Evaluation of the precision of magnetic resonance phase velocity mapping for blood flow measurements.

Evaluating the in vivo accuracy of magnetic resonance phase velocity mapping (PVM) is not straightforward because of the absence of a validated clinical flow quantification technique. The aim of this study was to evaluate PVM by investigating its precision, both in vitro and in vivo, in a 1.5 Tesla scanner. In the former case, steady and pulsatile flow experiments were conducted using an aortic model under a variety of flow conditions (steady: 0.1-5.5 L/min; pulsatile: 10-75 mL/cycle). In the latter case, PVM measurements were taken in the ascending aorta of ten subjects, seven of which had aortic regurgitation. Each velocity measurement was taken twice, with the slice perpendicular to the long axis of the aorta. Comparison between the measured and true flow rates and volumes confirmed the high accuracy of PVM in measuring flow in vitro (p > 0.85). The in vitro precision of PVM was found to be very high(steady: y = 1.00x + 0.02, r = 0.999; pulsatile: y = 0.98x + 0.72, r = 0.997; x: measurement #1, y: measurement #2) and this was confirmed by Bland-Altman analysis. Of great clinical significance was the high level of the in vivo precision (y = 1.01x - 0.04, r = 0.993), confirmed statistically (p = 1.00). In conclusion, PVM provides repeatable blood flow measurements. The high in vitro accuracy and precision, combined with the high in vivo precision, are key factors for the establishment of PVM as the "gold-standard" to quantify blood flow.

Quantification of mitral regurgitation with MR phase-velocity mapping using a control volume method.

Reliable diagnosis and quantification of mitral regurgitation are important for patient management and for optimizing the time for surgery. Previous methods have often provided suboptimal results. The aim of this in vitro study was to evaluate MR phase-velocity mapping in quantifying the mitral regurgitant volume (MRV) using a control volume (CV) method. A number of contiguous slices were acquired with all three velocity components measured. A CV was then selected, encompassing the regurgitant orifice. Mass conservation dictates that the net inflow into the CV should be equal to the regurgitant flow. Results showed that a CV, the boundary voxels of which excluded the region of flow acceleration and aliasing at the orifice, provided accurate measurements of the regurgitant flow. A smaller CV provided erroneous results because of flow acceleration and velocity aliasing close to the orifice. A large CV generally provided inaccurate results because of reduced velocity sensitivity far from the orifice. Aortic outflow, orifice shape, and valve geometry did not affect the accuracy of the CV measurements. The CV method is a promising approach to the problem of quantification of the MRV.

Quantification of the aortic regurgitant volume with magnetic resonance phase velocity mapping: a clinical investigation of the importance of imaging slice location.

BACKGROUND AND AIMS OF THE STUDY: Current techniques for assessment of aortic regurgitation (AR) are mainly qualitative. Magnetic resonance phase velocity mapping (PVM) provides accurate measurements of arterial blood blow. In AR, the aortic regurgitant volume (ARV) can be quantified with a single imaging slice measurement in the ascending aorta. The aim was to use PVM to: (i) quantify the regurgitant volume in patients with AR using an in vitro validated technique; and (ii) confirm in vivo our previous in vitro findings of the importance of measurement location. METHODS: Four healthy volunteers and 19 patients with AR, varying from mild to severe, were examined in a 1.5 Tesla MRI scanner. In 13 patients, the slice was placed: (i) between the aortic valve and the coronary ostia; (ii) at the sinotubular junction (SJ); and (iii) 2 cm above the SJ. In six patients, one measurement was taken as close as technically possible to the aortic valve. PVM measurements of the ARV were compared with angiographic/echocardiographic AR grading. RESULTS: No ARV was measured in healthy subjects. In patients, PVM results correlated well with angiographic/echocardiographic data. Repeatability of the PVM results was excellent and interobserver variability very small. The measured ARV decreased as the slice distance from the aortic valve increased, due to aortic compliance, in agreement to previous in vitro results. Close to the valve, acceleration did not affect the accuracy of velocity measurements. CONCLUSIONS: PVM has great potential to measure AR in a purely quantitative manner. Measurement location is important and results suggest that the closer the measurement to the valve the more accurate the ARV quantification.

The importance of slice location on the accuracy of aortic regurgitation measurements with magnetic resonance phase velocity mapping.

