Hee-Won Kim

Prognosis in Women With Myocardial Ischemia in the Absence of Obstructive Coronary Disease Results From the National Institutes of Health–National Heart, Lung, and Blood Institute–Sponsored Women’s Ischemia Syndrome Evaluation (WISE)

Background—We previously reported that 20% of women with chest pain but without obstructive coronary artery disease (CAD) had stress-induced reduction in myocardial phosphocreatine–adenosine triphosphate ratio by phosphorus-31 nuclear magnetic resonance spectroscopy (abnormal MRS), consistent with myocardial ischemia. The prognostic implications of these findings are unknown. Methods and Results—Women referred for coronary angiography for suspected myocardial ischemia underwent MRS handgrip stress testing and follow-up evaluation. These included (1) n= 60 with no CAD/normal MRS, (2) n= 14 with no CAD/abnormal MRS, and (3) n= 352 a reference group with CAD. Cardiovascular events were death, myocardial infarction, heart failure, stroke, other vascular events, and hospitalization for unstable angina. Cumulative freedom from events at 3 years was 87%, 57%, and 52% for women with no CAD/normal MRS, no CAD/abnormal MRS, and CAD, respectively (P < 0.01). After adjusting for CAD and cardiac risk factors, a phosphocreatine–adenosine triphosphate ratio decrease of 1% increased the risk of a cardiovascular event by 4% (P = 0.02). The higher event rate in women with no CAD/abnormal MRS was primarily due to hospitalization for unstable angina, which is associated with repeat catheterization and higher healthcare costs. Conclusions—Among women without CAD, abnormal MRS consistent with myocardial ischemia predicted cardiovascular outcome, notably higher rates of anginal hospitalization, repeat catheterization, and greater treatment costs. Further evaluation into the underlying pathophysiology and possible treatment options for women with evidence of myocardial ischemia but without CAD is indicated.

Comparison of Fat–Water MRI and Single-voxel MRS in the Assessment of Hepatic and Pancreatic Fat Fractions in Humans

The ability to accurately and noninvasively quantify fatty infiltration in organs such as the liver and the pancreas remains a critical component in understanding the link between obesity and its comorbidities such as type 2 diabetes and fatty liver disease. Single‐voxel (1H) proton magnetic resonance spectroscopy (MRS) has long been regarded as the gold‐standard noninvasive technique for such measurements. Recent advances in three‐dimensional fat–water magnetic resonance imaging (MRI) methods have led to the development of rapid, robust, and quantitative approaches that can accurately characterize the proportion of fat and water content in underlying tissues across the full imaging volume, and hence entire organs of interest. One such technique is called IDEAL (Iterative Decomposition with Echo Asymmetry and Least squares estimation). This article prospectively compares three‐dimensional (3D) IDEAL‐MRI and single‐voxel MRS in the assessment of hepatic (HFF) and pancreatic fat fraction (PFF) in 16 healthy subjects. MRS acquisitions took 3–4 min to complete whereas IDEAL acquisitions were completed in 20‐s breath‐holds. In the liver, there was a strong correlation (slope = 0.90, r2 = 0.95, P < 0.001) between IDEAL and MRS‐based fat fractions. In the pancreas, a poorer agreement between IDEAL and MRS was observed (slope = 0.32, r2 = 0.51, P < 0.02). The discrepancy of PFF is likely explained by MRS signal contamination from surrounding visceral fat, presumably during respiratory motion. We conclude that IDEAL is equally accurate in characterizing hepatic fat content as MRS, and is potentially better suited for fat quantification in smaller organs such as the pancreas.

Arterial spin labeling CMR perfusion imaging is capable of continuously monitoring myocardial blood flow during stress

Background Myocardial arterial spin labeling (ASL) is a non-invasive non-contrast CMR perfusion imaging technique [Zun et al., ‘09] that is compatible with adenosine stress testing [Zun et al., ‘11]. Here, we demonstrate its ability to continuously monitor MBF during stress, which has a variety of potential applications including interventional CMR and the study of endothelial function. We used mild sustained isometric handgrip stress.

Impact of ranolazine on myocardial metabolic ischemia detected by phosphorus-31 magnetic resonance spectroscopy

Background Ranolazine (RAN) is a novel late sodium current inhibitor, effective in treating angina pectoris in patients with chronic stable CAD. Its therapeutic effectiveness is not well understood. It is thought to reduce myocardial energy utilization by enhancing diastolic relaxation and by increasing myocardial blood flow. The purpose of the present study is to define the mechanism for the effectiveness of RAN. We applied myocardial phosphorus-31 magnetic resonance spectroscopy (P-31 MRS) at rest and during handgrip stress to demonstrate the relationship between RAN treatment and stress-induced energy utilization with myocardial ischemia.

Cardiovascular Magnetic Resonance and Multidetector Computed Tomography

The advanced imaging technologies, cardiovascular computed tomography (using X-ray), and cardiovascular magnetic resonance (using magnetic and radio frequency or RF fields) generally provide more comprehensive and frequently unique clinical information compared with other technologies. They are not used routinely, but rather for specific indications. Since they are more technically advanced, they are more expensive and require additional knowledge for proper acquisition and interpretation. The strength of CCT resides in its ability to provide excellent imaging quality of the large- and medium-sized coronary arteries using IV-administered contrast medium. While CCT utilizes X-rays, the radiation dose is drastically decreasing with improving technology. The strengths of CMR are the ability to visualize morphology, function, perfusion, viability, and metabolism without ionizing radiation, although sometimes requiring IV gadolinium contrast agent. These two technologies have received relatively recent Nobel prizes (one for CT and three for MRI), and both continue to improve with the advent of new software and hardware. This chapter provides a background for most of the commonly employed applications of computed tomography and magnetic resonance imaging of the heart.

Development of control system for optimal stress during cardiac MR spectroscopy

Introduction To induce changes in myocardial metabolism monitored by 31P MRS in patients with symptoms of coronary artery disease, handgrip stress test is frequently used. At a level of stress of 30% maximum voluntary contraction, it is critical to maintain a continuous stress level. Otherwise, the phosphate metabolic alterations tend to recover quickly, and any changes would disappear with involuntary loss of the stress. In practice, it is very difficult for patients to maintain a constant pressure level and involuntary adaptation of the patient would interfere with the measurement of such changes.

Stress P-31 MR spectroscopy for detection of myocardial microvascular disease in Latino type-1 diabetes mellitus patients

Introduction Diabetes mellitus (DM) have an increased incidence of coronary artery disease. However, diabetics are also known to have microvascular disease involving the kidneys, the peripheral nerves and the retina. Accordingly, in view of the multisystem involvement of microvascular disease, involvement of the myocardium is clearly feasible. We have previously used 31P MRS to detect microvascular disease. We observed that a decrease in phosphocreatine (PCr), adenosine triphosphate (ATP), PCr/ATP ratio with stress myocardial 31P MRS suggests myocardial ischemia in the absence of coronary artery stenosis.