A quadricuspid pulmonic valve diagnosed in a live newborn by two-dimensional echocardiography

Quadricuspid pulmonic valve is a rare congenital anomaly which appears to occur in the absence of other cardiac or systemic anomalies. It predominates in males and tends to be clinically quiescent. The first case of quadricuspid pulmonic valve in a live newborn infant diagnosed by two-dimensional echocardiography is presented here with a review of the literature.

Spontaneous closure of atrial septal defects in premature vs. full-term neonates

Our hypotheses were that the following factors influenced closure of atrial septal defects (ASDs) detected in neonates: estimated gestational age (EGA), the presence of a persistent ductus arteriosus (PDA), severity of pulmonary disease, gender, and the initial size of the ASD. Our population consisted of 82 newborns (38 premature and 44 term) who were found before the age of 1 month to have an ASD. Closure of ASDs was analyzed using both Kaplan-Meier survival analysis and the Cox proportional hazards model, each with the five covariates. The hazard ratio (or ratio of instantaneous closure rates) of term vs preterm infants was 3.60 (95% CI = 1.80-7.20), whereas the hazard ratio for infants with a PDA (compared to infants with no PDA) was 2.41 (95% CI = 1.28-4.54). Multivariate analysis showed that each of these terms (PDA and EGA) were independent predictors of ASD closure. The hazard ratio of ASD closure for each of four levels of pulmonary disease was 0.632 [95% CI = 0.453-0.881]. We conclude that the majority of neonatal ASDs will close, with EGA and PDA acting as important influences on closure.

Double-outlet right ventricle: an antenatal diagnostic dilemma

OBJECTIVE

The purpose of this study was to describe the antenatal ultrasonographic findings of fetuses with double-outlet right ventricle (DORV).

DESIGN

The records were reviewed of all fetuses scanned in our ultrasound unit which were suspected of having DORV during a 6-year period ending in April 1996. A medical record search for all infants with a postnatal diagnosis of DORV was also undertaken to identify cases that were not detected antenatally. Records were examined to determine the accuracy of antenatal diagnosis and the reasons for diagnostic errors. Fetuses without follow-up were excluded.

RESULTS

There were 20 fetuses with antenatally detected conotruncal defects that had DORV included in the differential diagnosis. Three fetuses were excluded, seven did not have DORV and ten were confirmed postnatally as having DORV. Two additional infants were found to have DORV from the medical record search, producing a total of 12 cases. Antenatal sonographic cardiac findings included malpositioned (overriding or transposed) great arteries (n = 11), ventricular septal defect (n = 11) and small pulmonary artery suggesting stenosis (n = 4). Confirmed postnatal cardiac findings that were missed antenatally included aortic coarctation (n = 2), right-sided aortic arch (n = 2) and pulmonary stenosis (n = 1). Seven of the 12 fetuses had extracardiac findings. Nine of the 12 fetuses tested had a normal karyotype. Eleven of the 12 infants were liveborn. Nine of these 11 survived the neonatal period and underwent surgical repair within the first year of life; two subsequently died. In total, seven fetuses survived and five did not.

CONCLUSIONS

Most fetuses with DORV can be identified antenatally as having an abnormal heart. However, it is very difficult to distinguish this particular defect from other conotruncal abnormalities.

Doppler velocity and flow through the aortic isthmus in normal term neonates

Our hypothesis was that the relationship between the internal aortic diameter and the Doppler flow velocity across the aortic isthmus could be modeled by applying the principle of conservation of mass flow. The aortic diameter decreased at the isthmus by a mean of 18% (t = 11.02, p < 0.0001), while the flow velocity increased by a mean of 44% (t = 10.09, p < 0.0001). The mean peak mass flow rate was 34. 5 ml/s preisthmus and 32.9 ml/s at the isthmus with excellent correlation (r = 0.830). We conclude that the increase in Doppler velocity observed in the descending aorta can be explained by the normal narrowing observed at the aortic isthmus and application of the continuity equation for conservation of mass flow.

