The role of magnetic resonance in the evaluation of functional results after CABG/PTCA

Surgical Reconstruction of the Left Main Coronary Artery: Fresh Autologous Pericardium or Saphenous Vein Patch

BACKGROUND

Isolated stenosis of the left main coronary artery is usually treated by coronary bypass surgery. However, this approach restores a less physiologic perfusion of the myocardium that leads to occlusion of the left main coronary artery, and restores only a retrograde perfusion of a rather extensive myocardial area. Coronary ostial plasty has been described as an alternative surgical technique in isolated ostial left main coronary artery stenosis without calcification. We review our experience with 15 patients.

METHODS

After placing the patient on cardiopulmonary bypass and aortic cross clamping, the main pulmonary trunk was retracted laterally. The left main coronary artery was approached anteriorly through a curved aortotomy. Reconstruction was performed using fresh pericardial patch or saphenous vein that was tailored as a patch.

RESULTS

There were no early mortality or perioperative myocardial infarctions. During mean follow-up of 55 +/- 39 months, no patients had any cardiac events or required repeated coronary intervention. All patients underwent follow-up transesophageal echocardiography, which demonstrated a wide open left main coronary artery (range 3 to 8 mm), normal flow pattern by pulsed-wave Doppler, and no aneurysmal dilatation or calcification of the onlay patch. Coronary angiography and intravascular ultrasound were performed in 2 patients because of nonspecific chest discomfort. In both cases, the left main coronary artery was found to be wide open, and there were no signs of patch calcification.

CONCLUSIONS

Surgical reconstruction of the left main coronary artery is safe and effective for the treatment of selected cases of isolated left main stenosis. The use of autologous pericardium appears to be as safe as saphenous vein patch. Neither method was associated with postoperative aneurysmal dilatation or calcification.

Transesophageal echocardiography evaluation and follow-up of left main coronary artery patch angioplasty

OBJECTIVE

Isolated ostial stenosis of the left main coronary artery is a rare but serious condition. The treatment is surgical with two options: coronary artery bypass grafting or surgical angioplasty of the left main coronary artery. Assessing surgical results as well as follow-up were traditionally done by angiography.

METHODS

We describe the use of transesophageal echocardiography (TEE) for evaluating and follow the surgical left main coronary artery (LMCA) angioplasty results in eight patients with isolated ostial left main stenosis.

RESULTS

All patients were alive and free of ischemic events 8 months to 7 years post-surgery. TEE demonstrated a widely opened left main coronary artery with a good flow.

CONCLUSIONS

Surgical angioplasty is an alternative option for treating ostial LMCA stenosis. TEE is an additional excellent non-invasive technique for assessing left main anatomy pre- and postoperatively, as well as being on of the quality control tools for evaluating new surgical techniques.

Non-invasive magnetic resonance imaging of coronary bypass grafts. comparison of the haste- and navigator techniques with conventional coronary angiography

OBJECTIVE

The aim was the study was to evaluate the patency of coronary artery bypass grafts with the 3D Navigator and the Haste magnetic resonance imaging techniques.

MATERIAL AND METHODS

Thirty-four patients with 82 grafts (18 internal mammarian artery and 64 saphenous venous grafts) were examined at 1.5 T using a phased arrray body coil. A 2D T-2 weighted turbo spin echo sequence (Haste) and a 3D-angiography sequence in navigator technique were used. Reference method was the conventional coronary angiography that was performed within 7 days.

RESULTS

With the HASTE sequence 54 of 56 patent and 12 of the 16 occluded grafts were recognized, the sensitivity and specificity was 96 and 75%. The distal anastomosis could be assessed in 28 of 76 cases. With the Haste sequence 54 of the 56 patent and 12 of the 14 occluded grafts were detected correctly. Eight patent and two occluded grafts were judged as not assessable. The sensitivity and specificity was 96 and 85%. Sixty-six percent (50/76) of the distal anastomosis were identified correctly. With both sequences none of the bypass stenosis could be detected.

CONCLUSIONS

The patency of coronary bypass grafts can be evaluated noninvasively with a sensitivity of 96% and a specificity of 76%. No inference can be made with respect to the nature of bypass graft stenosis. Better results can be expected with the development of a blood pool contrast medium, an improvement of the spatial resolution and in the combination of flow measurements.

