Quantitation of cardiac output with velocity-encoded, phase-difference magnetic resonance imaging.

Velocity-encoded, phase-difference magnetic resonance imaging (MRI) previously has been used to measure flow in the aorta, as well as in the pulmonary, carotid, and renal arteries, but these measurements have not been validated against currently accepted invasive techniques. To determine the accuracy of velocity-encoded, phase-difference MRI measurements of cardiac output, 23 subjects (11 men and 12 women, aged 15 to 72 years) underwent velocity-encoded, phase-difference MRI measurements of cardiac output in the proximal aorta, followed immediately by cardiac catheterization, with measurement of cardiac output by the Fick principle and by thermodilution. For MRI, Fick, and thermodilution measurements, stroke volume was calculated by dividing cardiac output by heart rate. The magnetic resonance images were acquired in 1 to 3 minutes. For all patients, the agreement between measurements of stroke volume was 3 +/- 9 ml for MRI and Fick, -3 +/- 11 ml for MRI and thermodilution, and 0 +/- 8 ml for MRI and the average of Fick and thermodilution. Compared with standard invasive measurements, velocity-encoded, phase-difference MRI can accurately and rapidly determine cardiac output.

Utility of the 12-lead electrocardiogram in identifying underlying coronary artery disease in patients with depressed left ventricular systolic function.

We assessed the utility of the 12-lead electrocardiogram (ECG) in identifying severe coronary artery disease (CAD) in patients with depressed left ventricular (LV) systolic function. In 336 patients referred for cardiac catheterization with LV ejection fractions < 0.50, we compared the 12-lead ECG of those with and without CAD by multivariate analysis. The sensitivities, specificities, and positive and negative predictive values of all dichotomous electrocardiographic variables for identifying the presence of severe CAD were determined. In comparison to subjects with CAD, those without disease were more likely to exhibit left-axis deviation (p = 0.01), left bundle branch block (p < 0.001), or LV hypertrophy (p < 0.001), and less likely to exhibit pathologic inferior Q waves (p < 0.001). The presence of anterior or any Q waves was similar between the groups. The presence of any diagnostic Q wave had a positive predictive value of 92%, sensitivity of 57%, and specificity of 80% for identifying severe CAD. In patients with LV systolic dysfunction, the 12-lead ECG is insensitive and nonspecific for identifying those with concomitant severe CAD.

Comparison of quantitation of left ventricular volume, ejection fraction, and cardiac output in patients with atrial fibrillation by cine magnetic resonance imaging versus invasive measurements.

Currently available invasive and noninvasive techniques for the determination of left ventricular end-diastolic and end-systolic volumes, ejection fraction, and cardiac output are more time-consuming and potentially less accurate in patients with atrial fibrillation (AF) than in those with sinus rhythm. Although magnetic resonance imaging (MRI) can rapidly and accurately measure these variables in patients with sinus rhythm, its ability to do so in subjects with AF is not known. To determine if left ventricular volumes, ejection fraction, and cardiac output can be measured accurately in patients with AF using MRI, 26 subjects (13 women and 13 men, aged 15 to 76 years) in sinus rhythm (n = 13) or AF (n = 13) underwent MRI followed immediately by invasive measurements of these indexes. For those in AF, MRI measurements of left ventricular end-diastolic volume, end-systolic volume, stroke volume, ejection fraction, and cardiac output correlated well with catheterization measurements (r = 0.90, 0.90, 0.95, 0.85, and 0.90, respectively). In addition, the mean difference between MRI and catheterization measurements was similar in subjects with AF and in those with sinus rhythm. Compared with standard invasive measurements, MRI provides an accurate noninvasive determination of left ventricular volumes, ejection fraction, and cardiac output in patients with AF.

Magnetic resonance imaging assessment of the severity of mitral regurgitation. Comparison with invasive techniques.

