An uncommon variant of double-chambered right ventricle masquerading as double-chambered left ventricle
This is a case report of a 62-year-old woman who underwent an echocardiogram due to an atypical chest pain with a complete left bundle branch block in the surface electrocardiogram. The pain characteristics pointed out a probable musculoskeletal aetiology, whereas physical examination, medical history and family history were unremarkable.
The echocardiogram demonstrated 2 muscular bands, a thicker muscular band on the left, corresponding to the interventricular septum, and a thinner muscular band on the right, which created a small aberrant cavity between the left ventricle (LV) and the right ventricle (RV) (Fig. 1A). Bubbles injected via the left antecubital vein were restricted to the RV, creating the impression that the aberrant cavity was in fact an accessory LV (Fig. 1B). A cardiac magnetic resonance study followed (Fig. 2, Videos 1 and 2) showing that a small smoothly bordered and well-contracting cavity (RV2) was located between the main RV (RV1) and the LV. A ventricular septal defect in the basal interventricular septum allowed communication between the diminutive RV2 and the LV. RV1 was anatomically and functionally normal. The left main coronary artery and the right coronary artery originated from the left sinus of Valsalva and the right sinus of Valsalva, respectively.
Our initial impression based on the bubble study, and the absence of communication between the small cavity and the main RV, was that this case represented a double-chambered left ventricle, a rare congenital malformation with only a few cases reported in the literature  However, the fact that the muscular band dividing the RV is located to the right of the interventricular septum, and the reduced ejection fraction of the small cavity on the cardiac magnetic resonance study compared with the left ventricular ejection fraction, led us to the conclusion that our case could represent an even more rare cardiac malformation, namely a double-chambered right ventricle (DCRV) masquerading as a double-chambered left ventricle [2–4]. The ‘classic’ DCRV is characterized by an intraventricular pressure gradient created by anomalous hypertrophic muscular bands [2, 3]. It is a rare congenital heart defect (0.5–2.0%) most frequently diagnosed in infants and children . It has been speculated that abnormal flow in the RV outflow tract may be causally associated with DCRV, leading to abnormal muscle hypertrophy (mainly involving the crista supraventricularis), thus it may be discovered even some years following ventricular septal defect repair . Surgical excision of the muscular bands, which has excellent long-term results , is indicated in symptomatic patients and/or in patients with a significant intraventricular pressure gradient, as the latter may lead to RV pressure loading and ultimately to RV failure . However, a rare variant of DCRV (anomalous apical shelf) has been described, in which a prominent septoparietal band with high take-off, along with hypertrophic apical trabeculations, formed an apical muscle shelf dividing the apical RV into 2 pouches, with only 1 communicating with the RV outlet, thus giving the impression of a double-chambered left ventricle [2, 4]. The clinical implications of this rare DCRV variant, which we believe our case also represents are largely unknown, as there is no communication between the 2 parts of the RV, therefore no pressure gradient exists. For the same reason, there should not be any impact of a coexistent ventricular septal defect on the pulmonary circulation even if the former is non-restrictive. Indeed, our patient went through the adult life being completely asymptomatic. The chest pain syndrome of the patient was rather musculoskeletal, and the patient was discharged without further diagnostic investigations or medical therapy.
Conflict of interest: none declared.