Recurrence risk of supraventricular tachycardia in pediatric patients

We analyzed risk of recurrence of supraventricular tachycardia (SVT) in 70 pediatric patients using both Kaplan-Meier survival analysis and logistic regression of likelihood of recurrence, each with covariates: (1) age at onset of SVT; (2) presence of Wolff-Parkinson-White syndrome (WPW), and (3) gender. Among 38 patients who had onset of SVT <1 year, only 11 had a recurrence, while among 32 older patients, 30 had a recurrence of SVT (p < 0.00001, Fisher's exact test). The survival analyses, stratified by age at onset <1 versus >1 year, were significantly different (p < 0.0001) as was stratification by presence of WPW (p < 0.01). Logistic regression analysis showed that the only significant predictor of recurrence was age at onset; the additional information provided by presence of WPW and gender did not significantly add to the prediction of recurrence. The odds ratio of recurrence for age at onset >1 versus <1 year was 34.6, with a 95% confidence interval of 6.98-172.

Fetal cardiac asymmetry: a marker for congenital heart disease

OBJECTIVE

To determine the sensitivity of prenatally detected fetal cardiac asymmetry as a sonographic marker for congenital heart disease.

METHODS

The normal ratios of pulmonary artery to aorta diameters and of right ventricle to left ventricle diameters were derived from normal fetuses scanned at 17 weeks or more in a 65-month period. Cross-sectional diameters of cardiac ventricles and great arteries were measured at the level of the valves at the time of the scan. Fetuses with confirmed cardiac anomalies detected prenatally during the study were examined to identify how many had cardiac asymmetry, determined by abnormal ratios.

RESULTS

Linear regression analysis of the group of 881 normal fetuses showed the normal pulmonary artery to aorta diameter ratio remained constant throughout pregnancy and the normal right ventricle to left ventricle ratio increased slightly with progressing gestational age. The 90% confidence intervals were 0.79, 1.24 for the right ventricle to left ventricle ratio and 0.84, 1.41 for the pulmonary artery to aorta ratio. Of the 73 fetuses with abnormal hearts, 66% had either ventricular or great artery asymmetry (at least one of the two ratios was abnormal). However, if no asymmetry was present, the cardiac defect was more likely to be a minor one.

CONCLUSION

Cardiac asymmetry was present in two-thirds of fetuses with cardiac anomalies diagnosed prenatally. If cardiac asymmetry is found, a more thorough examination of the fetal heart is indicated.

Sonographic screening to detect fetal cardiac anomalies: a 5-year experience with 111 abnormal cases

OBJECTIVE

To determine whether there is a difference between the types of cardiac lesions detected as abnormal prenatally and those that are not detected.

METHODS

Consecutive fetuses at 14 weeks' gestation or more were scanned in our unit from February 1990 through July 1995 and later were delivered at our hospital. Outcome information was obtained from neonatal echocardiograms and autopsies. Our results were compared to sensitivities for individual cardiac lesions based on pooled data from studies published previously.

RESULTS

There were 111 fetuses with cardiac anomalies, of which 73 (66%) were identified correctly as abnormal prenatally. Sensitivities for the most common cardiac lesions were as follows: 87% atrioventricular septal (endocardial cushion) defects, 65% tetralogy of Fallot, 63% transposition of the great arteries, 50% aortic coarctation, and 44% isolated ventricular septal defects. The lesions that went undetected most frequently were isolated septal defects (n = 17); most of these were ventricular and small or moderate in size. Based on our sensitivities and those calculated from previous studies, the fetal cardiac lesions with the highest detection rates involve hypoplastic ventricles and atrioventricular septal defects, followed by lesions of the great arteries and finally by isolated septal defects.

CONCLUSIONS

The sensitivity of sonographic screening to defect fetal cardiac anomalies varies with the type of lesion. Isolated septal defects are the most difficult lesions to detect.

Tetralogy of Fallot: prenatal diagnosis and postnatal survival

OBJECTIVES

To correlate prenatal echocardiographic findings with infant outcome in a large screening population affected by tetralogy of Fallot.

METHODS

Inclusion criteria required confirmed postnatal cardiac diagnosis, at least one fetal ultrasound examination with satisfactory heart visualization, and infant delivery at our institution. Aortic and pulmonary artery diameters were measured from real-time ultrasound or videotaped scans and compared against published nomograms. The pulmonary artery to aorta ratio was also evaluated in a similar manner. Infant survival was assessed 1 year after delivery.

