Dextrocardia

Dextrocardia is a position of the heart in the right hemithorax with the apex pointing to the right. It occurs in about 1 in 10,000 to 12,000 live births. The clinical question is the arrangement of the viscera and atria.

In dextrocardia with situs inversus totalis (mirror image arrangement of all organs), associated congenital heart disease is present in only about 3 to 5%.

In dextrocardia with situs solitus (isolated dextrocardia), complex congenital heart disease is almost always present (congenitally corrected transposition, double outlet right ventricle, pulmonary stenosis, ventricular septal defect).

In dextrocardia with situs ambiguus (heterotaxy), right isomerism (asplenia) or left isomerism (polysplenia) coexists with complex heart disease. Dextroposition is a different entity in which the heart is pushed to the right by an extracardiac cause.

About 20 to 25% of patients with situs inversus totalis have primary ciliary dyskinesia (Kartagener syndrome).

Pathophysiology. Abnormal determination of left right asymmetry in embryogenesis (nodal ciliary motion and Nodal, Lefty and Pitx2 signalling) produces mirror image or randomised organ position. Genes involved include ZIC3 (X-linked heterotaxy) and many ciliary genes.

Right isomerism gives bilateral right sided structures, asplenia and total anomalous pulmonary venous connection, with lifelong risk of overwhelming sepsis from encapsulated organisms.

Left isomerism gives bilateral left sided structures, polysplenia, interrupted inferior vena cava with azygos continuation, sinus node dysfunction or heart block, partial anomalous pulmonary venous connection, atrioventricular septal defect and biliary atresia. Malrotation of the gut accompanies heterotaxy.

• Situs inversus totalis with a normal heart is usually asymptomatic. The apex beat and heart sounds are loudest on the right, and the liver is on the left.
• Congenital heart disease: cyanosis, heart failure, murmurs, and arrhythmia.
• Primary ciliary dyskinesia: neonatal respiratory distress, chronic wet cough from infancy, recurrent otitis media and sinusitis, bronchiectasis and male infertility.
• Heterotaxy: bilious vomiting from malrotation or volvulus, prolonged jaundice with pale stools from biliary atresia, and sepsis in asplenia.
• ECG in mirror image dextrocardia: inverted P wave, negative QRS and inverted T wave in lead I; right axis deviation; R wave amplitude falling from V1 to V6. Right sided precordial leads (V3R to V6R) restore normal progression. Reversed arm leads alone give an inverted lead I with a normal precordial pattern.

Red flags.

• Neonatal cyanosis or heart failure
• Bilious vomiting
• Prolonged jaundice with pale stools
• Fever or sepsis in suspected asplenia
• Neonatal respiratory distress with chronic wet cough
• Bradycardia or syncope (sinus node dysfunction, heart block)

• Chest X-ray and abdominal imaging: right sided heart, position of the gastric bubble and liver, side of the aortic arch, bronchial symmetry.
• 12-lead ECG with right sided leads.
• Echocardiography with sequential segmental analysis: atrial situs by atrial appendage morphology and the relation of the inferior vena cava and aorta in the upper abdomen, ventricular loop, atrioventricular and ventriculo arterial connections, pulmonary and systemic venous return, and arch side.
• Abdominal ultrasound: spleen number and position, liver and gallbladder position, inferior vena cava, and gut.
• Blood film: Howell-Jolly bodies indicate absent splenic function.
• CT or MRI: complex anatomy, venous return and airways.
• Primary ciliary dyskinesia workup: nasal nitric oxide (low), high speed video microscopy of ciliary beat, genetic panel, and electron microscopy.
• Upper gastrointestinal contrast study: when malrotation is suspected.
• Genetic testing: ZIC3 and other heterotaxy and ciliary genes.

Differential diagnosis.

• Dextroposition from right lung collapse, hypoplasia or pneumonectomy, scimitar syndrome, congenital diaphragmatic hernia, or large left pneumothorax or effusion
• Mesocardia
• Limb lead reversal on ECG
• Isolated levocardia with situs inversus
• Congenitally corrected transposition of the great arteries
• Pectus excavatum displacing the heart
• Acquired right sided cardiac displacement from mediastinal mass

• Situs inversus totalis with a normal heart: no treatment. The patient carries a note stating the anatomy, because of risks of misdiagnosis: left sided appendicitis or biliary pain, misplaced ECG leads, and reversed auscultation sites. In resuscitation, place defibrillator pads in mirror image positions.
• Associated heart disease: treated by the lesion, usually by staged palliation or repair at a congenital cardiac centre, with mirror image surgical planning.
• Asplenia or hyposplenism (right isomerism and some left isomerism):
  • Penicillin V orally twice daily lifelong: 125 mg for age 1 month to 4 years, 250 mg for age 5 years and over (including adults). Reduce in severe renal impairment (creatinine clearance under 10 mL/min).
  • Vaccinate against pneumococcus, Haemophilus influenzae type b, meningococcus groups A, C, W, Y and B, and annual influenza.
  • Any febrile illness is an emergency: give ceftriaxone 2 g intravenously (children 80 mg/kg, maximum 2 g) immediately after blood cultures, then every 24 hours, or every 12 hours when meningitis is suspected. Avoid live vaccines if immunocompromised.
• Primary ciliary dyskinesia: airway clearance physiotherapy twice daily, prompt antibiotics for exacerbations directed by sputum culture (usually 14 days), annual influenza vaccination, and ENT and audiology review. Azithromycin 10 mg/kg (maximum 500 mg) orally three times weekly reduces exacerbations. Before starting, check baseline QTc, sputum for non-tuberculous mycobacteria and hearing; avoid with QT prolongation. Review benefit at 6 months. Monitor liver enzymes and QTc.
• Malrotation with volvulus: emergency surgery (Ladd procedure). Biliary atresia: surgical portoenterostomy ideally before 60 days of life.
• Sinus node dysfunction or heart block in left isomerism: permanent pacing when symptomatic.

Special groups. Pregnancy with situs inversus totalis and a normal heart carries no extra risk. In heterotaxy it depends on the heart lesion and on whether the patient has a Fontan circulation or pulmonary hypertension.

Monitoring. Echocardiography and ECG at least yearly in heterotaxy or when there is heart disease. Ambulatory ECG when there are palpitations or syncope. In primary ciliary dyskinesia, spirometry and sputum cultures every 3 months and CT chest when bronchiectasis is suspected. In asplenia, review vaccination and penicillin adherence yearly.

Referral and escalation. Refer every neonate with suspected heterotaxy to a paediatric cardiac centre. Urgent for cyanosis, bilious vomiting, or sepsis in an asplenic patient.