Electro Stethoscope in Detect Arteriovenous Fistula (AVF) Stenosis
Electro Stethoscope in Detect Arteriovenous Fistula (AVF) Stenosis
The incidence and prevalence of end-stage renal disease (ESRD) in Taiwan are both the highest
 worldwide from 2001 to 2008. In Taiwan, more than 90% of the ESRD patients are hemodialysis
 patients. Either arteriovenous fistula (AVF) or arteriovenous graft (AV graft) is essential
 for the vascular access of these patients. However, frequent AVF stenosis or thrombosis
 occurs in 10-30% hemodialytic patients, and the rates are even higher, around 30-70%, in
 those who has a past history of AVF/AV graft stenosis. Therefore, early detection of AVF
 stenosis is essential in caring for these hemodialysis patients in terms of medical economics
 and psychological impact. Unfortunately, angiographic study is expensive and invasive and
 needs contrast medium injection. The diagnostic accuracy of color duplex ultrasound in AVF
 stenosis remains satisfactory, but it is not always available when decreased AVF flow or an
 acute thrombotic event occurs. Continuous AVF/ AV graft flow monitoring by patient himself is
 a better option in terms of long-term care. Previous study indicated that stethoscope
 waveform analysis could be used as an alternative to diagnosis of vascular stenosis.
 Therefore, we aim to investigate AVF/ AV graft stenosis by using the electronic stethoscope
 (3M Littmann) for AVF sound recording, followed by software analysis by using waveform
 decomposition, principle component analysis (PCA) and sequential forward selection algorithm
 [xx]. Our study results will provide a new diagnostic option, which is low cost, non-invasive
 and self-monitoring, of AVF stenosis in ESRD patients.
Hemodialysis is a well-established method for removal of fluid and uremic toxins and
 prolonging survival in patients with end-stage renal disease (ESRD). The most common
 permanent vascular assesses are autogenous and non-autogenous arteriovenous (AV) fistula,
 referred as AV fistula and AV graft, respectively. In Taiwan, both incidence and prevalence
 of ESRD remain highest worldwide. However, frequent vascular stenosis/ thrombosis events
 occurred because of repeated needle punctures. These will exert a large economic burden to
 our society and psychological impacts on ESRD patients [1]. Therefore, it is essential to
 develop an easy and patient-centered method to monitor the flow status in either AV fistula
 or AV graft.

 Physical examination and auscultation are simple monitoring methods to assess the vascular
 access. There were several signs reported to be associated vascular stenosis, such as
 prolonged bleeding, arm edema, and changes in pulse characteristics of the vascular access,
 but they need a high level of skill and experience from the operator, such as doctors and
 nurses [2].

 Unfortunately, angiographic study is expensive and invasive and needs contrast medium
 injection. The diagnostic accuracy of color duplex ultrasound in AVF stenosis remains
 satisfactory, but it is not always available when decreased AVF flow or an acute thrombotic
 event occurs. Continuous AVF/ AV graft flow monitoring by patient himself is a better option
 in terms of long-term care. Previous study indicated that stethoscope waveform analysis could
 be used as an alternative to diagnosis of vascular stenosis. Previous acoustic studies
 indicated that increased sound intensity, extra sounds, and higher spectral energy
 infrequency domain, ranging between 300 Hz and 1000 Hz. These findings are associated with
 the change from laminar flow to turbulent flow downstream the site of vascular stenosis [3].
 In addition, phonoangiography studies pointed out that the systolic peak of stenotic segment
 is higher and narrower in the time domain compared to non-stenotic segment Methods: This is
 an observational cohort study. We plan to recruit 150 eligible patients with ESRD under
 regular hemodialysis for at least one year in national Taiwan University Hospital.

 1. Data gathering A. The first group of patients (study group) will be recruited from hose
 referred to endovascular intervention, e.g. angioplasty, due to vascular access
 dysfunction (n=30). An electronic stethoscope (3M-Littmann) will be used to record
 digital sound signals at 5 points with 30 seconds each, including AV junction, proximal
 and distal to both needle puncture sites, respectively. All data will be transferred to
 a computer for further anlaysis.

 B. The second group (validation cohort) will be recruited from patients with regular
 hemodialysis (HD) and received angioplasty at National Taiwan University Hospital
 (n=120). Those patients who received angioplasty for AVF or AV graft stenosis will also
 received follow-up angiography 12 weeks after angioplasty. We will record digital AVF/AV
 graft sound signals as mentioned above. In addition, blood pressure and AVF/AVG venous
 pressure, heart rate will be recorded. Diameter stenosis of restenotic segment will also
 be recorded and a diameter stenosis of 50% is regarded as significant.

 2. Post-processing The proposed method is based on the analysis of the envelope of the
 sound signals. Before, calculating the envelope, all signals will be down-sampled to 2k
 Hz, followed by a linear-phase, finite impulse response low-pass filter. PCA will then
 be applied to analysis as described previously [1-4]. PCA (principal components
 analysis)

 3. Analysis Sensitivity, specificity and diagnostic accuracy will be calculated based on
 each diagnostic criteria or basal function. Area under ROC curve will be calculated
 based on each diagnostic criteria derived from PCA method.
Inclusion Criteria:

 1. Age is more than 20 year-old.

 2. End-stage renal disease with regular hemodialysis for more than one year

 Exclusion Criteria:

 1. AVF/ AV graft is not located in upper arm.