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

Magnetic resonance imaging (MRI) is a non-invasive modality which can be used for direct visualization of coronary artery bypass grafts. Spin-echo and gradient-echo (cine-MRI) techniques are now available on standard MR machines and provide information on graft morphology and graft patency with a 90% accuracy. By combining the standard techniques with MR phase velocity mapping, the flow rate in the graft can be measured, thereby offering a unique non-invasive assessment of the graft function. Newer techniques include MR coronary angiography, pharmacologically induced stress MRI, ultrafast MRI of the first-pass (perfusion) of a paramagnetic contrast agent through the myocardium, and31P MR spectroscopy of high-energy phosphate metabolism of the myocardium. All of these may develop into valuable diagnostic tools for the assessment of functional results after CABG or PTCA, but still require clinical validation. At present, MRI is a useful screening procedure for assessment of graft patency and function in post-operative pain syndromes and in late graft occlusion or stenosis

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

Scar tissue and microvolt T-wave alternans

Microvolt T-wave alternans (MTWA) is an electrocardiographic marker for predicting sudden cardiac death. In this study, we aimed to study the relation between MTWA and scar assessed with cardiac magnetic resonance imaging (CMR) in patients with ischemic cardiomyopathy (ICM) or dilated cardiomyopathy (DCM). Sixty-eight patients with positive or negative MTWA and analysable CMR examination were included. Using CMR and the delayed enhancement technique, left ventricular ejection fraction (LVEF), volumes, wall motion and scar characteristics were assessed. Overall, positive MTWA (n = 40) was related to male gender (p = 0.04), lower LVEF (p = 0.04) and increased left ventricular end-diastolic volume (LVEDV) (p < 0.01). After multivariate analysis, male gender (p = 0.01) and lower LVEF remained significant (p = 0.02). Scar characteristics (presence, transmurality, and scar score) were not related to MTWA (all p > 0.5). In the patients with ICM (n = 40) scar was detected in 38. Positive MTWA (n = 18) was related to higher LVEDV (p = 0.05). In patients with DCM (n = 28), scar was detected in 11. Trends were found between positive MTWA (n = 15) and male gender (p = 0.10), lower LVEF (p = 0.10), and higher LVEDV (p = 0.09). In both subgroups, the presence, transmurality or extent of scar was not related to MTWA (all p > 0.45). In this small study, neither in patients with ICM or DCM a relation was found between the occurrence of MTWA and the presence, transmurality or extent of myocardial scar. Overall there was a significant relation between heart failure remodeling parameters and positive MTWA

Relationship between Framingham Risk Score and Left Ventricular Remodeling after Successful Primary Percutaneous Coronary Intervention in Patients with First Myocardial Infarction and Single Vessel Disease

Background: Limited data is available on the potential value of estimated cardiovascular event risk for prediction of left ventricular (LV) remodeling and size of infarcted tissue after ST-elevation myocardial infarction (STEMI). Methods: Therefore, we assessed in a consecutive series of patients with first STEMI, successful primary percutaneous coronary intervention (PCI), and single-vessel disease the potential relationship between the Framingham Risk Score and parameters of both LV remodeling and infarct tissue characteristics, as determined with contrast-enhanced (CE) cardiovascular magnetic resonance (CMR) 6 months after the index event. Parameters of LV remodeling were end-diastolic and end-systolic volumes, ejection fraction, and wall motion score index; infarct tissue characteristics comprised core, peri, and total infarct size, and transmural extent. Results: A total of 25 patients (21 men, 56 ± 10 years) were studied, and the mean Framingham Risk Score was 14.1 ± 5.8%. There was a significant relation between Framingham Risk Score and multiple parameters of LV remodeling: LV ejection fraction, end-diastolic volume, end-systolic volume, and wall motion score index after 6 months (r=-0.55-0.76; p=0.000 for all). Framingham Risk Score showed no relation with various infarct tissue characteristics (ns). Male gender was the only component of the Framingham Risk Score that correlated individually with a few parameters of LV remodeling: LV end-diastolic volume and end-systolic volume (p=0.000 for both). Conclusion: In a series of consecutive patients with first STEMI, successful primary PCI, and single-vessel coronary artery disease, we observed a significant relation between the Framingham Risk Score and several CMRbased parameters of LV remodeling. The results of our small hypothesis-generating study underline the supremacy of multifactorial risk scores as tools for prediction of unfavorable cardiovascular outcome. Additionally, the data support the hypothesis that there might be a future role for a novel and specific multifactorial risk score in predicting unfavorable LV remodeling, which finally could trigger risk-adjusted preventive measures