Perioperative myocardial ischaemia in non cardiac surgery

1. Dr Mukesh Wadhwa

2. Myocardial ischemia
It is a condition of insufficient blood flow to
the heart muscle via coronary arteries.
Myocardial Infarction
Death of myocardial myocytes due to
prolonged ischaemia.

3.  Myocardial ischemia can proceed to myocardial
infarction, and this peri-operative MI is associated
with a significant increase in 30 day mortality.
 Together myocardial ischemia and infarction is a
major cause of short and long term morbidity and
mortality in the surgical population.

4. Incidence- In patients with, or at risk of CAD, the
reported incidence of peri-operative myocardial
ischemia is 20-63%.
Pathophysiology
 Imbalance between myocardial oxygen supply and
demand.
 Reduced oxygen supply or low flow ischemia
(coronary vasoconstriction, intracoronary platelet
aggregation or thrombus formation) is mostly
responsible for unstable angina and MI

5.  Increased myocardial oxygen demand or high flow
ischemia is mostly responsible for ischaemic episodes
in chronic stable angina(tachycardia, exercise or
emotional stress)
 Often, myocardial ischaemia is a combination of
multiple factors and result from both a reduction in
supply and increase in oxygen demand.
 Two most common conditions that predispose to
myocardial ischaemia are CAD and left ventricular
hypertrophy(LVH).

6.  Clinical manifestations of myocardial ischaemia range
from asymptomatic or “ silent” episodes to angina,
arrhythmia, conduction blocks, wall motion
abnormalities, pulmonary congestion, infarction and
sudden cardiac death.

7. Systolic and diastolic dysfunction
↓
Electrocardiographic changes
↓
Chest Pain
- All these events often occur in a short time course of
less than 1 minute
 If the ischaemia becomes severe, the increase in left
ventricular end diastolic pressure may lead to
pulmonary oedema

8.  Myocardial stunning- After a brief period of severe
ischaemia , contractile function can return gradually.
 Myocardial hibernation- Severe chronic ischaemia can
result in diminished contractile performance, such as
chronic regional wall motion abnormalities.
 Partially damaged cardiomyocytes can be rescued to
full function after stunning as well as hibernation
provided normal blood flow is restored within the
critical time before irreversible cell damage has
occurred

9.  The single most common abnormality associated with
ischaemia is tachycardia, which by causing both an
increase in demand and reduction in supply can bring
about ischaemic changes in susceptible patients.
 Perioperative tachycardia can be due to light plane of
anaesthesia, endotracheal intubation/extubation,
hypovolemia, fever, anaemia, congestive heart failure,
and postoperative pain.
 Interestingly most ischemic episodes tend to start at the
end of surgery and during emergence from anaesthesia

10.  This period is characterized by increases in heart
rate(HR), Arterial blood pressure(BP), sympathetic
tone and procoagulant activity
 Increase in HR and BP may lead to subendocardial
ischaemia by increasing myocardial oxygen demand
in the presence of limited coronary vasodilator
reserve.
 Procoagulant activity during surgery may trigger
coronary artery thrombosis even in the absence of
acute plaque disruption.

11.  The diagnosis is usually based on clinical,
haemodynamic (pcwp/left atrial pressure wave),
electrocardiographic (ECG), functional
(Echocardiogram), metabolic (coronary lactate),
biochemical (CKMB/Troponin) or regional
perfusion(scintigram) parameters.
 Every technique has its limitation, varying
sensitivity/specificity and poor inter technique
correlation

12. Chest pain:
 During surgery under local or regional anaesthesia and
in recovery room. A Sense of chest constriction and
referred pain
 Silent ischemia in diabetics because pain pathways are
impaired by diabetic neuropathy
ECG
Myocardial ischaemia is predominantly detected and
defined by ECG.

