TRANSIT TIME FLOWMETRY IN CORONARY SURGERY-AN IMPORTANT TOOL IN GRAFT VERIFICATION

Th e aim of this study was to analyze the Transit time fl ow measurement (TTFM) experience in the fi rst  CABG operations. First  patients had coronary artery bypass grafting (CABG) performed in Cardiovascular Clinic, University Clinical Centre Tuzla, Bosnia and Herzegovina, between September,  and September, . CABG without use of cardiopulmonary bypass (CPB)-(OPCAB) was used as the preferential surgical method both because this method is reported to have equal or better results than CABG with use of CPB (ONCAB), and because of the signifi cant cost savings realized. TTFM was routinely used in all grafts as a quality assurance measure. Criteria for a poor functioning graft were: low mean fl ow (MF), pulsatility index (PI) above  and a poor diastolic fl ow pattern. When no reversible cause of poor TTFM results were identifi ed the graft was revised. A total of  grafts in OPCAB group and  in ONCAB group were performed. A total of  grafts (,) in  patients (,) were revised in OPCAB group, and  grafts (,) in  patients (,) in ONCAB group.  patient in OPCAB group needed  graft revisions. Graft revisions were more common in OPCAB, but with no signifi cant diff erence (p=,). Th e most frequently revised graft was LAD graft in both groups. Although the percentage of grafts revised are relatively low, it is still very important to record TTFM. More than  of patients in both groups needed graft revision. Although TTFM does not guarantee that grafts will stay open for a prolonged period of time we certainly believe that grafts that are occluded at the time of surgery will continue to stay occluded. TTFM is especially critical in OPCAB surgery where the technical challenge of grafting is higher then in ONCAB.


Introduction
Graft patency remains an important issue in coronary surgery ().Early graft occlusion is a frequent cause of early death and perioperative myocardial infarction.Occluded grafts will also limit the long term value of the operation.An accurate simple method of graft verification is therefore important ().We have routinely used Transit time fl ow measurement (TTFM) (Cardiomed Flowmeter, Medistim AS, Oslo, Norway) in all patients after starting our cardiac surgery program.Th e purpose of this study was to analyze the TTFM experience in the fi rst  coronary artery bypass grafting (CABG) operations performed until September, .

Materials and Methods
First  patients had CABG performed in Cardiovascular Clinic, University Clinical Centre Tuzla, Bosnia and Herzegovina, between September,  and September, .CABG without use of cardiopulmonary bypass (CPB)-(OPCAB) was used as the preferential surgical method both because this method is reported to have equal or better results than CABG with use of CPB (ONCAB) and because of the signifi cant cost savings realized ().However about  of all operations were done as ONCAB since it was necessary to retain perfusionist profi ciency.Th e patients operating room records were examined and in cases where a graft was performed more than once, the graft was counted as revised.
Grafts were revised according to criteria described earlier.In brief this criteria describes a poor functioning graft as a graft with low mean fl ow (MF), pulsatility index (PI) above  and a poor diastolic fl ow pattern ().In grafts where borderline values were obtained measurements were repeated after a short time period to allow removal of any air in the grafts.Sometimes papaverine was utilized to relieve any spasm.Also the mean blood pressure was sometimes raised to increase the perfusion pressure.A fi nal assessment of the TTFM results were obtained after administration of protamin and the graft accepted or revised.
In OPCAB surgery it is our routine to utilize proximal coronary snaring during grafting to control blood fl ow in the native vessel.Th is snare was left in place until after measurement of TTFM.Flows were measured with and without proximal snare.In this way obstruction at the toe of the anastomosis may be detected, since fl ow would decrease or stop completely when the snare was applied.When non acceptable TTFM parameters were seen graft revision was performed and any reason for graft obstruction recorded.Measurements were repeated after revision.In most cases the grafts were revised without CPB, but in some cases CPB was utilized due to technical considerations or hemodynamic instability.
In ONCAB surgery we do not use proximal snare during grafting and in general did not find it justified to use snare for measurements since at least theoretically snares may cause vessel damage.Th e grafts were examined after completion of all bypasses and after discontinuation of CPB.If grafts needed revision, CPB would be reinstituted and the grafts revised with or without cross clamp and cardioplegia, depending on the situation.

Results
A total of  grafts in OPCAB group and  in ON-CAB group were performed.A total of  grafts (,) in  patients (,) were revised in OPCAB group, and  grafts (,) in  patients (,) in ONCAB group. patient in OPCAB group needed  graft revisions.As can be seen graft revisions were more common in OPCAB group but with no signifi cant diff erence (p=,) (Table ).
As can be seen the most frequently revised graft in both groups was LAD graft (Table ).Graft revisions were seldom for RCA and DIAG grafts.Th ere were no significant diff erence in incidence of revision for same grafts in both groups.In both groups all grafts could be revised successfully and graft patency at the time of chest closure documented.

Discussion
Graft patency is an obvious goal in coronary surgery ().Early occlusion of grafts is the main cause of perioperative infarction and mortality.Many patients with graft occlusion survive only to develop recurrent angina postoperatively resulting in less than optimal clinical results or re-interventions ().
When interest in OPCAB surgery in the early  started to increase it became obvious to surgeons doing this type of operations that the technical challenge was higher than with ONCAB.In the beginning anastomosis were performed without mechanical stabilization as were done by surgeons from South America who had performed OPCAB surgery for two decades ().It therefore became a major task to find a practical instrument for graft verification.
Based on the experience from Buffalo, USA () we used TTFM to verify every graft performed in every patient since the initiation of the cardiac program.
The causes of revision were multiple with about  of the revisions clearly technique related and the rest more related to vessel factors.Most revision were seen in the graft to LAD whether the operation was done as OPCAB or ONCAB.However the rate of revision was higher in OPCAB operations but with no signifi cant diff erence.Th e fact that snare was not utilized in ONCAB may underestimate the graft problems in this group since obstruction at the toe of the graft may be missed when snare is not utilized.
Almost surprisingly graft revision in other territories were much lower than in the LAD area.Th is may be due to the fact that these other grafts were mainly veins and that the higher problems in LAD was due to the preferential use of LIMA to graft LAD.Arterial grafts are as known technically more difficult.Th ere may be some underreporting of revision in these series since the numbers were counted from the operation room report.In some cases it is possible that the surgeon has omitted recording of graft revisions.
Although the percentage of grafts revised are relatively low it is still very important to record TTFM.More than  of all patients needed graft revision.

Conclusion
Although TTFM does not guarantee that grafts will stay open for a prolonged period of time, we certainly believe that grafts that are occluded at the time of surgery will continue to stay occluded.TTFM is especially critical in OPCAB surgery where the technical challenge of grafting is higher then in ONCAB.In conclusion it is our opinion that TTFM should be performed in all coronary surgery.

List of Abbreviations
CABG-coronary artery bypass grafting CPB-cardiopulmonary bypass CX-Circumfl ex artery DIAG-Diagonal artery LAD-Left anterior descending artery OPCAB-coronary artery bypass grafting without use of cardiopulmonary bypass ONCAB-coronary artery bypass grafting with use of cardiopulmonary bypass RCA-Right coronary artery TTFM-Transit time fl ow measurement

TABLE 1 .
Total number of patients with revisions and revised grafts in both groups