ST SEGMENT ELEVATED MYOCARDIAC INFARCTION (STEMI)

Posted: October 19, 2010 by chao85 in Medicine

ST SEGMENT ELEVATED MYOCARDIAC INFARCTION (STEMI)

Objectives

These guidelines are intended to provide awareness and education in

  • Early recognition of STEMI
  • Evidence-based practice for the management of STEMI
  • Secondary prevention following STEMI with the intention of reducing the morbidity and mortality associated with

MANAGEMENT OF ACUTE ST SEGMENT ELEVATIORDIAL INFARCTION (STEMI)

Clinical Questions

• Diagnosis

• Treatment strategy

• Risk reduction

• Special group

– Elderly

– Diabetics

– Women

ELEVATION

TERMINOLOGY

Acute coronary syndrome (ACS) is a clinical syndrome of IHD ranging from unstable angina, NSTEMI to STEMI depending upon the degree and acuteness of coronary occlusion.

STEMI: Myocardial infarction due to acute TOTAL occlusion of the coronary artery

NSTEMI: Myocardial infarction due to acute SUB-TOTAL occlusion of the coronary artery

Pathogenesis of STEMI

STEMI is necrosis of heart muscle due to inadequate blood supply following an acute total coronary occlusion. This occlusion is usually due to atherosclerotic plaque rupture, fissuring or ulceration with superimposed thrombosis and coronary vasospasm. Rarely, it may result from nonatherosclerotic arterial disease such as coronary vasospasm alone, coronary embolism or vasculitis.

MANA GEMENT OF ACUTE ST SE GMENT ELE VATI ON

Diagnostic approach of STEMI

1)      Clinical hx of ischaemic type chest pain

2)    ECG

3)       Serum cardiac biomarkers (myocardial injury or necrosis)

Hx

1)      Chest pain – retrosternal, severe, crushing, squeezing or pressing in nature, pain may radiate to the jaw or down the left upper limb (pain may be burning in nature and of lesser severity.)

2)      Lasting > 30 min,

3)      Associated with profuse sweating, nausea, vomiting and SOB. It is sometimes described as chest tightness only.

4)      It may be in the epigastric region and be misinterpreted as indigestion or heart burn.

5)      Rarely may it be localized to the back in the interscapular region only resulting in a misdiagnosis.

6)      Other – unexplained nausea and vomiting, weakness, dizziness, light-headedness and syncope, which may occur in the presence or absence of chest pain.

7)      Diabetics, the elderly and females may not present with typical chest pains

  • dyspnoea and atypical chest pains.

8)      PMH:

  • Previous history of IHD, PCI or CABG
  • Risk factors for atherosclerosis
  • Symptoms suggestive of previous TIA or other forms of CVS disease
  • Symptoms suggestive of peripheral vascular disease

ECG

1)      Hyperacute changes of a tall peaked T-wave, ST segment elevation followed by the development of Q-wave, return of the ST segment to isoelectric and T-wave inversion.

2)      The cut off points for new or presumed new ST segment elevation ≥ 0.2mV in V1/V2/V3 and ≥ 0.1mV in other leads. This should be present in ≥2 contiguous leads.

3)      The presence of new onset or presumably new LBBB in a patient with typical type chest pain indicates an INFARCT.

Inferior STEMI

**However in early MI, the ECG may be normal or equivocal. Patients with continuous chest pain and in whom the clinical index of suspicion of STEMI is high, 12 lead ECG tracings repeated at close intervals of at least 15 min might show evolving changes.

Comparison with previous ECG’s may also be helpful in such situations. In patients with an inferior infarct, one should look for associated posterior, lateral and RV infarct. The latter requires right sided chest leads for diagnosis.

