Modified Cardiac Risk Index
     

Overview :

A modified cardiac risk index can be used to perform cardiac risk assessment prior to noncardiac surgery and to estimate a likelihood ratio for the patient. If the overall cardiac complication rate for the a noncardiac surgery (pretest probabilities) is known at an institution, then the likelihood ratio can be used to calculate the cardiac risk for the patient (post-test probability).

Finding

Grouping

Points

myocardial infarction within 6 months

coronary artery disease

10

myocardial infarction more than 6 months ago

coronary artery disease

5

Class III Canadian Cardiovascular Society angina

coronary artery disease

10

Class IV Canadian Cardiovascular Society angina

coronary artery disease

20

unstable angina within 6 months

coronary artery disease

10

alveolar pulmonary edema within 1 week

alveolar pulmonary edema

10

alveolar pulmonary edema, ever

alveolar pulmonary edema

5

suspected critical aortic stenosis

valvular disease

20

rhythm other than sinus or sinus plus atrial premature beats on last preoperative ECG

arrhythmias

5

more than 5 premature ventricular contractions at any time prior to surgery

arrhythmias

5

poor general medical status (pO2 < 60 mm Hg, pCO2 > 50 mm Hg, K < 3.0 mEq/L, HCO3 < 20 mEq/L, BUN > 50 mg/dL, creatinine > 3 mg/dL, abnormal SGOT, signs of chronic liver disease, bedridden for non-cardiac causes)

5

age over 70

5

emergency operation

10

The score is the sum from the individual points, up to a maximum score of 50. From the score, a likelihood ratio for the patient can be estimated.

Score vs Likelihood Ratios (from nomogram Figure 3, page 218)

Score

Likelihood Ratio

0

0.0004

5

0.23

10

1.10

20

4.06

30

7.54

40

10.85

50

13.51

A line approximating this data can be given as:

likelihood ratio =

= (-0.000138 * (score ^3)) + (0.0119553 * (score ^2)) + (0.0175033 * (score)) - 0.06541

If the rate of cardiac complications for a given procedure is known (pre-test probability), then Baye's formula can be used to estimate the risk of cardiac complications for the patient (post-test probability), as

post-test probability =

= ((pre-test probability) * (likelihood ratio)) / (((pre-test probability) * (likelihood ratio)) + (1 - (pre-test probability)))

Likelihood Ratios for Modified Index (at Toronto General Hospital)

Points

Class

Major Surgery

Minor Surgery

All Surgery

0 - 15

I

0.42

0.39

0.43

15 - 30

II

3.58

2.75

3.38

> 30

III

14.93

12.20

10.60

  References:

Detsky AS, Abrams HB, et al. Predicting Cardiac Complications in Patients Undergoing Non-cardiac Surgery. J Gen Intern Med. 1986; 1:211-219.

Devereaux PJ, Ghali WA, et al. Physician estimates of perioperative cardiac risk in patients undergoing noncardiac surgery. Arch Intern Med. 1999; 159: 713-717.

Reilly DF, McNeely MJ, et al. Self-reported exercise tolerance and the risk of serious perioperative complications. Arch Intern Med. 1999; 159: 2185-2192.