PubMed Health⌕ Search

Biomedical subjects

C K Phoon

Publications and source records attributed to C K Phoon.

At least 19 recordsLinked to original sources
PubMed2001

Estimation of pressure gradients by auscultation: an innovative and accurate physical examination technique.

BACKGROUND: Knowledge of pressure gradients across valves, arteries, and ventricular septal defects (VSD) is important in patient management. It was determined how well such gradients can be estimated by auscultation of a murmur's frequencies. METHODS: In 151 patients with pulmonary stenosis (PS) (n = 77), aortic stenosis (AS) (n = 30), or VSD (n = 44), the auscultation gradient was estimated by a murmur's frequencies by use of an "auscultatory scale." The auscultation gradient was recorded before Doppler echocardiography was performed by a blinded cardiac sonographer. RESULTS: Auscultation correlated highly with Doppler echocardiography (Doppler = 0.99. Auscultation + 7.12; r = 0.84, P <.0001). Agreement was good (mean difference [Auscultation - Doppler] = -6.8 +/- 15.8 mm Hg). In 95 patients (63%), agreement was within 10 mm Hg. Auscultation was more accurate when Doppler gradients were < or =60 mm Hg (r = 0.76, P <.0001, vs r = 0.22, P not significant for >60 mm Hg; mean difference -2.6 +/- 10.6 mm Hg vs -16.5 +/- 20.9 mm Hg for >60 mm Hg, P <.0001). Among lesions, PS showed the highest correlation, although agreement for PS, AS, and VSD was not significantly different. Isolated valvar PS showed excellent accuracy (r = 0.92, P <.0001; mean difference -5.6 +/- 8.9 mm Hg). CONCLUSIONS: Auscultation of a murmur's frequency composition can estimate gradients accurately in most patients with PS (especially valvar PS), AS, or VSD, although it is less accurate for gradients >60 mm Hg. This innovative technique can improve diagnostic accuracy, thereby further substantiating the value of physical examination.

Adolescent↗
PubMed2001

Pulmonary venous flow in large, uncomplicated atrial septal defect.

BACKGROUND: The pulmonary venous flow velocity pattern (PVFVP) in atrial septal defect (ASD) has not been previously studied in detail. Normally, PVFVP is primarily determined by the left heart performance. We hypothesized that the impact of left-sided heart dynamics on PVFVP is diminished in patients with ASD because of the presence of a left-to-right shunt into the low-resistance right side of the heart. METHODS AND RESULTS: Transesophageal echocardiography was performed in 19 adults and 3 children with a large, uncomplicated secundum ASD (maximum diameter 0.6 to 3.0 cm). All patients were in normal sinus rhythm with an average heart rate of 78 bpm in adults and 116 bpm in children. In 21 subjects the antegrade PVFVP lacked distinct systolic (S) and diastolic (D) waves. Instead, we observed a single continuous antegrade wave extending from the beginning of systole to the onset of atrial contraction. Furthermore, the amplitude of the atrial reversal (AR) wave was smaller than in historical controls. In 3 patients in whom ASD was surgically repaired, we observed an immediate return of distinct S and D waves postoperatively. This confirmed that PVFVP abnormality was indeed the result of the ASD. Also a large increase in the AR wave amplitude (46 + 15 cm/s) was noted postoperatively. CONCLUSIONS: This previously unrecognized PVFVP comprising a single continuous antegrade wave and a diminished AR wave sheds new light on the hemodynamics of ASDs. Its presence may also alert the echocardiographer to the possibility of an ASD when the septal defect cannot be visualized directly.

Adolescent↗
PubMed2001

Unusual echocardiographic views of bicuspid and tricuspid pulmonic valves.

The pulmonary artery is typically seen on transthoracic echocardiography in its longitudinal axis. Therefore, short axis views of the pulmonic valve leaflets are not generally obtained, and the distinction between tricuspid and bicuspid pulmonic valves is difficult or impossible. Bicuspid pulmonic valve is one cause of pulmonic stenosis, which is especially common in tetralogy of Fallot. Presented here are 2 patients in whom the orientation of the pulmonary artery was unusual, and the pulmonic valve was seen en face. The first patient had tetralogy of Fallot and a bicuspid pulmonic valve. The severe obstruction to right ventricular outflow was infundibular. The second patient had severe stenosis of a tricuspid pulmonic valve, which was treated with balloon valvuloplasty. These unusual views of the pulmonic valve leaflets were obtained because of anterior displacement of the pulmonary artery, and precise anatomic delineation of the problem in each case was possible with transthoracic echocardiography.

