Comparison of Bidirectional Palpation Test and Transit Time Flow Measurement for LIMA-LAD Graft Patency

The most important factor determining mortality and morbidity after coronary artery bypass graft (CABG) surgery is graft patency. The LIMA-LAD anastomosis is the most crucial anastomosis because it's revascularizing the most important and large region of the heart, has superior long-term graft patency rates and is considered the gold standard for CABG. Therefore, ensuring the patency of the LIMA-LAD anastomosis is vital for both early and late outcomes. The bidirectional palpation test (BPT), developed in our clinic to assess graft patency, is a subjective test, yet it is simple and reliable. Additionally, transit time flow meter (TTFM) measurements have also been performed. In this study, the efficacy of BPT and the results of TTFM measurements were compared by examining graft patency through early-period coronary CT angiography (CCTA).

STUDY DESIGN This study was designed as a retrospective-prospective hybrid cohort study. The study population was selected among patients who underwent LIMA-LAD anastomosis during CABG surgery at our clinic. Patients who wished to participate in the study gave informed consent by signing a preoperative consent form. Intraoperative BPT (Bidirectional Palpation Test) results and TTFM (Transit-Time Flow Measurement) values were recorded and compared with the early postoperative period (first month) CTCA (Coronary Tomography Angiography) findings. Data from 23 of the 73 patients included in the study were obtained retrospectively, while data from the remaining 50 patients were collected prospectively. All procedures performed on patients throughout the study were conducted in accordance with ethical standards, and patient information was kept confidential.

ETHICS COMMITTEE This study was conducted in accordance with the guidelines of the Clinical Research Ethics Committee of Istanbul University Cerrahpaşa and the principles outlined in the Declaration of Helsinki. In this retrospective-prospective hybrid cohort study, all data were anonymized. Throughout the study process, participant privacy and the protection of personal data were prioritized. Patient confidentiality was ensured in full compliance with ethical standards and relevant legal regulations. This approach ensured that ethical principles were maintained throughout the research process and that participants' rights were protected.

PATIENT SELECTION A total of 73 patients who underwent elective isolated CABG surgery or CABG in combination with other procedures such as valve surgery or ascending aorta surgery and gave informed consent were included in the study. However, 43 patients were excluded for reasons such as refusing to participate postoperatively, death in the early postoperative period (3 patients), or conditions like elevated postoperative creatinine that precluded CTCA. As a result, 73 patients remained in the final analysis, and a total of 73 LIMA grafts were evaluated. To minimize the impact of the anastomosis technique and quality on the study outcomes, all surgeries were performed by the same surgical team.

INTRAOPERATIVE PLANNING Following standard surgical preparation under general anesthesia, patients were properly draped. After a median sternotomy, pedicled LIMA and saphenous vein grafts were harvested. The patient was heparinized, and the Activated Clotting Time (ACT) was raised above 450 seconds. After opening the pericardium, arterial cannulation of the aorta and venous cannulation of the right atrium were performed, and cardiopulmonary bypass (CPB) was initiated. Diastolic arrest was achieved using antegrade cold Del Nido cardioplegia after applying the aortic cross-clamp. Once the distal anastomoses were completed, the cross-clamp was removed. Proximal anastomoses were performed on the beating heart using a side clamp. After de-airing and gradual reduction of flow, CPB was discontinued. Once the heart resumed circulation, a segment of the LIMA was stripped of surrounding tissue for measurement. With mean arterial pressure maintained above 60 mmHg, TTFM and ÇYPT assessments of the LIMA-LAD anastomosis were performed. If the BPT result on LIMA was positive and the flow rate and PI measured by TTFM were within acceptable ranges, TTFM measurements of the saphenous vein grafts were then conducted. Once acceptable TTFM values were confirmed for the SVGs as well, hemodynamic and arrhythmia monitoring continued. If hemodynamics remained stable, protamine was administered to neutralize heparin, and the heart was decannulated. After ensuring hemostasis, mediastinal and left thoracic drains were placed. Temporary epicardial pacing wires were inserted, the sternum was closed with wire sutures, and the subcutaneous and skin layers were closed anatomically to complete the surgery.

