Acute Myocardial Infarction (MI)
Best MI
Therapy See
Acute Coronary Syndrome
REF: ACP Medicine Best Dx/Best Rx 2006
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| Clinical
Features | Differential Diagnosis
|Best Tests |Best Therapy |Best
Evidence |
Clinical Features
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Sudden injury to the myocardium resulting from decreased
coronary perfusion
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Heaviness, pressure, squeezing, or tightness in the chest
for > 30 min
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Discomfort radiates to arms, neck, or jaw
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Diaphoresis, nausea, emesis
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Dyspnea
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Dizziness
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Arrhythmia, cardiac arrest
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Almost always caused by thrombotic occlusion
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Most elderly patients present with shortness of breath,
and many present with dizziness or symptoms of arrhythmia
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In one fourth of patients, symptoms are mild or
absent
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Differential
Diagnosis
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Esophagitis, rupture esophagus
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Pulmonary embolism
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Aortic dissection
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Spontaneous pneumothorax
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Pericarditis
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Cholecystitis
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| Best Tests
Clinical Definition of MI - Myocardial Infarction
(American College of Cardiology)
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Acute, evolving, or recent
MI
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Biochemical markers of myocardial necrosis (i.e., typical
rise and gradual fall of troponin or
more rapid rise and fall of creatine kinase-myocardial
band [CK-MB]) with at least one of the following:
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Ischemic symptoms
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Development of pathologic Q
waves on the ECG
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ECG changes indicative of ischemia (i.e.,
ST segment elevation or depression)
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Coronary artery intervention (e.g., primary coronary
angioplasty)
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Pathologic findings of an acute MI
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Established
MI
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Development of new pathologic
Q waves on serial ECGs; patient may or may not remember previous
symptoms; biochemical markers of myocardial necrosis may have normalized,
depending on the length of time that has passed since the infarct
developed
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Pathologic findings of a healed or healing MI
Physical
Exam
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History and physical exam are useful for excluding other
causes of chest pain rather than confirming MI
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Vital signs often normal, but sinus tachycardia may be
present
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Patient may be anxious and distressed
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Hypertension or hypotension may be present
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Pulse may be rapid or slow
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Lung exam is typically normal
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Cardiac exam may reveal dyskinetic apical pulsation,
third or fourth heart sound, murmur of ischemic mitral regurgitation, abnormal
splitting of second heart sound
ECG
-
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Elevated ST segment indicates > 90% likelihood of
MI and high risk of mortality
Laboratory
-
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CK-MB assays: lack specificity, because CK and CK-MB
levels require ≥ 3 hr of profound ischemia to rise
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Myoglobin level: rises more rapidly than CK but also
lacks specificity
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Troponin level: cardiac-specific; elevated level predicts
subsequent cardiac events
Imaging
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Echocardiography: treatment
should not be delayed for echocardiography when symptoms and ECG indicate
acute MI; may be useful in patients with left bundle branch block or abnormal
ECGs without ST segment elevation whose symptoms are atypical and in whom
the diagnosis is uncertain
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Radionuclide imaging: sensitive and specific for MI
Predischarge Exercise Testing
-
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Generally recommended before discharge from the hospital
to assess functional capacity and ability to return to activities of daily
living and work
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Contraindications: spontaneous postinfarction angina,
congestive heart failure, hypotension, malignant ventricular arrhythmia;
perform coronary angiography instead
Coronary Angiography
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Patients who have received
thrombolytic therapy: recommended only for those with hemodynamic instability
or those with spontaneous or exercise-induced ischemia following uncomplicated
MI
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Patients who have not received thrombolytic therapy:
may be helpful for those with hemodynamic compromise, postinfarction chest
pain, or possible multivessel disease or reduced ventricular function
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| Best
Therapy
See also Acute Coronary
Syndrome
Emergent
Therapy
(Remember MONA =
Morphine/analgesis,
Oxygen,
Nitroglycerin,
Aspirin/antiplatelets/antithrombus Rx)
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Evaluate symptomatic patients < 10 min after arrival
in ER; Avoid delay in treatment; Assess heart
rate and BP
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Perform 12-lead ECG
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M - Morphine
IV for immediate pain control (2-4 mg IV with increments of 2-8
mg IV at 5-15 min intervals as needed to control pain) or other pain med
as indicated for resistant pain. Watch for
hypotension & respiratory suppression!
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O -
Oxygen 100% mask or nasal canula
for the first several hours after admission
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N -
Nitroglycerin if BP > 90
mm Hg; sublingual 0.4 mg prn
+/- topical nitroglycerin ointment 0.5-1 inch q8h
if pain continues. Watch for
hypotension.
IV Nitroglycerin infusion, start at 5 ug/min, then may
increase at increment of 5 ug/min q3 - 5min till response seen. May give
up to 80 - 160 ug/min if needed.
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A -
Aspirin 162-325 mg
PO as soon as MI is diagnosed, and continue indefinitely; and
Antiplatelet therapy, Anticoagulation, ACE inhibitor, Angiotensin receptor
blocker.