Serum Cardiac Biomarkers

  • Confirm the diagnosis of STEMI.
  • One should not, however, wait for the results of these biomarkers before initiating reperfusion therapy.
  • Cardiac biomarkers:

a)      Cardiac troponins (cTnT and cTnI)

b)      Creatine kinase-Myocardial Band (CK-MB)

c)      Creatine kinase (CK)

d)     Myoglobin

e)      Fatty Acid Binding Proteins

  • CT and CK-MB are the most specific cardiac biomarkers. It takes about 3-8 hrs after STEMI for them to rise. Thus, too early a measurement may result in a misleadingly low level.
  • Diagnosis STEMI – CK-MB should be 2X the upper limit of normal. Persistently elevated values of CK-MB are almost never due to myocardial necrosis.
    • CK-MB rises early and falls early. Hence, CKMB measurements are useful for the diagnosis of reinfarction.
    • CK is not as sensitive or as specific as CK-MB. Nevertheless, it is also useful for the diagnosis of STEMI and reinfarction.
    • CTnT / CTnI – sufficient to indicate myocardial necrosis. They are useful in detecting MI in patients presenting with atypical histories and non-diagnostic ECG’s.
    • Troponin levels are more important for the diagnosis of NSTEMI than STEMI.
    • Troponins may remain elevated for up to 14 days.
      • Not useful for the diagnosis of reinfarction.

It is recommended that measurement of cardiac biomarkers be done at periodic intervals, at hospital admission and again at 12-24 hours. This would help to establish or exclude the diagnosis and may be useful for an estimation of infarct size.

AST and LDH levels are not sensitive or specific for AMI with frequent false positive elevations.

GMENT ELE VATI ON

Other Diagnostic Modalities

  1. CXR,
  2. Echocardiography – useful bedside imaging technique in difficult diagnostic situations.
  3. multislice computed tomography (MSCT) and
  4. radionuclide techniques
  • TRO or confirm the presence of acute infarction or ischaemia.
  • Identify non-ischaemic conditions causing chest pain such as valvular heart disease, pulmonary embolism, aortic dissection and pneumothorax.
  • Identify mechanical complications of acute infarction.
  • Provide prognostic information.

Difficult Diagnosis??

≈2-8% of patients presenting with chest pains to the ED have been misdiagnosed and sent home. The morbidity and mortality in these patients is high. To reduce this misdiagnosis, we suggest the following measures be taken in all patients presenting with chest pains:

  • They should be given priority in the emergency department and attended to urgently.
  • Myocardial ischemia or infarction should be excluded in all these patients.
  • Clinical suspicion should be high in all patients with predisposing risk factors for atherosclerosis.
  • A careful history will often help in making the diagnosis.
  • An ECG should be done as soon as possible in all patients with chest pains especially when the clinical suspicion of AMI is high. The threshold for doing an ECG in a patient presenting with chest pain should be low.
  • Where the initial ECG is non-diagnostic, it should be repeated and compared with old ECG’s.
  • Cardiac biomarkers especially the troponins, are helpful in ruling in or ruling out a MI.
  • Where the diagnosis is unclear but the clinical suspicion is high, these patients should be observed in the ED for a few hours and the resting ECG and cardiac biomarkers repeated to look for serial changes. If these remain stable, then the patient may be sent home but asked to return for an early review in the outpatient clinic.
  • In addition, the hospital needs to:
    • Educate all medical staff on the importance of early detection and treatment of AMI because this results in myocardial salvage and improved patient outcomes.
    • Have regular refresher courses on ECG interpretation.
    • Implement critical pathways for patients presenting with chest pains to the ED

MANA GEMENT OF ACUTE ST SE GMENT ELE VATI ON

MYOCARDIAL IN FAR CTI ON (STE MI)

PRE-HOSPITAL MANAGEMENT

Immediate measures to be taken in suspected cases of STEMI

For the general public:

  • Seek immediate medical attention at the nearest hospital.
  • Call for an ambulance (dial 991 or hospital direct line if known) or get someone to take you immediately to the nearest hospital.
  • Do not drive yourself.
  • If not on regular aspirin and with no history of allergy, chew and swallow one 300mg tablet of aspirin immediately.

For Patients with known CHD:

If the pain is suggestive of STEMI, take one dose of SL GTN and be rapidly transported to the hospital.

  • If the pain is not severe, take one tablet of GTN and repeat q 5 min for a max of 3 doses.
  • If the pain still persists after 15 min, go to the hospital.