RESULTS

Seventeen fetuses were confirmed to have a ventricular septal defect and an overriding aorta with varying degrees of right ventricular outflow obstruction after delivery. All karyotypes were normal. Ultrasound screening identified 12 of 17 abnormal hearts at a mean gestational age of 22.9 +/- 5.1 weeks; two of these fetuses were thought to have only ventricular septal defect before delivery. Five fetuses had enlarged aortic roots during the initial scan. Only two of the ten fetuses with a measurable pulmonary artery had initial sonographic evidence for valve stenosis. Six other pulmonary arteries became abnormally small with advancing pregnancy. The pulmonary artery to aorta ratio was decreased in six of the ten fetuses with a measurable pulmonary artery. Sixteen infants survived at least 1 year after birth and successfully completed either corrective or palliative cardiac surgery.

CONCLUSION

Fetuses with tetralogy of Fallot may present with only a ventricular septal defect and aortic septal override by prenatal ultrasound examination. Pulmonary artery stenosis is not always present at initial ultrasound examination, but this finding can develop or worsen during pregnancy. Furthermore, a normal aortic diameter does not exclude tetralogy of Fallot. Infant survival appears to be favorable in the absence of other major structural or chromosomal anomalies.

Prenatal screening for cardiac anomalies: the value of routine addition of the aortic root to the four-chamber view

OBJECTIVE

To determine whether the addition of the aortic-root view would detect more congenital cardiac anomalies than a standard four-chamber view alone.

METHODS

The study included fetuses of 14 weeks' gestation or more who were scanned in our unit during a 28-month period. Outcome information was obtained from postnatal echocardiograms and autopsies. Abnormal hearts were classified as to whether the four-chamber or aortic-root view was abnormal.

RESULTS

There were 5967 fetuses in whom a four-chamber view could be obtained. In 5111 of these, an aortic-root view could also be obtained. The four-chamber view detected 24 (47%) of the 51 fetuses with abnormal hearts. Adding the aortic-root view increased the sensitivity to 78%.

CONCLUSIONS

Visualization of the aortic root is a quick and easy means of evaluating the aortic outflow tract during routine scanning. Adding the aortic-root view to the standard four-chamber view will result in the detection of most cardiac anomalies prenatally.

Review of 180 episodes of chest pain in 134 children

This study intends to establish the etiology of chest pain in the pediatric population, to determine the causal relationship between a cardiac problem and chest pain in acutely sick children, and to provide a systematic approach to the management of these patients. The charts of 134 patients, up to 19 years of age, seen in the emergency department (ED) of Children's Hospital of Wisconsin (CHW) with the primary diagnosis of "chest pain" during a five-year period were reviewed. In 15% of these patients, a relationship was established between chest pain and actual cardiac disease. A thorough history and physical examination are the diagnostic "keys" in evaluating pediatric patients with chest pain; laboratory tests are often helpful when indicated by the history and physical examination. In the majority of the cases, reassurance is all that is required; occasionally, pharmacologic treatment is recommended. Hospitalization is rarely necessary.

Cardiac tamponade complicating a case of fever of unknown origin

A 16-year-old male was transferred to Children's Hospital of Wisconsin (CHW) after 17 days of fever of unknown origin. An echocardiogram revealed a small pericardial effusion only. Serial echocardiography demonstrated an increased size of this effusion with collapse of the right atrium during diastole. A subxiphoid open pericardiostomy was performed to relieve the impending tamponade and to assist in the diagnosis of his fever. The diagnostic criteria for cardiac tamponade are discussed.

Cor pulmonale as a complication of methylmalonic acidemia and homocystinuria (Cbl-C type)

We report an infant with a bronchiolitis-like illness and rapid deterioration who developed a cor pulmonale-like picture with a dilated right ventricle. Urinary organic acid assays established a probable diagnosis of Cbl-C-type methylmalonic aciduria, later confirmed by complementation studies. Despite medical intervention and cyanocobalamin treatment the patient died on his tenth hospital day. Postmortem examination showed the presence of thromboemboli in the pulmonary circulation. We hypothesize that acute cor pulmonale developed in this infant secondary to thromboembolism of his pulmonary circulation. A review of the literature shows that thromboembolism may be a part of this disease process.

