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Biomedical subjects

Christopher M Kramer

Publications and source records attributed to Christopher M Kramer.

At least 19 recordsLinked to original sources
PubMed2007

Can late gadolinium enhancement by cardiovascular magnetic resonance identify coronary artery disease as the etiology of new onset congestive heart failure?

BACKGROUND: New left ventricular systolic dysfunction affects 500,000 Americans and coronary artery disease (CAD) is responsible for two-thirds of cases. Identifying CAD has both prognostic and therapeutic implications. We evaluated the ability of late gadolinium enhancement (LGE) by cardiovascular magnetic resonance imaging (CMR) to detect CAD as the etiology of recent onset congestive heart failure (CHF). METHODS: CMR and LGE were performed in 26 patients with new onset left ventricular systolic dysfunction. All patients received an x-ray angiography for identification of CAD. Patients with an acute coronary syndrome with troponin I > 1.0 ng/ml or a history of CAD were excluded. The presence and distribution of LGE was evaluated. RESULTS: Significant coronary stenoses were present in 5 of 26 patients (19%). LGE in an infarct pattern was found in 2 of the 5 patients with CAD. Of the 21 patients without CAD, 2 had midwall enhancement but none had evidence of LGE in an infarct pattern. CONCLUSIONS: When present, LGE in an infarct pattern suggests CAD as the etiology of new onset CHF. However, the absence of LGE does not exclude CAD as the underlying etiology. A small proportion of patients with a nonischemic cause of new onset CHF have LGE limited to the midwall.

Adult↗
PubMed2007

Reproducibility and reliability of atherosclerotic plaque volume measurements in peripheral arterial disease with cardiovascular magnetic resonance.

A high resolution, noninvasive approach to quantify atherosclerotic plaque in the peripheral vasculature could have significant clinical and research utility. Seventeen patients with peripheral arterial disease (PAD) were studied in a 1.5T CMR scanner. Atherosclerotic plaque volume in the superficial femoral artery was measured and interobserver, intraobserver, and test-retest variability determined. Nineteen vessels were studied with mean acquisition time of 13.1 minutes per vessel. Mean plaque volume was 7.27 +/- 3.73 cm3. Intra-observer intraclass correlation was R = 0.997, inter-observer was R = 0.987, and test-retest reproducibility was R = 0.996. Thus, high resolution measurement of plaque volume in PAD is reliable and reproducible.

Adult↗
PubMed2007

MRI of atherosclerosis: diagnosis and monitoring therapy.

Atherosclerosis is a prevalent disease affecting millions of Americans. Despite our advances in diagnosis and treatment, atherosclerosis is the leading cause of death in America. High-resolution magnetic resonance imaging has overcome the limitations of current angiographic techniques and has emerged as a leading noninvasive imaging modality for atherosclerotic disease. Atherosclerosis of the arterial wall of the human carotid, aortic, peripheral and coronary arteries have all been successfully evaluated. In addition, the power of magnetic resonance imaging to differentiate the major components of atherosclerotic plaque has been validated. The ability to image the vessel wall and risk stratify atherosclerotic plaque will create management decisions not previously faced, and has the potential to change the way atherosclerosis is treated.

Atherosclerosis↗
PubMed2006

ACCF/ACR/SCCT/SCMR/ASNC/NASCI/SCAI/SIR 2006 appropriateness criteria for cardiac computed tomography and cardiac magnetic resonance imaging: a report of the American College of Cardiology Foundation Quality Strategic Directions Committee Appropriateness Criteria Working Group, American College of Radiology, Society of Cardiovascular Computed Tomography, Society for Cardiovascular Magnetic Resonance, American Society of Nuclear Cardiology, North American Society for Cardiac Imaging, Society for Cardiovascular Angiography and Interventions, and Society of Interventional Radiology.

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Cardiovascular Diseases↗
PubMed2006

Delayed calf muscle phosphocreatine recovery after exercise identifies peripheral arterial disease.