For the general practitioner / family physician:

  • Ask patient to chew and swallow one 300mg tablet of aspirin.
  • Give SL GTN.
  • If the ECG shows ischemic changes, give clopidogrel 300mg of if available.
  • Wherever possible, set up IV access.
  • Pain relief with IV opiates (morphine 3-5mg slowly).
  • Avoid IM injections since this could result in intramuscular hematomas if fibrinolytic agents are subsequently administered.
  • Call an ambulance or ask the patient’s relative or friend to send the patient immediately to the nearest hospital.
  • Wherever possible, contact the doctor at the hospital so that the patient can be treated promptly on arrival.

For Allied Health Care Personnel:

Immediate measures to be taken when there is an ambulance call:-

  • Note nature of complaint.
  • Obtain name of caller, address and telephone number.
  • If possible, request that a relative or friend wait at a strategic place to help locate the patient.
  • Dispatch an adequately equipped ambulance with trained paramedics immediately.
  • Patient should be given O2 & aspirin (if he has not taken) and transported to hospital.
  • Upon reaching the hospital, the patient should be taken directly to the ED
    • An ECG should be done as soon as possible.
    • In hospitals where networking facilities are available, allied health care personnel in the ambulance should relay/transmit the ECG to the call centre for review by the Specialist, for consideration of pre-hospital fibrinolysis or primary PCI.
    • Allied Health care personnel should be trained:-
      • to identify patients at high risk of developing CHD.
      • to identify patients presenting with AMI.
      • on the importance of early referral and treatment.
      • In basic and advanced CPR.

MANA GEMENT OF ACUTE ST SE GMENT ELE VATI ON

MYOCARDIAL IN FAR CTI ON (STE MI)

IN-HOSPITAL MANAGEMENT

Early management of STEMI is directed at:

  1. Pain relief
  2. Establishing early reperfusion
  3. Treatment of complications – arrhythmias

Initial Recognition and Management

When the patient with suspected STEMI reaches ED, evaluation and initial management should take place promptly (FAST TRACK – RED ZONE) because the benefits of reperfusion therapy is greater the earlier it is initiated.

A quick targeted hx should be taken and vital signs noted. The diagnosis should be confirmed with an ECG, which should be done ASAP, preferably within 10 min of the patient’s arrival in the ED.

It is important to relieve pain and quickly assess the patient’s suitability for reperfusion by either fibrinolytic therapy or primary PCI.

The following should be done immediately and concomitantly in the ED

* When clinically indicated

** Preferred option in

  • High rish patients,
  • Presence of C/I to fibrinolytic therapy &/or
  • PCI time delay [(door to balloon time) – (door to needle time)] of < 60 min

*** If door to balloon is within 90 min

  • Assessment and stabilization of the patient’s haemodynamics.
  • SL GTN if chest pain persists (unless SBP < 90 mmHg).
  • Continuous ECG monitoring.
  • 300mg of aspirin chewed and swallowed if not given earlier.
  • Clopidogrel at a dose of 300mg should be given if not given earlier.
  • O2 by nasal prongs / facemask.
  • Venous access established and blood taken for cardiac biomarkers, FBC, RP, glucose and lipid profile.

Preferably 2 IV lines should be set up.

  • Pain relief – morphine should be administered IV at 2-5mg q 5-15 min until pain is relieved. Watch for evidence of toxicity – hypotension and respiratory depression.
  • Anti-emetics ( IV metoclopromide 10mg or promethazine 25mg ) should be given.
  • IM should be avoided.
  • Assessment for reperfusion strategy.

MANA GEMENT OF ACUTE ST SE GMENT ELE VATI ON

I. Reperfusion Strategies

ü  Early and prompt reperfusion is crucial as TIME LOST MYOCARDIUM LOST.

ü  Despite overwhelming data showing that prompt reperfusion therapy improves survival it is still widely underutilized and delayed.

ü  Most studies indicate that primary PCI is superior to fibrinolytic therapy as a reperfusion strategy.

ü  However in patients who present within 3 hrs of symptom onset and are at low risk, both treatment strategies appear to have similarmbenefits.

ü  In the majority of our hospitals, fibrinolytic therapy is more readily available and constitutes the main reperfusion strategy.

