### Description

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