Gerbode-ish Defect

Abstract

Background

A Gerbode defect is a rare communication between the left ventricle and right atrium. Patients with congenital Gerbode defects require prompt diagnosis and medical therapy to temporize their disease until more definitive surgical correction can occur.

Case Summary

A 3-day-old male infant presented to urgent care after his mother noticed episodic cyanosis of the lips and tachypnea that self-resolved. On echocardiogram, he was found to have a Gerbode type 2 defect with a shunt from the left ventricle to the right atrium across the septal leaflet of the tricuspid valve.

Discussion

These rare defects are frequently missed at birth and are challenging to diagnose given their broad cardiac presentation.

Take-Home Messages

Cardiac causes must be included in early the differential diagnosis when evaluating cyanosis and respiratory chief complaints. Echocardiogram is valuable as a diagnostic marker for the progression of left-to-right shunts.

Graphical Abstract

History of Presentation

A 3-day-old newborn boy presented to urgent care after his mother noticed transient blue lips while at rest and irregular breathing. On presentation, his heart rate was 140 beats/min, his respiratory rate was 42 breaths/min with an irregular pattern, and a 4/6 holosystolic murmur was heard on cardiac auscultation. Despite the reported history of blue lips, his oxygenation saturation was 96% during examination. He was found to be hypoglycemic (blood glucose: 56 mg/dL) and was admitted to the neonatal intensive care unit (NICU) for further management.

Take-Home Messages

• •Cardiac causes must be included in early differential diagnosis when evaluating cyanosis and respiratory chief complaints.
• •Echocardiogram is valuable as a diagnostic marker for the progression of left-to-right shunts.

Past Medical History

Medical history from chart review revealed that the patient had spent his first day of life in the NICU because of hypoglycemia, which was attributed to his mother's poorly controlled type 2 diabetes mellitus. During his initial time in the NICU, no murmurs or issues with oxygen saturation were documented in the chart. Once his blood glucose had stabilized, he was subsequently discharged home on his second day of life.

Differential Diagnosis

In newborns, episodes of cyanosis and labored breathing can have multiple causes, requiring a workup of congenital causes in addition to an infectious workup. It is important to note that congenital heart defects (CHDs) may not be symptomatic at birth and may present later, in the early few months of life. Additionally, patients born to mothers with uncontrolled diabetes are at higher risk of developing CHDs, such as ventricular septal defect (VSD), transposition of the great arteries, and persistent truncus arteriosus. Given the new pathologic murmur and witnessed cyanotic episodes, it seemed that the patient likely had a CHD. More definitive diagnostic testing with transthoracic tchocardiogram (TTE) was needed to characterize the defect and help lead management.

Investigations

The patient underwent a TTE (Figure 1), which revealed a perimembranous restrictive ventricular septal defect (VSD) located beneath the tricuspid valve's septal leaflet and septal aneurysmal tissue, which was partially covering the VSD, hence reducing the effective shunting area. It also demonstrated a small fenestrated atrial septal defect with a small left-to-right shunt.

Figure 1.

First TTE

Long-axis view of restrictive ventricular septal defect (VSD) on the patient's initial transthoracic echocardiogram.

Management

Both defects were shown to be left-to-right shunts; however, the hemodynamic significance of the shunt was unclear at that time, as the patient's tachypnea self-resolved and the patient was discharged with cardiology follow-up. At his follow-up appointment <2 weeks later, the patient developed worsening tachypnea, work of breathing, and new head bobbing. He was admitted to the hospital from clinic because of his increased work of breathing. On physical examination, the murmur increased in intensity and was accompanied by a palpable thrill. On repeat TTE (Figures 2A and 2B), the results were astonishing. Originally, it was thought that the patient was now suffering from severe tricuspid regurgitation due to high jet velocity into the right atrium (RA) at 5 m/s, which would have indicated symptomatic pulmonary hypertension. However, with the known history of VSD, careful scanning during TTE showed that this jet velocity originated from the left ventricle (LV) and clarified that this was an LV-to-RA shunt. The well-rounded configuration of the end-systolic ventricular septal contour on TTE made tricuspid regurgitation secondary to pulmonary hypertension an unlikely diagnosis. Had a D-shaped septal morphology with leftward deviation been observed during end-systole, further evaluation for pulmonary hypertension via invasive cardiac catheterization would have been warranted.

