PERIOPERATIVE MYOCARDIAL INFARCTION

DR .Y. SASIKUMAR

Perioperative myocardial infarction ( PMI ) is the common cause of morbidity and mortality in patients who have had noncardiac surgery.

INCIDENCE

5.8% overall risk of postoperative major cardiac complications in patients undergoing

major noncardiac surgical procedures.

Defining PMI, is often difficult :

Most PMIs occur without symptoms in anesthetized or sedated patients.

The creatine kinase-MB isoenzyme has limited sensitivity and specificity because of coexisting skeletal muscle injury.

Consequently, PMI was often recognized late (postoperative day 3 to 5), resulting in high (30% to 70%) mortality.

Two distinct mechanisms may lead to PMI:

Acute coronary syndrome.

Prolonged myocardial oxygen supply-demand imbalance in the presence of stable coronary artery disease (CAD).

Pathophysiology

Acute coronary syndrome occurs when an unstable or vulnerable plaque undergoes spontaneous rupture, fissuring, or erosion, leading to acute coronary thrombosis, ischemia, and infarction.

External stressors ,those occurring postoperatively are believed to contribute.

Acute coronary syndrome (Type 1)

The sympathetic induced Tachycardia and Hypertension, common in the perioperative period, may exert shear stress, leading to rupture of plaques.

Increased postoperative procoagulants (fibrinogen, factor VIII coagulant, von Willebrand factor, α1-antitrypsin), increased platelet reactivity, decreased endogenous anticoagulants (protein C, antithrombin III), and decreased fibrinolysis have been reported.

Tachycardia is the most common cause of postoperative oxygen supply-demand imbalance.

Heart rates >80 bpm in patients with significant CAD can lead to prolonged ischemia and PMI.

Myocardial oxygen supply – demand imbalance ( Type 2)

Postoperative hypotension (hypovolemia, bleeding, or systemic vasodilatation), hypertension (elevated stress hormones, vasoconstriction), anemia, hypoxemia, and hypercarbia aggravate ischemia.

Stress-induced and ischemia-induced coronary vasoconstriction impairs coronary perfusion.

The 2007 ACC/AHA guidelines on cardiovascular evaluation for noncardiac surgery concluded that three elements must be assessed to determine the risk of cardiac events :

Patient specific clinical variables.

Exercise capacity.

Surgery-specific risk.

PRE-OPERATIVE EVALUATION

Major predictors that require intensive management and may lead to delay in or cancellation of the operative procedure.

Unstable coronary syndromes including unstable angina or recent MI.

Decompensated heart failure including NYHA functional class IV or worsening or new-onset HF

Significant arrhythmias

Valvular heart disease-severe AS/ severe MS

Patient specific clinical variables

Other clinical predictors that warrant careful assessment of current status.

History of ischemic heart disease

History of cerebrovascular disease

History of compensated heart failure or prior heart failure

Diabetes mellitus

Renal insufficiency

The 2007 ACC/AHA guidelines on cardiovascular evaluation for noncardiac surgery concluded that three elements must be assessed to determine the risk of cardiac events :

Patient specific clinical variables.

Exercise capacity.

Surgery-specific risk.

PRE-OPERATIVE EVALUATION

Patients with good functional status have a lower risk of complications.

Functional status can be expressed in metabolic equivalents (MET).

1 MET is defined as the oxygen uptake in a sitting position (3.5 mL O2 uptake/kg per min).

Perioperative cardiac risk is increased in patients unable to meet a 4-MET demand during most normal daily activities.

Exercise capacity

Indicators of functional status :

Can walk up a flight of steps = 4 METs

Can do heavy work around the house such as scrubbing floors or lifting or moving heavy furniture = between 4 and 10 METs

Can participate in strenuous sports such as swimming, singles tennis, football, basketball = = >10 METs

The 2007 ACC/AHA guidelines on cardiovascular evaluation for noncardiac surgery concluded that three elements must be assessed to determine the risk of cardiac events :

Patient specific clinical variables.

Exercise capacity.

Surgery-specific risk.

PRE-OPERATIVE EVALUATION

The type and timing of surgery significantly affects the patient's risk of perioperative cardiac complications.

High-risk procedures - Rate of cardiac death or nonfatal MI is > 5%

Intermediate-risk procedures – 1% - 5%

Low-risk procedures - < 1%

SURGERY-SPECIFIC RISK 

Institutional and/or individual surgeon experience with the procedure may increase or lower the risk.

Emergency surgery is associated with particularly high risk (5 times) than with elective procedures.