13.  Horizontal or downsloping ST segment depression of
1mm or more indicates significant subendocardial
ischaemia while ST segment elevation greater than
1mm indicates severe transmural ischaemia
 Routinely leads II and V5 are monitored
 Limitations-In Patients with LVH, LBBB, digitalis
effect, ventricular pacing and those not in sinus rhythm
are not suitable for ECG derived diagnosis of
myocardial ischaemia.
 Also perioperative acid base balance and electrolytes
affect ECG

14. Trans-oesophageal echocardiography (TEE):
 TEE demonstrates development of new RWMA ,
decreased systolic wall thickening and ventricular
dilation as a result of ischaemic events.
 Usually a transgastric view is obtained
 Less frequently used in non cardiac surgery
Limitations- Pre-intubation events are missed, image
plane may miss events in other areas of the
myocardium, need of technical expertise
Myocardial Lactate: Mainly a research tool

15. Clinical presentation: Patients receiving GA will not
complain of chest pain but may have hypotension,
arrythmias and signs of congestive heart failure
ECG : May show ST elevation or depression. The vast
majority of perioperative MI are of the non Q wave
type and preceded by episodes of ST segment
depression and T wave inversion.
 Long duration (single duration >20-30 min or
cumulative duration>1-2hr) ST changes rather than
merely presence of postopertive ST depression seems
to be associated with adverse cardiac outcome

16. The following 2 criteria satisfy the diagnosis of an acute ,
evolving or recent MI
i) A typical increase and gradual decrease in troponin
concentrations or more rapid increase and decrease in
CKMB concentration in combination with at least one-
a) Typical ischaemic symptoms
b) Development of pathological q waves in ECG
c) ECG changes of myocardial ischaemia (ST elev/dep)
d) Coronary artery intervention ; and
ii) Pathological findings of an acute MI

17. Biochemical markers: While CPK-MB concentrations
may rise only10-20 times of normal during infarction
and return to normal within 72 hrs, TnT and TnI levels
may rise more than 20 times above the reference range
within 3 hrs after onset of chest pain and may persist
for up to 10-14 days

19. Other biochemical markers are:
 Myoglobin- earliest rise after MI
 C-reactive protein- a marker of inflammation ,primary
acute physiological process leading to plaque rupture
and thrombosis
 B-type natriuretic peptide- sensitive but have non
specific response to LV pressure/volume overload
caused by severe ischaemia or heart failure
TEE- May detect MI by sudden appearance of severe
RWMA, may be difficult to distinguish evolving
infarction, stunned and hibernating myocardium

20.  Despite widespread use of TEE and PA catheter, the
ECG is still the best validated tool for detection of
ischaemia episodes postoperatively

21. The fundamental purpose is to
1) To determine at risk patients and whether any preop
treatment is required
2) To design intraoperative plan to reduce the incidence
and consequences of ischaemia
3) In these at risk patients attempt to reduce the risk of
adverse outcome by implementing aggressive
preventive and treatment modalities

22.  Multiple scoring systems are available to predict the
risk of adverse cardiac events.
 Lee’s Revised Cardiac Risk Index is widely used
scoring system to predict major cardiac complications
in major elective non cardiac surgery.

23.  In 1999, Lee et al. published a cardiac risk index
derived from 2893 patients and validated in 1422
patients aged ≥ 50 undergoing major noncardiac
surgery, which became known as the Revised
Cardiac Risk Index (RCRI).
 Lee identified six independent variables that
predicted an increased risk for cardiac
complications.

24. CRITERIA POINTS
 High risk surgery(emergency,major thoracic 1
Procedure,cardiac,aortic/vascular,>4hr )
 Ischemic heart disease 1
 H/o congestive heart failure 1
 H/o cerebrovascular disease 1
 Insulin therapy for diabetes 1
 Perioperative S.creat >2.0 mg/dl 1
--------------------------------------------------------------------------
Predicted cardiac event rate increases with increasing
numbers of risk factors present; 0 points-0.4%, 1 point-
0.9%, 2 points-6.6%, >3 points-11%

25.  Other risk factors are recent MI, recent insertion of
coronary stents, elevated preoperative troponin I,
valvular heart disease, decompensated heart failure
and arrythmias.

