A Membranous Septal Aneurysm Causing Right Ventricular Outflow Tract Obstruction in an Adult.

We describe a case of a 69-year-old female referred for the evaluation of exertional dyspnea, with a small membranous ventricular septal defect (VSD) and right ventricle (RV) outflow tract obstruction. Using transthoracic echo was diagnosed VSD with left to right shunting and transesophageal echo (TEE) was used to a better anatomical characterization. TEE showed a perimembranous subaortic VSD that developed a high-velocity flow in RV. Pulmonary valve appears normal and right ventricular infundibular hypertrophy or double-chambered RV was excluded from the study. Furthermore, TEE showed a malaligned VSD and the presence of perimembranous mobile tissue protruding in RV. We hypothesized that this tissue can be attributed to broken septum aneurysm and protruding during systole, it causes a dynamic RV output tract obstruction.

INTRODUCTION

Ventricular septal defect (VSD) is the most common congenital heart malformation (30%–40%), as an isolated finding and it developed from an incomplete formation of septum components.

Echo is used to characterize defect in terms of location and size, shunt severity, overload for the right chambers and left ventricle, and associated defects.

According to the different location along the interventricular septum, it can be divided into four groups: perimembranous, located in pars membranacea, adjacent to tricuspid and aortic valves with possible extension into inlet or outlet septum, it is the most common type (80%); muscular (15%–20%) located in pars muscularis, often multiple, frequently spontaneous closure; outlet or supracristal (5%), below the semilunar valves in the outflow part of septum; inlet or atrioventricular canal, just below to atrioventricular valve apparatus, in the inlet part of septum, rare, and typically occurring in Down syndrome.[1]

The severity of shunt through the defect depends on the width of it: if it is small causes an high-velocity flow (>4 m/s), whereas if defect is large causes a low-velocity flow (<4 m/s). The first is called “restrictive” and the last “nonrestrictive.”

An aneurysm of membranous ventricular septal is a tissue dilatation of this portion, and since it is weak, it bulges to right ventricle (RV) as a consequence of left ventricle pressure. It occurs in 0.3% of patients with congenital heart disease, it is most commonly associated with peri-membranous VSD, and it was found in 20% of perimembranous VSDs.[2] Aneurysm functionally reduced the VSD size; thus it is usually benign[3] and only an occasional find. However, it had the potential consequence of promoting tricuspid insufficiency, aortic valve prolapse, right ventricle output tract (RVOT) obstruction, rupture of the aneurysm, and bacterial endocarditis.[24]

If aneurysms are rare (0.3% of congenital heart disease) the possibility that they cause obstruction is more rare. This event was reported, for the fist time, by Baweja et al in 2004[3] and few other cases have been reported subsequently.[56]

CASE REPORT

A 69-year-old female was referred for the evaluation of exertional dyspnea. She was asymptomatic until the previous year when developed progressive dyspnea (New York Heart Association II). Since the ’70s, she had previous medical records that documented an interventricular aneurysm, but only a recent transthoracic echo (TTE) diagnosed a VSD with left to right shunt. To a better VSD anatomical characterization compared to TTE, she was referring to undergo transesophageal echo (TEE).

TEE confirmed the presence of hole in interventricular septum that was located at the level of pars membranacea. From parasternal short axis view at aortic valve level [Figure 1], shunt arise from 12 o’clock position, like a perimembranous type that extends to outlet septum (subaortic), malaligned with the aortic valve, anterior placed, and it was crossed by left to right shunt that was directed toward RVOT [Figures 2 and 3]. The defect was wide 9 mm, and continuous-wave Doppler analysis flow showed across defect, high velocity (>4 m/s), with a maximum pressure gradient of 85 mmHg [Figure 4]. The left ventricle was mild hypertrophic, with normal diameter, and ejection fraction (55%). The RV was slight hypertrophic (wall thickness 6 mm), with mid diameter 34.5 mm. Tricuspid regurgitation (TR) jet velocity showed a maximum pressure gradient of 83 mmHg, and right atrial pressure was 5 mmHg because inferior cava vein (ICV) was small (9 mm) and collapsing with inspiration. Assessing the presence of other associated abnormalities, we excluded a subaortic stenosis or regurgitation, that is more frequently reported when it is associated to VSD, but we found a low aortic valve origin, the presence of perimembranous mobile tissue protruding in RV [Figure 5], and a RVOT peak pressure gradient of 65 mmHg [Figure 6].