Multivariable analyses, identified combinations of factors, based upon routine clinical information and laboratory tests, that used to estimate the risk of cardiac complications.

It was developed by Goldman, Detsky, and Eagle

RISK INDICES

High-risk type of surgery ( vascular surgery and open intraperitoneal or intrathoracic procedures)

History of ischemic heart disease.

History of HF.

History of cerebrovascular disease.

Diabetes mellitus requiring treatment with insulin.

Preoperative serum creatinine >2.0 mg/dL (177 µmol/L).

Revised Goldman cardiac risk index

Rate of cardiac death, nonfatal myocardial infarction, and nonfatal cardiac arrest according to the number of predictors.

No risk factors - 0.4 %

One risk factor - 1.0 %

Two risk factors - 2.4 %

Three or more risk factors - 5.4 %

RECOMMENDATIONS CLASS

LEVEL

For patients with cardiac risk factor (s) undergoing inter meadiate or high – risk surgery

I B

For patients with cardiac risk factor (s) undergoing low - risk surgery

IIa B

For patients with no cardiac risk factors undergoing high / intermediate risk surgery

IIb B

Recommendation for pre –op ECG

RECOMMENDATIONS CLASS LEVEL

For patients with severe valvular heart disease.

I C

In patients undergoing high-risk surgery for LV assessment.

IIa C

Recommendations for pre-op ECHO

RECOMMENDATION CLASS LEVEL

For patients with > 2 cardiac risk factors undergoing high risk surgery

I B

For patients with < 3 cardiac risk factors undergoing high risk surgery

IIb B

For patients undergoing intermediate risk surgery

IIb C

Recommendations for pre-op stress test

RECOMMENDATION CLASS LEVEL

Acute STEMI / NON-STEMI /Unstable angina

Angina unresponsive to medical treatment I A

Cardiac stable patients undergoing high risk surgery

IIb

B

Cardiac stable patients undergoing intermediate risk surgery

IIb C

Recommendations for pre-op coronary Angiography

Diagnosis complicated by lack of symptomatic presentation in about half of patients with perioperative MI.

Deveraux et al, proposed the following diagnostic criteria:

Rise in troponin (or fall after an elevated value) plus one or more of following.

Ischemic signs or symptoms (e.g., SOB)

New pathologic Q waves on ECG.

New wall motion abnormality or fixed defect on echo.

Diagnosis of perioperative MI

BETA BLOCKERS Beta blockers have been used in patients undergoing

noncardiac sx, in those at high risk.

Possible mechanisms for such a benefit include

Reduction in myocardial oxygen demand Increase in myocardial oxygen delivery due to

prolongation of coronary diastolic filling time.

Prevention of fatal ventricular arrhythmias,

protection against plaque rupture in the setting of increased sympathetic activity .

Prevention and Treatment

The large Perioperative Ischemic Evaluation (POISE) trial reported increased mortality and, mostly in association with hypotension in patients treated with metoprolol.

The evidence does not support the initiation of prophylactic perioperative beta blocker therapy in most patients undergoing noncardiac surgery (RCRI ≤2).

POISE does not exclude benefit in high risk patients (RCRI ≥3)

If beta blockers are used 

Beta-1 selective agent, begin as an outpatient up to 30 days prior to operation, titrating to HR 50-60 BPM.

Longer-acting agent (atenolol or bisoprolol) may be more effective than shorter-acting agent (metoprolol).

Benefit was demonstrated when therapy was begun one month before surgery.

Statins

Recommend in those already being treated or with other indications for treatment.

There is no convincing evidence of benefit of starting therapy in those patients who otherwise do not meet accepted criteria for initiation of statin therapy.

Aspirin

The accepted practice is to discontinue aspirin 5 to 7 days before a surgical procedure to prevent bleeding.

Recent analyses suggest that there is only a mild increase in the frequency of bleeding with aspirin and no increase in mortality.

Possible exceptions are intracranial and prostate surgery.

Two recent prospective randomized trials (Coronary Artery Revascularization Prophylaxis [CARP] and Dutch Echographic Cardiac Risk Evaluation Applying Stress Echo [DECREASE] failed to show such benefit.

Revascularization prior to noncardiac surgery should only be performed in patients who have high-risk coronary anatomy that fulfill current criteria applicable to all patients with coronary disease.

REVASCULARIZATION

Treatment and prevention of postoperative myocardial ischemia and MI.

European Heart Journal (2009)

British journal of Anaesthesia 107; 83-96 (2011)

Up Todate 2011 (19.3)

Medscape

REFERENCES

Thank you