Perioperatve myocardial ischaemia

Patients at risk

Patients at risk

* Known coronary artery disease (CAD)
* Increased risk of CAD
- diabetes
- hypertension
- smoking
- hyperlipidaemia
- family history of CAD
- peripheral vascular and cerebrovascular disease
* Increased risk of cardiovascular complications
- renal insufficiency
- age over 65
- history of cardiac failure
- poor functional capacity (<4 METS)
- abnormal ECG
* Surgical factors
- major urgent surgery
- vascular surgery (inc peripheral)
- significant fluid shifts, blood loss

Risk reduction strategies

Risk reduction strategies

* Sympathetic modulation ­ avoid tachycardia
- BETA-BLOCKADE
- Alpha-2 agonists
- ? Anxiety control (premed), Good analgesia, Epidural (local anaes)
* Maintain normothermia postoperatively
* Haemoglobin > 90 ­ 100 g/L
* Avoid hypoxia ­ prolonged supplemental O2 (maybe > 3 days)
* Coagulation modulation
- sympathetic modulation
- aspirin, ketorolac
- heparin
- warfarin

(Periop period is a hypercoagulable state - thrombosis involved in pathogenesis of acute coronary syndromes and platelet inhibitors and anticoagulants are used to treat acute coronary syndromes)

How to monitor for ischaemia

How to monitor for ischaemia

* Symptoms:
- usually none
- pain, SOB, sweating, N &V, altered mentation
* Clinical signs:
- usually none
- sweating, CCF, HR changes, arrhythmias, hypotension
* ECG: key perioperative monitor
* Pulmonary artery catheter:
- increased PCWP
- new V waves on PCWP tracing
* TOE:
- SWMA
- change in mitral regurgitation
- diastolic dysfunction
- decrease in global contractility

ECG monitoring for ischaemia 1 - Optimal use

ECG monitoring for ischaemia 1 - Optimal use

* Lead selection ­ II and V4 or V5 (3 lead - modified V leads e.g. CM5, CS5)
* Correct electrode positioning
* Good electrode application
* Calibration (1mV = 1 cm)
* Mode: diagnostic (? Datex Stfilter mode)
* Printout baseline and any changes
* Automated ST segment analysis
(Always review measurement points to verify ST segment changes)

ECG monitoring for ischaemia 2 - Ischaemic manifestations

ECG monitoring for ischaemia 2 - Ischaemic manifestations

* ST SEGMENT CHANGES (most specific)
* T wave changes
(esp inversion in high risk groups)
* Dysrhythmias
* New conduction abnormalities
* New atrioventricular block
* Heart rate changes

ECG monitoring for ischaemia 3 - ST segment criteria for ischaemia

ECG monitoring for ischaemia 3 ST segment criteria for ischaemia

* Depression: subendocardial ischaemia, poor localisation
- Horizontal / downsloping depression > 0.1 mV (1 mm) at 60-80 msec after J point
- Upsloping depression > 0.15 mV at 80 msec after J point
* Elevation: transmural ischaemia, good localisation
> 0.1 mV at 60-80 msec after J point

ECG monitoring for ischaemia 4 - Other causes of acute ST changes

ECG monitoring for ischaemia 4 Other causes of acute ST segment changes

* Conduction disturbances
* R wave amplitude changes
* Hyperventilation
* Electrolyte changes, hypoglycaemia
* Hypothermia (< 30º)
* Body position changes / retractors
* Autonomic NS changes e.g. spinal
* Myocardial infarction or contusion
* Neurological changes (trauma, SAH)
* Acute pericarditis

ECG monitoring for ischaemia 5 Causes of chronic ST segment changes

ECG monitoring for ischaemia 5 Causes of chronic ST segment changes

* Non-specific changes ­ V4 most likely to be isoelectric
* LVH
* Early repolarization pattern
* Digitalis
* Bundle branch blocks esp LBBB
* Old myocardial infarction
* LV aneurysm

