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Biomedical subjects

C K Phoon

Publications and source records attributed to C K Phoon.

28 records · Page 2Linked to original sources
PubMed1997

Predicting feasibility of biventricular repair of right-dominant unbalanced atrioventricular canal.

BACKGROUND: In right-dominant unbalanced atrioventricular (AV) canal, there are no criteria to judge adequacy of the left ventricle for biventricular repair. The purpose of this study was to test the hypothesis that right ventricular volume overload in this condition results in right-to-left septal bowing and contributes to the appearance of a small left ventricle. METHODS: Five consecutive neonates and young infants (age range, 23 days to 5 months; median age, 3 months) with right-dominant unbalanced complete AV canal underwent biventricular repair. Preoperative and postoperative echocardiographic measurements of left (LV) and right ventricular size and AV valve component size were made. Potential LV volume was assessed preoperatively using a theoretic model that assumed a normalization of septal bowing. RESULTS: There was no perioperative mortality; 1 patient died 71 days postoperatively of problems related to the left AV valve. Preoperatively, all patients had severe LV hypoplasia, with a mean end-diastolic indexed true LV volume of 14.8 +/- 9.1 mL/m2, indexed potential LV volume of 32.0 +/- 18.8 mL/m2, left AV valve to total AV valve ratio of 0.30 +/- 0.06, and LV to right ventricular long-dimension ratio of 0.65 +/- 0.1. Postoperatively, all patients had indexed true LV volumes greater than 30 mL/m2 (mean volume, 35.6 +/- 3.9 mL/m2), and the left AV valve to total AV valve ratio and the LV to right ventricular long-dimension ratio increased to 0.42 +/- 0.03 and 0.88 +/- 0.11, respectively. Both preoperative potential and true LV volumes correlated well with postoperative true LV volumes: r = 0.90 (p = 0.040) and r = 0.93 (p = 0.023), respectively. Increases in LV length and left AV annulus size indicated contributions of volume loading and surgical patching to the right of the ventricular crest to the increase in LV size. CONCLUSIONS: In our small series, preoperative indexed potential LV volume of 15 mL/m2 or greater (present in all patients) allowed biventricular repair of right-dominant unbalanced AV canal. Any previous criteria for LV hypoplasia in this condition need to be reconsidered. This study also has implications for other right-sided volume-loaded lesions in which the left ventricle initially is judged to be hypoplastic but in which biventricular repair may be feasible.

Atrioventricular Node↗
PubMed1996

Left atrial isomerism detected in fetal life.

Left and right atrial isomerism, comprising congenital heart defects with disturbances in normal left-right asymmetry, are phenotypically distinct after birth, although animal models suggest a common embryologic origin. We postulated that the prenatal phenotype may indeed be similar in both syndromes but that differential fetal loss is responsible for the distinct postnatal phenotypes. Distinctive fetal echocardiographic features of these syndromes have not been described in detail. We therefore sought markers of left atrial isomerism that could be recognized prenatally by echocardiography and compared our results with postnatal data to identify unique intrauterine features. We reviewed 10 cases at our center and 28 published cases of cardiac malformations with atrial isomerism detected by fetal echocardiography. Postnatal imaging and autopsies provided definitive diagnoses. Ninety-five percent of cases exhibited left atrial isomerism and formed the primary study population. Echocardiographic markers included a large azygos continuation of an interrupted inferior vena cava, atrioventricular block with structural heart disease, and viscerocardiac heterotaxy. At least 1 of these markers was seen in all of our center's cases. The incidences of most cardiac lesions detected prenatally were similar to those detected postnatally. However, although the incidences of atrioventricular septal defect and pulmonary outflow obstruction in live births were 50% and 45%, respectively, they were found much more frequently among stillbirths (80% each). In summary, we identified key fetal echocardiographic features highly sensitive for left atrial isomerism. Fetal loss selects against certain lesions such as atrioventricular septal defect. The spectrum of cardiac disease suggests a greater primitivity of the fetal heart than previously shown; the typical cardiac phenotypes are closer to right atrial isomerism than are their extrauterine presentations.

Azygos Vein↗
PubMed1996

Electrophysiologic study and radiofrequency ablation in patients with intracardiac tumors and accessory pathways: is the tumor the pathway?

