R A Niezen

Leiden University Medical Centre, Leiden, South Holland, Netherlands

Are you R A Niezen?

Claim your profile

Publications (10)43 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In patients with the tetralogy of Fallot, QRS prolongation predicts malignant ventricular arrhythmias. QRS prolongation may result from right ventricular dilatation. The relation of ECG markers to biventricular wall mass and volumes has not been assessed. To investigate the relations of surface ECG markers of depolarisation and repolarisation to right and left ventricular volume and biventricular wall mass. 37 Fallot patients (mean (SD) age 17 (9) years) were studied 14 (8) years after surgical repair; 34 had important pulmonary regurgitation. Left and right ventricular size was assessed from tomographic magnetic resonance imaging (MRI), and the amount of pulmonary regurgitation by velocity mapping MRI. QT, QRS, and JT duration and interlead dispersion markers were derived from a standard 12 lead ECG. Mean QRS duration was significantly prolonged (133 (31) v 91 (11) ms in controls), as were dispersion of QRS (36 (17) v 20 (6) ms), QT interval (87 (48) v 42 (20) ms), and JT interval (93 (48) v 42 (19) ms). Biventricular volumes were increased (right ventricular end diastolic volume, 129 (41) v 70 (9) ml/m(2); left ventricular end diastolic volume, 83 (16) v 69 (10) ml/m(2)), as was right ventricular wall mass (24 (7) v 17 (2) g/m(2)). QRS duration correlated best with right ventricular mass (r = 0.55, p < 0.01). In patients operated on for tetralogy of Fallot and with pulmonary regurgitation, ECG predictors of ventricular arrhythmias are influenced by several mechanical factors that may occur simultaneously. These include increased right ventricular volume, but also increases in left ventricular volume and in right and left ventricular wall mass.
    Heart (British Cardiac Society) 11/2002; 88(5):515-9. · 6.02 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: To assess left ventricular function in adult Fallot patients with residual pulmonary regurgitation. The radiology department of a tertiary referral centre. 14 patients with chronic pulmonary regurgitation and right ventricular volume overload after repair of tetralogy of Fallot and 10 healthy subjects were studied using magnetic resonance imaging. Biventricular volumes, global biventricular function, and regional left ventricular function were assessed in all subjects. The amount of pulmonary regurgitation in patients (mean (SD)) was 25 (18)% of forward flow and correlated significantly with right ventricular enlargement (p < 0.05). Left ventricular end diastolic volume was decreased in patients (78 (11) v 88 (10) ml/m(2); p < 0.05), ejection fraction was not significantly altered (59 (5)% v 55 (7)%; NS). No significant correlation was found between pulmonary regurgitation and left ventricular function. Overall left ventricular end diastolic wall thickness was significantly lower in patients (5.06 (0.72) v 6.06 (1.06) mm; p < 0. 05), predominantly in the free wall. At the apical level, left ventricular systolic wall thickening was 20% higher in Fallot patients (p < 0.05). Left ventricular shape was normal. Adult Fallot patients with mild chronic pulmonary regurgitation and subsequent right ventricular enlargement showed a normal left ventricular shape and global function. Although the left ventricular free wall had reduced wall thickness, compensatory hypercontractility of the apex may contribute to preserved global function.
    Heart (British Cardiac Society) 12/1999; 82(6):697-703. · 6.02 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this article the value of magnetic resonance (MR) imaging for the evaluation of double outlet right ventricle (DORV) is reviewed from the literature and illustrated with several cases. MR imaging can be used for the determination of cardiac anatomy at initial diagnosis and may provide functional information during the follow-up of patients after surgical correction.
    International Journal of Cardiac Imaging 07/1999; 15(4):323-329.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Magnetic resonance imaging is one method for assessing cardiac function and perfusion at rest and under stress conditions. In this article, the potential of stress magnetic resonance imaging for evaluating ischemic heart disease is reviewed, and technical aspects of some developments that may contribute to comprehensive magnetic resonance imaging assessment of heart disease under rest and stress are discussed.
    Cardiology Clinics 06/1998; 16(2):247-65. · 1.06 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Our aim was to assess the feasibility of measuring great vessel flow during submaximal exercise using MR flow mapping. In 16 healthy volunteers, MR measurements of great vessel flow were obtained at rest and during two levels of submaximal physical exercise using an MR-compatible bicycle ergometer. Great vessel flow showed good correlation at rest and during exercise (r = 0.9, p < 0.0005). Significant increase in heart rate was observed during exercise. Aortic flow volume increased from 64 +/- 13 ml/beat at rest to 71 +/- 11 ml/beat at 50 W (p < 0.0005) to 79 +/- 13 ml/beat at 100 W (p < 0.0005). Pulmonary flow volume increased from 63 +/- 14 ml/beat at rest to 70 +/- 13 ml/beat at 50 W (p < 0.005) to 76 +/- 12 ml/beat at 100 W (p = NS). Quantification of great vessel flow can be performed safely in healthy volunteers using MR flow measurements during submaximal physical exercise. These measurements may be used to study hemodynamic abnormalities in patients with cardiac disease.
    Journal of Computer Assisted Tomography 01/1998; 22(2):194-201. · 1.60 Impact Factor
