Transit-time flowmetry (TTFM) allows grafts quality assessment during coronary artery bypass surgery by measuring the flow volume through them. Recently the intraoperative epicardial high-frequency ultrasound (HFUS) was introduced, with the possibility of capturing bidimensional images of the anastomoses. When combined, these two techniques provide high diagnostic yield reaching a positive predictive value of 100 percent.

Despite current guidelines recommend the employment of TTFM and HFUS, they remain largely underused probably because of limited information and the lack of standardization. Furthermore, surgeons must overcome a learning curve to handle both techniques properly, but few data are available according the current literature.

The main purpose of this study is to evaluate the complexity of HFUS and TTFM learning curve. This is a prospective, observational, monocentric cohort study. Adult patients undergoing coronary artery bypass surgery will be enrolled.

This is a prospective, observational, monocentric cohort study in which adult patients undergoing coronary artery bypass surgery will be enrolled.

Primary objective of this study is to evaluate the complexity of cardiac surgery residents' learning curve for grafts quality assessment with transit-time flowmetry (TTFM) and intraoperative epicardial high-frequency ultrasound (HFUS).

Secondary objectives are to evaluate the complexity of cardiac surgery residents' learning curve for grafts quality assessment with TTFM and HFUS as isolated techniques.

The study will last four months (three months for patients enrollment and data collection and one month for statistical analysis and scientific paper writing).

The trial will start after obtaining favourable opinion from the local Ethics Committee and could be considered completed when all the eight cardiac surgery residents involved have reached primary endpoint.

All patients with coronary artery disease and an indication for surgical revascularization (coronary artery bypass grafting) who meet the above-described inclusion and exclusion criteria will be enrolled by signing the informed consent the day before surgery.

Patient data (anamnestic data, surgery description, intraoperative echographic and flowmetric measurements) will be recorded in a dedicated database. All data recorded in the database are commonly acquired for all patients undergoing this type of surgery and no further examinations will be performed for patients included in the trial.

The study will involve cardiac surgery residents with different levels of training and an expert cardiac surgeon who acts as supervisor and benchmark. Each resident will sign a dedicated informed consent form in the presence of a doctor foreign to the study protocol (Cardiac Surgery ward cardiologist). The residents will be "blinded" about the trial objective and the adopted score system. They will undergo a specific training including a quick lesson and a practical workshop to familiarize with the equipment.

During surgery, every graft will be evaluated through transit time flowmetry (TTFM) and intraoperative ultrasound control (HFUS).

In details, the ultrasound control is carried out through a dedicated sterile ultrasound probe connected to a machine (MiraQ - MEDISTIM) as soon as each anastomosis is completed. The result of the evaluation is recorded together with surgery data. This evaluation is intended to confirm the correct realization of the anastomosis and provides a proof of its patency.

Once each graft is completed, the resident will be given 60 seconds to acquire two HFUS recordings (short and long axis). After that, the supervisor will perform his personal recording which will stand as benchmark. The following items will be evaluated:

A) Long axis recording acquired within 60 seconds [YES-> 1] [NO -> 0] B) Long axis recording judged as suitable by the supervisor [YES -> 1] [NO -> 0] C) Short axis recording acquired within 60 seconds [YES -> 1] [NO -> 0] D) Short axis recording judged as suitable by the supervisor [YES -> 1] [NO -> 0]

E) Correct interpretation of the anastomosis as adequate or inadequate [YES -> no penalty] [NO -> total score becomes 0 and the resident isn't allowed to perform TTFM]

Each resident will be given a HFUS-related score from a minimum of 0 to a maximum of 4.

Whenever one of the recordings will be judged as non-suitable by the supervisor and consequently useless for a correct interpretation of the anastomosis (score 0 for items A and/or C), item E won't be evaluated and the HFUS will be given a total score of 0.