CT and arteriography in the evaluation of indirect myocardial revascularization with a free-muscle transplant: initial experience

PURPOSE

To examine patients with advanced cardiovascular disease with radiology after indirect myocardial revascularization with a free-skeletal-muscle transplant and to determine whether the attached vessel remains patent over the middle and long terms.

MATERIALS AND METHODS

In 10 patients with advanced, inoperable cardiovascular disease treated with indirect myocardial revascularization with a free-muscle transplant, radiologic follow-up was performed postoperatively and every 6 months. All 10 patients underwent selective arteriography of the anastomosed vessel and contrast material-enhanced helical computed tomography (CT) (transverse sections and reconstructions).

RESULTS

All patients showed adequate vascular conditions postoperatively, as did nine of 10 patients after 1 year. In one patient, the anastomosed artery was occluded. CT showed time-dependent muscle degeneration in all patients. Postoperative, contrast-enhanced, superselective CT showed an area of high-attenuating uptake in the muscle transplant in all patients. After 1 year, CT depicted perfusion defects of the skeletal muscle in two patients. In eight patients, however, small vascular bridges from the skeletal muscle to the myocardium were detected. Radiologic results correlated well with clinical outcome and stress electrocardiograms.

CONCLUSION

Helical intraarterial CT and arteriography were sensitive in depicting enhancement and remaining vital function in nine of 10 patients after indirect myocardial revascularization with a free-muscle transplant. This combination seems promising for postoperative examination in such patients.

Morphologic and functional evaluation of coronary artery bypass conduits

There is clear evidence in the literature that conventional spin-echo and gradient-echo magnetic resonance imaging (MRI) is capable of assessing patency of coronary artery vein grafts. With more recently introduced breath-hold two-dimensional (2D) and contrast-enhanced 3D techniques, the predictive accuracy has further improved, with sensitivities and specificities in the 90% range. Limitations arise with regard to assessing obstructive disease and evaluating distal segments of sequential grafts, due to insufficient spatial resolution, low signal-to-noise ratio, and cardiac motion. Imaging of arterial grafts is complicated by the metallic clip artifacts. Adding information on graft flow patterns and flow reserve using velocity-encoded cine MRI may help to reduce some of the problems. Clinically, these functional measurements may become of use in non-invasive monitoring of gradually increasing graft narrowing. However, apart from a few exceptions, most patients undergo evaluation of their grafts because they are considered for a re-intervention by angioplasty or coronary artery bypass graft surgery. In these cases information on the status of the native coronary arteries is required. A broader clinical use of MRI in the evaluation of patients with coronary artery bypass grafts may therefore only be expected with further improvement in MR techniques for coronary angiography. J. Magn. Reson. Imaging 1999;10:734-740.

Evaluation of coronary artery bypass grafts by magnetic resonance imaging

Magnetic resonance (MR) angiography and flow mapping have the potential to become a major noninvasive diagnostic tool for the assessment of coronary artery bypass graft morphology and function. Several MR sequences, such as conventional non-respiratory compensated methods, and phase contrast cine flow sequences have been reported for the evaluation of bypass graft patency. However the visualization of different graft segments and the detection of graft stenosis remains difficult. Recent advances in MR coronary angiography and flow mapping are volume coronary angiongraphy with targeted scans, navigator gated angiography, contrast-enhanced angiography, and breath-hold or navigator gated flow sequences. Future approaches, such as navigator gated fast MR techniques resulting in high-resolution angiography in combination with breath-hold MR flow mapping with high temporal resolution, might allow a comprehensive evaluation of bypass graft stenosis and function. This review article will address the major issues concerning the MR evaluation of bypass grafts.

[Magnetic resonance imaging and spiral computed tomography in the diagnosis and follow-up of adults with congenital heart and vessel disease]

Management of patients with congenital heart disease requires detailed information on cardiac and great vessel morphology. In previous years the diagnosis and treatment of congenital malformations often depended on cardiac catheterization and in many institutions cardiac catheterization still remains the gold standard against which other modalities are measured. In the past decade, however, imaging methodologies have increasingly shifted toward the use of less invasive and noninvasive techniques. Currently, echocardiography is the initial method of choice in evaluating the anatomy, especially in younger patients. Meanwhile, several newer imaging techniques like magnetic resonance imaging (MRI) and computed tomography (CT) are in use. They offer extremely useful information about abnormalities of the heart and great vessels as well as for the assessment of cardiac anatomy and function. Echo, angiography, MRT and CT should be seen as complementary investigations in adult congenital heart disease.

