Risk scores for myocardial infarction and major adverse cardiac event following major amputation for limb ischemia with internal VQI validation.

OBJECTIVE

Numerous cardiac risk evaluation models exist for patients undergoing major vascular surgical interventions. These models, however, do not consider patients undergoing major amputation for limb ischemia. The purpose of this study was to create risk scores for myocardial infarction (MI) and composite adverse cardiac events after major amputation performed for limb ischemia.

METHODS

The first step was univariable analysis for the outcomes of perioperative MI and major adverse cardiac events (MACEs) for patients undergoing nonemergent major amputation for limb ischemia (primary risk score study group n = 10,260, validation group n = 5130). Univariable analysis was conducted with χ testing for categorical variables and the Student t test for comparison of means of ordinal variables. Next, binary logistic regression analysis was performed for the outcomes of perioperative MI and MACEs using variables that had achieved a univariable P value of .1 or less. Using this regression analysis, it was determined which variables have a multivariable association for the outcomes as defined by a multivariable regression P value of .05 or less. Weighted cumulative event scores were then created for the outcomes of perioperative MI and MACEs. Variables with a multivariable P value of .05 or less on the regression analysis were included in the scores and weighted based on their respective regression beta coefficient in a point scale. Area under the curve (AUC) analysis and Hosmer-Lemeshow goodness of fit was also conducted for the validation cohort using the same risk score variables and scoring system as the primary study group. A supplementary machine learning analysis was performed to reinforce variable importance.

RESULTS

Variables with a significant (P < .05) multivariable association and meeting inclusion or the MACE risk score included advancing age (adjusted odds ratio [aOR], 1.02/unit time; P < .001), female sex (aOR, 1.28; P = .01), asymptomatic coronary artery disease (CAD) (aOR, 1.36; P = .009), symptomatic CAD (aOR, 1.28; P = .049), coronary artery bypass graft (CABG) more than 5 years ago (aOR, 1.37; P = .014), class II congestive heart failure (CHF) (aOR, 1.30; P = .05), class III CHF (aOR, 1.75; P = .002), class IV CHF (aOR, 5.26, P < .001), COPD (aOR, 1.29; P = .012), end-stage renal disease (ESRD) (aOR, 2.20, P < .001), and renal insufficiency (aOR, 1.76, P < .001). Regarding the risk score for MACE following major amputation for limb ischemia, patients with risk scores of 1 or greater experienced MACEs in just 2.6% of cases. The MACE rate increased in an exponential fashion with rising risk score with rates of 26.9% for patients with scores 16 and higher indicating a 10-fold increased risk. In MI analysis, the following variables achieved a multivariable P value of .05 or less and were thus ultimately included in the risk score for MI: advancing age (aOR, 1.02/unit time; P = .007), asymptomatic CAD (aOR, 1.52; P = .022), symptomatic CAD (aOR, 1.56; P = .038), history of CABG more than 5 years ago (aOR, 1.51; P = .029), class III CHF (aOR, 1.84; P = .019), class IV CHF (aOR, 3.07; P = .002), ESRD on dialysis (aOR, 1.95, P < .001), renal insufficiency (aOR, 1.95, P < .001), and not being on an antiplatelet preoperative (protective aOR 0.65; P = .007). Regarding the risk score for MI, patients with risk scores of 0 or lower had MI rates of just 0.5% with steep escalation noted with advancing risk score as patients with risk scores of 10 and higher had MI rates of 6.0%, indicating a 12-fold higher risk of MI. Risk score AUC values were 0.70 and 0.71, respectively. Patients with MACEs and MI perioperatively had survival rates as low as 42% by the 2-year mark vs 67% to 69% for those without (P < .001). Machine learning confirmed the importance of the key variables and achieved AUC values ranging from 0.77 to 0.94.

CONCLUSIONS

Risk scores for perioperative MI and MACEs during hospitalization for major amputation owing to limb ischemia have been created with accurate internal validation. These data have the potential to impact preoperative and perioperative patient management to reduce adverse event rates. The most impactful variables increasing risk of MI and MACEs are advancing age, history of class III or IV CHF, history of CAD, CABG more than 5 years ago, renal insufficiency, and ESRD.