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Transfer function index: is it a reliable method for vein graft surveillance?
1Department of Vascular Surgery, Auckland Hospital, Auckland, New Zealand. chuanpingtan@hotmail.com
Introduction:
Duplex ultrasound scanning is currently the best available non-invasive method for vein graft surveillance. However, it is expensive and its results are highly operator dependent. The aim of the present study is to compare, another non-invasive method of graft surveillance, the transfer function index (TFI), with duplex ultrasound scanning in identifying significant stenoses in infrainguinal saphenous vein bypass grafts.
Methods:
Initially a retrospective pilot study was carried out between 1 January and 30 June 2002. Patients were identified from the vascular surgical operation database. The ultrasound report and TFI result of each patient were reviewed. Then a prospective comparative study was carried out between 1 July and 31 December 2002. Duplex ultrasound and TFI studies were undertaken at the 3 month interval. Comparisons were made between the accuracy and predictive value of ultrasound versus TFI in assessing significant graft stenosis.
Results:
In the present retrospective study TFI measurement was significantly lower in the at-risk grafts than in the normal grafts (P = 0.001). In the prospective group TFI was again found to be significantly lower in the at-risk group (mean TFI 0.86) than in the normal group (mean TFI 1.064, P = 0.001). The sensitivity and specificity of the TFI were 92% and 97%, respectively. The accuracy of TFI was calculated to be 98%.
Conclusion:
TFI is an accurate non-invasive method of vascular graft surveillance. TFI can be carried out in the vascular clinic and is quick and inexpensive. Normally TFI could replace duplex ultrasound surveillance, with ultrasound being reserved for those with an abnormal TFI.