Although several methods have been used clinically to evaluate the severity of aortic regurgitation, there is no purely quantitative approach for aortic regurgitant volume (ARV) measurements. Magnetic resonance phase velocity mapping can be used to quantify the ARV, with a single imaging slice in the ascending aorta, from through-slice velocity measurements. To investigate the accuracy of this technique, in vitro experiments were performed with a compliant model of the ascending aorta. Our goals were to study the effects of slice location on the reliability of the ARV measurements and to determine the location that provides the most accurate results. It was found that when the slice was placed between the aortic valve and the coronary ostia, the measurements were most accurate. Beyond the coronary ostia, aortic compliance and coronary flow negatively affected the accuracy of the measurements, introducing significant errors. This study shows that slice location is important in quantifying the ARV accurately. The higher accuracy achieved with the slice placed between the aortic valve and the coronary ostia suggests that this slice location should be considered and thoroughly examined as the preferred measurement site clinically.

Slice location dependence of aortic regurgitation measurements with MR phase velocity mapping.

Although several methods have been used clinically to assess aortic regurgitation (AR), there is no "gold standard" for regurgitant volume measurement. Magnetic resonance phase velocity mapping (PVM) can be used for noninvasive blood flow measurements. To evaluate the accuracy of PVM in quantifying AR with a single imaging slice in the ascending aorta, in vitro experiments were performed by using a compliant aortic model. Attention was focused on determining the slice location that provided the best results. The most accurate measurements were taken between the aortic valve annulus and the coronary ostia where the measured (Y) and actual (X) flow rate had close agreement (Y = 0.954 x + 0.126, r2 = 0.995, standard deviation of error = 0.139 L/min). Beyond the coronary ostia, coronary flow and aortic compliance negatively affected the accuracy of the measurements. In vivo measurements taken on patients with AR showed the same tendency with the in vitro results. In making decisions regarding patient treatment, diagnostic accuracy is very important. The results from this study suggest that higher accuracy is achieved by placing the slice between the aortic valve and the coronary ostia and that this is the region where attention should be focused for further clinical investigation.

Hypersensitivity myocarditis in heart transplant candidates.

Hypersensitivity myocarditis is a rare event; however, routine histologic examination of all (193) explanted hearts for heart transplantation in our institutions revealed hypersensitivity myocarditis in 15 patients (7%). This is a previously unreported finding in heart transplant recipients. None of the cases was detected clinically, although all manifested peripheral eosinophilia at some point during the 2 weeks before transplantation. Only one patient exhibited a skin rash interpreted as allergic. The severity of the interstitial infiltrate varied from grade I to grade IV (semiquantitative). This group of pretransplantation patients was receiving a multiplicity of drugs, some of which could have potentially triggered the hypersensitivity myocarditis, although in only one case was a definite association between a hypersensitivity reaction and a drug made. The unusually high rate (10.3% for the Emory cases) of drug-induced myocarditis in this group of patients, contrasted with the general autopsy population, probably reflects that these patients received more vigorous than usual drug treatment, particularly antibiotics, to sustain them until a suitable donor was found.

Comparison of cardiac function in surgically corrected and congenitally corrected transposition of the great arteries.

The capacity of the anatomic right ventricle to sustain normal function against systemic pressure long after atrial baffle procedures in patients with complete transposition of the great arteries remains unknown. Pulmonary and systemic ventricular function was measured by first-pass radionuclide studies in 11 children 7 +/- 3 years (+/- standard deviation) after baffle procedures. For comparison, similar measurements were made in eight patients with isolated congenitally corrected transposition of the great arteries and in 10 children in a control group. Exercise increased heart rate and cardiac index to similar levels in all three groups. Ventricular volumes were greater than control volumes in both groups with congenital heart disease. Exercise increased pulmonary ventricular ejection fraction in the control and congenitally corrected groups, but not in the surgically corrected group. Systemic ventricular ejection fraction increased during exercise in the control group, but remained unchanged in both transposition groups. These results show that cardiac index during exercise is maintained in patients after baffle procedures for complete transposition of the great arteries. However, pulmonary and systemic ventricular ejection fractions fail to increase with exercise, and ventricular volumes are markedly greater than normal.

In vitro hemodynamic characteristics of tissue bioprostheses in the aortic position.