BIDIRECTIONAL PALPATION TEST AND TTFM MEASUREMENTS In this method, after completing the anastomoses, CPB is temporarily discontinued to create a pulse pressure, and a segment on the LIMA with a palpable pulse is identified. In the first step, the distal part of the palpated segment is occluded using a bulldog clamp or the surgeon's hand, and if the pulse persists, proximal flow is confirmed. This assesses the antegrade flow from the subclavian artery into the LIMA. In the second step, the distal occlusion is released, and a bulldog clamp or manual occlusion is applied proximally to the palpated area. If the pulse remains palpable, retrograde flow and indirectly, the patency of the LIMA-LAD anastomosis are confirmed . Due to venous valve structures preventing backflow, BPT cannot routinely be used on SVGs. However, in cases of valve insufficiency causing regurgitation in the graft, SVGs can also be evaluated using BPT.

DATA RECORDING Data collection was carried out in three stages. In the first stage, preoperative data were obtained by reviewing patient files. In the second stage, intraoperative Bidirectional Palpation Test results and TTFM (Transit-Time Flow Measurement) values were evaluated and recorded by the surgeon. During postoperative follow-ups, patients were called in for a check-up in the first week after discharge, and blood tests-including renal function tests-were performed. Based on the test results, patients deemed suitable for CTCA (Coronary Tomography Angiography) were scheduled for imaging within the first postoperative month, and their imaging procedures were monitored. In the third stage, CTCA results were reported by rradiologist and recorded. Grafts showing more than 50% luminal stenosis were considered occluded. These steps were designed to enhance the accuracy and reliability of the data.

PATIENT FOLLOW-UP Patients included in the study were closely monitored in the cardiovascular surgery intensive care unit and on the ward during the postoperative period. Upon discharge, patients were prescribed necessary medications and provided with relevant recommendations. To prevent graft occlusion, all patients were routinely prescribed either dual or single antiplatelet therapy, cholesterol-lowering agents, beta-blockers to prevent arrhythmias, and anticoagulants when necessary. Compliance with these treatments was closely monitored. Each medication's purpose, possible side effects, and interactions with other drugs were explained to the patients in detail. As part of secondary prevention, risk factors such as obesity, smoking, hyperlipidemia, diabetes, and hypertension were addressed through both pharmacological treatment and lifestyle modifications. Routine follow-ups were scheduled on postoperative day 7, and at 1, 6, and 12 months using laboratory tests and imaging techniques.

STATISTICAL ANALYSIS The study data were analyzed using the SPSS 25.0 statistical software package. For descriptive analyses, frequency distributions and percentages were calculated, means were presented with standard deviations, and medians were shown with minimum and maximum values. Since the data did not follow a normal distribution, the Mann-Whitney U test and Kruskal-Wallis test were used for comparisons between groups. The relationships between categorical variables were evaluated using the Pearson Chi-square test. In 2x2 tables, when the expected value in at least one cell was less than 5, Fisher's exact Chi-square test was applied, and when any observed value ranged between 5 and 20, the Yates-corrected Chi-square test was used. ROC analysis was performed to determine cut-off values for certain variables. A p-value of less than 0.05 was considered statistically significant.

Eligibility Criteria:
Inclusion Criteria:

1. Elective Isolated CABG Surgery: Patients undergoing elective isolated coronary artery bypass grafting (CABG).
2. CABG with Additional Cardiac Surgery: Patients who had CABG surgery in conjunction with other cardiac procedures.
3. Informed Consent: Patients who provided informed consent to participate in the study.
4. Postoperative Follow-Up: Patients who were followed up postoperatively and completed the necessary evaluations.
5. CABG patients whose renal functions are suitable for CTA

Exclusion Criteria:

Refusal to Participate: Patients who did not wish to participate in the study after being approached.

Death in Early Postoperative Period: Patients who died in the early postoperative period (3 patients).

Inability to Perform CABG: Patients for whom CABG could not be performed due to postoperative complications (e.g., elevated creatinine levels leading to inability to perform CABG, 43 patients).

Patients in whom CT angiography is not appropriate: Such as acute or chronic renal failure