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M V McConnell

Publications and source records attributed to M V McConnell.

18 recordsLinked to original sources
PubMed2002

Echocardiographic and magnetic resonance methods for diagnosing hibernating myocardium.

Hibernating myocardium refers to regions of impaired left ventricular function at rest due to coronary artery disease that is reversible with revascularization. The accurate identification and assessment of myocardial viability is a critical aspect of the management of the patient with coronary artery disease and left ventricular dysfunction. Several non-invasive methods exist to assist the clinician in distinguishing those patients with significant regions of hibernating myocardium from those who have non-viable scar. This is important not only to identify those patients who would most benefit from percutaneous intervention or surgery, but also to spare the latter group from the morbidity and mortality associated with a revascularization procedure that would provide little benefit. While nuclear medicine imaging is the most widely used means for evaluating myocardial viability, alternative modalities have emerged and have gained increasing acceptance in recent years. This article will review the echocardiographic and magnetic resonance imaging (MRI) methods that are currently available or under investigation to assess myocardial viability. These techniques include rest and stress echocardiography, myocardial contrast echocardiography, stress MRI, contrast-enhanced MRI and magnetic resonance spectroscopy (MRS).

Cardiotonic Agents↗
PubMed2000

Imaging techniques to predict cardiovascular risk.

Conventional cardiovascular imaging, with a focus on identifying flow-limiting stenoses, does not directly image the atherosclerotic lesion. Recent clinical and pathobiologic data indicate that stenosis severity does not dictate cardiovascular risk and that there are functional, structural, and biologic features of atherosclerosis that are associated with cardiovascular events. Imaging technologies, such as ultrasound, light, x-ray, magnetic resonance, and targeted contrast agents, have been developed to characterize directly the atherosclerotic vessel wall. They provide promising approaches to predict cardiovascular risk and facilitate further study of the mechanisms of atherosclerosis progression and its response to therapy.

Coronary Artery Disease↗
PubMed2000

Clinical role of coronary magnetic resonance angiography in the diagnosis of anomalous coronary arteries.

Though rare, anomalous coronary artery disease is a well-known cause of myocardial ischemia and sudden death among children and young adults. The projectional nature of conventional x-ray angiography often leads to difficulty in the definition of anomalous vessels. Studies have now documented the high accuracy of coronary magnetic resonance angiography (MRA) for the noninvasive detection and definition of anomalous coronary arteries among patients with suspected anomalous coronary arteries of congenital conditions associated with anomalous coronary arteries. With increasing clinical experience, coronary MRA will likely emerge as the gold standard for the diagnosis of this condition.

Coronary Disease↗
PubMed1999

Contrast agent-enhanced, free-breathing, three-dimensional coronary magnetic resonance angiography.

For free-breathing, high-resolution, three-dimensional coronary magnetic resonance angiography (MRA), the use of intravascular contrast agents may be helpful for contrast enhancement between coronary blood and myocardium. In six patients, 0.1 mmol/kg of the intravascular contrast agent MS-325/AngioMARK was given intravenously followed by double-oblique, free-breathing, three-dimensional inversion-recovery coronary MRA with real-time navigator gating and motion correction. Contrast-enhanced, three-dimensional coronary MRA images were compared with images obtained with a T2 prepulse (T2Prep) without exogenous contrast. The contrast-enhanced images demonstrated a 69% improvement in the contrast-to-noise ratio (6.6 +/- 1.1 vs. 11.1 +/- 2.5; P < 0.01) compared with the T2Prep approach. By using the intravascular agent, extensive portions (> 80 mm) of the native left and right coronary system could be displayed consistently with sub-millimeter in-plane resolution. The intravascular contrast agent, MS-325/AngioMARK, leads to a considerable enhancement of the blood/muscle contrast for coronary MRA compared with T2Prep techniques. The clinical value of the agent remains to be defined in a larger patient series. J. Magn. Reson. Imaging 1999;10:790-799.

Contrast Media↗
PubMed1999

MRI of rabbit atherosclerosis in response to dietary cholesterol lowering.

