Unusual Coexistence of Atrial Fibrillation with Nonsurgically Acquired Complete Atrioventricular Block in a Patient with Ostium Primum Atrial Septal Defect

Abstract

Atrial septal defects (ASDs) make up about 10%-15% of congenital heart diseases. Clinical sequelae are insidious and present around the fourth decade of life. Arrhythmias such as atrial fibrillation and atrial flutter are common in patients with delayed presentation, while conduction abnormalities are rare. Conduction abnormalities mainly occur after defect closure by surgery or percutaneous device. Hereditary forms of ASD, as seen in the Holt-Oram syndrome, may also be associated with conduction disturbances. Our case is a female with newly diagnosed ostium primum ASD in the sixth decade of life and with the unusual presentation of atrial fibrillation coexisting with a complete atrioventricular block. We highlight the need for genetic testing in this uncommon clinical scenario.

INTRODUCTION

Atrial septal defect (ASD) refers to an abnormal communication between the left and right atria and accounts for 10%-15% of congenital heart lesions. Ostium secundum and ostium primum ASD account for the majority (75% and 15%, respectively) of cases.[¹] In some cases, there may be a specific underlying genetic disorder such as in the Holt-Oram or Down's syndrome.[²³] Clinical sequelae of ASDs are insidious and may present later in life. Arrhythmias such as atrial fibrillation and atrial flutter are common in patients with delayed presentation, while conduction abnormalities are rare. Our case is a female newly diagnosed with an ostium primum ASD in the sixth decade of life and with the unusual presentation of atrial fibrillation coexisting with a complete atrioventricular (AV) block.

CASE REPORT

A 55-year-old female was referred from a peripheral facility with a recent history of effort intolerance due to dyspnea and fatigue, as well as newly diagnosed bradycardia. History was negative for medications such as beta-blockers, calcium channel blockers, or digoxin. Her prior medical history was unremarkable and included five well-tolerated pregnancies. She was in good health until her symptoms started two months before presentation. On review, she was calm at rest with grade 2 edema and SP0₂ 94% in room air. Heart rate and blood pressures were 40 beats/min and 120/80mmHg, respectively. The jugular venous pressure was 9 cm H₂0 with positive hepatojugular reflux. Apex beat was laterally displaced, and there was left parasternal lift. She had a grade 3 ejection systolic murmur at the left upper sternal border. There was fixed splitting of the second heart sound. Her liver was enlarged and tender. Basic metabolic panel and hematologic tests were unremarkable. Electrocardiogram showed atrial fibrillation with a slow and regular ventricular response rate of 38 beats/min due to a complete (AV) block [Figure 1]. There were also left axis deviation, incomplete right bundle branch block, and left anterior fascicular block. The chest X-ray showed multichamber enlargement of the cardiac silhouette and accentuated pulmonary vessels [Figure 2]. Echocardiography showed a 1.8 cm ostium primum defect with left-to-right shunting and pulmonary-to-systemic blood flow ratio (Qp/Qs) of 3.5 [Figure 3]. A pulmonary artery systolic pressure (PASP) of 70 mmHg was estimated using tricuspid regurgitant velocity and the presence of dilated and poorly collapsing inferior vena cava. There was marked dilatation of the main pulmonary artery (3.2cm) and its right and left branches. There was a cleft anterior mitral leaflet and moderate mitral regurgitation. The left and right ventricular systolic functions were normal.

Figure 1: Electrocardiogram showing atrial fibrillation with regular R-R intervals and ventricular rate of 38 beats per min. There is left axis deviation, incomplete right bundle branch block, and left anterior hemiblock.

Figure 2: The chest X-ray showing multichamber cardiomegaly and accentuation of pulmonary vessels.

Figure 3: Subcostal view showing ostium primum defect, dilated right and left atria, and dilated right ventricle. ASD: Atrial septal defect, LA: Left atrium, LV: Left ventricle, RA: Right atrium, RV: Right ventricle.

She responded favorably to diuretics and arterial vasodilatation; however, her exercise tolerance remained suboptimal. She was counseled to undergo closure of the defect. She is currently scheduled for surgical closure of the defect and permanent pacemaker implantation.

DISCUSSION

Ostium primum ASD falls under the spectrum of AV septal defects. As in other forms of ASD, there is left-to-right shunting of blood that can result in right atrial and ventricular volume overload. The increased pulmonary flow can result in pulmonary vascular remodeling, which may cause pulmonary hypertension. Fortunately, Eisenmenger syndrome is uncommon in this condition. Patients with ostium primum ASDs may go undiagnosed in childhood and only present in later adulthood, around the fourth decade of life.[⁴] Effort intolerance in the form of dyspnea and fatigue is the most common presenting symptom and may be insidious and unrecognized by the patient or physician for several years. This may be due to gradually progressing pulmonary hypertension, as seen in our patient with estimated PASP of about 70mmHg. In addition, worsening of mitral regurgitation due to associated cleft mitral valve may ultimately result in left chamber dilatation and heart failure. On presentation, our patient already had multichamber dilatation, as was evident on the chest x-ray and echocardiogram. Recurrent pulmonary infections have been reported in patients with ASD due to pulmonary overcirculation, but this was not present in the index case.

The dilatation and stretching of the right-sided chambers and pulmonary artery can result in mechanical and electrical remodeling, which may result in supraventricular arrhythmias, particularly atrial fibrillation and atrial flutter.[⁵] These arrhythmias tend to occur later in life and can occur before or after surgical or percutaneous device closure of the defect. Older age at correction and larger shunt size, as seen in the index case, favor the development of theses arrhythmias.[⁶] Our patient indeed, presented with atrial fibrillation as evident in the irregular, vermiform fibrillatory waves; however, interestingly, she had a slow ventricular response of about 38 beats/min with regular R-R intervals, which is unusual for this type of arrhythmia. This is as a result of a coexisting complete AV block which is a rare finding in patients with uncorrected ostium primum ASD.[⁷] It has been proposed that AV block in ASD may be the result of displacement/disruption of the AV node and/or His bundle due to their proximity to the defect.[⁶] Surgical and device closures of ASDs may also result in various degrees of conduction disturbances due to factors such as trauma to conducting tissues or friction/pressure from closure devices.[⁸] Furthermore, mutations in myocardial transcription factors, NKX2.5, GATA4, and TBX5j, in a subset of ASDs patients are also associated with AV and other conduction abnormalities.[⁹] As an example, the Holt-Oram syndrome, characterized by congenital heart disease (commonly ASDs) and upper limb deformity is associated with conduction abnormalities such as AV blocks, sinus node dysfunction, and right bundle branch block. We were unable to carry out genetic testing for these factors because this kind of testing is unavailable to us. The patient did not exhibit upper extremity malformation, and echocardiographic screening of the first-degree relatives was negative. Nonsurgical (preoperative) complete AV block is a rare finding in patients with ostium primum ASD, and it is even rarer to find such patients with both atrial fibrillation and complete AV block. In addition, our patient had left anterior fascicular block and incomplete right bundle branch block. She was neither on beta blockers or digitalis nor did she have electrolyte abnormalities. It therefore, remains interesting to speculate on whether she has a hereditary form of ASD. This is important because individuals with hereditary ASDs are predisposed to a sudden cardiac death.[¹⁰] There is a need in Nigeria, to improve genetic testing capabilities for this and other conditions, such as cardiomyopathies, where genetics may have an underlying role.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

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Conflicts of interest

There are no conflicts of interest.