A for Antiplatelet
therapy, Anticoagulation, ACE inhibitor, Angiotensin receptor blocker
See
Anticoagulation Rx
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Antiplatelet therapy
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aspirin 162-325 mg initially then 75-160
mg daily indefinitely
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clopidogrel (Plavix) 300 mg initially,
then 75 mg daily for up 1 year, but should not be used within 5 days of CABG
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Combination therapy: a thrombolytic agent plus
a glycoprotein IIb/IIIa inhibitor;
not currently indicated !
glycoprotein IIb/IIIa inhibitor (Abciximab/Reopro, Eptifibatide/Integrilin,
Tirofiban/Aggrastat) if continuing ischemia, elevated troponin
level, TIMI risk score > 4, or anticipated percutaneous coronary intervention
(PCI); avoid abciximab if PCI not planned
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Eptifibatide/Integrilin 180 mcg/kg
IV bolus load, then 2 mcg/kg/min infusion for up to 72 hr. If percutaneous
coronary intervention (PCI) occurs during the infusion, continue infusion
for 18-24 hr after procedure.
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Anticoagulation
See Anticoagulation Rx
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low-molecular-weight heparin (enoxaparin/Lovenox)
1 mg/kg SC q12h for 2 to 8
days, preferred if conservative management, but avoid if creatinine clearance
< 60 mL/minute (unless anti-Xa levels monitored) or CABG within 24 hours
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unfractionated heparin is alternative
if early invasive management
- Heparin 60 Units/kg (max 4000
units) IV bolus, then 12 units/kg/hr infusion (max 1000 u/hr) IV drip to
maintain a PTT at 1.5 - 2.0 x control (~ 50-70 seconds)
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fondaparinux
(Arixtra)
2.5
to 7.5 mg daily as effective
as enoxaparin with less major bleeding and lower long-term mortality (level
1 [likely reliable] evidence)
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ACE inhibitor: as Lisinopril, Captopril
See BP Medications
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for all patients with ejection fraction < 40%, heart failure, hypertension,
or other high-risk features
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Angiotensive receptor blocker: as Cozaar
See BP
Medications
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if intolerant of ACE inhibitors; avoid combined use with ACE inhibitor acutely
but consider combined use if heart failure
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Admit to hospital
with continuous ECG
monitoring;
Admit high-risk patients directly
to CCU
Reperfusion Therapy
Thrombolytic Therapy
Thrombolytic therapy has been proved to reduce mortality 29% in patients
with ST segment elevation treated within 6 hours after the onset of chest
pain .
CONTRAINDICATION for t PA infusion
Rx:
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Active internal bleeding
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CVA & TIA within 12 months. CNS tumor or AV malformation.
Intracranial or intraspinal surgery or trauma within 2 months.
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General surgery, abrasive wounds or fracture < 2 wks, or hip surgery
< 3 wks.
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Recent traumatic CPR resuscitation.
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GI bleeding < 3 months, liver failure, uremia.
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Pregnancy.
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Over 75 y.o. or serious advance illness, such as cancer.
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Hypertension systolic > 180 or, diastolic > 110 mmHg.
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SBE, acute pericarditis, high likelihood of left heart thrombus (eg. mitral
stenosis with atrial fibrillation).
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Diabetic hemorrhagic retinopathy or other hemorrhagic opthalmic
conditions.
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Septic thrombophlebitis or occluded AV cannula at seriously infected
site.
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Patients on warfarin (Coumadin).
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Hemostatic defects as from severe liver or renal disease.
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Thrombolytic
& anticoagulant Rx (Not part of
ACP Medicine Best Dx/Best Rx 2006 )
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IV Streptokinase (Streptase) Rx 1.5 million u
IV over 1 hr.
PROTOCOL FOR IV STREPTOKINASE INFUSION:
-Stat 1/2 tab aspirin (160 mg) to be chewed.
-Insert 18 gauge heparin lock for blood sampling & 20 gauge heparin lock
for drug administration.
-Draw (before heparin flush) PTT, CPK, CPK MB, AST, LDH, CBC, BUN, lytes,
glucose, & type & hold 2 units of whole blood for 48 hrs.
-Prepare 1.5 million U of streptokinase in 50 cc
NS, & infuse over 1 hr (at 50 cc/hr).
-BP q10 min while streptokinase running.
-Notify M.D. if systolic BP falls by >20 mmHg.
-Stat EKG upon completion of streptokinase infusion.
-Start heparin 12,500 units subc q12h for at least 24h.
-CPK q4h for 24 hr, then daily for 2 more days.
-*** Consider hydrocortisone 100 mg IV before & q 8 12 hr during
streptokinase Rx may minimize allergic reactions. OR
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IV
tPA (Alteplase) Rx 15 mg
IV bolus, then 50 mg (0.75mg/kg) over 30 min, then 35mg (0.50mg/kg) over
60 min.
(Total max. dose <100mg).
PROTOCOL FOR t PA (tissue plasminogen activator) IV INFUSION
-Insert 18 gauge heparin lock for blood sampling & 20 gauge heparin lock
for drug administration.