ü  If both choices are available, the following factors help guide the choice of reperfusion strategies:

a)      Time from symptom onset to first medical contact

b)      Time delay to PCI (time from hospital arrival to balloon dilatation – door to balloon time)

c)      Time to hospital fibrinolysis (time from hospital arrival to administration of fibrinolytic therapy – door to needle time)

d)     C/I to fibrinolytic therapy

e)      High risk patients

The best reperfusion strategy will depend upon:

A) Time from onset of symptoms

• Early presentation (within 3 hrs)

If both treatment options are readily available, they have been shown to be equally effective except for the following situations where primary PCI is the preferred strategy:

– fibrinolytic therapy is contraindicated

– in high-risk patients

– PCI time delay [(door-to-balloon time) – (door-to-needle time)] is < 60 min.

• Late presentation (3 to 12 hrs)

Primary PCI is preferred. The door to balloon time should be within 90 min if the patient presents at a PCI capable facility.

If transferred from a center with no PCI facilities, it should be < 2 hrs. (including transfer delay)

If the time delay to primary PCI is longer than as mentioned, then fibrinolytic therapy should be given.

• Very late presentation (> 12 hrs)

Both primary PCI and fibrinolytic therapy are not routinely recommended in patients who are asymptomatic and haemodynamically stable.MYOCARDIAL IN FAR CTI ON (STE MI)

However, reperfusion therapy would still be beneficial in patients with persistent ischaemic symptoms, haemodynamic or electrical instability. In this subgroup, primary PCI is the preferred strategy.

B) Contraindications to fibrinolytic therapy

C) High risk patients

These include patients with:

• Large infarcts

• Anterior infarcts

• Cardiogenic shock

• Elderly patients

• Post revascularization (post CABG and post PCI)

• Post infarct angina

Primary PCI is the preferred strategy in these patients.

The goals of time to reperfusion therapy should be within:

• 30 minutes door to needle time

• 90 minutes door to balloon time

II. Fibrinolytic Therapy

When given within 1 hr from time of onset of symptoms, it is most beneficial and has been shown to be able to abort the infarction and reduce mortality by up to 50%.

The door-to-needle time should be within 30 mins.

Strategies should be put in place to achieve this target.

Fibrinolytic therapy should be made available in all hospitals and there should be protocols to initiate it in the ED.

Pre-hospital fibrinolytic therapy has been shown to achieve faster reperfusion.

Patients presenting with a low SBP < 90mm Hg should receive inotropic support prior to fibrinolytic therapy.

Indications

ü  Patients with STEMI. It has no role and may even be detrimental in patients with NSTEM.

C/I

  1. 1. Absolute
  • Risk of Intracranial haemorrhage
    • Any hx of intracranial haemorrhage
    • Ischaemic stroke within 3 months
    • Known structural cerebral vascular lesion (e.g. arteriovenous malformation)
    • Known intracranial neoplasm

  • Risk of bleeding
    • Active bleeding or bleeding diathesis (excluding menses)
    • Significant head trauma within 3 months
    • Suspected aortic dissection
  1. 2. Relative
  • Risk of intracranial haemorrhage
    • Severe uncontrolled hypertension on presentation (BP > 180/110 mm Hg)*
    • Ischaemic stroke > 3 months ago
    • History of chronic, severe uncontrolled hypertension
  • Risk of Bleeding
    • Current use of anticoagulation in therapeutic doses (INR > 2)
    • Recent major surgery < 3 weeks
    • Traumatic or prolonged CPR >10 minutes
    • Recent internal bleeding (e.g. GIT/UT haemorrhage) within 4 weeks
    • Non-compressible vascular puncture
    • Active peptic ulcer
  • Others
  • Pregnancy
  • Prior exposure (>5 days and within 12 months of first usage) to streptokinase (if planning to use same agent)

* The bp should be reduced prior to institution of fibrinolytic therapy.

Choice of Fibrinolytic Agent

  1. 1. Streptokinase

It is not fibrin specific and is less efficacious than fibrin selective agents.

Despite having a lower risk of intracranial haemorrhage, the reduction in mortality is less than with fibrin specific agents.

Streptokinase is antigenic and promotes the production of  antibodies. Thus the utilization of this agent for re-infarction is less effective if given again 5 days after the first administration .