The in vitro hemodynamic characteristics of a variety of old and new generation porcine and bovine pericardial bioprostheses were investigated in the aortic position under pulsatile flow conditions. The following valves were studied: Carpentier-Edwards porcine (Models 2625 and 2650), Carpentier-Edwards pericardial, Hancock porcine (Models 242, 250, and 410), Hancock pericardial, and Ionescu-Shiley (standard and low-profile) bioprostheses. The pressure drop results indicated that the old design valves had performance indices in the range of 0.30 to 0.42, whereas the new low-pressure fixed designs have performance indices of 0.50 to 0.70. Flow visualization and velocity and turbulent shear stress measurements, conducted with a two-dimensional laser Doppler anemometer system, indicated that all tissue valve designs created jet-type flow fields. The intensity of the jets and turbulence levels were less severe with the new designs. The old designs created higher peak jet velocities and higher levels of turbulent shear stresses. On the whole, pericardial bioprostheses have better in vitro hemodynamic characteristics than porcine bioprostheses. These observations should have applications regarding the clinical choice of bioprosthetic valves and have implications regarding further improvements in the preparation and design of bioprosthetic valves.

Catheter suction biopsy in diagnosis of an intrapulmonary artery tumor.

Unsuspected intracardiac masses are occasionally encountered when cardiac catheterization is performed in a patient with right ventricular or pulmonary artery occlusive disease. In one of two patients, suction biopsy of the mass has been successful in obtaining a histological diagnosis. The method and its contraindications are discussed.

Steady flow velocity measurements in a pulmonary artery model with varying degrees of pulmonic stenosis.

Velocity and flow visualization studies were conducted in an adult size pulmonary artery model with varying degrees of valvular stenosis, using a two dimensional laser Doppler anemometer system. Velocity measurements in the main, left and right branches of the pulmonary artery revealed that as the degree of pulmonic stenosis increased, the jet type flow created by the valve hit the distal wall of the LPA farther downstream from the junction of the bifurcation. This in turn led to higher levels of turbulent and disturbed flow, and larger secondary flow motion in the LPA compared to the RPA. The high levels of turbulence measured in the main and left pulmonary arteries with the stenotic valves, could lead to the clinically observed phenomenon of post stenotic dilatation in the MPA extending into the LPA.

In-vitro pulsatile flow visualization studies in a pulmonary artery model.

In-vitro pulsatile flow visualization studies were conducted in an adult-sized pulmonary artery model to observe the effects of valvular pulmonic stenosis on the flow fields of the main, left and right pulmonary arteries. The flow patterns revealed that as the degree of stenosis increased, the jet-type flow created by the valve became narrower, and it impinged on the far (distal) wall of the left pulmonary artery further downstream from the junction of the bifurcation. This in turn led to larger regions of disturbed turbulent flow, as well as helical-type secondary flow motions in the left pulmonary artery, compared to the right pulmonary artery. The flow field in the main pulmonary artery also became more disturbed and turbulent, especially during peak systole and the deceleration phase. The flow visualization observations have been valuable in helping to conduct further quantitative studies such as pressure and velocity field mapping. Such studies are important to understanding the fluid mechanics characteristics of the main pulmonary artery and its two major branches.

M-mode echocardiography in constrictive pericarditis.

M-mode echocardiograms from 40 patients with proven constrictive pericarditis and 40 subjects without evidence of cardiac disease were reviewed for features previously described in constrictive pericarditis. In this large series, no single feature of the M-mode echocardiogram could be considered diagnostic, although a pattern of normal left ventricular size and systolic function, mild left atrial dilation, flattened diastolic left ventricular posterior wall motion and abnormal septal motion was found in most patients. It is concluded that the M-mode echocardiogram can provide findings suggestive of constrictive pericarditis but must be used in conjunction with hemodynamic and other studies to establish the diagnosis.

Noninvasive determination of exercise cardiac function following Fontan operation.

The purpose of this investigation was to define mechanisms which increase cardiac output during exercise in patients without a functioning right ventricle. Radionuclide studies were performed at rest and during upright bicycle exercise on 16 patients following Fontan procedures and compared to studies in 10 normal children. The mean cardiac index of patients following Fontan procedures was 5.2 +/- 2.0 L/min/m2 (standard deviation) at rest and increased to 9.4 +/- 3.5 L/min/m2 during exercise (p less than 0.0001). Exercise values were similar to those observed in normal children. The mechanisms utilized to achieve high cardiac output following Fontan procedures included an increase in heart rate. Mean systemic ventricular ejection fractions were significantly less than in normal children. The resting ventricular end-diastolic volume and stroke volume indices were above normal and remained constant during exercise to high heart rates. These data clearly document that a large exercise cardiac output can be achieved by patients without a functioning right ventricle.

