Detecting left ventricular myocardial ischemia during intravenous dobutamine with cardiovascular magnetic resonance imaging (MRI)

Detecting patients with acute coronary syndrome in the chest pain center of the emergency department with cardiac magnetic resonance imaging

Managing patients with chest pain in the Emergency Department (ED) remains a challenge where advanced imaging technology may play a role. Detecting acute coronary syndrome in the emergency department with cardiac magnetic resonance imaging (MRI) was studied in 161 consecutive chest pain patients in a prospective observational study. Patients with ST elevation myocardial infarction were excluded from study participation. All patients underwent MRI study when hemodynamically stable, free of ongoing chest pain, and within 12 hours of symptoms onset. The MRI study takes an average of 38 +/- 12 minutes and included global and regional left ventricular function, myocardial perfusion, and gadolinium-enhanced myocardial infarction detection. The sensitivity and specificity for detecting acute coronary syndrome was 84% and 85% by MRI. The MRI was more sensitive than strict electrocardiogram (ECG) criteria for ischemia (P < 0.001) and peak troponin-I (P < 0.001). The MRI was more specific than an abnormal ECG (P < 0.001). Multivariate logistic regression analysis showed MRI was the strongest predictor of acute coronary syndrome and added diagnostic value over clinical parameters (P < 0.001). A nonstress cardiac MRI performed in this urgent clinical setting is safe and exhibited diagnostic operating characteristics suitable for triage of patients with chest pain in the emergency department. MRI accurately detected a high fraction of patients with acute coronary syndrome including patients with enzyme negative unstable angina.

Magnetic resonance imaging for the assessment of myocardial viability

The identification of myocardial viability in the setting of left ventricular (LV) dysfunction is crucial for the prediction of functional recovery following revascularization. Although echocardiography, positron emission tomography (PET), and nuclear imaging have validated roles, recent advances in cardiac magnetic resonance (CMR) technology and availability have led to increased experience in CMR for identification of myocardial viability. CMR has unique advantages in the ability of magnetic resonance spectroscopy (MRS) to measure subcellular components of myocardium, and in the image resolution of magnetic resonance proton imaging. As a result of excellent image resolution and advances in pulse sequences and coil technology, magnetic resonance imaging (MRI) can be used to identify the transmural extent of myocardial infarction (MI) in vivo for the first time. This review of the role of CMR in myocardial viability imaging describes the acute and chronic settings of ventricular dysfunction and concepts regarding the underlying pathophysiology. Recent advances in MRS and MRI are discussed, including the potential for dobutamine MRI to identify viable myocardium and a detailed review of the technique of delayed gadolinium (Gd) contrast hyperenhancement for visualization of viable and nonviable myocardium.

Stem cells for myocardial regeneration

Stem cells are being investigated for their potential use in regenerative medicine. A series of remarkable studies suggested that adult stem cells undergo novel patterns of development by a process referred to as transdifferentiation or plasticity. These observations fueled an exciting period of discovery and high expectations followed by controversy that emerged from data suggesting cell-cell fusion as an alternate interpretation for transdifferentiation. However, data supporting stem cell plasticity are extensive and cannot be easily dismissed. Myocardial regeneration is perhaps the most widely studied and debated example of stem cell plasticity. Early reports from animal and clinical investigations disagree on the extent of myocardial renewal in adults, but evidence indicates that cardiomyocytes are generated in what was previously considered a postmitotic organ. On the basis of postmortem microscopic analysis, it is proposed that renewal is achieved by stem cells that infiltrate normal and infarcted myocardium. To further understand the role of stem cells in regeneration, it is incumbent on us to develop instrumentation and technologies to monitor myocardial repair over time in large animal models. This may be achieved by tracking labeled stem cells as they migrate into myocardial infarctions. In addition, we must begin to identify the environmental cues that are needed for stem cell trafficking and we must define the genetic and cellular mechanisms that initiate transdifferentiation. Only then will we be able to regulate this process and begin to realize the full potential of stem cells in regenerative medicine.

Magnetic resonance imaging in detection and functional assessment of coronary artery disease

The past few years have brought significant improvements in the field of cardiovascular magnetic resonance imaging (MRI), which evolved from an experimental technique to a clinically accepted method of coronary artery disease detection (stress MRI) and viability assessment. In this article, we describe current MRI technology for detection and functional assessment of ischemia, such as dobutamine/atropine MRI, perfusion techniques, viability, and flow reserve in native coronary arteries and grafts. With further refinement in the technology, wide acceptance of cardiovascular MRI is anticipated in clinical practice.