PCI or fibrin specific agents should then be considered.

Regimen:

– 1.5 mega units in 100 ml NS or 5% dextrose over 1 hr.

Other regimens are:

– 1.5 mega units over 20 min, or

– 0.75 mega unit bolus and then repeated at the same dose after an interval of 50 min if there is no clinical reperfusion.

)

The last 2 regimens achieve a higher coronary artery patency rate and are associated with lower in-hospital mortality. However they are associated with a higher incidence of hypotension.

  1. 2. Alteplase

This agent is fibrin specific and achieves better reperfusion at 90 min as compared to streptokinase.

However there is a higher rate of reocclusion. Thus heparin needs to be given for 48 hours.

Regimen: For patients > 65 kg

15 mg bolus; then 50 mg over 30 min and 35 mg over the next 60min

For patients < 65 kg

15 mg bolus; then 0.75 mg/kg over 30 min and 0.5 mg/kg over the next 60min

  1. 3. Second generation fibrin specific agents: Tenecteplase, Reteplase

These second generation fibrin specific agents are as efficacious as alteplase .

Tenecteplase has been shown to have a slightly lower bleeding risk as compared to alteplase

The main advantage of using these agents is that they are easier to administer. They are given as single or double bolus injections and also do not induce antibody production.

Regimen: Tenecteplase (TNK-tPA) single IV bolus

30mg if < 60kg

35mg if 60 to < 70kg

40mg if 70 to < 80kg

45mg if 80 to < 90kg

50mg if >90kg

Heparin needs to be given for 48 hours

Indicators of Successful Reperfusion

There is no sensitive bedside clinical method to reliably detect successful reperfusion. Some useful guides are:

• Resolution of chest pain (may be confounded by the use of narcotic analgesics).

• Early return of ST segment elevation to isoelectric line or a decrease in the height of the ST elevation by 50% in the lead that records the highest ST elevation therapy within 60-90mins of initiation of fibrinolytic therapy.

• Early peaking of CK and CK-MB levels.

• Restoration and/or maintenance of haemodynamic and/or electrical stability

The occurrence of ‘reperfusion arrhythmias’ is not a reliable indicator of successful reperfusion. An exception is accelerated idioventricular rhythm and sudden sinus bradycardia which have been correlated with a patent infarct related coronary artery after fibrinolytic therapy or primary PCI.

Failed Fibrinolysis

Failure of fibrinolytic agents to open up the occluded infarct related artery is manifested as continuing chest pain, persistent ST segment elevation and hemodynamic instability. These patients are more likely to develop complications such as heart failure and arrhythmias.

The treatment of choice for these patients is rescue PCI. They should not be given a second dose of a fibrinolytic agent. This is because there has been no difference in event free survival demonstrated if these patients are given a repeat dose of a fibrinolytic agent or if they are treated conservatively.

III. Percutaneous Coronary Intervention (PCI)

Primary PCI

Primary PCI is the reperfusion strategy of choice as indicated earlier. It should be performed promptly by experienced operators and in centers performing a sufficient number of primary PCI procedures.

Facilitated PCI

Current evidence indicates that strategies combining fibrinolytic therapy are associated with higher reperfusion rates and TIMI flow.

However, it is associated with higher mortality and bleeding rates. It is therefore not recommended.

Rescue PCI

Rescue PCI may be considered in patients who have failed fibrinolytic therapy or have recurrent chest pain and/or ischaemic complications. Those who may benefit are patients with:

• ongoing chest pains

• haemodynamic and electrical instability

• cardiogenic shock in patient < 75 years old, within 36 hours of STEMI and <18 hours of shock whose coronary anatomy is suitable for revascularization

• heart failure and onset of chest pain within 12 hours

• cardiogenic shock – In these high risk patients, those who are <75 years of age and who present within 36 hours of STEMI and <18 hours of shock may be considered for rescue PCI if their coronary anatomy is suitable for revascularization. This strategy is associated with high mortality and morbidity rates. As such, patients should be individually evaluated.

Delayed PCI (> 72 hours after fibrinolytic therapy)

Routine angiography and PCI in asymptomatic and stable patients post fibrinolytic therapy is controversial.