BACKGROUND: In the patient with mitral regurgitation who is being considered for valvular surgery, cardiac catheterization is usually performed to quantify the severity of regurgitation and to determine its influence on left ventricular volumes and systolic function. Magnetic resonance imaging (MRI) potentially provides a rapid, noninvasive method of acquiring these data. Thus, this study was done to determine whether MRI can reliably measure the magnitude of mitral regurgitation and evaluate the effect of regurgitation on left ventricular volumes and systolic function. METHODS AND RESULTS: Twenty-three subjects (14 women and 9 men 15 to 72 years of age) with (n = 17) or without (n = 6) mitral regurgitation underwent MRI scanning followed immediately by cardiac catheterization. The presence (or absence) of valvular regurgitation was determined, and left ventricular volumes and regurgitant fraction were quantified during each procedure. There was excellent correlation between invasive and MRI assessments of left ventricular end-diastolic (r = .95) and end-systolic (r = .95) volumes and regurgitant fraction (r = .96). All MRI examinations were completed in < 28 minutes. CONCLUSIONS: In the patient with mitral regurgitation, MRI compares favorably with cardiac catheterization for assessment of the magnitude of regurgitation and its influence on left ventricular volumes and systolic function.

Assessment of left-to-right intracardiac shunting by velocity-encoded, phase-difference magnetic resonance imaging. A comparison with oximetric and indicator dilution techniques.

BACKGROUND: Velocity-encoded, phase-difference magnetic resonance imaging (MRI) has been shown to provide an accurate assessment of shunt magnitude in patients with large atrial septal defects, but its ability to determine shunt magnitude in patients with intracardiac left-to-right shunts of various locations and sizes has not been evaluated in a prospective and blinded manner. The objective of the present study was to determine whether velocity-encoded, phase-difference MRI can assess the magnitude of intracardiac left-to-right shunting in humans. METHODS AND RESULTS: Twenty-one subjects (15 women and 6 men; age range, 15 to 72 years) underwent velocity-encoded, phase-difference MRI measurements of flow in the proximal aorta and pulmonary artery, followed immediately by cardiac catheterization. The presence of left-to-right intracardiac shunting was assessed with hydrogen inhalation, after which shunt magnitude was measured by the oximetric and indocyanine green techniques. Of the 21 patients, 12 had left-to-right intracardiac shunting detected by hydrogen inhalation. There was a good correlation (r = .94) between the invasive and MRI assessments of shunt magnitude. In comparison to oximetry and indocyanine green, MRI correctly identified the 12 patients with a ratio of pulmonary to systemic flow (Qp/Qs) of < 1.5 (9 without intracardiac shunting and 3 with small shunts) and the 9 patients with a Qp/Qs of > or = 1.5 (6 with atrial septal defect, 1 with ventricular septal defect, 1 with patent ductus arteriosus, and 1 with both atrial septal defect and patent ductus arteriosus). CONCLUSIONS: Compared with measurements obtained during cardiac catheterization, velocity-encoded, phase-difference MRI measurements of flow in the proximal great vessels can reliably assess the magnitude of intracardiac left-to-right shunting.

Assessment of coronary arterial flow and flow reserve in humans with magnetic resonance imaging.

BACKGROUND: The noninvasive measurement of absolute epicardial coronary arterial flow and flow reserve would be useful in the evaluation of patients with coronary circulatory disorders. Phase-contrast magnetic resonance imaging (PC-MRI) has been used to measure coronary arterial flow in animals, but its accuracy in humans is unknown. METHODS AND RESULTS: Twelve subjects (7 men, 5 women: age 44 to 67 years) underwent PC-MRI measurements of flow in the left anterior descending coronary artery or one of its diagonal branches at rest and after administration of adenosine (140 microgram . kg(-1) . min (-1) IV). Immediately thereafter, intracoronary Doppler velocity (IDV) and flow measurements were made during cardiac catheterization at rest and after intravenous administration of adenosine. For the 12 patients, the correlation between MRI and invasive measurements of coronary arterial flow and coronary arterial flow reserve was excellent: coronary flow (MRI) (mL/min)= 0.85 x coronary flow (IDV) (mL/min)+17 (mL/min), r=.89, and coronary flow reserve (MRI) =0.79 x coronary velocity reserve (IDV) + 0.34, r=.89. For the range of coronary arterial flows (18 to 161 mL/min) measured by MRI, the limit of agreement between MRI and catheterization measurements of flow was -13+/-30 mL/min; for the range of coronary reserves (0.7 to 3.7) measured by MRI, the limit of agreement between the two techniques was 0.1+/-0.4. CONCLUSIONS: Cine velocity-encoded PC-MRI can noninvasively measure absolute coronary arterial flow in the left anterior descending artery in humans. PC-MRI can detect pharmacologically induced changes in coronary arterial flow and can reliably distinguish between those subjects with normal and abnormal coronary artery flow reserve.