26.  AHA/ACC published guidelines for perioperative
cardiovascular evaluation for non cardiac surgery. It
focuses on three major areas:
1) Clinical risk predictors
2) Surgery specific risks
3) Functional capacity

27. Major Intermediate Minor
Acute or recent
MI
Unstable angina
Decompensated
CHF
Significant
arrhythmias
Severe valvular
disease
Mild angina
Prior MI
Compensated
CHF
Diabetes mellitus
Renal
insufficiency
Advanced age
Abnormal ECG
Rhythm other
than sinus
History of stroke
Uncontrolled
hypertension

28. High(5%) Intermediate(<5
%)
Low(1%)
Emergent surgery
Aortic or major
vascular surgery
Periphral
vascular
surgery
Large fluid shifts
and blood loss
Carotid
endarterectomy
Head and neck
surgery
Intraperitoneal
intrathoracic
procedures
Orthopaedic
surgery
Endoscopic
procedures
Superficial
procedures
Cataract surgery
Breast surgery

29. Functional Capacity
Based on metabolic equivalents (METs)
(1MET= O2 consumption at rest- 3.5ml.kg-1.min-1)
 Functional capacity of less than 4METs of activity
confers a 4% risk of postoperative cardiac events,
whereas the risk is as low as 0.7%in patients with greater
than 4 METS of capacity.
 Examples of exercise equal to 4METs being, climbing
a flight of stairs/walking up a hill/ walking on level
ground at 4mph/running a short distance

30.  Careful consideration of all three aspects, including
clinical characteristics, functional capacity, and surgery
specific risk in accordance with the AHA/ACC
guidelines, form the basis for informed decision
making regarding further diagnostic testing and/or risk
reduction interventions

31.  Preoperative, intra-operative and
postoperative strategies for prevention
and management of perioperative
myocardial ischaemia

32.  AHA/ACC guidelines limit testing only to the
population groups deemed to be at the highest risk
(e.g. patients undergoing vascular procedures)
 The standard 12-lead electrocardiogram is an
insensitive test of the risk for myocardial ischaemia . It
is normal in up to 50% of patients with CAD, and some
patients have conduction defects that render the
electrocardiogram uninterpretable for ischaemia.
 When further workup is required cardiac stress testing
is used. The purpose of a stress test is to determine

33.  The status of ventricular function
 The amount of myocardium at risk for ischaemia, and
 The need for further interventions, e.g., medication,
angioplasty, or coronary artery bypass grafting, before
the proposed surgical procedure.
 Stress testing can be subdivided into exercise and
pharmacologic testing

34.  Exercise stress testing- The ability to achieve a target
heart rate of >100/min or 85% of the maximum
predicted HR predicts a low complication rate.
 ST segment depression greater than 0.1 mV on a
preoperative exercise stress test is an independent
predictor of perioperative cardiac complications.

35.  When exercise testing is contraindicated (LBBB,
significant arrhythmias, CHF) or if patient is unable to
exercise because of claudication , pharmacologic and
other testing is substituted which include ischaemia
monitoring by ambulatory ECG(AECG), ejection
fraction estimation by radionuclide ventriculography
(RNV), dipyridamole thallium scintigraphy (DTS) and
dobutamine stress echocardiography

36.  Two principal strategies used in an attempt to reduce
the incidence of PMIs and other cardiac events are-
i) Preoperative coronary revascularization- PCI or
CABG
ii) Pharmacological interventions

37.  Indications for preoperative coronary artery
revascularisation in patients at risk of myocardial
ischaemia are similar to the indications outside of the
perioperative setting.
 In particular, no benefit has been shown for
preoperative prophylactic revascularisation in patients
with stable or asymptomatic coronary artery disease
excluding patients with a strong indication for cardiac
surgery, such as left main stem disease or its equivalent