Adult↗
PubMed2001

Circulatory physiology in the developing embryo.

Knowledge of early developmental circulatory physiology has lagged behind advances in molecular cardiology. Cardiovascular physiology changes during embryonic development in a highly complex and carefully orchestrated manner, tightly correlated with structural development. Circulatory changes in early development include increasing heart rate, preload, and cardiac output; decreasing peripheral resistance; and increasing ventricular compliance, paralleling the increasing metabolic needs of the growing embryo. Newer techniques and the recent ability to study mammalian models of development have led to further insight into changes in myocardial and peripheral vascular physiology. The next major challenges include understanding the mechanisms regulating cardiovascular hemodynamics, normal physiologic adaptation of the growing embryo, and the physiology of abnormal cardiovascular development.

Biomechanical Phenomena↗
PubMed2000

Left ventricular volume after correction of isolated aortic coarctation in neonates.

To determine the capacity of the left ventricle to expand after biventricular repair of left ventricular (LV) outflow tract obstruction, we studied pre- and postoperative echocardiographic variables from 14 infants (< 2 months old) who underwent successful repair of isolated aortic coarctation. We show that in this lesion, LV volume is a dynamic entity, and that the left ventricle achieves a larger cavity size once surgery relieves compression and normalizes loading conditions.

Aortic Coarctation↗
PubMed2000

40 MHz Doppler characterization of umbilical and dorsal aortic blood flow in the early mouse embryo.

Physiological study of the developing mouse circulation has lagged behind advances in molecular cardiology. Using an innovative high-frequency Doppler system, we noninvasively characterized circulatory hemodynamics in early mouse embryos. We used image-guided 43 MHz pulsed-wave (PW) Doppler ultrasound to study the umbilical artery and vein, or dorsal aorta in 109 embryos. Studies were conducted on embryonic days (E) 9.5-14.5. Heart rate, peak blood flow velocities, and velocity time integrals in all vessels increased from E9.5-14.5, indicating increasing stroke volume and cardiac output. Heart rate, ranging from 192 bpm (E9.5) to 261 bpm (E14.5), was higher than previously reported. Placental impedance, assessed by the time delay between the peaks of the umbilical arterial and venous waveforms and by venous pulsatility, decreased with gestation. Acceleration time, a load-independent Doppler index of cardiac contractility, remained constant but seemed sensitive to heart rate. High-frequency PW Doppler is a powerful tool for the quantitative, noninvasive investigation of early mouse circulatory development.

Animals↗
PubMed2000

Intraoperative myocardial ischemia recognized by transesophageal echocardiography monitoring in the pediatric population: a report of 3 cases.

We used continuous intraoperative transesophageal echocardiography (TEE) monitoring to detect intraoperative myocardial ischemia in children after they had been weaned from cardiopulmonary bypass for cardiac surgery. Three pediatric patients are described here to illustrate the usefulness of such TEE monitoring in surgical procedures involving coronary arteries. The indications for intraoperative TEE monitoring and a simplified scheme for immediate qualitative interpretation are discussed.

Adolescent↗
PubMed1999

Pediatric echocardiography: applications and limitations.

Echocardiography is an extraordinarily useful imaging technique in fetuses, infants, children, and adolescents. Recent technologic innovations have expanded its versatility in the pediatric population. However, limited societal resources, limitations inherent to ultrasound imaging, and numerous imaging options even within the field of pediatric echocardiography necessitate the discriminate and thoughtful use of echocardiography in children. The clinical assessment remains a critical prelude to echocardiographic examination of the pediatric cardiovascular system.

Adolescent↗
PubMed1999

Transesophageal imaging of the mid to distal left pulmonary artery in congenital heart disease.

