MYOCARDIAL ISCHAEMIA

ST changes - elevation or depression
T wave flattening or inversion
Ventricular dysrhythmias

Pre-existing cardiovascular disease
Haemodynamic instability
Tachy- or bradycardia
Hyper- or hypotension
Desaturation
Pulmonary oedema
Awareness / light anaesthesia / intubation (2)

Inform the surgeon
Defer, or rapidly complete surgery
Ensure adequate oxygenation
Correct any haemodynamic derangement (3)
   If hypotensive
   If hypertensive
   If tachycardic
   If bradycardic
If ischaemia does not resolve rapidly (4)
     commence glyceryl trinitrate (50mg in 500ml 5% dextrose) Start at 0.1 ml/kg/hr
     titrate against clinical response
Consider multilead ECG monitoring (5)
Monitor ECG continuously
Aim for haematocrit - 30%
For significant myocardial ischaemia, consider a short-acting β-blocker to cover emergence from anaesthesia.(6)

Obtain a 12 lead unfiltered ECG as soon as possible to assist in the diagnosis.
Admit to HDU/ICU/CCU
Consider invasive monitoring:
     Blood pressure
     Cardiac filling pressures
Further investigation - serial ECG/cardiac enzymes
Continue oxygen therapy for at least 2 days.

The figures reported here are based on an analysis of 40 reports considered to demonstrate myocardial infarction or ischaemia, in the first 4000 AIMS anaesthesia incidents.
It was judged that correct use of the algorithm would have led to appropriate management in 90% of the reported cases, and would actually have led to earlier recognition of the problem and/or better management in 47% of the cases. The remaining 10% would have required the use of other sub-algorithms (e.g. air embolism).

(1) In all cases, ECG changes were reported as the means of detection. The diagnosis should be confirmed where possible by comparing monitor changes to a pre-operative trace.
In 73% of cases there were associated cardiorespiratory abnormalities:
     43% - hypotension;
     25% - tachycardia/hypertension;
     5% - desaturation.
(2) 15% of cases were judged secondary to light anaesthesia and 50% of these occurred with intubation.
(3) Resolution of ischaemia followed correction of cardiorespiratory abnormalities alone in 35% of cases.
(4) In the incidents reported, it was considered that in 40% of cases coronary vasodilator treatment, or more rapid treatment was indicated.
(5) It is well recognised that Standard 3 lead monitoring for ischaemia is very insensitive. Use the CM5 configuration to maximise the detection of ischaemia if multi-lead monitoring is not in use.
(6) Esmolol, a β-blocker with a rapid onset and a short duration of action, in a dose of 0.25 - 0.5 mg/kg IV, may be a suitable choice if available. Otherwise use atenolol 0.015 mg/kg as a slow IV bolus.