Craig H. Scott

Assessment of global and regional myocardial function in the mouse using cine and tagged MRI.

Mouse models are expected to play an important role in future investigations of human cardiac diseases. In the present report, MRI methods for determining global and regional cardiac function in the mouse are demonstrated. ECG‐gated cine images were acquired in five C57BL/6 mice at physiological temperatures (37°C) and heart rates of 500 ± 50 beats per minute. Left ventricular mass, ejection fraction, and cardiac output were estimated from the resulting images. Regional myocardial function was also determined in three animals by application of 2D SPAtial Modulation of Magnetization (SPAMM) in combination with the cine protocol. The quality of the tagged images was sufficient to allow mapping of myocardial strains and displacements. The results of the regional strain analysis were consistent with similar studies in larger animals. This work demonstrates the first characterization of regional myocardial function in the mouse via SPAMM techniques. Magn Reson Med 49:760–764, 2003.

Ultrafast three-dimensional contrast-enhanced magnetic resonance angiography and imaging in the diagnosis of partial anomalous pulmonary venous drainage

OBJECTIVES The purpose of our study was to evaluate patients with suspected anomalous pulmonary veins (APVs) and atrial septal defects (ASDs) using fast cine magnetic resonance imaging (MRI) and ultrafast three-dimensional magnetic resonance angiography (MRA). BACKGROUND Precise anatomic definition of anomalous pulmonary and systemic veins, and the atrial septum are prerequisites for surgical correction of ASDs. Cardiac catheterization and transesophageal echocardiography (TEE) are currently used to diagnose APVs, but did not provide complete information in our patients. METHODS Twenty consecutive patients with suspected APVs were studied by MRA after inconclusive assessment by catheterization, TEE or both. The MRI images were acquired with a fast cine sequence and a novel ultrafast three-dimensional sequence before and after contrast injection. RESULTS Partial anomalous pulmonary venous drainage was demonstrated in 16 of 20 patients and was excluded in four patients. Magnetic resonance imaging correctly diagnosed APVs and ASDs in all patients (100%) who underwent surgery. For the diagnosis of APVs, the MRI and catheterization results agreed in 74% of patients and the MRI and TEE agreed in 75% of patients. For ASDs, MRI agreed with catheterization and TEE in 53% and 83% of patients, respectively. CONCLUSIONS Fast cine MRI with three-dimensional contrast-enhanced MRA provides rapid and comprehensive anatomic definition of APVs and ASDs in patients with adult congenital heart disease in a single examination.

Effect of dobutamine on regional left ventricular function measured by tagged magnetic resonance imaging in normal subjects

The effect of inotropic stimulation on the pattern and magnitude of regional left ventricular contraction was studied using tagged magnetic resonance imaging to assess whether dobutamine exacerbates variation in regional contraction at rest. Dobutamine stress testing defines a normal response as a homogeneous increase in regional wall motion. In 8 normal subjects, 4 equally spaced left ventricular short-axis levels were imaged through systole using tagged magnetic resonance imaging. The baseline imaging sequence was repeated with 5-, 10-, 15-, and 20-microg/kg/min dobutamine infusion. Regional myocardial displacement, radial thickening, and circumferential shortening were measured. The left ventricle was analyzed by level (base to apex) and wall (septum, inferior, lateral, anterior). Dobutamine did not alter baseline regional functional heterogeneity. Dobutamine infusion resulted in a uniform increase in displacement, radial thickening, and circumferential shortening from baseline to 10-microg/kg/min infusion without additional increases at higher doses.

Cardiac-respiratory gating method for magnetic resonance imaging of the heart

In studies of transmural myocardial function, acquisitions of high spatial and temporal resolution tagged cardiac images often exceed the practical time limit for breath‐hold fast imaging techniques. Therefore, a dual cardiac‐respiratory gating device has been constructed to acquire SPAMM‐tagged cardiac MR images at or near end‐expiration during spontaneous breathing, by providing an external trigger to a conventional MRI system. Combined cardiac and respiratory gating essentially eliminates the respiratory motion artifacts in tagged cardiac MR images. Compared to cardiac‐gated images obtained during intermittent breath‐holds, cardiac‐respiratory gated images show improved tag‐myocardium contrast due to magnetization recovery during inspiration. Magn Reson Med 43:314–318, 2000.

Homocysteine: evidence for a causal relationship with cardiovascular disease.

