Left Atrial Isomerism

Age: 40 years

Gender: Female

Occupation: Priest

Working diagnosis: Left atrial isomerism, partial atrioventricular septal defect


The patient presented at 3 years of age following recurrent attacks of bronchiolitis when a murmur was identified. Development had been normal until that time with no reported cyanosis. Clinical examination revealed a relative bradycardia, a fixed split second heart sound with a pulmonary ejection systolic murmur, and a pan-systolic murmur at the left sternal edge and apex.

Electrocardiography demonstrated a nodal rhythm with partial RBBB and left-axis deviation (−71°).

Cardiac catheterization demonstrated a single atrium with a persistent left SVC draining into the left side of the atrial chamber. There was severe regurgitation of the left AV valve.

At the age of 4 the patient underwent surgical septation of the atrium. At surgery the presence of a common atrium was confirmed, with separate orifices of bilateral SVCs. “Clefts” of the anterior cusp of the mitral valve and the septal cusp of the tricuspid valve were identified and repaired. A pericardial patch was used to divide the common atrium with separation of the systemic from the pulmonary venous return.

Postoperatively residual “mitral” regurgitation was noted clinically and progressed over the following years with an associated deterioration in exercise tolerance and a requirement for diuretic therapy.

At the age of 14 the patient underwent further septation of the atrium using a Dacron patch, the original patch having broken down allowing significant left-to-right shunting.

From the age of 31, she developed increasingly frequent and troublesome atrial tachycardia, requiring multiple DC cardioversions and amiodarone therapy. At this stage she had moderate left AV valve regurgitation, but this progressed over the ensuing 3 years. She underwent left AV valve repair. Postoperatively she was maintained in sinus rhythm with amiodarone.

Subsequent Holter monitoring demonstrated periods of atrial tachycardia and pauses in excess of 4 seconds. A pacemaker was therefore implanted on the left side, but it proved impossible to advance a lead beyond the junction of the left SVC and the RA. Thus an AAI device was implanted.

Two years later, AV block was seen. Thus a new dual-chamber pacemaker was inserted on the right side. Subsequently atrial tachycardias were controlled with a combination of sotalol and occasional DC cardioversion, but atrial tachycardias were becoming more frequent and more symptomatic.

Comments: Recurrent lower respiratory tract infections may be common in children with ASDs.

The clinical features described combined with left-axis deviation on the ECG would suggest an ASD of the primum type (partial AV septal defect). The presence of a pan-systolic heart murmur supports this diagnosis, reflecting regurgitation of the left AV valve, which is an intrinsically abnormal trileaflet valve in this condition.

The presence of a nodal rhythm is surprising, since sinus rhythm would be expected with a primum ASD. This is a clue that the diagnosis may be more complex than it appears.

The finding of a common atrium indicates the possibility of a heterotaxy syndrome. The morphology of the atria and in particular of the atrial appendages then allows determination of LA or RA isomerism. This can usually be determined by echocardiography, although clues as to “sidedness” can be gained from analysis of the bronchial anatomy, pulmonary and systemic venous drainage, and the presence of asplenia or polysplenia.

In right atrial isomerism total anomalous pulmonary venous drainage is common, since pulmonary veins usually drain into the LA. In this situation pulmonary venous return is usually into the IVC or azygos system. Bilateral SVCs are common (50%–70%). RA isomerism is almost universally associated with bilateral right-sided bronchial anatomy and less consistently with asplenia.

In LA isomerism the IVC is usually interrupted, with azygos continuation of the IVC returning systemic venous blood from the lower half of the body into the SVC. In this situation the hepatic veins usually drain directly into the atrium. Bilateral left bronchial anatomy is usual and polysplenia is common. Biliary atresia occurs in 11% and gut malrotation in 13% of patients.

An AVSD is seen in one third of patients with LA isomerism. Ventriculoarterial connections are normal in 60% of patients with LA isomerism, but double-outlet RV, TGA, pulmonary stenosis or atresia, and subaortic stenosis are all common.

Dysrhythmias are frequent (26%) in LA isomerism, related to the underlying anatomy and shunt, AV valve regurgitation, and atrial scarring from surgical repair. Bradycardia occurs in 16% and is related to the lack of a sinus node (a right atrial structure absent in left isomerism) and consequent dependence on an ectopic atrial focus. Complete heart block is common, especially in patients with an AVSD. In 30% of patients with LA isomerism there is a dual AV node. Pacing was required in 12% of patients for a combination of sinus node disease and complete AV block.


The patient was able to walk on the flat without symptoms, but became breathless when climbing one flight of stairs. Short-lived palpitations still occurred with increasing frequency.

NYHA class: II


  • Warfarin (target INR of 2.0–3.0)

  • Sotalol 160 mg morning and 80 mg evening

  • Amiloride/furosemide 5/40 mg daily


  • BP 139/82 mm Hg, HR 80 bpm, oxygen saturation 98%

  • Height 176 cm, weight 61 kg, BSA 1.75 m 2

  • Surgical scars: Median sternotomy

  • Neck veins: JVP was 4 cm above the sternal angle, with a normal waveform.

  • Lungs/chest: Clear to auscultation

  • Heart: There was a midline cardiac impulse. A normal S1 was heard with fixed split S2. The pulmonary component was normal. A grade 2/6 pan-systolic murmur was audible at the apex.

  • Abdomen: Abdomen was soft. The liver edge and spleen tip were not appreciated.

  • Extremities: Peripheral pulses were all palpable. There was no peripheral edema.

Sep 11, 2019 | Posted by in CARDIOLOGY | Comments Off on Left Atrial Isomerism
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