OBJECTIVES: In this study we intend to characterize phosphocreatine (PCr) recovery kinetics with phosphorus-31 ((31)P) magnetic resonance spectroscopy in symptomatic peripheral arterial disease (PAD) patients compared with control subjects and determine the diagnostic value and reproducibility of this parameter. BACKGROUND: Due to the inconsistent relationship between flow and function in PAD, novel techniques focused on the end-organ are needed to assess disease severity and measure therapeutic response. METHODS: Fourteen normal subjects (5 men, age 45 +/- 14 years) and 20 patients with mild-to-moderate symptomatic PAD (12 men, age 67 +/- 10 years, mean ankle brachial index 0.62 +/- 0.13) were studied. Subjects exercised one leg to exhaustion while supine in a 1.5-T magnetic resonance scanner using a custom-built plantar flexion device. Surface coil-localized, free induction decay acquisition localized to the mid-calf was used. Each 31P spectrum consisted of 25 signal averages at a repetition time of 550 ms. The PCr recovery time constant was calculated by monoexponential fit of PCr versus time, beginning at exercise completion. RESULTS: Median exercise time was 195.0 s in normal subjects and 162.5 s in PAD patients (p = 0.06). Despite shorter exercise times in patients, the median recovery time constant of PCr was 34.7 s in normal subjects and 91.0 s in PAD patients. Area under the receiver-operating characteristic curve was 0.925 +/- 0.045. Test-retest reliability was excellent. CONCLUSIONS: The PCr recovery time constant is prolonged in patients with symptomatic PAD compared with normal subjects. The method is reproducible and may be useful in the identification of disease. Further study of this parameter's ability to track response to therapy as well as its prognostic capability is warranted.

Adult↗
PubMed2006

Technology insight: in vivo cell tracking by use of MRI.

Animal studies have shown some success in the use of stem cells of diverse origins to treat heart failure and ventricular dysfunction secondary to ischemic injury. The clinical use of these cells is, therefore, promising. In order to develop effective cell therapies, the location, distribution and long-term viability of these cells must be evaluated in a noninvasive manner. MRI of cells labeled with magnetically visible contrast agents after either direct injection or local or intravenous infusion has the potential to fulfill this goal. In this Review, techniques for labeling and imaging a variety of cells will be discussed. Particular attention will be given to the advantages and limitations of various contrast agents and passive and facilitated cell-labeling methods, as well as to imaging techniques that produce negative and positive contrast, and the effect on image quantification of compartmentalization of contrast agents within the cell.

Animals↗
PubMed2006

The evolving role of cardiovascular magnetic resonance imaging in nonischemic cardiomyopathy.

Over the last several years, the role of cardiac magnetic resonance imaging in the diagnosis and management of heart failure has been rapidly expanding. The techniques unrivaled flexibility, accuracy in defining ventricular structure and function, and capacity to characterize tissue makes it particularly well suited for the study of the nonischemic cardiomyopathies. In this article, we provide an overview of the existing literature highlighting the diagnostic utility and prognostic power of cardiac magnetic resonance imaging in the nonischemic cardiomyopathies.

Amyloidosis↗
PubMed2006

Reperfused myocardial infarction in mice: 3D mapping of late gadolinium enhancement and strain.

We developed mathematical modeling tools for mapping 3D infarct geometry from multislice late gadolinium enhancement data, allowing fusion with multislice MR tagging data, in mice with myocardial infarction. Five C57BL/6 mice were imaged at baseline, 1, 7 and 28 days after 60 min occlusion of the left anterior descending coronary artery. The 3D infarct geometry was mapped in material coordinates, and registered with 3D strain, showing permanent dysfunction in infarcted segments, intermediate function in the adjacent zone, and maintained function in the remote zone. 3D mapping of late enhancement and strain allows registration of multiple studies in a consistent framework.

Analysis of Variance↗
PubMed2006

Magnetic resonance for the assessment of myocardial viability.