Figure 2.

Follow-Up TTE

(A) Long-axis view of jet velocity into the right atrium (RA) seen originating from the left ventricle (LV). (B) Short-axis view demonstrating LV-to-RA shunt across the tricuspid leaflet.

This defect is formally known as a Gerbode type 2 defect shunting from the LV to the RA across the septal leaflet of the tricuspid valve. This likely formed from the tricuspid tissue that originally made the VSD restrictive, coalescing with a tricuspid leaflet. This allows blood to flow at a high velocity across the shunt through the septal leaflet and directly into the RA. His atrial septal defect, seen on previous TTE, was now better characterized as a patent foramen ovale and was hemodynamically insignificant.

With this diagnosis, the patient was ultimately referred to the pediatric cardiothoracic surgery team for a patch closure of the VSD with tricuspid valve repair. This decision was complex, but with the coordination of the surgical team, it was deemed that surgery was necessary, as the patient was more likely to suffer from early progressive heart failure because the defect was unlikely to close. Because of the patient's young age, it was determined that he should be medically managed until the age of 6 months. He was then started on furosemide at 1 mg/kg/d and was discharged home with close follow-up. The patient was readmitted to the hospital for a respiratory illness, which subsequently caused a heart failure exacerbation requiring higher doses of diuretics. Since then, the patient has remained hemodynamically stable on his furosemide dosage of 1 mg/kg/d. The patient is currently awaiting his surgery to correct his defect.

Discussion

A Gerbode defect is defined as a very rare, typically congenital, communication between the LV and RA.¹ Current estimates are that Gerbode defects account for only 0.08% of all CHDs.² First described in 1838 on an autopsy, the defect has been continuously studied over the years, and there are now more formal classifications for the disease. Current guidelines, described by Sakakibara and Kono, are based on anatomical classifications, which have now identified 3 distinct types of Gerbode defects.³

Type 1 defects, also known as a direct Gerbode defect, involve direct LV-to-RA shunting across the atrioventricular part of the membranous septum, which is positioned above the tricuspid valve. Type 1 defects are more typically acquired from prior surgeries or trauma rather than congenital malformations.^1,4 Type 2 defects, also known as indirect Gerbode defects, affect the interventricular part of the membranous septum at a level at or below the tricuspid valve (Figure 3).¹ This defect usually involves tricuspid valve defects, which allow for the shunt to bypass the tricuspid valve and function as an LV-to-RA shunt.⁵ Additionally, type 2 defects more commonly arise as congenital defects as opposed to type 1 defects. Lastly, type 3 Gerbode defects, known as the intermediate form, involve both the interventricular and atrioventricular part of the membranous septum and are much less common than types 1 and 2.⁴

Figure 3.

Gerbode's Defects

Illustrative depiction of the different types of Gerbode defects.¹ Ao = aorta; IVS = interventricular septum; LV = left ventricle; RA = right atrium; TV = tricuspid valve.

Recent data have shown that the incidence breakdown of the 3 types of Gerbode defects is 76% for type 1, 16% for type 2, and 3 8% for type 3.⁶ This distribution is heavily influenced by the fact that a majority of Gerbode defects are acquired rather than congenital malformations.⁶ The etiology of type 2 Gerbode defects, which are largely due to congenital malformations, has been thought to arise from an endocardial fusion defect, and recently the genes NKX2-5, GATA4, and TBX5 were identified as likely sources of this defect.⁷ Although this genetic evidence is promising, there are still large gaps in understanding how Gerbode defects arise in utero and how to best treat these patients.

The case we present is unique in that the patient was later found to have a type 2 Gerbode defect that was not present at birth. While most type 2 defects are present at birth, this patient developed the defect as an infant, not in utero. This is important because the original TTE (before Gerbode defect diagnosis) may help provide a better understanding of the pathogenesis of congenital Gerbode defects.