-Draw (before heparin flush) the following blood tests: PTT, Protime, fibrinogen,
CBC, type & hold 3 units of whole blood
-or 48 hr, & CPK, CPK MB, AST, LDH.
-t PA IV 15 mg IV bolus, then 50 mg (0.75mg/kg)
over 30 min, then 35mg (0.50mg/kg) over 60 min. (Total dose
<100mg).
-Lidocaine 1 mg/kg IVP over 1 min interval, then Lidocaine 1 gm in 250 cc
D5W at 1 4 mg/min.
-Heparin 60 Units/kg (max 4000 units)
IV bolus, then 12 units/kg/hr infusion (max 1000 u/hr) IV drip to maintain
a PTT at 1.5 - 2.0 x control (~ 50-70 seconds).
-EKG q30 min x4, then at 3, 6, 12 hr post, then daily.
-CPK MB q1h x3, then q6h x4, then daily CBC q8h x2d, then daily PTT 4 hr
after initiation of heparin IV, q6h x4, then daily. Have pharmacist to adjust
dose to obtain PTT 2 2.5x control. Do not initiate warfarin (Coumadin).
-Four hr after completion of t PA infusion, obtain: discard initial 5 cc
blood) Protime, PTT, fibrinogen, CBC.
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Immediate Angioplasty
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Preferred therapy for acute MI at institutions where
it can be performed without delay; associated with lower morbidity and mortality
than thrombolytic therapy alone
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Alternative treatment strategy for patients with ST segment
elevation MI initially assessed at a hospital without on-site cardiac surgery
facilities
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Combined use of stents and platelet glycoprotein inhibitors
may normalize antegrade blood flow and reduce need for repeat procedures
the following year
Coronary
Artery Bypass Surgery
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Achieves reperfusion more slowly than thrombolytic therapy
and primary coronary angioplasty
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Should be reserved for patients in whom primary coronary
angioplasty is precluded or has failed and those with a ventricular septal
defect, severe mitral regurgitation, or myocardial rupture
Adjunctive Medical Therapy
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I.V. heparin: recommended for patients with suspected
MI who are not treated with thrombolytics; should be discontinued > 24
hr before discharge
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Low-molecular-weight heparin: may be as effective as
unfractionated heparin; optimal dose is unknown; avoid in renal failure
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Direct thrombin inhibitors: bivalirudin may reduce incidence
of reinfarction but has been associated with increased bleeding events
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Beta blockers: recommended for all patients with acute
MI and without contraindications as early as possible, whether or not they
receive reperfusion therapy; patients with the largest infarctions benefit
the most; continue indefinitely in the absence of contraindications or side
effects
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ACE inhibitors: use in all patients with significant
ventricular dysfunction (i.e., ejection fraction < 40%) contraindications;
begin within the first 48 hr of infarction and increase cautiously to avoid
hypotension
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I.V. nitroglycerin: indicated in patients with
persistent/recurrent chest pain after reperfusion therapy and those who do
not receive reperfusion therapy
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Prophylactic antiarrhythmic therapy: not recommended
for patients without malignant ventricular ectopy
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Calcium channel antagonists: indicated in patients with
ischemia that persists despite use of aspirin, beta blockers, nitrate therapy,
and I.V. heparin
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Magnesium: indicated in patients with MI who have torsade
de pointes–type ventricular tachycardia and those with
magnesium deficiency
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Other
Therapy:
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Early Beta-blocker Rx
- it may reduce infarct size by reducing heart rate, blood pressure, and
myocardial contractility.
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Early ACE-inhibitor Rx
- All patients with significant ventricular dysfunction (an ejection fraction
< 40%) without contraindications should be treated with an ACE inhibitor;
treatment should begin within the first 48 hours of infarction and be increased
cautiously to avoid hypotension.
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I.V. nitroglycerin
- is probably most likely to be beneficial in patients with persistent or
recurrent chest pain after reperfusion therapy and in patients in whom
reperfusion therapy is not administered.
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| Preventive Therapy
Lipid-Lowering Therapy
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Measure cholesterol < 24 hr after presentation; prescribe
HMG-CoA reductase inhibitors for those patients with LDL level >130
mg/dl
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Exercise
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Weight reduction in overweight patients
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Avoidance of dietary saturated fat and cholesterol
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Smoking cessation
Aspirin
Holter
Monitoring
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When used before discharge, can help identify patients at increased
risk for sudden cardiac death
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Routine antiarrhythmic therapy not recommended
Risk-Factor Modification
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Treatment of hypertension and hypercholesterolemia
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Smoking cessation
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Cardiac rehabilitation
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Exercise program
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Best Evidence
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Berger PB, et
al: Circulation 100:14, 1999 [PMID 10393675]
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Braunwald E,
et al: J Am Coll Cardiol 40:1366, 2002 [PMID 12383588]
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Keeley EC, et
al: Lancet 361:13, 2003 [PMID 12517460]
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Myocardial infarction
redefined: J Am Coll Cardiol 36:959, 2000 [PMID
10987628]
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Rana JS, et al:
Am Heart J 147:841, 2004 [PMID 15131540]
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