for Adult Medicine |
REF: ACP Medicine Best Dx/Best Rx 2006
Acute Myocardial Infarction
Peter B. Berger, M.D. Duke University School of
Definition/Key Clinical Features
Sudden injury to the myocardium resulting from decreased
Heaviness, pressure, squeezing, or tightness in the chest
for > 30 min
Discomfort radiates to arms, neck, or jaw
Diaphoresis, nausea, emesis
Arrhythmia, cardiac arrest
Almost always caused by thrombotic occlusion
Most elderly patients present with shortness of breath,
and many present with dizziness or symptoms of arrhythmia
In one fourth of patients, symptoms are mild or
Clinical Definition of MI - Myocardial Infarction
College of Cardiology)
Acute, evolving, or recent
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:
Development of pathologic Q
waves on the ECG
ECG changes indicative of ischemia (i.e.,
ST segment elevation or depression)
Coronary artery intervention (e.g., primary coronary
Pathologic findings of an acute MI
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
Pathologic findings of a healed or healing MI
History and physical exam are useful for excluding other
causes of chest pain rather than confirming MI
Vital signs often normal, but sinus tachycardia may be
Patient may be anxious and distressed
Hypertension or hypotension may be present
Pulse may be rapid or slow
Lung exam is typically normal
Cardiac exam may reveal dyskinetic apical pulsation,
third or fourth heart sound, murmur of ischemic mitral regurgitation, abnormal
splitting of second heart sound
Elevated ST segment indicates > 90% likelihood of
MI and high risk of mortality
CK-MB assays: lack specificity, because CK and CK-MB
levels require â¥ 3 hr of profound ischemia to rise
Myoglobin level: rises more rapidly than CK but also
Troponin level: cardiac-specific; elevated level predicts
subsequent cardiac events
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
Radionuclide imaging: sensitive and specific for MI
Predischarge Exercise Testing
Generally recommended before discharge from the hospital
to assess functional capacity and ability to return to activities of daily
living and work
Contraindications: spontaneous postinfarction angina,
congestive heart failure, hypotension, malignant ventricular arrhythmia;
perform coronary angiography instead
Patients who have received
thrombolytic therapy: recommended only for those with hemodynamic instability
or those with spontaneous or exercise-induced ischemia following uncomplicated
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
Evaluate symptomatic patients < 10 min after arrival
Avoid delay in treatment
Assess heart rate and BP
Perform 12-lead ECG
for the first several hours after admission
analgesia immediately (as Morphine
aspirin as soon as MI is diagnosed, and
nitroglycerin if BP > 90 mm Hg
Admit to hospital with continuous ECG
Admit high-risk patients to CCU
Best therapy achieves coronary patency most rapidly,
depending on the capabilities of the institution
Should be administered < 60 min after presentation,
< 30 min if possible
ST segment elevation in = or > 2 leads and < 12
hr of chest pain
Classic symptoms of infarction and a bundle branch block
that precludes detection of ST segment elevation
6-12 hr of chest pain on presentation
Risk of intracerebral bleeding (e.g., advanced age, low
body weight, hypertension, warfarin use, previous stroke, GI bleeding, recent
t-PA & I.V. heparin:
moderately superior to other thrombolytic regimens but much more expensive;
associated with a greater frequency of intracerebral hemorrhage than
Streptokinase & I.V.
heparin: contraindicated in patients
who have recently received a dose of streptokinase
Streptokinase and subcutaneous heparin
Combination of I.V. t-PA and streptokinase given concurrently
with I.V. heparin
t-PA): given as two boluses, together
with aspirin and I.V. heparin; as effective as t-PA
Combination therapy: a thrombolytic agent plus a
glycoprotein IIb/IIIa inhibitor; not
|Thrombolytic & anticoagulant
Rx (Not part of ACP Medicine
Best Dx/Best Rx 2006 )
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
tPA Rx 15 mg IV bolus, then 50 mg (0.75mg/kg)
over 30 min, then 35mg (0.50mg/kg) over 60 min.