CARDIAC CARE UNIT MANAGEMENT

1) General Measures

  • A period of at least 12 hrs of complete bed rest is recommended following admission to CCU. Patients with uncomplicated infarcts are encouraged to ambulate early. Those with  aemodynamic instability will need a longer period of monitoring.
  • Sedatives may be useful.
  • Use of bedside commodes and assisted bedside washing should be safe in most patients.
  • The Valsalva maneuver has been shown to precipitate dangerous haemodynamic and ECG changes particularly in the young and thus prevention of constipation with stool softeners is encouraged.

2) Monitoring

The general condition of the patient, vital signs, pulse oximetry and the ECG should be continuously monitored following STEMI, looking for complications.

3) Concomitant Therapy

a) Oxygen

  • Oxygen is indicated in the presence of hypoxemia. In uncomplicated cases, its use should probably be limited to the first 24 hours.
  • Oxygen, via nasal prongs, at 2 – 4 litres/min is usually adequate. One should aim to maintain the oxygen saturation above 95%.

b) Antiplatelet Agents

  • Aspirin

Aspirin is indicated in all patients at diagnosis and should be continued indefinitely unless contraindicated. The initial dose of 100-300mg should be followed by a maintenance dose of 75 – 150mg daily

  • Clopidogrel

Clopidogrel, when given together with aspirin and fibrinolytic therapy in STEMI, has been shown to reduce the odds of an occluded infarct related artery, death or reinfarction without increasing the risk of bleeding or cerebrovascular accidents. A loading dose of 300 mg should be given followed by a maintenance dose of 75 mg daily. We recommend treatment for at least 1 month after fibrinolytic therapy. Following PCI, a longer period of dual antiplatelet therapy

(up to 12 months) is necessary particularly when drug-eluting stents are used.

IN FAR CTI ON (STE MI)

c)  β-blockers

Current recommendations are to use oral β-blockers early in all patients without specific contraindications. In patients with asymptomatic LV dysfunction (LV ejection fraction on echocardiogram < 40%) and not in overt heart failure, carvedilol has been shown to reduce the frequency of death and recurrent AMI. When indicated, it should be started in patients who are

hemodynamically stable after 48 hours.

Contraindications to β – blockers:

1) Bradycardia < 60/minute

2) SBP < 100mmHg

3) Pulmonary congestion with crepitations beyond the lung bases

4) Signs of peripheral hypoperfusion

5) Second or third degree atrio-ventricular (AV) block

6) Asthma or chronic obstructive airway disease ( COAD)

7) Severe peripheral vascular disease

c) ACEI and Angiotensin Receptor Blockers (ARB)

Early use of ACEI (within 24 hours) following STEMI has been shown to improve survival. ACEI should be started when the bp is stable and SBP remains above 100mmHg.

The benefits of ACEI are greatest in patients with:

• Heart failure

• Anterior infarcts

• Asymptomatic left ventricular dysfunction ( LV ejection fraction < 40% on echocardiography)

In patients who cannot tolerate ACEI, the ARB, valsartan, has been shown to have a similar survival benefit.

C/I to ACEI and ARB therapy:

1) Systolic BP < 100mmHg

2) Established contraindications e.g. bilateral renal artery stenosis, worsening renal function.

Type Initiation dose Target dose

Metoprolol 25mg bd 100mg bd

Atenolol 25mg od 100mg od

Propranolol 5mg tds 80mg tds

Carvedilol 3.125mg bd 25mg bd

SE GMENT ELE VATI ON

MYOCARDIAL IN FAR CTI ON (STE MI)

d) Nitrates

The routine use of nitrates has not been shown to have a survival

benefit.

Nitrates can be considered in patients with:

• Continuing chest pain and / or ischemia

• Heart failure

• Hypertension

In the acute stage, IV nitrates are recommended because of their rapid onset of action, ease of titration and potential for prompt termination in the event of side effects. After the first 48 hours, oral or topical nitrates may be continued in patients with persisting ischemia and/or heart failure.

C/I to nitrate therapy:

1) Hypotension (SBP< 90mmHg)

2) RV infarction

3) History of phospho-diesterase 5 inhibitors ingestion depending upon the half-life of the agent.

e) Calcium Channel Blockers (CCB)

There is no data to support the routine use of CCB post STEMI.

