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PATENCY OF BYPASS GRAFTS ON MSCT ANGIOGRAPHY, AFIC EXPERIENCE.

Byline: Muhammad Nadir Khan, Muhammad Adil, Syed Shahid Abbas, Sohail Aziz, Jahanzab Ali, Abdullah Hamid Gondal, Muhammad Hamza Jahangeer and Arslan Mehmood

ABSTRACT

Objective: To determine the patency of coronary artery bypass grafts (CABG) in patients presenting with recurrent angina.

Study Design: Descriptive study.

Place and Duration of Study: Cardiac Catheterization Lab AFIC/NIHD, Rawalpindi, from Jan 2011 to Jan 2014 over a time period of about 3 years.

Material and Methods: A total of 955 patients who presented with recurrent angina or atypical chest pain or newly developed ECG changes after prior bypass surgery were included in study. Patients with chest pain at rest, cardiac arrhythmias and history of allergy to contrast, renal failure, hemodynamically unstable patients and pregnant females were not enrolled in study. All 955 patients were selected by non-probability consecutive sampling. Patient's demographic and multi-slice computer tomography (MSCT) angiography findings were recorded. Finally data was analyzed by using SPSS version 21.

Result: Out of 955 patients 863 (90.4%) were male while remaining 92 (9.6%) were female. Age range was 34-91 years. LIMA was the most frequently implanted graft i.e. 861 (90.16%). RIMA is the least implanted graft. Out of 861 LIMA grafts 788 (91.5%) were patent as visualized by MSCT, 55 (6.4%) were occluded while 18 (2.1%) were atretic. A total of 2001 saphenous venous grafts were implanted out of which 1234 (61.66%) were patent, 682 (34.08%) were occluded while 85 (4.3%) were diseased. In case of RADIAL a total of 33 (91.7%) grafts were patent, 3 (8.3%) were occluded and in case of RIMA 19 (82.6%) grafts were patent and 4 (17.4%) were occluded. Overall 91.30% of arterial grafts were patent. In case of both RADIAL and RIMA no graft was diseased.

Conclusion: SVG were patent in 61.66% of the grafts while arterial grafts had a patency rate of 91.30%. Thus arterial grafts have high patency rate as compared to others.

Keywords: CABG, Graft patency, MSCT angiography.

INTRODUCTION

With the commencement of digital era and industrialization coronary artery disease has become one of the most common causes of hospital admission and mortality. As a result coronary artery bypass graft surgery (CABG) is most often frequently performed surgical procedure in advanced countries1. In USA, around 427000 patients undergo CABG annually2. CABG has emerged as an effective treatment for patients with intractable angina and in patients having stable coronary artery disease3. However its long term results are limited by failure of grafts4. Generally speaking graft occlusion occurs in 10-15% of patients shortly after surgery or during first year and in 25% patients in 5 years5. Venous graft patency is reduced to 50% at 10 years after surgery, and at 15 years about 80% of the venous grafts become occluded while 90% of the arterial grafts remain patent even after 10 years of surgery. LIMA have much improved survival rates6,7.

Recurrent angina after CABG has become an important issue in cardiology, as reflected by increasing number of patients presenting with thoracic discomfort raising a question of bypass graft stenosis. Therefore evaluation of the bypass graft as well as native arteries is indispensable. Coronary interventional angiography is the gold standard technique in the evaluation of bypass graft patency and stenosis. As it is invasive and complicated technique, therefore both immediate and follow up control of graft patency are not performed8. Therefore since the early 1980s, CT and MRI were in use as an alternative to invasive techniques to visualize bypass grafts. However both techniques cannot judge graft stenosis and distal graft anastamosis9. Similarly electron beam tomography on the other hand is limited by three dimensional resolutions, cost and its availability.

With advancement in technology, both temporal and spatial resolution could be substantially increased by use of Multi-detector row spiral computed tomography (MSCT). MSCT with retrospective ECG gating has partly overcome the limitations of EBCT and MRI and show high accuracy in the detection of graft diseases10,11. Many studies have demonstrated good diagnostic accuracy of MSCT for the detection of significant stenosis in grafts with high diagnostic accuracy (sensitivity 96% to 99%, specificity 95% to 100%)12,13.