38. Type of PCI Timing of Noncardiac Surgery after
PCI
Balloon angioplasty
Bare-metal stent
Drug-eluting stent
14 days
6 weeks-3 months
180–365 days

39.  Several drugs have been proposed but based on current
clinical data only aspirin, beta blockers,α-2 agonists and
statins may have the potential to affect perioperative
cardiovascular outcome.
1) Β-blockers-
According to AHA/ACC unless there is a clear
contraindication, perioperative β blockers should be given
to
 patients undergoing vascular surgery
 to most patients with cardiovascular disease undergoing
major non cardiac surgery, and
 in patients positive for inducible ischaemia in myocardial
stress test

40.  Cardioprotective effects of β blockers are attributed to
numerous cardiovascular and other effects(anti-
arrythmic, anti-inflammatory, altered gene
expression,protection against apoptosis etc)
 β blockers may be given intravenously during or after
surgery in patients unable to take oral drugs
2)Antiplatelets- Aspirin, Clopidogrel and glycoprotein
IIb/IIIa inhibitors- Aspirin has to be continued till day
of surgery unless there are specific haemorrhagic risks
associated with the surgery

41. 3) Alpha2 agonists
Attenuate perioperative haemodynamic instability,inhibit
central sympathetic discharge, reduce peripheral NE release
There is no evidence of benefit from prophylactic use of
preoperative clonidine
4) Statins-
Statins may reduce the incidence of perioperative MI. All
patients undergoing vascular surgery should be established
on a statin
5) Nitroglycerine
No evidence of benefit of its prophylactic administration
before anaesthesia and surgery

42.  ACE inhibitors-
Patients with vascular disease and diabetes mellitus
should be maintained on ACE inhibitors
perioperatively.ACE inhibitors have anti ischaemic
actions with a 20 % relative reduction for myocardial
infarction.
But continuing these drugs may result in greater risk of
hypotension and renal failure also can be precipitated
by hypotension, hypovolemia, radiocontrast or
NSAID administration

43. High risk patients benefit from optimal preoperative
antiischaemia and antihypertensive therapy which
should be continued in perioperative period.
Intraoperative management:
The basic challenge during the perioperative period
is to prevent myocardial ischaemia, this goal is logically
achieved by maintaining the balance between oxygen
delivery and demand

44.  Decreased oxygen delivery-Decreased coronary blood flow,
Tachycardia, hypotension, Hypocapnia ( coronary artery
vasoconstriction) Coronary artery spasm
 Decreased oxygen content-Anaemia , Arterial hypoxaemia
Shift of the oxyhaemoglobin dissociation curve to the left
 Increased oxygen requirements- Increased preload (wall
tension) Sympathetic nervous system stimulation,
Tachycardia, Systemic hypertension, Increased myocardial
contractility, Increased afterload

45. Physiological Goals to
Increase Myocardial Oxygen
Supply
Physiological Goals to
Decrease Myocardial Oxygen
Demand
Low-normal heart rate
High oxygen content of blood (
SaO2, Hb)
High-normal aortic pressure
Reduced coronary vascular
resistance
Low left-ventricular end
diastolic pressure
Low-normal heart rate
Low myocardial wall tension or
afterload (avoid hypertension
and excessive fluid
administration)
Avoid increased myocardial
contractility

46.  There is no strong evidence to support a specific
anaesthetic technique in preventing myocardial
ischaemia. High risk patients ,such as those who have
had a recent MI or PCI, are more likely to be on
antiplatelet therapy, which may preclude neuraxial and
regional techniques
General Anaesthesia : If patient is undergoing GA, Then
the pressor response to laryngoscopy and intubation
should be minimized.
 In Normal LV function-combination of N2O –opioid
with addition of a volatile agent is acceptable

47.  In patients with severely impaired LV function, opioid
based anaesthesia may be used. However if giving high
doses, need for post operative ventilation should be
considered.
Neuraxial Anaesthesia-
High dermatomal levels can potentially result in
hypotension and reflex tachycardia if preload becomes
compromised or blockade of the cardioaccelerators
occurs.
- Otherwise no difference with GA in terms of cardiac
morbidity.