PURPOSE OF REVIEW: Cardiac magnetic resonance imaging has an expanding role as a preferred modality for the detection and characterization of myocardial viability. RECENT FINDINGS: Improving the accuracy of cardiac magnetic resonance for detecting viable myocardium has been one focus of investigators. In segments with intermediate transmurality of late gadolinium enhancement, dobutamine response improves the predictive power of cardiac magnetic resonance. A subtractive imaging technique with both short and long inversion times can enhance discrimination of subendocardial infarction and blood pool, but with increased noise and misregistration artifacts. Similar pharmacokinetics between cardiac magnetic resonance contrast agents and computed tomography contrast allows delayed enhancement imaging with computed tomography. Contrast between normal segments and scar remains vastly superior with cardiac magnetic resonance and no radiation is administered. Quantitation of blood flow demonstrated that resting myocardial blood flow is reduced in hibernating myocardium. SUMMARY: Because of its safety, accuracy, ease of interpretation, and increasing availability, cardiac magnetic resonance-based assessment of myocardial viability has quickly transitioned from bench to bedside. Routine clinical implementation has prompted improved diagnostic capabilities and easier image interpretation. As a research tool, cardiac magnetic resonance continues to provide valuable insights into the fundamental nature of viability.

Cardiomyopathies↗
PubMed2006

Dobutamine response and myocardial infarct transmurality: functional improvement after coronary artery bypass grafting--initial experience.

The Investigational Review Board approved the protocol, and all patients provided signed informed consent. The protocol was compliant with HIPAA. The purpose of the study was to prospectively test the hypothesis that addition of low-dose dobutamine and quantification of inotropic reserve in segments with 1%-50% infarct transmurality (IT) would improve the predictive value for functional recovery after revascularization in chronic infarction. Fifteen patients with multivessel coronary artery disease and left ventricular systolic dysfunction were enrolled prior to coronary artery bypass grafting (CABG). Late gadolinium-enhanced cardiac magnetic resonance (MR) imaging was used to assess IT. The percentage of wall thickening was measured with cine cardiac MR imaging at rest and during infusion of 10 (microg . kg(-1))/min dobutamine. Repeat cardiac MR imaging was performed 20 weeks +/- 4 (standard error) later. Functional parameters according to segment were compared before and after CABG by using F tests with repeated-measures models. In segments with 1%-50% IT, similar functional recovery was noted in those with 1%-25% or 26%-50% IT. However, in the same segments, those that improved with dobutamine to normal range demonstrated greater improvement in the percentage of wall thickening (22% +/- 4) after revascularization than those that did not (9% +/- 4) (P < .04). In 1%-50% IT, a normal dobutamine response helps differentiate segments with greater functional recovery after CABG.

Adult↗
PubMed2006

Carotid artery calcification on CT may independently predict stroke risk.

OBJECTIVE: The purpose of our study was to quantitatively evaluate calcified atherosclerotic burden in the cervical carotid arteries using MDCT to determine the relationship of scores with luminal stenosis and symptomatology. MATERIALS AND METHODS: Calcium plaque volume was measured in 106 cervical carotid arteries (53 patients) using MDCT angiography. The study group included 32 asymptomatic patients (mean age, 70.2 +/- 8.7 [SD] years; 15 women, 17 men) and 21 patients with ischemic neurologic symptoms (69.6 +/- 12.9 years; eight women, 13 men). By vessel, there were 43 high-grade stenotic (> or = 60% by North American Symptomatic Carotid Endarterectomy Trial [NASCET] criteria), 15 moderate-grade stenotic (30-59%), and 44 mild-grade stenotic or normal (0-29%) vessels, with four excluded for prior carotid endarterectomy. Volume scores were calculated by summing the area of calcium in the common and extracranial internal carotid arteries on axial slices and multiplying by the slice increment. RESULTS: Controlling for cardiovascular risk factors and luminal stenosis, we found that scores were significantly related to the occurrence of symptoms (p = 0.003). Even with patient age as a covariant, patients with high-grade stenosis had significantly higher scores than those without high-grade disease (p = 0.004). Moreover, quantitative burden was associated with luminal stenosis on adjusted multivariate analysis (p = 0.034). The specificity and positive predictive value for high-grade luminal narrowing were notably lower on individual vessel analysis than on total score analysis, likely secondary to variability in vascular remodeling. CONCLUSION: Calcium scores in the cervical carotid arteries may represent an independent marker for luminal stenosis and ischemic symptoms. A prospective longitudinal study examining calcium levels and morbidity may be warranted to examine whether burden has a role in risk stratification.

Aged↗
PubMed2006

Surgical and endovascular repair of aortic coarctation: normal findings and appearance of complications on CT angiography and MR angiography.