Direct imaging of the atherosclerotic plaque, rather than the angiographic lumen, may provide greater insight into the response of atherosclerosis to cholesterol-lowering therapy. Aortic plaque was studied in vivo by MRI in rabbits undergoing dietary cholesterol intervention. Thirty-one rabbits underwent aortic balloon injury and high-cholesterol diet for 4 months and then were assigned to low-cholesterol versus continued high-cholesterol diet for up to an additional 16 months. High-resolution (310 micrometer) fast spin-echo MRI of the abdominal aorta was performed at 4, 12, and 20 months and compared with histology. MRI demonstrated a significant reduction in % area stenosis in rabbits placed on low-cholesterol diet (44.6+/-2. 1% at 20 months versus 55.8+/-1.5% at 4 months, P=0.0002). In contrast, % area stenosis increased in rabbits maintained on high-cholesterol diet (69.8+/-3.8% at 20 months versus 55.8+/-1.5% at 4 months, P=0.001). Similarly, plaque thickness decreased significantly in the low-cholesterol group (0.60+/-0.05 mm at 20 months versus 0.85+/-0.06 mm at 4 months, P=0.006), with a trend toward increase in the high-cholesterol group (1.02+/-0.08 mm at 20 months versus 0.85+/-0.06 mm at 4 months, P=0.1). Thus, in rabbits undergoing dietary cholesterol lowering, MRI detected regression of aortic atherosclerotic plaque in vivo. Plaque progression was seen with maintenance of high-cholesterol diet. MRI is a promising noninvasive technology for directly imaging atherosclerosis and its response to therapeutic interventions.

Animals↗
PubMed1997

Effects of a single, daily alcoholic beverage on lipid and hemostatic markers of cardiovascular risk.

There is substantial epidemiologic data, but limited experimental data, supporting the mortality benefit of low-dose alcohol consumption. A regimen of a single, daily alcoholic beverage was sufficient to increase both high-density lipoprotein (HDL) (4.4%, p = 0.03) and HDL2 (7.7%, p = 0.04) in men and women, but did not significantly affect hemostatic markers of cardiovascular risk.

Adult↗
PubMed1997

Prospective adaptive navigator correction for breath-hold MR coronary angiography.

Current MR coronary angiography (MRCA) methods use breath-holding to minimize respiratory motion. A major limitation to this technique is misregistration between imaging slices due to breath-hold variability. Prospective adaptive correction of image location using real-time navigator measurement of diaphragm position is a potential method for improving slice registration in breath-hold MRCA. Ten subjects underwent MRCA using an ECG-gated, fat-suppressed, segmented k-space, gradient-echo sequence. Transverse and coronal images were acquired using standard breath-holding with and without prospective navigator correction. Breath-hold MRCA with prospective navigator correction resulted in a 47% reduction in craniocaudal slice registration error compared to standard breath-holding (0.9 +/- 0.2 mm versus 1.7 +/- 0.4 mm, P = 0.04). Prospective adaptive navigator correction of image location significantly improves slice registration for breath-hold MRCA and is a promising motion correction technique for cardiac MR.

Adult↗
PubMed1997

Prospective navigator correction of image position for coronary MR angiography.

PURPOSE: To determine the potential benefit of prospective navigator correction of image position for coronary magnetic resonance (MR) angiography. MATERIALS AND METHODS: Two-dimensional MR angiograms were obtained with free breathing in 12 adult subjects. Navigator gating was used with and without prospective correction and with gating windows set at 3, 5, and 7 mm. MR angiograms were compared with those obtained with conventional, end-expiratory breath holding. RESULTS: Navigator gating with correction resulted in image quality equivalent to that obtained with breath holding, even with the 7-mm gating window. In contrast, navigator gating without correction allowed only maintenance of image quality similar to that obtained with breath holding for the 3- and 5-mm windows and resulted in decreased image quality with the 7-mm window (P < .05). Use of navigator gating with correction and the 7-mm window resulted in a 28% decrease in imaging time compared with breath holding and a 33% decrease compared with the 3-mm gating window (P < .05 for both comparisons). CONCLUSION: Prospective, adaptive navigator correction of image position for free-breathing coronary MR angiography is a promising, novel approach to compensate for respiratory motion.

Adult↗
PubMed1997

Comparison of respiratory suppression methods and navigator locations for MR coronary angiography.