48.  Most of the cardiac events in noncardiac surgical
patients occur postoperatively, so post op pain
mangement is very crucial
 Patient controlled analgesia are associated with lower
pain scores and greater patient satisfaction
 Epidural anaesthesia/analgesia have lower opioid dose
requirement, better ablation of the catecholamine
response and a less hypercoagulable state
 An effective analgesic that blunts the stress response
must be included in the perioperative plan

49.  Perioperative morbid cardiac events have been found to
occur less frequently in the normothermic population
than in the hypothermic group
 We should maintain normothermia ( forced air warming
devices)

50. 1)Prevention-
 Maintain adequate depth of anaesthesia to prevent
tachycardia
 Measures to attenuate pressor responses to
laryngoscopy and endotracheal intubation
 To correct haemodynamic changes if preceding
myocardial ischaemia (tachycardia, hypotension)
2)Treatment of myocardial ischaemia without
accompanying haemodynamic alterations:
 In these patients nitroglycerine can be useful

51.  Nitroglycerine decreases preload and wall tension,
dilates epicardial coronary arteries and increases
subendocardial blood flow
3)Treatment of myocardial ischaemia accompanied by
tachycardia and hypertension
 After ensuring adequate ventilation, oxygenation and
anaesthetic depth, β blockers (esmolol, metropolol)
may be administered in a titrated manner provided
there is no evidence of CHF or bronchospasm

52.  Both can drastically reduce myocardial oxygen supply
 Volume replacement, restoring coronary perfusion and
slowing the rate may help
5) Severe resistant myocardial ischaemia:
 Occasionaly in case of severe myocardial ischaemia
resistant to all antianginal drugs, IABP can be useful; it
acutely decreases myocardial oxygen requirements and
may increase myocardial oxygen supply

53.  Once the diagnosis of acute MI is made, it is important to
monitor the patient carefully
 Pulse oximetry, NIBP/ABP,ECG
 100% oxygen should be administered, discontinue volatile
agent
 Aspirin325 mg –orally/RT and is continued
 Tachycardia is treated with IV β blockers like esmolol
 Nitroglycerine is the drug of choice in the presence of
normal to modestly elevated systemic BP
 Morphine is venodilator that reduces preload and oxygen
requirement, in pulm congestion complicating ACS

54.  Hypotension should be rapidly treated in order to
restore coronary perfusion pressure(CPP). If severe
hypotension (60-80 mm Hg systolic) persists despite
volume expansion, vasoactive or inotropic drugs may
be given to elevate CPP above critical value

55.  Sinus bradycardia is common- Atropine/temporary
pacemaker
Some patients with severe bradycardia may require
emergency cardiac pacing (transvenous or
transcutaneous as appropriate)
 Atrial fibrillation(AF) occurs in > 10% after acute MI
• Haemodynamically significant- cardioversion
• If well tolerated –β blocker therapy
 Ventricular tachycardia- electrical defibrillation/drugs
(lidocaine, procainamide, amiodarone)

56.  Ventricular fibrillation(VF) - rapid defibrillation
IABP
Insufficient evidence of benefit vs risk of prophylactic
administration in non cardiac surgery patients

57.  Myocardial ischemia and infarction is a major cause of
short and long term morbidity and mortality in the
surgical population
 ECG, 2 D ECHO and Cardiac Troponins are used for
diagnosis
 Identifying at risk patients helps in intraoperative
planning to reduce the consequences of ischaemia
 No role of prophylactic coronary revascularisation
 Attempt to reduce the risk of adverse outcome by
implementing aggressive preventive and treatment
modalities of ischemia and infarction.

58. THANK YOU