Faculty Bibliography

BACKGROUND: In the intact immature heart, how much digoxin can drive sodium-calcium exchange has not been studied in the context of sodium-calcium exchanger abundance. METHODS AND RESULTS: The effects of digoxin and low potassium on contractility in the intact, paced and isovolumically contracting immature rabbit heart were studied in both the absence and presence of L-type calcium channel blockade. Without calcium channel blockade, digoxin increased contractility minimally and only at 10(_6) M/L. In contrast, low potassium (2.2 mM/L) substantially increased contractility in all experiments, a result indicating abundant sodium-calcium exchanger activity. During nifedipine-induced calcium channel blockade, digoxin (10(_6) M/L) allowed modest recovery of contractility, whereas digoxin and low potassium together allowed complete recovery as assessed by dP/dt(max); however, all hearts so perfused subsequently developed ventricular fibrillation, presumably because of calcium overload. CONCLUSIONS: In intact immature rabbit heart, digoxin can drive sodium-calcium exchange and thus increase contractility to only a minimal extent. This effect does not appear to be limited by intrinsic exchanger activity, which appears abundant in this preparation. Rather, digoxin's inability to drive the sodium-calcium exchanger may be due to developmental differences in binding to the sodium pump. The sodium-calcium exchanger itself seems capable not only of providing enough intracellular calcium for normal contraction, but also of overloading the myocardium with calcium, despite L-type calcium channel blockade

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

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

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

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

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