Discussion

The surgical form of inverted left atrial appendage is mechanically straightforward. De-airing at the end of cardiopulmonary bypass abruptly decompresses the atrium, generating a negative intracardiac pressure spike that the appendage—narrow-necked, thin-walled, and trabeculated—cannot sustain. ^{Reference Buttar, Andersen, Poulsen and Thyregod4,Reference Meredith and Kimball7,Reference Liaqath Ali, Bharucha, Karane and Hayes10,Reference Ekanem, Gattani, Shea, Zhao, Singh and Liam11} The same pressure logic operates after left ventricular assist device implantation, where haemodynamic shifts of comparable magnitude have triggered inversion. ^{Reference Ankersmit, Mohl and Moser5,Reference Fadia, Vaideeswar and Pandit8}

The question of why only some appendages invert received its first quantitative answer in 2024. Vella et al. built the field’s first biomechanical computational model of inverted left atrial appendage, simulating pressure conditions across all four morphological subtypes. ^{Reference Vella, Musotto, Cook, Bosi and Burriesci1} The data show that windsock and cauliflower appendages—characterised by longer, narrower necks—bear disproportionately higher wall stress under equivalent pressure loads, making them meaningfully more susceptible to inversion. In spontaneous cases, where no surgical trigger intervenes, appendage geometry may itself be the decisive variable.

Spontaneous inverted left atrial appendage stands apart. The entire published record, including the present case, amounts to fewer than ten patients worldwide. Table 1 makes the pattern legible: the common denominator across spontaneous cases is a transmural pressure imbalance rather than a surgical event. In three cases including ours, ^{Reference Fadia, Vaideeswar and Pandit8,Reference Gecmen, Candan and Guler9} pericardial effusion drove the process—accumulated fluid exerted external compression on the appendage wall and forced it inward. A fourth case followed a different but equally coherent mechanism: supraventricular tachycardia curtailed diastolic filling so sharply that transient negative pressure developed within the left atrium. ^{Reference Meredith and Kimball7} Two distinct triggers, one shared result.

Table 1.

Summary of published cases of spontaneous left atrial appendage inversion (updated literature review 2001–2024)

Table 1. Long description

Fields: year, sex, age, history, diagnosis, treatment, mechanism. 1) Ankersmit 2001, female, 38 years, none, stroke work-up, surgery, undetermined. 2) Motoyasu 2003, male, 19 years, mitral valve prolapse, echocardiography and magnetic resonance imaging (MRI), resolved spontaneously, undetermined. 3) Meredith 2004, male, 1 month, supraventricular tachycardia, transoesophageal echocardiography and MRI, adenosine, shortened diastole, negative pressure. 4) Fadia 2006, female, 4 months, Down syndrome with atrioventricular canal defect, autopsy, none, raised pericardial pressure. 5) Gecmen 2011, male, 48 years, pericardial effusion, intraoperative, surgery, raised pericardial pressure. 6) Buttar 2022, female, 3 years, repaired atrial septal defect, intraoperative transoesophageal echocardiography, manual eversion, cannula dislodgement. 7) Liaqath Ali 2024, male, 3 months, repaired ventricular septal defect, epicardial echocardiography, manual eversion, negative pressure at de-airing.

The clinical course of inverted left atrial appendage is not uniform. Most spontaneous cases follow a benign trajectory, discovered incidentally and never causing symptoms. Several complications, however, are serious enough to warrant explicit attention:

• • Thromboembolism: The most clinically consequential complication. The earliest published spontaneous case ^{Reference Ankersmit, Mohl and Moser5} presented as cryptogenic cerebral stroke, with inverted left atrial appendage later identified as the embolic source. The irregular trabecular surface of the inverted appendage likely creates a prothrombotic microenvironment.

• • Mitral inflow obstruction: A progressively inverted appendage may bulge towards the mitral annulus during diastole, producing functional mitral stenosis, pulmonary hypertension, and right ventricular failure. ^{Reference Fadia, Vaideeswar and Pandit8,Reference Ekanem, Gattani, Shea, Zhao, Singh and Liam11}

• • Arrhythmias: The mass effect of the inverted appendage against the atrial wall can mechanically irritate the myocardium and trigger atrial arrhythmias.

• • Appendiceal incarceration and necrosis: Rare but potentially fatal, requiring urgent surgery. ^{Reference Ekanem, Gattani, Shea, Zhao, Singh and Liam11}

Transoesophageal echocardiography is the diagnostic modality of choice. The characteristic picture is recognisable: a mobile, finger-like mass at the anterolateral left atrial wall, with no colour-flow Doppler signal traversing it and a diastolic excursion towards the mitral annulus. ^{Reference Ekanem, Gattani, Shea, Zhao, Singh and Liam11} When these features cluster together, the diagnosis is essentially secured. Cardiac MRI resolves residual ambiguity. In the operative setting, routine post-bypass TOE—or direct visual inspection of the left atrium before chest closure—constitutes a straightforward safeguard that surgical teams should apply whenever the anatomy raises any doubt. ^{Reference Liaqath Ali, Bharucha, Karane and Hayes10,Reference Ekanem, Gattani, Shea, Zhao, Singh and Liam11}

This case advances the literature on two specific points. First, spontaneous inverted left atrial appendage in an infant without CHD has not, to our knowledge, been previously documented. Its occurrence in the setting of mitochondrial cytopathy raises a question the data cannot yet answer: does impaired myocardial energy metabolism alter the biomechanical properties of the appendage wall, reducing its resistance to pressure-driven inversion? The hypothesis is speculative, but the case places it on the record for future investigation. Second, the diagnosis was reached exclusively at autopsy. The finding was not subtle; it was invisible because the treating team’s attention was, understandably, directed entirely at a life-threatening metabolic emergency.

Management of inverted left atrial appendage in a living patient follows the clinical context. Manual eversion—intraoperatively or via catheter-based techniques—is the preferred first step when anatomically feasible. Where the appendage has already served as an embolic source, surgical ligation or device-based closure (AtriClip, WATCHMAN) addresses the risk of recurrence. ^{Reference Ankersmit, Mohl and Moser5,Reference Gecmen, Candan and Guler9} Anticoagulation functions as a bridge when thrombogenic risk is high and surgical intervention cannot be arranged promptly.