Additionally, there is room for improvement in terms of increasing the diagnostic accuracy and early diagnosis of Gerbode defects. Rojas et al found that specific protocols for fetal echocardiography can improve the detection rate of VSD, which would presumably encompass all Gerbode defects, from 27% to 93%.⁸

More importantly, there are no centralized guidelines for the medical management and treatment of Gerbode defects.⁹ There are multiple case reports in the literature showing how diuretics have improved individual patient outcomes and indicating the need for either percutaneous or open surgical correction; however, there is a large gap in terms of how clinicians should treat patients.

In this case, the patient was ultimately referred for surgical correction to resolve left-to-right shunting, mitigate endocarditis risk, stop progression of valvular destruction, and decrease volume/pressure load on the right atrium.¹ He is scheduled to undergo patch closure of the VSD with tricuspid valve repair. The current plan is to use autologous pericardium for VSD closure, and the tricuspid valve will likely require commissuroplasty sutures to ensure competence. One of the challenging portions of the case will be delineating the rims of the VSD that will be encased in the tricuspid valve tissue. The turbulence around the VSD and tricuspid valve in these types of defects often causes significant scarring of the endocardium and valvular tissue, which requires careful dissection to delineate the VSD rims. If the rims of the VSD are not delineated, this can result in residual left-to-right shunting, valvular damage, or heart block.

Conclusions

Gerbode defects are rare but life-threatening diseases that require prompt diagnosis and management. Clinicians must be aware of the hemodynamic profile seen with this unique condition and how to appropriately work up patients. This case highlights how congenital conditions may not be present at birth but still need to be considered in the differential diagnosis for young patients experiencing cyanosis

Visual Summary.

Timeline of the Case

Timeline	Events
Day 1	A 3-day-old newborn boy presented to urgent care after his mother noticed transient blue lips while at rest and irregular breathing. He was tachypneic and was found to have a 4/6 holosystolic murmur on cardiac auscultation. The patient was admitted for hypoglycemia. Hemodynamically stable.
Day 2	TTE showed perimembranous restrictive VSD beneath the tricuspid valve's septal leaflet and septal aneurysmal tissue with a left-to-right shunt. The patient's hypoglycemia and tachypnea resolved, which led to his being discharged home with outpatient cardiology follow-up
Day 13	Patient presented to cardiology clinic for follow-up TTE. His mother reported tachypnea, work of breathing, and new head bobbing at home. Owing to his increased work of breathing, he was admitted to the hospital from the clinic. TTE showed new high-velocity jet in the RA (5 m/s) originating from the LV. Pulmonary hypertension was excluded as a diagnosis given the well-rounded end-systolic ventricular septal contour. This LV-to-RA shunt was best described as a Gerbode type 2 defect.
Day 14	The patient was started on furosemide 1 mg/kg/d for symptomatic management of his congenital heart defect. The case was discussed with the pediatric cardiothoracic surgery team, who deemed his condition amenable to surgical correction at a later date, as his defect would be very unlikely to self-resolve.
Day 16	Patient was discharged home on furosemide 1 mg/kg/d.
Day 26	Follow-up outpatient clinic visit with TTE demonstrated an unchanged Gerbode type 2 defect. Patient was hemodynamically stable on diuretic therapy.
Day 48	Patient was admitted to the hospital for shortness of breath and was diagnosed with a respiratory illness, which precipitated a heart failure exacerbation. While hospitalized, his diuretic regimen increased for volume overload status.
Day 50	Patient was discharged home hemodynamically stable on furosemide 1 mg/kg/d.
Day 62	Patient was seen in clinic, TTE showed unchanged LV-to-RA shunt. Patient was scheduled to undergo patch closure of the VSD with tricuspid valve repair in 5 months.

LV = left ventricle; RA = right atrium; TTE = transthoracic echocardiogram; VSD = ventricular septal defect.

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Funding Support and Author Disclosures

The authors have reported that they have no relationships relevant to the contents of this paper to disclose.