**5. Etiology**

All of the causes in the etiology of acute pericarditis can become chronic and lead to constriction (**Table 1**) [30]. However, pericarditis caused by some etiological agents, especially tuberculosis, tends to become more chronic. Tuberculosis from these etiological agents; In regions such as China, Iran, and South Africa, it is the dominant cause of constrictive pericarditis with a rate of 22.2–91% [31–33]. A South African institution reported 121 cases of constrictive pericarditis over 22 years (1990–2012) and of these, tuberculosis was confirmed as the cause in 29.8% of cases and suspected in an additional 61.2% of cases. However, tuberculosis was historically the most common cause for constrictive pericarditis in North America; a report from 1962 cited tuberculosis as the cause of 48% of cases of constrictive pericarditis. And at the present time, in developed countries (North America and Europe), constrictive pericarditis due to tuberculosis is very low (less than 5.6%). In these regions, idiopathic or previous cardiac surgery, radiotherapy to the thorax, human immunodeficiency virüs and AIDS old acute pericarditis are more common in the etiology of constrictive pericarditis [34–38]. It is known that there is a relationship between hemopericardium and constructive pericarditis [39, 40]. Radiation-induced "late pericarditis". Constructive pericarditis requiring pericardiectomy develops in 20% of cases [41, 42]. Constructive pericarditis occurs an average of 23 months after cardiac surgery [39, 40].

Recent studies show that changes in gene expression could be directly associated with inflamation and the subsequent formation of fibrosis [43], the key pathological process underlying the constrictive pericarditis. Furthermore, an array of changes in noncoding RNAs, including micro RNAs (miRNAs), long non-coding RNAs(IncRNAs) and circular RNAs(circRNAs) were belived to play a critical role in the relevant molecular

```
• Irradiation
```

Viral (Echovirus, Coxsackie virüs, Adenovirus, CMV, Hepatitis B, EMN, HIV/AIDS) Bacterial (Pneumococcus, Staphylococcus, Streptococcus, Mycoplasma, Lyme disease, Haemophilus influenza, Neisseria menengitides, Others)

Mycobacterial Mycobacterium tuberculosis M.avium-intracellulare complex

Fungal Histoplasmosis Coccidiodomyocosis

Protozoal


#### **Table 1.**

*Causes of constrictive pericarditis (AIDS: acquıred immunodeficiency syndome; HIV: Human immunodeficency virus).*

signaling pathways and biological processes leading to fibrosis.Nevertheless, how these molecular substrates mediate the constrictive pericarditis is still poorly understood. High-throughput sequencing and bioinformatics analysis have been widely exploited to identify specific genes associated with various diseases [44]. These interesting findings promoted researchers to explore if there are abnormally expressed genes and sigaling pathways involved in the inflammation and fibrosis processes of Constrictive pericarditis. Molecular biological experiments are neede to further delineate the roles of these circRNAs identified in Constrictive pericarditis [45].