In current study we analyze bypass graft patency by using 64 slice MSCT in patients who has underwent CABG and presented with recurrent chest discomfort at Armed Forces Institute of Cardiology, Rawalpindi.

MATERIAL AND METHODS

This descriptive study was performed at Catherization laboratory, Armed Forces Institute of Cardiology, from Jan 2011 to Jan 2014 over a time period of about 3 years. All 955 consecutive patients who were scheduled for invasive coronary angiography (ICA) were included in the study. Patients with chest pain at rest, cardiac arrhythmias and history of allergy to contrast, renal failure, hemodynamically unstable patients and pregnant females were not enrolled in study. All 955 patients were selected by non-probability consecutive sampling. Written informed consent was taken from all the patients. In all patients 64 slice MSCT angiography was performed within 15 days before ICA. Patients were given metoprolol 100mg orally 3 hours before the procedure to bring heart rate below 65beats/min. Heart rate, electrocardiogram, and blood pressure were monitored; and additional intravenous metoprolol (10-15mg) was administered if necessary to achieve the target heart rate.

Sublingual nitroglycerin 0.5mg was given 1 minute before image acquisition. Computerized tomography angiography (CTA) images were taken using 64 slice MSCT scanner. During scan 80-120ml of contrast agent usually iopamidol was injected continuously at infusion rate of 4.5 ml/s through antecubital vein for MSCT images. Contrast was followed by injection of 30-50ml saline chasing bolus. Scanning was initiated in craniocaudal direction. This was done during a single inspiratory breath hold for an acquisition time of 12-15 sec. For an optimal heart phase selection, retrospective ECG gating was used. Retrospective reconstruction of the image data was performed for acquisition of phase images starting from early systole (10% of the R-R interval) and ending at late diastole (90% of the R-R interval) using 10% increments.

All images were reconstructed with a display field of view of 25cm, a standard soft tissue filter as suggested by the manufacturer and an effective slice thickness of 0.625mm with an increment of 0.625mm. The best phase was selected for analysis of grafts and native vessels. After scan images were reformatted and were analyzed by two experts and findings were agreed upon. Only excellent (with no motion or gating artifacts present), good (with minor motion artifacts present) and diagnostic (with substantial motion artifacts present, but luminal assessment of significant stenosis still possible) images were selected for graft evaluation.All the grafts were assessed for the origin, the body, the distal anastamosis and the native recipient coronary arteries after the grafts. Patient's demographic data and MSCT angiography findings were recorded. Finally data was analyzed by using SPSS version 21.

Various descriptive statistics were used to calculate frequencies, percentages and standard deviation. The numerical data such as age were expressed as Mean +- Standard deviation while the categorical data were expressed as frequency and percentages.

Table-I: Frequency of grafts implanted.

Grafts###Characteristics

LIMA###861 (90.16%)

SVG to LAD###90 (9.42%)

SVG to DIAG###389 (40.73%)

SVG to OM1###732 (76.65%)

SVG to OM2###75 (7.85%)

SVG to RCA###715 (75.87%)

RADIAL###36 (3.77%)

RIMA###23 (2.41%)

Table-II: MSCT findings.

LIMA###788 (91.5%)###55 (6.4%)###18 (2.1%)

SVG to LAD###60 (66.7%)###23 (25.6%)###7 (7.8%)

SVG to DIAG###243 (62.5%)###132 (33.9%)###14 (3.6%)

SVG to OM1###438 (59.8%)###251 (34.3%)###43 (5.9%)

SVG to OM2###54 (72%)###18 (24%)###3 (4%)

SVG to RCA###439 (61.4%)###253 (35.4%)###23 (3.2%)

RADIAL###33 (91.7%)###3 (8.3%)###0 (0.0%)