OBJECTIVE: Currently, breath-holding during MR coronary angiography is used to minimize respiratory motion. This technique requires patient cooperation and is associated with slice registration errors. The goal of this study was to evaluate alternative non-breath-hold techniques for MR coronary angiography during free breathing. SUBJECTS AND METHODS: Subjects underwent MR coronary angiography using an ECG-gated, fat-suppressed, segmented K-space, gradient-echo sequence. Images were obtained during free breathing using both real-time navigator gating and respiratory bellows gating. These were compared with images obtained during conventional breath-holding. The optimal navigator location (diaphragmatic or cardiac) was also studied. Image quality, registration error, and scan time were measured for all scans. RESULTS: Navigator gating for MR coronary angiography during free breathing resulted in image quality equivalent to that obtained during breath-holding and was superior to that obtained with respiratory bellows gating (p < .04). Also, navigator gating reduced registration errors by 75% compared with breath-holding (p < .01) and did not increase scan time. No significant differences in the parameters measured were observed among the different navigator locations. CONCLUSION: Real-time navigator gating for MR coronary angiography during free breathing achieved image quality and scan time equivalent to breath-holding. Navigator gating also significantly reduced registration error. Compared with breath-holding and respiratory bellows gating, navigator gating during free breathing is a more optimal approach for suppression of respiratory motion during MR coronary angiography.

Adult↗
PubMed1996

Pathogenic mechanisms of atherosclerosis: effect of lipid lowering on the biology of atherosclerosis.

Numerous trials have demonstrated that cholesterol-lowering therapy leads to marked reductions in cardiovascular and overall mortality and in the need for coronary revascularization. Angiographic regression trials have shown that cholesterol lowering can reduce progression and, in some instances, achieve regression of coronary atherosclerotic lesions. However, recent studies have contradicted the traditional view that the clinical course of coronary artery disease is closely linked to the severity of coronary artery stenosis. It is now apparent that stenoses responsible for myocardial infarction or unstable angina are typically mild rather than severe. These observations suggest that regression may not be the principal mechanism by which cholesterol lowering affects cardiovascular risk. Two mechanisms---plaque stabilization and improved endothelial function-have been examined in this regard. Basic studies suggest that cholesterol lowering favorably alters those features of atherosclerosis that promote plaque stability. Recent clinical studies have clearly established that aggressive lipid-lowering therapy improves endothelial function and reduces myocardial ischemia in patients with hypercholesterolemia.

Acetylcholine↗
PubMed1996

Regional right ventricular dysfunction detected by echocardiography in acute pulmonary embolism.

This study analyzed the regional pattern of right ventricular (RV) dysfunction on transthoracic echocardiograms in patients with and without acute pulmonary embolism. Quantitative (centerline) and qualitative (wall motion score) analyses of segmental RV free wall motion were performed on a "training" cohort of 41 patients (group 1), including 14 patients with acute pulmonary embolism, 9 patients with primary pulmonary hypertension, and 18 normal subjects. Patients with acute pulmonary embolism had a distinct regional pattern of RV dysfunction, with akinesia of the mid-free wall (centerline excursion: -0.2 +/- 0.8 mm, p = 0.0001 vs normal) but normal motion at the apex (centerline excursion: 5.7 +/- 0.8 mm, p = NS vs normal). In contrast, patients with primary pulmonary hypertension had abnormal wall motion in all regions (p <0.03 vs normal). This echocardiographic finding of normal wall motion at the apex and abnormal wall motion in the mid-free wall in acute pulmonary embolism was then tested in a "validation" cohort of 85 patients (group 2), consisting of hospitalized patients with RV dysfunction from any cause, including 13 patients with acute pulmonary embolism. The finding had a 77% sensitivity and a 94% specificity for the diagnosis of acute pulmonary embolism, with a positive predictive value of 71% and a negative predictive value of 96%. Thus, a distinct echocardiographic pattern of regional RV dysfunction, in which the apex is spared occurs in acute pulmonary embolism. This finding should raise the level of clinical suspicion for the diagnosis of acute pulmonary embolism.

Acute Disease↗
PubMed1995

Identification of anomalous coronary arteries and their anatomic course by magnetic resonance coronary angiography.

BACKGROUND: Anomalous coronary arteries are a rare but recognized cause of myocardial ischemia and sudden death. Identification currently requires x-ray angiography, which may have difficulty defining the three-dimensional course of the anomalous vessel. Magnetic resonance coronary angiography (MRCA) has been shown to image coronary artery anatomy noninvasively. We hypothesize that MRCA may be useful in the identification of anomalous coronary arteries and their anatomic course. METHODS AND RESULTS: Sixteen patients (9 men, 7 women, age 44 to 81 years) with anomalous aortic origins of the coronary arteries by conventional x-ray angiography underwent MRCA. Multiple images of the major epicardial coronary arteries were obtained by use of a breathhold, fat-suppressed, segmented-k space, gradient-echo technique by investigators blinded to all patient data. Anomalous coronary artery pathology, by x-ray angiography, included right-sided left main coronary artery (n = 3), right-sided left circumflex artery (n = 6), separate left-sided left anterior descending and left circumflex arteries (n = 2), left-sided right coronary artery (n = 4), and an anteriorly displaced right coronary artery (n = 1). MRCA correctly identified the anomalous coronary vessel(s) in 14 of 15 patients. In 1 patient, the anomalous vessel was incorrectly identified, and in 2 patients the course of the anomalous vessel was not clearly seen; one of these was a nondominant, anomalous right coronary artery. CONCLUSIONS: MRCA is a useful technique for the noninvasive identification of anomalous coronary arteries and their anatomic course.