Figure 1

Transthoracic echo parasternal short axis view at aortic valve level with right ventricle output tract aliasing

Figure 2

Transesophageal echo four chamber at mid-esophageal echocardiography: The membranous ventricular septal defect with aliasing

Figure 3

Transesophageal echo long axis at mid-esophageal echocardiography: The membranous ventricular septal defect with left to right shunt

Figure 4

Transthoracic echo continuous-wave analysis flow across ventricular septal defect

Figure 5

Transesophageal echo long axis at mid-esophageal echocardiography: perimembranous mobile tissue protruding in right ventricle (arrow)

Figure 6

Transthoracic echo continuous-wave analysis flow at right ventricle output tract

DISCUSSION

In our case, the defect was large but nevertheless, it developed high-velocity flow in RV. However, these data were discordant, and they generate a lot of perplexities:

Despite a VSD developed a high-velocity flow in RV that pathophysiology does not cause pulmonary volume overload, TR jet velocity was high and this finding contrast with lack of RV overload signs and small size of ICV

TR pressure gradient and pressure gradient across defect were similar, 88 mmHg and 85 mmHg, respectively.

Our suspicion was a RVOT obstruction and confirmed by high-pressure gradient sampled in pulmonary artery. Therefore, sPAP cannot be measured, and gradient of 85–88 mmHg corresponds to RV pressure.

Despite in most of the described cases of RVOT obstruction, obstruction had a valve location (80%–90%) due to hypoplasia or dysplasia of pulmonary valve; in our case, pulmonary valve appears normal.

The most common cause of RVOT obstruction in isolated perimembranous VSD is right ventricular infundibular hypertrophy or double-chambered right ventricle (DCRV) that was prominent muscle bundles in the right ventricular.[5] A small subaortic VSD is seen in >90% of DCRV cases, but this is a rare clinical diagnosis at the age of the 5th decade of life, and only a handful of cases have been described in adulthood.[678] In our patient, even though it has a RV slight hypertrophy sign; however, it was not observed infundibular abnormal muscle bundles.

Baweja et al. show that, in adult with VSD, more likely RVOT obstruction could be due to an aneurysm.[3] Membranous ventricular septal aneurysms are commonly associated with perimembranous VSD. Yilmaz et al. have reported that aneurysms were found in 20% of perimembranous VSDs.[2] There is a general agreement that they are congenital origin, due to anomalous closure of the atrioventricular canal or due to spontaneous closure of a septal defect, as an attempt of the tricuspid valve to close a congenital VSD.[4] In fact, perimembranous VSD may reduce its size for paratricuspid tissue apposition at the defect edges, producing an aneurysm. Thus, a membranous VSD in infancy progresses to a functionally smaller defect with aneurysmal formation.[9] Aneurysm formation functionally reduced the VSD size and it is usually benign.[3] Usually, it is only an occasional find, but it had the potential consequence of promoting tricuspid insufficiency, aortic valve prolapse, RVOT obstruction, rupture of the aneurysm, and bacterial endocarditis.[24] Therefore, in some patients, rarely, it can become obstructive, if below the semilunar valves in the outflow part of septum. Our case is similar to those reported for the first time by Baweja et al.[3510]

We hypothesized that mobile septal tissue can be attributed to the septum aneurysm that is broken. This event may have happened recently, considering that previous medical records of patient documented aneurysm and only a recent TTE documented shunt. Because tissue is mobile, it protrudes in RVOT during systole, and it obstructs RVOT, causing a dynamic obstruction.

CONCLUSION

A perimembranous septal aneurysm can break and lead to a creation of a VSD. The aneurysmal tissue protruding in RVOT can cause dynamic obstruction.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.