We assessed how well transesophageal echocardiography (TEE) images the left pulmonary artery (LPA) in congenital heart disease (CHD). Seventy-nine consecutive patients with CHD were studied. Ideal imaging displayed the mid to distal LPA from the takeoff of the upper lobe artery through the second bifurcation. Imaging quality was graded from 1 (excellent) to 5 (not visualized). Imaging quality was excellent in 8 (10%) patients, good in 25 (32%), fair in 23 (29%), and poor in 12 (15%); the LPA was not visualized in 11 (14%) patients. Imaging grade averaged 2.9 +/- 1.2 (SD) and correlated poorly with weight (r = 0.24) but was better in patients without prior operation (grade 2.8 vs 3.3, P <.05). In 2 patients, TEE showed residual stenosis. Thus informative LPA imaging by TEE can be achieved in many patients with CHD and has the potential to change intraoperative or postoperative treatment.

Adolescent↗
PubMed1998

Geometric mismatch of pulmonary and aortic anuli in children undergoing the Ross procedure: implications for surgical management and autograft valve function.

BACKGROUND: There is often substantial mismatch between the diameters of the pulmonary and aortic anuli in young patients with systemic outflow tract disease. To implant the autologous pulmonary valve in the aortic position under such circumstances, it is necessary to adapt the geometry of the systemic outflow tract. The effects of such adaptations on autograft function in children are not well known. METHODS: To determine factors predictive of autograft regurgitation, we analyzed 41 cases of children who have undergone the Ross procedure. The diameter of the pulmonary valve was greater (by at least 3 mm) than that of the aortic valve in 20 cases, equal (within 2 mm) in 12 cases, and less (by at least 3 mm) in nine cases, with differences ranging from +10 to -12 mm. In 12 patients with a larger pulmonary anulus, aortoventriculoplasty was used to correct the mismatch. In patients with a larger aortic anulus, the mismatch was corrected by gradual adjustment along the circumference of the autograft, rather than by tailoring of the native aortic anulus. RESULTS: At follow-up (median 31 months), two patients had undergone reoperation on the neoaortic valve for moderate regurgitation. In the remaining 38 cases, autograft regurgitation was as follows: none or trivial in 30, mild in seven, and moderate in one. There was no correlation between regurgitation and age, geometric mismatch, or previous or concurrent procedures. CONCLUSIONS: Subtle technical factors that may result in distortion of the valve complex are probably more important determinants of autograft regurgitation than are indication for repair, geometric mismatch, or previous or concomitant outflow tract procedures. Significant mismatch of the semilunar anuli is not a contraindication to the Ross procedure in children.

Adolescent↗
PubMed1997

Conditions with right ventricular pressure and volume overload, and a small left ventricle: "hypoplastic" left ventricle or simply a squashed ventricle?

OBJECTIVES: We modeled the utility of preoperative potential left ventricular (LV) volume in predicting postoperative volume in conditions causing LV compression. BACKGROUND: With right ventricular (RV) overload lesions, LV "hypoplasia" may be primarily due to compression by reverse septal bowing. If so, preoperative potential LV volume should correspond 1:1 with postoperative volume. The potential volume for a given endocardial circumference can be calculated from the maximal potential cross-sectional area (where A = circumference(2)/4pi) and LV length. METHODS: We studied echocardiographic variables from 22 patients with RV overload lesions perioperatively. RESULTS: Preoperative LV volume was 15.0 +/- 7.1 ml/m2 (59% of patients had a volume <15 ml/m2); potential volume was 20.0 +/- 9.8 ml/m2. Postoperative volume increased to 28.2 +/- 8.6 ml/m2 (100% of patients had a volume >15 ml/m2). Preoperative potential volume correlated well with, but generally underestimated, postoperative volume (r = 0.75, p < 0.0001). Postoperative increases in both LV circumference and length contributed to this discrepancy. CONCLUSIONS: In RV overload lesions, LV "hypoplasia" is primarily due not to compression; rather it is due to underfilling. Even "hypoplastic" ventricles can achieve an adequate cavity after operation normalizes loading conditions. Both true and potential preoperative volume can predict postoperative volume well. However, potential volume, which is less prone to underestimating ventricular adequacy, may better help to determine suitability for biventricular repair in lesions of RV overload associated with a "hypoplastic" LV.

Cardiac Volume↗