Increasing extracellular calcium concentration does not prevent hypotensive effects of verapamil in neonatal swine

Effects of CaCl2 on cardiac function and regional circulatory responses to verapamil (V) infusion were studied in pentobarbital-anesthetized 2-week-old swine. V 100 micrograms/kg (n = 15) or 300 micrograms/kg (n = 15), given as a 2-min intravenous infusion, was repeated after 30 min. Only V was given to 15 of these. The other 15 were given CaCl2 (15 mg/kg) over 2 min, pre-V (protocol A), and over 4 min, 2 min pre-V and during V (protocol B). Positive chronotropic and negative inotropic responses to V were attenuated by CaCl2; hypotensive effects were unaltered. Renal, but not mesenteric and femoral, vasodilation was augmented by CaCl2, CaCl2 alone produced marked positive inotropic and renal vasodilatory effects which contributed to maintenance of the hypotensive effect of V.

Treatment of severe imipramine poisoning complicated by a negative history of drug ingestion

The wide use of imipramine (Tofranil) for the treatment of nocturnal enuresis continues in spite of the unique dangers associated with this drug. Young children are particularly susceptible to the potentially lethal central nervous system and cardiovascular toxicities, yet the toxic potential of imipramine remains unrecognized by both parents and too many physicians. Management of severe imipramine intoxication can be difficult. This report describes a 12-month-old patient with severe imipramine intoxication whose treatment was complicated by a negative history at presentation.

Young long distance runners. Physiological and psychological characteristics

This study presents the physiological and psychological characteristics and the running histories of 16 subjects who began long distance running at age 4-12 years. Running duration was 3-15 years (mean 8.4 +/- 3.6 yrs). Seven children completed 41 marathons, seven 30-mile races, and eight 60-mile races. The other nine competed at shorter distances. All trained at 30-105 miles/week. Two stress fractures, one back sprain and one knee injury occurred. Athletes who reported injuries from recollection may have underreported some injuries. At age 15.4 +/- 4.2 years bone age was 15.3 +/- 2.6 years and height was at 51 +/- 26.0 percentile. Athletes had larger left ventricular diastolic diameter, higher max O2 uptake, and delayed onset of anaerobic metabolism compared to controls. Psychological profile: IQ = 121 +/- 11, scholastic grade point average (GPA) (n = 13) was less than or equal to 3.0 in four, 3.6-3.9 in four, and 4.0 in five. Cattell 16 personality factor (PF): Seven scored above the 85th percentile on boldness, warmth, conformity, sensitivity, dominance, and high drive with tension. Eight scored above the 93rd percentile for self discipline and emotional stability. Human Figure Drawing showed a distorted body image in seven. Two developed anorexia nervosa, and another girl committed suicide. Thus, high physical fitness and no growth retardation were observed. These runners, however, shared distinct positive and negative personality characteristics. The relatively high incidence of severe psychological disorders possibly suggests a need for psychological screening for young children entering a strenuous training program and for close monitoring for development of psychological problems during the program.

Age-related digoxin-verapamil interactions in the adult rat

We have previously described a method for inducing atrial ectopic tachycardia (AET) in the anesthetized adult rat using digoxin, 30 mg/kg s.c. In this study, we used this model to study digoxin-verapamil interactions in young and older male rats and have found age-related differences in their responses to digoxin alone and to digoxin-verapamil interactions as well. Overall, 90% of the animals of both groups combined that developed AET, developed a ventricular proarrhythmic response to verapamil. Thus, this model might broaden the pre-clinical evaluation of anti-arrhythmic agents and predict which drugs are most likely to have a proarrhythmic effect.

Dilated cardiomyopathy complicating a case of epidermolysis bullosa dystrophica

A child with epidermolysis bullosa dystrophica, recessive type (EBDR) developed significant anemia at 9 years of age and was treated with long-term transfusion therapy. At age 17 he had symptoms of congestive heart failure secondary to dilated cardiomyopathy. Treatment with digoxin and vasodilators for the past year has failed to improve his cardiomyopathy significantly. Chronic iron overload and secondary hemosiderosis may have contributed to his problems, and we propose that chelation therapy be used in any child receiving long-term transfusion therapy.

