This case demonstrates the extent to which the body can compensate leading to significant alterations of anatomical structures. It also highlights the importance of clinical acumen, integrating history and examination along with multi-modal imaging into the management of the critically ill patient.

A 64-year-old woman was admitted to the Intensive Care Unit (ICU) after a medical emergency team (MET) call from the cardiology ward due to a reduced level of consciousness and respiratory distress. Past medical history included rheumatic fever as a child and chronic atrial fibrillation. She had been admitted to hospital 3 days previously with worsening shortness of breath. On observation she was drowsy but rousable to voice, with a respiratory rate of thirty breaths per minute. Examination revealed a raised jugular venous pressure, a pan-systolic murmur as well as a long mid-diastolic murmur, both loudest at the apex and radiating to the axilla, a soft first heart sound, a displaced tapping apex beat, and bi-basal medium-intensity inspiratory crepitations. Her electrocardiogram showed atrial fibrillation with a rapid ventricular response of 126 beats per minute. Her arterial blood gas demonstrated an acute on chronic respiratory acidosis with a pH 7.02, PaCO₂ 176 mmHg, and a HCO₃^- of 43 mmol/L. An antero-posterior (AP) chest x-ray on admission displayed cardiomegaly, splayed carina and hilar venous congestion, with a lateral film showing the left atrium occupying a significant part of the chest cavity (see Figure 1a, Figure 1b).

A dramatically dilated left atrium was seen on a TTE (see Figure 2a, Figure 2b, Figure 2c, and Figure 2d). Severe mitral stenosis with associated regurgitation was evident, with a mean gradient across the valve of 11mmHg and a hyperdynamic left ventricle. The left atrial volume measured by Simpson’s biplane method (see Figure 2c) was 2108mL, or 1548.5 ml/m², based on height 1.55 metres and weight 44 Kg. Normal left atrial volume in a woman is 16 - 34 ml/m²1. The computed tomography scan (CT) chest AP view (see Figure 3) is also shown.

Massive left atrial dilatation is a recognized phenomenon in chronic mitral stenosis, and is considered by some to be protective against the development of pulmonary oedema in mitral regurgitation 2. Left atrial dilatation to this extent is not usually seen in living patients, however. The largest described left atrium was 3000 ml at autopsy, with another measuring 1760 ml at autopsy in 19313. Other reports in living patients include a left atrium that was estimated at approximately 2000ml on magnetic resonance imaging 4.The more precise measurements for the left atrial size we recorded on cardiac ultrasound have not been described previously. Considering the size of the left atrium, it is surprising that the mean gradient across the mitral valve was only 11mmHg. Although this is certainly severe, it could be expected that a gradient would be higher based on the severity of the left atrial dilation. We hypothesize that the gradient may have been greater previously, however the massive dilation of the left atrium may have subsequently led to a dilation of the mitral annulus, leading to an improvement in the mitral valve effective orifice area, and hence a reduction in the severity of the mean mitral valve gradient.

Our patient was an overseas visitor who had previously refused an offer of cardiac surgery. She improved clinically with two days of non-invasive ventilation and diuresis, and was discharged to the cardiology unit for ongoing medical management. It was likely that without surgery her prognosis would have been poor as she would have been at significant risk of further and cardiorespiratory compromise. One month later she successfully underwent surgery, and subsequently returned overseas after an uncomplicated post-operative recovery.