
==== Front
Intern Med
Intern Med
Internal Medicine
0918-2918
1349-7235
The Japanese Society of Internal Medicine

38104988
10.2169/internalmedicine.2946-23
Case Report
Coconut Atrium Causing Restrictive Physiology in the Right Ventricle
Wakaki Tomitaka 1
Sato Wakana 1
Suzuki Mayu 1
Watanabe Hiroyuki 1
1 Department of Cardiovascular Medicine, Akita University Graduate School of Medicine, Japan
Correspondence to Dr.　Hiroyuki Watanabe, hirow@doc.med.akita-u.ac.jp

18 12 2023
15 8 2024
63 16 22892292
21 9 2023
8 11 2023
Copyright © 2024 by The Japanese Society of Internal Medicine
https://creativecommons.org/licenses/by-nc-nd/4.0/ The Internal Medicine is an Open Access journal distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. To view the details of this license, please visit (https://creativecommons.org/licenses/by-nc-nd/4.0/).
We herein report a 61-year-old woman with a history of mitral valve replacement for rheumatic fever who presented with crural edema and ascites. Computed tomography showed massive left atrial (LA) calcification involving the interatrial septum, termed “coconut atrium.” Catheterization revealed not only pulmonary artery hypertension but also a large V-wave in the pulmonary artery wedge pressure waveform and a dip-and-plateau pattern of right ventricular pressure. Three-dimensional transthoracic echocardiography confirmed the early attainment of peak LA volume and a decreased LA expansion index. Stiff LA syndrome due to coconut LA results in the development of restrictive right ventricular physiology.

left atrial calcification
right ventricular restrictive physiology
left atrial expansion index
coconut atrium
dip-and-plateau
stiff left atrial syndrome
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pmcIntroduction

Although cardiac calcification is relatively common in long-lasting rheumatic valve disease (1), massive calcification of the left atrium (LA) is rare. Massive LA calcification occasionally appears as a high-density ring encircling the LA on chest X-ray and non-contrast computed tomography. The term “coconut atrium” is used when severe calcification is observed in the free wall of the LA and mitral valve (2-4).

We herein report a patient with coconut atrium who developed reservoir and contractile dysfunction of the LA, resulting in reduced pulmonary artery (PA) compliance and right ventricular (RV) restrictive physiology.

Case Report

A 61-year-old woman was hospitalized for fatigue, crural edema, and ascites. She had been diagnosed with a rheumatic fever at 11 years old and developed mitral valve stenosis and infective endocarditis of the mitral valve at 22 years old. At 28 years old, she experienced prosthetic valve failure and underwent revision surgery to replace the valve with a Bjork-Shiley mechanical valve.

Her vital signs were as follows: heart rate 60 beats/min, blood pressure 100/60 mmHg, SpO2 98%, and temperature 36.4 °C. Blood tests indicated an elevated brain natriuretic peptide level (84.3; normal 0-125) pg/mL, serum creatinine level of 1.29 (normal 0.46-0.79) mg/dL, and D-dimer level of 1.87 (normal 0-0.99) μg/mL. All other parameters were normal. Electrocardiography showed atrial fibrillation with complete AV block. Chest radiography showed cardiac enlargement but no findings suggesting pulmonary congestion. Transthoracic echocardiography (TTE) revealed an enlarged LA (left ventricular volume index of 109 mL/m2), pulmonary hypertension (transtricuspid pressure gradient, 40.0 mmHg), and RV contractile dysfunction (tricuspid annular plane systolic excursion, 13.8 mm). The prosthetic valve function was normal (Fig. 1).

Figure 1. Transthoracic echocardiographic images on admission. Apical four-chamber view (A) and parasternal short axis view (B) showing enlargement of the left atrium but not of the right atrium. Continuous wave Doppler images of transmitral flow showed a normal prosthetic valve function (C). The peak mitral E wave velocity was 208 cm/s, mean gradient pressure was 4 mmHg, and pressure half time was 76 ms. LA: left atrium, LV: left ventricle, PG: pressure gradient, RA: right atrium, RV: right ventricle

Non-contrast computed tomography of the chest showed plate-like calcification of the free wall of the LA and atrial septum, suggesting a “coconut atrium” (Fig. 2), whereas no calcification of the pericardium was detected. On transesophageal echocardiography, calcification with an acoustic shadow was evident in the atrial septum (Fig. 3). Right heart catheterization revealed RV systolic and diastolic pressures of 56 and 9 mmHg, respectively; a dip-and-plateau pattern of RV pressure; a mean right atrial pressure of 24 mmHg; a mean PA wedge pressure (PAWP) of 23 mmHg (Fig. 4); and a cardiac index of 3.8 L/min/m2 (Fick method). Intriguingly, a large V-wave consisting of a steep ascending limb with a giant peak of 41 mmHg was observed in the PAWP waveform, implying a stiff pulmonary vessel and LA. Indeed, real-time three-dimensional TTE confirmed the early attainment of peak LA volume (Fig. 5) and a significantly decreased LA expansion index (7%), suggesting LA reservoir dysfunction.

Figure 2. Axial (A) and sagittal (B) images from non-contrast CT showing calcification of the free wall of the LA and atrial septum. Ao: aorta, LA: left atrium, LV: left ventricle, RA: right atrium, RV: right ventricle

Figure 3. Transthoracic echocardiography showed LA septum calcification with an acoustic shadow. LA: left atrial, RA: right atrium

Figure 4. Pressure tracings showed a large V-wave of PAWP and a dip-and-plateau pattern of the RV. PA: pulmonary artery, PAWP: pulmonary artery wedge pressure, RA: right atrium, RV: right ventricle

Figure 5. Real-time 3D TTE revealed an early peak of LA volume before the appearance of a large V-wave in the PAWP. ECG: electro-cardiogram, LA: left atrial, LV: left ventricular, PAWP: pulmonary artery wedge pressure, TTE: transthoracic echocardiography

Based on these findings, the patient was diagnosed with longstanding LA dysfunction due to severe LA wall calcification after mitral valve surgery, which resulted in pulmonary hypertension and RV restrictive physiology. She was treated with diuretics and did not require hospitalization for two years.

Discussion

Coconut atrium is a rare complication of rheumatoid valvular disease that manifests in patients who have previously undergone mitral valve surgery (5). To our knowledge, this is the first report of hemodynamic-like development of coconut atrium-induced RV restrictive physiology.

Stiff LA syndrome is defined as the combination of LA reservoir dysfunction and heart failure symptoms. Atrial fibrillation, catheter ablation, and left ventricular diastolic dysfunction reportedly contribute to its pathogenesis (6-8). As shown in Fig. 5, the expansion index in our patient was substantially reduced, suggesting that the LA reservoir function was severely impaired. Notably, three-dimensional TTE revealed the early attainment of the peak LA volume before the appearance of a large V-wave in the PAWP.

Stiff LA syndrome is characterized by a primary increase in LA filling pressure, resulting in secondarily elevated PA pressure. In the present case, right heart catheterization showed decreased PA compliance and elastance (1.75 mL/mmHg and 0.85 mmHg/mL, respectively). In addition, we observed a dip-and-plateau pattern of RV pressure with a systolic area index (9,10) of 1.1, indicating RV restrictive physiology. These findings suggest that LA calcification over a long period leads to pulmonary vascular remodeling and decreased PA compliance, resulting in persistent pulmonary hypertension and restrictive physiology in the RV.

Conclusion

We encountered a rare case of stiff LA syndrome due to coconut LA that resulted in the development of restrictive physiology in the RV.

The authors state that they have no Conflict of Interest (COI).
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