OBJECTIVE: A variety of treatment options exist for aortic coarctation, both surgical and catheter-based. Knowledge of the normal radiologic appearance of these, as well as their typical complications, is essential for interpretation of CT and MR angiographic studies in these patients. CONCLUSION: CT and MR angiography are noninvasive techniques that are well suited to follow patients after coarctation repair.

Adult↗
PubMed2006

High left ventricular mass index does not limit the utility of fractional flow reserve for the physiologic assessment of lesion severity.

OBJECTIVES: To demonstrate that fractional flow reserve (FFR) of vessels in patients with high left ventricular mass index (LVMI) should be similar to that of matched vessels in patients with normal LVMI. BACKGROUND: FFR is a physiologic index of coronary lesion severity. It is not known whether FFR remains useful in the setting of increased LVMI, when microvascular abnormalities may be present. METHODS: LVMI was calculated in 84 patients using contrast left ventriculography after validation with cardiac magnetic resonance imaging. Cardiac risk factors, LV ejection fraction (LVEF), minimal lumen diameter (MLD), percent diameter stenosis (%DS), lesion length and FFR were compared in 22 patients with high LVMI to 62 patients with normal LVMI and angiographically-matched vessels. RESULTS: LVMI was 126 +/- 21 g/m2 in the high LVMI group and 84 +/- 21 g/m2 in the normal LVMI group. There were no differences in age, LVEF, diabetes, hypertension or dyslipidemia between groups. Angiographic lesion characteristics were well matched in patients with high versus normal LVMI (MLD 1.3 +/- 0.6 mm vs. 1.3 +/- 0.6 mm, %DS 61 +/- 13% vs. 62 +/- 13%, and lesion length 14.2 +/- 7.0 mm vs. 14.3 +/- 7.0 mm; p = NS for all). Importantly, no difference in FFR was observed (0.79 +/- 0.12 vs. 0.78 +/- 0.16; p = NS) between the groups, and LVMI did not correlate with FFR in a multivariate analysis. CONCLUSIONS: FFR of coronary lesions in patients with high LVMI is no different than FFR of angiographically-matched lesions in patients with normal LVMI, suggesting that high LV mass should not limit the utility of FFR as an index of coronary lesion severity.

Blood Flow Velocity↗
PubMed2005

Interaction between AT1 and AT2 receptors during postinfarction left ventricular remodeling.

The relative contribution of the angiotensin II type 1 and 2 receptors (AT1-R and AT2-R) in postmyocardial infarction (MI) remodeling remains incompletely understood. We studied five groups of C57Bl/6 mice after 1 h of left anterior descending artery occlusion-reperfusion: 1) wild type, untreated (n = 12); 2) wild type, treated with the AT1-R blocker losartan (10-20 mg.kg(-1).day(-1) in drinking water) from day 1 to day 28 post-MI (n = 10); 3) cardiac overexpression of the AT2-R [AT2-transgenic (TG); n = 14]; 4) AT2-TG treated with losartan (n = 13); and 5) AT2-TG and null for the AT1a-R [AT2-TG/AT1 knockout (KO); n = 10]. Cardiac magnetic resonance imaging (CMR) measured ejection fraction and left ventricular end-diastolic and end-systolic volume (EDVI and ESVI) and mass indexed to weight on days 0, 1, 7, and 28 post-MI. Infarct size was measured on day 1 by late gadolinium-enhanced CMR. Regional myocyte hypertrophy and collagen content were measured on day 28 post-MI. Infarct size was similar among groups. Systolic blood pressure was lowest in AT2-TG/AT1KO. By day 28 post-MI, when corrected for baseline differences, EDVI and ESVI were higher and ejection fraction was lower in wild type than other groups. Ejection fraction was highest and EDVI and mass index were lowest in AT2-TG/AT1KO at day 28. The AT2-TG/AT1KO demonstrated less fibrosis in adjacent regions. Regional myocyte hypertrophy was similar in all groups. The AT1-R and AT2-R are intricately intertwined in post-MI remodeling. Pharmacological blockade of AT1-R is equivalent to AT2-R overexpression in attenuating post-MI remodeling. Genetic knockout of the AT1a-R is additive to AT2-R overexpression, due, at least in part, to blood pressure lowering.

Animals↗