Acute rheumatic fever in Wisconsin

Medical records of patients discharged from Children's Hospital of Wisconsin from January 1980 to May 1988 who fulfilled the revised Jones criteria for acute rheumatic fever were reviewed. A total of 13 patients were hospitalized with a first attack of acute rheumatic fever during this period. Migratory polyarthritis was present in 92% of the patients and carditis in 62%. Mitral regurgitation was present in all cases of carditis. Only six patients (46%) had a history of a preceding streptococcal infection, half of whom were treated with antibiotics. While there is no evidence to support a new outbreak of acute rheumatic fever in Wisconsin, our data demonstrate that the disease is still prevalent within the eastern region of the state. Patients with Group A streptococcal pharyngitis must be identified and treated to prevent this disease from increasing in incidence.

Cardiac glycoside toxicity in small laboratory animals

Cardiac glycosides are frequently administered to laboratory animals for research purposes. The effects achieved depend not only upon the particular glycoside and dose administered, but also upon an entire array of variables from the species of animal to the temperature of the animal housing facility. We review a number of these factors and their influence upon the effects achieved by the administration of cardiac glycosides to laboratory animals.

Bilateral origin of the left anterior descending coronary artery in a young man

Abnormalities of coronary artery origin from the aorta have been implicated in sudden death in sports among young athletes. We describe an 18-year-old patient who presented with nonspecific chest pain, developed ventricular couplets during recovery from a stress test, and whose coronary angiograms revealed bilateral left anterior descending coronary arteries, an abnormality that has not been previously reported.

A model of atrial ectopic tachycardia in the rat

A model of atrial ectopic tachycardia (AET) in the adult rat is described. Pentobarbital-anesthetized adult male rats given digoxin 30 mg/kg s.c. develop AET 50 min after administration. Heart rate and rhythm were determined by electrocardiography using limb leads, I, II and III. This model of AET is simple, sustained and economical. As a supplement to models of ventricular arrhythmias, this model might broaden the pre-clinical evaluation of antiarrhythmic agents.

Reevaluation of digoxin-encainide interactions using an animal model

The effects of intravenous encainide on digoxin-induced atrial ectopic tachycardia (AET) were investigated in the rat using 3-channel simultaneous limb-lead electrocardiography. Pentobarbital-anesthetized (35 mg/kg, intraperitoneal) adult male rats were given digoxin subcutaneously, 30 mg/kg. After onset of AET, rats received either saline (0.5 ml/kg) or encainide; 0.25, 0.5, 1.0, or 2.0 mg/kg intravenously in repeated doses at 15-min intervals. At all doses, encainide converted digoxin-induced AET to ventricular arrhythmias, prolonged recovery time, and increased mortality in comparison to saline-treated animals. An additional group of anesthetized rats was not given digoxin. These animals received encainide (2.0 mg/kg, intravenously) in repeated doses at 15-min interval and developed dose-related increase in the P-R interval only. Blood samples were obtained by cardiac puncture from 12 additional anesthetized, digoxin-treated rats 5 min after the fourth intravenous dose of saline (0.5 ml/kg, n = 6) or encainide (1.0 mg/kg, n = 6). Serum was prepared and analyzed by affinity column-mediated immunoassay. Digoxin levels were the same in both groups. These results suggest that encainide may exacerbate digoxin-induced arrhythmias (proarrhythmic effect) in this species. In view of our findings of digoxin-encainide interactions in the rat, we recommend caution if these drugs are coadministered in humans.

Lyme disease presenting as heart block

Lyme disease is now recognized as an infectious process capable of involving multiple organs including the cardiovascular system. We recently treated a boy whose complaints on admission related only to symptomatic heart block that was severe enough to require transvenous pacing. This boy was subsequently determined to have had Lyme Disease after his medical testing was reevaluated for possible tick exposure. In rare instances symptomatic heart block may be the sole presenting complaint of Lyme Disease in children.

