20. ST Segment Changes

Question 1

What is the significance of ST segment change?

Answer 1

The ST segment of the ECG represents
repolarisation of the ventricles.

Changes in the appearance of the
ST segments are caused by myocardial
ischaemia or myocardial infarction.

In the face of ischaemia, ST segment
depression or elevation may occur relative to the isoelectric line.

Movement away from the isoelectric line
of ≥1 mm is significant.

Intra-operative ST segment changes require rapid detection and management in order to correct and optimise coronary blood flow and reduce myocardial work.

Intra-operatively, the most common causes of
myocardial ischaemia are rate-related ischaemia and hypotension.

Question 2

How would you manage an
anaesthetised patient with ST
segment changes?

Answer 2

> Immediate management:
• Give 100% oxygen.

• Call for help and inform the surgeons of the need to conclude surgery as soon as possible.
• Perform a rapid but thorough assessment of the patient, looking for precipitating causes, e.g. hypoxia, tachycardia, hypotension and acute blood loss. Address any correctable problems.
• Ensure adequate coronary perfusion pressure

increase aortic diastolic pressure),

optimise arterial oxygen content
(increase FiO2 and ensure
normal Hb concentration),

optimise coronary blood flow

(increase diastolic time and promote coronary vasodilatation)

and reduce myocardial oxygen consumption

(reduce heart rate and force of
contraction).

Vasoactive drugs such as intravenous nitrates, β-blockers or vasopressors may be required.

Question 3

> Early management:

Answer 3

• Consider additional monitoring:

arterial line, cardiac output monitoring
and central line if there seems to be physiological deterioration as a result of cardiac ischaemia.

• If relevant, use cardiac output monitoring to guide fluid and inotropic therapy.
• Check electrolytes and Hb, correct any abnormalities.

Question 4

> Post-operatively:

Answer 4

• Following the operation, transfer the patient to an area of high dependency care for observation and investigation.
• Perform a 12-lead ECG and if abnormal, continue to take serial ECGs.
• Repeat U&Es and FBC and glucose.
• Take blood for a troponin I level at 6 and 12 hours after the event.

• Request an urgent review by the on call cardiologist/medics.
Do not wait for the results of blood tests before referral. Full anticoagulation/ thrombolysis is unlikely to be possible immediately post-operatively
and the patient may need urgent angiography.

• Document events clearly in the notes.