Myocardial infarction
Cardiology STEMI bleep 999.
All other enquiries to be directed to Cardiology Registrar bleep
CUH Cath lab phone xxxx
ECG criteria
- 1mm ST elevation in >2 contiguous limb leads (II, III, AVF, I,AVL)
- 2mm ST elevation in >2 contiguous chest leads (V1-V6)
- new LBBB ( and clinically suspected AMI )
The ECG criteria are explicit. There is no benefit in thrombolysing patients with suspected MI's with normal ECG's or ST depression.
Posterior MI's ECG changes are: dominant R in V2 with ST depression. The diagnosis can be confirmed by performing an ECG with posterior leads. Referfusion (PCI or thrombolysis) should be considered in this case, especially if ST depression > 2 mm.
With infarction, the initial ECG may be normal (in up to 30% of cases) [Bestbets]. All patients with an MI history (normal first ECG) need a repeat the ECG every 10-15 min while the patient still has pain, after analgesia. The patient will either develop changes (i.e. infarct) or the pain will settle with no change in the ECG (unstable angina or a non Q wave infarct).
If a pain free patient develops further pain repeat the ECG.
ECG examples
Anterior AMI
Inferior AMI
General management
Prehospital
- Oxygen therapy- continue at 2 litres/min
- Aspirin 300mg chewed and swallowed as early as possible [Bestbets]. If this has not occurred then administer in the ED (the only absolute contraindication is anaphylaxis!).
- Aspirin can be given PR if patient is vomiting.
Emergency department
- Aspirin (as above if not already given)
- PO Clopidogrel 600mg or Prasugrel 60mg
- Prasugrel if
(see more)
- Age <75, Wt >60kg, No Hx of TIA/CVA
- GTN spray or Suscard Buccal (2mg or 5mg)
- Morphine 2.5-5 mg titrated to the patients response
- In cases where there is continued or recurrent pain it is worth considering iv Β-blockers (1-10mg atenolol titrated to pain)
- Β-Blockers are contraindicated in:
- heart failure, asthma or bronchospasm, heart block, HR<50, SBP< 90mmHg
Thrombolysis contraindications see Critical care pathway page1
Absolute contraindications
- Active internal bleeding
- CVA within 6 months
- Cranial or spinal surgery within 2 months
- Cerebral or spinal tumour or AV malformation
- BP >200/120 not amenable to ED treatment
- Severe bleeding problem
(moderate, such as von Willebrands acceptable)
* Angioplasty is an alternative when there is a contraindication to thrombolysis (discuss with duty cardiologist).
Relative contraindications
- Cerebrovascular disease
- Gastrointestinal or urological bleeding within 10/7, including puncture of non compressible vessels.
- BP >180/110
- Suspected left heart thrombus (i.e. mitral stenosis with AF)
- Suspected aortic dissection or pericarditis
- Infective endocarditis
- Known coagulation defect (inc. severe liver disease)
- Pregnancy
- Active haemorrhagic ophthalmic disease
- Warfarin (manufacturers recommendation, no data)
- For rpa, age >75, small infarctions, MI onset >6hrs
- For sk, streptococcal infection or sk use in the past
Thrombolytic agents
We use : Streptokinase (sk) and Reteplase (rpa) at MUH and expensive (without any patient advantage) Tenectaplase (CUH only)
Streptokinase
is used in all situations except when
- It has been administered in the past (unless within 4 days)
- In patients <70yrs with anterior MI and within four hours of pain (ie. meet all 3 criteria)
- When systolic BP< 85mmHg prior thrombolysis
The dosage is 1.5 million units to be given over 1 hour
Dose should be reduced to 1 million units in patients:
- on anticoagulants
- those <65kg
- aged 70 and over.
Reteplase
- Given as two bolus injections of 10U 30 minutes apart
- Followed by bolus of 4000iu of unfractionated heparin
- Then heparin infusion starting at 1000iu / hr
- Aim for APTT between 1.5 - 2.0 for at least 24 hours.
Alteplase
- 15 mg bolus
- Then 0.75 mg/kg (max 50 mg) IV over 30 mins
- Then 0.5 mg/kg (max 35mg) IV over next 60 mins
Informed consent
The main risk of thrombolysis is haemorrhage and the patient must be made aware of this prior to treatment.
The risk of CVA is 4/1000 treated above normal incidence for sk, 9/1000 for rpa.( Note half of each of these die - it's a haemorrhagic stroke). The risk of non-cerebral bleed is 7/1000 treated.
Troubleshooting
Treatment of hypertension
- Ensure adequate analgesia
- In the first instance try 800mcg (2 puffs) GTN
- iv B blockade (see above)
- iv nitrate infusion(or buccal suscard)
Complications of thrombolysis
Hypotension
Is common with strep.
Should not prevent completion of the dose.
If SBP<90mmHg then:
- Tip the patient head down
- Administer 200ml Gelofusine
- Slow the infusion down, or stop temporarily
- If marked bradycardia then atropine 0.6-1.2mg iv
Reperfusion arrhythmias
Common, generally short (and therefore non-sustained) runs of VT or idioventricular rhythm.
- Consider lidocaine if problematic
- Cardiac arrest - follow the ALS protocol
- Heart block - Acute myocardial infarction can be associated with any degree of heart block. If haemodynamically stable and asymptomatic observe closely but continue treatment and seek senior advice so that pacing can be considered.
- Treat the bradycardia according to the ALS peri-arrest protocols.
Allergic reactions
- Stop the infusion
- Hydrocortisone 200mg and
- Chlorpheniramine 10mg as iv injections
- Consider rpa as an alternative thrombolytic agent
Bleeding
Minor haemorrhage - compression.
For larger bleeds -
- Stop thrombolysis
- Resuscitate
- Call for ED senior help
For catastrophic bleeds (massive GI or intracranial)
- Stop thrombolysis
- FFP (4 units) and packed cells
- Consider tranexamic acid (10mg/kg)
- Consider protamine 10mg/1000iu heparin infused.
If the patient develops neurological symptoms then an immediate CT scan is required
In CUH: Tranexamic acid injection (Cyklokapron) is kept in the haematology section of the drugs cupboard in Resus and in the clean utility room behind the nurses station.
Warfarin
- For patients on warfarin take blood samples for INR and group and save.
- This is only a relative contraindication to thrombolysis
- If in doubt discuss with a senior.
LBBB and paced rhythms (Scarbossa criteria)
The diagnosis of MI is complicated in these cases. There are certain features which have been noted to increase the likelihood of a concurrent MI.
ST >1mm elevation in leads where QRS is positive (V5 V6)
ST >5mm elevation in leads where QRS is predominately negative (V1 - V3)
ST depression >1mm V1-V3
If there are any of the above features treat as a new thrombolysable event.
Ask for ED senior help now.
Continuing care
Thrombolysed patients should receive their ongoing care on the CCU. Transfer to CCU will be arranged by the nursing staff, but the on call cardiology team must also be informed of the admission. Prior to transfer the details of the admission should be clearly documented on theThrombolysis Proforma. A copy of this and the ECG's recorded
An inpatient drug chart should also be completed and the following prescribed:
- Opiate analgesia
- Anti emetic
- Nitrates
- Aspirin 150mg od
- Heparin for DVT prophylaxis (either unfractionated heparin 5000iu bd or Enoxaparin 20mg od) in patients given Streptokinase.