RIMA###19 (82.6%)###4 (17.4%)###0 (0.0%)

RESULTS

Out of 955 patients 863 (90.4%) were male while remaining 92 (9.6%) were female. Age range was 34-91 years with mean of 60.72 +- 9.52. Hypertension was most common risk factors followed by smoking, diabetes mellitius and hyperlipidemia. Maximum number of grafts implanted in a patient was 4 while minimum of 1 graft was implanted in a patient. A total of 2001 saphenous venous grafts were implanted out of which 1234 (61.66%) were patent, 682 (34.08%) were occluded while 85 (4.3%) were diseased. In case of RADIAL a total of 33 (91.7%) grafts were patent, 3 (8.3%) were occluded and in case of RIMA 19 (82.6%) grafts were patent and 4 (17.4%) were occluded. Overall 91.30% of arterial grafts were patent. In case of both RADIAL and RIMA no graft was diseased. Frequency and type of graft implanted and MSCT angiography findings are shown in table-I and II.

DISCUSSION

MSCT is the latest breakthrough in CT technology. It is in use since 1992 in the form of dual spiral scanning, while first 4 slice unit was introduced in 199814. Systems with 8, 10, 16, 32 and 64 detector arrays have become available over the last few years. Compared with previous generations, 64 slice MSCT scanner provides improve temporal and spatial resolution15.16. Although promising results have been reported for MRI recently. Langerak et al evaluated 56 venous grafts with the help of MRI17. Similarly in another study, patients who presented with recurrent chest pain were assessed by MRI to detect stenosis. A sensitivity and specificity of 94% and 63% were observed for the detection of single vein grafts with stenosis [greater than or equal to]50%; sensitivity and specificity rose to 96 and 92%, respectively, when stenosis [greater than or equal to]70% was considered.

Other non-invasive techniques like exercise ECG, stress myocardial imaging and stress echo are also available for the assessment of post CBAG patients however they lack the anatomical details of the grafts and native vessels.

In present study we assess the patency of arterial and venous graft in patients who presented with recurrent chest pain. In our study the overall patency rate of saphenous venous grafts was 61.66%, however it depends upon the grafted vessel (59.8-72%), similarly patency rate of arterial graft ranges from 82.6%-91.7%. These results are consistent with the results described by Basri et al18. He stated a patency rate of 86.3-91.5% for saphenous venous grafts while patency rate for arterial grafts was 95% including 97.3% for the LIMA grafts, 50% for the RA grafts, and 50% for the RIMA grafts. These results are also confirmed by another study in which a patency rate of >90% was stated18. Naveed et al19 conducted a study on 64 post CABG patients to evaluate the patency of bypass grafts. He showed a patency rate of 66% for SVG and 92% for arterial grafts.

Various studies have shown that 10-15 year post CABG graft patency is 50-60 % for venous grafts and 85 % for the arterial grafts20,21. The best quality images are always obtained in patients with low heart rate. However recent study has demonstrated that heart rate is not a crucial determinant of image quality22. However temporal resolution varies with patient heart rate. Therefore we gave beta blockers in cases to lower the heart rate.

MSCT can not be called as risk free investigation because of radiation exposure and contrast administration. Compared with ordinary coronary CT, the scan range was extended by 37% which results in high radiation dose23. Although 64 slice MSCT has become gold standard for evaluation of post CABG grafts, still development of new generation scanners are still under way. Cardiac freeze frame technique, dual-source CT, flat-panel CT will help to improve further temporal resolution, abolishes the problem of breadth holding further reduces motion artifacts and artifacts related to variations of heart rate during the scan.

CONCLUSION

MSCT in our setup has comparable results to the data available from other cardiology facilities around the world and it has become a standard care for the evaluation of graft disease. Our data showed that 61.66% SVG were patent while arterial grafts were patent in 91.30% of the grafts.

CONFLICT OF INTEREST

This study has no conflict of interest to declare by any author.

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Publication:Pakistan Armed Forces Medical Journal
Date:Feb 28, 2018
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