Management of suspected intraoperative ischaemia

Management of suspected intraoperative ischaemia

* FIRSTLY
Secure system ­ ensure adequate oxygenation, BP, volume, Hb
* SECONDLY
- Verify change
- Optimise haemodynamics - especially tachycardia and blood pressure
* THIRDLY
* Consider
- increase FiO2
- Glycerol Trinitrate (GTN)
- increased monitoring ­ CVP, PCWP, TOE
- inform surgeon, alter surgical plan
- postoperative management

Management of suspected intraoperative ischaemia - Verify change

Management of suspected intraoperative ischaemia Verify change

* check ECG (calibration, mode, previous ECG printouts)
* verify automatic ST segment analyses
* look for associated features
- dysrhythmias, hypotension
- increased filling pressures or new V waves
- TOE changes (check all LV segments)
* consider
- other causes of ECG change
- patient’s risk of CAD

Management of suspected intraoperative ischaemia - Tachycardia

Management of suspected intraoperative ischaemia Tachycardia management

* FIRSTLY treat cause e.g. hypovolemia, anaesthetic depth, CO2
* NEXT:
Beta-blockade (aim for HR < 60)
- esmolol ­ 0.25 - 0.5 mg.kg bolus, 25 - 300 mg/kg/min infusion - atenolol ­ 0.5 - 10 mg titrated bolus over 15 minutes
- metoprolol ­ 1- 15 mg titrated bolus over 15 minutes
If beta-blockade contra-indicated
- verapamil ­ 2.5 mg - repeat as needed. Infuse at 1-10mg/hr [may be first choice if ST segment elevation (coronary spasm)]
- alpha-2 agonists ­ clonidine, dexmedetomidine

Management of suspected intraoperative ischaemia - Blood pressure

Management of suspected intraoperative ischaemia Blood pressure management

* Hypotension
SIMULTANEOUSLY
o treat cause e.g. hypovolemia, anaesthetic depth, PEEP, surgical manipulation
o vasopressors (metaraminol, phenylephrine) (inotropes with caution as increase O2 demand)
* Hypertension
FIRSTLY:
o treat cause e.g. anaesthetic depth, CO2
NEXT:
o GTN - sublingual (0.3-0.9 mg ­ works within 3 min)
o IV infusion (0.25 - 4 mgm/kg/min ­ titrate to effect)
o clonidine (30 mg every 5 minutes up to 300 mg)
o dexmedetomidine (1mg/kg load, infuse at 0.2-0.7 mg/kg/hr)

Management of persistent ischaemia with optimal haemodynamics

Management of persistent ischaemia If ischaemia persists with optimal haemodynamics

* keep increasing GTN (may combine with vasopressor if hypotension)
* maybe increase monitoring ­ CVP, PCWP, TOE
* CONSIDER Acute Coronary Syndrome (unstable angina, infarct)
- aspirin or ketorolac
- heparin (5000 U bolus, then 1000 U/hr) if surgery permits
- continue beta-blockade (aspirin & beta-blockade reduce risk of infarct and mortality)
- observe for complications- dysrhythmias, CCF, infarct
- Cardiology consult - urgent reperfusion - within 12-24 hours (especially if persistent ST segment elevation)
- PTCA most practical (thrombolysis CI after surgery)
- ? IABP

Postoperative management of perioperative ischaemia

Postoperative management of perioperative ischaemia

* CONSIDER
- ICU or CCU postop and/or Cardiology referral
- Surveillance for periop MI
- ECG immediately postop and on day 1 and 2
- Cardiac troponin at 24 hrs and day 4 (or hosp discharge) (CK-MB of limited use)
(Depending on
- obvious reversible cause of ischaemia
- severity and duration
- associated features
- response to treatment)
* LONG TERM
- letter to GP / cardiologist
- risk factor management
- aspirin, statins, beta-blockade, ACE inhibitors