Q-Notes
for Adult Medicine |
STAT |
CARDIOLOGY

REF: ACP Medicine Best Dx/Best Rx 2006
Acute Myocardial Infarction
Peter B. Berger, M.D. Duke University School of
Medicine
Definition/Key Clinical Features
Differential Diagnosis
Best Tests
Best Therapy
Best Evidence
Definition/Key
Clinical Features
-
Sudden injury to the myocardium resulting from decreased
coronary perfusion
-
Heaviness, pressure, squeezing, or tightness in the chest
for > 30 min
-
Discomfort radiates to arms, neck, or jaw
-
Diaphoresis, nausea, emesis
-
Dyspnea
-
Dizziness
-
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
absent
Differential
Diagnosis
-
Esophagitis
-
Pulmonary embolism
-
Aortic dissection
-
Spontaneous pneumothorax
-
Pericarditis
-
Cholecystitis
Best
Tests
Clinical Definition of MI - Myocardial Infarction
(American
College of Cardiology)
-
Acute, evolving, or recent
MI
-
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:
-
Ischemic symptoms
-
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
angioplasty)
-
Pathologic findings of an acute MI
-
Established
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
developed
-
Pathologic findings of a healed or healing MI
Physical
Exam
-
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
present
-
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
ECG
-
-
Elevated ST segment indicates > 90% likelihood of
MI and high risk of mortality
Laboratory
-
-
CK-MB assays: lack specificity, because CK and CK-MB
levels require ⥠3 hr of profound ischemia to rise
-
Myoglobin level: rises more rapidly than CK but also
lacks specificity
-
Troponin level: cardiac-specific; elevated level predicts
subsequent cardiac events
Imaging
-
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
-
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
Coronary Angiography
-
Patients who have received
thrombolytic therapy: recommended only for those with hemodynamic instability
or those with spontaneous or exercise-induced ischemia following uncomplicated
MI
-
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
Best Therapy
Emergent
Therapy (Remember
MONA =
Morphine/analgesis,
Oxygen,
Nitroglycerin,
Aspirin/antiplatelets/antithrombus Rx)
-
Evaluate symptomatic patients < 10 min after arrival
in ER
-
Avoid delay in treatment
-
Assess heart rate and BP
-
Perform 12-lead ECG
-
Administer oxygen
for the first several hours after admission
-
Administer
analgesia immediately (as Morphine
IV)
-
Administer
aspirin as soon as MI is diagnosed, and
continue indefinitely
-
Administer sublingual
nitroglycerin if BP > 90 mm Hg
-
Admit to hospital with continuous ECG
monitoring
-
Admit high-risk patients to CCU
Reperfusion Therapy
-
Best therapy achieves coronary patency most rapidly,
depending on the capabilities of the institution
Thrombolytic Therapy
-
Should be administered < 60 min after presentation,
< 30 min if possible
-
Indications
-
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
-
Contraindications
-
Significant bleeding
-
Risk of intracerebral bleeding (e.g., advanced age, low
body weight, hypertension, warfarin use, previous stroke, GI bleeding, recent
surgery)
-
Thrombolytic agents
-
Front-loaded, weight-adjusted
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
-
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
-
Reteplase (recombinant
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
currently indicated
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
<100mg).
-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.
-
Pregnancy.
-
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
conditions.
-
Septic thrombophlebitis or occluded AV cannula at seriously infected
site.
-
Patients on warfarin (Coumadin).
-
Hemostatic defects as from severe liver or renal disease. OR
|
Immediate Angioplasty
-
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
facilities
-
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
-
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
effects
-
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
-
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
magnesium deficiency
Preventive Therapy
Lipid-Lowering Therapy
-
Measure cholesterol < 24 hr after presentation; prescribe
HMG-CoA reductase inhibitors for those patients with LDL level >130
mg/dl
-
Exercise
-
Weight reduction in overweight patients
-
Avoidance of dietary saturated fat and cholesterol
-
Smoking cessation
Aspirin
Holter
Monitoring
-
When used before discharge, can help identify patients at increased
risk for sudden cardiac death
-
Routine antiarrhythmic therapy not recommended
Risk-Factor Modification
-
Treatment of hypertension and hypercholesterolemia
-
Smoking cessation
-
Cardiac rehabilitation
-
Exercise program
Best Evidence
Berger PB, et
al: Circulation 100:14, 1999 [PMID 10393675]
Braunwald E,
et al: J Am Coll Cardiol 40:1366, 2002 [PMID 12383588]
Keeley EC, et
al: Lancet 361:13, 2003 [PMID 12517460]
Myocardial infarction
redefined: J Am Coll Cardiol 36:959, 2000 [PMID
10987628]
Rana JS, et al:
Am Heart J 147:841, 2004 [PMID 15131540]
March
2006
2004 Update: ACC/AHA Guidelines for the Management
of Patients With Acute Myocardial Infarction:
Executive Summary and Recommendations