Ann Thorac Surg 2006;81:145-147
© 2006 The Society of Thoracic Surgeons
Original article: Cardiovascular
Upper Extremity Arteriovenous Fistulas Induce Modest Hemodynamic Effect on the In Situ Internal Thoracic Artery
Rodeen Rahbar, MD
a
,
William R. McGee, BS
a
,
b
,
Thomas J. Birdas, MD
b
,
Satish Muluk, MD
b
,
James Magovern, MD
b
,
Thomas Maher, MD
b
,
*
a Department of General Surgery, Allegheny General Hospital, Pittsburgh, Pennsylvania
b Department of Cardiovascular Surgery, Allegheny General Hospital, Pittsburgh, Pennsylvania
Accepted for publication June 7, 2005.
* Address correspondence to Dr Maher, Department of Cardiothoracic Surgery, Allegheny General Hospital, 320 East North Ave, Pittsburgh, PA 15212 (Email: tmaher{at}wpahs.org).
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Abstract
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BACKGROUND: The left internal thoracic artery is the ideal conduit for coronary artery revascularization due to superior patency compared with venous grafts. The hemodynamic effects of an arterio-venous fistula on the native in situ internal thoracic artery and the potential for coronary flow steal after revascularization with the internal thoracic artery, are not well-characterized.
METHODS: Fifteen chronic hemodialysis patients with functioning left upper extremity arterio-venous fistulas were evaluated with the use of transthoracic color Doppler analysis. Flow characteristics of the left and right internal thoracic arteries at baseline, with arterio-venous fistula occluded, and during hemodialysis were recorded. Peak systolic and diastolic velocities for the right and left internal thoracic arteries were calculated for each fistula state (occluded, open, and on-dialysis). One-way analysis of variance was used to compare the different means.
RESULTS: Mean flow velocity calculations failed to identify any statistically significant differences between the ipsilateral and contralateral internal thoracic artery in any fistula state. In addition, mean internal thoracic flow velocities were similar between the different fistula states.
CONCLUSIONS: Changes in arteriovenous fistula flow state did not significantly alter Doppler flow hemodynamics of either the ipsilateral or contralateral in-situ internal thoracic artery. Further studies of the possible effects on internal thoracic arteries used as pedicled coronary grafts may be required.
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Introduction
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End-stage renal disease (ESRD) is a significant risk factor for morbidity and mortality in patients undergoing coronary artery bypass grafting (CABG). In a recent study of 279 ESRD patients, preoperative dialysis-dependent renal failure was associated with a 4.4 times increase in perioperative mortality after CABG [1]. Nevertheless, clinical data from small, retrospective trials suggest surgical coronary revascularization in patients with ESRD is associated with improved outcomes compared with medical therapy alone [2].
It is generally accepted that the internal thoracic artery (ITA) is a superior surgical conduit in any coronary revascularization procedure with established improved patency compared with venous conduit [3, 4]. Its superiority, however, has been challenged recently in the ESRD population on entirely different grounds. In a small study by Gaudino and colleagues [5], decreased flow velocities in the left ITA as well as myocardial hypokinesis was demonstrated in five post-CABG patients during hemodialysis. These patients all had upper extremity arteriovenous (AV) fistulas and an ipsilateral ITA-coronary graft, suggesting dialysis-induced reduction of ipsilateral ITA flow velocity as a potential etiology of coinciding ventricular wall hypokinesis. Other individual case reports of diminished ITA flow do exist in the literature, including a report by Kato and colleagues [6] demonstrating diastolic retrograde flow in the in situ ITA in a patient with ipsilateral ateriovenous fistula.
Given that an upper extremity fistula and its ipsilateral ITA arise from the same vascular root (the subclavian artery) it is possible that significant hemodynamic interference does occur among subclavian artery branches in patients with a functioning ipsilateral upper extremity AV fistula. Hemodynamic interference has in fact been well-documented in other patient groups; it is well-known that coronary-mammary steal can occur in patients with proximal subclavian stenosis [7, 8]. It is now suggested by Guadino and colleagues [5] that a similar, albeit distinct, mechanism of diminished flow may occur in the post-CABG dialysis-dependent patient population as well. We thus propose a formal study of the hemodynamic effects of an upper extremity AV fistula on the in situ internal thoracic arteries; significant results demonstrating either decreased flow velocities or frank retrograde flow "steal" of the in situ ITA would imply a need for preoperative assessment of dialysis-dependent ESRD patients prior to performing CABG.
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Material and Methods
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Within the patient population who receive routine outpatient dialysis at Allegheny General Hospital, 36 patients with functioning left upper extremity arteriovenous fistulas were identified. Patients undergoing hemodialysis through an indwelling vascular catheter were excluded. Twenty patients were then randomly selected by computer and invited to participate in our study; 15 agreed to do so. Our institutional review board approved the study. Funding was obtained through the Allegheny Singer Heart Institute.
The average patient age was 59.2 years; there were 9 male and 6 female patients. All patients underwent chronic hemodialysis and all patients had well-functioning left upper extremity arteriovenous fistulas. Ten (66%) patients had forearm fistulas. No patients had prior CABG, therefore all internal mammary arteries were in situ. Full patient demographics are reported in Table 1.
Doppler imaging of the left and right internal thoracic arteries was performed for three different AV fistula states: (1) fistula occluded, (2) fistula open, and (3) fistula connected to standard flow hemodialysis. A Phillips ATL 5000 Ultrasound machine (Philips Medical Systems, Bothell, WA) with a 7.4 MHz linear probe was used to obtain images of the right and left ITAs. Visualization of the ITA was obtained by placing the probe at the left and right third intercostal spaces; if difficulty was encountered with visualization at that level, the fourth intercostal space was used for verification. Both a single peak systolic and a single peak diastolic velocity measurement were obtained at one position for each ITA and for each fistula state (open, on hemodialysis, or occluded).
