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R-P Time Ratio: A Novel Index of Lower Extremity Arterial Hemodynamic Assessment
Jun Fujisaki1, Makoto Utsunomiya2, Makiko Kaneko1
1Department of Clinical Functional Physiology, Toho University Ohashi Medical Center, Meguro-Ku, Tokyo, Japan.
Objective:
Ankle-brachial index (ABI) is widely used for the blood flow assessment of the lower extremity arteries. In recent years, the number of patients with arteriosclerosis obliterans, including below-knee lesions (BK), has been increasing with the increase of diabetes patients and patients undergoing dialysis. The blood flow assessment by ABI in this patient group or below-knee arteries is considered inadequate. R-P time ratio (RPR) may be useful in this patient group. In this study, to investigate a hemodynamic assessment of the lower extremity arteries by duplex ultrasound, a comparative study of blood flow assessment in the presence or absence of lesions and blood flow improvement before and after endovascular treatment (EVT) using ABI and RPR was performed.
Subjects:
The control group consisted of 107 patients without lesions in their lower extremity arteries between April 2019 and September 2020. The lesion group consisted of 102 patients with 135 lesions (above-knee: 75 lesions, below-knee: anterior tibial artery [ATA]: 35 lesions, posterior tibial artery [PTA]: 25 lesions) who underwent EVT for lesions beyond the common femoral artery (CFA) and received duplex ultrasonography and an ABI test at the same timing before and after EVT.
Methods:
The blood flow waveform sampling on CFA was performed using the pulse Doppler method, and the time from the peak of the electrocardiogram R wave to the peak of the simultaneous phase Doppler blood flow waveform (R-P time) was measured. Similarly, R-P time was measured for ATA and PTA at the ankle joint, and ATA/CFA RPR and PTA/CFA RPR were calculated based on the R-P time of CFA. ABI and RPR were compared between the control group and the lesion group. In addition, ABI and RPR were investigated as indices for evaluating blood flow improvement before and after EVT.
Results:
ABI was significantly lower, and RPR was significantly higher in the lesion group than in the control group. RPR showed a negative correlation with ABI (r = -0.677). The comparison of before and after EVT showed that ABI and RPR were significantly improved after EVT (p < 0.001) in above-knee lesions, and RPR was improved considerably after EVT (p < 0.001) in BK.
Conclusion:
The possibility of a new index, RPR, to evaluate the hemodynamics of lower extremity arteries more accurately compared to the conventional assessment by ABI in below-knee arteries was suggested.
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