Dysrhythmias and conduction disturbances
  • 2. Cardiac failure
  • 3. Mechanical complications
  • 4. Pericarditis
  • 5. Right Ventricular Infarction
  • 6. Other

  • Occurs in 72-100 of AMI pts treated in coronary
    care unit
  • PVCs are common in AMI
  • occur in 90 of AMI patients
  • Atrial premature contractions are also common
  • occur in up to 50 of AMI patients
  • not associated with increased mortality

  • Early in AMI, pts often show increased autonomic
    nervous system activity
  • sinus brady, AV block, hypotension occur from
    increased vagal tone
  • Later, increased sympathetic activity results in
    incr catecholamine release
  • thus creates electrical instability PVCs,
    Vtach, Vfib, accelerated idioventricular rhythms,
    AV junctional tachycardia

  • Hemodynamic consequences of dysrhythmias are
    dependent on ventricular function
  • Normal hearts have a loss of 10-20 of left
    ventricular output when atrial kick is eliminated
  • Reduced left ventricular compliance can result in
    35 reduction in stroke volume when the atrial
    systole is eliminated

  • Persistant tachycardia is associated with poor
  • due increase myocardial oxygen use
  • When Vtach occurs late in AMI course, usually
    associated with transmural infarct and left
    ventricular dysfunction
  • induces hemodynamic deterioration
  • mortality rate approaches 50

Conduction Disturbances
  • First degree and Mobitz I (Wenckebach)
  • more common with inferior AMI
  • intermittent during the first 72 hrs after
  • rarely progresses to complete block or pathologic
  • Mobitz II
  • usually associated with anterior AMI
  • does progress to complete heart block

Conduction Disturbances
  • Complete Heart Block
  • occurs in setting of inferior MI
  • usually progresses from less AV blocks
  • this form is usually stable should resolve
  • Mortality is 15 in absence of RV involvement
    increases to 30 when RV is affected
  • Complete block in setting of anterior MI results
    in grave prognosis

Conduction Disturbance
  • New RBBB
  • occurs in approximately 2 of AMI pts
  • associated with anteroseptal AMI
  • associated with increased mortality because often
    leads to complete AV block

Conduction Disturbance
  • New LBBB
  • occurs in 5 of pts with AMI
  • associated with high mortality
  • Left posterior hemiblock associated with higher
    mortality than isolated anterior hemiblock
  • represents larger area of infarction

Cardiac Failure
  • 15-20 of AMI pts present in some degree of CHF
  • More severe the degree of left ventricular
    dysfunction, the higher the mortality
  • dependent on the net effect of prior myocardial
    dysfunction, baseline myocardial hypertrophy,
    acute myocardial necrosis, acute reversible
    dysfunction (stunned myocardium)

Cardiac Failure
  • B-type natriuretic peptide
  • useful for risk stratification of pts with non ST
    elevation MI and UA
  • elevated levels of BNP early in the hospital
    course predict a worse outcome at 30 days

Mechanical Complicationsof AMI
  • Sudden decompensation of previously stable AMI pt
    should raise concern of the mechanical
  • Free wall rupture
  • occurs in 10 of AMI fatalities, usually 1 to 5
    days after infarction
  • rupture of LV free wall usually leads to
    pericardial tamponade and death (90 of cases)

Mechanical Complicationsof AMI
  • NSAIDs, steroids, and late administration of
    thrombolytics have been linked to an increased
    likelihood of cardiac rupture
  • however, studies remain contradictory
  • LV hypertrophy appears to be protective

Mechanical Complicationsof AMI
  • Rupture of interventricular septum
  • is more often detected clinically than
    ventricular wall rupture
  • pts have chest pain, dyspnea, sudden appearance
    of new holosystolic murmur
  • murmur often associated with palpable thrill and
    best heard at lower left sternal border
  • more common in pts with anterior wall MI and pts
    with extensive (3 vessel) CAD

Mechanical Complicationsof AMI
  • Papillary Muscle Rupture
  • occurs in 1 of pts with AMI
  • more common with inferior wall MI
  • usually occurs 3 to 5 days after AMI
  • occurs with a small to modest sized MI
  • posteromedial m. commonly ruptured
  • receives blood from only one coronary a.
  • present with acute dyspnea, increasing CHF, and
    new holosystolic murmur consistent with mitral

  • Occurs in 10-20 of post-AMI pts
  • more common with transmural MI
  • usually occurs 2-4 days after AMI
  • Pericardial friction rubs detected more often
    with inferior wall and right ventricular infarcts
  • Pericardial effusions may also be present may
    take months to resorb

  • Dressler Syndrome
  • post AMI syndrome
  • occurs 2 to 10 weeks after AMI
  • pts presents with chest pain, fever, and

Right Ventricular Infarction
  • Usually seen as a complication of an inferior
  • approximately 30 of inferior wall MI involve the
  • Presence of RV infarction is associated with
    significant increase in mortality and
    cardiovascular complications

Other Complications
  • Left ventricular thrombus formation
  • arterial embolization
  • venous thrombus
  • pulmonary embolism
  • postinfarction angina
  • infarct extension
  • these are diagnoses to think about when a pt
    presents to the ER after recent discharge from
    the hospital

Postprocedure Chest Pain
  • Pts who present with symptoms of ACS shortly
    after angioplasty or stent placement should be
    assumed to have abrupt vessel closure
  • Subacute thrombotic occlusion after stent
    placement occurs in approximately 4 of pts 2 to
    14 days after procedure
  • this less common than closure after angioplasty

  • Pts with chest pain syndromes after CABG
  • may have abrupt vessel closure
  • symptoms of recurrent ischemia can be confused
    with post-AMI pericarditis

  • All patients with acute chest pain need to be
    evaluated for the possibility of ACS
  • pts are admitted to appropriate level of care
    depending on their risks
  • Results of prior cardiac catheterization are very
    useful for risk stratification

Cardiac Cath Results
  • pts with previously documented minimal stenosis
    excellent long-term prognosis
  • more than 90 of these pts are free from MI 10
    yrs later
  • a recent cardiac cath (within last 2 yrs) with
    normal or minimally diseased vessels almost
    eliminates the possibility of ACS due to
  • doesnt eliminate vasospasm or small vessel dz

Stress Tests Results
  • When pts complete all stages of the stess
    protocol, have no ECG changes and normal imaging
    studies, exercise testing can r/o acute ischemic
    syndromes with sensitivities b/w 80-90
  • If all criteria are not met, stress test have
    poor sensitivity

  • 1. Which of the following is false about new
  • a. Occurs in 2 of AMI pts
  • b. Occurs most commonly with inferior wall MI
  • c. Often leads to complete AV block
  • d. Associated with increased mortality

  • 2. True or False Inferior wall MI can result
    from occlusion of left circumflex a. or RCA
  • 3. True or False Left ventricular free wall
    rupture occurs in 10 of AMI fatalities usually
    3-4 weeks after initial infarct

  • 4. True or False B type natriuretic peptide
    has a high specificity in diagnosing CHF
  • 5. True or False Reproducible chest wall pain
    rules out ACS.
  • Answers B, true, false, false, false

  • Tintinalli, J. Emergency Medicine A
    Comprehensive Study Guide. 6th edition. pg.
  • Ma, O.J. and David Cline. Emergency Medicine
    Just the facts. 2nd edition. pg. 91-97.
  • Rivers, C. Preparing for the Written Board Exam
    in Emergency Medicine. 4th edition. pg. 60-76.
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