Mechanisms of digoxin-amiodarone interaction in the rat

Amiodarone and digoxin are often used in combination and clinical experience suggests that amiodarone may increase serum digoxin levels and toxicity. We have investigated the influence of amiodarone on digoxin pharmacokinetics and tissue distribution in the rat. Forty-nine rats were injected with 10 mg/kg amiodarone sc three times a day for 7 days, while 49 others were injected with saline only. On the eighth day, all the rats received 0.5 mg/kg digoxin ip; 4, 5, 6, 7, 8, 10, and 12 hr later, groups of 7 amiodarone-pretreated and control animals were sacrificed, and plasma, heart, liver, muscle, brain, and kidney digoxin concentrations measured by radioimmunoassay. Data were analyzed by two-way ANOVA, with group comparisons using the Waller-Duncan multiple comparison procedure. Digoxin levels were significantly higher in the plasma, heart, muscle, and kidney of the amiodarone-pretreated rats at most points of measurement (P less than 0.05) whereas liver digoxin levels were elevated at 8, 10, and 12 hr. Kidney/plasma, heart/plasma, muscle/plasma, and especially liver/plasma ratios in the control groups significantly exceeded the values found in the amiodarone-pretreated group at most time points. Concentrations of digoxin in brain were not changed. This suggests that the volume of distribution is significantly altered in the amiodarone-pretreated group. Amiodarone increases plasma digoxin levels in rats as it does in humans, but the mechanism is unclear.

Cor pulmonale due to adenoidal or tonsillar hypertrophy or both in children. Noninvasive diagnosis and follow-up

Four children, aged 1 to 3 1/2, were first seen with cor pulmonale, pulmonary edema and severe respiratory distress due to chronic upper airway obstruction secondary to adenoidal or tonsillar hypertrophy or both. Arterial blood gas values, electrocardiograms and chest x-ray films were compatible with cor pulmonale. Echocardiography (four cases) and radionuclide angiography (two cases) showed severe right ventricular and right atrial dilation with reduced right ventricular ejection fraction. Following surgery, all four children improved; their echocardiographic and radionuclide findings returned to normal. Cardiac catheterization, traditionally performed in such cases, was unnecessary. The diagnosis and follow-up of this syndrome are adequately performed noninvasively.

False aneurysm of the right ventricle due to endocarditis in a child

An eight-year-old boy with supravalvular pulmonic stenosis, supravalvular aortic stenosis, and ventricular septal defect developed Staphylococcus aureus endocarditis. The infection was complicated by formation of a false aneurysm of the right ventricular outflow tract, which was demonstrated by contrast echocardiogram. Surgical treatment was successful. This is a unique case of false aneurysm of the outflow tract of the right ventricle, because it is secondary to endocarditis without known previous trauma to the right ventricular wall.

Viral myocarditis simulating dilated cardiomyopathy in early childhood: evaluation by serial echocardiography

Left ventricular dimensions and function were assessed by serial M mode and cross sectional echocardiography in ten infants and young children with heart muscle disease characterised by left ventricular dilatation and impaired systolic function presenting in congestive heart failure, severe respiratory distress, or both. The patients were followed for 8-60 months after their initial admission. The aetiology was probably viral in all cases. One patient died three weeks after diagnosis. Left ventricular size and function returned to normal in only one child; however, various degrees of improvement were found in seven others who were symptom free at follow up. This study demonstrates that serial echocardiography adequately defines this disease in infants and young children and that invasive evaluation is seldom required. Furthermore, it emphasises the fact that even in symptom free children an echocardiographic picture that is indistinguishable from dilated cardiomyopathy may persist; such patients required continued follow up.

Plasma and tissue levels of digoxin in the rat following pretreatment with verapamil

Verapamil and digoxin are frequently used in combination, and clinical experience suggests that verapamil may increase digoxin toxicity. We have investigated the influence of verapamil on digoxin pharmacokinetics in the rat. Rats were injected with 10 mg/kg verapamil s.c. twice a day for 7 days while control rats were injected with saline only. On the 7th day, all the rats received 0.5 mg/kg of digoxin i.p. Two, 4, 6, 8 and 10 hours later, groups of 6 to 8 verapamil pretreated and control animals were sacrificed and plasma, heart, brain, liver, kidney and muscle digoxin concentrations were assayed. Digoxin levels were significantly higher in the plasma, heart, liver and muscle of the verapamil pretreated rats at 6, 8 and 10 hours (p less than 0.01).

