MANAGEMENT OF ASYMPTOMATIC POPLITEAL ANEURYSMS - THE USE OF A MARKOV DECISION TREE TO DETERMINE THE CRITERIA FOR A CONSERVATIVE APPROACH

With recent improvements in the results of treatment of popliteal aneurysms, it has been suggested that it may be preferable to treat asymptomatic aneurysms conservatively and to operate only if symptoms develop. This hypothesis has been tested using decision analysis, with sensitivity and threshold analysis to establish the conditions under which such a policy would be appropriate. A Markov decision tree has been used to model the problem and the relevant probabilities have been obtained from a review of the current literature. A computer spreadsheet was used to calculate the results of policies of immediate operation or operation only if symptoms occur. Sensitivity and threshold analysis have been carried out to assess the effect of inaccuracy or alteration in the key variables and to determine the optimum policy under different conditions. The results suggest that early elective operation produces better results than conservative management at 1-2 years after presentation. Sensitivity analysis reveals that the most crucial data are the rate of development of symptoms in patients with asymptomatic aneurysms and the expected limb loss and mortality of treatment for symptomatic aneurysms. Threshold analysis has been used to define the values of these parameters that would be necessary for conservative management to be preferred. It is concluded that, based upon the currently available data, the optimum policy is elective treatment of asymptomatic aneurysms. To adopt a conservative approach it would need to be shown that symptomatic aneurysms could be treated with mortality and limb loss close to that of elective surgery, or that a group of patients could be selected in whom the risk of development of symptoms is less than 10% per year. © 1993 Grune & Stratton Ltd.