INTRODUCTION: There is a strong association of cardiac rhabdomyomas with the Wolff-Parkinson-White syndrome. This report describes the results of investigations in two patients with accessory pathway-mediated AV reciprocating tachycardia coexisting with intracardiac tumors. METHODS AND RESULTS: Two patients with intracardiac tumors had mapping of the accessory pathway. Echocardiograms obtained in the electrophysiology laboratory while the ablation catheter was at the site of successful radiofrequency ablation demonstrated a close correspondence between the site of intracardiac tumor and the location of the accessory pathway. CONCLUSIONS: These results lend support to the hypothesis that accessory pathways in patients with intracardiac tumors, such as rhabdomyomas, are not typical Kent bundles, but instead are either part of the intracardiac tumor or are closely related to the tumor. Ablation is possible in at least some patients with accessory pathways associated with intracardiac tumors.

Adolescent↗
PubMed1994

Asplenia syndrome: insight into embryology through an analysis of cardiac and extracardiac anomalies.

Asplenia syndrome is characterized by complex congenital heart defects, asplenia and abdominal heterotaxy. Recent interest in the syndrome has been increased by new knowledge arising from animal models and by continuing improvements in surgical outcome in childhood. To further elucidate the embryologic timing and mechanisms of the asplenia syndrome, 32 necropsy cases were reviewed and 487 published autopsy cases were reanalyzed at the hospital. The most common congenital heart defects were atrial septal defects, common atrioventricular canals and conotruncal anomalies. With use of current information on the timing of normal development, it was hypothesized that most defects originate at Streeter Horizon XIII; patients averaged 3.2 Horizon XIII defects, more than at any other stage. Distribution was unimodal. Extracardiac anomalies also exhibited a developmental spectrum. Because the normal spleen develops by Horizon XIII, asplenia, the sine qua non of the syndrome, originates then or earlier. Abnormal pulmonary lobation occurred in 80% of cases, with right isomerism occurring most often; pulmonary branching asymmetry also originates at or before Horizon XIII. Abdominal heterotaxy occurred in 72% of cases, but the timing of origin is unclear. Anomalies of other systems, including genitourinary, musculoskeletal, endocrine, and nervous systems, develop later (typically XV to XXIII); specific anomalies were less frequent, although much more prevalent than in the general population. It is concluded that asplenia syndrome is a focal developmental disturbance in laterality which occurs primarily at Horizon XIII.

Abnormalities, Multiple↗
PubMed1993

Deep hypothermic circulatory arrest during cardiac surgery: effects on cerebral blood flow and cerebral oxygenation in children.

Deep hypothermic circulatory arrest has become an essential technique to allow repair of complex congenital cardiac lesions in children. The arrested state has concerned the surgeon, cardiologist, and anesthesiologist alike, and yet deep hypothermic circulatory arrest has been highly successful with a low incidence of neurologic sequelae. Studies of cerebral blood flow and cerebral oxygenation demonstrate that the arrest hypothermic brain does not develop the immediate postarrest hyperemia or hyperoxia seen in normothermic ischemic brain models. However, both hypothermic and normothermic ischemic brains exhibit hypoperfusion beyond the immediate recirculation period, likely coupled with a reduced cerebral metabolic rate. That the hypothermic arrested brain likely becomes anoxic and recovery of the anoxic brain depends in large part on recirculatory hemodynamics suggests that the lack of hyperemia and hyperoxia may play more major roles than was previously believed. The mechanism of protection may be related to suppression of oxygen free radicals.

Brain↗
PubMedDate not supplied

Aberrant left coronary artery arising from the right sinus of Valsalva with a right coronary arteriovenous malformation.

An 11-year-old boy presented with myocardial ischemia and was found to have an aberrant left main coronary artery from the right sinus of Valsalva coursing between the aorta and pulmonary artery, as well as a small arteriovenous malformation from a right atrial branch of the right coronary artery to the right atrium. Distinctive echocardiographic findings were supported by angiographic and magnetic resonance imaging studies. Treadmill and scintigraphic stress testing were normal. Corrective surgery was accomplished by a modified technique to unroof the intramural proximal course of the left coronary artery, without postoperative complications. The anatomy and pathophysiology of this rare coronary lesion are reviewed.

Arteriovenous Malformations↗