Verapamil and digoxin: interactions in the rat

Verapamil and digoxin are often used in combination and clinical experience suggests that verapamil may increase digoxin toxicity. We have explored the effects of verapamil upon digoxin induced tachyarrhythmias and have undertaken a preliminary study of the influence of verapamil on digoxin pharmacokinetics in the rat. Anesthetized rats received 20 mg/kg of digoxin intraperitoneally followed by verapamil i.v., 0.3 mg/kg, in repeated doses either immediately after digoxin or only after the onset of digoxin induced arrhythmias. Digoxin alone produced prolonged paroxysmal atrial tachycardia in 88-100% of rats and verapamil converted 75% of rats to sinus rhythm and significantly reduced digoxin induced mortality. In a later study, rats were injected with 10 mg/kg verapamil i.p. twice a day for 7 days or only with saline. On the seventh day all the rats received 0.5 mg/kg of digoxin i.p. Eight hours later the animals were sacrificed and plasma, heart, brain, liver, kidney and muscle (diaphragm) digoxin concentration was measured by radioimmunoassay. Digoxin levels were twice as high in plasma, heart, liver and muscle of verapamil pretreated rats (p less than 0.01). Two types of verapamil - digoxin interactions are demonstrated in the above studies; one in which verapamil modifies digoxin induced arrhythmias and a second pharmacokinetic effect in which pretreatment with verapamil increases digoxin concentration in the plasma and in several tissues.

Comparison of digoxin-induced cardiac toxicity in resistant and sensitive species

We have examined the species-specific arrhythmogenic effects of digoxin in the rat (resistant species) and in the guinea-pig (sensitive species). 26 adult rats and 23 adult guinea-pigs were anaesthetized with pentobarbitone and injected subcutaneously with varying doses of digoxin. Electrocardiograms were monitored continuously for 4 1/2 h following digoxin administration. The arrhythmogenic dose (AD50) and lethal dose 50 under anaesthesia (LD50) were determined using the method of Litchfield & Wilcoxin. AD50 in rats was 13.0 +/- 1.0 mg kg-1 (mean +/- s.d.) compared with 0.60 +/- 0.04 (P less than 0.01) in the guinea-pig and LD50 was 30.0 +/- 1.9 mg kg-1 in the rat compared with 0.60 +/- 0.04 (P less than 0.01) in the guinea-pig. The onset of arrhythmias was not dose-dependent in the rat but was clearly so in the guinea-pig; for example 102 +/- 15 min (mean +/- s.e.m.) following 0.5 mg kg-1, and 43 +/- 2 min following 1 mg kg-1. In the rat the onset of arrhythmias was 54.0 +/- 11.5 min. Supraventricular arrhythmias (paroxysmal atrial tachycardia) appeared in 73% of rats compared with only 18% of guinea-pigs whereas ventricular arrhythmias (ventricular tachycardia), multiple premature ventricular contractions and or multifocal PVC's occurred in 100% of guinea-pigs compared with only 32% of rats. All guinea-pigs that developed arrhythmias died whereas several rats recovered from supraventricular tachycardias. In conclusion, the guinea-pig is much more sensitive to digoxin toxicity than the rat, develops arrhythmias at much lower doses and these arrhythmias are much more likely to be ventricular in origin and cause fatality.

Modification of digoxin induced arrhythmogenicity in adult rats following atropine administration

Atropine alone in the two lower doses (20mg/kg and 40mg/kg) did not produce any arrhythmias while 80mg/kg of atropine produced arrhythmias in 33% of animals after 31.0 +/- 7.5 min. Only 11% of these rats developed paroxysmal atrial tachycardia. Atropine in lower doses (20,40mg/kg) with digoxin (40mg/kg) decreased the total percent of digoxin induced arrhythmias, delayed their onset, and changed the type of arrhythmias as compared with the digoxin group alone. Atropine given in higher dosage (80mg/kg) with digoxin (40mg/kg) produced arrhythmias in 100% of rats as did digoxin alone, but significantly shortened their onset and modified the types of arrhythmias seen. In conclusion, atropine in varying doses significantly modified digoxin toxicity.

Severe rheumatic mitral valve disease in children. Evaluation by echocardiography

Severe rheumatic mitral stenosis with or without mitral insufficiency is virtually unseen in children in the affluent countries of the western world, but is not uncommon in developing countries. Fifteen cases of rapidly progressive rheumatic mitral valve disease in children are presented to illustrate the value of echocardiography in the diagnosis and evaluation of this lesion. Cardiac catheterization was performed in nine and simply confirmed the diagnosis made noninvasively. Our experience demonstrates that thorough echocardiographic examination in these cases frequently enables the examiner to assess the need for surgical intervention without cardiac catheterization.