Statistical analysis was performed with the use of Stat View 5.0 (SAS Institute Inc, Cary, NC). The means of the peak systolic and end diastolic velocities for both ITAs and for each fistula state were then compared with the use of one-way analysis of variance (ANOVA). Fischer's projected least significant difference test, an ANOVA post-hoc test, was used to specifically examine the effect of the individual variables. Statistical significance was set at a p level less than 0.05.
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Results
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In three patients, the left ITA could not be visualized; therefore, data for only 12 patients is reported for the ITA. In one patient, the upper extremity arteriovenous fistula was found to be minimally stenotic but clearly functional with excellent flow on the hemodialysis machine; this patient was therefore not excluded from the study. The mean peak systolic and peak diastolic ITA velocities (PSV and PDV, respectively) in the different fistula states and for both sides are shown in Table 2
and represented graphically in Figures 1 and 2.
One-way ANOVA was performed for the peak systolic and peak diastolic velocity means. No statistical significant differences were found between the different fistula states (PSV, p = 0.66; PDV, p = 0.11); ITA site (PSV, p = 0.98; PDV, p = 0.84), or their interaction (PSV, p = 0.84; PDV, p = 0.9). The results of Fischer's protected least significant difference test are shown in Table 3. Peak diastolic velocity differences between occluded AV fistula and open AV fistula with (p = 0.09) or without (p = 0.06) hemodialysis approached, but did not reach, statistical significance.
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Comment
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Although ESRD is a significant factor for morbidity and mortality after coronary revascularization [1], acceptable results have been reported along with evidence of improved outcomes compared with medical therapy of coronary disease [2]. Recent isolated reports have raised concerns about the use of the left ITA as a pedicled graft in ESRD receiving hemodialysis through a left upper extremity arteriovenous fistula [5, 6]. We have found no information available in the literature regarding the hemodynamic changes of an AV fistula on the ipsilateral ITA flow. Our study addresses that issue.
After Doppler examination of the ITA flow both ipsilateral and contralateral to a functioning left upper extremity AV fistula, we were unable to demonstrate any significant differences. Furthermore, different hemodynamic states of the AV fistula (open, occluded, and during hemodialysis) failed to produce significant differences. Only differences in peak diastolic ITA velocities between the occluded and open AV fistula states approached statistical significance. This finding may be important, since it is well-known that the predominant hemodynamic change of the ITA after its use as coronary conduit is an increase in the diastolic flow and reversal of the physiologic systolic-diastolic ratio [9].
Our study has several limitations. The sample size may be inadequate to detect subtle differences. Risk factors can certainly exist that may induce significant hemodynamic interference in some patients. For example, IMA retrograde flow with an AV fistula has previously been demonstrated in a case report by Kato [6], but it was not observed in any of our patients. Factors known to predispose to steal, such as altered IMA anatomy and/or subclavian stenosis, may not have been present in the patient population of this study. Furthermore, it is impossible to predict with certainty if grafting of the IMA would alter hemodynamic resistance in a manner that could be conducive to hemodynamic interference. Additionally, anatomic location of the fistula may play an important role. A majority of the patients in this study had forearm AV fistulas; proximity of the fistula to the subclavian artery could potentially alter results.
In conclusion, our study found statistically insignificant small differences between average mean velocities in either internal thoracic artery with change in fistula state. There were also statistically insignificant small differences between the right and left internal thoracic arteries for each fistula state. From this data, it is concluded that AV fistula placement and use have modest hemodynamic effect on the in situ internal thoracic artery. Larger prospective studies of post-CABG and pre-CABG patients are needed to identify risk factors for potential AV fistula-internal thoracic artery hemodynamic interference.
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Acknowledgments
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The authors acknowledge funding through a grant from the Allegheny Singer Heart Institute.
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References
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- Liu JY, Birkmeyer NJ, Sanders JH, et al. Risks of morbidity and mortality in dialysis patients undergoing coronary artery bypass surgery Circulation 2000;102:2973-2977.[Abstract/Free Full Text]
- Keeley EC, McCullough PA. Coronary revascularization in patients with end-stage renal diseaserisks, benefits, and optimal strategies. Rev Cardiovasc Med 2003;4:125-130.[Medline]
- Cameron A, Kemp Jr HG, Green GE. Bypass surgery with the internal mammary artery graft15 year follow-up. Circulation 1986;74:III30-III36.
- Loop FD, Lytle BW, Cosgrove DM, et al. Influence of the internal-mammary-artery graft on 10-year survival and other cardiac events N Engl J Med 1986;314:1-6.[Abstract]
- Gaudino M, Serricchio M, Luciani N, et al. Risks of using internal thoracic artery grafts in patients in chronic hemodialysis via upper extremity arteriovenous fistula Circulation 2003;107:2653-2655.[Abstract/Free Full Text]
- Kato H, Ikawa S, Hayashi A, Yokoyama K. Internal mammary artery steal in a dialysis patient Ann Thorac Surg 2003;75:270-271.[Abstract/Free Full Text]
- Elian D, Gerniak A, Guetta V, et al. Subclavian coronary steal syndromean obligatory common fate between subclavian artery, internal mammary graft and coronary circulation. Cardiology 2002;97:175-179.[Medline]
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- Gaudino M, Serricchio M, Tondi P, et al. Non-invasive evaluation of mammary artery flow reserve and adequacy to increased myocardial oxygen demand Eur J Cardiothorac Surg 1998;13:404-409.
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Abstract
Introduction