  • Annals of Hematology 01/1997; 75(1-2):71-7. · 2.40 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We sought to assess right ventricular diastolic function in young patients with corrected tetralogy of Fallot and pulmonary regurgitation. Pulmonary regurgitation is an important problem in repair of tetralogy of Fallot. Its effects on right ventricular diastolic function in children are unknown. Nineteen children with repair of tetralogy of Fallot (mean age [+/- SD] 12 +/- 3 years, mean age at operation 1.5 +/- 1) and 12 healthy children were studied. Summation of magnetic resonance velocity mapping pulmonary and tricuspid volume flow curves provided right ventricular time-volume curves. Ventricular size was assessed with tomographic magnetic resonance imaging (MRI). Graded exercise testing was performed. Systematic and random differences (mean +/- SD) of velocity mapping and Doppler tricuspid time to peak velocities (peak E: 1 +/- 26 ms, r = 0.43; peak A: 2 +/- 11 ms, r = 0.76), E/A ratio (0.04 +/- 0.5, r = 0.63) and duration of pulmonary regurgitation (20 +/- 35 ms, r = 0.74) were satisfactory. In 6 patients (group I), late diastolic forward pulmonary artery flow was absent; in 13 patients (group II), this flow contributed 1% to 14% to right ventricular stroke volume. Significant differences were increased deceleration time (315 +/- 91 vs. 168 +/- 28 ms, p < 0.001), decreased filling fraction (44 +/- 11 vs. 55 +/- 16%, p = 0.02) and increased peak early filling rate (378 +/- 124 vs. 286 +/- 112 ml/s, p = 0.018) between control subjects and group I, and increased deceleration time (230 +/- 40, p = 0.03) between control subjects and group II. Pulmonary regurgitation, ventricular size and ejection fraction did not differ significantly between patient groups. Exercise function was diminished with restrictive right ventricular physiology (p < 0.001, group II vs. control subjects). Impaired relaxation and restriction to filling affect right ventricular function in children with repair of tetralogy of Fallot and pulmonary regurgitation. Restrictive right ventricular physiology is associated with decreased exercise function.
    Journal of the American College of Cardiology 12/1996; 28(7):1827-35. · 15.34 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: To study biventricular systolic function and mass of the heart in young patients with residual pulmonary regurgitation who had undergone surgical correction of tetralogy of Fallot. Transverse gradient-echo magnetic resonance (MR) images covering both ventricles were obtained in 19 patients who had undergone corrective surgery for tetralogy of Fallot at the age of 1.5 years +/- 1 and in 12 age-matched control subjects. In addition, MR velocity maps of the pulmonary artery were obtained. Biventricular volumes, ejection fraction and myocardial mass, and pulmonary flow volumes were measured. Exercise tests were performed in 17 patients. The right ventricular ejection fraction was lower (P < .001) and the right ventricular mass was higher (P < .0005) in patients than in control subjects; the left ventricular ejection fraction was lower (P < .0005) in patients and correlated statistically significantly with pulmonary regurgitation (r = -.68; P < .005). Exercise performance inversely correlated with pulmonary regurgitation (tau = -0.5; P = .01). In children who undergo early surgical repair of tetralogy of Fallot, residual pulmonary regurgitation correlates with biventricular systolic dysfunction and diminished exercise capacity. Despite successful surgical correction, right ventricular hypertrophy may persist.
    Radiology 10/1996; 201(1):135-40. · 6.21 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Cine gradient-echo (GRE) magnetic resonance (MR) imaging and MR velocity mapping can be applied to assess cardiovascular function and to measure volumetric flow in patients with repaired and untreated congenital heart disease. GRE images, particularly when displayed in a cine loop, are very useful for visualizing surgical anastomoses and conduits and for detecting stenosis, regurgitation, and left-to-right shunts. Multisection cine GRE imaging is a suitable method for measuring global right ventricular function, an important issue in congenital heart disease. MR velocity mapping is used for quantitative assessment of hemodynamics. Pressure gradients can be estimated from peak blood flow velocities in stenotic pulmonary arteries or surgical conduits. Because flow volume can be measured with MR velocity mapping, main-, left-, and right pulmonary artery flow, valvular regurgitation, left-to-right shunts, and ventricular filling can all be quantified. The abilities to elucidate complex cardiac anatomy and to measure cardiac function and flow in one examination make MR imaging a useful comprehensive tool for follow-up of congenital heart disease.
    Radiographics 06/1996; 16(3):467-81. · 2.73 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: An automated contour detection algorithm was developed for the objective and reproducible quantitative analysis of velocity-encoded MR studies of the ascending aorta. The only user interaction required is the manual definition of a center point inside the cross-section of the aorta in one of the available images. The automated contour detection algorithm detects an initial model contour in this image and subsequently corrects for motion and deformation of the aortic cross-section in each of the acquired images over the complete cardiac cycle using dynamic programming techniques. Integrating the flow velocity values for each pixel within the detected contour results in an instantaneous flow value. Next, by integrating the instantaneous flow values for each acquired phase over the complete cardiac cycle, left ventricular stroke volume measurement could be obtained. The results of the automated method were compared with results derived from manually traced contours in MR studies from 11 healthy volunteers. An excellent agreement in stroke volume measurements was observed: signed difference 0.61+/-1.15%. Inter- and intraobserver variabilities were <2% for both manual and automated image analysis methods. Manual tracing of contours required on the order of 10 min; the analysis time for automated contour detection was <6 s/study. The present contour detection allows fast and reliable left ventricular stroke volume measurements from aortic flow studies using velocity-encoded MR studies in healthy volunteers. Further study is required to assess the accuracy and reproducibility of the algorithm in patients with aortic and aortic valve disease.
    Journal of Computer Assisted Tomography 22(6):904-11. · 1.60 Impact Factor