Elevated plasma homocysteine levels are associated with vascular disease and thrombosis. Premature atherosclerosis and thromboembolism are seen in children who are homozygotes for defects in enzymes responsible for the metabolism of homocysteine. Adults with heterozygous defects have less marked elevations of homocysteine, and onset of atherosclerosis and vascular disease are delayed into the fourth and fifth decade of life. Homocysteine can damage vascular endothelium, cause proliferation of vascular smooth muscle, activate platelets, promote lipid peroxidation, and activate the coagulation cascade. Epidemiologic studies have linked elevations in plasma homocysteine with coronary artery disease, cerebrovascular disease, and thromboembolism. Folic acid, in combination with vitamins B6 and B12, can normalize homocysteine levels in most patients. Although randomized trials assessing the efficacy of homocysteine reduction have yet to be completed, treatment with vitamin supplementation should be considered in all patients at risk for vascular disease.

Arrhythmogenic Right Ventricular Cardiomyopathy

Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVC), first described in 1977, remains an enigmatic disease.1 ARVC is a rare disorder, but it is the most common cause of sudden cardiac death (SCD) in younger populations. ARVC is a progressive disease2,3 characterized by structural and functional abnormalities of the heart, initially presenting in the right ventricle (RV) but eventually resulting in a biventricular cardiomyopathy in its late stages. The disorder often is familial in origin (30%–50% of cases), with both autosomal dominant and autosomal recessive (“Naxos disease”) inheritance patterns. The genetic defect appears to map to chromosomes 1, 2, 3, and 14 for the dominant pattern and to chromosome 17 in the recessive form of the disease.4 The major pathologic finding is replacement of the myocardium by fatty and fibrous tissue, and numerous structural abnormalities of the RV, including areas of thinning with single or multiple aneurysms, or formation of diverticula. Current opinion indicates that this replacement process is due to 1 of 3 processes: apoptosis, inflammatory heart disease, or a genetically determined myocardial dystrophy.1 These structural abnormalities predispose patients to a number of arrhythmias of RV origin, ranging from single premature ventricular contractions to sustained ventricular tachycardia (VT). Not uncommonly, the initial presentation may be ventricular fibrillation and SCD. An imbalance of adrenergic innervation has been detected in ARVC patients,5,6 resulting in dispersion of refractoriness and development of delayed afterdepolarizations, which promote an arrhythmic substrate. In a recent study of SCD victims who had autopsy-proven ARVC, a premortem QRS dispersion of ≥40 msec was the strongest predictor of sudden death.7 Four stages of the disease have been proposed: (1) a “concealed” phase, in which anatomic changes are subtle and arrhythmias may be minor, but where SCD may be the first indication of the disease; (2) an overt electrical disorder presenting with VT or SCD, in which RV structural and functional abnormalities are more apparent; (3) progressive RV failure with preserved left ventricular function; and (4) biventricular dysfunction.8 Despite advances in diagnostic techniques and the availability of formalized diagnostic criteria, identification of ARVC remains problematic, particularly in individuals with the concealed form of the disease. Endomyocardial biopsy has been used to confirm the presence of the characteristic fibrofatty infiltration in vivo.9 How-

Diagnosis of a persistent coronary fistula after ventricular septal defect patch closure

Penetrating chest trauma can result in multiple clinical syndromes depending on the structures involved. Tamponade, valvular regurgitation, ventricular septal defect (VSD), conduction system abnormalities, and coronary lacerations have been reported. We report a case of right ventricular free wall laceration, VSD, and coronary artery fistula involving a septal perforator.

Evaluation of Ventricular Function

Heart failure is the final common pathway of a number of cardiovascular diseases. Hypertension, valvular disease, coronary artery disease, congenital heart defects, and disorders of the myocytes or extracellular matrix may result in abnormalities in both systolic and diastolic function. Noninvasive imaging techniques that have the spatial and temporal resolution to assess both global and regional cardiac function, valvular function, and patterns of blood flow greatly enhance the diagnosis and management of patients with heart failure. In addition, important prognostic information may be derived from these imaging techniques.

Dynamic Practical Electrocardiography

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Adult Clinical Cardiology Self-Assessment Program: ACCSAP 2000

Conti CR, Lewis RP, eds. Bethesda, MD: American Coll of Cardiology; 2000. Single-user price,