Acute lower limb ischemia: determinants of outcome

Previous studies have documented high rates of morbidity and death after acute peripheral arterial occlusion. To date, however, few studies have identified parameters predictive of successful therapy.

The Thrombolysis or Peripheral Arterial Surgery Trial of intraarterial recombinant urokinase or immediate operation for acute lower extremity arterial occlusion provided data on 544 patients randomized at 113 centers. A Cox proportional hazards multifactor analysis was performed to identify those main effects predictive of amputation-free survival and to document any baseline variables useful in deciding whether a patient would be treated best initially with thrombolysis or operation.

Of 28 variables analyzed, eight main effects were predictive of amputation-free survival. These included two demographic factors: white race (risk ratio [RR] = 1.75; p = 0.003) and younger age (RR = 1.015; p = 0.046). Comorbidities comprised four of the main effects: history of central nervous system disease (RR = 1.726; p = 0.005), history of malignancy (RR = 1.615; p = 0.024), congestive heart failure (RR = 2.202; p < 0.001), or low body weight (RR = 1.007 per pound; p = 0.006). The severity of the process was also predictive, as gauged by the presence of skin color changes (RR = 1.585, p = 0.007) or pain at rest (RR = 0.503; p = 0.003). All eight effects were similar in the two treatment groups; none of these variables predicted improved outcome with one form of initial therapy over the other (i.e., there was no therapy-by-variable interaction). The length of occlusion, however, predicted whether a patient would fare better with thrombolysis or operation. With a threshold occlusion length of 30 cm, the RR for longer occlusions to shorter occlusions was 43% better in patients who received thrombolysis, whereas the situation was reversed for those who were randomized to operation.

A variety of baseline variables can be identified that are predictive of outcome after treatment for acute lower extremity ischemia. In addition, the length of the occlusive process appears to predict whether a patient will be best served with thrombolysis or operative intervention; longer occlusions appear to respond best with an initial thrombolytic strategy.