Adult↗
PubMed1989

Cellular basis of allograft rejection in vivo. V. Examination of the mechanisms responsible for the differing efficacy of monoclonal antibody to CD4+ T cell subsets in low- and high-responder rat strains.

MRC OX35, an anti-CD4 mAb, was used to treat high responder Wistar Furth (W/F) (RT1u) and low responder DA (RT1a) rats which had been grafted with directly vascularized hearts from PVG (RT1c) rats across a full MHC plus non-MHC incompatibility. Four doses of mAb at 7 mg/kg given in the first 2 wk postgrafting induced indefinite graft survival (greater than 150 days) in DA hosts, but only delayed rejection to 18 to 42 days in W/F as compared to rejection times of 6 to 8 days in untreated rats. The extension of MRC OX35 treatment to 6 wk in W/F rats induced indefinite graft survival in three of six rats. During treatment MRC OX35 therapy only partially depleted CD4+ cells, and all circulating CD4+ cells were coated with MRC OX35. The capacity of naive CD4+ and CD8+ cells from W/F and DA to be activated to PVG alloantigen was compared both in vitro in an MLC assay and in vivo by an adoptive transfer assay of their capacity to restore rejection of PVG heart grafts in irradiated syngeneic hosts. CD4+ cells from both W/F and DA proliferated in MLC and restored graft rejection. W/F CD8+ cells both proliferated in MLC and restored rejection, but DA CD8+ cells neither proliferated nor reconstituted rejection. Examination of lymphocytes from MRC OX35 treated hosts with long-surviving grafts showed that they were neither depleted of CD4+ T cells nor did they lack the capacity to proliferate to PVG Ag in MLC, this response being similar to that to third-party Ag or by naive lymphocytes. Compared to first-set rejection, PVG skin graft rejection was delayed 2 to 3 days in W/F and 10 to 12 days in DA rats with long-surviving grafts after MRC OX35 therapy, whereas they rejected third-party skin grafts in first-set tempo. These studies show that differences in graft survival in anti-CD4 treated low and high responder strains may be due to the inherent capacity of CD8+ cells to be activated to effect rejection independent of CD4+ cells in W/F but not in DA. In those hosts that accept grafts, there is no evidence of clonal deletion, but there appears to be a form of unresponsiveness akin to that induced in adult rats by other immunosuppressive therapies that protects the graft from rejection.

Animals↗
PubMed1985

Pacemaker diagnostic diagrams.

Dual-chamber pacemakers interact with cardiac rhythms in complex ways. The resultant surface electrocardiograms (ECGs) are often very difficult to interpret. A simple and automatic diagnostic diagram is described that graphically illustrates pacemaker-heart interactions. Pacemaker operation is explained by a continuous series of lines and symbols that interconnect any sequence of paced and sensed events in both chambers. Fixed, programmable, and adaptive pacemaker timing intervals are all shown in a simple format. The pacemaker diagnostic diagram is plotted directly below the ECG to help users interpret the paced cardiac rhythm. The pacemaker diagnostic diagram is generated by software in a pacemaker programmer from: (1) telemetered real-time event markers; (2) fixed and programmable timing parameters (lower rate, AV interval, etc.); (3) pacemaker conditional logic. If this computer analysis of the telemetered event markers is not consistent with normal pacemaker operation, a specific error-message is printed. The pacemaker diagnostic diagram should be useful for instruction, pacemaker follow-up, and troubleshooting.

Arrhythmias, Cardiac↗
PubMedDate not supplied

Adaptive correction of imaging plane position in segmented k-space cine cardiac MRI.

Variability among breath-holds frequently produces registration errors, a situation that may contribute to reproducibility error in anatomic indices. A navigator-echo-based method for real-time prospective correction of imaging slice level was applied to breath-hold cine cardiac imaging of 13 subjects. Repeat acquisitions with correction in the cardiac short-axis orientation showed significantly improved reproducibility in fractional area change and endocardial centroid location as compared with conventional noncorrected methods.

Adult↗