Left main coronary artery patch angioplasty: midterm experience and follow-up with spiral computed tomography

BACKGROUND

Patch angioplasty is an alternative surgical technique in cases of left main coronary artery stenosis. We report our experience with this technique, with particular mention of the use of spiral computed tomography for the follow-up of our patients.

METHODS

In this retrospective study we analyzed the results obtained in all 7 patients (3 women and 4 men) who were operated on with this technique in our institution between July 1992 and August 1994. Five consenting patients also underwent graft patency assessment with spiral computed tomographic imaging.

RESULTS

The operation was uneventful in all patients and there were no hospital deaths. Two patients required reoperation (1 of them dying at reoperation), 1 because of restenosis of the graft and 1 because of the presence of a new stenosis in the proximal anterior descending coronary artery. The remaining 5 patients were asymptomatic after 51 +/- 2 months. Spiral computed tomographic images were artifacted and of poor quality.

CONCLUSIONS

Patch angioplasty of the left main coronary artery can be a valuable therapeutic method in selected cases. Conventional spiral computed tomography is not an optimal noninvasive method for the assessment of graft patency.

A practical approach to MRI of coronary artery bypass graft patency and flow

Direct visualization of coronary artery bypass grafts can be obtained non-invasively by magnetic resonance imaging. Several studies demonstrated a high sensitivity and somewhat lower specificity for detection of vein-graft patency, using the conventional spin-echo and gradient-echo techniques. In addition, the true functional status can be assessed by determining the flowrate within the graft using phase velocity mapping. Important limitations of the previously applied techniques include the inability to accurately evaluate the different segments of jump grafts and the presence of graft stenoses. Further improvement is to be expected from the recent introduction of breath-hold imaging sequences and the forthcoming introduction of bloodpool-avid contrast agents.

Quantification of coronary artery bypass graft flow by magnetic resonance phase velocity mapping

OBJECTIVES

Determination of the true coronary artery bypass graft function requires quantification of the flow rate within the graft. The purpose of the present study was to assess the feasibility of characterizing and quantifying graft flow by magnetic resonance phase velocity mapping.

MATERIALS AND METHODS

Twenty-seven patients with 41 angiographically patent coronary artery bypass grafts underwent electrocardiographically gated magnetic resonance phase velocity mapping. Imaging was performed at 0.6 Tesla using a surface coil. Velocity maps of the bypass grafts were obtained throughout the cardiac cycle with a temporal resolution of 50 ms and a spatial resolution of 1.9 x 1.2 x 5 mm3, allowing calculation of phasic and mean graft flow.

RESULTS

Adequate flow measurements were obtained in 84% (41 out of 49) of the grafts. Coronary artery bypass graft flow was characterized by a biphasic pattern with a first peak during systole and a second peak during diastole. Average maximum systolic and diastolic velocities over the cross-section of the grafts were 14 +/- 8 cm/s and 15 +/- 9 cm/s, respectively. Mean coronary artery bypass graft cross-sectional area was 0.28 +/- 0.13 cm2. Mean volume flow was 87 +/- 59 ml/min.

CONCLUSION

Flow in coronary artery bypass grafts can be characterized and measured noninvasively by magnetic resonance phase velocity mapping.

Contrast media for MR imaging of the heart

The role of contrast media for quantitative characterization of ischemic myocardial events with magnetic resonance (MR) imaging has advanced considerably in the past few years. Contrast material-enhanced MR imaging is useful for identifying and sizing myocardial infarcts and for distinguishing between occlusive and reperfused myocardial infarcts. Recent results suggest that contrast-enhanced MR imaging can also be used to identify areas of cell death in regions of reperfused myocardial infarction. With the aid of MR contrast media, fast MR imaging techniques may be useful in estimating regional myocardial perfusion. Although no simple relationship between signal intensity and concentration exists, contrast-enhanced MR perfusion imaging can demonstrate the presence and relative severity of hypoperfused myocardium. Combining myocardial perfusion imaging with the anatomic and functional information provided by other MR imaging techniques could make MR imaging a comprehensive noninvasive means of evaluating ischemic cardiac disease.