Importance of perioperative myocardial ischaemia

• Adverse cardiac events are major cause of post-surgical morbidity and mortality
• Perioperative ischaemia (esp postoperative and prolonged) is associated with adverse cardiac events (early and late)
• Most perioperative ischaemia is silent
• Real-time detection may allow therapeutic intervention

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 1

• 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)

Risk reduction strategies 2

• Coagulation modulation
- sympathetic modulation
- aspirin, ketorolac
- heparin
- warfarin

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

• 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

• 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

• 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 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

• 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

• 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

• 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 (slide 11)
- patient’s risk of CAD (slide 3)

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

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

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

• 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