In vitro fluid dynamic characteristics of Ionescu-Shiley and Carpentier-Edwards tissue bioprostheses.

In the study reported here, the in vitro fluid dynamic characteristics of the Ionescu-Shiley (calf pericardial) and Carpentier-Edwards (porcine) aortic tissue valves were studied. The experiments conducted were pressure drop measurements, leaflet photography, flow visualization, and velocity measurements. The pressure drop studies indicated that both types of tissue valves created relatively large pressure drops. These pressure drops were larger than those observed with the corresponding sizes of Bjork-Shiley, Hall-Kaster, and St. Jude aortic prostheses. The photographs of the opening of the valve leaflets indicated that the tissue valves do not open as ideally as do the natural valves. It was also observed that the Ionescu-Shiley aortic valves opened more symmetrically and with reproducibility than the corresponding Carpentier-Edwards aortic valves. Velocity and shear stress measurements made with a laser-Doppler anemometer indicated that the flow that emerged from the leaflets for both types of tissue valves was like a jet and could lead to turbulent shear stress on the order of 1,000-3,000 dynes/cm2. Such turbulent shear stresses could be harmful to blood components. The jet-type flow could also damage the endothelial lining of the wall of the ascending aorta. The velocity measurements also indicated an annular region of stagnant fluid between the outflow surfaces of the leaflets and the flow channel wall. Such a region could lead to the build-up of thrombotic, fibrotic, and/or calcific material on the outflow surfaces of the leaflets. Both types of valve designs, however, created relatively low wall shear stresses and regurgitant volumes.

In vitro fluid dynamic characteristics of the Medtronic-Hall pivoting disc heart valve prosthesis.

The need for better low-profile mechanical valves led to the design and development of the Medtronic-Hall (formerly known as the Hall-Kaster valve) pivoting disc heart valve prosthesis in 1976. In vitro flow studies indicate that it has improved pressure drop characteristics compared to the Lillehei-Kaster and convexoconcave Björk-Shiley (60 degrees model) tilting disc valves. It does, however, have a somewhat larger regurgitant volume compared to the Björk-Shiley valve design. Velocity measurements with a laser-Doppler anemometer in the immediate downstream vicinity of the Medtronic-Hall valve indicate no region of stagnation near the outflow face of the disc. Regions of stagnation were, however, observed adjacent to the two titanium "pivot stops" situated on either side of the disc in the major orifice and along the pivot post in the minor orifice, together with a region of flow separation adjacent to the sewing ring of the minor outflow region. The results of the present in vitro study indicate a small but significant improvement in the overall fluid dynamic performance of the Medtronic-Hall valve, compared to the convexo-concave Björk-Shiley (60 degrees model) and Lillehei-Kaster tilting disc prostheses in current clinical use.

The Björk-Shiley heart valve prosthesis. Flow characteristics of the new 70 degrees model.

Thrombus formation on the outflow face and tissue overgrowth along the sewing ring adjacent to the minor outflow region are major clinical pathologic problems observed with the Björk-Shiley tilting disc valve. In the hope of reducing these pathologic conditions the convexo-concave Björk-Shiley valve was designed. A new modification to the convexo-concave model has further improved most of the fluid dynamic characteristics of the valve. In vitro flow studies indicate an average improvement in pressure drop characteristics of about 20 to 30%. Velocity measurements made with a laser-Doppler anemometer in the immediate downstream vicinity of the modified convexo-concave valve indicate that the design changes have further reduced the size of the stagnation zone near the outflow face of disc. It was observed, however, that the regurgitation across the valve increased by about one to two percentage points.

Early diastolic sound of constrictive pericarditis.

In two patients with constrictive pericarditis an absent or faint early diastolic sound became prominent with squatting, phenylephrine infusion or injection of contrast medium and was obliterated by nitroglycerin. The lability of the sound allowed correlations to be made with acute changes in the right ventricular pressure curve. By eliciting an otherwise inaudible early diastolic sound, squatting may be a useful bedside maneuver in the diagnosis of constrictive pericarditis.