Next step will be the TFM evaluation, which is carried out through a specific sterile device connected to the same machine (MiraQ - MEDISTIM) once the patient has been weaned from the cardiopulmonary bypass and before protamine administration. This recording is performed under EKG and pressure-controlled conditions. Although there is no general agreement on the optimal mean arterial pressure at which the measurement has to be recorded, the investigators will adopt the standard used in the REQUEST study protocol (16), that is an average pressure of 80 mmHg.

The resident will acquire the TTFM recording after each graft is completed. To make the comparison as accurate as possible, the resident will perform TTFM evaluation on one graft at a time and successively the supervisor will do the same for each graft (making sure that delta between the pressure during the two recordings is lower than 10 percent and that no drug has been administered). The following items will be evaluated:

F) Time necessary to acquire the measures [< 30 sec -> 1] [> 30 sec, < 60 -> 0.5] [> 60 sec -> 0] G) Need for multiple measurements before the final one: [>2 -> 0] [1 -> 0.5] [ 0 -> 1] H) Need to change probe dimensions: [NO -> 0] [YES-> 1]

I) ACI [delta between resident and supervisor measurements < 10%-> 1] [> 10%, < 20% -> 0.5] [> 20% -> 0] L) Mean Flow [delta between resident and supervisor measurements < 10%-> 1] [> 10%, < 20% -> 0.5] [> 20% -> 0] M) Pulsatility Index [delta between resident and supervisor measurements < 10%-> 1] [> 10%, < 20% -> 0.5] [> 20% -> 0] N) Backward Flow [delta between resident and supervisor measurements < 10%-> 1] [> 10%, < 20% -> 0.5] [> 20% -> 0] O) Diastolic Filling [delta between resident and supervisor measurements < 10%-> 1] [> 10%, < 20% -> 0.5] [> 20% -> 0]

P) Correct interpretation of the graft quality as working [YES -> no penalty] [NO -> total score becomes 0]

Each resident will be given a TTFM-related score from a minimum of 0 to a maximum of 8.

The final score for each graft will be the sum of the two scores (HFUS and TTFM), from a minimum of 0 to a maximum of 12.

The same procedure will be repeated for each graft performed during the surgery.

Each resident will continue until reaching a ratio between total score and number of evaluated anastomoses of 11.

Our cardiac surgery unit performs between 5 and 10 coronary artery bypass grafts surgeries per week on average. Considering the inclusion and exclusion criteria and assuming that some patient may not give their informed consent, the investigators expect to enroll 4 patients per week. Considering that the involved residents (8 in total) will take part to the procedures in turn and that around 10 surgeries are needed to become autonomous, the investigators estimate to enroll 80 patients during a period of 3 months.

Data will be collected in a specific database (Microsoft Excel worksheet). The Kolgomorov-Smirnoff test was used to check for variables distribution. Continuous variables with a normal distribution are summarized by mean and standard deviation. Continuous variables with a non-normal distribution are expressed with median and interquartile range.

Categorical variables are reported as absolute frequency distribution and percentage. Continuous data are analyzed using the unpaired t-test or the Mann - Whitney test according to their distribution. Categorical data are compared with the Fisher's exact test. Statistical findings were considered significant if p value was less than 0.05. Statistical analysis will be performed with the statistic software SPSS (IBM).

Inclusion Criteria:

• Age >= 18 years old;
• Written informed consent;
• Indication to CABG surgery (both "on-pump" and "off-pump");
• Stable angina, unstable angina or acute coronary syndrome without ST elevation (NSTEMI).

Exclusion Criteria:

• Age >= 18 years old;
• Written informed consent;
• Indication to CABG surgery (both "on-pump" and "off-pump");
• Stable angina, unstable angina or acute coronary syndrome without ST elevation (NSTEMI).

All patients with coronary artery disease and an indication for surgical revascularization (coronary artery bypass grafting) who meet the above-described inclusion and exclusion criteria will be enrolled by signing the informed consent the day before surgery.