Transit-time flow measurement (TTFM) is the most widely used technique for intra-operative graft quality control in coronary artery bypass surgery (CABG) [1-3]. However, for more than 20 years vein graft quality control had been traditionally done with a roller-pump flow measurement (RPFM) as the standard method, up to the time when offpump coronary artery bypass grafting was introduced as the standard revascularization method in the year 2009 at our institute. According to RPFM, the proximal side of a vein bypass is cannulated and connected with a roller-pump after completion of the distal anastomosis. Thereafter, a cardioplegic solution is perfused with a constant pressure of 80 mmHg and the flow rate is measured [4]. The aim of the present study is to compare TTFM with RPFM.

From February to September 2005, 31 patients (5 females)

undergoing CABG at our institute were included into the study. All patients had a preoperative left ventricular ejection fraction > 50%. The average age was 67 years. Twenty four (77%) patients undergoing CABG had a left main stem stenosis. Six patients (19%) suffered from diabetes mellitus, and eight patients (26%) had a myocardial infarction in their medical history. All patients were operated with cardiopulmonary bypass for ioslated coronary revascularization. In those patients, 27 distal anastomoses were done with the left internal thoracic artery and 99 anastomoses were done with vein grafts. Those 99 vein grafts including 4 grafts to the left anterior descending artery (LAD), 23 grafts to the diagonal artery (Dx), 44 grafts to the obtuse marginal artery (OM) and 28 grafts to the right coronary artery (RCA) were evaluated in this study. A sequential grafting technique was not applied in any of the patients. After completion of the distal vein graft anastomoses, a cold blood cardioplegic solution was given through the vein grafts using a roller pump with the perfusion pressure of 80 mmHg and the flow rate through these grafts was assessed. After the patients were weaned from cardiopulmonary bypass, these vein grafts were controlled with a TTFM device with the mean blood pressure of 80 mmHg (Medistim VeriQ System, Oslo).

Results are presented as the mean ± standard deviation. Student’s t test was used for comparison of flow values measured by the TTFM method and RPFM method. Simple linear regression was used to analyse the relationship between the TTFM method and RPFM method. A p value of less than 0.05 was considered significant. SPSS 10.0 software (SPSS Inc., Chicago, IL) was used for statistical analysis in this study.

CABG could be safely performed in all cases. There were no operative deaths, perioperative myocardial infarctions, no need for an intra-aortic balloon pumping, and no cerebral infarctions. Also, no other major complications occurred postoperatively.

Flow values measured by the TTFM method and the RPFM method were compared and the result is listed in Table 1. In all target vessels, bypass flow measured with RPFM method was significantly higher than that measured with TTFM method.

Simple linear regression revealed no correlation between the TTFM measurement and the RPFM measurement (r = 0.08, p = 0.21) and the result is presented in the Figure 1.

In two patients, a bypass revision was indicated by TTFM measurement. These two cases are described more in detail:

Case 1. In a 59-years-old male patient with coronary 3-vessel disease and left main stem stenosis, CABG (LITA to the LAD and vein grafts to the Dx and the OM) was performed. After the completion of distal anastomosis to Dx, the value of the RPFM measurement was 50 ml/min, however, after the proximal anastomosis of this graft, the value of the TTFM measurement was close to zero (Figure 2(a)). According to this finding, the distal anastomosis to the Dx was revised and thereafter the value of the TTFM measurement became acceptable (Figure 2(b)). The postoperative course was uneventful.

Table 1. Flow measurement with TTFM and RPFM.