However they may be used as adjunctive therapy in patients with hypertension and/or on-going ischaemia despite β-blockers and nitrates.

In patients who cannot tolerate β-blockers, verapamil or diltiazem may be used for secondary prevention.

Calcium channel blockers should be avoided in patients with LV dysfunction, pulmonary congestion, bradycardia and AV block.

Type Initiation dose Target dose

Captopril 6.25mg bd –tds 25 – 50mg tds

Ramipril 2.5mg bd 10mg od

Enalapril 2.5 – 5mg od 10mg od

Lisinopril 5mg od 10mg od

Perindopril 2mg od 4mg od

Valsartan 80mg od 160mg bd

GMENT ELE VATI ON

f)  Antithrombotics

The antithrombotics that have been studied in STEMI are:

• Unfractionated heparin

• Low molecular weight heparin

• Synthetic pentasaccharide – fondaparinux

Heparin is indicated in patients with :

– post infarct angina

– atrial fibrillation

– mural thrombus

– extensive anterior infarction

– post fibrin-specific fibrinolytic agent 31,32,33

– post non fibrin-specific fibrinolytic agent 31

A) Unfractionated heparin (UFH)

Unfractionated heparin is administered as a bolus of 60units/kg (maximum 4000units) followed by an infusion rate of 12units/kg/hour (maximum 1000units/hour) adjusting the dose to maintain the aPTT of 1.5 to 2.5 times control.

B) Low molecular weight heparin (LMWH)

Low molecular weight heparin is given subcutaneously twice a day. LMWH was associated with better clinical outcomes as compared to UFH when given following fibrinolytic therapy in STEMI. This benefit was seen with both fibrin-specific and non-fibrin specific agents, but at an increased risk of bleeding. These studies however, were done prior to the usage of clopidogrel in STEMI. In patients >75 years of age and with renal impairment (serum creatinine > 200umol/L in women and >250umol/L in men), UFH is preferable to LMWH.

Patients given aspirin, clopidogrel, fibrinolytic therapy and LMWH have been found to have a higher rate of patency of the infarct related artery without an increase in the risk of bleeding complications in one substudy.

We caution the use of all 4 agents (aspirin, clopidogrel, fibrinolytic therapy and UFH/LMWH) together until the efficacy and safety of the combination is established in future trials.

C) Synthetic pentasaccharide

A trial on fondaparinux at a dose of 2.5mg/kg per day, given for 8 days, or the duration of index hospitalization to patients who were given fibrinolytic agents or who were not reperfused, was shown to reduce death or reinfarction at 30 days when compared to UFH. The risk of bleeding was not increased.

g)  Glycoprotein IIb/IIIa Receptor Inhibitors

Glycoprotein IIb/IIIa receptor inhibitors are used mainly in the setting of primary PCI. In primary PCI, the glycoprotein IIb/IIIa receptor inhibitor, abciximab, has been shown to improve patient outcomes.

h)  Statins

Recent data has shown that statins started within 24 hours of admission or continued after admission leads to a reduction in major adverse cardiac events.

MANA GEMENT OF ACUTE ST SE GMENT ELE VATI ON

i)  Aldosterone Antagonists

Eplerenone, a selective aldosterone receptor antagonist, when added to β-blockers and ACE-I, has been shown to reduce mortality and hospitalizations when given to patients post myocardial infarction with impaired LV function and mild HF.

j) Others – Mg, Lignocaine, Glucose – Insulin K Infusions

Mg and Lignocaine are not recommended for routine use in patients with STEMI.

Although earlier studies and meta-analysis seem to indicate that Glucose-Insulin–K infusions are beneficial, more recent studies have not shown reduction in mortality or infarct size.

Recommendations:

• All patients should receive 100 – 300 mg aspirin and 300 mg clopidogrel followed by a maintenance dose of 75-150 mg of aspirin long term and 75 mg of clopidogrel daily for at least a month.

• All patients should be on β blockers if there are no specific contraindications.

• Other medications that have been shown to improve survival if given early are ACE inhibitors (or ARB if ACE intolerant) and statins.

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