(Total 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.
-Heparin 5000 u IV push.
-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
-Lidocaine 1 mg/kg IVP over 1 min interval, then Lidocaine 1 gm in 250 cc
D5W at 1 4 mg/min.
-Heparin 1000 u/hr IV drip.
-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.
IV TNKase (Tenecteplase) single IV
bolus over 5 seconds; <60 kg give 30 mg; 60-69 kg give 35 mg; 70-79
kg give 40 mg; 80-89 kg 45 mg; >90 kg give 50 mg.
IV Anistreplase (Eminase) Rx 30 units IV over
2- 5 min. or
IV Retavase (Reteplase) 10 U and 10 U double
bolus dosing give 30 min apart. (6/1999)
CONTRAINDICATION for t PA infusion Rx:
CVA & TIA within 12 months. CNS tumor or AV malformation. Intracranial
or intrspinal surgery or trauma within 2 months.
General surgery, abrasive wounds or fracture < 2 wks, or hip surgery
< 3 wks.
Recent traumatic CPR resuscitation.
GI bleeding < 3 months, liver failure, uremia.
Over 75 y.o. or serious advance illness, such as cancer.
Hypertension systolic > 180 or, diastolic > 110 mmHg.
SBE, acute pericarditis, high likelihood of left heart thrombus (eg. mitral
stenosis with atrial fibrillation).
Diabetic hemorrhagic retinopathy or other hemorrhagic opthalmic
Septic thrombophlebitis or occluded AV cannula at seriously infected
Patients on warfarin (Coumadin).
Hemostatic defects as from severe liver or renal disease. OR
Preferred therapy for acute MI at institutions where
it can be performed without delay; associated with lower morbidity and mortality
than thrombolytic therapy alone
Alternative treatment strategy for patients with ST segment
elevation MI initially assessed at a hospital without on-site cardiac surgery
Combined use of stents and platelet glycoprotein inhibitors
may normalize antegrade blood flow and reduce need for repeat procedures
the following year
Artery Bypass Surgery
Achieves reperfusion more slowly than thrombolytic therapy
and primary coronary angioplasty
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
I.V. heparin: recommended for patients with suspected
MI who are not treated with thrombolytics; should be discontinued > 24
hr before discharge
Low-molecular-weight heparin: may be as effective as
unfractionated heparin; optimal dose is unknown; avoid in renal failure
Direct thrombin inhibitors: bivalirudin may reduce incidence
of reinfarction but has been associated with increased bleeding events
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
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
I.V. nitroglycerin: indicated in patients with
persistent/recurrent chest pain after reperfusion therapy and those who do
not receive reperfusion therapy
Prophylactic antiarrhythmic therapy: not recommended
for patients without malignant ventricular ectopy
Calcium channel antagonists: indicated in patients with
ischemia that persists despite use of aspirin, beta blockers, nitrate therapy,
and I.V. heparin
Magnesium: indicated in patients with MI who have torsade
de pointesâtype ventricular tachycardia and those with
Measure cholesterol < 24 hr after presentation; prescribe
HMG-CoA reductase inhibitors for those patients with LDL level >130
Weight reduction in overweight patients
Avoidance of dietary saturated fat and cholesterol
When used before discharge, can help identify patients at increased
risk for sudden cardiac death
Routine antiarrhythmic therapy not recommended
Treatment of hypertension and hypercholesterolemia
Berger PB, et
al: Circulation 100:14, 1999 [PMID 10393675]
et al: J Am Coll Cardiol 40:1366, 2002 [PMID 12383588]
Keeley EC, et
al: Lancet 361:13, 2003 [PMID 12517460]
redefined: J Am Coll Cardiol 36:959, 2000 [PMID
Rana JS, et al:
Am Heart J 147:841, 2004 [PMID 15131540]
2004 Update: ACC/AHA Guidelines for the Management
of Patients With Acute Myocardial Infarction:
Executive Summary and Recommendations